Wikipedia:Reference desk/Archives/Science/2009 July 15

= July 15 =

Beetle factoid
Something I heard on the radio the other day.

"If you were to randomly arrange all the macroscopic animal life on earth in one long line - then every fifth creature would be a beetle."

Confirm/debunk? --Kurt Shaped Box (talk) 00:23, 15 July 2009 (UTC)


 * I see what they were getting at but if you were to arrange them in a truly random nature, then there is no telling just where in the line the beetles would fall. I know, I'm picking nits...  Dismas |(talk) 00:28, 15 July 2009 (UTC)


 * They are claiming that 1/5th (20%) of all macroscopic life is beetles. See beetle.  The percentage is closer to 25%.  So, every 4th creature would be a beetle. --  k a i n a w &trade; 01:59, 15 July 2009 (UTC)
 * That figure appears to refer to number of species, not of individuals. Algebraist 02:00, 15 July 2009 (UTC)
 * Indeed, the source has "Beetles comprise 25% of all described animals and plants, single-handedly making them the primary contributor to earth's biodiversity. The 350,000 descrubed beetle species are members of largest order of life on Earth. Coleoptera." Algebraist 02:03, 15 July 2009 (UTC)
 * There are lots of beetle species, but I'm pretty sure that if you did this over half of the animals would be ants. Looie496 (talk) 02:18, 15 July 2009 (UTC)
 * The term "macroscopic" is kinda vague - I'm sure you could make the answer come out anyway you wanted by picking a more exacting standard for what size of creature you're talking about. Haggling over whether the number is 20% or 25% is kinda silly in the face of that. SteveBaker (talk) 04:40, 15 July 2009 (UTC)
 * The famous biologist J. B. S. Haldane was once asked what he had learned about God from his study of biology. He said: "The Creator, if He exists, has an inordinate fondness for beetles." SteveBaker (talk) 04:37, 15 July 2009 (UTC)
 * Also see The Last Continent :-) 71.236.26.74 (talk) 18:32, 15 July 2009 (UTC)
 * "The Creator, if He exists, has an inordinate fondness for beetles." -- Was that what John Lennon meant when he said that the Beatles were "more popular than Jesus"? ;-) 76.21.37.87 (talk) 05:08, 17 July 2009 (UTC)
 * I suspect that what he meant was that the Beatles were never publicly crucified, which is not what one usually a great sign of popularity. Googlemeister (talk) 13:51, 17 July 2009 (UTC)

Ultimate Revenge/Punishment - Paralysis with no possibility of communication
Is it theoretically possible to perform an operation on someone/dose them with something that would render them completely and permanently paralyzed with no way to communicate (no blinking, no twitching etc) but still leave them completely aware of themselves and their surroundings (without killing them of course)?

They could then live out a full lifespan knowing that someone did this to them but never being able to tell anyone who - the ultimate revenge/punishment? Exxolon (talk) 00:39, 15 July 2009 (UTC)
 * Disregarding the fact that I now hope I never meet you in real life (☺), yes, it is certainly possible, although they would have to be on life support, and future advances in medicine may be able to tap directly into people's brains, allowing them to communicate despite any neurological damage. - Running On Brains (talk page) 00:43, 15 July 2009 (UTC)

I think that if you sever the spinal cord just below the medulla oblongata, you can paralyze the subject from the neck down. FWiW 76.21.37.87 (talk) 00:51, 15 July 2009 (UTC)
 * How about we cut the brain off and keep it alive in a jar (relatively easy) and make it aware that it is a brain in a vat and can't do anything about it (still sci-fi).-- Lenticel ( talk ) 01:08, 15 July 2009 (UTC)


 * It would probably be simpler with present technology to simply (in addition to the above) put out the eyes, puncture the eardrums and use chlorine gas to destroy the senses of taste and smell for a similar effect. The victim's conscious mind would probably vanish into a black hole after a few weeks/months. --Kurt Shaped Box (talk) 01:24, 15 July 2009 (UTC)
 * The OP says "still leave them fully aware of their surroundings". So personally, I'd go with severing the spinal cord, and pull out the tongue so the subject can't say anything to anyone (not that I'd do that to anyone, of course, except to a terrorist or to a child molester).

76.21.37.87 (talk) 01:59, 15 July 2009 (UTC)


 * This is not the ultimate revenge or punishment. As covered many times in literature for thousands of years, loss of hope is the ultimate punishment.  To lose hope, you must first have hope.  Classic example: Imprison a person for, say, 30 days.  On the last day, punish the person for something that happened over the imprisonment and extend the punishment another 30 days.  On the last day, punish the person again with another extension.  Repeat this until all hope is lost. --  k a i n a w &trade; 02:03, 15 July 2009 (UTC)


 * I deem your portrayal of hope to be a good thing as somewhat facile. It's only when we lose hope that we begin to gain some beginnings of a true, sustainable, authentic self. To hope is to dislike your present reality. Vranak (talk) 18:28, 16 July 2009 (UTC)

It's certainly possible. All you would have to do is take somebody with locked-in syndrome and paralyze the eyes. People with end-stage Parkinson's disease may be in a state something like this. In principle it would still be possible to communicate with such a person by directly reading brain activity, but if you ignore that approach, it is definitely possible. Looie496 (talk) 02:12, 15 July 2009 (UTC)


 * As Looie496 pointed out, even with complete loss of motor control, communication is still theoretically possible. I recall recently seeing a news report or documentary on experiments where subjects were able to control a mouse cursor using brainwave activity picked up by a sensor filled skull cap.  I wasn't able to find a wikipedia article, but did find this similar story on the web.  Such technology could allow your paralyzed victim to pick letters off the screen, form words, and eventually tell the police who dunnit.  -- Tcncv (talk) 02:19, 15 July 2009 (UTC)


 * Actually, this is the state we are all in, all the time. We think we can communicate with people. But that is actually an illusion. We are just a brain in formaldehyde. The formaldehyde has wikipedia molecules added to it. Bus stop (talk) 02:21, 15 July 2009 (UTC)


 * Nonsense. There is no 'we'. My consciousness is the entirety of existence. Everything else I may perceive is merely a delusion constructed unconsciously in order to maintain my sanity. --Kurt Shaped Box (talk) 02:42, 15 July 2009 (UTC)
 * Is it working? Algebraist 02:46, 15 July 2009 (UTC)
 * 50% of the time, on average. I suppose that existence would be boring otherwise. --Kurt Shaped Box (talk) 02:49, 15 July 2009 (UTC)
 * The most relevant Wikipedia article is brain-computer interface. Looie496 (talk) 02:48, 15 July 2009 (UTC)
 * I believe I could send Morse code (slowly) by turning the Alpha waves on and off, even if all sensory nerves and motor nerves were out of commission. These are easily monitored by scalp electrodes. Regardless of whether they were in fact monitored, I would amuse myself by cursing my captor. The role model for this is Malcolm, the black guy in 2001 Maniacs who is about to be crushed by a large press controlled by an antebellum racist zombie, Mayor Buckman. Mayor Buckman says "Do you have any last wish?" Malcolm says,"Yeah. Kiss my black ass!" and spits in the zombie's one functioning eye. Zombie says to assistant, "Next year remind me to omit the'"Last wish' part." Edison (talk) 04:19, 15 July 2009 (UTC)


 * locked-in syndrome, in which sometimes the patient even looses control of her eyes, would be a nightmare scenario for most. But as this article documents, some people can cope even with this. EverGreg (talk) 10:30, 15 July 2009 (UTC)


 * I have actually suffered from this a couple of times on waking up. It only lasts about 10 seconds though and a huge hypnic jerk knocks me out of it.
 * This is actually known as sleep paralysis, caused by a persistence of REM atonia after waking. I used to get it regularly when I was younger, definitely the scariest thing I ever experienced, until I understood what was going on and could just relax until I woke up properly.Mikenorton (talk) 15:24, 15 July 2009 (UTC)
 * The trick is to hold ones breath. Under sleep paralysis I have found that I still have control over my breathing. Asphyxiation wakes up whatever part of me that is still sleeping. EverGreg (talk) 21:30, 15 July 2009 (UTC)


 * Anyway, an equally harsh punishment would be to gas the person with an amnesia-causing drug, then inject them with MPTP. If permanent Parkinson's is too harsh, then maybe inject one of those long-lasting anticholinergics (EA-3167 or 3-quinuclidinyl benzilate) --Mark PEA (talk) 11:07, 15 July 2009 (UTC)
 * (EC) I would question both the efficiency and the costs of any such measure. Punishment has three major functions: deterring other individuals from committing the same type of crime, motivating the individual who committed a crime to change his/her behavior in future to conform to legally/socially accepted behaviors and preventing the individual who committed the crime from doing it again.  The effectiveness of [{capital punishment]] in general is debated.  Your method would exacerbate the costs and further reduce any impact.  Since your prisoners would be unable to communicate, there would be no reports from them on the horrors of their situation.  So you'd have to bank on prospective perpetrators finding the mental image of locked-in syndrome and pictures of individuals in prison hospital beds connected to a barrage of tubes and monitors more objectionable than life in prison or a death sentence.  IMHO not very likely.  More likely would be that this type of punishment would add to the suffering of the victims and their families.  Even if they feel entitled to retribution at first they may feel remorse later because this punishment doesn't provide sufficient closure.  Depending on their moral and ethics views they may feel diminished by the harshness of the punishment. (They are also much more likely to consider the punishment harsh than someone who has stepped so far out of society as to consider committing a crime.)  Most societies have a hard time these days covering the cost of caring for critically ill individuals.  Your version would artificially increase the numbers in the category requiring the most intensive care and that on a long term basis.  (Most patients requiring intensive care are either so ill that they die after a while or they recover sufficiently to classify for less intensive care options or even release from hospital.)  I couldn't think of any way to justify that.  At least in the US, there's criticism that a large portion of the prison population is suffering from some mental illness.  Providing adequate care for those and improving living conditions in high crime areas would be a better use of funds to reduce the rate of violent crimes than the method you are considering.71.236.26.74 (talk) 17:20, 15 July 2009 (UTC)
 * You have a good point here -- why go to all that trouble paralyzing a terrorist or child molester and then keeping him alive for many years, when it would be more effective to just shoot him and be done with it?76.21.37.87 (talk) 01:14, 16 July 2009 (UTC)
 * The above is a good review of penology i.e. reasons for punishment. It does not admit the motive of revenge that the OP considers. Cuddlyable3 (talk) 09:37, 16 July 2009 (UTC)


 * Dramatic results of Sensory deprivation of a person in an Isolation tank were shown in the movie The Mind Benders (1962). Here is a clip. Cuddlyable3 (talk) 17:06, 15 July 2009 (UTC)
 * Note: the movie cuddlyable mentions is a work of fiction and not a documentary. Effects scientific studies report for isolation tanks are usually positive . 71.236.26.74 (talk) 08:24, 16 July 2009 (UTC)
 * That link is to a 600+ page book. Which page? Cuddlyable3 (talk) 09:37, 16 July 2009 (UTC)
 * Sorry I came to it via a more direct link p227/278 have something. Probably not the best reference, but there are quite a few studies out there. It's used in therapy.  Will try to post better stuff if I can find the time. 71.236.26.74 (talk) 01:36, 17 July 2009 (UTC)
 * 71.236 all I found on p227 was about consoling the dying, and p278 is not available at the link you gave. Cuddlyable3 (talk) 02:12, 19 July 2009 (UTC)
 * Sensory deprivation used in therapy?! With all due respect, I really have trouble believing that.  I know that it was one of the tests used for astronaut training, and most astronaut interviews state that even a few hours of sensory deprivation is extremely distressing.  Also, there are (unconfirmed) reports that the Soviets used sensory-deprivation-like techniques for prisoner interrogation / punishment, and almost all of the prisoners either spilled the beans within a few days (couple of weeks at most), or lost their mind.  I don't see how sensory deprivation can be used in therapy.

76.21.37.87 (talk) 04:01, 17 July 2009 (UTC)
 * I am going to say, considering the excellent points presented above, it is impossible to do so whilst leaving the person as a conscious, sapient mind. The mind is just something the brain is doing, and far from being the mysterious black box of puzzles it once was, we now have the capacity to look in and watch the brain doing that. That mouse cursor brain thing shows the key point. No matter how much you detach the person's mind from any natural, "everyday" output channel (speech, hand gestures, eyebrow waggling, whatever), there is still an output channel you can't possibly disconnect (that is, the brain activity that makes up the mind itself) without killing the mind. Maelin (Talk | Contribs) 12:52, 16 July 2009 (UTC)

Staying upright on a bike
Why is it easy to stay upright on a bicycle when moving forward, yet very difficult when at a standstill? —Preceding unsigned comment added by 86.176.50.146 (talk) 02:45, 15 July 2009 (UTC)
 * I assume the answer is in Bicycle and motorcycle dynamics somewhere. Algebraist 02:48, 15 July 2009 (UTC)
 * I haven't looked at that article, but the basic reason is because when you're moving, you can compensate for an error by turning the wheel a little bit to the side you're falling toward, but that doesn't work when you're at a standstill -- you can only compensate then by shifting your weight, which involves a much longer time delay. Looie496 (talk) 02:55, 15 July 2009 (UTC)


 * Read Angular Momentum conservation. Rkr1991 (talk) 03:37, 15 July 2009 (UTC)


 * The first answer is correct. Angular momentum plays very little role on a bicycle. it is more important for the understanding of the motorcycle dynamics. Dauto (talk) 05:29, 15 July 2009 (UTC)


 * Our Article says Angular momentum conservation plays more of a role on lighter vehicles like bicycles. Angular momentum conservation through counter leaning un addition to balancing with the handlebars is the complete answer, as given in our article. Rkr1991 (talk) 05:52, 15 July 2009 (UTC)


 * The article is wrong. Dauto (talk) 07:01, 15 July 2009 (UTC)
 * Algebraist 10:08, 15 July 2009 (UTC)
 * Non-technical answer: The spinning wheels act like a gyroscope. -- penubag  (talk) 06:00, 15 July 2009 (UTC)
 * Non-technical, perhaps - but quite utterly wrong - definitely! Gyroscopic forces have little if anything to do with it. SteveBaker (talk) 07:21, 16 July 2009 (UTC)
 * Nuh-uh, Looie's answer is correct. There have been experiments with bicycles with locked steering. I suppose I ought to be able to cite that, and I can't, and anyway I probably read it on the reference desk in the first place ... but I believe it's true. Bike wheels do make nice gyroscopes but aren't significant in that capacity in stopping you falling off. 213.122.68.146 (talk) 06:58, 15 July 2009 (UTC)


 * Just to clear up any confusion: 213.122.68.146, Dauto and Looie496 are correct, as is our article on Bicycle and motorcycle dynamics. Bikes and motorcycles stay upright primarily through small steering corrections, gyropscopic and angular momentum effects play a minor role (if any). See all the external links from our bike dynamics article, or do a Google search. &mdash; QuantumEleven 10:16, 15 July 2009 (UTC)


 * The idea here is that because the contact-patch of the wheel is BEHIND the axis it pivots on, when you lean it automatically tends to steer into the lean. Exactly what you would want it to do to keep you upright. This built-in feedback makes it very easy to stay balanced because the bike is constantly "trying" to steer itself under your center of gravity. APL (talk) 13:06, 15 July 2009 (UTC)


 * In other words, the angular momentum does help by providing a force which completes a (mechanical) negative feedback loop; the actual balance is accomplished with the steering corrections. As Dauto has pointed out, the net effect of the angular momentum is small; but the bicycle attempts to self-right because of the fork mounting of the front tire.  (Consider the front tire fork mounting as a mechanical "amplifier" which senses deviations in angular momentum, and magnifies them via the kinetic energy sourced from the forward motion of the bicycle).  The human can hold the handlebars and assist in the steering.  Perturbations from balance upset the angular momentum, and push the tire back towards the upright steering.  This is why minutely different designs of front wheel mounting dramatically change the steerability and stability of the bike.  Nimur (talk) 22:04, 15 July 2009 (UTC)


 * Nimur, the fork feedback works even if the bike is not moving at all (try it) and therefore has nothing to do with angular momentum. A bike's wheel doesn't spin fast enough to have any important effect. A motorcycle is a different matter. Ask anybody that knows how to drive a motorcycle if steering it is any different than steering a bike. Ask them if they have to pull right in order to turn left Dauto (talk) 04:56, 16 July 2009 (UTC)
 * WP:OR... I know how to drive a motorcycle... Nimur (talk) 08:57, 16 July 2009 (UTC)


 * I strongly recommend that everyone who is even considering replying to this thread carefully re-read our Bicycle and motorcycle dynamics article before replying. IMHO, it's one of the finest science articles in the whole of Wikipedia (why isn't it an FA?†) - and it's correct, well written, approachable, beautifully illustrated - and properly referenced - as opposed to about half of the replies here so far that are complete twaddle! SteveBaker (talk) 07:21, 16 July 2009 (UTC)


 * †It's presently a Good Article, but it looks like there are still some TODO items listed on its talk page from the unsuccessful FA nom a few years ago. DMacks (talk) 08:05, 16 July 2009 (UTC)


 * The simple answer is that the wheels of a bike can be easily moved back under the center of mass, in response to an undesired lean, when moving forward, by steering the front wheel in the direction of the lean. The faster the bike is moving, the more quickly the contact patches move for the same steering input. When stationary, there is some ability to move the front wheel contact patch from side to side because of the front wheel steering geometry, specifically the feature called trail, but it is limited and slow compared to when moving forward.


 * The geometry and mass distribution of many bikes is such that the torque necessary to turn the front wheel appropriately can be generated by the bike itself, if moving forward at the right speed. The factors that influence this self-stability include the "trail" mentioned above, mass distribution of the entire bike and of just the front end, and inertia of the wheels, especially the front wheel.


 * While the gyroscopic effects of the spinning wheels is often cited, David Jones proved by experimentation that they are not necessary for a bike to be "easily ridden" in his famous 1970 Physics Today article. A spinning wheel provides no direct resistance to tipping. Instead, when the spinning front wheel is subject to a tipping torque, it reacts be precessing about a third axis, perpendicular to both its spinning axis and the axis of the applied tipping torque. This is approximately the steering axis. Thus, this precessing can contribute to the bike's ability to steering in the direction of a lean automatically. -AndrewDressel (talk) 12:16, 16 July 2009 (UTC)

Note you can most easily stand stationery on a track bike, which has no freewheel. Standing that way is for that reason sometimes called a track stand. 67.117.147.249 (talk) 08:28, 21 July 2009 (UTC)

light beams repel each other?
What's this about? Do we have an article explaining the effect?


 * http://www.sciencedaily.com/releases/2009/07/090713131556.htm

Thanks. 70.90.174.101 (talk) 03:55, 15 July 2009 (UTC)


 * Article here (doi:10.1038/nphoton.2009.116), poorly formatted draft at arXiv:0903.5117. They seem to be talking about a nonlinear interaction in a medium which (they say) is already predicted by Maxwell's equations, so it's theoretically very old. It isn't literally a force between electromagnetic waves, but between charged particles in the medium. The reason for the newspaper reports is not that the paper is important, it's that Yale issued a press release, and most science reporters don't know how to do anything but parrot press releases. Why they issued the press release I don't know, but inevitably they're going to inflate the importance of the work because the point is to get free advertising for Yale. I would ignore it. The paper is science as usual, the reporting is horrible science reporting as usual. -- BenRG (talk) 10:08, 15 July 2009 (UTC)


 * Here is another recent article on the subject from LiveScience. ~ A H  1 (TCU) 13:22, 15 July 2009 (UTC)

Psychology / Lying Videos
There are plenty of studies on facial tics, or microexpressions related to lying, but I'm curious if anyone knows of a source of videos or other resources on the specific issue. What I'm ultimately interested in are source videos that compare people lying to those that aren't, and in high enough format that they're useful. Bonus points if they involve law enforcement. I realize this is a tall order, but if there are any good studies (even without video) outside of what I can find on pubmed/jstor I'd be interested. Thanks. Shadowjams (talk) 05:27, 15 July 2009 (UTC)

Cross posted to the humanities page.
 * Click! Cuddlyable3 (talk) 13:25, 15 July 2009 (UTC)

torque
I want to show that the torque caused by gravity is equal to the torque that would be produced by an point particle of mass M at the centre of mass. I've been trying to evaluate the sum Σ (m_i*g*r_i*sin(θ)_i), but I haven't been able to reduce this to MRg*sinθ (where R denotes the position of the centre of mass). Is there a way to do this, or does it suffice to show that the total force due to gravity is equal to the force produced by a point particle of mass M at R, and then multiply this by R to get the torque? (I wouldn't think so). —Preceding unsigned comment added by 70.52.44.188 (talk) 05:44, 15 July 2009 (UTC)


 * I don't understand. About which point are you taking Torque ? If it is the centre of mass, as conventionally taken, wouldn't the torque that would be produced by an point particle of mass M at the centre of mass be zero ? Rkr1991 (talk) 05:58, 15 July 2009 (UTC)


 * Oh, well maybe this is a clearer explanation of what I'm asking (sorry if I can't explain myself properly!): Supposed an object is fixed in such a way that it will pivot about a certain axis. Assuming that the gravitational field is constant, what is the torque produced by gravity? I know that the answer should be MRxg, where R is the position vector of the centre of mass, but I don't know how to derive it. My normal approach would be to sum all the torques τ_i acting on each particle of the object, which by Newton's Third Law should equal the total external torque (ie the total torque produced by gravity, should that be the only external torque acting). On the other side of the equation, I get Σ (m_i*g*r_i*sin(θ)_i), which I'm having trouble evaluating. PS I know that the total force due to gravity can be treated as if the entire mass were concentrated on the centre of mass, but can we extrapolate from this that the total torque due to gravity is equal to MRxg? —Preceding unsigned comment added by 70.52.44.188 (talk) 06:29, 15 July 2009 (UTC)


 * $$\mathbf{\tau}=\sum_i\mathbf{\tau}_i=\sum_i\mathbf{r}_i\times \mathbf{f}_i=\sum_i\mathbf{r}_i\times (m_i\mathbf{g})=(\sum_im_i\mathbf{r}_i)\times \mathbf{g}=M\mathbf{R}\times \mathbf{g}$$. Dauto (talk) 06:54, 15 July 2009 (UTC)


 * LoL that was easy, thanks. —Preceding unsigned comment added by 70.52.44.188 (talk) 07:03, 15 July 2009 (UTC)

Jade
What is the maximum percentage of iron in Tremolite (which forms jade). Is it possible to make tremolite and mix it with iron in, say, a factory?174.3.103.39 (talk) 08:32, 15 July 2009 (UTC)


 * The Nephrite variety of Jade consists of amphiboles in the solid solution series tremolite-actinolite-ferroactinolite. Jade is either iron-rich tremolite or actinolite, the former being lighter green and the latter darker. The maximum iron content for tremolite is 10% Fe of the total Fe+Mg, from 10-50% it's an actinolite, any higher then it's a ferroactinolite. Synthetic tremolite and actinolite certainly exist, but I doubt it would be cost effective to try to produce large quantities. Mikenorton (talk) 09:30, 15 July 2009 (UTC)

Water Wheel Power
Would it be possible to power a household which uses 1000 kWh per month using a water wheel? How big would it have to be and could I possibly build several smaller ones or is one big one the way to go? TheFutureAwaits (talk) 12:24, 15 July 2009 (UTC)
 * Micro_hydro shows other households that have done it. One of them is only getting 90W though, which wouldn't meet your needs. It seems worth further investigation. AlmostReadytoFly (talk) 13:12, 15 July 2009 (UTC)
 * By the way, 1000 kWh per month is 1369W. — DanielLC 14:15, 15 July 2009 (UTC)
 * A household usually has peak energy demands around 10kW though, so if you are only generating 2kW, probably can not run the refrigerator, the oven the AC and the clothes dryer at the same time. Googlemeister (talk) 14:29, 15 July 2009 (UTC)


 * The short version: yes. "Power via water wheel" is a useful approximation of hydroelectric power.  Examining industrial applications, it's clear that multiple smaller systems are a useful way to scale requirements.  As for "how big", a more useful question is what sort of water flow you need.  This thermodynamics book includes a sample problem for ideal power generation at the Hoover Dam.  Note that both water flow rate and elevation change are relevant to the power that can be supplied.  &mdash; Lomn 14:45, 15 July 2009 (UTC)


 * Water power is far more reliable and continuous than solar or wind (unless the creek goes dry or the pipe freezes or the intake gets clogged with twigs). Your water wheel or Pelton wheel microgenerator should be sized to supply your peak load.This will be several times your average load. If you cogenerate, then the utility absorbs the excess and supplies the deficiency, reducing the required size and cost. For a Pelton wheel, high pressure water from a point quite elevated is desirable. The flow of water is the limiting factor for how many kilowatt hours you can produce before the water level drops. An old water wheel like mills of the 19th century is not the ideal way to run a generator, but is has been done. Years ago on TV they showed a former textile mill where a man had hooked up the old water wheel to an alternator,. It produced 30 kilowatts continuously. This would be 518,000 kilowatt hours each month, worth perhaps $20,000 when sold to the utility. It was probably extremely inefficient. The typical microhydro has a 100 foot drop from water intake to Pelton wheel and the flow is a few gallons per minute. As for number, for such a small load it would be practical and economical to buy one turbine/generator. If you set up to sell the surplus to the utility, then you should be able to use the utility as a backup, eliminating any advantage of multiple units. Keep things simple. See Micro hydro or Google the term.  Some of the vendors can advise you on components suitable for your situation. Edison (talk) 16:20, 15 July 2009 (UTC)
 * Before you go ordering parts online and calculate a setup, check local EPA regulations and county water resource/use rules. Depending on your location you may have to provide alternative habitats for local wildlife, have to pay a fee for operating your water-wheel or it may be outright prohibited.  Try to find an official in charge at your county government who can help you finding out what laws and regulations apply.  Work your way up from there. (If you take this as legal advice, I'd have to instruct you to contact a lawyer instead.) 71.236.26.74 (talk) 17:41, 15 July 2009 (UTC)
 * This water wheel would give DC right? And most houses I know are wired to use AC, so there might need to be other modifications as well.  Googlemeister (talk) 18:45, 15 July 2009 (UTC)
 * Probably - yes. But you're probably going to need to store the power for when you need it and to smooth out variation in your day/night demand cycle - so most likely, you'd have a basement full of car batteries that you'd charge from the water wheel - and then use an Inverter (electrical) to convert the output of the batteries to AC. SteveBaker (talk) 19:07, 15 July 2009 (UTC)
 * It might be more efficient to build a dam and only let through the amount of water you need at any given time. During off-peak times the water level behind the dam will build and then go down again during peak times. You might annoy being further downstream, though! --Tango (talk) 19:38, 15 July 2009 (UTC)
 * If you build a dam, the level of permitting needed may be quite high, since a dam which holds back a large volume of water can cause considerable damage if it fails. Microhydro often uses an intake which is not really a dam, above the falls of a stream, rather than having a dam sufficient to produce the required head. Microhydro often produces say 24 volt DC which is stored in batteries and converted to AC through an inverter. An inverter which ties to the utility may eliminate the need for batteries, as you cogenerate. Utility permission should be sought. They have brochures on how elaborate the interface and protective relaying has to be. It gets more complex as the generator gets larger. For a few kilowatts it should be minimal. Edison (talk) 21:58, 15 July 2009 (UTC)

Thanks for all the great info! So if I were to use a Pelton wheel to generate 1000 kwh per month is there a reasonable estimation of what the radius of the wheel would need to be? The water flows at about 5 mph and drops about 10 feet in the area I want to build the wheel although I suppose I could use tubes to divert the flow and create a steeper, higher pressure drop. TheFutureAwaits (talk) 21:03, 16 July 2009 (UTC)
 * Well, I'm not an expert on water-wheel design - but I'd guess that you want the weight of the water to be pushing down on the wheel for as much of the drop as possible because any water that falls through any distance without being attached to the wheel is wasting energy. However, to do that - you'd have to have a 20' wheel with the hub of the wheel level with the surface of the water - and having it drag through the water would cause a lot of energy loss...hence, I presume the basic design for a classic over-shot wheel (like in the photo to the right) where the water is fed in at the top of the wheel - roughly level with the inlet height - falls with the wheel for as close to half a rotation as you can manage - then empties out at the bottom - roughly level with the outflow height.  That would require (in your case) a 10' diameter wheel.  That would capture as much of the energy as possible.  However, knowing the speed of the water doesn't help unless you also know the volume (ie the flow rate.  After all - I could probably get a 5mph, 10' drop water flow from a super-soaker...but that's not going to turn a 10' diameter water wheel!  You would need to vary the width of the wheel and/or the size of the 'buckets' or 'scoops' in order for it to store all of that volume of water as it falls - without any spilling over and going to waste.  The knowing the volume of water that the wheel is holding would allow you to calculate the torque that the wheel could exert - and with appropriate adjustments for frictional losses, you could use that to estimate the energy output.
 * If you knew the flow rate (cubic feet per second or whatever) - we could make an estimate of the energy you might be able to extract...but without that information, we have no clue. SteveBaker (talk) 23:59, 16 July 2009 (UTC)
 * You may need a water turbine instead of a water wheel. (I would have thought they are synonyms, but there seems to be only a partial overlap.)  This page says there are several options depending on the specifics of your site.  71.236.26.74 (talk) 02:19, 17 July 2009 (UTC)
 * So would a Pelton wheel be considered a "water wheel" or a "water turbine"? 76.21.37.87 (talk) 04:08, 17 July 2009 (UTC)
 * I've just read the article Water turbine -- from what I gather, a 10' drop ain't enough for a Pelton wheel (it needs at least 15' for best efficiency), but a Kaplan turbine would be right at home with a 10' drop (in case you don't know, a Kaplan turbine is the kind of turbine that looks like a ship's propeller). So, TheFutureAwaits would be better off putting in a Kaplan turbine instead of a Pelton wheel.  Also, SteveBaker, a Pelton wheel ain't like your regular water wheel cause it don't use the weight of the water but its velocity for propulsion -- so you don't have to install it level with the inflow, and in fact it's better to place it as low as possible so's you get the most velocity from the drop.

76.21.37.87 (talk) 04:25, 17 July 2009 (UTC)
 * Have you considered using a Banki turbine?71.236.26.74 (talk) 05:43, 17 July 2009 (UTC)
 * Good idea, 71 IP -- a Banki turbine's a better choice for a small / variable flow rate, while a Kaplan turbine's better for a fairly big, more-or-less constant flow rate. It really depends. 76.21.37.87 (talk) 05:59, 17 July 2009 (UTC)
 * There's also the maintenance issue. It says Bankis are easier to maintain. I remember the first private wind turbines often overtaxed their builders' time, energy and abilities that way. 71.236.26.74 (talk) 06:14, 17 July 2009 (UTC)
 * On second thought, the chart in the Water turbine article says a 10' drop's still not quite enough for a Banki turbine... 76.21.37.87 (talk) 06:43, 17 July 2009 (UTC)
 * I should get a job at Nasa :-). The chart's in meters.  OP only has a 3 m drop. Kaplan it is. (I should buy myself a trout and whack myself.) 71.236.26.74 (talk) 18:17, 17 July 2009 (UTC)
 * Hahaha, good one! LOL! 76.21.37.87 (talk) 01:38, 18 July 2009 (UTC)
 * As an aside, if the flow rate is more-or-less constant, the OP should consider a Kaplan turbine with fixed-pitch blades instead of variable-pitch, it should save him / her a whole bunch of maintenance. If the flow rate is very variable, though, then variable-pitch blades are the only option.

76.21.37.87 (talk) 01:38, 18 July 2009 (UTC)

What are pavement cells?
The English wiktionary defines "pavement cell" as Brachycystidia in the gills of some species of Coprinus. But pavement cells also exist in plants. So what exactly is a pavement cell? --Leptictidium (mt) 13:28, 15 July 2009 (UTC)
 * I'm not familiar with pavement cells of any sort, but I can tell you that it is quite common in microbiology for names like that to be given to multiple things that have no meaningful relationship to each other. In the brain, for example, there are "granule cells" all over the place, and the only thing they have in common is that they are all small.  Most likely "pavement cells" are just cells that look sort of like they are paving a surface, under a microscope. Looie496 (talk) 14:26, 15 July 2009 (UTC)


 * In plants a pavement cell is an unspecialized epidermal cell, from which the other types of cell in the epidermis (outer covering of the plant) develop. Mikenorton (talk) 14:35, 15 July 2009 (UTC)
 * In fish, pavement cells are also known as 'respiratory cells' and in saltwater fish they are very flat, so Looie is likely to be right in suggesting that they have been named for their shape, rather than any biological similarity to plant epidermal cells. Mikenorton (talk) 14:59, 15 July 2009 (UTC)

Cleaning oil stain from thermal plastic elastomer
How would one clean oil off of the surface of a thermal plastic elastomer  (mixture of PVC and silicone)? I've tried soap and water. Also alcohol, but no luck. --68.102.170.184 (talk) 13:43, 15 July 2009 (UTC)
 * Use WD40 on an absorbant rag or towel.
 * You can clean the wd40 off with soap.

83.100.250.79 (talk) 16:11, 15 July 2009 (UTC)
 * Wouldn't that melt the PVC? --68.102.170.184 (talk) 11:27, 16 July 2009 (UTC)
 * No.83.100.250.79 (talk) 13:57, 16 July 2009 (UTC)

Computer chassis of sisal?
How likely do you think it is that a small computer which makes a computer case made of water-proofed sisal woven over a frame, will be adopted by major computer companies like Dell and HP? N.B. sisal would save energy by allowing heat to escape. (Cross-posted to computing board) --Patar knight - chat/contributions 17:43, 15 July 2009 (UTC)


 * People who run their computers with the case off not uncommonly fry some part because the airflow generated by the fans no longer reaches that part. Manufacturers'd have to start over with testing for airflow/heat management.  Other than the flow in an enclosed case, the leakage through your "open" case would be hard to quantify and would likely vary wildly.  Dust entering the case and sisal fibers disintegrating from the weave would be other factors to consider.  You could coat the fiber to prevent that, but that would somehow run counter to the whole "natural" idea.  Admitting that most computers would be obsolete and replaced before the case got too grimy would also not in the manufacturers' best interest.  There might possibly be a small market in the ecologically conscious home computer market, but for most business applications it's rather unlikely to become a widespread option IMHO. 71.236.26.74 (talk) 18:01, 15 July 2009 (UTC)


 * It strikes me as a remarkably bad idea to make a computer case out of flammable material. Looie496 (talk) 18:12, 15 July 2009 (UTC)
 * I thought of that at first, but quite a few plastic materials used for cases start out as "Class A" and just reach higher grade by having Flame retardants added. If it works on cotton it should work on sisal, too. (See the article why that would make the case a lot less "green") 71.236.26.74 (talk) 18:46, 15 July 2009 (UTC)


 * I think you could extract fibres from the sisal and make some sort of a paper mache-like substance that would make a reasonable case - it could easily be treated to make it fire-resistant. The problem would certainly be heat though - a metal case acts like a huge heat-sink - a case made of pretty much any kind of plant material would probably make a good insulator - and that's a disaster.
 * However, this is all really unnecessary. Computer cases are commonly made of aluminium - and that's a VERY recyclable metal.  It would be simple to dump computer case panels into the same recycling stream as old coke cans.  The difficulty with recycling computers isn't the case - it's the circuit boards, hard drives, keyboards and (especially) displays.  These are very 'mixed' materials which are almost impossible to separate out into useful recycling streams.  A typical circuit board has fibreglass and resin for the board itself - with layers of valuable copper buried inside it and bonded very firmly to it's surface - with lead/tin alloy solder firmly affixed to it, plastic and ceramic chip casings, all manner of little plastic and brass parts. Steel connectors often with gold plating.  Then inside the chips you've got silicon, more gold, who-knows-what nasty stuff inside resistors, capacitors and any little batteries and such - all kinds of exotic metals inside things like LED's.  Glass and LCD-panel monitors are an even bigger nightmare - lead and phosphors in the CRT, weird liquid crystal chemicals in the LCD's.  Power supplies often have toxic chemicals in the windings of the transformer coils.  It's really a mess to sort this out in a cost-effective way.
 * So fixing the problem of recycling the cases of old computers is solving a non-problem and creating a bunch of new problems (as alluded to above) in the process. What's needed (and it's hard to see how it'll happen) is to figure out how to recycle everything OTHER than the case.


 * If for some reason we were really passionate about case recycling, the solution (since cases never break or wear out) would be to require the circuitry of all new computers to fit into a standard sized case (deskside computers pretty much do that already). The manufacturers could then offer to sell you a new set of electronics that slotted right in to your existing case.  This isn't difficult for an individual person to deal with.  I haven't bought a new computer for 16 years!  I just keep swapping out parts (and occasionally cases) from one generation of machine to the next.


 * SteveBaker (talk) 18:57, 15 July 2009 (UTC)
 * Computer cases=steel not Al, Transformer windings = not toxic at all really - just glue. (Large industrial transformers from the 1960s ~10kW+ = toxic yes). 83.100.250.79 (talk) 22:31, 15 July 2009 (UTC)
 * (83.100.250.79: Please don't interpose your replies in the middle of someone else's comments - it rapidly gets very confusing. I've moved your reply to the proper place). Anyway - the cases of all three of my home PC's are aluminium - including all of the internal rails and bracings...there may be the odd steel one - but it doesn't change the conclusions.  Steel (like most other pure metals) is also childishly easy to recycle.  It's not the problem here.  Consider recycling CRT's, hard drives and motherboards...it's tough.  I'll take your word for the nature of the goop in the transformer windings - but again, the precise details don't matter - the issue is that there are a LOT of weird and wonderful materials (many of them toxic) inside a typical computer - and sorting them out at any reasonable price is FAR beyond our current ability. SteveBaker (talk) 07:14, 16 July 2009 (UTC)
 * sorry that was an accident
 * Actually I don't totally agree on the toxicity of computer parts - in a landfill there's no much issue, BUT if they are incinerated then yes there is a toxicity issue.
 * One part that is trivially recyclable is the solder. It's also possible to extract the copper by shredding and density separation - I'm not sure if this is economically viable. As part of the desoldering recycling operation there should be all the surface mount components separated - as for re-using these - I doubt intel et al would be very keen on losing out on the obsolescence/replace product lifestyle. The chips, capacitors, and resitors I wouldn't know what to do with - possibly the caps could be density separated and recycled. That leaves the ICs mostly - as far as I know they are totally unrecyclable in terms of materials/energy - especiallly in an economic sense. (Though they do have a store of energy as order - so if you can make a "order converts to entropy=electricity" machine you might be onto a winner. One product of the recycling process I've left out is the shredder glass fibre/epoxy board - any suggestions as to what to do with this.
 * Recycling of electronic parts can be done, and is done - though not total recycling. And only a fraction of the waste goods actually gets recycled as far as I know.83.100.250.79 (talk) 14:59, 16 July 2009 (UTC)83.100.250.79 (talk) 14:19, 16 July 2009 (UTC)
 * The capacitors and resistors could be taken out and resold, as long as they're still in working order. 76.21.37.87 (talk) 04:30, 17 July 2009 (UTC)

Desktop and deskside computer cases are easy to re-use if you really want to. If you don't want to re-use the case, they are also trivially easy to recycle, since they have effectively the same mix of materials as an automobile body. On average there are thousands of times more material in car bodies than in computer cases, so the computer cases have effectively zero additional impact on recycling if done correctly (i.e., throw the old case in the back of a car on the way to the car recycling center, or if your municipal garbage system uses magnets to separate out the steel, the cases will be treated like "tin" cans.) For servers and other large installations, the industry is trying to find more elegant solutions such as blade computers that have relatively less case material per computer. As Steve said above, the stuff inside the case a a much bigger problem. If you have a computer at home, you should worry about the energy it uses, not about recyclinghte case. You can also worry about all tjhe plastic in a laptop case, but these are more similar to other small appliances. Computers are becomming a whole lot more effecient by every purely technical measure: cost per instruction executes, power per instruction exececuted, weight (material to recycle per instruction executed.) A modern Mac mini or plug computer is massivley more capable than a ten-year-old desktop, but uses less tha a tenth of the energy or material. Unfortunately, we all just keep upgrading to better conputers and then don't actually use the extra capability. This appears to be changiong somwhat with the advent of the netbook. -Arch dude (talk) 22:05, 15 July 2009 (UTC)


 * Arising from the above, are computer cases made out of aluminium rather than steel


 * 1) because it's cheaper,
 * 2) because it's lighter, or
 * 3) because it prevents people using office/fridge magnets to attach things, thereby damaging the disks? 87.194.161.147 (talk) 12:54, 16 July 2009 (UTC)
 * I'm still amazed that computer cases are made of Al, the ones I'm aware of have all had a skin of steel or plastic.(Not counting mac books etc) However I accept SteveBakers comments about the rails (ie the internal frame and attachment points) being made made out of Al - there is one really good reason for this - and that's that alumimium is a lot easier to machine than steel - specifically putting screw holes in steel is a lot harder. Al is not cheaper. I doubt the reason is lightness (excluding laptops were this matters)83.100.250.79 (talk) 14:04, 16 July 2009 (UTC)
 * I'm skeptical about the aluminium case too. All the aluminium cases I've seen are premium cases like Lian-Li cases, whereas most normal cases are made from SECC (most, if not all, of these and these are made from steel). I'm putting a [citation needed] tag on Steve's claim. --antilivedT 01:39, 17 July 2009 (UTC)

I don't think it's likely that Dell or HP would ever make a sisal computer case, but it sounds like a typical thing that the case mod community might do, especially with lower powered motherboards. mini-itx.org has a lot of photos that you might like. Look down the list of projects on the lower right hand edge of their main page. 67.117.147.249 (talk) 08:32, 21 July 2009 (UTC)

decarboxylation
I assume carbon dioxide a good leaving group? What's the mechanism of heat-driven decarboxylation usually, e.g. like in THC? I can't imagine protons being good nucleophiles, however... does the CO2 usually take the electrons with it? Does the bond cleave homolytically?

I suspect the CO2 LG takes the bonding electrons with it, such that you get a carbocation (or a carbocation-like transition state?) -- would that explain why longer-chain COOH's are easier to decarboxylate? Is a tert-COOH group the easiest to decarboxylate? John Riemann Soong (talk) 18:24, 15 July 2009 (UTC)

Generally, it's aromatic COOH groups (such as the one in salicylic acid that are the easiest to decarboxylate (even easier than tert-COOH groups). FWIW 76.21.37.87 (talk) 01:26, 16 July 2009 (UTC)


 * Someone uploaded an image displaying the mechanism for the decarboxylation of a ketoacid. I haven't been able to find the mechanism of decarboxylation of something like acetic acid.

http://commons.wikimedia.org/wiki/File:3-ketoacid_decarboxylation_mechanism.PNG Calamus Fortis  21:17, 15 July 2009 (UTC)


 * "does the CO2 usually take the electrons with it" sounds like you will have a redox problem, unless you plan on losing H– (hydride) later:
 * RCOOH → R+ + –COOH
 * And homolytic cleavage of C-C bonds is also unlikely unless you have some radical initiator. Is there a reason you need to look further than
 * RCOOH → RCOO– + H+
 * RCOO– → R– + CO2
 * ? The two examples given, salicylic acid (which looks like the relevant substructure in THC) and β-ketoacid, in essence each just help accelerate one or both of those steps. A Lewis base intramolecular deprotonation (step #1) via 6-membered transition-state looks even better than "just" an acid doing its acidic business, and making it a 6-e– pericyclic reaction with no formal charges in product is easier than two steps with charged alkyl structures. DMacks (talk) 05:13, 16 July 2009 (UTC)

coommon cold
why do we get cold after we drench our head in rain for long19:02, 15 July 2009 (UTC)117.197.208.57 (talk) 19:02, 15 July 2009 (UTC)


 * Several reasons come to mind. One would be that the temperature of the water you are drenching your head with is usually cooler then the ambient air temperature and almost certainly cooler then your body surface temperature.  Added to that, when the water evaporates, it takes away heat similar to how an ice cube works to cool your drink.  Finally, sometimes your sense of touch has a difficult time telling the difference between damp and cool.  Googlemeister (talk) 19:18, 15 July 2009 (UTC)
 * The OP might be referring to contracting the common cold rather than feeling the sensation of coldness. Algebraist 19:21, 15 July 2009 (UTC)


 * Our article on the common cold notes that current science finds no causal link between cold weather and the cold. While behavior favored in cold weather increases your likelihood of getting sick, and while exposure to cold weather can cause cold-like symptoms, standing in the rain does not increase your chances of getting the cold. &mdash; Lomn 19:45, 15 July 2009 (UTC)
 * Lowering your body temperature weaksn your immune response, doesn't it? Could make catching a cold easier. Vimescarrot (talk) 23:15, 15 July 2009 (UTC)
 * That's actually a back-formed explanation for the old-wives tale that having a wet head causes the common cold. While having a chronicly low body temperature (like hypothermia levels) may weaken the immune system, at that point you have other things to worry about than the sniffle you may get. When studies have been done, there is no causal link between ANY non-infectious external stressors and getting a cold. You get a cold because you have been in contact with someone else with a cold. And that's about it. --Jayron32. talk . say no to drama 01:15, 16 July 2009 (UTC)
 * According to these British researchers the final word isn't out yet on cold weather and colds . However OP seems to have the top and bottom confused according to this link  also featured in our article it's cold feet, rather than a cold head that contributes to catching a cold. 71.236.26.74 (talk) 05:22, 16 July 2009 (UTC)

It's very simple really. Water, in it's native state, is cold. Our heads are very warm. So, cold things make hot things colder. Vranak (talk) 18:44, 16 July 2009 (UTC)

And exposure to cold temperatures can cause vasoconstriction, which keeps white cells from getting where they're needed -- so it could make it easier to catch a bug (although it doesn't by itself cause the common cold). FWIW 76.21.37.87 (talk) 05:37, 17 July 2009 (UTC)

question about ticks
I was reading our article about ticks and came across this

"Some species stalk the host from ground level, emerging from cracks or crevices located in the woods or even inside a home or kennel, where infestations of "seed ticks" (the six-legged stage of newborn ticks) can attack in numbers up to 3,000 at a time[citation needed]. Weak or elderly dogs and puppies are particularly endangered and can die from anemia from a sudden influx of seed ticks[citation needed]. Seed ticks also attack horses, cattle, moose, lions and other mammals, causing anemia, various diseases, paralysis and even death."

This sounds rather unlikely, but I do not know enough about ticks to know if this is vandalism, or what. Does anyone know about these seed ticks? Googlemeister (talk) 19:05, 15 July 2009 (UTC)
 * wikipedia seems broken, google keywords from your text and you'll find the pages it's from. Could't save edit with links - getting "out of captcha". 71.236.26.74 (talk) 20:04, 15 July 2009 (UTC)


 * I poked around in Google Book search, and although I didn't find any mentions of seed ticks specifically causing anemia, I did find many references to ticks causing anemia, and to seed tick infestation of livestock. So it doesn't seem too improbable to me, based on the minimal amount of research I did.  —Dominus (talk) 20:49, 15 July 2009 (UTC)


 * I know original research is frowned upon but I witnessed in southern Spain, several years ago, many hundreds of tiny ticks ascending the wall of an enclosed yard where two dogs had previously been kept. It was an unnerving experience. Richard Avery (talk) 21:41, 15 July 2009 (UTC)


 * Hope it'll work this time. googling gave following ghits  mentions anemia,  seems like a likely source for the numbers. 71.236.26.74 (talk) 04:35, 16 July 2009 (UTC)

Calculating the odds
How the heck does Spock calculate the odds on things? He is always doing this in Star Trek. Are the odds quoted in the dialogue accurate or are they just technobabble? —Preceding unsigned comment added by 216.154.20.38 (talk) 19:32, 15 July 2009 (UTC)
 * Star Trek is fiction. The circumstances it portrays are fiction.  Any odds related to those circumstances are fiction.  We could make in-universe guesses about "how Spock does it" (my guess is that computers are good at math), but at the end of the day, the writers pick a number backed up by an uncertain degree of educated guesswork. &mdash; Lomn 19:40, 15 July 2009 (UTC)
 * It's probably just technobabble. If you give a specific example we can try and see if we can work out how the odds would be calculated. --Tango (talk) 19:44, 15 July 2009 (UTC)
 * No - that's really the whole problem. Jim will say "Call the guards - I'll pretend to have a mild tummy ache and when they rush in you just do the old Vulcan neck pinch - then we'll grab their guns and fight our way out through that army of guys with oddly wrinkled foreheads." - then Spock will say "But the odd of that working are only 2.34574950596%" - and then they go do it anyway and it works.  There is simply no way to put "odds" on that because the 'unknowns' are easily enough to push the error bars on the estimate out to 100% such that any decision based on that estimate would be no better than flipping a coin.  The problem with writing a script for a supremely logical being is that scripts are written by script writers - who are without doubt NOT supremely logical people! SteveBaker (talk) 22:00, 15 July 2009 (UTC)


 * Obviously he asks C3PO Googlemeister (talk) 19:52, 15 July 2009 (UTC)
 * Who, in turn asked Twiki &lt;shudder&gt; - who asked B-9 (who is 97.43% likely to continue have no Wikipedia article written about him by about the middle of next week) SteveBaker (talk) 21:53, 15 July 2009 (UTC)
 * Who IS B-9, anyway? 76.21.37.87 (talk) 01:34, 16 July 2009 (UTC)
 * B-9 is the robot from the original "Lost in Space" TV series who says "DANGER, Will Robinson, DANGER!"...whilst waving his arms around crazily (I'd like to meet the programmer who thought THAT was a useful engineering feature!) and being completely unable to tell anyone what the danger actually is! He also gave probability estimates with crazy over-precision for unfathomable events.  (You can just imagine the scene at NASA's robotics division: "Hey boss - I'm coding the emergency response subroutine for the new B-9 'bot.  I'm thinking that it should say "DANGER!" in a loud, assertive voice, flash it's front-panel lights and then carefully explain the reason for the emergency?"..."Well, that's alright but could you maybe make it also mention the names of any nearby crew members whom it happens to like?  Oh - and how do you feel about making it wave it's arms around in a wild and panicky way?  But do we really need to bother explaining what the danger is?  I think we could save some money and not bother implementing that part.")  SteveBaker (talk) 09:02, 16 July 2009 (UTC)
 * Thanks for the answer, Steve, I'll try and create an article about B-9 if I have time. 76.21.37.87 (talk) 04:36, 17 July 2009 (UTC)
 * The worst thing about Spock's estimates is that they are ALWAYS wrong. SPOCK: "Well Captain, we've only got a 1.234% chance of getting away with your crazy plan." - KIRK: "That's good enough for me!"...and Kirk is always right (or at least extremely and consistently lucky).   You're left just itching to hear:  SPOCK: "Your plan has a 99.99% chance of working!"...but we just know that Kirk would then think of an even sillier plan. SteveBaker (talk) 21:53, 15 July 2009 (UTC)
 * Ironically, the law of large numbers should start to kick in (well, 72 episodes or something). If Spock consistently suggests the odds of success are 10%, doesn't that mean that by the end of 10 shows, there should have been 9 catastrophic failures?  There are only so many times you can "beat the odds" before you must conclude that the odds were not properly calculated.  Nimur (talk) 22:15, 15 July 2009 (UTC)
 * And that's really the horrible part of it: Spock is supposed to be amazingly logical - yet he seemingly ignores his own utter failure at estimating realistic odds. Worse still, he always gives a ridiculous amount of precision to his estimates - which is really not the sign of a logical mind.  The script writers couldn't resist doing the same thing with "Data" in STTNG - but at least the remainder of the crew are given the opportunity to mock him for doing it.  They made an entire plot-line out of Data's inability to speak 'contractions' (do not - rather than don't, etc) - where his "brother" is able to do so easily.  Data continually strives to be more human no matter the cost - and is able to reprogram himself and teach himself singing, painting, playing a musical instrument and (with rather less success), dancing...yet he is quite unable to add the following five lines of code to the input of his speech unit:

if ( situation == casual && word [ n ] == "do" && word [ n+1 ] == "not" ) {    word [ n ] = "don't" ; word [n+1] = "" ; }


 * ...but this is why it's fiction...other than that the scriptwriters needed this in order to 'sell' the character - there is no reason for it. Why did Suung fail to use a more realistic color of plastic on Data's skin when almost every other aspect of his master-work is so stunningly human?   And for chrissakes why doesn't the Enterprise raise it's shields automatically when an unrecognised craft comes within 10,000km rather than waiting for some dithery old captain to tell the weapons officer guy to do it?!? SteveBaker (talk) 23:07, 15 July 2009 (UTC)
 * "Captain, what shall we do?" "Commander Data?  Commander Data?".  --Sean 13:48, 16 July 2009 (UTC)
 * Fortunately, Data isn't programmed in C++... SteveBaker (talk) 23:40, 16 July 2009 (UTC)

Steve you raised the subject of English contractions. Check your usage of it's and its. Cuddlyable3 (talk) 10:39, 16 July 2009 (UTC)
 * I'm not self-reprogrammable. Hence fixing that bug is a little harder! SteveBaker (talk) 23:40, 16 July 2009 (UTC)
 * Two points here : 1) Even if I knew that it was standard operating procedure for the computer to raise shields automatically on a "Red Alert", I might still give the order to double-check. Especially with the number of automation problems Enterprise seems to have. (It would also give me a few extra seconds to think before my crew expected some brilliantly unorthodox solution to the crisis.)  2) There are probably lots of times where Spock estimates some mundane thing and is right. If Spock says "I estimate a 97.25% chance we will survive this with no difficulty." and then he turns out to be right, it wouldn't wind up on TV. We have to assume that there are 'ordinary' missions between the exciting ones that make it on the show. Otherwise the entire crew would be insane by the end of the first season. APL (talk) 05:36, 16 July 2009 (UTC)
 * "Red Alert" is supposed to raise them automatically, according to an episode of ENT. So why the captain needs to say so is unfathomable. If you calculate it, the chances of a 10% plan working 10 times in a row are small - but not impossible. If you were enacting daring plans that were fairly likely to succeed - who'd want to watch something that boring? Vimescarrot (talk) 23:14, 15 July 2009 (UTC)
 * In their defence, his problem may have been with working when they should and shouldn't be used - it isn't as simple as casual vs formal. It depends on the emphasis, intonation and even cadence of the sentence. --Tango (talk) 00:23, 16 July 2009 (UTC)
 * The new film made similar mistakes. In the early sequence, everybody on the bridge of whatever ship it was is being blinded by some time travel anomaly thing, which is looming huge and ridiculously bright out the viewscreen. Finally the captain arrives on the bridge and says, "Computer: polarise viewscreen" which causes a sunglasses-style darkening to slowly wipe down over the viewscreen. I almost choked at the idiocy of this and the way it heralded further potential idiocies almost ruined the film for me. Why didn't the viewscreen do that automatically? I wondered. Why does nobody else on the bridge have the authority to order that? Star Trek - especially the original series - is written to be cinematic and entertaining to the seething masses who aren't likely to think too much about it, not to be realistic or sensible. Maelin (Talk | Contribs) 01:18, 16 July 2009 (UTC)
 * Even the captain's order doesn't make sense. The viewscreen isn't some kind of periscope where the same light as is emitted by the object you are looking at gets to your eye - it's a camera and a screen. Polarised lenses block light, that isn't needed when there is a computer inbetween the object and the image. --Tango (talk) 04:42, 16 July 2009 (UTC)
 * No. A polarizing filter reduces reflections from non-metallic surfaces and can increase the contrast of sky views. It is equally useful with the eye or with a camera. Cuddlyable3 (talk) 10:52, 16 July 2009 (UTC)
 * Yes, but I don't think that's what was intended. I haven't actually seen the film yet, but it sounds like it was just meant to darken the image in the same way sunglasses work. --Tango (talk) 12:44, 16 July 2009 (UTC)
 * It's not as bad as Total Recall, though. They have a big red button that has to be pressed to close the shutters and prevent the air being sucked out and taking the people with it. --Tango (talk) 12:44, 16 July 2009 (UTC)
 * Um, why is this at the Science desk anyways. Let's see, for those of you that take this shit WAY to seriously, Dramatic tension and Plot device and Macguffin are good places to start.  The whole point is that Spock makes the situation look worse because he decides there's no way Kirk can work his way out of it.  When Kirk does it's even more amazing.  There's not anything more complicated than that.  Of course, since it is a work of fiction, 100% of the time the ending is predetermined.  --Jayron32. talk . say no to drama  01:11, 16 July 2009 (UTC)

Spock could be making some rough assumptions, and then estimating the odds out to way too many decimal places. (Perhaps to show off his innate Vulcan ability for mental math?) It's like he's doing a Fermi problem and giving the answer to the nearest hundredth of a piano tuner. APL (talk) 05:30, 16 July 2009 (UTC)


 * The best place I know of to discuss this is here: . — DanielLC 04:36, 17 July 2009 (UTC)

What is the danger of using 3-ohm speakers with 4-ohm receiver?
(Cross-posted from Entertainment desk on advice of someone there) My A/V receiver says the minimum speaker impedance it supports is 4 ohms. You have to set it to a special setting for 4-ohm speakers which I have done. But my front left and right speakers say that their impedance is 3 ohms. What is the danger in this? Is the danger to my speakers (which would be okay), or to my receiver (which would not be okay)? Thanks, Mike R (talk) 19:58, 15 July 2009 (UTC)

This discussion (http://www.soundreproduction.com/discussion/loudspeaker/messages/528.html) suggests running 3-ohm speakers on 4-ohm receiver will potentially lead to overheating. ny156uk (talk) 21:11, 15 July 2009 (UTC)


 * There isn’t that big of a difference between 3 and 4 ohms in this situation. You’re unlikely to cause damage to either your receiver or your speakers.  The power that your speakers would need to handle if the volume was cranked all the way up will be a little more than if they were 4 ohm speakers, but that’s unlikely to be a problem as long as the volume is kept at a reasonable level.  Because of the lower speaker impedance, the damping factor is going to be a little lower than the designers intended when they were planning the receiver’s impedance bridging, so the audio quality may be slightly lower than if the speakers were 4 ohms.  But most people wouldn’t hear a noticable difference.  Red Act (talk) 21:20, 15 July 2009 (UTC)


 * It would be difficult to say whether the speakers or the output stage transistors would fail first if you connected 3 ohm speakers to an amp rated at 4 ohms minimum and cranked up the volume, but as a testing engineer, I wish I could be there when the smoke test was performed. Edison (talk) 01:40, 16 July 2009 (UTC)


 * Would you by any chance know the power rating (wattage rating) of your amp, and of your speakers? That would be helpful to help judge which of your amp or your speakers would get smoked first if the volume got cranked too high.


 * Edison’s EE-fu is much stronger than mine (I have a minor in EE and a little professional experience with electronics, but Edison's a fully qualified, experienced pro), but it seems like your amp probably ought to be safe as long as it wasn’t turned up more than about ¾ of the way. If I were in your shoes, though, I would probably limit it to turning it up to no more than half way, though, just to provide an extra margin of safety.  Depending on the power rating of your speakers, it’s possible that they wouldn’t be able to handle the volume turned up even half way (or they might possibly be able to handle the volume turned all the way up), but it sounds like you aren’t as concerned about potential damage to your speakers as to your amp.


 * When I said that you were unlikely to cause any damage to your amp or speakers, I guess I was making the assumption that you like listening to your music at a peaceful, calm level like I do. I never come anywhere close to pushing the limits of my amp or my speakers.  However, rereading your post, there’s actually nothing in your post that precludes the possibility that you’re someone who’s wanting to crank your system as high as you can possibly take it.  Were you hoping to blast some AC/DC at full volume, or were you just wanting to peacefully mellow out to a little Bach?  (The type of music isn’t actually important, of course, just the volume.)  Red Act (talk) 05:01, 16 July 2009 (UTC)


 * Fry's no longer is as well stocked in small parts as they used to be, but it should be no problem to find a small case, a 1 ohm resistor and a couple of connectors (plug/socket) online. Heck, if you don't trust yourself with a soldering iron you can probably even find the wire-wrap no-solder type somewhere.  Tinker, tinker plug-in, problem solved.  71.236.26.74 (talk) 08:48, 16 July 2009 (UTC)


 * Actual loudspeaker impedance is more complicated than just the quoted nominal impedance. The output power of audio amplifiers is usually specified for a simple resistor load even though that is not typical of a loudspeaker. The shape of the curve in the above link suggests that changing from a 4 ohm to a 3 ohm speaker would only cause a slight loss of damping at a few hundred Hz which might give some barely perceptible ringing. (Putting a 1 ohm resistor in series makes this worse not better.) Cuddlyable3 (talk) 11:21, 16 July 2009 (UTC)
 * Besides damping factor, there is the actual power dissipation to consider. Voice coils on loudspeaker can overheat and burn out. If the amp were putting out an average power of 40 watts per channel the 1 ohm resistor would have to dissipate 10 watts when in series with a 3 ohm speaker (ignoring resistance of the resistor versus impedance of the speaker). A 1 watt resistor would burn out after a while. Avoid injury or property damage which might result from smoking the resistor. Speaker cones can also tear, which the OP did not indicate was a big worry. Edison (talk) 19:12, 16 July 2009 (UTC)