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November 16

Centrifugal force

I'm doing a lab report on ficticious forces, and something doesn't seem to make sense. The design of the experiment is as follows: a stationary channel has a ball roll slowly through it, while the channel is overtop some paper on a rotating platform. Again, the ball is NOT rotating (just going in a straight line), but it's making contact with the paper that it rotating, and every 30 ms or so the ball makes a mark on the paper, so that's its trajectory is traced out. Now according to the lab manual (and in agreement with the results we obtained), the ball will slow down as it approaches the centre, and speed up while it's leaving, and apparently this is due to centrifugal forces.

Now to me, this doesn't make much sense. The ball itself shouldn't be experiencing any forces (ignoring friction), and even in the reference frame of the rotating paper, the ficticious force acting on it should be directed towards the centre, allowing it to continue in a circular path. After all, if the ball wasn't moving at all, it wouldn't start moving away from the centre, so I have trouble believing that there would be a ficticious force acting on it. But I wasn't actually there for the lab; is it possible that it was the ball that was rotating while the paper was stationary, and that my lab partner is just an idiot? —Preceding unsigned comment added by 24.200.1.37 (talk) 00:31, 16 November 2009

In the nonrotating lab frame, the velocity of the ball relative to the paper is the velocity of the ball relative to the lab (a constant) minus the velocity of the paper relative to the lab at the point where the ball is at that moment. The paper is moving more slowly near the center of the rotation, so it's reasonable to suppose that the difference of the velocities will be smaller nearer the center. That's why the marks on the paper were more closely spaced there.

In the real world (as real as academic physics gets, anyway), that would be enough. You don't have to analyze the problem in every frame, you can just pick one and do the analysis there. But since this is a lab, I suppose they want you to repeat the analysis in a rotating frame where the paper is at rest. That seems to be a lot more complicated in this case, so if the intent of the lab is to show you the usefulness of fictitious forces then it isn't doing a very good job. In the rotating frame, the ball experiences the centrifugal force (which acts outward from the center) and the Coriolis force (which acts at right angles to the ball's velocity). You're probably supposed to ignore the fact that the ball is constrained by the channel and supported by it against gravity; the important thing is that the ball moves as it would in empty space with no external forces (other than the fictitious forces). You can write down the equations of motion and try to solve them, but it's going to be ugly. I don't see any easy way to do it aside from solving the problem in the nonrotating frame and then changing the coordinates.

In the case of an object at rest in the nonrotating frame, the centrifugal force in the rotating frame points outward, but the Coriolis force points inward and is twice as large. So the net force is inward; that's the centripetal force that keeps the object moving in a circle. In this case, too, it's easier to see what's going on in the nonrotating frame. -- BenRG (talk) 01:11, 16 November 2009 (UTC)

If the ball is stationary, then it's radial velocity is zero. Since the coriolis force is proportional to the radial velocity, how can it cause a centripetal force? —Preceding unsigned comment added by 24.200.1.37 (talk) 08:21, 16 November 2009 (UTC)

An object following a circular path with constant angular velocity $\omega$ relative to a rotating reference frame which is itself rotating with constant angular velocity $\Omega$ (where axis of path coincides with axis of rotation of frame) requires a centripetal force of magnitude

$mr(\omega +\Omega )^{2}=mr\omega ^{2}+mr\Omega ^{2}+2mr\omega \Omega$

The first term is the centripetal force that is "expected" relative to the rotating reference frame; the second term is a "correction" due to centrifugal force; and the third term is a further "correction" due to Coriolis force. In BenRG's example the object is stationary relative to the non-rotating reference frame, so $\omega =-\Omega$, the Coriolis force term is negative, and the net required centripetal force (after the "corrections") is 0. Gandalf61 (talk) 11:59, 16 November 2009 (UTC)

Stone artifact need help with what it is...

I need help with a stone that my daughter found on Myrtle Beach S.C. It is very old and it is either indian or maybe even from the stone age. We have pictures and would appreciate any help with whom we could email for assistance. Thank you for your time —Preceding unsigned comment added by Donald Cohee (talk • contribs) 00:54, 16 November 2009 (UTC)

If you post the pictures, someone here might be able to help identify the stone. Otherwise, we don't have a directory of Wikipedians with expertise in identifying Native American artifacts. —Akrabbim^talk 01:23, 16 November 2009 (UTC)

Since you actually are in possession of this artifact, you might consider talking to a history or archaeology professor at the nearest university, who may be willing to spend some time looking at it. Nimur (talk) 03:07, 16 November 2009 (UTC)

It's worth noting that removal of antiquities can be regulated in some places. -- Scray (talk) 04:59, 16 November 2009 (UTC)

Also, Native American artifacts are "stone age", excepting those acquired through trade or from far into the "historic" period. Pfly (talk) 06:27, 17 November 2009 (UTC)

tuned circuit

I'm trying to create a tuned circuit for a science project to show how 60 Hz power line frequency intensity can be monitored and displayed on a computer based osciliscope. When I calculate the wavelength for 60Hz however I get an antenna length that is way beyond a length of wire that I can mount in the yard and tune. I know there must be harmonic that I can use with a reasonably shorter antenna and with a coil and capacitor circuit to cilate and perfectly match 60 Hz but I can not find any references or information as to how to calculate the length of the size of the coil and capacitor for a specific 60 HZ harmonic antenna length that will work. Does the Wikipedia have any references for the complete calculations? 71.100.7.189 (talk) 01:52, 16 November 2009 (UTC)

You will pick up 60 Hz whether you want to or not... I have a lot of experience setting out antennas of varying sizes and we always get 60Hz interference. Our AWESOME antennas pick up 60Hz and dozens of its harmonics; you can see its antenna size and download schematics for the antennas, as well as the preamplifier and data acquisition system. I think you can even purchase the hardware and equipment at-cost from Stanford for around $500. In any case, if your preamplifier and amplifier have a good low-frequency response (e.g. similar to a high-quality audio amplifier), you'll have no trouble tuning to the 60Hz at baseband ("zeroth harmonic") even with a small ~ 1 meter antenna. Nimur (talk) 03:15, 16 November 2009 (UTC)

I assume the horizontal lines are the 60HZ harmonics but what I need is a circuit specifically tuned to 60Hz or at least the equations necessary to create the antenna, coil and capacitor to resonate at 60Hz. 71.100.7.189 (talk) 03:47, 16 November 2009 (UTC)

The links I've provided show circuit schematics for a broad-band amplifier; if you want to tune to 60 Hz, take a look at tuned circuit and Q factor. The equations are trivially easy; the difficulty is finding components and getting a good amplifier at such low frequencies. That is why I suggest using a broad-band system (like the one I linked above) and digitally processing the result to analyze the 60Hz band. Nimur (talk) 05:03, 16 November 2009 (UTC)

So are Maxwell equations but their usefulness and comprehension exceeds the elegance of their simplicity. 71.100.7.189 (talk) 05:17, 16 November 2009 (UTC)

After reviewing the few questions you have asked, I think the best advice for you is to review some basic physics; we have some good articles on electronics, electromagnetism, and atomic theory that are all very well-sourced. If you still have specific questions after you are up to speed on the fundamentals, or if you're having conceptual problems understanding parts of the articles, feel free to ask here. Nimur (talk) 06:52, 16 November 2009 (UTC)

You should not be trying to establish a pattern of thinking based on any of my questions since only two questions I have asked originated from the same member of our group. Also if you don't know the answer just say so. 71.100.7.189 (talk) 07:42, 16 November 2009 (UTC)

I would avoid constructing a passive resonator circuit for so low a frequency as 60Hz because of the inconveniently large LC product needed. It is easier to make it either as a bandpass Active filter or as a digital Goertzel algorithm. THe latter is used in DTMF detectors in telephony and might be readily implemented in your computer based oscilloscope. Nimur has given good advice above. BTW I have found that in many urban areas one need only bury a couple of earth rods a few meters apart to be able to pick up a few tens of millivolts of power line frequency between them. Cuddlyable3 (talk) 10:45, 16 November 2009 (UTC)

The phrasing of your initial question implies that you think it is necessary to have an LC circuit tuned to 60 Hz in order to "monitor and display" 60 Hz EMF. You also seem to believe that the antenna has to be resonant at 60 Hz to detect that low frequency. Responders have pointed out the error in these assumptions. You need not imply that the responders "Don't know the answer." You may just be asking the wrong question so far as your research goal is concerned. EMF is commonly measured by small instruments which allow display on PC's without some impossible 2500 km antenna. I have used them myself, and they are fairly small. I expect that some of the electronics hobbyist magazines have published "build-it-yourself" instructions for such a meter with 3 small coil antennas. A pickup coil producing 1 mV per 20 mG is available for under $5 online [1]. Edison (talk) 20:16, 16 November 2009 (UTC)

Here is a warning if the OP is considering measuring the electric field near high voltage power or overhead tram cables using some kind of homemade probing antenna. Don't. Cuddlyable3 (talk) 21:29, 16 November 2009 (UTC)

You will easily pick up lots of mains frequency (60Hz) signal just by connecting a short piece of wire to your oscilloscope input. To make the waveform look more sinusoidal, just use a passive RC low pass filter directly at the scope input and connect your wire to that. —Preceding unsigned comment added by 79.75.63.71 (talk) 00:30, 18 November 2009 (UTC)

Tsar Cannon with two ton cannonballs?

Sorry about the random inquiry, was just interested with reading a random article I found. Apparently the Tsar Cannon has cannonballs placed in front of it, weighing two tons each according to my interpretation. The cannon was also fired at least once, with gunpowder, according to analysis. Although the diameter of the cannonballs is larger than the barrel diameter of 35 inches, and they were made only for the purposes of decoration, if the cannonballs could fit, would a reasonable amount of gunpowder be sufficient enough to propel a two ton cannonball? And if so, to what distance? Thanks, ♠The Ace of Spades^♣♥_♦ 02:00, 16 November 2009 (UTC)

Not a cannonball, but two tons. Nimur (talk) 03:55, 16 November 2009 (UTC)

Well, this Tsar Cannon gun maybe isn't a suitable design; but a modern battleship from the 1980s was armed with a 66-foot long main battery capable of firing a 1200 kg projectile up to twenty miles. The explosive powder propellant is much more advanced than "gunpowder" (as it would have existed in the 16th century). Our article describes the propellant as "smokeless Powder Diphenylamine (SPD)" with a "titanium dioxide and wax compound known as 'Swedish Additive'"; and polyurethane jackets placed over the powder bags. When the USS New Jersey bombarded the coast of Lebanon, the Navy referred to the projectiles as "flying Volkswagens"[2] in an effort to demoralize the enemy[3]. Targeting for these 2-ton projectiles was grossly inaccurate (blamed on calibration errors in the explosive powder mixture). Shells from this barrage missed their intended targets by many miles, resulting in massive civilian casualties; this was cited as a motivation for the subsequent attack on the United States Marine barracks in October 1983. Nimur (talk) 03:43, 16 November 2009 (UTC)

Perhaps, seeing that the grapeshot that the Tsar Cannon fired weighed about a ton and three-quarters, according to the article. bibliomaniac15 04:15, 16 November 2009 (UTC)

20 miles? ha ha ha ha ha ha ha. Lucky if it went 20 yards. Here are my calculations, first the initial assumptions;

• explosive pressure of black powder = 67 ton/m² (might need adjusting - I got that from a fireworks article)
• energy content of black powder = 3 MJ/kg
• mass of projectile = 800 kg (from article - don't know where Bibliomaniac got ton and three quarters, I don't see it)
• calibre: 890 mm
• barrel = 5.34 metres

From the calibre I get a csa of 0.622 m² and from the pressure a force of 44.3 tons. Newtons second law arrives at an acceleration of 543 m/s². From $\scriptstyle v={\sqrt {2ax}}$ we get a muzzle velocity of a measly 76 m/s - you would probably do more damage head butting the enemy. Maximum elevation and ignore aerodynamics etc gets you a flight time of 7.77s and a distance just over 300 metres. The kinetic energy on leaving the barrel is 118 MJ which, if energy is transferred 100% efficiently, requires about 40kg of black powder.

For a 2 ton projectile it comes out at 118 metres and 16 kg of charge. Of course, many subtleties are neglected here, not least of which is the assumption that the charge continues to burn all the way up the barrel and is completely used by the time the projectile exits. That can be wrong both ways, the charge could burn up before we are done accelerating the projectile, or the charge might not burn fast enough leaving part of it uselessly burning after the projectile has exited. An ideal weapon has the barrel length "tuned" to the missile you are trying to launch and the propellant you are using to launch it, but this one most probably isn't. SpinningSpark 22:23, 16 November 2009 (UTC)

Actually, I've made an error in the amount of powder calculation, it comes out the same for both cases and is less than 1kg, but I don't believe for a minute that is the correct load for this gun in reality. SpinningSpark 22:48, 16 November 2009 (UTC)

The 20 mile range I quoted was never for the Tsar Cannon. It was for the main battery of an Iowa-class battleship; I only mentioned it to illustrate that large artillery does exist, but it is a very different and much more modern design than Tsar Cannon. As for "head-butting", an 800 kg object moving at 70 meters per second would have an impact equal to a large car going faster than highway speeds (150+ mph); I don't know why you would consider that weaker than headbutting. It's still no battleship, though. Nimur (talk) 01:01, 18 November 2009 (UTC)

You are assuming the enemy are too stupid to move out of the way. They will have plenty of time, it must take all day to load the thing, and even in the seven seconds flight time, they could still run a considerable distance. SpinningSpark 18:42, 18 November 2009 (UTC)

Thanks, all. ♠The Ace of Spades^♣♥_♦ 03:34, 17 November 2009 (UTC)

String theory and GUTs

Could there be string vacua that approximate the standard model without allowing proton decay? 76.67.73.245 (talk) 04:09, 16 November 2009 (UTC)

Nobody knows whether there are string vacua that look enough like the standard model to be consistent with experiment. Of course, the proton lifetime doesn't have to be infinite to be consistent with experiment, it just has to be larger than 10³⁴ years or whatever the latest lower bound is. If you're wondering whether string vacua with an infinite proton lifetime have been ruled out, then I don't know, but I imagine not. -- BenRG (talk) 23:08, 17 November 2009 (UTC)

Recreating extinct species

Okay, this is mostly just a small idea that I've been toying with. With current genetics research, I am fairly sure that at some point we will have the capability to clone and reintroduce extinct animals to the wild, but only some have enough intact DNA to do this. I was just trying to think of a list of the more important extinct species that could be brought back. For example, the passenger pigeon and the Carolina parakeet have enough DNA remaining via feathers to clone them and have genetic variation, but the dodo bird likely does not. I was wondering if anybody could add to the list of animals where enough material remains to clone them and retain genetic variability in the cloned population?

1. Passenger Pigeon
2. Carolina parakeet
3. Elephant bird - long shot unless the eggs retain enough DNA.
4. Great auk
5. Thylacine
6. Quagga

Thanks, Falconus^{p t c} 05:11, 16 November 2009 (UTC)

[4] looks like an interesting read. It's currently cited in the Passenger Pigeon article. --Jayron32 05:19, 16 November 2009 (UTC)

Thanks, that was interesting. Also, apparently feathers don't actually contain DNA. Falconus^{p t c} 05:31, 16 November 2009 (UTC)

Bad idea. Eventually they'd figure out how to mate and then we'd have to listen to some flirty nonsense about chaos theory. In all seriousness though, the issue is going to be the "intact" part. DNA samples won't hold very well and the amount of reconstruction one would have to do would be enormous, to a point where you would likely have a very different animal (assuming viability). It's doable for things like the recreation of the 1918 flu since there are only 8 genes. ~ Amory (u • t • c) 13:58, 16 November 2009 (UTC)

The mammoth is often put forward as a likely candidate for the "Jurassic park" treatment. Large amounts of mammoth meat can be found deep-frozen in the north of Siberia - and it's thought that a modern elephant could provide the necessary egg & womb for turning DNA into living animal. Pidgeons & parakeets could be similarly dealt with if the DNA is in good enough shape - but finding a parent animal for an elephant bird, auk thylacine or quagga might be tough. SteveBaker (talk) 14:03, 16 November 2009 (UTC)

Steve, have a look at Quagga Project. ZUNAID●FOREVER 14:57, 16 November 2009 (UTC)

And Neanderthal genome project for a jockey?.Cuddlyable3 (talk) 21:21, 16 November 2009 (UTC)

Re-expanding a shrunk cotton shirt

Some questions regarding the hydrophilic properties of cellulose fibers such as cotton and wool:

• Why is it that materials made from cotton or wool shrink when immersed in hot water and allowed to dry? I mean, what's happening to the polymer? Does the water become permanently bound into it, resulting in permanent swelling of the fiber, thereby decreasing its length, or does the water evaporate and somehow leave behind a shrunk fiber?
• Why does this not happen with cold water?
• Is it possible to re-expand the fibers to the original length after shrinking in this fashion?

My inquiring mind was unable to find answers in the articles about cellulose, cellulose fiber, or hydrophilic. ~Amatulić (talk) 06:54, 16 November 2009 (UTC)

This is not a perfect fix but it helps if you hang a shrunk tee up wet. It would be nice to understand what is happening. My uninformed guess is that being wet allows the shirt fibers to become more disordered, increasing the entropic force of the fabric against stretching. -Craig Pemberton 08:42, 16 November 2009 (UTC)

The process of turning cotton fibers into threads and then weaving them into clothes involves pulling and twisting the fibers. As a result many of the fibers (and their constituent molecules) are distorted into an elongated state. They are weakly bound into that state by binding against other fibers and threads. Heat, water, and/or agitation (e.g. a hot wash) cause some the fibers to free themselves and relax into their natural, unstressed state. It's that act of relaxing that causes the clothing to shrink. Cotton and other organic fibers that have complex textures are more prone to stretching and shrinking than simple synthetic fibers. To a degree one can reduce / counteract shrinkage by manually stretching out the article with applied force but this will never be more than a partial solution since no about of pulling will really replicate the effects of making thread. Dragons flight (talk) 11:21, 16 November 2009 (UTC)

I guess, then, making a garment from pre-shrunk cotton thread won't prevent the garment itself from shrinking later, because the act of weaving would stress the threads. ~Amatulić (talk) 18:28, 16 November 2009 (UTC)

Flying Machine

Could this machine fly?

Are there theoretical limits on size? (I mean way beyond Spruce Moose size) TheFutureAwaits (talk) 07:26, 16 November 2009 (UTC)

The machine depicted appears to have no wing structures - even in a cutaway diagram one might expect to see spaces for their supports: is it actually meant to be an aircraft, or merely an airscrew-driven hydroplane?

If flight is postulated, I suspect it would be too heavy, especially given the old fashioned and bulky natures of many of its components. I don't think there are any theoretical limits on an aircraft's absolute size, but there must be practical limits determined by the aerodynamics of a given atmosphere and the strengths and weights of available materials. A major consideration would be the square-cube law, which dictates that as the linear size of an object increases, its surface area increases proportionallty to the square of the linear increase, but its volume (and hence weight) increases proportionally to the cube - this rapidly increases the wing loading of a conventional aircraft design beyond what will allow flight. 87.81.230.195 (talk) 08:49, 16 November 2009 (UTC)

You could try to demonstrate infeasibility by using a rough and ready calculation for the torque which would be applied to the propeller shaft, and see if any known material has the required strength. -Craig Pemberton 09:08, 16 November 2009 (UTC)

I don't see anything that indicates that this isn't just a multihull boat.-Craig Pemberton 09:11, 16 November 2009 (UTC)

The pontoons are labeled as being "retractable," which I would think would be more likely in the design for a plane than for a boat. My presumption is that it's intended to be a plane, with the wings just not visible in the cutaway. Red Act (talk) 09:22, 16 November 2009 (UTC)

Silly; any vehicle this extravagant is bound to be pimped out. -Craig Pemberton 22:47, 16 November 2009 (UTC)

Also, the rudder sticks up above the craft, not down below it like would make sense for a boat. Red Act (talk) 09:27, 16 November 2009 (UTC)

From the style of the sketch (that's all it is) especially looking at the cars, this was drawn around 1920-30. Anything can "fly" if it gets enough lift. So start by estimating what this monster weighs. Cuddlyable3 (talk) 10:21, 16 November 2009 (UTC)

From the drawing I would have thought that this is meant to be a blended wing body / flying wing aircraft. See alsoJunkers G.38. Boeing clearly thinks this to be an option for future aircraft and is designing one for 800 passengers which can use existing runways. --Cookatoo.ergo.ZooM (talk) 11:06, 16 November 2009 (UTC)

You only showed us one picture...there are more! [5] and [6]. Clearly it's not intended to be a boat. It's very clear that it wouldn't have stood a chance of flying...at least not with the internal design as shown. The artist clearly didn't understand anything about airplane design.

As a flying machine - it's pretty impractical. Using a steerable rear propeller and more props out on the "wings" for turning the thing is a really clunky idea (especially as there is no indication of how those things are powered) - and the de-icing trick results in the need for a double skin which would be heavy. There is a pathetically small fuel supply - yet the fact that there are "quarters" even for the crew and vast amounts of water storage suggests anticipated flight durations of more than just a few hours. There is essentially zero internal structure that would give the thing strength - all we see are partition walls separating rooms...no structural girders except in areas where the artists couldn't think of any useful purpose for the interior space. The weight of things like fuel and engines - plus water tanks and heavy cargo are not well-distributed through the structure - it looks like it would tear right down the middle where the super-weak elevator shaft splits the two heavy sections! The center-of-gravity of an airfoil needs to be at the same place as the center-of-pressure - and that's at the thickest part of the cross-section - this doesn't look like it would have enough weight up-front...but then with those gigantic diesel engines...who know?

There are certainly a lot of oddities to the design...the elevator motors are gigantic! Any idiot could see that if they had moved some of the cargo storage forwards into the bottom of the craft and put the reception areas and offices on upper floors - they'd have needed far fewer stairwells and elevator shafts and perhaps stood a chance of getting the center of gravity in the right place.

This is a classic example of something an engineer would never come up with. Some artist sketched a design for an interesting-looking exterior in 2 minutes flat and then spent the next couple of days carefully filling every cubic inch with something that a cruise liner might need - without giving any consideration whatever for structural strength, power-to-weight ratio, center of gravity, etc.

Bottom line: No - it wouldn't fly.

SteveBaker (talk) 11:18, 16 November 2009 (UTC)

It would make a great submarine. Cuddlyable3 (talk) 11:57, 16 November 2009 (UTC)

Especially if there was a large body of water right at the end of the runway! :-) SteveBaker (talk) 13:58, 16 November 2009 (UTC)

Look how much it's banking in that cover shot! I hope nobody is in those bathtubs! APL (talk) 16:21, 16 November 2009 (UTC)

It's an ocean liner with wings. It is designed just like an ocean liner and would probably weight as much (thousands of tonnes). There is no way to get something that heavy to fly by conventional means. It's not that it was designed by a non-engineer, it was designed before the realities of flight were well understood. It looks like it was designed by a nautical engineer (or someone with experience of ship design) thinking flight would be the same kind of thing. --Tango (talk) 20:05, 16 November 2009 (UTC)

Now I've seen the full magazine item at the page linked to below I see it doesn't have wings, per se. It is supposed to be one big wing. This seems like an obvious idea until you realise that greater weight requires greater wingspan, which means that you need to be able to increase the wingspan without increase the weight much, which means having light wings. That necessitates a design like a regular aircraft with a central thick body and thin wings (although the wings don't have to stick out the sides, they could go forward and back - there have been some interesting ideas along those lines). --Tango (talk) 21:10, 16 November 2009 (UTC)

The design is from 1932 or 1934 (the page says both), and is estimated by its designer to be 10,000 tons. Dragons flight (talk) 20:31, 16 November 2009 (UTC)

It's from '34. The article refers to an earlier design from '32. --Tango (talk) 20:59, 16 November 2009 (UTC)

BTW, we have an article on the guy that designed this thing: Hugo Gernsback. --Tango (talk) 21:17, 16 November 2009 (UTC)

Another couple of problems with the design:

1) Transonic propellers: At 80 feet in diameter, and at the speeds those propellers would need to rotate to keep this monstrosity aloft, the tips would go supersonic, while near the shaft they would remain subsonic. The forces on such propellers would rip them apart.

2) Unstable flying wing design: A flying wing is inherently unstable, requiring continuous control surface adjustments to keep it flying straight. This made flying wings a bad idea in the 1930's. They are more feasible today, since we can use a computerized fly-by-wire system to make those adjustments many times a second. However, if the computer fails, you're in trouble. StuRat (talk) 23:20, 17 November 2009 (UTC)

not exactly dreaming?

I think dreaming refers to REM sleep, a stage that occurs after you've been asleep for a while. There's another dreamlike experience when initially falling asleep. It's possible to forget where you are and what you're doing, and confuse imagined activities with reality, while drifting off. Is there a name for that, if it's not technically the same thing as a dream? 69.228.171.150 (talk) 07:29, 16 November 2009 (UTC)

The article Hypnagogia may give you some leads, both in itself and through the links in its "See Also" section, such as Hypnopompic. 87.81.230.195 (talk) 08:34, 16 November 2009 (UTC)

Thanks, that article is great. 69.228.171.150 (talk) 21:20, 16 November 2009 (UTC)

mathematcal model of PMSM/AC servo motor

hi everybody my project is to control the position of AC servo motor by FPGA by sliding mode control so i need the mathematical model i am try to derive the model but i m facing a lot of problem i m very new to the electric machines i know the basics of the servo motor but it is three phase motor not like Dc motor which is qite simple and its modeling also so any body on wiki kindly help me i want state space modellike[A][B][C][D] matrix so that i can simulate it in MATLAB/SIMULINK and then implementation of sliding mode control technique on AC servo motor i want help about the sliding mode algoritham thanks in advance kindly reply

regard abhay

anembryonic gestation

does anembryonic gestation negatively affect further pregnancy?202.83.57.17 (talk) 09:33, 16 November 2009 (UTC)remy

Not an answer, I'm just adding a link to the Anembryonic gestation article, for others who might be interested. --NorwegianBlue ^talk 15:20, 16 November 2009 (UTC)

Perhaps you meant subsequent -- apparently, spontaneous abortion is thought to include the subset of anembryonic gestation. DRosenbach ^{(Talk | Contribs)} 17:18, 16 November 2009 (UTC)

Special Relativity

In special relativity, if you measure a particle of having an average lifetime of say n seconds as measured in the rest reference frame, and you know its speed, do you just use distance = speed x time to find the average distance it travels in the rest reference frame? —Preceding unsigned comment added by 94.193.67.204 (talk) 10:24, 16 November 2009 (UTC)

If by "rest reference frame" you mean the reference frame of the laboratory, then the average distance a particle travels as measured in that frame, is calculated as Average_speed x Average_rest_life_time x Gamma, where Gamma is 1/sqrt( 1-v^2/c^2 ). The average "time" that was measured of the "still" particles gets dilated by a factor gamma when the particles are moving. DVdm (talk) 10:48, 16 November 2009 (UTC)

The average lifetime is measured as the particle is moving, in the laboratory reference frame, so to find the average rest life time would you divide the average lifetime by gamma? —Preceding unsigned comment added by 94.193.67.204 (talk) 11:26, 16 November 2009 (UTC)

Yes, if the average lifetime is measured on moving particles. Average_rest_life_time x Gamma = Average_moving_life_time. See Time dilation#Time dilation due to relative velocity.

By the way, please sign your messages with 4 tildes (~~~~)? Thanks. DVdm (talk) 11:38, 16 November 2009 (UTC)

Hang on. I think there is some confusion here. You only need to use gamma if you are converting from one frame to another. So, if you are measuring the average life time and the distance travelled in the same frame then you can just do distance=speed*time. If the average life time is measured with the particle at rest (which is the normal value quoted) and the distance is measured in the laboratory frame, then you need to convert the life time at rest to a life time in the lab frame by multiplying it by gamma. You can multiply that by the speed to get distance. --Tango (talk) 19:40, 16 November 2009 (UTC)

Yes. To avoid that confusion I introduced the names Average_rest_life_time and Average_moving_life_time. DVdm (talk) 20:55, 16 November 2009 (UTC)

Recycling

In the United States, is it generally a problem or not to include paper envelopes with plasticine address "windows" with mixed paper recycling? Thank you --71.111.194.50 (talk) 13:10, 16 November 2009 (UTC)

No it isn't. Recycling plants have techniques for removing small amounts of contaminants like this. I can't believe I just answered a refdesk question with a link to Yahoo Answers... —Akrabbim^talk 15:46, 16 November 2009 (UTC)

Bahahahah... you're a regular though, so we have to let that slide. :-) ♠The Ace of Spades^♣♥_♦ 03:32, 17 November 2009 (UTC)

Many such envelopes have a plastic lining that makes them fairly unrecycleable. If you wet your fingers and rub the envelope, the paper will rub off and you'll see a very thin plastic sheet. Ones like that should just be thrown away. --Sean 17:17, 16 November 2009 (UTC)

I don't think you meant plasticine... --TammyMoet (talk) 19:46, 16 November 2009 (UTC)

I have seen many that simply have a hole cut in the paper, and replaced with a clear plastic piece. —Akrabbim^talk 19:59, 16 November 2009 (UTC)

Yes indeed - but that's simply clear plastic, not plasticine, which if you read the linked article, you will see is based on modelling clay! --TammyMoet (talk) 10:23, 17 November 2009 (UTC)

The OP's "plasticine" was clearly a slip for "glassine". I don't think glassine is used much in window envelopes these days, having been superseded by clear plastics as noted above, but it used to be. Deor (talk) 13:02, 17 November 2009 (UTC)

Just to check if my notions are still correct, recycling still is a worthless waste of resources to persue an unrealistic hippie dream right?Bastard Soap (talk) 11:34, 18 November 2009 (UTC)

Perhaps for some materials. We are pretty good at recycling metals though. Googlemeister (talk) 14:13, 18 November 2009 (UTC)

Do arrows have "lift"?

My question concerns the following claim made in this version of the "Quarrel" article:

"Bolts and arrows have different flight characteristics. Bolts fall at the same rate, independent of the speed of flight. Arrows, in contrast, depend on gaining lift in flight, and hence have their centre of balance at a point about 9% of their length forward of their center. This is called 'point planing'."

No reference is (at present) cited in-line for this information. What I'm wondering is: does that make any sense?
On the "Quarrel" talk page I made the comment:

"To have lift, you need an airfoil, but the fletching article makes it clear that the fletchings are there only to "stabilize the arrow in flight" (ie., they are not wings). There is no mention of "lift" in the arrow article."

But then I started wondering about eg. paper airplanes, hang gliders, etc. – the "wings" of which do not (necessarily) seem to have an airfoil shape, either. Some of the "lift" in those cases apparently derives from "angle of attack" issues, but could that really be what's going on (in a consistent, reliable way) with arrows, too? Wikiscient 17:20, 16 November 2009 (UTC)

Air foil shape is useful for getting lift while minimizing drag. Ever see pieces of plywood flying around during a hurricane? Those are not airfoil shape and certainly have lift. Googlemeister (talk) 17:29, 16 November 2009 (UTC)

Well, that refutes my "to have lift, you need an airfoil" remark, but I had already done that myself by bringing paper airplanes etc. into it.

I'm still trying to understand better how "lift" works with arrows, if, in fact, there is any (which, presumably, would be attributable somehow to the fletchings, which neither bolts nor bullets have). Wikiscient 17:40, 16 November 2009 (UTC)

Some (but not all) crossbow bolts do have fletchings. See Crossbow#Projectiles, and this picture. Red Act (talk) 18:15, 16 November 2009 (UTC)

Ok, thanks for the clarification. I guess that just makes the statement in the crossbow bolt article which prompted my question all the more interesting or "incorrect," I'm still not sure which! :S Wikiscient 18:31, 16 November 2009 (UTC)

Wouldn't a crossbow bolt also have that same sort of lift if it was fired at the appropriate angle of attack? APL (talk) 17:32, 16 November 2009 (UTC)

I'm not completely certain of this, but I think the answer to that would be: yes, but not much! Wikiscient 17:43, 16 November 2009 (UTC)

That doesn't make sense to me - shouldn't the centre of balance be further back than the centre of the arrow in order for it to have positive angle of attack and thus have lift? That said, I think the key difference between arrows and bolts is that bolts go faster. That means they don't really need any lift in order to maintain level flight, there just isn't time for them to fall far before hitting their target. --Tango (talk) 18:31, 16 November 2009 (UTC)

Well, again, my question is about this quote (from the crossbow bolt article):

"Bolts fall at the same rate, independent of the speed of flight. Arrows, in contrast, depend on gaining lift in flight..."

There is no reason an arrow couldn't be launched with a higher velocity than a bolt, so I don't think that is the "key difference" in this case.

The "key difference" does seem to have something to do with the location along the length of the projectile of the center-of-gravity. And I am wondering the same thing: placing that forward of the center-of-length would, intuitively, seem likely to create a downwards angle-of-attack force! On the other hand, if the fletchings were providing lift the way an airfoil does (ie. even in level flight), you'd want to have your center-of-gravity forward of center-of-length to compensate for that "upwards-from-the-rear" force.

So, anyway, I'm still trying to understand what the quote in question is trying to say... Wikiscient 19:00, 16 November 2009 (UTC)

See, I'm just confusing myself with this, *sigh*...Wikiscient 19:04, 16 November 2009 (UTC)

Arrows are fired by a bow, bolts are fired by a crossbow. The ways those two devices work mean that bolts are fired faster. That is (part of) why different projectiles are used. As I understand it, the fletches make the arrow spin, providing stability by the gyroscopic effect. Since the arrow is spinning, there is no way the fletches could provide lift (any such force would rotate with the arrow and could average itself to zero). --Tango (talk) 19:31, 16 November 2009 (UTC)

I should clarify - the fletches probably are aerofoil shaped in order to get optimal torque. Each fletch will provide a force in a different direction and, since they are equally spaced, they will all cancel out so there is no resultant force, just a torque (rotational force). --Tango (talk) 19:33, 16 November 2009 (UTC)

No, both of these claims are wrong. Fletches are, modulo production errors, straight and symmetrical. They do not stabilize the arrow by rotation, but simply act as aerodynamic fins. If the arrows velocity is not parallel with its heading, the increased drag of the fletches acting on a long lever will right it again. --Stephan Schulz (talk) 22:39, 16 November 2009 (UTC)

Agreed. So, hmmm... Wikiscient 22:50, 16 November 2009 (UTC)

Assuming that an arrow/bolt behaves in a similar manner to a javelin, the center of gravity is placed relative to the center of pressure to achieve optimal lift. By sport rule, javelins have the center of gravity pushed forward to make them plummet and stick into the ground as opposed to gliding along and skipping along the ground when they land. -- kainaw™ 18:53, 16 November 2009 (UTC)

Optimal lift for an arrow or bolt would, presumably, be the amount of life required to keep the flight level (so you don't have to compensate for trajectory when aiming). That, I would think, would require the centre of gravity to be just behind the geometric centre. (Of course, arrows are sometimes fired up so they travel a greater distance and hit the enemy from above - that would have a different optimal lift, although to get maximum range I would thing it would still want the centre of gravity behind the geometric centre.) --Tango (talk) 19:31, 16 November 2009 (UTC)

Google finds many sources for the "point planing" claim and 9% figure but I leave it to others to decide if any meet WP:RS. Cuddlyable3 (talk) 20:57, 16 November 2009 (UTC)

Almost all those hits look like Wikipedia mirrors to me. --Tango (talk) 21:41, 16 November 2009 (UTC)

Has anyone found a good way to exclude those pesky mirrors from search results? A lot of them don't even say where they got it from so a simple -wikipedia doesn't work. —Akrabbim^talk 22:32, 16 November 2009 (UTC)

If you only want to exclude mirrors of a particular article, just choose a sentence from the article that doesn't sound likely to appear in other articles by change and do -"that sentence". --Tango (talk) 22:35, 16 November 2009 (UTC)

However, "-" terms don't always work in Google if the page uses frames. I think it applies the search criteria separately to each frame but returns the whole page. Unless it's changed since I asked about it and they answered. --Anonymous, 23:52 UTC, November 16, 2009.

Yes, there is a lift force that acts on arrows. There is also lift on crossbow bolts (especially those bolts that have fletching), but the lift is not as significant there.

The primary purpose of the fletching on an arrow is to provide stability. The stability is the strongest in the case of a helical fletch, which imparts a strong rotation around the roll axis. However, a helical fletch results in a slower arrow, and can cause problems with the fletching clearance on the arrow rest. For that reason, a straight fletch is often used, or an offset fletch, which is intermediate between a helical and a straight fletch.

In addition to stability, the fletching also provides lift. Fletching is not shaped like an airfoil, as a glance at the pictures in the fletching article will show, but that's not necessary for lift to occur.

To visualize the forces involved, it's convenient to first think about a horizontal arrow that you just drop, and then consider how that picture changes due to forward motion of the arrow. That won't work well quantitatively, because Bernoulli's principle makes life complicated, but it will at least help to picture some of the physics involved qualitatively.

When you just drop a horizontal arrow, the air resistance on the arrow causes an upward force, especially on the fletching, that wouldn't exist if the only force involved were gravity. That upward force is considered to be drag, which is defined as the component of the aerodynamic force acting opposite to the direction of the arrow's motion, which in this case is downward. Now suppose the arrow also has a horizontal component to its velocity. The upward aerodynamic force still exists, but now that upward force is mainly considered to be lift, since that's defined as being the component of the aerodynamic force that's perpendicular to the arrow's direction, which is now mainly in the horizontal direction. The fletching doesn't have an airfoil shape, so with a straight fletch and an arrow moving purely horizontally (implying a zero angle of attack), there would be no lift. But during the second half of the arrow's trajectory, at least, the arrow is also falling, and the air's resistance to that vertical motion counts as lift.

The quarrel article gives a poor explanation of why an arrow's center of gravity is placed where it is. The reason is that it's a tradeoff between lift and stability.

First, consider how the arrow's center of gravity affects lift. Suppose most of the arrow's mass was right near the tip. Now if you hold the arrow horizontally and let go, the tip of the arrow will drop faster than the nock end, because the upward force on the fletching is in this case much more effective at holding up the nock end of the arrow than the tip. Now consider the same arrow, with the tip still sagging below the nock end, but now with also a horizontal motion to the arrow. Due to the attack angle of the fletching, there isn't going to be as much lift on the arrow, or the lift might even be negative. So the arrow's going to take a nosedive. In contrast, if the arrow's center of mass was back far enough that it stayed horizontal when it was dropped, the loss of lift would be avoided. So for the sake of lift, it's good to keep the center of mass back away from the tip.

Now, consider how the arrow's center of gravity affects stability. Suppose most of the arrow's mass was in the nock, behind the fletching. In this extreme situation, the inertia of the nock tends to keep the nock going at a constant speed, while the drag on the fletching works to make the fletching part of the arrow lag behind. So the forces on the arrow favor the arrow turning around, in obviously a completely unstable situation. As the center of mass is moved forward, the arrow's stability improves, with the maximum stability occurring when the center of mass is at the tip.

Trading off keeping the center of mass away from the front for the sake of lift, and keeping the center of mass away from the back for the sake of stability, leads to a (somewhat empirically determined) optimal compromise between the two.

For a good discussion of the technical details of arrows, go to here, and click the "Archery Technical" link. The "Fletching Arrows" and "Arrow Rotation" articles are particularly helpful toward this question. Red Act (talk) 01:59, 17 November 2009 (UTC)

Thank you for a very clear explication of the issue! Wikiscient (talk) 21:10, 17 November 2009 (UTC)

Dreaming

Why does it seam so realistic, as to be virtual reality?Accdude92 (talk to me!) (sign) 20:28, 16 November 2009 (UTC)

No one can tell you that it's all nonsense without waking you up, so what else can you believe? Cuddlyable3 (talk) 21:01, 16 November 2009 (UTC)

If it seemed unreal then you could pass off whatever messages your subconscious is giving you as being unimportant. Vranak (talk) 22:48, 16 November 2009 (UTC)

This is a Reference Desk, so let's at least attempt to supply some references, people. My only reference is the obvious Dream article which seems to have a lot of problems and does not address your excellent question. It has many, many links to other interesting articles. Comet Tuttle (talk) 23:07, 16 November 2009 (UTC)

Freud, subconscious, ego. I thought this stuff was common knowledge! Vranak (talk) 01:58, 17 November 2009 (UTC)

I have to point out that Virtual reality is not nearly as realistic as dreams. Not yet, anyway. APL (talk) 23:41, 16 November 2009 (UTC)

Don't forget that it's not your eyes that see during the day, it's your brain. If a dream is just a series of images created by your brain, well then that's no different that what happens when you look at something normally. While awake, you know and can tell the difference between what you are seeing and your imagination (the latter is probably hampered by the former) but you don't have that luxury while asleep. ~ Amory (u • t • c) 23:53, 16 November 2009 (UTC)

That's a good point. It ties into the ideas of some contemporary neurologists (Damasio, Ramachandran), who say that memories of sensory experience seem to activate the same brain centers as actual physical sensations. But memories usually seem less real because we have a constant stream of more vivid sensory information coming in to contradict them. If new sensations stop coming in (sensory deprivation, phantom limbs, possibly other neurological conditions like schizophrenia) we can't make that distinction anymore, and we experience convincing hallucinations. Neat stuff. Indeterminate (talk) 07:33, 17 November 2009 (UTC)

microwave cooker question

What would happen to a person who is standing in front of your standard home microwave for 2 minutes if it was running with the door open? I presume most of the microwaves are focused towards the center of the device and you would only encounter a few stray bits that were reflected? Googlemeister (talk) 21:16, 16 November 2009 (UTC)

The Wikipedia article on Microwaves leads me to believe you might get burns and the radiation could possible cause cataracts, though it seems no long term effects (other than tissue damage) would be suffered. Obviously nothing good can come of this, and since it is non-ionizing radiation, there's no way to get super powers 206.131.39.6 (talk) 21:27, 16 November 2009 (UTC)

Someone with metal or electrical implants might fare worse. Before microwaves were properly shielded they posed a threat to people with pacemakers. APL (talk) 21:30, 16 November 2009 (UTC)

Two summers ago I was living in a place with a shared kitchen and I used the microwave a number of times before I realized that there was a hole two-inches in diameter in the front door. I never used it again, and did not develop anything afaict. ~ Amory (u • t • c) 23:49, 16 November 2009 (UTC)

How could an infinite universe expand?

As far as I understand it the possibility of an infinite universe has not yet been removed from the drawing board but how would this play into the big bang and inflation, can infinity originate from a point and can infinity expand?Bastard Soap (talk) 22:22, 16 November 2009 (UTC)

If the universe is infinite then it as always been infinite. At the big bang it wouldn't have been a point of infinite density, it would have been an infinite volume of infinite density. However, the observable universe (all the space light has had time to reach us from) is definitely finite, so that would have been a point. People often refer to the observable universe as simply "the universe" (since it contains everything that can have any effect on us, meaning we can just ignore anything outside it), which is the cause of this confusion. --Tango (talk) 22:26, 16 November 2009 (UTC)

Think about all the real numbers in [0,1]. They are uncountably infinite. If you take a new set, 2[0,1], it is "larger", yet it is still infinite. You can do the same thing with an unbounded set such as [0,$\infty$). Cardinality theory might help you. -Craig Pemberton 22:54, 16 November 2009 (UTC)

The OP wasn't asking about different sized infinities, but rather how something of zero size can being infinite, which is a good question. Also, what makes you think the OP understands interval notation and terminology like "unbounded set"? While they might well do, it is best not to assume certain prior knowledge without good reason. --Tango (talk) 23:30, 16 November 2009 (UTC)

As BenRG puts it, universal expansion is just "stuff moving away from other stuff". Think about it that way and it shouldn't be so confusing. --Trovatore (talk) 23:03, 16 November 2009 (UTC)

I don't know if that's the quote I want to be remembered for. But, yes, when astronomers say the universe is expanding what they mean is that the galaxies are moving apart, and they can do that no matter how many of them there are—even if it's an infinite number. -- BenRG (talk) 11:46, 18 November 2009 (UTC)

An infinite volume of infinite density? That stuff is still on the drawing board? Doesn't that involve infinite energy?92.251.33.207 (talk) 19:30, 17 November 2009 (UTC)

Does it bother you that an infinite universe might have an infinite energy? Why? Dauto (talk) 19:52, 17 November 2009 (UTC)

Wouldn't infinite energy rule out a final heat death? Googlemeister (talk) 21:36, 17 November 2009 (UTC)

We need Stephen Hawking for this question. Is Stephen Hawking in the house? Bus stop (talk) 21:45, 17 November 2009 (UTC)

Why do you keep saying that? -- BenRG (talk) 11:46, 18 November 2009 (UTC)

Dauto is it being picky now to expect the universe to have finite energy? Universes these days, going to hell in a handbasket I tell ya!! Must be that rock music and violent video games! Can you have the positive and negative forces equalling themselves if mass is infinite? Googlemeister seems to me that if the universe can expand from a state in which every god damn piece of it is undergoing fusion to the current state, it must also be able to expand to ultimate heat death state, at least my common sense suggests so, don't know if the universe is laughing maniacally at my puny notions though.193.188.46.64 (talk) 11:31, 18 November 2009 (UTC)

Generally speaking, because physics is local (speed-of-light-limited), it doesn't matter how much stuff there is out there. What happens in one part of the universe only depends on what happened earlier in that part. If you assume the universe is (approximately) homogeneous, then what happens in one part also happens (approximately) in other parts, for parallel reasons. So there's no intrinsic problem in introducing a large or even infinite number of galaxies that evolve largely independently from one another, but in similar ways. -- BenRG (talk) 11:46, 18 November 2009 (UTC)

How does this fit in the free lunch theory of the universe? Is infinity equal to infinity?Bastard Soap (talk) 08:40, 19 November 2009 (UTC)

Why isn't more money spent on SETI?

Why isn't more money spent on SETI, or a similar search for extraterrestrial signals? Although there is no guarantee that there are other intelligent civilisations, or that they would broadcast information that we could use in a short timeframe (rather than us having to make contact and then wait decades, or hundreds of years) - it would seem that the potentially massive technological benefit if we happened upon a broadcast of an advanced civilisation would warrant a bit more of a gamble. Billions, likely trillions, are spent every year on various kinds of scientific research, whereas it seems that SETI has a budget of around $500,000, and finding this stream of information could bypass all of that other spending. On a similar subject, is there an organised effort to transmit our knowledge out into space? I guess that it is likely that any civilisation receiving it would likely not be much less advanced than us, so it may be that our knowledge would not be useful in a pure technological sense, but would be in an athropological sense. I guess the above reasoning for spending money on SETI could also be applied to the development of AI, but it seems that workable that advances our knowledge AI is many, many years away, whereas that signal from the clever aliens could be available right now. QuickSnow (talk) 23:14, 16 November 2009 (UTC)

On the former point, it all comes down to the likelihood of success (small), the enthusiasm for donating money to it (modest), and the political difficulties of dumping public money into a program that has absolutely no realistic prospects for public rewards (difficult), and the fact that trying to communicate with extraterrestrials is rightly considered political poison (crank stuff). All of this, of course, avoids the fact that most people think there are more pressing uses for money (and there are a lot of scientific competitors out there in the "long-shots that could actually pay off" category). Add to it a squeamishness about the fact that meeting extraterrestrials does not, on the face of it, sound like the kind of thing humans would be very good at (how often has the encountering of one advanced civilization with a less advanced one gone well for the former?). On the latter point, see Arecibo message. --Mr.98 (talk) 23:29, 16 November 2009 (UTC)

Transmitting our knowledge into space might not be a good idea. If we ever contact and successfully communicate with aliens we're going to want something to trade with. APL (talk) 23:39, 16 November 2009 (UTC)

What if we're the advanced civilization and find a less-advanced one? The cost of sharing all of our technology could destroy our economy... Seriously though, SETI and similar programs don't get a lot of play because it's hard for people to see the benefit. In the long run, yeah there might be something but compared to that, living on Mars is right around the corner. People would rather see money go towards other things, and it is usually hard to justify spending billions on SETI instead of AIDS or other medical research that will have a much larger benefit much sooner, or any of a thousand other projects. ~ Amory (u • t • c) 23:46, 16 November 2009 (UTC)

I would expect any civilisation we made contact with to be more advanced than we are - we have had the ability to send and receive messages between stars for only a few decades (and even now we can only barely do it). Chances are slim that we would make contact with another civilisation during those few decades where they are less advanced than we are now.

However, regardless of who is we make contact with, we won't get any meaningful communications for a long time. The nearest civilisation might, at best, be 20 light years away, that means a 40 year round trip for any message. The first few messages will probably just be establishing a language to communicate in (it is possible the first message sent will be able to teach a usable language to the other civilisation, but I would expect a bit of trial and error to be required - as we discussed on the Language desk a few days ago, it is very difficult to learn a language (even one designed for the purpose) without 2-way communication. So it would likely be centuries before we could exchange technology. Getting funding for such long term projects is very difficult. Public funding is difficult to get for anything that won't happen before the next election. You'll only get commercial funding if you can turn a profit within a few years, certainly within the lifetime of the investor. That leaves charitable donations and you'll get limited amounts that way.

All that said, there is actually quite a lot being spent on SETI. Consider the recently launched Kepler Mission. That wasn't cheap. While it isn't solely devoted to SETI, discovering terrestrial planets would make it much easier to know where to look for ETIs (or where to send messages to them on spec).

--Tango (talk) 23:55, 16 November 2009 (UTC)

I was imagining a one way communication in the sense that a civilisation mght decide to transmit some, or all (perhaps with the exception of information it thought could be dangerous to itself or the receiver), of its technological informaton along wth the means to decode/translate it, as a constant transmission on a loop. There's no proof that such a signal exists, but it would seem very likely that advanced civilisations do exist out there and perhaps it is likely that they would choose to send such a signal (purely for altruistic purposes, no different to one country sharing its technology with another, simply for the benefit of the receiving country). I can understand that spending billions on this might not be politically sound, but $500,000 a year seems very low (I take on board your point about the Kepler mission though), as there are a lot of people who would spend close to that on a new car. When you take into account that tapping into such a signal would possbly replace decades (or perhaps even hundreads or thousands of years of research)it would seem that somebody somewhere would take a slightly bigger gamble (maybe not with public funds, but with private ones perhaps). QuickSnow (talk) 00:21, 17 November 2009 (UTC)

Finding a way to transmit a message containing instructions to build advanced technology without any pre-existing common language would be very difficult. Anyway, the receiving civilisation would need to technology to receive the message. Assuming a similar technological progression to ours, that puts them at no more than a few decades behind us, we wouldn't have much to teach them, probably nothing. Another issue is that people don't like to devote time and money to something that they won't know worked - we would need a reply to know we had achieved anything, so that's still going to take more than a lifetime for anything but the nearest stars. Also, working out what technology wouldn't be dangerous would be hard - even the simplest technologies can be harmful in the wrong hands. --Tango (talk) 00:59, 17 November 2009 (UTC)

I'm not sure why you think it is "likely". As the Drake equation does a good job of showing, there are a lot of probabilistic factors involved in whether there are even civilizations out there that could communicate with us during the tiny (tiny!) period of geologic history that we have had the ability to listen for them. Taking those and then saying, "so what are the odds that said advanced civilization has decided to broadcast their information to us with a strong-enough signal to be detected and on a continuous loop over the course of at least hundreds of years?"... to me, it doesn't look very likely. The biggest problem here is time itself—look at the history of just our own planet, and how long our civilization has been able to do this kind of thing. Now extrapolate a little bit and say that any civilization that can really grok radio-wave transmission is going to also, within a century or so, grok nuclear weapons and genetic engineering. Now extrapolate the likelihood of any given civilization to survive in a world where there are creatures that grok nuclear weapons and genetic engineering—how many centuries of a "window" does that give you before your civilization can no longer send or receive signals? Much less if we postulate them having anything like politics. Obviously all of this is intangible—we don't know how likely our situation is, much less theirs—but it does seem to imply that there is a much better chance that there is no one out there sending/listening at the same time we can send/listen. --Mr.98 (talk) 00:59, 17 November 2009 (UTC)

I hear this "alien civilisations will probably destroy themselves" argument a lot. The evidence doesn't support that. 100% of species known to have achieved civilisation are still going strong. --Tango (talk) 01:49, 17 November 2009 (UTC)

Human societies have regularly collapsed, e.g. Amazonian civilisations, Ur, Easter Island. So the premise is that if human societies can collapse so easily, so could alien civilisations. See our articles on Societal collapse, Risks to civilization, humans and planet Earth, Existential risk and Extinction event. Fences&Windows 03:35, 17 November 2009 (UTC)

I was careful to speak in terms of species. Human societies and civilisations have certainly collapsed, but they have always been replaced by others. --Tango (talk) 04:03, 17 November 2009 (UTC)

Assuming an alien civilization's lust for bandwidth is similar to ours, they compress their data, which is virtually indistinguishable from background noise. A Quest For Knowledge (talk) 03:50, 17 November 2009 (UTC)

Except it is concentrated in a specific band. However, that only refers to us overhearing their internal communications. It is more likely that we could detect signals intentionally sent into space (we are moving towards wired communication for long range communications so it is likely that other civilisations will do the same, so they would only send out significant amounts of radio pollution for a few decades, we're unlikely to be looking for them during that slot). They would hopefully start with sequences of primes or something else that would stand out from noise very clearly. --Tango (talk) 04:03, 17 November 2009 (UTC)

"It is more likely that we could detect signals intentionally sent into space". Really? Given that a) Homo Sapiens is the only known species who have intentionally attempted such a communication, and b) they've only attempted it once, what is the likelihood that another species would so such a thing? A Quest For Knowledge (talk) 04:28, 17 November 2009 (UTC)

Perhaps it is unlikely that another civilisation will send such a message, but it is even less likely that we'll detect an unintentional message. With the amount of noise we're sending out at the moment and the strength of our radio telescopes we could only detect ourselves if we were at best one light year away, so we could only detect the noise from other civilisations if there is much more of it than we emit and it looks like we aren't going to emit much more than we are now (since we're moving towards wired communications for long range things - ie. the internet vs. regular TV and radio). --Tango (talk) 04:48, 17 November 2009 (UTC)

And that signal power would need to be squared to double the distance right? Googlemeister (talk) 17:18, 17 November 2009 (UTC)

Not quite. Power needs to be multiplied by x² to multiply the distance by x, so you have to quadruple power to double distance. I expect that is what you meant. --Tango (talk) 18:02, 17 November 2009 (UTC)

You all forgot to mention another explanation. It is not scientific (potential benefit and probabilities) or economical (cost effeciency) but political, there is conspiracy in high level government circles to conceal the information that the ETI has been already found and possibly contacted. (Igny (talk) 04:59, 17 November 2009 (UTC))

We didn't all forget - we're all part of the conspiracy. -- Scray (talk) 06:07, 17 November 2009 (UTC)

You were part of it. I'm sure the black helicopters will be arriving soon. --Tango (talk) 08:19, 17 November 2009 (UTC)

Thanks for the warning. I was beamed out by my "friends" just in time. -- Scray (talk) 00:29, 18 November 2009 (UTC)

Somebody forgot a small tag close. Or maybe it was... abducted? Nimur (talk) 01:02, 18 November 2009 (UTC)

November 17

Name of process in which complex material things appear from nowhere?

I've just forgotten this term, but I think it had "brain" in there somewhere. The idea is that in an infinite space, or infinite time, or both, you could have anything happen, including our world simply appearing out of nowhere 5 minutes ago. Myles325a (talk) 01:40, 17 November 2009 (UTC)

Infinite monkey theorem? Mitch Ames (talk) 02:06, 17 November 2009 (UTC)
(That's complex structured data of course, not real physical material) Mitch Ames (talk) 02:19, 17 November 2009 (UTC)

Maybe something to do with brane? DMacks (talk) 02:17, 17 November 2009 (UTC)

Boltzmann brain -- Coneslayer (talk) 02:26, 17 November 2009 (UTC)

OP myles back. Yep, it's Boltzmann's brain (or brane) alright. Thanks. Myles325a (talk) 03:06, 17 November 2009 (UTC)

'For God, all things are possible'. Vranak (talk) 17:06, 17 November 2009 (UTC)

Why is urea planar?

I've drawn the Lewis dot structure of urea, and I just don't understand how it can be a planar molecule with a double bond between the carbon and the oxygen. Why don't the two nitrogen atoms have tetrahedral structures? Is there a double bond that resonates among the O-C and C-N bonds? What's going on here? —Preceding unsigned comment added by 134.10.29.252 (talk) 05:08, 17 November 2009 (UTC)

If we're talking about the configuration of urea around the central carbon atom, it would be expected to be trigonal planar since there are no unpaired valence electrons (using one of the simplest approaches to molecular geometry). Of course, if you mean the amine groups, they will have tetrahedal configuration. So, the entire molecule is not planar, but the carbon is.Thanks Jayron32 for setting me straight below, sloppy work on my part. -- Scray (talk) 06:00, 17 November 2009 (UTC)

The lone pair on the amine nitrogens can enter into conjugation with the pi-bond in the C=O. Lone pairs are not confined to any one geometry, so the amines can take whatever geometry will produce the lowest energy configuration. In this case, the ability for the unbonded pair on the amines to enter into conjugation means that the amins will take on sp² hybridization, and the lone pair will occupy an unhybridized "p" orbital. As a result, the entire molecule will be planar. --Jayron32 06:13, 17 November 2009 (UTC)

To Scray: Its an easy mistake to make. If there is not a neighboring sp² carbon to conjugate with, then amines will take the standard tetrahedral sp³ shape, since that is the lowest energy configuration normally. However, the ability of unbonded pairs in the valence level to move freely, and thus change the geometry of the rest of the molecule, is what makes molecules like Imidazole planar (and thus aromatic) as well; the carbon-only analog, Cyclopentadiene, is clearly NOT planar or aromatic. --Jayron32 06:47, 17 November 2009 (UTC)

I was surprised you used Cyclopentadiene as an example - it seems less than "clearly" non-planar. Our article say's it's planar, as reflected in the Talk page discussion. -- Scray (talk) 12:00, 17 November 2009 (UTC)

The carbons are in a plane, but the hydrogens attached to the non-double-bonded carbon (the sp³ carbon) are not in that plane. Thus, while the ring part of the molecule is in the same plane, the whole molecule is not. This is different from Imidazole, where every single atom is in the same plane. --Jayron32 15:00, 17 November 2009 (UTC)

Resonance in amide functional groups is a pretty important thing...it's one of the reasons proteins are fairly stable (one of the most stable types of acyl group). The result—the C–N bond looks a bit like a double-bond—affects the geometry of protein backbones (like an alkene C=C, a C=N cannot rotate freely the way a single bond can). DMacks (talk) 07:00, 17 November 2009 (UTC)

What is a scientific body of national or international standing?

On Scientific opinion on climate change, we're trying to create a FAQ so the watchers and frequent editors don't have to answer the same questions over and over. One such question is What exactly is a "scientific body of national or international standing"? I've posted the answer I came up with here on the article's talk page. However, I am not a scientist of any kind, so I'm not sure if it's accurate. Any comments, suggestions, or feedback I can get from any scientists out there would be greatly appreciated.

An Academy of Sciences or a scientific society that maintains a national or international membership, and that is well-regarded within the scientific community could be said to be of "national or international standing." Discerning how well-regarded a particular scientific body is requires some familiarity with the scientific community. However, in general, this can be determined by the impact factor ratings of the body's journal as provided by Journal Citation Reports. The journals Science, from the American Association for the Advancement of Science, and PNAS, from the US National Academy of Sciences, are considered amoung the world's most influential and prestigious.[7][8][9]

Thank you.--CurtisSwain (talk) 10:14, 17 November 2009 (UTC)

Well, you may need to be clear whether you mean prestigious in terms of membership, or prestigious in terms of publications. The two are somewhat correlated but not synonymous. For example, NAS membership is highly selective, while membership (as opposed to "Fellow"-ship) in AAAS and most such scientific societies is essentially open to any graduate in the field. On the other hand NAS's sister societies National Academy of Engineering and Institute of Medicine, while being selective, do not publish any journal; while prestigious and high impact journals such as Cell (journal) and Nature (journal) are published by private companies. Finally, the prestige of a society depends on its relevance to a particular field; so IEEE may not be as well known as NAS and the Royal Societies, but when it comes to wireless communication standards, its opinion and publications are more relevant than theirs. Abecedare (talk) 10:37, 17 November 2009 (UTC)

For the UK, probably the best suggestion would the the Royal Society. --Phil Holmes (talk) 10:39, 17 November 2009 (UTC)

Yes, figuring out the best examples is easy - most national academies of science qualify. The question is where to set the lower level. Looking at a fairly harmless field, I'd say AAAI qualifies - what about AAR or FLAIRS? On the one hand, FLAIRS is a Florida group, but both AAR and FLAIRS organize internationally attended conferences. --Stephan Schulz (talk) 17:11, 17 November 2009 (UTC)

Your efforts are noble, but they may be in vain; essentially, you're trying to draw the bottom demarcation line of the "gray zone," which is inherently subject to debate. Take a look at Wikipedia:Reliable sources for previous consensus opinions about how to do this. Nimur (talk) 01:08, 18 November 2009 (UTC)

Wow, this is so cool that people have taken the time to help with this. Thank you. I think what Scientific opinion on climate change really needs is some sort of criteria for distinguishing a respected, legitimate scientific body (like those mentioned above) from one of dubious standing (like Oregon Institute of Science and Medicine). Is there a way to do that? It doesn't have to be perfect.--CurtisSwain (talk) 21:54, 18 November 2009 (UTC)

There are numerous problems with trying to categorise organisations in articles. But any smart reader would check out any organisations they don't recognise. Reading the linked article, it doesn't take a genius to figure what kind of organisation "OISM lists six "faculty members,"[1] but does not enroll students or teach courses." In any case, there may be merit to exclude organisations who's opinions carry no weight. And indeed there is no mentioned of the OISM in the article. Oregon Petition is in a see also that's all. But the merits of the petition have only limited connection to the organisation starting it. And the petition article does have criticism of the petition. And more importantly perhaps the intrinsic problems with any petition of scientists is documented in a number of places in wikipedia I'm pretty sure. E.g. Project Steve Nil Einne (talk) 07:12, 19 November 2009 (UTC)

Further digital television enquiry

This is a UK-related TV problem. I posted a few weeks ago about a solution for digital television in my home and had a useful answer, though not the one I was hoping for. I'm still finding it really hard to get objective information about the best solution for my needs. All I really want is to be able to get TV into several rooms in the house (3 rooms at least) in a way that different channels can be watched simultaneously. Only looking for the main free-to-air channels: BBC1 to 4, Channel 4, ITV. We already have digital co-ax running from a central point to those rooms, so distribution should in theory be possible. At the moment we are with Virgin Media and I have a quote for adding two extra digiboxes (installation plus extra subscription), but I want to work out if Freesat is a better option. Not considering Freeview due to poor reception in the area. At the same time, we want to replace two old analogue TVs with new ones. If we get a Freesat dish, then presumably we can distribute the signal around the house easily enough, either with the current (powered) connections, or with a distribution box that I have seen on the Maplins website? Then should the new TVs be Freesat TVs rather than normal digital TVs? They are much more expensive. I assume that normal digital TVs can actually be used in a Freesat system, since analogue ones can. But what about HD? Most sets sold at the moment are HD-ready, but will a typical HD-ready digital TV receive Freesat HD, either now or in the near future? Many thanks if you have borne with this long explanation and can understand where I have got to. The idea of queuing in Maplins for twenty minutes and then having to go through all this to one of their vendors is a bit daunting. Itsmejudith (talk) 11:44, 17 November 2009 (UTC)

I can't answer your query directly, but you may wish to have a look at Digital Spy forums: here's a link to the Virgin Cable one [10] --TammyMoet (talk) 12:23, 17 November 2009 (UTC)

And I Am Not An Expert, but my understanding is that with Freesat you need a tuner for every TV you want to use to view content. So if you have 3 rooms, then you will need a Freesat dish and LNB with at least 3 (I think 4 is common) outputs. These are distributed (I think with co-ax) to where the TV is. You can then either have a Freesat TV (they are more expensive because the satellite tuner is more expensive) or a "normal" HD one with HDMI in. If you get a Freesat HD tuner, I would expect it to have HDMI out, and so you connect them using that. You then have HD sent from the tuner to the TV where you can view it. If you don't have HD/HDMI on the TV, you could use SD with a SCART cable. Think this is accurate and Hope It Helps. --Phil Holmes (talk) 12:32, 17 November 2009 (UTC)

Does help, thanks both. I also spoke to the local Maplins store on the phone, and they are recommending buying a lot of equipment, so it may work out better to stick to Virgin in the short term at least. The devil you know... Itsmejudith (talk) 13:45, 17 November 2009 (UTC)

Bear in mind that TVs (e.g. Panasonic) are starting to appear which have both Freeview and Freesat receivers built-in. Bazza (talk) 14:13, 17 November 2009 (UTC)

Can confirm some correct data above - 3 TVs on Freesat need a dish with a Quad (4) or Octo (8) LNB (and a cable from the dish to each TV - you cannot split them!) A Freesat recorder also needs it's own cable (and if it's a dual tuner, then it needs 2 cables!) Most Freesat TVs have Freeview as well - hence the high price. Remember that when analogue goes off the digital signal will be much stronger - I'm on Lancaster at 200W, last year we lost a whole day's TV while they modified it to be able to go to 2kW on Dec 4th. Also note that a lot of TVs are marked as HD ready - but they only show 720p, only the more expensive ones will do 1080p. Also BBC & ITV intend to transmit a few HD channels on Freeview, but existing boxes/TVs might not be able to decode the signal without a software update. As you say, it may well pay to sit tight until the dust settles.  Ronhjones  ^(Talk) 19:53, 17 November 2009 (UTC)

To clarify, a 720p TV will still display a 1080 channel, just at the lower resolution. StuRat (talk) 22:55, 17 November 2009 (UTC)

The Mystery of Almond Milk

Hello! Almonds are pretty high in calories (nearly 200 per 1. 0z serving), like all nuts. So why is almond milk so low in calories? (30-50 cals per 8 0z. serving, depending upon brand). Since it's made from almonds, you'd think a cupful of almond milk would be about as many calories as a cupful of almonds, but it's not. O_o Anyone know why? 128.239.150.20 (talk) 12:43, 17 November 2009 (UTC)mimosa

It's not as much of a mystery as you might expect. The process produces an almond "pulp" that needs to be watered down to get the consistency of milk. This dilution reduces the fat by volume content. Fribbler (talk) 12:53, 17 November 2009 (UTC)

species diversity

How species diversity affect ecosystem —Preceding unsigned comment added by 61.2.193.124 (talk) 16:59, 17 November 2009 (UTC)

The more species you have the more complex food chain you get. The rest is very much depend on the kind of species, the enviroment they live in and etc. Humans proved time after time that they not fully understand how different ecosystems work (but they do know how to destroy them).--Gilisa (talk) 18:17, 17 November 2009 (UTC)

See Biodiversity. We have a brief article about the measure Species diversity too. Fences&Windows 00:41, 18 November 2009 (UTC)

Scar removal?

I was wondering if it was possible to remove a scar completely.

I know there are treatments to reduce the appearance of them but I was wondering if it is or if there might be potential with new medical technologies to remove scars completely.

Just emphasizing once again, if there is a way through plastic surgery or dermabrasion or something to remove a scar completely. If they are not too deep like the singer, Seal's and just look normal. —Preceding unsigned comment added by 139.62.167.186 (talk) 18:00, 17 November 2009 (UTC)

This sounds like a request for medical advice. The best person to seek to answer your question would be a dermatologist; without an actual live person to actually examine you, it would be impossible for anyone to make a determination on a correct course of action in your unique case. --Jayron32 19:07, 17 November 2009 (UTC)

That doesn't sound like a request for medical advice at all. He is asking if it is possible to do it, not wheather he should do it. I don't think it is possible. Dauto (talk) 19:33, 17 November 2009 (UTC)

Cosmetic surgery can do all kinds of things to reduce the visual impact of scarring, but I've never heard of anything that can remove them perfectly. --Tango (talk) 19:42, 17 November 2009 (UTC)

Given requisite time and resources, your body takes care of business. That includes scar tissue. It re-absorbs the collagen or something of that nature. Vranak (talk) 21:21, 17 November 2009 (UTC)

Really, because I have several scars, some of which I have had for 20 years or more. Googlemeister (talk) 21:35, 17 November 2009 (UTC)

This is why I also said 'resources'. Rejuvenative juices, if you will. Vranak (talk) 22:06, 17 November 2009 (UTC)

That's interesting Vranak. So what 'rejuvenative juices' are you talking about here. I also have a scar that is about 55 years old. Am I lacking some vital process in my body that should have corrected and repaired this or am I the same as the enormous majority of the human race who have life-long scars? Richard Avery (talk) 08:18, 18 November 2009 (UTC)

All I'm saying is that scars can be totally healed. That they commonly don't is not disproof that they can and do. Vranak (talk) 19:44, 18 November 2009 (UTC)

Mucosal scars are much easier to restore to virtual perfection than dermal scars -- you didn't specify type or location of scar. DRosenbach ^{(Talk | Contribs)} 17:36, 18 November 2009 (UTC)

See also, Scar#Treatments_for_skin_scars. "Currently no scar can be completely removed... all treatments will leave a trace." --Mr.98 (talk) 22:58, 18 November 2009 (UTC)

Flying birds that are very weak in the air

Which bird species, whilst being capable of flight is considered to be the worst, or weakest flier? I know that domestic chickens are technically able to fly but even without their wings clipped, they can just sort of flutter about four feet off the ground for a few seconds but I'm not counting these as they are not wild birds. --90.241.8.92 (talk) 18:12, 17 November 2009 (UTC)

Well, there are a large variety of birds that will not fly except when absolutely necessary. I don't know which is the weakest, but birds like peacocks and wild turkeys don't seem to be likely candidates for flying long distance. Falconus^{p t c} 19:20, 17 November 2009 (UTC)

I think you are looking for the albatross. It can glide extremely well, but it has a hard time with takeoffs. Googlemeister (talk) 19:30, 17 November 2009 (UTC)

I will second wild turkeys. Vranak (talk) 21:20, 17 November 2009 (UTC)

According to our article on wild turkeys, they are actually agile flyers, but don't fly far off the ground, and rarely for more than 400m.Falconus^{p t c} 21:28, 17 November 2009 (UTC)

Clapper Rail, Hoatzin. Fences&Windows 00:37, 18 November 2009 (UTC)

The Flying Steamer Duck is the only one of the four Steamer Duck species that can actually fly at all (hence its name): however (although our article doesn't mention this) while smaller specimens of the species can get themselves airborne, the largest and heaviest (usually adult males) cannot. More details can be found in this [11] post on Palaeontologist Dr. Darren Naish's excellent Tetrapod Zoology blog. 87.81.230.195 (talk) 11:29, 18 November 2009 (UTC)

Elevator stuck

A couple days ago, one of my friends was stuck on an elevator for 45 minutes. Apparently he and a large group got on on the first floor, and more joined on the second floor. It just stopped soon after. Unsurprisingly, 18 geniuses on board and 700lbs over the weight limit seemed to be a contributing factor. Anyway, my friend commented to me that it's good they didn't try to force the door open, because it may have caused the elevator to fall. The elevators break frequently here, so my guess is that they only told them that so that in the future they wouldn't try and damage the door mechanism. Surely the engineers would not have designed the safety catches to be dependent on closed doors? How does that work? Thanks, Falconus^{p t c} 18:17, 17 November 2009 (UTC)

Oh, I should mention that I am in the US. I know foreign elevators tend to be different. Falconus^{p t c} 18:20, 17 November 2009 (UTC)

Elevator#Cable-borne elevators is your friend: your suspicions are confirmed - the door thing is a canard. --Tagishsimon (talk) 18:21, 17 November 2009 (UTC)

Alright, thank you. That's what I thought. Now that statistic of 10000 out of 120 billion elevators having even minor anomalies is interesting. In this building, it seems someone gets stuck on an elevator weekly (usually it has little to do with overloading). Falconus^{p t c} 18:29, 17 November 2009 (UTC)

That's 120 billion elevator rides, not elevators. That many elevators would mean we would each have over 20, and I barely even own a dozen. :-) StuRat (talk) 22:43, 17 November 2009 (UTC)

Did your friend notice what was the weight rating and the person limit on the elevator? Edison (talk) 18:49, 17 November 2009 (UTC)

There is no posted person limit, but the weight rating is 2500lbs. I'm not sure if he noticed that or cared until they got stuck, at which point they decided to kill time by adding up everybody's weight. Apparently they totalled 3198lbs. Falconus^{p t c} 19:10, 17 November 2009 (UTC)

Might want to add up to a 5% error margin since a lot of people habitually under report. Googlemeister (talk) 19:28, 17 November 2009 (UTC)

If an elevator is overweight, it's supposed to stand and refuse to even close the doors. So how did they get stuck? It stopped midway? It closed the doors and wouldn't open them? The reason I ask is that it doesn't sound like being overweight was the reason they got stuck. If I were making an elevator I would add at least a 50% margin to the weight limit. Ariel. (talk) 21:47, 17 November 2009 (UTC)

I believe that it started to move and then stopped, leaving them stuck. It wouldn't surprise me though if it was just acting up anyway, because it does that stunt regularly (once a week or so) with only a couple people on it. It's somewhat ironic that these elevators are in the dorm of a very well respected engineering school, but yet they can't even figure out how to maintain them. Falconus^{p t c} 23:11, 17 November 2009 (UTC)

One thing that surprises me is that they don't just make it impossible to overload an elevator with people. For example, if the elevator is 5 feet by 5 feet, I figure it could hold at most maybe 25 people at 200 pounds each, so would make it able to haul 5000 pounds. If it could only haul 3200 pounds, then I'd make it only 4×4. Do they really expect people to start asking each other's weight and adding them all up, before they get on the elevator ? Of course, some idiot could still try to fill the elevator with heavy machinery or something, but at least the common case of too many people would be handled. StuRat (talk) 12:09, 18 November 2009 (UTC)

Presumably, the elevator company's customers are people who are building buildings. If you're trying to make your building as nice as possible (to satisfy your customer) are you going to choose the company that makes uncomfortably small elevators? APL (talk) 15:34, 18 November 2009 (UTC)

Well, if I were hiring an elevator company I sure wouldn't want them to give me elevators that won't work whenever they are full of people, would I ? I'd expect them to provide an adequate lift capacity for everyone who could fit in there. I'd also expect there to be safety regulations which would require this. StuRat (talk) 16:32, 18 November 2009 (UTC)

But for much cheaper, you could get ones that just don't work under the very rare chance that you put too many people in them. If money is no object, you could just get so many elevators people would never have to crowd onto them. — DanielLC 16:35, 18 November 2009 (UTC)

An elevator would have to be very uncomfortably tiny (relative to its weight capacity.) to make it impossible to over-stuff it. See Phonebooth stuffing. Any elevator designed this way would not be pleasant to ride. Normal elevators are usually strong enough to carry people when they 'fill' the elevator with reasonable personal space allowances, but not necessarily if you cram every cubic inch with human flesh. APL (talk) 21:17, 18 November 2009 (UTC)

I seem to recall reading that passenger elevators, for safety reasons, have to be able to stand at least 10x their rated weight. That is, for an elevator to be rated at 2500 lb, it must be capable of functioning safely with a 25,000 lb load. Freight elevators were said to have a 2-5x safety factor instead. Again, I can't remember where I read this, so I can't say it's definitely true, but I would be *very* surprised if the safety margin is sol slim that it can't stand an extra 3-4 people. -- 128.104.112.237 (talk) 17:32, 19 November 2009 (UTC)

I got stuck in an elevator in spain. I was jumping in it and it stopped.18:03, 19 November 2009 (UTC)

"Stand" is a relative term. It means that the cable won't break, the brakes won't fail, and the floor won't fall out of the car. It says nothing about the ability of the motor to lift the car: it's quite possible that the extra load will cause the motor to burn out (or a circuit breaker to trip), stalling the car halfway between floors. --Carnildo (talk) 01:42, 20 November 2009 (UTC)

What's the strongest acid and the strongest base?

What's the strongest acid and the strongest base? Are they known to be the strongest possible, or have there merely been no stronger ones found? --75.6.4.21 (talk) 22:04, 17 November 2009 (UTC)

Fluoroantimonic acid. Vimescarrot (talk) 22:22, 17 November 2009 (UTC)

I'd also like to point out the redirect, strongest acid. Which makes the link for strongest base a little annoying. Vimescarrot (talk) 22:23, 17 November 2009 (UTC)

The answer is somewhat ambiguous, and depends on the definition of 'base' one prefers. Is a base a material which produces hydroxide ions when dissolved in water (the Arrhenius definition), a material which is a proton acceptor (the Brønsted definition), or a material which can act as an electron pair donor in a chemical reaction (the Lewis definition)? You can find some useful discussion in our article on superbase, however. TenOfAllTrades(talk) 22:51, 17 November 2009 (UTC)

Not sure if it is strictly the strongest under all definitions, but tert-Butyllithium is the strongest I have ever worked with. Its particularly unpleasant stuff. --Jayron32 23:08, 17 November 2009 (UTC)

The strongest acid is actually helium hydride Which will add a proton to any other material (apart from a proton). Graeme Bartlett (talk) 01:37, 18 November 2009 (UTC)

That's pretty exotic stuff, though, considering that you can't even keep it in a jar, since it will protonate the material making up the jar. It is literally impossible to handle in any way, and all its properties, save basic spectroscopic properties, are only known theoretically, and not empirically. We can say that it exists, but there is almost nothing else that could be said about it. As far as a substance a person could reasonably consider to handle, the strongest acid would be HSbF₆. --Jayron32 04:38, 18 November 2009 (UTC)

Pretty exotic indeed. I hereby invent hydrogen hydride (H₃), which would even outclass helium hydride :-) DVdm (talk) 08:28, 18 November 2009 (UTC)

The article on this is H3+ or Trihydrogen cation, and it is a weaker acid, HeH⁺ will protonate H₂ to make H₃⁺. Neutral H₃ could only exist as an excimer as it is unstable in the ground state H₃ --> H₂ + H.—Preceding unsigned comment added by Graeme Bartlett (talk • contribs)

Dang, too late! Thanks for the information. DVdm (talk) 21:31, 18 November 2009 (UTC)

Perhaps you can turn your invention into a redirect! Your invention is actually a very common ion in space. Graeme Bartlett (talk) 21:34, 18 November 2009 (UTC)

The Spanish version of a H₃ article exists: es:Hidrógeno triatómico I suppose the English equivalent is triatomic hydrogen. Graeme Bartlett (talk) 11:55, 20 November 2009 (UTC)

Expansion of the universe

If we were to lay a rope from here to some distant galaxy and tie the end there, will it stretch and break because the distance increases but the electromagnetic force overpowers the expansion of the universe within the rope? Or will it just "lengthen" without stretching, expanding along the universe? --78.176.22.9 (talk) 23:12, 17 November 2009 (UTC)

The expansion of the universe is actually overcome quite easily by small forces such as gravity, the effect is not generally visible on anything smaller than the galaxy size; that being said, if you could attach such a rope to said galaxy and hold it to yourself, the two objects would be "bound" and thus would not be suject to the Metric expansion of space. There are some patrollers at these refdesks who hold that the so-called expansion of space isn't real; that its just the objects in the universe moving out into emptiness, but many cosmologists would disagree with that assessment. --Jayron32 00:18, 18 November 2009 (UTC)

So is that to say that the rope is strong enough that it could exert enough force accelerate an entire galaxy enough to overcome the expansion? Rckrone (talk) 00:30, 18 November 2009 (UTC)

In the light of what you have just said, does an object larger than galaxy-size expand within (along?) the space? The article states that the cosmological constant acts as a repulsive force even on individual atoms. So, am I right thinking that the rope that "binds" the galaxies together will be subject to tremendous forces? --78.176.22.9 (talk) 00:47, 18 November 2009 (UTC)

Tremendous forces, yes. But dark energy is largely irrelevant. You'd encounter tremendous force for the same reason that one sees tremendous force if you throw a lasso around a moving car. In other words, simply because it has a lot of momentum from it's existing motion and you are trying to stop it. Dragons flight (talk) 01:17, 18 November 2009 (UTC)

Attach a rope to anything that is currently moving away from you and there are only two outcomes. Either the rope exerts sufficient force to slow and stop the object it is attached to from moving further away (relative to you), or the rope breaks. Same holds at astronomical scales, except it is virtually certain your rope would break for any physically constructed rope. Dragons flight (talk) 01:02, 18 November 2009 (UTC)

Sorry, maybe I should rephrase the question, Forget the galaxies seperating and pulling the rope. Let's just have the rope. Does a rope or rod-like object millions of light years long expand/stretch ordinarily? I mean, does this object experience a force like being pulled from each end? Or does it expand "freely" without "being pulled", similar to relativistic length contraction? Like its "coordinates" moving or something? I'm not a native English speaker, I hope I made myself clear... --78.176.22.9 (talk) 01:33, 18 November 2009 (UTC)

Neither. It doesn't expand. Assuming you laid it out so that the rope was stationary to begin with (and ignoring the self-gravity of the rope) then it would stay that way. Dragons flight (talk) 01:38, 18 November 2009 (UTC)

The electromagnetic forces holding the atoms and molecules together would be more than enough to stop there being an expansion. Even if the rope were long enough for the two ends to be causally disconnected (that is, one end is not within the observable universe of the other end) it still wouldn't be ripped apart since the expansion on an atomic scale is tiny so it is easily overcome by the EM forces and if there is no expansion on small scales there can be no expansion on large scales, since the expansion between A and C is just the sum of the expansions between A and B and between B and C (assuming the points are in alphabetical order). --Tango (talk) 02:50, 18 November 2009 (UTC)

That doesn't seem quite right. The longer the rope is, the more either end is forced to accelerate in order for the rope to remain the same length. There's only so much acceleration the end of the rope can withstand before it simply breaks off. In other words, the very small amount of acceleration needed locally to overcome the tendency to expand is cumulative over the full length of the rope. Rckrone (talk) 03:21, 18 November 2009 (UTC)

Acceleration relative to what? What matters is acceleration relative to the bit of rope it is connected to, which is the bit right next to it. --Tango (talk) 03:28, 18 November 2009 (UTC)

Acceleration relative to a local inertial frame. Assume the first bit of rope is not accelerating in its frame (for example it's the center of the rope). The second bit of rope has to accelerate a little in its frame to stay next to the first bit. The third bit has to accelerate a little to stay next to where the second used to be, but the second bit is also accelerating away from the third bit due to the bond with the first bit, so the third bit has to accelerate twice as much to stay with the second bit. The fourth bit has to accelerate more, etc. Rckrone (talk) 03:46, 18 November 2009 (UTC)

A rope at rest will stay at rest. All local frames are equivalent and it doesn't need to accelerate anywhere. Now creating a rope at rest would be complicated since at least one end of the rope would appear to be moving very rapidly compared to the inertial frame of the local stars, but that's a problem of experimental design, not one of physics. All each bit of the rope knows is that it is at rest with respect to neighboring bits of the rope, and nothing about the expansion of the universe acts in such a way to change that. Dragons flight (talk) 05:22, 18 November 2009 (UTC)

Is it not the case that two very distant inertial objects that start at rest relative to one another will begin to move away from each other? I'm not an expert on cosmology, but that's the impression I got from articles like Metric expansion of space and Cosmological constant. I know there are still a lot of different theories, but I thought there was evidence that the expansion of the universe was accelerating, and not just caused by objects moving away from each other due to inertia. Is this incorrect? Rckrone (talk) 06:44, 18 November 2009 (UTC)

For Hubble expansion they never move. Cosmological constant type dark energy can be modeled as a psuedoforce $F={4\pi \over 3}Gm\rho r$ where ρ = 1×10⁻²⁵ kg/m^3. So at a megaparsec it is the same as applying an acceleration on the rope of order 1 ×10⁻¹² m/s^2, or thirteen orders of magnitude less than Earth's gravity. Any real rope would have sufficient tensile strength to resist such forces. So again, the ends wouldn't move appreciably (just enough to provide the tension to counter dark energy and then stop). Dark energy is only just observable if you consider objects at cosmological scales and assume if has been acting for billions of years. It is not a big force. Dragons flight (talk) 07:15, 18 November 2009 (UTC)

Ok thanks. I didn't realize just how tiny the acceleration was.

However, regarding the megaparsec rope, I think it still would not be able to withstand the kind of tension that would result. The acceleration necessary is small, but the mass that needs to be accelerated is pretty large. Suppose the density of the rope is 0.1 kg/m, then the masses being accelerated are of order 10²⁰ kg, and the tensions involved would be of order 10⁸ N, which is probably more than a rope like that can exert. On the other hand, a real rope has some elasticity. If it could stretch up to 10% of it's original length before breaking, it could be stretching for a billion years before it failed. Rckrone (talk) 19:09, 18 November 2009 (UTC)

Quite true. My answer below was predicated on a rope (tether) of length comparable to cosmological distances; a thought experiment similar to that in Davis and Lineweaver's paper. Such a rope is not something that could ever be constructed physically. The main thing is... expansion isn't a force that would make things expand or contract. Galaxies continue to expand by inertia. Local concentrations of matter easily hold together by their own gravity regardless of the tiny hypothesized pressure from dark energy to accelerate expansion; our galaxy does not expand, for example. —Duae Quartunciae (talk · cont) 07:38, 18 November 2009 (UTC)

Whether inertial objects that start out at rest relative to each other will accelerate away from each other depends on whether the rate of expansion is accelerating or not. The point is, as many people have been saying, is that the expansion of the universe is not a force that makes things expand. It is a description of the large scale motions. Galaxies expand away from each other not because they are being pushed, but because they they started out expanding away from each other. So what about a really long rope that DOESN'T start out expanding or contracting? Expansion is not a force to push on it and change it. However, there are forces to consider; forces that also work to change the rate at which the universe in general is expanding.

In the models of the universe before dark energy was inferred, it was thought that expansion was slowing due to the effect of gravity to pull everything back together again. In this case, the very very long rope initially at rest with respect to itself (zero rate of change of proper distance all along the rope, to get technical) would start to compress (the second derivative of proper distance along the rope is negative). With dark energy, there is a kind of pressure that accelerates expansion; if dark energy is sufficiently dominant (as it appears to be in the current epoch) then the rope will start to stretch.

This does get pretty technical. The best account is probably Davis, Tamara M; Lineweaver, Charles H.; Webb, John K. (2003), "Solutions to the tethered galaxy problem in an expanding universe and the observation of receding blueshifted objects", American Journal of Physics, 71: 358–364 {{citation}}: Cite has empty unknown parameter: |1= (help). —Duae Quartunciae (talk · cont) 07:06, 18 November 2009 (UTC)

Hmm.. what I understand from this is: The universe started with an initial push causing the expansion and that initial push exists no more. But we also have the dark energy, which pushes today and the expansion accelerates.

So, does the rope stretch? 78.176.22.9 (talk) 09:49, 18 November 2009 (UTC)

Yes; you can call the inflationary epoch the initial push; after which everything was flying away from everything else, and the space everything occupies increases in volume also. Once inflation shut down, the universe "coasts", with gravity working to slow the rate of expansion. But (apparently) there's still a tiny little bit of dark energy around, so that after 5 to 8 billion years or so, density has dropped enough that the effects of dark energy actually overcome the effect of gravitation from mass, and the expansion rate starts to accelerate again. Or at least, that's how it looks at present.

But as for the rope, it depends. As has been pointed out, dark energy is really really weak, up until you get to cosmological scales. pretty much any kind of force within a "rope" binding it together would be enough to hold it together just fine.... unless perhaps you have a rope hundreds of Megaparsecs long. The Davis and Lineweaver thought experiment may be more useful. Just think of the end points of rope. Take two galaxies, give them peculiar (local) motion so that the "proper" distance between them has a rate of change of zero, and then release them and just let them coast along with the rest of the universe. Ensure they are far enough apart that you can neglect gravity between them. You can image a rope between them if you like; but the question is, do they start to recede from each other, or remain at a fixed distance?

1. In the empty universe model, they remain always at the same distance from each other.
2. In a matter or radiation dominated universe, the expansion rate is slowing, and the two galaxies actually start to approach. In the long run, they pass through each other and then asymptotically approach the Hubble flow on the other side of the sky.
3. In a dark energy dominated universe (which is the present leading model), the two galaxies will start to recede from each other, with a very slow acceleration.

Full gory details in Davis and Lineweaver (2003). —Duae Quartunciae (talk · cont) 11:13, 18 November 2009 (UTC)

Thank you for your explanation. I found the the aforementioned article (or a summary of it, seven pages long). While the math is above my understanding, the rest isn't gory at all but pretty fun to read, with graphs and diagrams! Thanks again for your time! 78.176.22.9 (talk) 17:17, 18 November 2009 (UTC)

fermentation - what's the correct term for this?

Which is the correct term for one whose profession is fermenting? Fermenter OR fermentor? (I'm not interested in other synonyms) I already checked multiple dictionaries. ike9898 (talk) 23:25, 17 November 2009 (UTC)

This question stands a better chance of being answered at the Language Desk. You might try moving it over there. --Jayron32 23:46, 17 November 2009 (UTC)

Brewer. 75.41.110.200 (talk) 01:33, 18 November 2009 (UTC)

Narrower term of Brewer or Vintner. Graeme Bartlett (talk) 01:32, 18 November 2009 (UTC)

Dunno if it exists, but zymurgist would suit. From zymurgy. [12] --TammyMoet (talk) 11:05, 18 November 2009 (UTC)

It depends on what you're producing via fermentation. If it's beer you're a brewer, if it's wine you're a vintner, if it's bread you're a baker. If it's vinegar, cheese, or something else, then I'm not sure if there's a specific name, but the general terms zymurgist and zymologist might apply. StuRat (talk) 11:59, 18 November 2009 (UTC)

Thanks, but I said I wasn't interested in synonyms. ike9898 (talk) 18:53, 18 November 2009 (UTC)

It's also worth noting that there are a number of words that end -er and -or with no correct one. Adviser/advisor, for example. --Phil Holmes (talk) 15:45, 18 November 2009 (UTC)

Merriam-Webster does not indicate the usage of either word for the person doing the fermenting; they have fermenter as the organism that causes fermentation or an apparatus used in fermenting, and they indicate fermentor as an alternate spelling for the second definition only. The -or suffix is usually confined to meaning "a person who does X", while the -er suffix can be used in many other ways. As Phil Holmes indicates, there is likely no "correct" answer, and of the synonyms provided by others (although you clearly said you weren't interested in such) might be more precise. --LarryMac | Talk 16:04, 18 November 2009 (UTC)

Thanks, this helps! ike9898 (talk) 18:53, 18 November 2009 (UTC)

snowboard jump equation/formula

if i were to snowboard straight off an 8 foot tall ledge at about 7mph how far from the ledge would i land given there tas no wind and i rode right off the edge w/o jumping?. what would the formula be for this? ihave been trying to find it but all the equation i have found are extremly complicated. thanks for the help --99.89.176.228 (talk) 23:27, 17 November 2009 (UTC)

The vertical motion and the horizontal motion can be considered separately. In the vertical direction you start with no velocity, but there's acceleration from gravity pulling you down (about 32 ft/s²). Given that figure out how long it would take to fall 8 feet. In the horizontal direction you start with a velocity of 7 mph (you should probably convert that to ft/s), with no acceleration. Figure out how far that would get you in the horizontal direction during the time it takes to fall. Rckrone (talk) 23:41, 17 November 2009 (UTC)

(edit conflict)Everything has the same acceleration downward while falling thanks to gravity, and that is 9.8 m/s². In order to figure out how far you would land you need to first figure out how long you would fall for, which is given by the equation h=.5at² where h is the height, a is the acceleration due to gravity, and t is the time taken to fall. Make sure your units are correct! 9.8 m/s² is roughly 32 feet/s². Next, you just have to multiply your horizontal speed by the time you have to move before hitting the ground (again, making sure your units are the same - convert mph to feet per second) and then you'd have a good estimate! ~ Amory (u • t • c) 23:41, 17 November 2009 (UTC)

It's slightly more complex than that. All decent snowboard and ski jumps are sloping, usually quite steeply, in the landing zone, so as to minimize the impact. Jumping onto a flat is quit difficult, unpleasant, and dangerous, especially if you start with an 8 foot drop. So for a real answer, we would need a better specification of the slope. --Stephan Schulz (talk) 00:07, 18 November 2009 (UTC)

No i wouldnt jump the ledge onto flat ground so me and my friend were going to make a landing ramp. i needed to know the distance so that i dont missjudge the jump and miss the landing.I also needed to know this so that i can angle the jump to minimize the impact of landing. Is there a straight clear forward formula to find all these things out such as a formula i can enter into a graphing calculator?--99.89.176.228 (talk) 01:00, 18 November 2009 (UTC)

All the equations you need are found at Trajectory of a projectile. It is probably worth calculating the sensitivities to various parameters, if you are really building a ramp - i.e. "what would happen if you mis-estimate the slope by 10%?" "What would happen if you miscalculate the initial velocity by 10%? 50%?" This is called sensitivity analysis and can become very complex, but you can do a simplified version by varying your inputs to the formulae. This will help you design a safety factor into your ramp. Also keep in mind that simplified ballistic equations don't account for non-point-like, non-spherical humans - you have significant air resistance, rotational inertia, non-rigid dynamics, etc. All of this should be considered - at least, in the simplest sense, by having a robust safety factor. It would be a big error to assume that you will exactly land at a particular spot unless you are a small marble in a vacuum chamber launched by a precisely calibrated launcher at an exact velocity and angle. Nimur (talk) 01:18, 18 November 2009 (UTC)

November 18

Fluoroantimonic acid

Is fluoroantimonic acid only considered the strongest acid because no one has discovered any stronger acid, or is it physically impossible for a stronger acid to exist? --75.50.50.76 (talk) 02:40, 18 November 2009 (UTC)

I;m not sure what you mean by "physically impossible". Acid strength is determined relatively; it is determined by how the acid reacts with other substances. Consider the model Brønsted–Lowry reaction:

HA + B^- <---> A^- + HB

The strength of two acids HA and HB are determined relative to each other such that if HA is the stronger acid, then the equilibrium above will favor the forward reaction, while if HB were the stronger acid, the equilibrium would favor the reverse reaction. There is a "standard acid equilibrium constant" known as K_a, which is calibrated for B to be water, and HB to be hydronium; however in practice HA and HB could be any two acids. Thus, to compare acid strength, you just compare how the equilibrium lies, and you can literally "rank" every acid against every other acid based on how well it reacts compared to each other. The acid at the top of this list is fluoroantimonic acid; there is nothing about the structure that would make a stronger acid actually impossible, its just that for every known substance so far, fluoroantimonic acid is the one at the top of the list. Hypothetcially, any number of substances could be discovered/isolated/created which may end up being even stronger; there is no theoretical upper limit to acid strength, since its not an absolute value; it is only a relative value. --Jayron32 04:30, 18 November 2009 (UTC)

The article calls it "the strongest known acid", so that just means nobody discovered a stronger acid. — DanielLC 16:32, 18 November 2009 (UTC)

Another possibility is that at least one of our articles is wrong (since they are mutually exclusive): the article Helium hydride ion also describes its subject as "the strongest known acid". I'm surprised this has not already been raised, since Graeme Bartlett just mentioned helium hydride on this page. -- Scray (talk) 01:59, 19 November 2009 (UTC)

It could be that helium hydride is only being obtainable in near-vacuum gas-phase conditions ("HHe+ cannot be prepared in a condensed phase"), whereas fluoroantimonic acid is something that can exist at "standard" lab conditions. So fluoroantimonic acid is the strongest known acid that you could put in a flask on a lab bench, whereas helium hydride is the strongest acid which exists under any condition. -- 128.104.112.237 (talk) 17:22, 19 November 2009 (UTC)

Need derivations of the solar insolation inside earths atmosphere and latitude at any point

I need derivations of all insolation related parameters like latitude, declination and insolation itself...please help —Preceding unsigned comment added by 220.225.125.246 (talk) 03:53, 18 November 2009 (UTC)

There isn't much to derive; it's just trigonometry. The insolation is the solar constant times the cosine of the angle that the sun makes with the zenith. That angle depends on both the latitude and the day-of-year/time-of-day. We have a nice diagram of this effect in the insolation article. We also have a formulation for the position of the sun as a function of time and date. (If you want to derive this, it will be a matter of geometric projection of the orbital parameters of Earth - the math is not complicated, but there is a lot of it). Earth's orbit explains these parameters; ironically, they are derived by the inverse process - measuring the sun's declination and reprojecting it back to an orbital specification. So, you might as well take the solar declination formula at face-value, since it is basically an empirical (observation-based) formula.

As far as other parameters - are you working with a more sophisticated atmospheric absorption model? Usually, the effect of longer travel through the atmosphere is negligible compared to the geometric projection (that I described above), but you can read about optical depth if you want to try to apply that formula and estimate the total amount of gas between the sun and a particular location on earth. For this approach, you would also need an atmospheric profile model - you can look at Earth atmosphere to get some background. I believe there are several reference atmosphere profiles published by NOAA and the American Geophysical Union; I will try to dig up some links. Nimur (talk) 04:55, 18 November 2009 (UTC)

The "U.S. Standard Atmosphere" and the Jacchia's thermosphere profile are hosted at NASA Goddard's website; I know people who have used COSPAR parameters for pressure as a function of height; you can use these to estimate atmospheric absorption if you dare... this approach may require some integral calculus... but as I mentioned above, if you actually calculate it out, you will find that the optical depth variation with angle is negligible for most purposes. This is because the "longer paths" traced out end up traversing through the (sparse) high atmosphere. If you don't like these atmospheric profiles, our article has a list of other common atmosphere models; or you can create your own simple gas-density model based on the hydrostatic equilibrium approximation (e.g. exponential fall-off with height). Nimur (talk) 05:00, 18 November 2009 (UTC)

Dog Whisperer

On the Dog Whisperer last night (I'm in Edmonton, Canada), a woman is bound via wheelchair because of a 3 last name disease (Cabot is a name?). It affected her brother, mother and I think their dad. They died. Her leg muscles don't work that well, I think. What is this disease?174.3.102.6 (talk) 05:31, 18 November 2009 (UTC)

Charcot-Marie-Tooth disease? --TammyMoet (talk) 11:02, 18 November 2009 (UTC)

Season 5 (the current season), episode 20, "Mad Dogs", which first aired on September 11, 2009,[13] does involve a brother and sister who live together, who both have Charcot-Marie-Tooth disease.[14] Red Act (talk) 19:47, 18 November 2009 (UTC)

what canadian animal stores apples in the fork of branches ?

This fall, I've found apples (presumably fallen for nearby apple trees) stuck in the fork of branches in trees near my south-eastern canadian home and I'm wondering what kind of animal stores fruits that way ? The apples seem damaged on top, but sides and bottom look undamaged to me. They are placed 2 to 4 meters (6 to 12 feet) high in the forks of main branches of young trees, quite near the trunk. The tree trunks are 5 to 8 cm (2 to 3 inches) in diameter at that height and the branches are about 1 to 2 cm (3/8 to 3/4 of an inch) in diameter at the fork. The apples are all quite solidly stuck. 207.96.217.70 (talk) 05:45, 18 November 2009 (UTC)

Occam's Razor gut reaction - someone is placing those there intentionally to feed birds & small mammals. Just a guess, though. 218.25.32.210 (talk) 07:38, 18 November 2009 (UTC)

I would guess a squirrel. Normally they bury things, but an apple is too big, plus maybe it knows it would rot. I would guess it went to eat it, and got distracted, or in a fight and lost it. If it then got stuck it was unable to remove it, so just ate the top. Just a guess. Ariel. (talk) 09:49, 18 November 2009 (UTC)

A squirrel is a good guess, as they are known to "squirrel" things away. However, I'd guess that the apples were intentionally stored. I agree that they won't last as long as nuts, so they probably eat them within a few days. The damage on top is probably just from where they carried it with their mouths. StuRat (talk) 11:46, 18 November 2009 (UTC)

Knife against bone / nails on a chalkboard

I've read the Wikipedia articles about nails on a chalkboard and psychoacoustics, but have another twist I'd like to share/ask about on the SciRefDesk. When I'm cutting apart raw chicken thighs, occasionally the knife will strike the bone at an angle. I find this kinetic sensation even more immediately revolting than nails on a chalkboard. I'm feeling physically uncomfortable right now just thinking about it. Note that I've never had any bad experiences with knives, been stabbed, lost a loved one to a stabbing, or suffered any other sort of event that might provoke an unusual psychological reaction to this particular situation. I've also noticed that at work when I slice the plastic seals off new watercooler bottles with scissors I feel vibrations/textures/whathaveyou quite similar to the knife into bone, and then of course the corresponding involuntary physical reaction is also quite similar. The nails-chalkboard example is an auditory stimulus, but mine with the knife is a kinetic stimulus - is this a personal quirk, or is there an equally well-recognized phenomenon for particular vibrations and such? Thank you! 218.25.32.210 (talk) 07:07, 18 November 2009 (UTC)

I'm not sure if it's related, but vibrations at a certain frequency (the resonant frequency ?) cause me searing waves of pain. One example was when I tried to hit a baseball with a wooden bat and hit it outside of the "sweet spot". StuRat (talk) 11:40, 18 November 2009 (UTC)

Sounds similar to the reason I can't file my nails. It's giving me shivers just to think about it. So, you're certainly not the only one experiencing this, but I don't think it can be universal: it is were, other people wouldn't be able to file their nails. 86.142.231.220 (talk) 15:22, 18 November 2009 (UTC)

Absolutely subjective -- as a periodontal resident, I cut bone, soft tissue and teeth with no revulsion whatsoever -- and it's not like the first 3 times I did it, I was cringing. Pretty much the only thing I can't handle is watching someone vomit -- it makes me gag. DRosenbach ^{(Talk | Contribs)} 15:45, 18 November 2009 (UTC)

My wife files her nails almost every day, but I can always give her a shiver by giving one of her fingernail a light scratch with one of mine. She says that it makes her teeth hurt. (?!) Kingsfold (talk) 19:39, 18 November 2009 (UTC)

Directed graph condensation terminology

The strongly connected components of a directed graph form a poset. What is the terminology for lesser, greater, minimal, maximal components?

For example, some websites (strongly connected components made of pages (nodes)), can't be reached from the rest of the internet (have no hyperlinks coming back in). So in a sense this site is locally maximal, or "outgoing only". But what is the actual term? -Craig Pemberton 08:41, 18 November 2009 (UTC)

We have a glossary of graph theory which might help you, which suggests k-edge-connected graph may be what you are looking for. This is more a question for the Mathematics desk though. I'm not sure I really understand your question though, a poset does not have to be strongly connected and just because a graph is strongly connected does not make it a poset. They are two different things. SpinningSpark 10:06, 18 November 2009 (UTC)

In the context of Markov chains, one calls the strongly connected components "communicating classes" and calls them "closed" if they are minimal in the reachability ordering (i.e. you can't get out of them) and "open" if they are not. I don't know a term for maximal classes, or anything for minimal classes in more general graph theory. Algebraist 12:41, 18 November 2009 (UTC)

Accuracy of Sonar?

I was just thinking, sonar works by sending out pings and then timing the time it takes to come back from different directions right? Is there a reason why you couldn't make sonar goggles, for seeing in total black conditions or something, or even being able to see through things sound can go through, or is there an inherant low resolution to it? What about radar? Gunrun (talk) 10:46, 18 November 2009 (UTC)

I would think one problem would be sonar-absorbing materials, like cloth, which would look "black". Not sure about the resolution, although bats manage to catch insects with it. On the other hand, they will also go for a tossed rock, so that supports the "inherently low res" theory. StuRat (talk) 11:34, 18 November 2009 (UTC)

See Medical ultrasonography, Gynecologic ultrasonography and lot's of images. The wavelength of 100 kHz ultrasound in air is .343mm. Since you can't see sound, sonar goggles would have to contain a 2-D phased array of microphones, a processor to convert the microphone signals to an image, and a screen to display it on. Include a Wheelbarrow to carry all that stuff. Cuddlyable3 (talk) 11:45, 18 November 2009 (UTC)

There has been research into enabling the blind to form an image through transmitted sound, some of these devices working on a scanning principle. It is called sonification, our article is not very informative, here's a magazine article. The theoretical resolution in the audible band is going to be on the centimetre scale - you could find the beach but not individual grains of sand. SpinningSpark 13:28, 18 November 2009 (UTC)

The Make Magazine blog recently had a link to this : DIY sonar visualizer with Processing + Arduino. But, of course, that's 2d. APL (talk) 15:29, 18 November 2009 (UTC)

8 or 9 abreast seating in Airbus A300 & A330 airliners.

What is the percentage of Airbus A300 & A330 airliners operating with 9 abreast seating, rather than the standard Airbus 8 abreast seating ?

This question is partly to resolve whether 9 abreast seating constitutes an "unusual layout" in A300/A330 aircraft, and therefore that fact should be included on the Monarch Airlines page. --JustinSmith (talk) 14:11, 18 November 2009 (UTC)

Why not just say that the seating is 9 abreast and don't make any commentary on it at all. No need to analyze whether it is unusual or non-standard or anything, just make the statement and let the reader reach his own conclusions about how he should feel about 9 abreast seating. --Jayron32 15:40, 18 November 2009 (UTC)

Some contributors to the Monarch Airlines Talk page do not consider that the 9 seats abreast is relevant, saying it`s not an unusual layout. For my part every other A300/A330 I`ve been on has 8 abreast seating. I`m prepared to accept 9 abreast seating may not be unusual if someone is able to tell me what percentage of these aircraft have each layout. Why argue about an objectively provable fact ? --JustinSmith (talk) 18:36, 18 November 2009 (UTC)

The number of seats is based on the type of seats used. I haven't been on an Airbus, but I have flown very often. Identical aircraft owned by two different airline companies commonly have different seat configurations. The cheaper company will cram in more seats. The more expensive company will use less (wider) seats. It is a normal aspect of commercial aircraft, not an odd feature. -- kainaw™ 18:55, 18 November 2009 (UTC)

For most aircraft models, the way that one airline "crams in more seats" is to reduce the spacing between them (seat pitch). But information of this kind, whether seat pitch or number of seats in a row, seems automatically notable to me as people may find it useful to decide on how to value the price difference between airlines. I like the suggestion to mention the fact without comment as to how rare or common it is. But that discussion belongs on the article's talk page or a general talk page about air travel or similar, not here. The question for the RD was how rare or common it is. This, I can't help with. --Anonymous, 20:15 UTC, November 18, 2009.

Why do you feel more tired after a few hours sleep than when you went to bed?

It seems that people generally feel more tired when they have only had a few hours sleep than when they went to bed. No doubt they would have felt more tired if they hadn't gone to bed at all, but why would you feel more tired than when you went to sleep? I guess it must be simply a perception, perhaps influenced by different hormone levels at night and during the day. QuickSnow (talk) 14:12, 18 November 2009 (UTC)

• REM sleep is crucial to rest.
• The air quality where you repose may be compromised, if you wake up groggy. Vranak (talk) 14:23, 18 November 2009 (UTC)

"No doubt they would have felt more tired if they hadn't gone to bed at all" - actually, with me, that's hardly ever true. Usually after I have gone to sleep, for just a short period, or, for a longer period, I wake up feeling much more tired than if I had actually stayed up, even if I had stayed up a full 8 hours. So I reject this hypothesis :p Rfwoolf (talk) 14:34, 18 November 2009 (UTC)

To the contrary, when I have had to work for more than 24 hours, and get a few hours sleep, I feel far more alert than before the sleep. Even a 1 hour nap helps. Chalk it up to individual differences. Part of it may be how lousy you feel for a short while when you first wake up. Edison (talk) 14:38, 18 November 2009 (UTC)

Ditto. As a chronic insomniac, there is, for me, a huge difference between 4 hours of sleep (which ain't great, but is something) and zero hours of sleep. The former can actually get me through the day; the latter will get me until about 5pm and then I'm zonked (unable to concentrate, agitated, physically and mentally exhausted). --Mr.98 (talk) 22:53, 18 November 2009 (UTC)

It is called Sleep inertia. That article may be of some help. --Tango (talk) 14:51, 18 November 2009 (UTC)

Very interesting. Thanks. QuickSnow (talk) 01:31, 19 November 2009 (UTC)

An object at rest tends to stay at rest unless acted upon by an outside force. — DanielLC 16:28, 18 November 2009 (UTC)

When I had keep crews working for 3 days in an emergency, I would send some home after 24 hours for 8 hours, perhaps allowing them 5 or 6 hours of actual sleep, allowing for travel, family interaction, etc. A worker who got 5 hours actual sleep on 3 consecutive nights was demonstrably more safe and productive than someone who went 36 or 48 hours with no sleep. It may feel rough to wake up after a short sleep, but an hour or two later there is all the difference in the world. In the American Civil War Nathan B. Forrest's smaller Confederate force in one battle pursued a larger Union force for several days. Forrest had his men take turns napping, while the Union forces were constantly at battle stations. In the final battle, after which the Union forces surrendered, the Union forces were falling asleep in combat. Edison (talk) 05:16, 19 November 2009 (UTC)

health care

what type of national health care does New

Zealand have? —Preceding unsigned comment added by 76.210.215.156 (talk) 16:02, 18 November 2009 (UTC)

Have you read our article on health care in New Zealand? — Lomn 16:29, 18 November 2009 (UTC)

Small passive solar water heater

Hi all,

If I wanted to build a small solar water heater for just a gallon or so of water, would there be any reason not to allow the water itself move through the solar collector by convection, looping around and around?

Most of the instructions I've seen suggest using antifreeze in the tubes, and then having tubes loop back inside the tank warming the water, but I wonder if this extra step is necessary for such a small system.

Any thoughts? Thanks! — Sam 63.138.152.155 (talk) 16:12, 18 November 2009 (UTC)

I agree that such a system seems like total overkill for 1 gallon. Instead, just get a 1 gallon glass water bottle and place it on a reflective surface, say aluminum foil, on top of an insulator, like Styrofoam. On a sunny day, this should get the water warm. Don't leave it out when it's below freezing and/or dark, or it could freeze and break the bottle (but then again, a broken 1 gallon glass bottle isn't exactly a disaster). If you can arrange a large inverted cone of aluminum foil with the water bottle at the bottom, you might even get the water hot. If you add some dark food coloring to the water it will get somewhat hotter, but that depends on how you want to use it. Here's some images of solar ovens to give you a few ideas: [15]. StuRat (talk) 16:20, 18 November 2009 (UTC)

You should paint the bottle black so it absorbs heat, rather than put in on foil that will reflect heat. --Tango (talk) 18:44, 18 November 2009 (UTC)

Sounds like Sun tea. 75.41.110.200 (talk) 18:51, 18 November 2009 (UTC)

Take a look at concentrating solar power for ideas about how to build solar energy concentrators, both large and small. The simplest can be built easily by lining a convex-shaped object (like a large bowl or tube) with foil; and placing the object you want to heat (hot dog) at the focal point of this mirror. You can paint that object dark colors to help it absorb heat; the rest of the apparatus can be foil-lined to increase the energy collected and concentrated. If you are good at plumbing, you can run water through the hot-spot and then plumb it to where ever you need the heated water. Here's an article with a photo of such a device. Nimur (talk) 19:20, 18 November 2009 (UTC)

I disagree on painting the bottle black, because this will generate heat at the surface, and much of it will radiate back off the bottle. The goal is to create the heat in the interior. This can be accomplished by having a black object in the center and/or by having the fluid itself absorb solar energy by being a dark color (but not so dark that all the heat is absorbed right at the surface of the bottle). StuRat (talk) 23:08, 18 November 2009 (UTC)

We have a very detailed article on Solar water heating. It describes several schemes of increasing complexity; the simplest one(s) are passive and use just water in a single open loop (no closed loops, no antifreeze, no forced circulation). I think that's what you are looking for. --Dr Dima (talk) 01:26, 19 November 2009 (UTC)

Thermosiphoning will cause cold water to sink and hot water to rise, maintaining circulation through a solar water heating system. A collector might include serpentine (curving back and forth) copper tubing, soldered to a steel back plate, all of that painted flat black. Facing the sun should be a pane of glass. Behind the steel should be good insulation to reduce loss. The assembly should be sealed against air leaks. Expect about 1 kilowatt per square meter of solar energy input in full sun, if the collector is oriented at an angle equivalent to the latitude. If it goes below freezing at night, the collector will freeze and burst after radiating off all the energy you collected during the day, so it would need provisions for draining at night and pumping the water up in daytime. I have collected solar energy with a simpler system consisting of a black garden hose lying on a roof, connected to the top and bottom of a storage tank. Hot water rises, cold water falls, and warm water results. There are actually places in the world where it rarely goes below freezing, and an antifreeze loop would seem to create unnecessary expense and complexity there, but you get what you pay for. Edison (talk) 05:08, 19 November 2009 (UTC)

Aluminum borohydride

When researching sources to create the article aluminum borohydride, I found a source stating that aluminum borohydride reacts violently with water, even reacting with the trace amounts of moisture in the air. However, another source I found states that aluminum borohydride has an NFPA-R rating of 0, meaning that it doesn't react with water. Which source is correct? ----J4\/4 <talk> 17:31, 18 November 2009 (UTC)

I'm pretty sure all borohydrides are quite reactive with water, so I would guess that the source which indicates a reactivity rating of 0 is probably in error. I would find additional sources before proceeding, however, just to be sure. --Jayron32 20:53, 18 November 2009 (UTC)

According to the Riedel/Janiak, Anorganische Chemie, 7. Auflage, de Gruyter 2007, p. 577 Aluminum Borohydride is a covalent compound that is liquid at 25°C. It therefore should hydrolyze quite easily to give B(OH)3 and H2. Regards --91.6.28.130 (talk) 18:46, 20 November 2009 (UTC)

Evolution of separate sexes

Sexual reproduction obviously has a survival advantage, in that it increases genetic diversity, thus allowing species to adapt faster. However, this doesn't explain the evolution of separate sexes. After all, genetic diversity would increase faster if any organism could reproduce with any other organism. Why did separate sexes evolve despite this? ----J4\/4 <talk> 18:26, 18 November 2009 (UTC)

I'm having difficulty comprehending the question. Maybe I'm just dense, or maybe there's a faulty assumption or two contained in the question. Vranak (talk) 18:40, 18 November 2009 (UTC)

If organisms reproduced by a variant of sexual reproduction, where any organism could produce an offspring, which would contain the DNA of both parents, with any other organism, genetic diversity would increase more that under the artificial limits on diversification created by having each organism only able to reproduce with approximately half of the other organisms of that species. ----J4\/4 <talk> 18:43, 18 November 2009 (UTC)

I'm still baffled by the scientific lingo. I used to understand this stuff, but I'm glad I've forgotten. Vranak (talk) 19:42, 18 November 2009 (UTC)

To simplify as much as possible: "Why don't we all have both male and female parts". Some animals do indeed work like this, but they tend to be "lower orders", not mammals and birds, for instance. The advantage of different sexes is that it provides a way to have a division of labor with each gender customized for it's role. Males, not having to carry babies, can be faster and fight more, while females can concentrate on rearing the kids. StuRat (talk) 23:01, 18 November 2009 (UTC)

For a novel, decidedly nonscientific perspective, I would suggest that life would be so boring as to verge on the intolerable if there were no sexes. Video games and comics books just aren't that compelling much past the age of 14. Something needs to keep our interest, so why not a separate gender that is both like yet unlike? Doesn't totally cover it for everyone I know. Vranak (talk) 05:09, 19 November 2009 (UTC)

This is a big question that a lot of evolutionary biologists have worked on. Our article, Evolution of sexual reproduction, should give you a good introduction. --Tango (talk) 18:46, 18 November 2009 (UTC)

Actually, having just skimmed through that article, it doesn't seem to address this exact issue. It probably should... --Tango (talk) 18:53, 18 November 2009 (UTC)

Sexual reproduction allows for specialization. There are further advantages to sexual reproduction than just genetic diversity. Specialization can take on a wide variety of forms. Survival is enhanced by sexually divergent members contributing advantageous characteristics that it would be more difficult to develop by evolutionary means in an all-in-one organism. Bus stop (talk) 19:14, 18 November 2009 (UTC)

I'm pretty sure this ^ is the essence of the answer, although it might help to also ask why the gender balance is roughly 50:50. Let's consider a hypothetical species in which every individual is fully hermaphrodite and can reproduce with any other individual. Assuming they are otherwise mammal, one of these individuals will have to gestate the offspring. Let's say that the normal situation is that individuals both impregnate and are impregnated. While an individual is pregnant, they can still impregnate others although they cannot be impregnated themselves. And towards the end of gestation, they are less capable of impregnating others. Once the child has been born, the individual who gave birth to them has to devote resources to caring for them. The individual who also contributed to this child's DNA can choose whether they invest resources in them or not, but they are also responsible for a child they gave birth to.

Let us imagine that an individual is born who does not allow themselves to be impregnated, or physically cannot be impregnated. They can still pass on their DNA by impregnating others, but they never have to devote resources to a developing child within themselves, nor do they have times when they cannot impregnate others, nor do they have to devote resources to any given child. They might increase some of their children's survival chances by devoting resources to them, but they might equally spend all their resources begetting as many children as possible. This individual has a clear advantage over the hermaphrodites.

But if more than 50% of the individuals in a species use this tactic, it starts to be an advantage to be the one bearing the children. The individuals who have taken the male route cannot reproduce with each other: they need to find a mate who can bear young if they want to reproduce. Those who can bear children can pick their mate more carefully, because they have a choice of willing partners: they need to choose carefully because they invest more in each child. And, to maximise their chance of grandchildren, it's in their interest to bear both types of children: those who can bear children, and those taking the male route. A 'male' should also beget both 'male' and 'child bearing' children to maximise grandchildren. Since the quirk that produced the 'male' individuals is almost certainly carried by the 'males', as long as the 'males' are only passing it on to about half their children, it is in the child-bearing individuals' interest to reproduce with the 'males' rather than with other child-bearing individuals. And thus, we have two genders.

If the males passed on the tendency to be male to every child, or females carried a recessive gene, two copies of which rendered a child male, you might expect some hermaphroditism to remain. But in an XY situation, two genders emerge. 86.142.231.220 (talk) 19:30, 18 November 2009 (UTC)

this old article discusses the evolution of Anisogamy--Digrpat (talk) 19:21, 18 November 2009 (UTC)

It's all about the gametes (sperm and eggs) and finding "a selective advantage of large, immobile gametes (eggs) ... An assumption that eggs produce a pheromone sperm attractant leads, by established physical principles, to a more than sufficient advantage of large egg size. Without pheromones, combinations of increased target size and weaker increased zygote fitness or increased gamete longevity also provide sufficient selection."[16] Also see [17][18][19]. Fences&Windows 01:40, 19 November 2009 (UTC)

There are two strategies for gametes: get big so it'll survive longer, or get smaller and try to impregnate the big ones. Imagine Reason (talk) 04:20, 19 November 2009 (UTC)

That's right. There is a division of labor at the gamete level. Some of them are big (female) to provide enough of a head start for the new organism while the other ones are mobile (male) to increase the chances that they will find each other. Dauto (talk) 13:53, 19 November 2009 (UTC)

ATSC standards

I am trying to understand how television channels use the ATSC standards to broadcast their information. The RF channel is 6 MHz wide, but is there usually only one signal that is modulated over the entire 6 MHz? I know that there was two different carriers for video and audio under NTSC, and that DTV is supposed to be able to make possible additional features to broadcast television, like what is available to cable and satellite TV, but I can't make out from the articles whether a TV station would be able to use something like "sub-channels", within their allotted bandwidth. How does ATSC account for this? Thanks —Akrabbim^talk 19:05, 18 November 2009 (UTC)

I have received subchannels over-the-air, so I know they exist. I don't know how it's done. --Jc3s5h (talk) 21:48, 18 November 2009 (UTC)

Specifically, in the US I've seen three subchannels per frequency. StuRat (talk) 22:52, 18 November 2009 (UTC)

I guess my question can be rephrased as this: Does the ATSC have different carriers on the same channel for different content like the NTSC had with audio and video, or do subchannels and the like come from one compressed signal on one carrier, spanning the entire channel. I have hooked up an antenna to a spectrum analyzer, and it looks like there is approximately equal power across all 6 MHz of the channel, but I can't tell if there is information split between more than one carrier or not. Thanks for the responses so far. —Akrabbim^talk 04:57, 19 November 2009 (UTC)

The subchanels are multiplexed in the digital realm, not the rf realm. The rf signal contains a single mpeg transport stream. Inside that stream are the various subchannels and audio for them. There is no separate rf band for audio, or for any of the subchannels. Ariel. (talk) 06:33, 19 November 2009 (UTC)

Fantastic, thank you. —Akrabbim^talk 13:22, 19 November 2009 (UTC)

Vacuum-Forming PMMA (Acrylic)

Can PMMA (Lucite, Acrylic, Plexiglas, Perspex) be heated and vacuum-formed using a partial-vacuum machine?

Will it discolor? Will it separate ("sweat") into subcompounds? Will the addition of semi-transparent aluminum film on the acrylic substrate have an adverse effect on the forming process?

I'm working on forming some custom visors for movie prop helmets and am trying to find a suitable material. The final shapes of these visors precludes the use of commercial tinting after the forming process, and the tint will burn off, discolor or tear if applied to the plastic sheet before heating and forming.

Thanks, Nullexe (talk) 23:03, 18 November 2009 (UTC)

I have heated tinted perspex with a hot air gun until plastic (fairly soft), then formed it by hand/vice etc into the required shape. It did not discolor. It did not decompose. I would put the semi transparent film on after forming if poss. This will avoid wrinkling of the film under heating. I see no reason why it could not be formed on a vacuum m/c. Just be careful you dont get it too hot and dont expect small radii.--79.75.63.71 (talk) 15:15, 19 November 2009 (UTC)

PMMA is used extensively in dentistry and to increase setting rate and quality, pour-ups are placed into pressure pots with warm water. I don't exactly know what you mean by the use of a vacuum in your question, but better setting occurs under positive pressure, so perhaps to a worse extent under negative pressure. DRosenbach ^{(Talk | Contribs)} 16:52, 19 November 2009 (UTC)

Do you expend more energy with intense exertion over a smaller exertion for a longer period of time?

Per the title, say I:

• Run hard ten miles and it takes me thirty-five minutes (seven minute miles); or
• Jog ten miles and it takes me one hour (twelve minute miles); or
• Leisurely stroll ten miles and it takes me two hours and five minutes (twenty-five minute miles).

My impression is that I burn more energy with high exertion even if I complete the same task no matter that at lower exertion I take more time at it. Is my impression correct? Is it wrong? What are the comparisons in energy expended? And why does one burn more energy than another, if indeed that is the case? Purely from musing on it, it seems to me the only reason one would expend more energy than another is efficiency of the movement, breathing, respiration and so on, rather than something inherent about expending energy faster verses slower, but even with that hypothesis, I don't even have a guess as to whether slower verses faster is more energy efficient.--108.1.106.132 (talk) 23:05, 18 November 2009 (UTC)

Bear in mind that you also burn energy when doing nothing (basal metabolic rate), so, the longer you take to travel the ten miles, the more energy will be burnt up that way. So, for that reason I'd say the stroll would burn the most energy total. However, if you add in resting time afterwards to make the total time the same in each case, then that changes the equation. In that case the fastest run (and rest afterwards) would burn the most calories, since running is less efficient. StuRat (talk) 23:23, 18 November 2009 (UTC)

I don't think "time" here is the only factor—muscles use energy differently depending on exertion and time (see the chart on Aerobic exercise), and so I don't think StuRat's reasoning works out. That being said, I have read studies that implied that using up a lot of energy vigorously does trigger your body into seeking out more calories, and thus a lot of people, after hitting the gym, consume far more calories than they would have otherwise, even more than were burnt exercising. For that reason I have heard it recommended that light, regular exercise (e.g. walking regularly, rather than running) can be more productive if the overall goal is weight-loss, as it avoids less over consumption. --Mr.98 (talk) 00:51, 19 November 2009 (UTC)

You'll also burn more calories the longer you keep your heart rate up. That's why swimming or playing squash for 30-60 minutes will likely burn far more calories than a game of baseball. It's also part of the reason why marathoners are thin as paper whereas sprinters actually have some fat and muscle on them (I'm simplifying, there are other reasons as well). ~ Amory (u • t • c) 01:42, 19 November 2009 (UTC)

For a fixed distance, running burns more energy per mile than walking, because the body moves up and down a lot more during running. (The exception is if you're walking really fast -- the movement is so inefficient then that switching to a slow jog at the same speed can reduce energy output.) Also the faster you run, the more energy you burn per mile, but the difference is not all that large until you hit the point where you are getting close to maxed out. Looie496 (talk) 20:08, 19 November 2009 (UTC)

November 19

Photo-electric cells for the home?

a) Will they eventually become cheap enough to cover the roof and walls of your house with, or is there any fundamental reason for them staying expensive? b) If you did cover the roof and walls of your house with them, what proportion of the electricity useage would they provide, for somewhere like London for example? 92.29.45.37 (talk) 00:24, 19 November 2009 (UTC)

Rule of thumb: in moderate climates, one square meter of a roof photovoltaic system provides about 0.5 - 1.0 kilowatt-hour of electric energy per day. Average Domestic energy consumption in UK is about 2000 kg of oil equivalent a year, which is 8.4 gigajoules per year = 8.4x10⁶/3600 kilowatt-hours per year = 2300 kilowatt-hours per year = 6.4 kilowatt-hours per day. So you need something in the ballpark of 10 m² of solar panels to satisfy energy needs of an average UK household. Regarding the prices: yes, they will come down, but not dramatically and not very soon. You need 10 m² of semiconductor on your roof, for crying out loud. However, simple solar water heaters discussed in one of the previous questions are dirt-cheap (they are essentially copper tubes painted black) and can save some significant bucks / pound sterling / euro / whatever your currency is. --Dr Dima (talk) 03:06, 19 November 2009 (UTC)

10 square meters is not all that large. 3.3 x 3.3 meters square should adequately fit on the roof of a single family home; that amounts to a square about 11 feet on a side. Other configuratiosn, such as 2 meters x 5 meters (6 1/2 feet by 16 1/2 feet) would also work nicely, and may fit better on some roofs. It's a lot of semiconductor material, which is where the cost comes in; the material cost is largely due to supply and demand. If everyone in a large metropolitan area started installing solar electric panels, prices would drop drastically. --Jayron32 03:12, 19 November 2009 (UTC)

Um - technically - the law of supply and demand says that if everyone started installing these things, the price would go UP not down! However, "economies of scale" might push the price down - so I don't entirely disagree with Jayron's point. SteveBaker (talk) 12:52, 19 November 2009 (UTC)

You are both right. Initially the cost would go up, but the increase in demand would very likely cause the people who make the things to raise production levels and increase the supply so prices would eventually drop. Googlemeister (talk) 14:33, 19 November 2009 (UTC)

I think Dr Dima's estimate may be low. If a typical house is oriented with the roof crest East-West, then the entire roof-half facing the sun might, in the future, be covered with photovoltaic solar cells, tied into the grid through an inverter. When the sun is shining brightly, the solar electricity could well exceed the usage, and the meter would "spin backward," or more realistically the homeowner would accrue credit against electricity used when the sun is not shining. Solar energy striking a square meter oriented normal to sunlight, i.e. at an angle appropriate for the latitude(horizontal at the equator, 45 degree angle at 45 degree latitude, vertical at the poles,) receives about a kilowatt per square meter. Then the efficiency of the solar cell (currently still not all that high), and the degree of cloudiness must be factored in, as well as the efficiency of the inverter. I believe that solar shingles will be in common commercial use in a few years. See [20] and [21]. Such companies as Dow and Johns-Manville have tested solar shingles which can be installed by just nailing them down, like regular shingles, with easy electrical connections. A house roof might be 20 square meters on the side facing the sun, with peak solar input of 20 kilowatts. The DC output from the solar installation can be fed through an inverter to one circuit on the normal breaker panel, and a smart meter can credit the homeowner for any generation larger than demand. Generation smaller than demand would simply slow down the spinning of the meter and reduce the electric bill. The Museum of Science and Industry in Chicago presently has on its grounds a "smart house" which has solar panels on the roof and a small wind generator, There is synergy in this combination, because the wind is often blowing when the sun is not shining brightly. On most days, the electrical records show that the house has, for some period during the day, generated more electricity than it has used. If the solar energy striking the sun-facing roof half is not turned into electricity then (in the summer at least) it is just a wasted resource, or it heats up the house (in the summer) and requires more air conditioning. Edison (talk) 04:49, 19 November 2009 (UTC)

There are several efforts to drive down the price of solar panels - and if one of these comes off then perhaps the price might drop significantly enough. However, the big problem with solar panels is with energy storage. You get all the power you need (and then some) during the day (when you're probably out at work) - but zero at night when you mostly need it for lighting, cooking and heating. The amount of batteries you'd need to store that energy would be enormous...far more than most householders have room for. Right now, you can solve that in many parts of the world by effectively selling your excess daylight energy to the power utility and using the money to buy it back at night. Not all electric companies allow that - but many do. However, that model is only sustainable while your 24 hour production is less than your usage. If you are simply using your electricity provider as a large battery without giving them money for the privilage - they aren't going to want your business for long! If this model of borrowing electricity at night and paying it back during the day becomes the norm for 99% of households - then that will require a new pricing model for these utilities - and that's an unknown quantity right now. The utilities might manage to keep things together by selling excess daytime power to factories and such - and using the profits to generate power for homes at night. But there is also a longer term issue in the more extreme latitudes - that your solar production in the winter is much lower than in summer - but the winter has longer nights and colder weather - so more power is needed for lighting and heating. In the summer, there is plenty of power - but warm nights and long days mean less power is needed. While it's possible that storage solutions might cover the day/night problems - there is unlikely to be a solution for storing power in those quantities over 6 months of the year. SteveBaker (talk) 12:52, 19 November 2009 (UTC)

As for long-term storage of energy, one way to do that is by pumping water from a low reservoir to a high one, then later use this gravitational potential energy to run turbines, as the water goes back down to the lower level. StuRat (talk) 13:40, 19 November 2009 (UTC)

@Dima: I think you are off by at least a factor of 10. 100m2 is a more likely estimate for the required area. @Steve: The storage of energy is a problem only if solar becomes our ONLY source of energy. A combination of solar, wind and hydro might solve that problem quite easily. Biofuels and Nuclear power are also likely to remain important components of our energy portofolio even after we run out of fossil fuels. Dauto (talk) 13:31, 19 November 2009 (UTC)

Yeah - Dima is WAY off on energy requirements for a typical US/European home. Our article Photovoltaic_system#System_performance agrees that the best you're going to get from solar panels is 1kW/hr per square meter each day. At worst (and I'd guess that London is close to the worst) you'll get maybe a third of that on average - assuming average cloud cover over the year - and some way to store unused summer power for the winter (tough!). Remember: London is pretty far north (Americans: It's at the same latitude as Southern Alaska) - and it can be cloudy for weeks at a time. So 0.3kW/hr per sq.m is about right for London. The Domestic energy consumption article gives the average energy in a household a year consists of 20,000kW-h (and breaks that down according to usage) - which is close to ten times what Dima estimated. So you need 55kW/hr per day. That means that you're going to need 160 square meters of panels in London. 50 sq.m in Texas/Arizona. Completely covering the rooftop might be enough if you have a large-ish house - but not if you live in an apartment! Covering the walls is less useful because vertical surfaces are at entirely the wrong angle to the sunlight at the times of day (around noon) when the energy is mostly being delivered. The reality seems far, FAR worse. Look here [22] - this is for systems sold in Austin, Texas - where there is a LOT of sunshine. A $17,000 installation comprising 15 one meter panels produces 2,800 – 4,000 kWh per year. Between a fifth and a tenth of what you need...in Texas. So expect to pay $80k to $170k to completely power your home - and expect to need between 80 and 150 square meters of panels to do it...which fits very well with my estimates. This manufacturer claims a 30 year lifespan for the product - but fails to mention that the amount of power they produce steadily declines over the years. But at (say) $100k capital cost - you'll be paying perhaps $300 a month on top of your mortgage to pay for them. So unless your electricity bill is well over $300 a month - it's not a money-making proposition until the price of panels comes way down...and that's in sunny Texas...in London...forget it! SteveBaker (talk) 18:49, 19 November 2009 (UTC)

Steve, careful with your notation - there is a very big difference between kilowatt/hr (a rarely-useful rate of power-per-unit-time) and kilowatt·hr (a unit of energy). I think you have repeatedly used "kilowatt/hr" when you mean "kilowatt·hr". I think your calculations are all square, but other readers may naively misinterpret your notation, especially when trying to calculate energy and power consumptions over average time periods. Nimur (talk) 19:31, 19 November 2009 (UTC)

A couple thoughts:

1) How much electricity a home uses depends greatly on whether you use electricity for heating and A/C. If not, then a small patch of solar cells on the roof and a way to store that energy for night (either with batteries or by using the power company) should satisfy your demand. If you do heat and cool your home with solar energy, then even a house completely covered with solar cells might not be enough.

2) Solar cells are quite inefficient, in that they only change a few frequencies (colors) or light into electricity (this is also true of leaves converting sunlight into chemical energy). Passive solar heating, on the other hand, can change all frequencies of visible light, and even infrared and ultraviolet, into heat. So, you can heat your home much better by just letting light in large, insulated windows than by having solar cells convert it into electricity that you then use to generate heat inside. A/C is more of a problem, though, as any method of using light to cool your home is highly inefficient. StuRat (talk) 13:50, 19 November 2009 (UTC)

I qwonder if a world electricity grid would be theorectically feasible, allowing electricity to be moved from day to night and summer to winter. 78.146.97.208 (talk) 20:14, 19 November 2009 (UTC)

Transmission-line losses would be huge. Take a look, for example, at HVDC. Loss estimates range widely; our article claims "3% per 1000 km" (for example, so says Siemens' marketing brochure); but I think it would be significantly higher (researchers I work with have cited dramatically higher numbers - at least an order of magnitude worse). HVDC Transmission Systems Technology Review is a good overview, but does not quote power-loss estimates for any of the case studies. This dismal but well-sourced policy analysis indicates that it is more efficient (in terms of energy and dollars) to ship energy in the form of rail-cars full of coal, than to turn said coal into electricity and pipe it by transmission lines. Though the proposal for piping solar-electric power via long-range electric transmission lines does not bear the direct carbon-related costs due to the burning of coal, this analysis is helpful in establishing the ballpark kinds of efficiency numbers. This is not to say such projects are never undertaken - the Pacific DC Intertie is an HVDC line largely designed to sell cheaper-to-generate hydroelectricity from the Pacific Northwest to the electricity-starved Los Angeles area. Nimur (talk) 21:14, 19 November 2009 (UTC)

The Nord Pool is the first multinational exchange for trading electric power between Norway, Denmark, Sweden and Finland.. Cuddlyable3 (talk) 12:17, 20 November 2009 (UTC)

What about super-conducting electricity cables? If technology can put several gas piplines from one side of europe to the other and beyond, then a super-cooled conductor inside some liquid gas and insulation is not impossible. 92.27.157.99 (talk) 19:42, 20 November 2009 (UTC)

Definition of “taxon”

Monkeys are a paraphyletic group (because the Old World monkeys are closer relatives to certain non-monkeys than to the New World monkeys). Does it follow that monkeys are not a taxon? Our article taxon says: “Today it is common to define a good taxon as one that reflects presumptive evolutionary (phylogenetic) relationships. But this is not mandatory” (emphasis added). If a taxon can be paraphyletic (such as reptilia, an example given in the taxon article), then our article monkey is wrong when it says “The term 'monkey' is an artificial grouping; it is not a taxon..., but instead it is a paraphyletic group, like ‘fish’.” This question was asked here three months ago but the answer given then is inconsistent with the discussion in the taxon article. —Mathew5000 (talk) 05:22, 19 November 2009 (UTC)

The entire Linnean system is not terribly internally consistant on these issues. The classification of "monkeys" as two seperate taxa, while classifying reptiles (reptilia) into a single taxon is simply a statement of existing practice. Monkeys ARE currently classified under two seperate taxa, and reptiles ARE currently classified under a single taxon. That this is not consistant is moot; perhaps monkeys should be put into a single taxa, OR perhaps reptilia should be removed entirely from the classification system and replaced with more appropriate taxa, however neither of these reflects what is actually being done. Should either of these things be "officially" adopted by whatever body is in charge of officially adopting this stuff? Maybe. Is it inconsistant as it stands now? Possibly. --Jayron32 05:38, 19 November 2009 (UTC)

'Not a clade', might be better than, 'not a taxon'. A taxon is pretty much any name for a group of organisms that has ever been published by a taxonomist. A phrase like "All primates that are not prosimians (lemurs and tarsiers) or apes" hints at a 'ragbag', indicating that further work is required. William Avery (talk) 11:31, 19 November 2009 (UTC)

I've taken a shot at improving the wording in the monkey article; please check that I got it right if you can. Looie496 (talk) 18:27, 19 November 2009 (UTC)

The term '"good" taxon' went through my mind later. I think that's clearer. William Avery (talk) 21:02, 19 November 2009 (UTC)

Thanks; the edit improved the article. It would be good to have a bit more discussion in the Etymology section of that article. I assume that when Europeans first encountered the platyrrhines in the Americas, they called them "monkeys" because they looked more similar to the cercopithecoids than either group did to the apes; then at some point later (but when?) it was realized that cercopithecoids were closer to apes. Or am I wrong about that; maybe it is only in English that there is one term applying to the platyrrhines and cercopithecoids? This goes beyond etymology; it belongs in an encyclopedia article on the broad subject of monkeys. —Mathew5000 (talk) 01:39, 20 November 2009 (UTC)

Out of curiosity I had a look at articles from other-language Wikipedias, and it turns out that the English turn “monkey” is unusual: most other languages have no single term encompassing platyrrhines and cercopithecoids but not great apes. For example, the French article fr:singe says “Les anglophones distinguent deux types de singe, Apes et Monkeys, le premier terme regroupe les Hominoidea et les gibbon, ceux-ci sont donc plus grand et sans queue contrairement aux seconds. Également polyphylétique, ces distinctions anglophones n'ont pas de correspondances précises en français.” (Anglophones distinguish two types of singe, Apes and Monkeys, the first term including Hominoidea and gibbons, which are bigger and lack a tail, in contrast with monkeys. Equally polyphyletic, these anglophone distinctions do not have precise correspondences in French.) The Dutch article nl:apen says “In verscheidene talen wordt een onderscheid gemaakt tussen apen en mensapen (bijvoorbeeld het Engels: monkey (aap) en ape (mensaap)). Het Nederlands maakt dit onderscheid niet, en mensapen worden ook apen genoemd.” (In several languages, a distinction is made between apen and mensapen (for example in English: monkey (aap) and ape (mensaap)). Dutch does not make this distinction; mensapen are also called apen.) The Spanish article es:mono says “Los términos mono y simio son sinónimos, pero en la jerga zoológica suele distinguirse entre ambos por influencia del inglés, idioma en el que los términos equivalentes monkey y ape tienen diferente significado.... Este uso de la palabra simio como traducción de la palabra inglesa ape, restringida a los primates sin cola, es erróneo, y no corresponde al castellano. Se recomienda para este uso la palabra hominoideo.” (The terms mono and simio are synonymous, but in zoological jargon they usually distinguish between the two under the influence of English, a language in which the equivalent terms monkey and ape bear different meanings.... The use of the word simio as translation of the English word ape, restricted to primates without tails, is erroneous, and does not correspond to Castilian. For this use the word hominoideo is recommended.) —Mathew5000 (talk) 03:00, 20 November 2009 (UTC)

Nut

What's the nut inside of peach/nectarine stones? jc iindyysgvxc (my contributions) 11:15, 19 November 2009 (UTC)

As far as I know, they are called pits and are not nuts. The Peach is a relative of the Almond, and Amaretto is flavoured using the pit from inside an Apricot.Popcorn II (talk) 12:10, 19 November 2009 (UTC)

You can call it a nut, just as with the related almond, but it's actually the seed of the peach tree, not a true nut. The "pit" or "stone" is the endocarp of the fruit, a drupe. These nuts are not necessarily safe to eat (in quantity), as plants in this family usually contain some amount of cyanide. See bitter almond and apricot kernel. --Sean 13:18, 19 November 2009 (UTC)

Least Densest Fabric

I don't know if I spelled that right, but what fabric is most like "light as air"? --Reticuli88 (talk) 19:49, 19 November 2009 (UTC)

for clothing? --Reticuli88 (talk) 19:55, 19 November 2009 (UTC)

I would guess that would be paper clothing. You're probably familiar with the paper gowns you get to wear in the hospital, but there was also a fad of wearing disposable paper dresses in the 1960's: [23]. StuRat (talk) 23:27, 19 November 2009 (UTC)

I doubt that paper clothing would be lighter than fine silk. But there aren't any fabrics that are literally "light as air" because the lightest solids known to man are 'aerogels' - those are not quite as light as air (although they come amazingly close) - but they aren't really robust enough to make into fabrics. SteveBaker (talk) 03:14, 20 November 2009 (UTC)

What about a birthday suit? :-) Mitch Ames (talk) 08:10, 20 November 2009 (UTC)

Lace and gossamer are mostly air.--Shantavira|^{feed me} 08:17, 20 November 2009 (UTC)

And a good thing, too! "Boss, I, er, let our, uh, $100,000 slab of aerogel float away. Sorry." --Sean 19:03, 20 November 2009 (UTC)

Looking for a particular female scientist.

I'm trying to remember the name of a particular female scientist. All I remember about her currently is that her given name started with S and was German-sounding, she was some type of Germanic or Eastern European, and she worked in the early 20th century. Any suggestions? --✶♏‭ݣ 20:35, 19 November 2009 (UTC)

That's probably a pretty big category. Could you be a bit more specific about the scientist? What area of research (biology, physics, chemistry, medicine)? Major award winner of some sort? TenOfAllTrades(talk) 20:42, 19 November 2009 (UTC)

I think it was physics or chemistry (or both). Were there really that many Eastern European female scientists whose given names started with S in the early 20th century? (I mean prior to World War II.) --✶♏‭ݣ 20:53, 19 November 2009 (UTC)

Oh, and she definitely never won a Nobel, since I went over the list of female Nobel laureates. Other than that, I can't speak to awards. If you could point me to lists of female science award winners for awards that were created before 1940, that might be helpful (but I wouldn't know where to start looking for such lists). --✶♏‭ݣ 20:55, 19 November 2009 (UTC)

Hmmm. I thought you may have be thinking about Maria Skłodowska, much better known under her married name Marie Curie, but she has a Nobel (well, she has two ;-). --Stephan Schulz (talk) 20:58, 19 November 2009 (UTC)

How about Sulamith Goldhaber or Stephanie Kwolek, although they did most of their work after WWII I assume. Mikenorton (talk) 21:07, 19 November 2009 (UTC)

It wasn't either of those two. Her given name was very Germanic sounding. --✶♏‭ݣ 23:05, 19 November 2009 (UTC)

Any of these? Gertrude Scharff Goldhaber, Luise Meyer-Schützmeister, Hertha Sponer. Red Act (talk) 00:33, 20 November 2009 (UTC)

I do realize that's it's not the given name that starts with S on those, but they all do at least have a name starting with S. Red Act (talk) 00:38, 20 November 2009 (UTC)

A wild guess, which does not quite satisfy the criteria, but Sofia Kovalevskaya. (Igny (talk) 00:37, 20 November 2009 (UTC))

Lise Meitner does not start with S, but contains an S, and she was a notable Austrian-born physicist working before WW2 who never won a Nobel Prize. --Anonymous, 00:50 UTC, November 20, 2009.

Take a look at:

• List of physicists
• List of women scientists
• Contribution of 20th century women to physics
• and, if you are really dedicated to the task: Category:Lists of scientists or Category:Women scientists

Let us know if you find what you are looking for. Abecedare (talk) 01:09, 20 November 2009 (UTC)

Assuming that you mixed up the given and surname, there's Hertha Sponer, one of the first women to get a PhD in physics in germany. It could also be Stephanie Kwolek, inventor of Kevlar and with a given name which could be pronounced in a very german way. If you recalled what the person was famous for, it would help. There's too many female physicists from the 20th century to easily check them all. Which when you come to think of it, is really great. :-) Too bad most of us can only recall the names of Marie Curie and Lise Meitner. EverGreg (talk) 13:32, 20 November 2009 (UTC)

Boating the Amazon River

Has anyone recently, like NatGeo, navigated the whole (or most) of the Amazon river? Strictly for exploratory, scientific reasons? --Reticuli88 (talk) 20:37, 19 November 2009 (UTC)

Navigating the whole Amazon is actually not much of a feat, because at the point in Peru near Iquitos where the Ucayali and Maranon join to form the Amazon, they are both already huge rivers. If you want to go farther upstream, you have to decide which river to follow. Looie496 (talk) 22:38, 19 November 2009 (UTC)

We don't need no steenkin' boats! --Sean 19:11, 20 November 2009 (UTC)

smoke stream

Moved from Computing desk by Falconus^{p t c}

In thomas the tank engine tv show the trains make loads of smoke. how is this done, and where can one make such a device to make smoke —Preceding unsigned comment added by 82.44.55.114 (talk) 15:38, 19 November 2009 (UTC)

This might get a better answer on the science desk. We have an article on fog machines. I would speculate that the tv show uses dry ice and a little water, which spews out steam and condensed water mist (not smoke). Dry ice is cheap and comparatively safe; and the fumes are just carbon dioxide and water mist. However, because the "fog" it produces is mixed with CO2 (which is heavier than air), the smoke often appears to hug the ground. It's possible that other techniques are used, like glycol theatrical fog, or even just a real steam boiler. Nimur (talk) 15:50, 19 November 2009 (UTC)

Is this the same questioner from this archived question? Our article on Thomas and Friends has a section about animation and one about models which talk about some of this. The 1:32 model trains had smoke generators (which are discussed in the archived section I just linked), and CGI seems to be the preferred method now. --LarryMac | Talk 16:23, 19 November 2009 (UTC)

Yes it's the same questioner, and sorry I missfired and posted on the wrong desk. Could you move my question to the right desk? Thanks, and sorry for the mistake —Preceding unsigned comment added by 82.44.55.114 (talk) 16:37, 19 November 2009 (UTC)

November 20

Temperature's Affect on Metabolic Activity

Hello,

I know that as temperature goes up, enzymes become more reactive because substrates move faster and are more likely to bind to the active site. But is temperature proportional to enzymatic activity linearly, quadratically, exponentially, etc? It would help if you can give some kind of justification like a journal article. Thank you. —Preceding unsigned comment added by 69.139.218.4 (talk) 00:30, 20 November 2009 (UTC)

I don't know for sure. But, if the enzyme activity is proportional to the speed of the atoms moving around in the liquid, you can just check how the average velocity of particles is related to temperature. From Maxwell Boltzmann distribution it seems the average speed is proportional to the square root of the temperature. I assume you read Enzyme kinetics, which doesn't cover temperature, but might help anyway. It's possible the speed of the activity of the enzyme itself might change, but I think that it's overwhelmed by variations in when the enzyme comes in contact with the atom, so could be ignored. But it's possible that at low temperature it becomes more important, and at high temperature the atoms move so fast the enzyme has no time to work. So it's probably not a simple relationship over an entire temperature range. Ariel. (talk) 10:30, 20 November 2009 (UTC)

Note that in birds and mammals, attempts to control body temperature may cause us to slow down our metabolic activity when we overheat, so this could figure into it, too. For example, digestion may slow down when we get hot. StuRat (talk) 10:37, 20 November 2009 (UTC)

Your assumption is wrong: Enzymatic activity has no easy and generalizable correlation with temperature. All enzymes have an optimal working temperature, and deviations from this slow reactions down, in general. The exact relationship is different for every single enzyme, and depends an substrate, protein structure and in general the thermodynamics of the reaction catalized. Most human enzymes, for example, would have evolved an optimum around 37°C body temperature (and many start to denature already 10°C above that, so will not be functional any more at this point), but there are enzymes from the archaea which have optimums near the temperature of boiling water, and almost no activity at room temperature. I don't exactly have a journal article for this, but every biochemistry textbook should have a chapter about influence of temperature on enzymes and proteins in general. --TheMaster17 (talk) 10:48, 20 November 2009 (UTC)

The Molecular Basis of the Effect of Temperature on Enzyme Activity. Axl ¤ [Talk] 13:03, 20 November 2009 (UTC)

Technical question about movie cameras used in traditional filmmaking

Does the film used in motion pictures cameras requires film developing? i found the article lack of such specification.

Any help would be kindly appreciated.

If so, which part of the postproduction process is that related. Film editing perhaps?.HappyApple (talk) 02:49, 20 November 2009 (UTC)

Yes. If you look around Kodak's website you will find information about developing motion picture film. --Jc3s5h (talk) 03:02, 20 November 2009 (UTC)

Yes - the film uses the same chemical processes (more or less) as you find in regular still image film cameras. The film stock is generally sent off for processing as quickly as possible after the end of filming each day - LONG before the editing or post-production stages. There is more information in our article: Dailies - the prints that are made immediately after processing to allow directors and producers to see the footage shot on the previous day. These days, they'll use digital cameras mounted alongside the film camera in order to get instant feedback after shooting - but the dailies are still useful to ensure that exposures, color balance and focus were correct. SteveBaker (talk) 03:03, 20 November 2009 (UTC)

Movie cameras for a long time (incl. before the digital era) have had a video tap for similar purposes. 69.228.171.150 (talk) 03:52, 20 November 2009 (UTC)

Thank you for helping me realize where all those clips on YouTube came from! Cuddlyable3 (talk) 11:58, 20 November 2009 (UTC)

Further, most movies include the name of the company that processed the film at the end of the credits. It is not a trivial task. When processing film, it is easy to have one strip of film be slightly more processed than another strip of film. The difference in color on the overprocessed film is very easy to see. If you compare a very old movie to a modern movie, you can see how the picture quality jumped around in old movies but stays steady in new movies. You can also see how experiments to maintain a constant picture quality have progressed through the ages. Most people can recognize a film from the last 60s/early 70s just by the color of the movie. It was a side-effect of the processing of the time. Now, with digital, there is still a need for the people who color balance the films. So, that part of processing isn't going away. It is just done on a computer now instead of with actual film. -- kainaw™ 06:44, 20 November 2009 (UTC)

There was an interesting problem with a batch of film for Lord of the Flies that caused it to get washed out every few seconds, for a few frames. They traced it down to the developer, who was smoking a cigar while developing the film. When he inhaled, the tip of the cigar got brighter and ruined the film. They had to reshoot. StuRat (talk) 10:32, 20 November 2009 (UTC)

Seeing the effort needed to process a single film strip increases one's respect for what was done for the early multi-strip Technicolor versions. Cuddlyable3 (talk) 11:58, 20 November 2009 (UTC)

Thanks for the answers it helped me a lot. --HappyApple (talk) 14:11, 20 November 2009 (UTC)

Static electricity

When you pull a sweater off in the winter and you get sparks between your undershirt and the sweater, what causes that? I know it's static electricity but how does it get there? Dismas|^(talk) 04:08, 20 November 2009 (UTC)

That's called the Triboelectric effect, described in that article and more superficially in our Static electricity article. -- Scray (talk) 04:22, 20 November 2009 (UTC)

Static charges build up easily in dry air, which is typically found in a room with electric heating. Cuddlyable3 (talk) 11:44, 20 November 2009 (UTC)

Lunar water

Hi, the Moon is hotter (I guess) than the hottest desert during most of its daytime. Because of this lunar water is suspected only to exist in those cratered areas near the poles which are in permanent darkness. This makes sense because the water is frazzled and evaporates in the searing month-long heat. What is often claimed is that this evaporated water is then lost to, or flys off into, space. How does the vapor reach exit velocity? i.e. wouldn't it be impossible for vapor to find its way beyond the moons gravitational force without a big push? Does what goes up not come down on La Lune? ~ R.T.G 12:00, 20 November 2009 (UTC)

The moon's scape velocity is small enough that water can reach it simply by random thermal movement. That's why the moon doesn't have an atmosphere. Dauto (talk) 13:03, 20 November 2009 (UTC)

That's true - but it also provides another mechanism for water to get into those always-dark craters. When there are a few molecules of water in the lunar soil, they get repeatedly hit by all sorts of particles and photons of various energies and get thrown out of the soil and up, away from the surface. Some, indeed, gain so much energy that they escape the moon entirely. However, lots of them don't - and eventually float slowly back to the lunar surface - ready to get whacked again. You can envisage this as a bunch of molecules bouncing around the surface of the moon - randomly jumping from place to place...until they just happen to end up inside one of those always-dark craters. Once a molecule happens by random chance to end up in one of those places, it's shielded from all of that incoming energy and there is no way for it to get out. Hence water accumulates in those places - even water that wasn't conveniently deposited there in the body of an icy asteroid impact. There isn't much water in the lunar soil - but when the water from the entire surface of the moon is gradually collected in just a few special places, it can add up to a lot. SteveBaker (talk) 13:59, 20 November 2009 (UTC)

Extending that idea, couldn't other particles (dust) gradually cover (fill-in) the bottom of such craters, such that we could envisage most locations on the moon's surface as having once been the site of a crater? If so, couldn't the buried water be more widely-distributed, and not "in just a few special places"? -- Scray (talk) 14:24, 20 November 2009 (UTC)

No, because water that accumulated anywhere else would evaporate when the Sun heats it up again. Thus it would be kept in motion until it finds a stable position, either in a permanently shaded polar crater or by escaping the Moon entirely. Now for an analogy: Have you ever seen a spot in the center of a road intersection where no cars drive, that accumulates debris ? The debris gets knocked all over the place by the cars, until it finds it's way to that spot, then it stays there. This effect also causes debris to accumulate on the shoulders. StuRat (talk) 17:51, 20 November 2009 (UTC)

To an extent, yes, but dust is much heavier than water (by several orders of magnitude, I think). That means it doesn't move about anywhere near as much. You may find Lunar dust#Moon fountains and electrostatic levitation of interest. --Tango (talk) 14:44, 20 November 2009 (UTC)

It's just hard to imagine natural flow being enough to blow vapour into space. The moon as a low gravity thresh-hold but its not as if you could trip and fly off it not by a long shot. Isn't the upper-Earth atmosphere in a lower gravity state but gas blowing away is only a minor event? Of course vapour collection could be such a minor event too but on the Earth, heat affected gas reacts in conjuction with other gas i.e. is bouyant but on the moon there is little to nothing hosting bouyancy. Would the affected by heat rising off the moon not disipate long before escape velocity and distance and wouldn't our upper atmosphere be blowing away rapidly through the hole over the antartica? Bit vague to answer now sorry but just flaoting away doesn't apply to our familiar surroundings. Thanks for answers ~ R.T.G 16:52, 20 November 2009 (UTC)

The solar wind bombards the planets (especially the inner planets) with high energy particles. This can blow loose those molecules in the upper atmosphere. The gravitational attraction in Earth's stratosphere is only slightly less than on the surface, because it's only slightly farther from the center of the Earth (the atmosphere is very thin relative to the radius of the Earth). However, the solar wind still blows away the lightest molecules, such as those of hydrogen. That's one reason why we have hardly any H₂ molecules in the air. Here's a diagram:

      ->   ->_____->    -> ATMOSPHERE BLOWN LOOSE
      ->    /     \ 
SOLAR ->  
WIND  ->   | MOON  |
      ->  
      ->    \_____/
      ->    ->    ->    -> ATMOSPHERE BLOWN LOOSE    StuRat (talk) 17:42, 20 November 2009 (UTC)
  

The process is called Jean's escape and it is one of many processes which can cause a gas particle to reach escape velocity. We have an article on Atmospheric escape. Basically, what happens is that the Maxwell distribution has a long tail - some gas molecules are always statistically going to have much faster velocities; and as those escape orbit, the thermal distribution re-equilibrates. The mechanism of showing that a gas always follows a Maxwell-like distribution is a very complicated derivation of statistical physics and thermodynamics, but it can be done. Nimur (talk) 16:59, 20 November 2009 (UTC)

Unit conversion

Now, I'm pretty bad with anything mathematical, but it turns out to be quite essential for the work I'm doing with regards to converting units. I've used spectrometry to obtain absorbencies, and I've been given an ε₂₈₀ (constant at 280nm) value to use in the simplified Beer-Lambert law (concentration = absorbency/ε₂₈₀), so I can work out concentration like that.

However, I'm pretty sure that value would give me a concentration in the units of moldm^-3. I need the values in μg cm^-3. I get really confused when trying to convert this values. I can't just multiply or divide the value because it's composed of two parts (the amount, and the volume). How can I convert moles to μg, and dm^-3 to cm^-3 in the same method? Thanks. Regards, --—Cyclonenim | Chat  12:43, 20 November 2009 (UTC)

I don't think I could improve on our article explaining factor-label conversion of units, but if you have a question after looking at that, please ask and we'll try. I found this by first going to the Dimensional analysis page, which is a more standard, but general, term for this type of math. -- Scray (talk) 14:05, 20 November 2009 (UTC)

I'm not sure I know how to apply that technique to this case. The equation I'm using is concentration = absorbency/a constant. If I put in the units, it'll be moldm-3 = one arbitrary value / another arbitrary value. Regards, --—Cyclonenim | Chat  14:50, 20 November 2009 (UTC)

If you have mol/m³ and you want to get to μg/cm³, then you just multiply in a chain, e.g.: (mol/m³)(molar_mass g/mol)(10⁶ μg/g)(10^-2 m/cm)³. Multiplication and division are Associative. -- Scray (talk) 14:59, 20 November 2009 (UTC)

BTW, this sort of math is VERY important in biomedicine - practice it a lot. -- Scray (talk) 15:02, 20 November 2009 (UTC)

I know it's really important, which is why I'm so pissed that I can't understand it! I think I need to work through an example, so I'll provide one and have a go. If C=A/ε, then I can do 0.088/3.65x10^4 and get 2.41x10^-6 moldm^-3, not mol/m³. The problem is that's all I have to work with, I don't have any conversion factors. So to convert moles to mcg, I need to know the molecular mass of BSA. I don't have the molecular mass, sure I could probably find it but something tells me I don't need to. Converting dm-3 to cm-3 is the easy bit because I know how many dm-3 go into cm-3, but I don't know how many moles go into a gram of substance without knowing it's molecular mass. I'm probably missing something, I'm really sorry for me stupidity! Regards, --—Cyclonenim | Chat  15:06, 20 November 2009 (UTC)

If it helps, one of the tables I have actually gives me the volume of BSA in the test tube. For the example above it's 1cm3 of BSA and 4cm3 of H20. It also says the concentration of the BSA stock is 250mcg. Regards, --—Cyclonenim | Chat  15:10, 20 November 2009 (UTC)

This is clear: the conversion from moles to mass is the molar mass, by definition! BTW, I really find it confusing when you write moldm^-3. What's a "moldm"? Yes, I'm pretty sure you mean mol•dm^-3, but I should not have to guess. Ambiguity is the bane of both science and medicine! This is of course meant constructively - best wishes in your studies, -- Scray (talk) 16:25, 20 November 2009 (UTC)

I noticed another point of confusion - you refer to the "volume of BSA". That should bother you a little, since BSA is not a liquid. Therefore, it would not generally be measured by volume, unless the BSA is packed in a reproducible way (like sugar or salt might be, but even then we only measure those by volume in the kitchen). Thus, you're almost certainly talking about a solution of BSA, and the volume would only help (in the problem above) if you knew the concentration of that solution. Of course, if you knew that you wouldn't be using the Beer-Lambert law in the first place. -- Scray (talk) 16:42, 20 November 2009 (UTC)

biotechnology - monoclonal antibody

Respected sir.

why not use sendai virus after started to use PEG in monoclonal production —Preceding unsigned comment added by Marimathan kumar (talk • contribs) 12:30, 20 November 2009 (UTC)

Perhaps a more detailed elaboration of what you'd like to know would help. DRosenbach ^{(Talk | Contribs)} 12:46, 20 November 2009 (UTC)

aluminium chloride colorimetry

This is the method to determine total flavonoid content in crude drug. I want to know the principle and limitation of this technique. —Preceding unsigned comment added by 161.200.255.162 (talk) 12:49, 20 November 2009 (UTC)

Did you forget to ask a question? Dauto (talk) 19:39, 20 November 2009 (UTC)

Fevers and Calories

I had a fever the other day and it got me thinking. How many extra calories does it take to raise an "average" person's body temperature by 1 deg F (or deg C if you want). I know there's all kinds of factors that go into this question, that's why I asked about average, I'm interested in an answer even if it's close to a guess. Also, what's the survival advantage of a fever due to infection? Does it make the immune system more efficient? or is there another reason? Tobyc75 (talk) 14:39, 20 November 2009 (UTC)

Table 3-4 in this book suggests a 12% increase in caloric need for every 1 degree above 37 centigrade, but I don't think that directly answers your question about how much energy it takes to raise body temperature 1 degree. I suppose a direct answer would be to determine the specific heat capacity of an average human body and multiply by average body mass! For the second part of your question, we have a page for that, which provides a number of hypotheses (difficult to prove)! -- Scray (talk) 14:42, 20 November 2009 (UTC)

For a rough back-of-the-envelope sketch per Scray, the human body can be appropximated as a bag of water of the same mass. Since it takes one kilocalorie (exactly, and confusingly, equal to one food calorie) to raise the temperature of one kilogram of water by one degree Celsius, the actual amount of heat energy absorbed by a 70 kg adult is about 70 kcal (70 food calories) per degree Celsius of temperature increase. As noted, actually maintaining an elevated temperature relative to one's surroundings (mostly against the cooling effects of heat radiated away from the skin and carried away by warm exhaled air) will require continuous input of energy. TenOfAllTrades(talk) 15:51, 20 November 2009 (UTC)

You forgot to mention the ugly part. Nimur (talk) 17:03, 20 November 2009 (UTC)

A fever doesn't just work by burning more calories. It uses the same techniques used to prevent hypothermia (just with the thermostat set a little higher). Constricting blood vessels in the extremities to reduce thermal losses, for example. --Tango (talk) 15:59, 20 November 2009 (UTC)

Creationist evolution

I was thinking and not sure, whether this idea exists, but what is the possibility of evolution, which includes the concept of initial intelligent design (thus supporting the existence of God amid self-going, but artificially prepared evolution)? That is, in order to successfully launch the mechanism of evolution, there should be: first, the original evolutioning species (chicken or the egg, where chicken is supposed to be created by the God); second, favourable conditions for the existence of evolutioning life forms, which fall under the concept of entropy and ultimately under the concept of fine-tuned Universe. In other words, such complex process as evolution could not start spontaneously, without some assistance from the outside. Are there any references to that concept? Brand[t] 18:42, 20 November 2009 (UTC)

Well, there is the concept of the "watchmaker God", who sets everything in motion and then stands back and watches what develops. In some versions of this concept, God actually dies after setting it all in motion. StuRat (talk) 19:04, 20 November 2009 (UTC)

The Universe

a) How fast in mph is the universe expanding? b) what exactly is it expanding into? c) if it is not expanding into anything then how do we know that the older inner parts of it are not just shrinking and giving the illusion that the outer parts are expanding? d) how old is the universe compared with the age of the earth? I've read its only ten times, which does not seem much. 92.27.157.99 (talk) 19:46, 20 November 2009 (UTC)