Wikipedia:Reference desk/Science

July 4

Identify this lizard

We saw this lizard in Galveston, TX. It is approximately 3 to 4 inches in length, and we've seen it several times at night. Does anyone know what it is?

anonymous6494 02:10, 4 July 2007 (UTC)

Mediterranean House Gecko, Hemidactylus turcicus [1] [2]? --mglg_(talk) 02:33, 4 July 2007 (UTC)

I think it looks like a Tropical house gecko, though the one in the article is a bit different. [3] [4]A.Z. 20:57, 9 July 2007 (UTC)

dealcoholize alcohol?

I love the tastes of certain beers, but I don't want to get drunk. (I'm extremely easy drunk.) Is there something I can do to the alcohol to keep the original flavour and fizziness but remove all or some of the alcoholic content?--Sonjaaa 03:49, 4 July 2007 (UTC)

Try near beer 161.222.160.8 04:39, 4 July 2007 (UTC)

I feel really terrible for suggesting this, but if you insist on drinking beer for the flavor, it might be better to try to get your tolerance up. Sadly, the near beer article doesn't say how dealcoholization is done, but judging from the terribly reception that near beers get, it cannot possibly be good for the flavor! See Effects of alcohol on the body, Ethanol#Metabolism and toxicology and Hangover for more information that you could possibly need. My personal recommendation is to drink slower, and alternate a glass of water between each glass of beer. Eat something, too! Finally, check the label! Great beers are not necessarily high in alcohol! --Mdwyer 04:51, 4 July 2007 (UTC)

Easy drunk = cheap date. Yah, per what Mdwyer said, drink a lot and soon your liver will be like a chunk of concrete, and you will have a huge tolerance for alcohol, and you will literally be able to drink your peers under the table. However, this does not bode well for your longevity. Edison 05:22, 4 July 2007 (UTC)

Huh? Drinking low-alcohol beers and drinking slower are bad for your liver? Sorry, Edison, you're not living up to your name here. For centuries, Europeans have drunk beer in stead of plain water because it was less disease-ridden. But it was also extremely light beer. I don't know if such beer is still made. Also, judging by Sonjaaa's post, she's never going to be able to drink others under the table. Some people have a lower tolerance for beer than others. I wonder if that also affects how much damage the same alcohol-consumption will do to the liver (if any). DirkvdM 10:00, 4 July 2007 (UTC)

I thought I read somewhere before that in medieval times the "beer" that they have are a lot stronger than what we have nowadays... --antilived^{T | C | G} 22:56, 4 July 2007 (UTC)

See Small beer. Also, unless Edison has edited his comments since you replied Dirk, you seem to have drawn the opposite conclusion to that which his words suggest to me :-) Skittle 14:54, 5 July 2007 (UTC)

Getting back to the original question, it's an interesting problem in physical chemistry. Distillation and freeze distillation/fractional freezing come to mind immediately, but distillation is no good because the CO₂ would come out of solution before you could boil off a significant amount of ethanol (leaving you with flat beer), and freeze distillation is no good because most of the flavor compounds would remain in the alcohol-rich liquid portion and the solid would be almost pure water ice.

There seem to be two major commercial methods of adjusting the alcohol level of wine (which should be applicable to other alcoholic beverages as well). Both methods involve first separating the color and flavor components ("retentate" or "essence"), then decreasing the alcohol level of the remaining alcohol-water fraction, then re-adding the flavor components. Vinovation's method involves reverse osmosis, and ConeTech's method uses some complicated apparatus to achieve something similar to steam distillation (please correct me if that's wrong).

Anyhow, those are both large-scale industrial process that would be difficult to recreate in your kitchen, so if you like the taste of a certain beer, you'll have to either live with the alcohol content, or hope they produce a light version. —Keenan Pepper 02:43, 5 July 2007 (UTC)

Need to identify soundfile

- I need to identify which of the four goldfinch articles this belongs to. Original clip came form here. Borisblue 05:22, 4 July 2007 (UTC)

Planet of the Apes

I was watching the old Planet of the Apes, specifically the second one Beneath the Planet of the Apes and in the movie the doomsday device is an atomic bomb with a cobalt casing. How does the cobalt casing affect the efficency of the bomb?68.120.85.164 05:33, 4 July 2007 (UTC)

See cobalt bomb for a full explanation, but the idea is that the cobalt casing would be turned into the extremely nasty isotope cobalt-60, which would be spread as fallout, and remain lethal for a couple of decades. --Bob Mellish 07:13, 4 July 2007 (UTC)

Thank you.67.121.105.12 02:02, 5 July 2007 (UTC)

Humming Bee?

I saw the strangest animal the other day. It looked like a cross between a bee and a humming bird. It was about an inch long (2.5cm) had a brown body, and a small fan tail, like a bird. It's wings looked slightly like bird's but were moving so quick it was hard to tell. It also had a long 'beak' which it was using to suck stuff out of flowers, and two 'antennae' on top of it's head, also long and thin like the 'beak'. It hovered while sucking, moved about quickly, and was the only thing of it's kind, in a patch of flowers with many bees. This was in central Europe. Any ideas what sort of creature this was, I am clueless? Cyta 08:07, 4 July 2007 (UTC)

Take a look at Sphingidae. --Mdwyer 08:55, 4 July 2007 (UTC)

Thanks a lot, that's definitely the one. What a crazy animal! Cyta 09:11, 4 July 2007 (UTC)

The article doesn't say where they live, but a friend in the Netherlands spotted one in his garden. Nor did the article mention that this is a nice example of convergent evolution, so I added that. DirkvdM 09:50, 4 July 2007 (UTC)

Your description was spot on for http://en.wikipedia.org/wiki/Image:Bee_hawk_moth_newspaper.jpg . They look pretty interesting. Lanfear's Bane

Here in south eastern ontario, canada the larval forms/caterpillars are called "hornworms". They use thier large size, colour patterns and the biotoxins from the very specific plants that they eat to ward off would be predators. Sadly, most people who love to see the adult kill the larval forms! OOPS, forgot to sign. I'm a newbie, mea culpa. Rana sylvatica.

The article on Macroglossum stellatarum mentions their distribution. What it doesn't mention is that these critters are on the increase now in places such as southern England and the Netherlands. People are blaming global warming.--Shantavira|^{feed me} 13:27, 4 July 2007 (UTC)

Earth Natural Satellites

Completely by chance I came across the article 6R10DB9. It says that further study will be avaliable around 14 June 2007. As i'm sure you're all aware this date has passed. Do we have any more information about this object? Can we expand the article? 213.48.15.234 11:10, 4 July 2007 (UTC)

The article has a link to the Great Shefford Observatory's page about this object, which includes an update from 16th June. I feel sure that this could be used to expand the article, however lack the aastronimical knowledge to do this myself. DuncanHill 11:20, 4 July 2007 (UTC)

I've tagged it with an {{update}} request.--Shantavira|^{feed me} 13:22, 4 July 2007 (UTC)

Great, i'm new to all this :) 213.48.15.234 13:29, 4 July 2007 (UTC)

Jar lid motion on counter top

Hi - My wife has challenged me to see if there is a formal name of the oscillation/rotation motion that a jar lid makes when dropped onto a counter top. Any suggestions? ````Cavermedic

No. There isn't. For more information on this phenomenon see Euler's disk. 213.48.15.234 12:22, 4 July 2007 (UTC)

Scrap that, a manufacturer of the disk [5] uses the verb "spoll" as a portmanteau of spin and roll. I can't find it in any dictionary though. I don't think it's a real word. 213.48.15.234 12:30, 4 July 2007 (UTC)

I would go with Precession. The lid is acting kinda like a gyroscope. SteveBaker 16:16, 4 July 2007 (UTC)

Hmm, I'm not sure. The contact point of the disc isnt fixed, it's rolling/slipping. 80.229.228.229 18:45, 4 July 2007 (UTC)

Well, yes - that's why I said kinda' like a gyro, however, precession is still the right word. SteveBaker 22:08, 4 July 2007 (UTC)

I don't believe that the motion is the same, though. If you watch it, The disc is hardly spinning. You always get that funny bit at the end where the coin doesnt look like it's vibrating at all, it's just hovering and turning slowly. I think this (and the similar movement before that when you can see the oscillation) is what they refer to as "spolling" and is what the OP is looking for. It's certainly a very interesting phenomenon. 213.48.15.234 06:41, 5 July 2007 (UTC)

I googled 'spolling' and I only see a handful of relevent hits (most are typo's for spelling or spooling) - all but one of them come from www.eulersdisk.com and that one comes from a patent filed by that same company. I don't find the word in any of the four dictionaries I have at hand right now. So, no - spolling is a neologism at best - most likely it's a word that one guy made up that hasn't been taken up by the worlds of physics and mathematics. The rate of wobble of the axis of rotation is not equal to the rate of rotation around that axis - that's what precession is - and that's what the lid is doing. What's happening with the lid is certainly interesting though. SteveBaker 14:43, 5 July 2007 (UTC)

I'm aware that it's a made up word :). The precession that's happenning with the lid is certainly happening at a very different rate to what I would normally consider to be precession. The resultant motion is quite different. Capuchin 06:46, 6 July 2007 (UTC)

I'm unaware of any definition of the word 'precession' that specifies any limits on the rate of the motion. SteveBaker 13:49, 6 July 2007 (UTC)

efficiency?

hey friends ..

can anyone help me regarding increasing the efficiency of an ic (2-stroke) engine by temperature variations.

Sameerdubey.sbp

Have you looked at heat engine or carnot cycle ? Nimur 16:43, 4 July 2007 (UTC)

i have read that article ,it is clearly stating that increasing temperature of source(inlet/atmospheric air in case of 2-stroke engine) or decreasing the temperature of sink(exhaust gas in case of 2-stroke engine) would increase the efficiency.so ..a freak but why dont we increase the temperature of inlet gases using some heaters or decrease the temperature of exhaust gases by some coolers.please comment that why?/why dont? we use those procedures. Sameerdubey.sbp

In short form, because you can't get that energy for free. Where does the heat energy come from? Another engine. Does that engine use less energy than the energy saved on the initial engine? No. Entropy increases. — Lomn 13:24, 5 July 2007 (UTC)

I disagree. Firstly, I'm surprised that heating the inlet would help - it certainly doesn't on a 4-stroke engine. In fact, most cars run significantly more efficiently in cooler air because there is more oxygen present and that allows a more efficient fuel burn and less energy goes into driving the coolant around and providing energy to the radiator fan. I've actually dyno'ed my MINI Cooper S and found that I get about 10% more horsepower in winter than in summer (that's in Texas). Note also that we do in fact employ special 'engines' to compress (and thereby heat) the air on the way into car engines - we call them 'Turbochargers' and 'Superchargers'. In fact, they heat the air up so much that some cars use a secondary radiator called an Intercooler to try to drop the temperature back to ambient again before the air gets into the cylinders. The Turbo is powered by the waste energy in the exhaust gasses (the fact that they are emitted at higher than ambient pressure means that the exhaust gas can spin a little turbine to power the pump that pushes the extra air in. The Supercharger is powered from a belt taking power directly from the engine - the supercharger produces more extra efficiency than it consumes - so this is a worthwhile thing to do. So clearly you can do something to help without invoking Entropy and saying "it's impossible" - millions of cars out on the roads today prove conclusively that this is true! SteveBaker 14:31, 5 July 2007 (UTC)

You're correct; I was looking at the question in terms of "why don't we go above and beyond present engine technology", assuming that turbos, etc, were assumed as integral where appropriate. Heat engines are more or less as efficient as they're going to get from a conceptual standpoint, and hooking up an air conditioner to cool the exhaust is a net loss. — Lomn 15:34, 5 July 2007 (UTC)

Well, if cooling the exhaust helped (and I honestly don't see how it could!) you could simply provide a big expansion chamber somewhere shortly after the engine - the exhaust gas is under pressure - so letting it expand out into a big chamber would certainly cool it down - and at zero energy cost. But aside from the issue of back-pressure (which is actually somewhat advantageous in some cases), once the exhaust is outside of the engine block, who cares what temperature it's at?! SteveBaker 19:29, 5 July 2007 (UTC)

SteveBaker, the idea of the heat engine is that the action of cooling has the ability to perform work. You could "waste" that work by allowing the gas to cool adiabatically, as you mention. If a hypothetical method to use the remaining heat existed, that energy could be used by the engine (powering the drive shaft, or something). That is why cooling the output would make the "theoretical" engine more efficient. In a practical scheme, I don't know that it's so trivial to harness excess energy outside the combustion chamber just by refrigerating the exhaust gas. On the other hand, a more efficient engine would inherently yield cooler exhaust gases. Nimur 04:35, 6 July 2007 (UTC)

Yeah - I agree entirely - if you can capture some of the heat from the exhaust (and thereby cool it) but use that heat to do more work - then for sure, it's a win/win situation. But forcably cooling it with refrigeration is nuts! The idea that a heat engine that happens to have a cooler exhaust is more efficient than one with a hotter exhaust is also true - but we're turning that around and saying that cooling the exhaust of a hot-exhaust heat engine makes it more efficient - and that's just nuts! FWIW, BMW have been playing with using the exhaust heat to do some work - they've demonstrated a small steam engine (powered by engine exhaust heat) that would have enough power to run the cars' A/C and recharge the battery - thereby relieving the main engine of that work and resulting in a more efficient car overall. Since the exhaust gasses will have been routed through those pipes which are full of cold water, the exhaust gasses are indeed cooled by doing this. But that's not refrigeration. As I also mentioned earlier, lots of cars have Turbochargers that extract power from the exhaust gasses in order to get more engine efficiency. So this is a well-understood phenomena. SteveBaker 13:46, 6 July 2007 (UTC)

hymen

Can the hymen of a girl ruptutred, if her vigina is contacted(not penetrated) by a finger strongly even if she wears a trouser or under pant.

I don't think you know what vagina means. But, yes, hymens are damaged quite frequently by things other than penetration. Friday (talk) 17:29, 4 July 2007 (UTC)

Horse riding was frequently blamed in less enlightened days. Corvus cornix 23:34, 4 July 2007 (UTC)

Or maybe the secret lover's name was "Horst" and she didn't enunciate. Edison 14:41, 5 July 2007 (UTC)

You should see Hymen#What might damage the hymen. — Laura Scudder ☎ 14:44, 5 July 2007 (UTC)

vagina

who can tell me the size of the viginal opening?

We can. Welcome to Wikipedia. You can easily look up this topic yourself. Please see vagina. For future questions, try using the search box at the top left of the screen. It's much quicker, and you will probably find a clearer answer. If you still don't understand, add a further question below by clicking the "edit" button to the right of your question title. .

Determining the proper pump for a water fountain.

I have a question regarding matching the right pump for a specific purpose. I have a water pump that is 40gpm and it has 1 1/2" intake and outlet. The pump will be set below the water level by 24". I will divide the outlet into 3 seperate lines that will push water up. I have a trough that contains 11 inches of water included in the overall height to push the water. The goal is to have the water bubble above the surface of the water in this trough bu no more than 12". Do I have the right pump and how do I accomplish the task. This is also in the exterior environment.

Accuracy of Weather Forecasting

This is a rather difficult question, and although I think I read something on it several years back, I have been unable to find any statistics.

The question, in its simplest form, is something like this: as a function of time (edit: where time is defined as the time between the forecast and the event), how accurate are the modern weather forecasting computer models?

The problem is how we define accuracy, and although I have a few ideas, none of them are perfect. Can anyone find me information on this subject? Any kind of relevant statistic will be very helpful.

Thanks a lot. 69.255.38.193 19:21, 4 July 2007 (UTC)

One example I know of where long systematic studies have been done is in the accuracy of hurricane landfall locations. This image is a good summary. Dragons flight 21:32, 4 July 2007 (UTC)

http://www.forecastadvisor.com will show you the accuracy of a range of different weather services for a particular US zipcode - and also how one particular weather forecast has changed over the five days prior to the actual day of the forecast. You can use this to see how the prediction homed in on the final value. There is a scientific-looking study of forecasting accuracy here http://www.customweather.com/accuracy/2003study.html. Here is another www.omninerd.com/2007/02/08/articles/69. Our article on the WxChallenge explains the criteria that are used for judging weather forecasting competitions. SteveBaker 22:05, 4 July 2007 (UTC)

How could I engineer weather inside my house?

I wish to satisfy my God complex. Vitriol 22:39, 4 July 2007 (UTC)

Central heating and air conditioning should take care of the temperature. Fans will provide wind. To obtain rainfall, you will have to increase humidity dramatically, consider a paraffin heater (they produce a remarkable amount of water vapour). DuncanHill 22:44, 4 July 2007 (UTC)

Or consult our article on humidifiers. Root⁴(one) 22:57, 4 July 2007 (UTC)

If you built your "house" large enough, like the size of a gigantic aircraft hanger. You can have precipitation occurring inside your "house". Especially if you use technological devices to change the humidity and temperature inside your "house". 202.168.50.40 04:44, 5 July 2007 (UTC)

Would God need to ask? :) DirkvdM 06:33, 5 July 2007 (UTC)

One of the crucial aspects of weather is convection between air masses. You will want to make sure that you have a source of hot air and a source of cold air, and allow them to swirl around and such. If you have sufficient temperature differences, you can induce condensation (imagine leaving a bathtub full of hot water near the open freezer - as the warm moist air rises and hits the cold freezer air, it will form a steam cloud and will almost certainly drop some precipitate water). If you're lucky, the rapid condensation may even make some ice crystals and you can call it snow. Using a fan will move air, but it won't be "wind" (at least not to my satisfaction). Wind is the natural flow of air masses as a result of pressure differences. You'll get a more realistic wind effect with the bathtub-freezer mash-up. In summary, you should seek to provide sources and sinks for pressure, humidity, and heat, and the natural air motion will take care of the rest. You might want to read about Biosphere 2; their engineered indoor weather was quite expensive. Nimur 07:16, 5 July 2007 (UTC)

The Vehicle Assembly Building may have its own internal weather system, with reports of clouds forming inside the building on humid days. Gandalf61 10:17, 5 July 2007 (UTC)

I heard that happened in some of the larger sports arenas too. SteveBaker 14:20, 5 July 2007 (UTC)

Some original research - if you go to an indoor pool with warm water and cold weather outside, opening the doors to the outside will cause a cloud, and eventually precipitation, to form. It's actually quite remarkable -- Sturgeonman 23:54, 8 July 2007 (UTC)

Map of the North and South Magnetic Hemispheres

Magnetic declination is more relevant than the "magnetic hemisphere" for most purposes, so it is easier to find such a map.

Campasses are made for both the North and the South Hemispheres. Where can I find a map of the dividing line between the two magnetic hemispheres? Ugly bag of mostly water 23:26, 4 July 2007 (UTC)

Compasses always point to Magnetic North, in both hemispheres. If you're talking about compass balancing, that's not essential because you can always compensate for the inclination of the magnetic field by tilting the plane of the compass away from horizontal. There's definitely no such thing as a "dividing line" such that you need one specific kind of compass to the north and a different kind to the south. Compasses work anywhere on Earth. —Keenan Pepper 01:57, 5 July 2007 (UTC)

Not if you're on the actual magentic poles themselves... :p --antilived^{T | C | G} 02:14, 5 July 2007 (UTC)

Sure they do! You just notice that the needle is trying to tilt away from horizontal, so you tilt the plane of the compass until the needle becomes perfectly vertical. Then you know you're at the magnetic pole. The magnetic field isn't zero at the poles; it just points straight up or down. —Keenan Pepper 02:45, 5 July 2007 (UTC)

Compass#Compass balancing describes geographic "zones" - compasses are calibrated for the strength of the vertical component of the magnetic field, not the direction of the horizontal component. The compass always points towards magnetic north/south. As far as the dividing line between the "hemispheres", I don't believe there is much use for such a distinction. You could draw a great circle centered at either pole and set its equator. Finally, you may be interested in a map of magnetic declination, which I have added to this section. Nimur 03:04, 5 July 2007 (UTC)

While agreeing with both Keenan Pepper and Nimur that there is not much use for it in terms of compasses, the line that separates north from south is the line of zero inclination (not declination, although declination is much more important for actual navigation). An inclination similar to the one already posted for declination exists: [6] and shows that the line of zero inclination is a wavy line grossly sub-parallel to (but by no means coincident with) the geographic equator. Cheers Geologyguy 04:12, 5 July 2007 (UTC)

Thanks. Zero degrees inclination serves my purpose well. Thanks. Ugly bag of mostly water 10:39, 11 July 2007 (UTC)

vitamin B12 and vivid dreams

I've had extremely vivid and surreal dreams the past few days, and I think it's because I've been taking 1.5 mg of vitamin B12 (orally) as a dietary supplement before sleeping. I've found some anectodal evidence and new age-y stuff on the internet that seem to confirm my suspicions, but I've found no actual medical information. Have there been any scientific studies dealing with this phenemonon? --Krsont 23:46, 4 July 2007 (UTC)

I don't know of scientific studies, but it is widely accepted that B12 can increase vividness/lucidity in the Lucid Dreaming community. As well as a few other things like Nicotine patches. You might be interested in reading people's experiences on ld4all.com, and if you ask around there you might also find some studies on the matter --_ʇuǝɯɯoɔɐqǝɟ 00:08, 5 July 2007 (UTC)

Interesting... I've had a few lucid dreams in the past, but they didn't last very long. Maybe I should take the chance to experiment further with lucidity :) --Krsont 00:35, 5 July 2007 (UTC)

I highly recommend it. I really enjoyed doing it. I stopped doing when I started getting depressed, since those dreams were very lame anyway, and I'd rather just relax when I go to sleep than MILD myself --_ʇuǝɯɯoɔɐqǝɟ 01:27, 5 July 2007 (UTC)

Vitamin B12 is usually considered safe with very few side effects. A quick search in PUBMED (Database for published medical literatures) did not reveal any such association. Consult your doctor and see if you can take tablets in the daytime.--Countincr ^{( T@lk )} 00:31, 5 July 2007 (UTC)

Why would I want to take them in the daytime? I guess I wasn't clear: I like the dreams, I just want to know more about it ;) --Krsont 00:35, 5 July 2007 (UTC)

July 5

SpaceShipOne Orbit Style

Could Rutan's method of lifiting spacecraft then launching them into space be used to achieve orbit? Does his engines, if scaled up, a bit meet the requirement for reaching orbit or would diffrent kind of engines be needed?67.121.105.12 02:04, 5 July 2007 (UTC)

No physical law precludes that approach. It has yet to be seen whether the engineering and financial challenges can be feasibly and safely overcome. Among the major challenges are control and stability, and carrying enough fuel. Nimur 03:06, 5 July 2007 (UTC)

The idea has been floated a number of times, both in science fiction and real life. Using an airplace in lieu of a first stage makes reusing the first stage quick and easy (in principle) and it means that your rocket will start out with significant speed and altitude, as well as above much of the atmosphere and weather. (The idea of using a balloon to get above a lot of the atmosphere has also been proposed; it was even used for suborbital sounding rockets in the 1950s: see rockoon.)

This page has a list of air-launched rocket craft (proposed and flown). The Soviet Union developed and tested an air-launched spaceplane (called MAKS), but the program ended with the Cold War, and it never reached orbit: [7]. TenOfAllTrades(talk) 13:23, 5 July 2007 (UTC)

Some of the X-planes were launched that way - and many of them reached "the edge of space", so SpaceShip One was hardly the first. Rutan certainly claims to be able to reach orbit with a similar approach to his first effort - and he's a pretty smart guy, so I'm inclined to believe him. My best guess is that his approach to re-entry is his biggest problem. SpaceShip One only just got out of the atmosphere - so that on re-entry it was moving rather slowly and managed to cope without needing fancy heat tiles or ablative coatings. When you re-enter from orbit, you've been falling for a long time without air resistance by the time you hit atmosphere - so your speed is much greater and slowing down becomes a major problem. SteveBaker 14:16, 5 July 2007 (UTC)

The Pegasus rocket from Orbital Sciences is a commercial satellite launch system that is launched from a modified commercial airliner. They have launched quite a few satellites. -Arch dude 02:53, 6 July 2007 (UTC)

Wow! Interesting! They do say though that the primary reason for the air launch has nothing to do with getting the thing up high and going fast at the point of the launch - they do it to save on the cost of ground-based launch failities and to avoid launch delays due to bad weather. That's a fascinating thing! Thanks for the link. SteveBaker 20:23, 7 July 2007 (UTC)

ultrasound???

hey friends is anyone having idea about the ultrasound machine: 1.consumption according to a particular frequency generation. 2.minimal space requirement for specifc 20,000hz machine.

please help in urgent need

Sameerdubey.sbp

SameerDubey, with all due respect, I can't tell what you are asking. You might be interested to know that 20 kHz is probably not ultrasound, since it is approximately in the range of human hearing (on the high end, so it may be barely out of audible range for many people). A machine would consume energy (probably electrical energy), and would most likely be an ultrasonic transducer. Nimur 06:50, 5 July 2007 (UTC)

Agreed - Ultrasound is more often in the MegaHertz (MHz) to GigaHertz (GHz) range - but unless we know what it's for - we can't answer either question. It's not just about the frequency - the power required and the way it's going to be used and the way that results are collected and displayed at much more relevent! The ultrasound units used for checking the health of unborn babies are totally different from the units used to detect cracks in welded steel which in turn are completely different from the ultrasonic cleaning bath I have at home for cleaning gunk off of old car parts. SteveBaker 14:06, 5 July 2007 (UTC)

Even ~30 or 50 kHz is usually called ultrasonic, but 20 kHz is probably not. Nimur 17:31, 5 July 2007 (UTC)

Hmmm - well I wouldn't have said so - but our article on Ultrasound says 20kHz. Weird. SteveBaker 19:12, 5 July 2007 (UTC)

Short of an ANSI or ISO standard, there's not going to be a well-defined border for the nomenclature. But if professional audio is anything to gauge, it is extremely common to have 44.1 kHz and 48.0 kHz recordings - which would indicate a folding frequency at 22.05 and 24 kHz, respectively. That, to me, suggests that there must be some audibly discernible signals at those frequencies. I worked with a SONAR system for a while that operated at 34 and 70 kHz, and it was most certainly ultrasonic; but it also produced some unwanted harmonics (undertones?) that could be heard as mild, faint buzzing. (The system was operating at 100+ dB in the ultrasonic range...) Nimur 21:15, 5 July 2007 (UTC)

Satisfaction of Swallowing

Why is it that we must swallow food to enjoy it? I tried "eating" ice cream by savoring the food, then spitting it out and chasing it with a spoonful of rice. My stomach picked up on the bait-and-switch and I was not satisfied. Why does swallowing the food complete the satisfaction effect? If this weren't the case, it would be much simpler for people to not gain wait brought on by heavy foods. HYENASTE 05:03, 5 July 2007 (UTC)

Evolutionarily, we want to swallow food because only then can we begin the digestion process to extract nutrients and fat from it. It's only in the modern world that we eat so much high fat foods that we want to lose weight, our body systems havent caught up with the modern world. We get very little nutrients from food we don't swallow. 213.48.15.234 06:46, 5 July 2007 (UTC)

It is our stomach that tells us when we are satisfied. Check out the articles on hunger and appetite.--Shantavira|^{feed me} 10:38, 5 July 2007 (UTC)

Yes, but the OP asked why they couldn't spit out ice cream and substitute rice. This should satisfy the stomach, while the ice cream satisfies the tongue. The Question is "why didn't this work?" I would say that most likely, the ice cream contains something which your body craves that the rice does not. For instance, plain rice is low in fat. I would suggest that you try eating just a little bit of ice cream maybe a couple of spoons to fool the stomach then starting the bait and switch with the rice. Let us know how it works for you. - Czmtzc 15:02, 5 July 2007 (UTC)

I guess the problem is that enjoying the taste of something - and having your hunger satisfied are two completely independent sensations. What we want from food is a combination of both things. It's possible to taste ice cream without swallowing it (well, technically: "you can if your willpower is a lot stronger than mine"!) - but I think it would be hard to swallow enough rice without tasting it along the way. So I think the reason you aren't happy with the experiment in an overall way was not that the rice didn't satisfy your hunger - but that it was boring to eat and even the occasional mouthful of ice cream didn't help that. It's a hard experiment to do well because the only reasonable way to get the bland food into your stomach is going to involve tasting bland food. I wonder about chewing gum though...hmmm. I admire your efforts to employ good scientific methodology though - everyone should do more to experiment with the things around them! SteveBaker 15:16, 5 July 2007 (UTC)

Food For The Homeless and $1,000,000

I have been discussing a question with a friend of mine for quite some time (~1 month). I have my ideas, he has his; I wanted to see what the Wikipedia Refernce Desk community could come up with. This is in no way a ultra-precise or "nit-picky" question.

Let us imagine that you have $1,000,000 cash.

You want to feed the maximum number of American homeless people possible using this money.

What should you buy? White Rice? Cans of Meat and Beans? "For Maximum Value"-Brand Cheerios?

What is the healthiest, but cost effective (read: dirt cheap) food to buy?

About how much of it would you be able to purchase? How many people would it feed?

The costs of delivery to the homeless people is not a factor - they must come TO your food stockpile to recieve the food.

--67.177.170.96 05:40, 5 July 2007 (UTC)

Just to add onto the question above, would it be more effective to buy land and seed and fertilizer and to grow the food? 213.48.15.234 06:48, 5 July 2007 (UTC)

One million dollars isn't really a lot of money. But first, you should evaluate some philosophical choices - is it better to feed a small amount of people for a small number of meals ( ... buying a full lunch for a million people), or to feed a few people many times (buy a year's supply of food for 500 people)? What level of cost-nutrition tradeoff are you willing to accept?

In any case, it may be easier to imagine the cost-per-meal. If you are an effective negotiator, you can probably buy bulk ingredients at cost. How "raw" you go will determine how much preparation and labor you need to turn it into a meal. But if you could get the ingredients down to ~$1 per meal, (say, a peanut butter sandwich on two pieces of bread; a carrot, and a glass of juice), you could feed 1,000,000 people one small meal. It is not even clear that there are this many homeless people near enough to walk to your sandwich depot, but census numbers vary wildly for that demographic (these statistics indicate that 13 million Americans (7.4%!) self-identify as having been homeless at some time, while conservative estimates place the number much much lower).

But this leaves you with a nasty predicament. This hypothetical solution has fed a million people one meager sandwich, and now they are off again on their own. The contribution to their health is debatable; only a very minuscule percentage would have starved if not for your sandwich contribution. Those who would have starved may not be much better off anyway, because you have only given them one meal (enough food to last another few hours?)

It would make significantly more sense for you to prioritize how hungry people have to be, and give them aid based on that level. But that will require a bureaucracy, a lot more labor on your part, and you may have to make a few gut-wrenching decisions between who gets to eat and who may not. Nimur 07:02, 5 July 2007 (UTC)

You could invest the million dollars, reinvest enough of the profits to keep up with inflation, and spend the rest of the profits on food. This way you would have a steady inflow of money. —Bkell (talk) 07:11, 5 July 2007 (UTC)

Surely what the homeless need is housing. Anyway, the best investment would be to buy lots of fishing rods and teach them to fend for themselves.--Shantavira|^{feed me} 07:43, 5 July 2007 (UTC)

The problem is much more complicated. Firstly, you need to think about transportation. There is very often excess food produced in the more fortunate parts of the world that could be had for $0 (I was listening just this morning to an NPR report that European grape growers are being paid to destroy part of their crop because of the effect that over-production is having on price) - but getting those excesses into the right place is a big issue - perhaps your best use of that $1,000,000 is to pay for transportation instead? Secondly, over what time-period are we talking? If you take the $1,000,000 and invest it wisely, you'll get a 5% or so return on it - which means that you have $50,000 per year FOREVER. After 20 years, you'll have helped the same number of people as with $1,000,000 spent all in one lump today - but after 100 years, you'll have done much more good. Invest the money as micro-finance loans to people in the area and you'll be doing good while you are making that money. Thirdly, simply giving people food doesn't solve anything over the long term. If you give them food, they might stop farming and live on the food you provide - that means that when you run out of your $1,000,000 - they may be worse off than when you started. It would be better to invest that money in improving their food production infrastructure than to provide direct food aid. (Although, clearly there are emergency situations where immediate short term food aid is both necessary and beneficial). In the end, to take the ultimate 'long view', the problem is that much of Africa's climate and soil conditions simply doesn't allow it to produce enough food for all of the people who live there - the solution is to have less people. There is merit in providing funding for long term population control. To answer your actual question - the answer is Rice. SteveBaker 14:01, 5 July 2007 (UTC)

Not to mention those pesky civil wars that keep blowing up all the infrastructure that endemic corruption even allow to be built in the first place. As for the OP - white rice is less nutritious than the whole stuff, but SteveBaker I believe is correct in suggesting rice as *the* answer for a single staple to feed the masses, although I seem to recall that bananas put in a pretty good showing if you do not have to worry about spoilage. Consider the rolling population explosion across southeast Asia as rice cultivation spread, and then factor in all the breeding and other genetic modifications (e.g. golden rice) that have happened since. As for pricing your solution, a lot depends on how much volunteer labor you can mobilize to cook for you, as processing adds to food costs. -Eldereft 07:48, 7 July 2007 (UTC)

Re:Protons, Electrons, Neutrons and such

What produces these charges? Does heat produce electron? If it does, then what does cold produce? How do you know if something is positively charged (protons) or negatively charged (electrons)? And secondly, does lightning come from the ground? Finally, if a car produces a large number of electrons, and the road produces an equal number of static charge, will the car be pushed away from the road? -Zacharycrimsonwolf 13:05, 5 July 2007 (UTC)

Lightning travels most commonly from cloud to cloud, however what most people think of when you refer to lightning is from cloud to ground. The article does indicate that lightning can also travel from ground to cloud . Lanfear's Bane

Okay. Thanks for that! Cheers!!! -Zacharycrimsonwolf 13:28, 5 July 2007 (UTC)

We don't really know what creates charges, they are just a quantum number, an intrinsic property of particles, which determines how strongly they interact with photons, i.e. the electromagnetic field. I'm not sure what you mean does heat produce electrons? Heat in itself doesn't no, but the energy from heat can ionise atoms, that is remove a negative electron, leaving a positive ion. Cold is simply an absence of heat energy, not an opposite so produces nothing. Positive/negative charges can be deduced from the direction of curvature during motion in a magnetic field, or the direction of force in an electric field. Which is positive and which negative is simply a matter of convention, we could equally well swap the names round. The important point is they are opposite charges. Lightning has been covered above. The car question has me confused again! Maybe the simplest thing to say is that electrons are not really produced, simply moved around. If the car gains eletrons from the road somehow (static electricity in effect) it will leave behind a positive road and be attracted to it, not repelled. Charge is conserved, basically moved around not created. Cyta 13:32, 5 July 2007 (UTC)

Electrostatics may also be helpful to you. DuncanHill 13:33, 5 July 2007 (UTC)

Let's break this up for more manageable answering:

• What produces these charges?

The charge on these fundamental particles is just an innate property of the particle - nothing 'produces' it - it's just a property - like their mass. SteveBaker 13:43, 5 July 2007 (UTC)

• Does heat produce electron? If it does, then what does cold produce?

Heat is just the measure of how fast (on average) the molecules are moving/vibrating. Heating some substances may cause them to emit electrons - see Thermionic emission. SteveBaker 13:43, 5 July 2007 (UTC)

To clarify, heating something can cause it to release electrons as opposed to creating electrons. — Laura Scudder ☎ 14:51, 5 July 2007 (UTC)

• How do you know if something is positively charged (protons) or negatively charged (electrons)?

You bring something whose charge you know to be (say) positive close to the unknown thing and see if it is attracted or repelled by it. Like charges repel, unlike charges attract. SteveBaker 13:43, 5 July 2007 (UTC)

The mathematical and moral definitions of the terms positive and negative don't apply to positive and negative charge, they're just arbitrary polar descriptions of a property. -- JSBillings 14:21, 5 July 2007 (UTC)

That's true - but we needed a pair of names with opposite meanings! Physics is full of arbitary names for things - that's how we ended up with Strangeness, Charm, Bottomness and Topness. One certainly cannot garner extra meaning from the names chosen. So you can tell whether two electrical charges have the same sign by whether they attract or repel each other - but is you don't have a 'known-to-be-negative' or 'known-to-be-positive' object handy then there is no 'absolute' way to tell (that I'm aware of). SteveBaker 14:52, 5 July 2007 (UTC)

You could look at how the charged object interacts with other EM things...throw it through a magnetic field of known direction and see which way it curves or throw it past a compass and see which way the compass points. But still, need some known starting point. DMacks 17:03, 5 July 2007 (UTC)

Or apply a magnetic field to a conductor through which current is flowing and measure curvature via the Hall effect. -Eldereft 08:04, 7 July 2007 (UTC)

Right - there are plenty of ways to determine this - but (I believe) that all of them depend on you having something with known polarity (either a positive or negative charge/potential-difference or a current whose direction of flow you know or a magnet for which you know which end is north and which is south). Since we know the polarity of the earth's magnetic field, then a compass needle is one way to get that with certainty. But how would you tell if you didn't have anything like that? SteveBaker 14:18, 7 July 2007 (UTC)

How about ionzing some helium or hydrogen and sending it past a magnet or unknown orientation: positive ions curve one way, negative ones the other. Nuclei are much heavier than electrons for the same amount of charge, so will curve much less, so looking at the curvature tells you the mass (and therefore identity) of that particle. Look at the direction of that particle stream's deflection, now you know the orientation of the magnet. Build yourself a bubble chamber. DMacks 18:48, 10 July 2007 (UTC)

• And secondly, does lightning come from the ground?

See Lightning#Leader_formation - it's rather complicated. SteveBaker 13:43, 5 July 2007 (UTC)

• Finally, if a car produces a large number of electrons, and the road produces an equal number of static charge, will the car be pushed away from the road?

Well, if a static charge were being built up on the car by virtue of the tyres rubbing on the road, you'd maybe get electrons building up on the car - and left-over protons on the road (or vice-versa) - this would result in the car being attracted towards the road - not pushed away from it. However, the force would be very tiny indeed and in any case, I'm pretty sure that the static charge that builds up on cars comes from friction with the air - not the road. SteveBaker 13:43, 5 July 2007 (UTC)

Many thanks, all! To tell the you truth, its my teacher who told us that heat (somehow) produces electrons. And if you remove the tires of a car while its moving, leaving only the rim, the rims will produce electrons (because of heat). The road produces electrons as well (because of friction, which produces heat), and because of that, the car will (literally) 'fly' because the electrons repel each other. -Zacharycrimsonwolf 13:47, 8 July 2007 (UTC)

I sometimes worry about how educated teachers actually are. But now you can teach them something. Cyta 07:08, 9 July 2007 (UTC)

Well, the answers certainly had helped me. So..I would like to thank you all again. Cheers!! -Zacharycrimsonwolf 09:19, 9 July 2007 (UTC)

Facial hair (from Humanities)

What is record of earl facial hair and late facial hair? --Vess 07:29, 5 July 2007 (UTC)

I don't understand your question. Have you read facial hair and Earl "Facial Hair" Derby?--Shantavira|^{feed me} 08:05, 5 July 2007 (UTC)

I think they meant early facial hair. WAFFLESOAP 09:28, 5 July 2007 (UTC)

I meant early and late facial hair. --Vess 10:03, 5 July 2007 (UTC)

Pituitary adenomas can cause the growth of ancillary and facial hair at virtually any age. These are hormonal variations, and therefore there wouldn't really be a "record." Instead, there would be various disease states, and those with either the lack of facial hair despite functional male gonads or the presence of facial hair despite the lack of mature male sex hormonal organs would suffer from other symptoms and would be distinctly suffering. Geogre 11:55, 5 July 2007 (UTC)

NO! Pituitary adenomas are extremely unlikely to produce facial hair-- not one in 10,000 cases. This is all nonsense offered by an editor who should know better. alteripse 19:25, 6 July 2007 (UTC)

A condition of very early precocious puberty in boys causing early growth of facial hair – possibly as early as from age 1 – is testotoxicosis. Delayed puberty, possibly indefinitely delayed, can be caused by a variety of conditions, including Klinefelter's syndrome and androgen insensitivity syndrome. By the way, a more appropriate spot for this question is the science section of our reference desk.  --Lambiam^Talk 12:38, 5 July 2007 (UTC)

Not facial hair by itself. Advanced precocious puberty may be associated with beard growth in a boy, but only after advanced maturation of the genitalia and bones. alteripse 19:25, 6 July 2007 (UTC)

I suspect the original poster may have meant early and late in a historical sense - that is to say, changes in styles of facial hair through history. DuncanHill 12:45, 5 July 2007 (UTC)

I meant without disease. Howewer, by the way, what was the known historical period in which men had early facial hair and what n which they had late facial hair? --Vess 14:47, 5 July 2007 (UTC)

Even at birth there is a fine 'peach fuzz' of hair on babies faces - it's just a matter of degree - you're not going to find "WOW! A boy born in transylvania in 1796 had a full beard at age 3." (I just made that up OK!)...because it's just not a clear-cut thing. SteveBaker 14:59, 5 July 2007 (UTC)

Closer but still not quite. There are several types of facial hair that are being confused in these answers, and the difference IS generally a "clear-cut thing". The two main categories are vellous and androgenic. Vellous hair is not hormone dependent and is normally present all over the body at all ages but in widely varying densities. There are genetic differences in heaviness, color, and density in healthy people, and sometimes it distresses people from a cosmetic perspective. There are extremely rare cases of defective control of this type of hair growth due to single gene mutations, sometimes familial, resulting in generalized hypertrichosis,-- someone who might get a job as a "wolfman" in a carnival. This condition becomes apparent in early infancy. Exaggerated growth of fine vellous facial hair can also accompany some chronic non-hormonal diseases in childhood (like chronic renal failure), and this too can appear before 5 years of age. This also can occur in chronically malnourished adolescent girls with anorexia nervosa. Lanugo hair is a type of fine hair present in fetal life and would qualify as the earliest facial hair. Androgenic hair is what normally grows at puberty as a result of rising testosterone levels in both males and females. It can occur in childhood as a result of any form of androgen excess but is an advanced, rather than an early manifestation: pubic hair is the first place androgenic hair grows in conditions of androgen excess. alteripse 19:36, 6 July 2007 (UTC)

Vellus & Androgenic hair --JWSchmidt 04:40, 7 July 2007 (UTC)

Valence electrons

In most metals (I assume all, but I know someone will find one counter-point) there are electrons that float on the surface of the metal, giving it the metallic luster. Are these electrons called valence electrons or is there another more exact name for them? The article claims that valence electrons are in the outer-most shell and the ones on metal are not really in any shell. They just float on the surface - or is that just an apparent floating from outer shell of one atom to another? -- Kainaw^(what?) 16:17, 5 July 2007 (UTC)

I'm no chemistry expert, but this is what I figure: That each atom of the metal has its valence electrons, in the outer most shell. But then, between metal atoms, metallic bonding exists, so that metals are held together so to say by a 'sea of electrons', delocalised electrons floating that broke off from valence shells?

See the Metallic Bond article, if it helps.74.102.89.241 16:37, 5 July 2007 (UTC)

The electrons aren't just "floating on the surface" of the metal, but can move throughout the whole piece of metal (see the metal article for more details about this bonding picture). There are indeed surface effects on metallic materials and other conductors, but the idea of valence electrons is in relation to each atom, not bulk material. DMacks 16:57, 5 July 2007 (UTC)

Thanks - conduction electrons is what I was looking for. -- Kainaw^(what?) 17:16, 5 July 2007 (UTC)

UDDERS

What happens to wild cows and goats (and the like) when their udders are full? I know this is a dumb question but it has been torturing me for some time now.

They stop producing milk. The reason milking cows and goats produce so much milk is because they are milked regularly. It is an adaptive reaction. The more they are milked, the more milk they produce. They less they are milked, the less milk they produce. By the way, humans function the same way. See breastfeeding. -- Kainaw^(what?) 17:18, 5 July 2007 (UTC)

In the long term, (scale of days to weeks), they adapt as Kainaw mentions. Over the scale of a few hours, a full udder is a discomfort for the animal. Nimur 17:35, 5 July 2007 (UTC)

Plus, remember domestic breeds have been selectively bred for generations to produce huge quantities of milk, and to keep producing it. Wild breeds would not have a problem to the same extent as a domestic (dairy) breed. Skittle 21:31, 7 July 2007 (UTC)

Domestic dairy cattle are fed and watered in huge quantities; this helps produce vast quantities of milk. Nimur 02:07, 9 July 2007 (UTC)

Hooking up solar panel to appliance

Hi all,

The computer in my apartment is probably the most energy-consuming appliance have. I'd love to be able to hook up a solar panel to it and have it run off of green energy. However, obviously it isn't as simple as that.

I am renting, so have little ability to change the wiring in my apartment or sell back to the grid or anything. And if I just hooked up the panel to my computer, I might get a little power in the day (or I might not, this is Boston), and would certainly get nothing at night.

Is there any system I can use whereby the solar power just suppliments the energy I'm drawing from the grid? Ideally I'd like to be able to instal a solar panel on my roof and attach some kind of large battery (so that it's always charging even when I'm not consuming electricity), and then, when I start consuming electricity, it jumps in and supplies as much electricity it can and lets the grid take up the rest of the slack.

Is there any system remotely like that? And what kind of price would you figure would be on it?

Thanks! --Mike. 17:05, 5 July 2007 (UTC)

There are many systems for it, but they are not as "green" as you may like. You need a collector (such as a solar panel and a windmill propped out your window). You can hook up a stationary bike if you like also. Anything that produces electricity is fine. Then, you need an electronic device that uses the electricity collected to charge batteries. It limits incoming electricity (in case of, say, a lightning strike) and stops charging when the batteries are maxed out. You obviously need batteries - a lot of them. That is the least "green" part of the process. Batteries are rather nasty, but are slowly being replaced with greener ones. Then, you need a power regulator to manage supplying power from the batteries. Unless you want to hack your computer, you will be converting the DC in the batteries to AC and then the computer will convert the AC back to DC for you. A good regulator will let you connect your wall outlet to supplement power when necessary. Now, that is a lot of electronics you will need. Electronic production requires a lot of chemicals and power. So, you are trading the electricity production from the power company for the electronic production of your "green" system. -- Kainaw^(what?) 17:24, 5 July 2007 (UTC)

As a renter, green energy possibilities are limited. You're not going to get anything really cost-effective in terms of generating your own power as a renter. Your best bet instead is to move towards conservation. Don't leave your computer on at all times, for example. Switch to a laptop model (laptops are designed to be very power efficient). Put as much of your electronics as possible onto power strips and turn off the power strips when they're not in use. Use compact fluorescents in all your light fixtures. When you purchase anything new (say a TV or refrigerator), look for something that's power efficient. Note that a plasma TV will use more power than the same size LCD TV. Incidentally, it's actually your fridge which is the highest power user in your apartment. Finally, if your local power party offers it as an option, sign up for green power. If they don't offer it, pester them about it until they do (or they block your phone number from calling). Donald Hosek 17:47, 5 July 2007 (UTC)

I VERY much doubt that your computer is the biggest energy user. Lets examine the facts: According to Energy use in the United States:

32% space heating

13% water heating

12% lighting

11% air conditioning

8% refrigeration

5% electronics

5% wet-clean (mostly clothes dryers)

So all of your electronics (including TV, VCR, Satellite, radio, phone, etc) is only 5% of the total - your computer is probably 1% or maybe 2% of your total usage. Your best bet is to turn down the heat/A.C - since heat is eating a third of your budget, saving even 10% of the cost of heating will more than compensate for the PC! Then you can take shorter showers and fewer baths (and share with a *close* friend!) - turn off lights when you aren't truly, honestly using them and switch to compact florescent bulbs. If you can do even slightly better at even just one of those things, it'll wipe out the cost of running your PC. Next time you buy a refrigerator/oven/microwave/dishwasher/A.C/water-heater/freezer - look at the energy consumption and cost of ownership numbers. SteveBaker 18:53, 5 July 2007 (UTC)

It all depends on individual circumstances -- you can't just take a statistical summary and declare that everyone follows that. For example, that "32% space heating"? It doesn't apply to me: I've never run the baseboard heaters in my apartment. Likewise, the A/C only gets a day or two of use each year. And there's no clothes dryer in my apartment. I prefer dark environments, so "12% lighting" is a massive over-estimate in my case. For me, it would look more like:

30% water heating

30% computer (always on, and reasonably busy)

25% refrigeration

10% oven/stove

3% lighting

1% air conditioning

0% space heating

--Carnildo 22:52, 5 July 2007 (UTC)

I think you are over-estimating your computer(s), as the average computer's power supply is only rated at less than 500W, it usually uses around 200W at full power for a pretty average computer on high load, plus 50W for a 17" LCD monitor that's just 250W for your "average" computer. On the other hand, Water heating, stove/microwave and fridges are count in kilowatts, and although they may not be always on, I doubt they are used less than say 2 hours a day. --antilived^{T | C | G} 00:07, 6 July 2007 (UTC)

I agree he's probably overestimating his computer, but you're overestimating everything else! Not everyone uses electric heating (and a good thing, too, as it's horribly inefficient). If you have natural gas or fuel oil heating, and a gas stove, and a gas water heater, and no air conditioner, your electricity cost for heating/cooling is 0. And refrigerators are a relatively small load, nothing like a kilowatt. (Off the top of my head, I think a typical refrigerator draws 4 amps or so, and of course it's not -- or shouldn't be -- on all the time, either.) So the other big draws are lighting, and major appliances such as dishwashers, microwave ovens, washing machines, and clothes dryers. (For that last, there's obviously another huge difference in electricity load between the gas and electric models). --Steve Summit (talk) 00:21, 6 July 2007 (UTC)

See [8] for some typical consumption figures. Donald Hosek 00:24, 6 July 2007 (UTC)

OK - so you're telling us that this 'oksolar' site is reliable? Let's examine what they said. Firstly, they don't seem to understand the difference between kWatts and kWatt/hours which is a red flag right away for a company that's selling solar panels!! But we'll forgive that. They claim that your computer uses 240 Watts and consumes 1248kWatt(/hours) in a year. For that to be true, the computer would have to be pulling 240 Watts 24 hours a day for 216 days out of the year - or 14 hours a day 365 days of the year!! Who are these online junkies?! Even if you forget to turn off the PC, when it's idle, the power drops way below 240 Watts when the computer isn't working hard. Even if you are leaving it on 24/7 to run a website or something, turning off the CRT monitor or letting it powersave properly will get you way below 240 Watts. 240 Watts is when the PC is working hard with graphics and CPU running something really heavy duty - probably with with the hard drive and CD-ROM drive both spinning and the monitor lit up. Even 500W power supplies don't deliver 500W continually - that's a peak number for when absolutely everything is going at full power at the same time. The number they give has to be the very most a dedicated net junkie can rack up. My (really high end) laptop runs from a 24V/4.5A supply - that's AT MOST 108 Watts and typically more like 30 Watts - it runs for maybe 6 hours a day, 356 days of the year. So the number for me ought to be something like 44kWatt/hrs - not 1248kWatt/hrs. If they produced such a ridiculous set of numbers for the computers - I don't trust them to get the other things right either. Last month my apartment used 513kWatt/hrs (air conditioning - Texas!) - of which maybe 3.6kWatt/hrs was my laptop - much less than 1%. SteveBaker 01:37, 6 July 2007 (UTC)

I double-checked against last month's electric bill, and if anything, I'm underestimating. Assuming that my computer (actually, one new high-power computer, one very old low-power computer, one router, one cable modem, one KVM switch, and one CRT monitor) draws an average of 250 watts, and is on 24/7/30, then my computer makes for 45% of my monthly electric bill. My apartment is wired for electric baseboard heating, but I don't use it. My stove is typically used for 20 minutes every other day (I live alone, so I cook for two days at a time), and the microwave for less than five minutes a day. Since there's only one of me, and clothes washing is done at a laundromat, I use far less hot water than "average", and I don't have a clothes dryer. --Carnildo 22:49, 6 July 2007 (UTC)

Sure - it's possible for the PC to be that big a share of your bill - but you must surely recognise that you are one the very extreme end of the bell-curve here! (I actually don't believe your 45% figure even so - don't you have a refrigerator? It'll easily out-consume your PC collection.) You have two computers (one old and therefore inefficient), you have lots of peripherals, you have a CRT monitor rather than an energy-efficient LCD - and you don't use electricity for much else. You obviously live in an extremely mild climate. But is it reasonable to answer a question like this on the basis of your (extreme!) situation? It is vastly more likely that our questioner is in the middle of the range of users - for which the number is around 5% for all electrical items (including TV's which are typically a big chunk of it). Taking an extreme statistical anomaly isn't the way to answer this question in a helpful manner. For almost everyone, the best policy is to cut down on heating/AC, turn off unneeded lights, switch to compact flourescent lightbulbs, use the microwave more than the stove, set washing machine and dishwasher onto the cooler settings, take showers rather than baths, shower quickly, hand clothes out to dry naturally instead of using a drier, unplug the TV/DVD/Satellite/Cable-box when it's not in use ("Turninng it off" probably doesn't really turn it off), turn off your PC when not in use (or at the very least, turn on all of the power saving settings and turn off the monitor whenever you walk away from the keyboard for a few minutes or more. Unless you are a VERY anomalous electricity consumer or already very diligent about these things - then doing any ONE of those things will save more electricity than it takes to run your computer. SteveBaker 20:36, 7 July 2007 (UTC)

Although not effective use of money, solar panels could be carefully connected into the power supply of the computer, somewhere where there is DC; probably close to large capacitators. This would reduce the computers usage of mains power a little bit. Easy to burn out things though. Could be dangerous. Polypipe Wrangler 00:52, 6 July 2007 (UTC)

This is dumb - this is INSANELY DUMB advice. It's a stupid thing to do your PC. Of all of the appliances in your home - the PC is by FAR the most vulnerable to power supply glitches. If you have solar cells - connect them up to your refrigerator, use it to charge a 12v battery and use an inverter to drive a table lamp or your TV - it doesn't give a damn if the sun goes behind a cloud or a pidgeon lands on the panel and casts a shadow over the cells. Truly - it is not thinking at all logically to pick the PC as the thing to improve. Literally every other thing you own that consumes electricity can be addressed as a source of power savings that will be easier and more effective than messing around with what is probably the most expensive, delicate and precise appliance you own! WHAT ARE YOU THINKING?!?!?!? SteveBaker 01:37, 6 July 2007 (UTC)

There's nothing to do but second this. Trying to use a solar panel in an apartment, and especially to power your computer, will probably cost you more than it saves, especially when your PC blows up --_ʇuǝɯɯoɔɐqǝɟ 02:00, 6 July 2007 (UTC)

Modern computers are actually quite robust when it comes to power. As long as your solar panels are supplying enough power to keep the computer running, or you've got a battery to take up the slack, there's nothing wrong with hooking your computer up to them. A light bulb is about the worst possible thing you can hook up to a solar panel: since you usually don't need artificial light during the day, you must have a battery to store the power, and batteries use an incredible mix of toxic chemicals. --Carnildo 22:53, 6 July 2007 (UTC)

Ok, if you're doing this for environmental reasons, check out http://terrapass.com/ - it will help far more than a solar panel ever will. If you're doing it for cost reasons... it would be best to just buy cheaper appliances. The 200$ maximum your PC might possible cause you in costs if you run it constantly is not worth any solar panel powerful enough to offset it. --_ʇuǝɯɯoɔɐqǝɟ 02:05, 6 July 2007 (UTC)

Klinefelter's syndrome and homosexuality

Is there any links between Klinefelter's syndrome and homosexuality? Are there any scientific proof that Klinefelter's syndrome may cause homosexuality? Has there ever been any (non-scientific) speculation about the possible connections? ► Adriaan90 ( Talk ♥ Contribs ) ♪♫ 17:33, 5 July 2007 (UTC)

A cursory examination of the relevant literature indexed by PubMed reveals very little work that looks at homosexuality in the context of Klinefelter's. Ratcliffe S. (1999) "Long-term outcome in children of sex chromosome abnormalities" PMID 10325742 Arch. Dis. Child. 80(2):192-5 failed to identify a link, though the study was relatively small (19 XXY boys, none of whom demonstrated homosexual tendencies).

Worth bearing in mind is that the incidence of Klinefelter's is about 1 in every 700 men, whereas the fraction of the male population that is homosexual is on the order of 1 in 10—so even if all Klinefelter's individuals were homosexual, it would make a relatively small contribution to the total number of homosexual individuals. TenOfAllTrades(talk) 19:04, 5 July 2007 (UTC)

Oh ok, I see. Thanks for the info! ► Adriaan90 ( Talk ♥ Contribs ) ♪♫ 22:37, 5 July 2007 (UTC)

Where does that one in ten figure come from, I hear it a lot, but in my personal experience (I know, not statistically significant) I wouldn't think it was even close. Are there really 6 million homosexuals in the UK? Cyta 07:00, 6 July 2007 (UTC)

I don't have a source to hand, Cyta, but expect I can find one soon with some digging. I used to be on the Equalities group of a community regeneration company, and that is the figure we worked with. One thing to remember is that you almost certainly know many more gay people than you think you do - it's just that some will not be "out" at all, others will only be out with certain people or in certain circumstances. DuncanHill 09:28, 6 July 2007 (UTC)

I think the actual number is about 3% from the last peer reviewed study I've seen with some varations in rural and urban settings. --Tbeatty 17:26, 7 July 2007 (UTC)

I read somewhere that no-one is completely defined as homosexual ro heterosexual or whatever. They said that some people are only more straight or gay than others. I guess that there are fewer more-gay people than there are bisexuals and straight people. ► Adriaan90 ( Talk ♥ Contribs ) ♪♫ 09:18, 6 July 2007 (UTC)

The article Kinsey scale is relevant to the theory of a continuum of human sexual orientation. DuncanHill 09:21, 6 July 2007 (UTC)

Obviously in order to quote the '1 in 10' concept we would have to get our terms better defined. As others have mentioned the term 'homosexual' leaves the field rather open to include people that may define themselves as straight/heterosexual in society but are nonetheless somewhat homosexual. Even the word 'homosexual' can mean anything from a) a person that identifies themselves as homosexual, to b) a person that is attracted to the same sex, to c) a person that engages in sexual activity with members of the same sex but not necessarily exclusively (e.g. bisexuals, curious, etc), to d) people that exclusively or predoiminantly engage in sexual activities with only members of the same sex, etc. Indeed a rainbow. My point is, that I don't agree with the "1 in 10" statement at face value. I don't believe that 1 in 10 people are predominantly gay. I would accept the 3% rule, however. But if you change it around to include c) a person that engages in sexual activity with members of the same sex but not necessarily exclusively, then maybe it's more accurate. Rfwoolf 12:29, 8 July 2007 (UTC)

The UK government puts the figure at 6% (they wanted to asses the "cost" of civil partnerhip as couples pay less tax) but they didnt do any original research, they just collated all the previous studies. Helpfully, they refuse to add the question in the census. Also, hasn't Kinsey been wildly discredited? I could perhaps accept that 10% of men have "done stuff" with other men but cleary the 10% gay figure is way off the mark. I like 5% - one in twenty. a nice round number...130.88.205.43 11:10, 11 July 2007 (UTC)

An unusual application of tack adhesive

Would it be even theoretically possible to use tack adhesive to hold a shelving unit full of books to a wall? NeonMerlin 18:17, 5 July 2007 (UTC)

Theoretically - yes - practically - no! Well, there are two issues here:

1. What area of shelf is in contact with the wall via the adhesive? Every square inch of tack will require a certain amount of force to pull it off the wall - the more square inches there are, the more force it'll take - so the more weight it can support. If the area is large enough - it should hold. So your best chance is to fix (using nice strong screws/nails) a large 'back board' to the back of the shelf - then cover that with tack adhesive.
2. Shear forces. The weight of the shelf+books (which are insanely heavy BTW!) is acting downwards, parallel to the wall - but the tack adhesive is also resisting pulling forces at 90 degrees to the wall. The complicating factor is that if it more or less resists the shearing force, the front edge of the shelf is trying to move down - while the back of the shelf is staying stuck. That's causing a rotation - so what's going to happen is that the tack behind the bottom of the shelf will be squashed while the tack at the top of the shelf is being pulled - the tack that's being squashed is doing some work in resisting the shear forces - but the tack at the top of the shelf is being pulled off the wall at more or less 90 degrees...AND resisting the shear forces. This suggests that you want to have more area of tack above the shelf than below it in order to better resist that force.

But no - it's bloody obvious that it's going to fall down! Duh! SteveBaker 18:37, 5 July 2007 (UTC)

If you're in an earthquake zone (like me!) you might want a sturdier shelf than that. I recall a statistic (probably from this book) that most earthquake injuries are due to falling books and bookshelves, and falling glass from lights and windows. (Specifically, they cite "For example, in the 1994 magnitude 6.7 Northridge earthquake, 55% of quake-related injuries were caused by falling objects, such as televisions, pictures and mirrors, and heavy light fixtures." Nimur 21:24, 5 July 2007 (UTC)

Excuse a poor Englishman... what is tack adhesive? DuncanHill 22:39, 5 July 2007 (UTC)

Blu Tack. Also, you should consider that if the wall is painted, it's not the wall that will be holding up the shelf, but the paint. Paint has a nasty habit of peeling right off if you pull too hard. —Bkell (talk) 22:47, 5 July 2007 (UTC)

That's not a problem so long as the adhesion between paint and wall is better than between paint and tack adhesive. So that if something is going to give, it'll be the adhesive, not the paint! It is an important property of Blu Tack that it does NOT pull paint off the walls - it's the single property that it has that makes people use it! So unless the walls are in terrible shape (such that even tacking up a poster with blu-tack would pull off the paint), it doesn't matter how much weight you try to hang off of it - the tack will give up before the paint does. SteveBaker 13:32, 6 July 2007 (UTC)

That's a good point. —Bkell (talk) 00:32, 11 July 2007 (UTC)

Burning wood = carbon neutral??

On the Terrapass.com site there is a list of FAQs about energy consumption. Link (though it's a php page, so not certain if you'll see the FAQs without further navigation). The last FAQ is this:

= What about my wood stove? =

Technically, the burning of wood is carbon neutral. Of course there are many other 
downsides to it, and we're not recommending it as a substitute for gas or other more 
traditional energy sources.

Really? I had understood that combustion of wood releases all the carbon that was stored in the wood out as carbon dioxide into the air. Is that not correct? The wood and combustion articles don't help much, except that I see that CO2 is indeed often on the right side of the chemical equation.

Maybe by "technically carbon neutral" they mean that no new CO2 got created, because it was in the air before the tree consumed it? If so it seems that the wording is a little silly -- after all, the carbon in fossil fuels may well have been CO2 before it went into the fossils...

Thanks! Mike. 18:53, 5 July 2007 (UTC)

The idea is that if you want to use wood as a fuel, you're going to have to keep growing new trees. Burning any plant that you've grown from scratch is carbon neutral, in that you pulled all the carbon in the plant out of the air in the first place. The key difference between burning wood and burning oil is that we actually can grow new trees (on a non-geological timescale). TenOfAllTrades(talk) 19:27, 5 July 2007 (UTC)

Do all of the carbon in the wood go into the air though? Because, what is that black stuff (ash) that remains after you burn wood? Isn't that like the left-over carbon? ► Adriaan90 ( Talk ♥ Contribs ) ♪♫ 22:41, 5 July 2007 (UTC)

If the fire is properly oxygenated, and you let it burn to completion, the stuff left has almost no carbon content. --Carnildo 22:56, 5 July 2007 (UTC)

So long as there is no deforestation being caused by people cutting down trees for firewood - then we're carbon-neutral. The important thing is that new trees are being planted and looked after until maturity. If this really bothers you - dig a deep hole in your back yard - every time you burn a log - toss another one into the hole and bury it. That way you're not only carbon neutral - you're actually 'sequestering' carbon. SteveBaker 01:03, 6 July 2007 (UTC)

I hope it's carbon neutral. That means burning oil is carbon neutral, since it came from plant matter. Points out the silliness of "carbon neutral" though. --Tbeatty 17:22, 7 July 2007 (UTC)

I thought oil was algae and zooplankton, not plants? It's coal that's plants. Anyway, burning fossil fuels would be carbon neutral if you burnt them at the same rate as, or slower than, the rate they are being made at. Skittle 21:25, 7 July 2007 (UTC)

surely if you're burning wood slower than you're growing it it can't be carbon NEUTRAL, which would suggest no loss or gain of CO₂. :-P Aamackie 06:07, 9 July 2007 (UTC)

Terminal shoot - English botanic name?

Hello, please does anyone know the term of "Terminaltrieb" (German) in English, it is the main shoot of a tree and determinates the direction of its growth (in contrary to the offshoots). Many thanks in advance, --birdy _{(:> )=|} 20:44, 5 July 2007 (UTC)

You have it perfectly in the title of your question, unless I have misunderstood you. The english term is indeed 'terminal shoot'. Lanfear's Bane

Try Apical Shoot. Hardyplants 00:02, 6 July 2007 (UTC)

Thanks a lot! So terminal shoot and apical shoot are synonyms? --birdy _{(:> )=|} 12:03, 6 July 2007 (UTC)

I'm not sure about horticulture but in botany you're probably looking for either the apical meristem (most likely) or the shoot apex which is properly the shoot apical meristem plus the leaf primordia. KP Botany 04:00, 7 July 2007 (UTC)

dimmer switch efficiency

I want to buy a dimmer switch for an incandescent, not cfl, bulb. I understand that modern dimmers are more efficient than old variable resistor style. My question is: Are some brands or models of dimmer more energy efficient than others? I notice that one manufacturer markets what looks like the same switch at the same price with two different styles of packaging, one of which says it is 1/4 more efficient (but does not specify what this means).

Modern dimmer switches work because they are powered off an AC circuit; as a result, they can take advantage of the fact that the voltage varies by only allowing a current to pass when the voltage is high enough; as a result, they waste less energy as heat than an old-fashioned resistors (no energy is needed by circuit that doesn't flow). Presumably the more efficient one is of a lower resistance (as dimmers no longer rely on internal resistance to work); check whether the back of the box gives either resistance or heat output (both would be good indicators of efficency). Laïka 23:17, 5 July 2007 (UTC)

Don't they use PWM so there isn't much variation on structrually similar units. --antilived^{T | C | G} 23:25, 5 July 2007 (UTC)

You could call what a dimmer does PWM, though it's sort of a poor-man's simulation; I've usually heard it called "chopping". But it does still have the property that the dimmer is always either "on" or "off", and hence (theoretically) there's no loss, and the process is perfectly efficient.

If there are efficiency variations between models, they're bound to be slight.

What people here are calling "old-fashioned", resistive dimmers are more than just old-fashioned, they're positively obsolete. I've never seen one, and I doubt anyone reading this (at least, if they're in the U.S.) has, either. As far as I know, all dimmers have been choppers, for decades now. --Steve Summit (talk) 00:13, 6 July 2007 (UTC)

My college still had one in one of it's original buildings. It had this monstrous heat sink attached to it. It just looked like such an obviously bad idea. — Laura Scudder ☎ 01:11, 6 July 2007 (UTC)

I think the correct term for the circuitry in a dimmer switch is triac, which is similar to PWM in concept, but not in implementation. The article elaborates on the details. Nimur 04:42, 6 July 2007 (UTC)

"Triac" is the name of the principal component in those dimmers. You can (and many people do) call it "a triac circuit", but that's an imprecise term, as there are of course other circuits that also use triacs. (That is, saying that "the" name for the circuitry in a dimmer is "Triac" is like saying that the name for the circuit inside a radio is "transistor", or that the name for the circuit inside a computer is "microprocessor".) —Steve Summit (talk) 05:08, 6 July 2007 (UTC)

I have definitely seen resistive dimmers. At a motion picture theater built in the 1920's which had been a vaudeville palace in bygone years, the dimmer system had a bank of resistive dimmers, which could be gang-operated by a motor. The resistance element could have been nichrome wire, but in earlier years it could have been iron wire. It could be set up to dim individual lights or groups of lights, much like present-day theatrical lighting systems. Edison 04:16, 7 July 2007 (UTC)

To answer the original question, all phase control dimmers are very efficient. The triac (the power switching element) drops less than a volt when switched "on" and dissipates no power when switched off, so even on a 120 volt circuit, less than 1% of the voltage is dropped in the switch; on a 230 volt circuit, less than 0.5% of the voltage is lost in the power switch. Because of this, I think we can safely call the efficiency of the dimmer >99%. Even a perfect dimmer would only improve that efficiency by 1% (120 vac) or 0.5% (230 vac).

The big improvement that's coming is sine wave dimming instead of phase-control dimming. By replacing the slow triacs with high-speed power MOSFETs, the dimmers will be able to preserve the sine wave shape of the power voltage. This, in turn, will eliminate the problem of lamps "singing" and fan motors "buzzing" when dimmed down.

Atlant 13:48, 8 July 2007 (UTC)

hi , my guestion is about c++

hi , i have some guestions about c++ programing language they are very important for me i didn't find the answer for these guestions ,, i will be delighted if someone help me in this field (c++) and answer my questions first which is difficult for me to know how to make it in matrix - i want to make the size of the array is variable , which is entered by the user or the size depends on variables . or there is no way to make the size of the array variable ,,,it should be the size constant(value).

i.e : int main () { int b; cout<<"enter the size of the array "; cin>>b;

int a[b]; } return 0;

please help me in this matter , it means a lot to me .....

Go to the computing reference desk --_ʇuǝɯɯoɔɐqǝɟ 23:31, 5 July 2007 (UTC)

Future computing questions are best asked at the computing desk. In this case, you should read about malloc. Wikipedia is an encyclopedia, not a tutorial service; you might be interested in the C++ wikibook. Nimur 00:37, 6 July 2007 (UTC)

Almost. C++ typically uses (well emphasizes) new and delete instead of malloc/free, although the latter are still available. Look at dynamic memory allocation in any beginning C++ book. But yes, the Computing Desk will probably be more open to these sorts of questions. --Bennybp 00:45, 6 July 2007 (UTC)

Just replace 'int a[b];' with 'int *a = new int[b];' - when you are finished with the array, run 'delete [] a;' SteveBaker 00:57, 6 July 2007 (UTC)

Also the C++ Standard Template Library (STL) has lots of useful containers, for example in this case a std::vector<int> which have variable size. [9] is a good guide. Not sure if it's possible to set an upper size limit, so it may not be what you want now, but these containers are useful and have a series of preprogrammed functions (such as .size() which tells you the size of the vector) which can come in handy. Cyta 07:07, 6 July 2007 (UTC)

July 6

Voltage to Current converter (2A)

Is there a way to simply generate a 0-2 A current source proportionally to a 0-5 V or 0-10 V control voltage signal. I would like to replicate the functionality of this device. --Jcmaco 00:46, 6 July 2007 (UTC)

That would be an amplifier. Do you intend to design the circuit, or are you hoping to buy a commercially available one? In either case, you will need more thorough specification of requirements (what load will the 2 amps be driven into? How much variation can you tolerate?) 2 amps may be a lot of juice, so be careful if you try to build it yourself. Nimur 00:51, 6 July 2007 (UTC)

The load is variable (4-8 ohm). I intend to design and built the circuit myself since the available commercial solutions are too expensive. Could a high current Op-Amp (like the OPA548) be used if I were to control the current limit? --Jcmaco 01:02, 6 July 2007 (UTC)

See current source to start with--Tugjob 01:29, 6 July 2007 (UTC)

Yes, you want a voltage to current converter. see Voltage-to-current converter and this for some ideas. --Duk 05:54, 6 July 2007 (UTC)

Spherical mirror

After seeing the result of what happens when two mirrors face each other, I wondered what things would look like inside a spherical mirror. Then I began to wonder about the physics of such a situation. Imagine you are inside a spherical object or room where the inner surface is a highly reflective mirror. If you turn on a flashlight for a brief moment and turn it off again, how long would you be able to see, since most of the energy is constantly being reflected? Some of the energy would be absorbed by the mirrored surface, some by your body, some would impact the eyes and be absorbed by the retina, etc. but surely most of it would be reflected many times before being absorbed. Or would the shape of the spherical mirror focus the light on the center of the sphere? Suppose you turned the flashlight on and left it on. Would the trapped light significantly raise the temperature inside the sphere? 152.16.59.190 07:23, 6 July 2007 (UTC)

Don't forget that conservation of energy still applies, so it won't get much warmer, at least not quickly. About focusing: See curved mirror - a perfectly focusing mirror is actually paraboloid, not spherical. A small segment of your sphere, at which the light from the flashlight hits the surface nearly at an angle of 90 degrees, can be viewed as an approximation to a paraboloid, but then the distance from the surface to the focal point is half the radius of the sphere. Icek 09:01, 6 July 2007 (UTC)

Even the very best telescope mirrors absorb 5–10% of the energy (each time the light is reflected), so it wouldn't take long for almost all the energy to be absorbed.--Shantavira|^{feed me} 09:29, 6 July 2007 (UTC)

Even if you ignore everything inside the mirror, the light won't last for long. Say the mirror was 99.9999% reflecting (that's about the absolute best possible mirror you can make, but in reality such a mirror would only reflect that well over a narrow band of wavelengths and reflection angles - we'll ignore that for now). So the mirror reflectivity is R=0.999999. After N bounces of the light from the mirror, the intensity of the remaining light is I = I0 * R^N, where I0 is the light's starting intensity. Now say the sphere is such a size that light travels an average of 1 metre between each bounce. So the time taken to make N bounces is just N/speed of light. Now work out those numbers; after 50 milliseconds, the light has made 150 million bounces, and the intensity of the light is 1/(30 millionth) of what it started at. So only 50 milliseconds after you turn off the light, the remaining light bouncing inside the sphere is essentially undetectable. --Bob Mellish 09:36, 6 July 2007 (UTC)

I don't think that a flashlight left on would increase the temperature significantly. In every reflection, only a part of the energy is being absorbed (and the remaining reflected). At the end of all reflections, the mirror would have absorbed all the energy. This energy absorbed would be equal to the energy absorbed by a black body (without any reflection). I don't expect a (non reflecting) black spherical mirror to become very hot due to a torch light left inside it and hence a reflecting mirror would be even less hotter -- WikiCheng | Talk 12:30, 6 July 2007 (UTC)

"Black mirror". What? Capuchin 13:07, 6 July 2007 (UTC)

No matter what - all of the heat energy that's created during this process came from a couple of little batteries inside the flashlight. The total amount simply cannot be more than that. Even if the outside of the sphere is exceedingly well insulated, the amount of heat gained won't be all that much. The situation is similar to the parallel mirrors case in that the light would bounce around forever if it were not for the fact that no mirror is perfect - and anything you place between the mirrors/within the sphere such as yourself and your flashlight - will inevitably absorb light themselves. However, small the imperfection is, it'll eventually end up absorbing all of the light and turning it into heat. SteveBaker 13:24, 6 July 2007 (UTC)

I have measured a flashlight with 2 D alkaline cells to produce and consume .35 amps at 3 volts, which is 1.05 watts, or about 1 Joule/second. Now take the mass and specific heat of the air and any person inside the sphere, plus the sphere itself, and figure how fast it would heat up, even if it were insulated and no heat left it. Compare that to the heat evolved from the observer, which might be 60 to 80 watts. The flashlight would be a negligible addition. Edison 14:20, 6 July 2007 (UTC)

... similar to the parallel mirrors case in that the light would bounce around forever ... -- Actually, it's my understanding that light would fall to the ground in the perfectly-reflecting parallel mirrors case. [10] --TotoBaggins 14:32, 6 July 2007 (UTC)

Hah! I guess that depends on how you define parallel. If the mirrors were aligned perpendicular to spacelike geodesics, then sure, the light would fall. But if they were aligned perpendicular to null geodesics, the light would go back and forth along the same path, because light always follows null geodesics. One could argue that that's a better definition of parallel. In practice, the only way to align the mirrors that accurately is by interferometry... and it's obvious what definition that leads to. —Keenan Pepper 18:05, 6 July 2007 (UTC)

Missing diffraction spikes

In the picture at right exhibiting diffraction spikes, the spikes seem to be proportional to the brightness of the star. However, in today's Astronomy Picture of the Day (see here), the effect seems to be either off or on, with nothing in between, and not depending strictly on brightness. Explanations I can think of are 1) the image was composed of shots from different telescopes, or 2) the spikes that are there are photoshopped in for effect. Is there some more compelling explanation? Thanks. --TotoBaggins 16:28, 6 July 2007 (UTC)

I have mentioned before that I believe many of these astronomical photographs use digital effects for artistic purposes, and that it can blur the distinction between "scientific data" from "art." I cannot think of a good reason why those diffraction spikes should only appear selectively, as you mention. Nimur 19:09, 6 July 2007 (UTC)

In fact, the source of that image specifically states:

“ Separate black and white exposures through clear, red, green and blue filters are digitally combined and stretched, using Adobe Photoshop and other image processing software, to create full color pictures.
--Cosmotography ”

.

It is difficult to know "how much" post-processing is used. Nimur 19:11, 6 July 2007 (UTC)

I wrote to the photographer, and he replied with a very helpful and friendly response which read in part:

"Diffraction spikes are proportional to the brilliance of the star that causes them. Only a handful of stars had sufficient brightness in this particular image.

Interestingly, the diameter of stars in astronomical images are usually perceived as a metaphor for their relative brightness to one another. In the case of this photograph, some of the brighter stars were digitally reduced (their were diameters decreased) so that would not appear distracting. You can spot these fairly easily- they are the ones with diffraction spikes. Notice that they also have a colorful halo- those halos give a good indication of their original size in the raw data. I purposely left the halos surrounding each star (and their diffraction spikes) as a way of showing the true size of the star and as an substitute metaphor for brightness.

This is a fairly common approach used in astronomical photography, by the way...

Significantly, nothing was artificially added to this image- the diffraction spikes were not drawn onto the picture."

So I guess the answer is not that spikes were added to a few of the stars, but that they were subtracted from a bunch of them. Thanks for the replies, Nimur. --TotoBaggins 20:38, 6 July 2007 (UTC)

Well, no, spikes were neither added nor subtracted. The brightest stars were dimmed. Diffraction spikes are indeed "proportional to the brightness of the star" as you wrote initially, and in this image noticeable spikes occurred only at the very brightest stars. Because the apparent brightness of these stars was artificially dimmed, the expected proportionality between star brightness and spike brightness was thrown off. Thus you were right to sense that something was strange. --mglg_(talk) 23:53, 6 July 2007 (UTC)

And if you look at the APOD photo again, you will see that the diffraction spikes on the two bright blue stars to the right of the galaxy are longer than the others, although not by much. --Anonymous, July 6, 2007, 21:45 (UTC).

Nasty Bread

Can potentially deadly types of mold (or other gross stuff) grow on artisan bread if it's left out for a wicked long time?

This source (and my mycologist sister-in-law) say that it is unsafe to eat moldy bread. "Deadly" is relative, of course, as people have survived arsenic and died from peanut butter. The bread being "artisanal" is unlikely to have an effect, as mold doesn't know how lovingly and authentically and with how much integrity its delicious substrate was prepared. --TotoBaggins 20:31, 6 July 2007 (UTC)

It's generally not safe to eat anything moldy. "Deadly" is definitely relative. People have died from water. Bart133 ^{(t) (c)} 22:02, 6 July 2007 (UTC) (Link changed --Anon, July 6, 23:00 (UTC)).

Artisan bread wouldn't contain anywhere near the amount of preservatives found in, say, brand-name packaged white bread... would that make a difference in the amount and number of types of organisms able to grow on the bread.

Killroy filter

"Part of a band pass filter" according to Pynchon

I'm no electrical engineer, but isn't this a band-stop filter? —Keenan Pepper 18:11, 6 July 2007 (UTC)

Correct. To be painfully precise, it is a parallel resonant band-stop filter. -- Kainaw^(what?) 18:23, 6 July 2007 (UTC)

It depends where you take the output, doesn't it? Nimur 19:15, 6 July 2007 (UTC)

I'm assuming that the missing part of the circuit (the left/right ends that go off the edges) loop back and connect to some sort of source. See http://www.eng.cam.ac.uk/DesignOffice/mdp/electric_web/AC/02127.png for an example. -- Kainaw^(what?) 19:18, 6 July 2007 (UTC)

As shown here

• 
  High Pass Filter
• 
  Low Pass Filter

Identical components, in the same topology, function as either a pass- or a stop- filter depending on where the input and output are placed. Nimur 19:21, 6 July 2007 (UTC)

The circuits you have shown are not "parallel resonant" circuits like the one asked about (with the inductor and capacitor in parallel). To turn this into a "pass" filter, the load resister is also put in parallel (see http://www.eng.cam.ac.uk/DesignOffice/mdp/electric_web/AC/02125.png for an example of a parallel resonant band-pass filter). I must make a disclaimer that I only work with common circuits. I'm sure someone knows how to get these circuits to do things they are not intended to do. However, if you are taking an AC electronics test and they show you an RLC circuit with the cap/inductor in parallel and ask if it is a stop or pass filter. If the load resister is in series, it is stop. If the load resister is in parallel, it is pass. -- Kainaw^(what?) 23:26, 6 July 2007 (UTC)

I thought someone was having a little fun. Look in the trivia section of Kilroy was here, which was the first thing I thought of when I saw this. Lanfear's Bane

It's Chad! DuncanHill 10:27, 7 July 2007 (UTC)

Oddly - it's Chad in the UK, Kilroy in the USA. Having said that - when I lived in UK - I saw plenty of Chad's adorned with the words "Kilroy woz 'ere" - so it is perhaps not that clear-cut! SteveBaker 14:01, 7 July 2007 (UTC)

Enthaply Change

how do i calculate the mean molar bond entalpy of Br-F bonds in Bromine Pentaflouride.

I have th following figures: molar bond enthalpy F-F-159, Br-Br 193

the overall enthalpy change is -429

many thanks

ΔH = ΣBonds broken - ΣBonds formed. So, you have the equation 1/2Br₂ + 5/2F₂ --> BrF₅.

Figure out how many bonds of each there are, and use algebra to find out what you want. 74.102.89.241 22:05, 6 July 2007 (UTC)

Shaking arm

Why is that when you flex your arm, or any other body part, it begins to shake, even if it is at rest on a table? Imaninjapirate^{talk to me} 21:28, 6 July 2007 (UTC)

See Muscle contraction. A brief perusal of the article leads me to believe it may have something to do with frequency summation (apparently only approx 30% of the fibers are firing at any given time), but muscular contractions are complex processes so I am sure there is more to it than that. Is there a doctor in the house? 161.222.160.8 22:35, 6 July 2007 (UTC)

It is not clear what you mean by "flex your arm". You may mean that you are activating both flexors and extensors at the same time and trying consciously to hold the limb in a particular position. This creates a feedback problem for the muscles and nerves, a problem that is not solved efficiently without practice. --JWSchmidt 04:15, 7 July 2007 (UTC)

BFS?

July 7

Black olives...

Why do black olives taste nice to me on a pizza when combined with other flavours (tonight's topping was cheese, tomato, doner meat and olives), yet taste absolutely foul when eaten by themselves? --Kurt Shaped Box 00:15, 7 July 2007 (UTC)

Maybe because it was masked by the other flavors? Black olives taste like vulcanized rubber to be, regardless of whether it's by itself, on pizza, or with other toppings. bibliomaniac15 ^{BUY NOW!} 01:39, 7 July 2007 (UTC)

"Black" olive is a loose term for a huge number of styles, marinades, and flavors of olive. Some indeed taste like rubber. Quality black olives are a delicious treat by themselves or with other food. I recommend Kalamata olives, instead of the canned junk you probably tasted. You can get them at a Greek, Middle Eastern, or other grocery store. Nimur 05:27, 7 July 2007 (UTC)

• Yeah, but the stuff you get on a pizza is almost always the California black olive, which is an unfermented Mission olive, with pretty much no character (and, I think, still some remnant flavor of the lye, but I may be imagining that.) --jpgordon^∇∆∇∆ 15:22, 7 July 2007 (UTC)

And thank you for the link to doner meat. I didn't think it had anything to do with the Donner Party but I liked having the link to verify that.  :-) Dismas|^(talk) 15:35, 7 July 2007 (UTC)

The thing about donner meat is that you can never be entirely sure by look and taste what manner of flesh you are consuming - it's just, well, slabs of 'generic meat'. Still, it tastes good when you're drunk and it doesn't poison you - so you don't say anything. --Kurt Shaped Box 21:57, 7 July 2007 (UTC)

Thanks for the tip, Nimur. I don't know what type of olives I had on the pizza but the ones I tried to eat by themself were from a jar of 'black olives in brine' from the supermarket (no other information specified). Yes, they did taste like how vulcanized rubber smells. --Kurt Shaped Box 22:02, 7 July 2007 (UTC)

Personally, I'd blame the brine, which probably contributed as much to the flavour as the olives themselves. Confusing Manifestation 09:35, 8 July 2007 (UTC)

This is a common phenomenon, strong flavors are often nasty by themselves, but help to improve the flavor of a meal, once diluted by the rest. Garlic would be another example, not many people enjoy eating garlic cloves straight, but many like a bit added to their meal (excluding vampires, of course). StuRat 07:10, 10 July 2007 (UTC)

RNA/DNA pills

Browsing a local bulk food and health food store, I came to find the vitamin aisle. I was looking to buy a daily vitamin, but a bottle caught my eye. I didn't buy it, nor did I want to/do I think I have a need for it. Out of curiosity, what benefit would it be for someone to take a supplement pill containing DNA and RNA of some random animal or plant? Vitamins and minerals and what not are in foods and other vitamin pills, so what good is the DNA of some other organism? 74.102.89.241 01:08, 7 July 2007 (UTC)

It's not going to be bad for you (we eat DNA & RNA in, well, basically everything.), but a pill of nucleic acids is wasted money. Completely. — Scientizzle 02:26, 7 July 2007 (UTC)

Yep - that's a scam for sure. Every cell of every living thing contains DNA and RNA - every plant or animal you eat (which is indeed pretty much everything) is stuffed full of the stuff. So this stuff is just a scam. They can get away with this because 'food supplements' are not vetted by government agencies like drugs - and notably there is no requirement for them to actually do what they claim to do. SteveBaker 03:01, 7 July 2007 (UTC)

Now you might think, we need more DNA and RNA "building blocks" all the time, for all the new nuclei in all the cells of ours that are dividing, and all the RNA that's being used in expressing metabolic reactions. And you might think, what better place to get those necessary building blocks than from a jar specifically full of the stuff?

However, if you're building new DNA, the essential building blocks are not adenine, guanine, cytosine, and thymine, but rather, carbon, hydrogen, oxygen, and nitrogen -- and we can, of course, get those raw materials from anywhere. [Well, okay, it's not quite that simple, because of course we can't fix our own nitrogen, but the point remains, we construct new DNA from generic organic building materials, not DNA-specific building materials.] —Steve Summit (talk) 03:53, 7 July 2007 (UTC) [augmented 03:58, 7 July 2007 (UTC)]

We don't digest nucleic acids down into the constituent atoms and build them back up when we need them, it is possible for the body to absorb those water-soluble molecules. Also, keep in mind, the molecules used in DNA are also used in other organic reactions in the body. For example, Adenosine is used in nearly every energy transfer cycle your body uses to convert fuel into energy. -- JSBillings 12:26, 7 July 2007 (UTC)

That adenine used to be considered "vitamin B4" is new and interesting to me... — Scientizzle 05:08, 7 July 2007 (UTC)

preventing pregnancy

Last night i made a sex with my girl friend using a condom. However, the condom ruptured while we made sex. We don't have a plan to have a child at this time. What we have to do now inorder to prevent the pregnancy?

Go see a doctor, he'll probably prescribe a morning after pill. - Dammit 07:29, 7 July 2007 (UTC)

And after that, review condom handling instructions. Generally speaking condoms should not break very often if used correctly. --24.147.86.187 11:39, 7 July 2007 (UTC)

That's wise advice - but to emphasise, they DO break occasionally even when used correctly. Our article on the condom says that even if you use them correctly, you still have a 2% per year chance of getting pregnant - and if you don't use them right, the chance is 10 to 18% which is definitely getting a little high! For the "Morning After" pill to work, you need to get to a doctor fast - you don't literally have to get there the next morning - but 72 hours is the utter, utter limit beyond which the doctor should not prescribe them. SteveBaker 13:55, 7 July 2007 (UTC)

But those are statistics over the whole population, and don't tell you about individual odds at all. If you use them right and they are not, say, out of date, then you should have almost no chance for pregnancy at all. A few people who use them wrong and etc. throws the whole sample off. --24.147.86.187 15:25, 7 July 2007 (UTC)

Those stats are probably based on a very large study group. So how would "a few people" throw the data off that much? Dismas|^(talk) 15:32, 7 July 2007 (UTC)

It's hard to see how a few people can cause a 10% to 18% change in the results - wouldn't that have to be 10% to 18% of the people surveyed? If you only surveyed 30 people - then three of them ('a few') could throw it off - but if you surveyed 3000 people then between 300 and 500 would have to have had condom failures in order to get this result - I don't think you can call 300 people "a few" in any reasonable version of reality! SteveBaker 03:32, 9 July 2007 (UTC)

Note that the 2% (for "perfect" use) pregnancy rate doesn't have anything to do with failure or misuse of the condom - I recommend you read the article - paying special attention to the Condom#Causes of failure section. This has nothing to do with a few misusers spoiling the sample - it's just a fact of the way these things work. Anyone using condoms for regular sex needs to be well aware that they don't work 100% of the time. SteveBaker 20:15, 7 July 2007 (UTC)

Vegetarian vs Non-Vegetarian

I have always had this doubt.....People who prefer Non-Vegetarian, are more physically fit, healthy and stronger than people who go for Vegetarian. Is it True ?

With a balanced diet, I don't see how there would be any difference between a vegetarian and non-vegetarian diet. As a matter of fact because vegetarians are more conscious of what they eat and more concerned about their health I think the "average" vegetarian would be more physically fit than the "average" omnivorous people. --antilived^{T | C | G} 10:25, 7 July 2007 (UTC)

Several studies have suggested that vegetarians are healthier. See vegetarian nutrition for more details.--Shantavira|^{feed me} 14:25, 7 July 2007 (UTC)

Heavyweight boxer Peter Hussing is said to have been vegetarian, as well as football legend Stanley Matthews. Unfortunately we don't seem to have a list of famous vegetarians, though we do have a list of vegans which includes several athletes.--Shantavira|^{feed me} 14:34, 7 July 2007 (UTC)

And there are so many versions of vegetarianism, it can be hard to make a direct side-by-side comparison. Nimur 15:50, 7 July 2007 (UTC)

All of the vegetarians I know are so skinny they look like ethiopians. I think vegetarians tend to be less healthy because it is harder to organize a healthy vegetarian diet compared to eating meat and people don't do it right, but if done right it can be more healthy.

Wrong. Vegetarians actually care about their diets, compared to the average meat eater who will shove down whatever they see --_ʇuǝɯɯoɔɐqǝɟ

It's more like the average eater period, not the average meat eater. By restricting one's diet one by nature has some care of what one eats. Someguy1221 06:51, 8 July 2007 (UTC)

Like all diets, a vegetarian diet can be harmful if one does not receive adequate nutrition from it. Many prominent examples show that one can be healthy and eat a strictly vegetarian diet. However, the more one restricts what one will eat, the more likely that nutritional deficits will develop if one is not mindful to such things. This is true for both vegetarians and omnivores (imagine eating nothing but red meat!). There are common potential problem with vegetarian nutrition, such as deficiencies in vitamin B12 or copper, that can be managed either with supplements or explicitly eating plants rich in those nutrients. Our article on veganism, for example, has a large section of precautions for managing such risks. In extreme cases, people have been convicted of child abuse for forcing highly restricted diets on children without concern for the resulting nutritional deficits. So, like many things, a vegetarian diet can be healthy or not depending on how it managed and the details of what one is eating. Dragons flight 20:11, 7 July 2007 (UTC)

Exactly. Vegetarianism is just as healthy as eating meat- which is, if you're reckless, you will hurt yourself. --_ʇuǝɯɯoɔɐqǝɟ 20:19, 7 July 2007 (UTC)

Contrasting Colour Pallette

I have posted this on the Computer reference desk, but I'd like to see what the science-people think...
I am looking for a palette of colours (preferably with their hex codes (eg. 0xFFFFFF)) and they must be CONTRASTING COLOURS so that users can easily distinguish between them.
The highest number of colours I could get was 16 here: List_of_palettes#Microsoft_Windows_default_16-color_palette
I will be using thse colours in a chart, and I need the viewer to be easily able to distinguish the colours. Rfwoolf 16:03, 7 July 2007 (UTC)

• Web colors might be useful. --jpgordon^∇∆∇∆ 17:16, 7 July 2007 (UTC)

You can do this mathematically. If you pick any really bright/vivid colour, and you have the hex representation, you can find the most contrasting colour very easily: Take the six digits in the hex code - break them up into three groups of two digits - then subtract each of the three resulting hex numbers from 0xFF (if you don't have a calculator that can do hex - you might want to convert to decimal notation first!). The result will be the complementary colour. Hence, if you take a bright green (0x00FF00) then the complement is 0xFF00FF - which is magenta. Of course for very subtle colours, such as a very subtle green (0x7F8F7F perhaps), you'll get a very subtle pink (0x807080) as the complement which won't be easy for users to distinguish. For very dark green (0x002000 maybe), you'll get a very bright colour as the complement (0xFFDFFF). SteveBaker 20:09, 7 July 2007 (UTC)

Effects of electricity and magnetism on humans

Are there any known effects that electricity and magnetism may have on human beings' bodies? I've read that magnetism doesn't have any effects on a person, but maybe electricity does? Does it cause cancer or does it have any other effects? Has there ever been any scientific proof of this? ► Adriaan90 ( Talk ♥ Contribs ) ♪♫ 16:58, 7 July 2007 (UTC)

Well, I'm assuming you mean an electric field? Because there are a lot of ways you could interpret "effect of electricity" if you aren't specific! (Toaster in a bathtub?) --24.147.86.187 17:07, 7 July 2007 (UTC)

The effects can be shocking. --Tbeatty 17:17, 7 July 2007 (UTC)

Electric currents, whether direct current, alternating current or radio frequency current passing through human beings can cause burns, can cause traumatic effects on the functioning of the brain (as in electroshock therapy) and can cause death by stopping the heart. It only takes a few milliamperes to cause pain,and a little more can cause the muscles of the hand to contract on a wire and be unable to let go. Magnetic effects on the body are harder to prove. In MRI scans the human body is exposed to extraordinarily high magnetic fields without apparent effects, although there have been some studies which showed effects of magnitic stimulation of the brain on mental states such as depression. For decades there have been assertions that much weaker magnetic and/or electric fields from power lines and from wiring and appliances in the home cause cancer. These effects cannot be immediately and directly demonstrated in the laboratory (in the same way that electric shock can be immediately demonstrated to have an effect). They require large databases looking statistically at whether the rare occurrence of cancer is statistically related to exposure to electromagnetic fields (EMF). The results have sometimes come down as a slight tendency for EMF to cause cancer, and other equally careful studies have found no effect. Several public utility commissions have adopted a philosophy of "prudent avoidance ," which calls for avoiding unnecessary exposure to large EMF, by such means as routing a power distribution line so it does not go next to a school building, when another route is available. This policy in the absence of sound scientific proof of a link between cancer and EMF has been criticized as a waste of resources which could be spent in other ways to reduce illness.[11] If 100 studies are done to see if there is a statistical relationship between X and Y, 5 of the studies should find a significant effect at the usual .05 level, just because of random variation. The evidence is still only suggestive of a link [12] [13] [14] , but evidence suggests a biological effect of powerline frequence EMF or radio frequency EMF is quite possible [15] [16] , that prudent avoidance is justified, and that more research is needed. There should not be any supposition that EMF is the only cancer causing agent, and it should not receive an unjustified portion of public health funding, since exposure to sunlight and pollutants in air, food and water probably cause far more, and failure to use seat belts causes far more deaths per year. In recent years there has also been concern about Mobile phone radiation and health. Clearly there is nothing like the strength of association between Xrays and cancer, or smoking and cancer, or sunlight exposure and cancer. Edison 17:21, 7 July 2007 (UTC)

I agree with Edison - there are a bazillion problems with electric fields and essentially zero with magnetic fields. Just one little addition to that - there was a piece on Mythbusters (gotta love that show for all it's flaws!) that mentioned that old-fashioned tattoos were done with iron-based pigments and that the intense magnetic fields gemerated by an MRI machine could cause a tremendous amount of heating in the ink causing severe burns and such. Modern tattoos generally don't have that problem. SteveBaker 19:59, 7 July 2007 (UTC)

See Transcranial magnetic stimulation for the effect of magnetism on the brain. --Heron 20:34, 7 July 2007 (UTC)

Hey, thanks a lot for all your help. If you have anything to add, please do so! I appreciate all of your help. ► Adriaan90 ( Talk ♥ Contribs ) ♪♫ 21:32, 7 July 2007 (UTC)

There's also this Microwave Auditory Effect, which I believe may be dubious. However, academic peer reviewed papers have investigated it, and an earlier Science Reference Desk query suggested that high intensity electromagnetic waves might have unusual effects. You can also see Active Denial System for a less-lethal electromagnetic weapon. Nimur 03:37, 8 July 2007 (UTC)

I find it interesting that there are a "bazillion problems with electric fields and essentially zero with magnetic fields" when either can induce the other... Aaadddaaammm 04:38, 8 July 2007 (UTC)

Or more accurately a change in each can induce the other. You could also always consider getting hit by a laser beam an effect of electricity and magnetism. Someguy1221 06:10, 8 July 2007 (UTC)

history of emission control standards in automobiles

can i get the details of the various emission control standards set up worldwide chronologically and the organisations which ensure their implementationDeepu rdy 19:28, 7 July 2007 (UTC)

One is the Kyoto Protocol. The Clean Air Acts in various countries also qualify. See Emission standard for more info. StuRat 06:55, 10 July 2007 (UTC)

Voltage drop

I was debugging the network of electric cables in an old caravan and started to wonder if the voltage drops I seemed to have in the cables were reasonable. For example, there is one set of six lights in parallel, using about $5\,\mathrm {W}$ of power each. I connected this set to the $12\,\mathrm {V}$ battery that powers it all, and found that the battery voltage settled on $12.1\,\mathrm {V}$. Then I measured the voltage over one of the lights and got only $8.5\,\mathrm {V}$. :-( Isn't this difference quite large? —Bromskloss 20:07, 7 July 2007 (UTC)

Yes. Your cables are too thin. You are losing nearly 9 watts in them! --Heron 20:26, 7 July 2007 (UTC)

You're right. :-( Is it likely that connections between cables degrade over time (or never were any good) with a large resistance as a consequence? —Bromskloss 20:41, 7 July 2007 (UTC)

That's seems an awfully large drop. If that's true - then you should be able to feel the wires getting warm. But yeah - car lamps do pull quite a bit of current - so heavy wires are required. SteveBaker 20:50, 7 July 2007 (UTC)

It is very likely that the connections do degrade over time and Ill bet that that is where most of your power is being disippated. My advice: clean up/ replace all connectors for full lamp briteness!--Tugjob 22:47, 7 July 2007 (UTC)

If you do the math, the resistance of your cable+connection is 2 ohms. The lights in parallel are about 4 ohms (28 ohms each). --Tbeatty 15:29, 8 July 2007 (UTC)

The voltage drop sounds way too high, if the battery was in fact still putting out 12 volts. In an old rustbucket car the ground connection from a light can also corrode and cause a voltage drop. It is common to carry wires from the battery positive through switches to a terminal of a bulb, and to achieve the other battery connection through the car body. If there is a lot of rust around the light, the resistance may be in the negative return path. On really old cars, the polarity was sometimes reversed. A supplemental ground connection can sometimes help. In troubleshooting, you can also start at the bulb terminal where you see 8.5 volts to the battery negative, and check the voltage at points further back (closer to the battery positive) to see where the voltage drop is. Of course you should not tinker with electricity unless you are fully conversant with safety procedures. Edison 19:06, 8 July 2007 (UTC)

July 8

RPM and car control

Why does downshifting, and running your engine at a higher RPM give you more steering control of the car?

Does it? I don't see why it would. Is it something you have actually experienced yourself? —Bromskloss 11:06, 8 July 2007 (UTC)

It gives you greater control over the speed of your car - engine braking means you can slow down just by lifting your foot off the accelerator. A slower speed then gives you more steering control. Gandalf61 12:45, 8 July 2007 (UTC)

Your power steering pump is incorrectly producing more hydraulic pressure at higher RPM? Generally, systems are designed to either produce a steady pressure or, often, less pressure at high speed when there's less need to overcome the enormous static friction of tires when you're stopped.

Atlant 14:05, 8 July 2007 (UTC)

Also, by slowing down, your car will 'dive', putting more weight on the front wheels, so they are less likely to slip.

It sure does feel like it, doesn't it? I suspect, however, that it is just an illusion from aforementioned control over speed and improved control at lower speeds. Properly done, the downshift also puts you well into the "preferred" (there is almost certainly a proper term for this, but I do not know it) range for the engine, where it can supply plenty of power and either accelerate or decelerate while maintaining responsiveness. There is a related argument for not dropping into neutral to coast down hills, but that is more about maintaining control of you speed. With the engine engaged, even in a high gear, your acceleration will be slower, providing more control. Furthermore, there is also the quality of life issue - accelerating around turns is just plain fun. -Eldereft 21:40, 8 July 2007 (UTC)

Race drivers and drifting and autocross enthusiasts most certainly do rely on the 'weight transfer' (terrible choice of words!) effect of braking to get more down-force (and therefore more grip) at the front wheels - and they sometimes to deliberately weaken the grip at the back. That certainly has an effect on steering because it allows you to turn sharper without the front wheels skidding and/or to allow the rear wheels to 'drift' outwards and thereby induce over-steer. This is also beneficial for front wheel drive cars in that you have a brief window of opportunity for stamping on the gas and getting more accelleration without wheel-spin (a major reason why I love front wheel drive cars - and loath rear wheel drive cars!). But that's only going to be noticable at extremes of driving when you'd probably skid off the road entirely if you hadn't done that. Stamping on the brakes also causes weight transfer - and heel/toe driving where the gas and brake are operated together can take advantage of this. For ordinary street driving, I'd be surprised if this effect was anything other than an illusion. SteveBaker 03:24, 9 July 2007 (UTC)

Wet Hair

What could happen to you if you sleep with wet hair? Thanks in advance.

Your pillow gets damp. DuncanHill 12:40, 8 July 2007 (UTC)

...and you wake up with *really* messy hair. --Kurt Shaped Box 12:49, 8 July 2007 (UTC)

Off-topic joke posts.

And the hair fairy gets herpes. 12:51, 8 July 2007 (UTC)

I have hidden this anonymous comment. See the Reference Desk guidelines. Nimur 18:10, 8 July 2007 (UTC)

In hot humid weather, the hair and/or pillow might mildew. Edison 19:00, 8 July 2007 (UTC)

My mother used to tell me that going to bed with wet hair would give me a chill (or something).

My cat won't sleep on my bed when I have wet hair. Weird thing. JoshHolloway 22:32, 8 July 2007 (UTC)

My wife picked up a variety of "wet" superstitions from her mom, including one that going to bed with wet hair would make her sick and/or was a generically "bad" thing to do. So far as I can tell, it just makes your hair really messy the next day. And, just to close my initial anecdote, she also was told that wetness caused by rain was much more likely to make you sick than wetness caused by, say, a shower. So, if she got wet from the rain, she was expected to take a brief shower to get rid of the "bad wet" and replace it with, I dunno, "good wet". (Insert punchline here). Matt Deres 23:28, 11 July 2007 (UTC)

science / jupiters moons

how do jupiters moons stay in orbit around jupiter?

See orbit. Gdr 11:53, 8 July 2007 (UTC)

Re:Lucid dreaming

Does lucid dreaming make you exhausted? And how do you actually invoke that dream? -Zacharycrimsonwolf 14:18, 8 July 2007 (UTC)

Lucid dreaming has a lot of interesting information, including how to initiate one, though I didn't see anything on whether the quality of sleep is lower. Someguy1221 16:17, 8 July 2007 (UTC)

Zachary, check out Wikibooks, one of our sister projects, they have a rather good guide to it. Also see ld4all.com, a good Lucid Dreaming community site. As far as making you exhausted- no, not at all. Well, it could be mentally draining, but it doesn't affect your sleep at all. Like, if you have a lucid nightmare, you could very well be out of it the next day like you hadn't slept well, but in general no. Lucid Dreaming takes place during REM sleep, which is what really counts anyway, so you will be just as rested in the morning as you did when you fell asleep. Unless of course your dream is a nightmare which causes you to wake yourself up, but most lucid dreams aren't nightmares unless you want them to be. --L^augh! 19:22, 8 July 2007 (UTC)

Ah. Okay. Thank you, but it'll probably take a long time for me to try to do it. Cheers!! -Zacharycrimsonwolf 09:27, 9 July 2007 (UTC)

One small step for man, one giant leap for mankind

I know who said it! But who wrote it? Armstong or NASA PR?

Thanks for any help.

The article on Neil Armstrong and a cited reference say that he came up with it an hour or two before saying it. Weregerbil 14:39, 8 July 2007 (UTC)

I believe it was recently corrected to be "One small step for a man, one giant leap for mankind." The a is inaudible in the original. --Tbeatty 15:15, 8 July 2007 (UTC)

Thank you all for your help. But...do you really think NASA and the government would have let him go up without first deciding on what to say on an occasion they knew would be historic?

In a sense, that particular "instant" became historic because that was the moment of most memorable dramatic effect after the fact. That's sort of hindsight analysis, though. Many historic first "instants" occurred during the entire mission - the first time a spacecraft touched down on the moon was marked with the (less memorable?) quip, "The Eagle has landed." NASA would have a hard time pre-planning every single historic occurrence and it's sort of arbitrary that the first "step" is any more historically important than the first "breath" or first "landing," or first golf game. Nimur 18:04, 8 July 2007 (UTC)

In recent bios of Armstrong, he says that he made this up not long before the landing. See First Man by James Hansen (2005) and One Giant Leap by Leon Wagener (2004). I don't have the books right here, but I read them not too long ago. As I recall Armstrong says that he planned to say "one small step for a man" (which makes more sense), but accidentally omitted the "a" when he actually stepped on the surface of the moon. So the first version "one small step for man" is correct.--Eriastrum 18:17, 8 July 2007 (UTC)

He has at various times said that he either was or was not aware of having omitted the 'a' - to be honest, I doubt that he knows - after all, he knows for sure that he INTENDED there to be an 'a' in there - it makes no sense without it. There is information out on the Internet someplace (I really can't be bothered to track it down) that says that very careful analysis of the available recordings show that he did say "a" - but something related to the fans and such in the suit masked it out. Something like that. The bottom line is that the odds are extremely good that he DID say "One small step for a man, one giant leap for mankind." - and that's without doubt what he intended to say. SteveBaker 20:41, 8 July 2007 (UTC)

And here’s a source from the BBC to prove it. S.dedalus 06:07, 9 July 2007 (UTC)

Has anyone ever heard of this fish disease?

I've been trying to assess and clean up the vet med articles here on wikipedia, and I ran across Rotting nose disease. I can not find anything on a google search about this disease that is not wikipedia-derived, or about its potential cause, a type of protozoa called Ocimita. I've also tried a few variations in the spelling of Ocimita, but with no luck. The symptoms and treatment of rotting nose disease seem remarkably similar to hole in the head disease, making me think that it is someone's made up name for the same disease. Before I proceed with any type of deletion effort, I wanted to see if anyone had heard of this disease or the elusive Ocimita species that may or may not cause it. --Joelmills 16:36, 8 July 2007 (UTC)

Sounds like either a hoax or a good faith duplicate of HITH. Either way, it should be prodded. Rockpocket 01:08, 9 July 2007 (UTC)

Perhaps not, Rockpocket. I believe that it could be a redundant article about Hole in the head disease or it could be Head & Lateral Line Erosion Disease [17][18][19]. The problem with common names for these diseases is that confusion is bound to appear between fish keepers living in different parts of the English speaking world. I suggest you inquire at Wikipedia talk:WikiProject Aquarium Fishes before nominating the page for AfD. S.dedalus 05:41, 9 July 2007 (UTC)

RTD is certainly fake; there's no record of the offending protozoan anywhere and there's no grasp of science patent in the article. HITH is very real. Bendž|Ť 17:12, 9 July 2007 (UTC)

Thanks for the responses. I think S. dedalus may have found the basis for this article with head and lateral line erosion disease, especially since the first EL give the possible protozoan cause as Octomita. However, I see someone already put it up as an AfD, and I'm not going to contest it. It's presence has not prevented anyone from creating a head and lateral line erosion disease article, since searching for that would certainly not lead you to rotting nose disease. --Joelmills 02:08, 10 July 2007 (UTC)

Question concerning Fourier

In Heat conduction there's a chapter called Conductance. In this section, there's an alternative statement of Fourier's law. In fact, I couldn't find this statement anywhere else in the internet. I wonder, whether it is true, I would need it for a paper. Could anybody please check this law? Lskywalker 18:20, 8 July 2007 (UTC)

If it is true, it's very badly written. None of the symbols he's chosen (apart from 'U') are defined. My text books on this subject are 180 miles away - I won't be able to check on it until late tonight or tomorrow. SteveBaker 18:34, 8 July 2007 (UTC)

Well, all the symbols are defined above (A, Δx, ΔT are defined, k is standard). I use other's, too, but I think that would be ok. But it would be great if you could look it up. Lskywalker 18:39, 8 July 2007 (UTC)

The problem is that in the lead section, the symbol Q is used to denote thermal energy transfered (in Joules), but in the following sections the same symbol Q is used to mean energy transfer rate (in Watts). That is an error and should be corrected. Apart from that, the alternative statement of the law is the same as the integrated form of the law stated earlier, but with the definition of U substituted in. --169.230.94.28 18:59, 8 July 2007 (UTC)

Error in myeloid article?

The myeloid article says: In describing hematopoiesis, the terms "myeloid" and "lymphoid" are often used to discriminate between cells originating from the marrow and from lymph tissue, respectively. - but this doesn't make sense because lymphoid cells originiate from the bone marrow (where B cells mature while T cells mature in the lymph nodes). Should someone correct the article? --Seans Potato Business 19:33, 8 July 2007 (UTC)

Black hole production

Is it possible to produce a BH on earth using current technology? If we did produce one, how would we control it?

(a) No. No chance, not even close. (b) In principle, we could feed it some electrons to charge it up, and suspend it in a vacuum chamber using electric fields. We would have to do that at the same time as we created it. Making one would be a really bad idea, however, because the first time some klutz dropped it, the black hole would fall into the Earth and start slowly engulfing it. To avoid turning our whole planet, and ourselves, into a black hole, we would be forced to keep this electric-field trap setup in continuous glitch-free operation forever, or try to get rid of the darned thing by launching it into space. --169.230.94.28 20:32, 8 July 2007 (UTC)

Correction to (a): In some non-standard theories, it is conceivable that tiny black holes could be produced in particle accelerators. These, however, would evaporate through Hawking radiation faster than they could accrete new mass, and would therefore disappear in a fraction of a second. The European particle physics lab CERN has done a safety study on this, which concluded "We find no basis for any conceivable threat." --169.230.94.28 21:03, 8 July 2007 (UTC)

There was some discussion about whether RHIC could produce a black hole which might then eat the Earth, but it was decided that it was unlikely and the collider was allowed to operate.

Atlant 20:56, 8 July 2007 (UTC)

The answer to the first question is 'very probably not'. There are some variants of string theory (and some more exotic physics models) that suggest that creating micro black holes might be just within the reach of our largest existing or planned particle accelerators. Note that such black holes, if created, would have a very short lifetime—talking about storing or controlling one wouldn't be meaningful. TenOfAllTrades(talk) 20:58, 8 July 2007 (UTC)

Night sky

I´m looking in the southern direction and in front of me there is a particularly bright planet (? - I think) not far above the horizon (about 45º up). What is it? Thanks. --AlexSuricata 20:35, 8 July 2007 (UTC)

Where are you, and what time is it? (Or rather, when did you observe this planet?)

If you're looking at a point on or near the ecliptic and it's not too long after sunset, then Venus should be about 40 degrees above the horizon and very bright: [20]. Jupiter is also high and bright right now, thought not as bright as Venus. TenOfAllTrades(talk) 21:12, 8 July 2007 (UTC)

I´m in Andalucía and it´s 23:45, if you look south but at little towards south-west, and then up about 40º up above the horizon - it´s very bright, is it Venus then? --AlexSuricata 21:57, 8 July 2007 (UTC)

I think that you are probably seeing Jupiter. Venus is usually closer to the horizon unless it is close to sunset. There are a number of websites that will automatically generate a skymap given your location and time; here's one: [21]. TenOfAllTrades(talk) 22:16, 8 July 2007 (UTC)

Yep, it must be Jupiter. Great link btw - thanks! --AlexSuricata 22:26, 8 July 2007 (UTC)

Cleaning pen from whiteboard

What would remove felt-tip pen from a whiteboard? DuncanHill 21:39, 8 July 2007 (UTC)

Methylated spirits or alcohol on a paper towel, or use a normal whiteboard marker to scribble over the top and then rub that off. GB 21:46, 8 July 2007 (UTC)

Isopropanol (isopropyl alcohol) will also work; it's sold as 'rubbing alcohol' in the drugstore. TenOfAllTrades(talk) 21:52, 8 July 2007 (UTC)

Acetone has worked for me for permanent markers; it is a pretty common gentle solvent. If you are at a school, the chemistry department almost certainly has some. Failing that, many nail polish removers are acetone-based. If you are not at a school, ethanol is another readily available solvent. Actually your friendly neighborhood chemists probably have some of this too, though perhaps not in the form I just linked. -Eldereft 21:54, 8 July 2007 (UTC)

I tried meths already - no joy. I'll get some acetone tomorrow and try that. DuncanHill 21:55, 8 July 2007 (UTC)

Try using a normal whiteboard market to scribble over the top and then rub it off, as GB suggested :). Has worked every time in the past for me JoshHolloway 22:29, 8 July 2007 (UTC)

Thanks - never thought of that before! DuncanHill 22:31, 8 July 2007 (UTC)

Here's a comparative test of a bunch of different cleaning options and techniques. A word of caution about acetone, though—I'd test it on a small area in the corner of the board before you go crazy with it, because it might damage the surface. Acetone also dissolves many plastics and synthetics, so be careful how you handle it. TenOfAllTrades(talk) 23:05, 8 July 2007 (UTC)

I don't think I would call acetone a "mild" or "gentle" solvent - I've seen it dissolve some pretty dense plastics! It's selective about what it will react with and dissolve, but it will probably take the ink off the board. Test on a corner to make sure it doesn't take the board down with it (more realistically, the worst it would probably do is just destroy the glossy finish, but who knows what variant of "standard" whiteboard material you have on hand...). Nimur 00:57, 9 July 2007 (UTC)

Ok, gentle is relative - it is no hydrofluoric acid, but you still should not bathe in it. It is *always* worthwhile to read the MSDS and be aware of potential reactions and hazards. Respect, but do not fear. -Eldereft 09:39, 11 July 2007 (UTC)

If all else fails, fire will cleanse your board. Forever. --Tbeatty 01:49, 9 July 2007 (UTC)

I had a whiteboard that someone wrote on once with a permanent marker, and a commercial whiteboard-cleaning product didn't remove the mark at all... but ordinary dishwashing liquid, that we used in the kitchen sink, did. Of course everything depends on the particular ink formulation. --Anonymous, July 9, 2007, 03:01 (UTC).

Are you talking about dry-erase markers scribbles that have been left too long on the board and baked themselves in to the point where you can't get them off? Or are you talking about the situation where someone brought a permenant marker - and wrote on the board mistaking it for a dry-erase marker? In the former case, I would definitely go and buy a bottle of whiteboard cleaner - most office supply companies have them and they work very well - they aren't generally too much of a health hazard - and it's worth keeping some in your desk drawer because this does happen quite a lot. In the latter case - you'd need to resort to some stronger chemicals - and all kinds of organic solvents are worth trying. Acetone and Isopropyl alcohol would be good things to try. However, many of those are dangerous - so beware! Vodka works moderately well in an emergency with at least one brand of permenant marker. (you don't want to know how I found this out!). SteveBaker 03:06, 9 July 2007 (UTC)

I said a permanent marker and I meant a permanent marker. It was a visiting child who didn't know the difference between permanent and dry-erase markers. I don't say that other whiteboard-cleaning products wouldn't have worked, but the one I tried didn't. I don't remember further specifics. --Anon, July 9, 22:44 (UTC).

It was a felt-tip pen (the sort that children use - I know, because it was me wot done it, I was in a foul mood because 1) I had just been cleaning chewing gum off the Scout Hut floor, and 2) someone had nicked the whiteboard pen). Forgot to get any acetone today, but to date I've tried Meths (very slight effect), n-hexane (very slight effect), white spirit (no effect whatsoever), and writing over it with a whiteboard pen and then rubbing off (no discernible effect). DuncanHill 22:50, 9 July 2007 (UTC)

Interesting whiteboard actually briefly mentions a lot of the suggestions. BTW, this is probably a dumb suggestion but if it's a felt-tip pen, did you try water? If you have the pen, try and find out from the brand etc what solvent it contains (I would have thought it water based though!)? I'm actually a bit surprised it's so hard to get off. I thought those kind of pens are usually supposed to be washable and fairly easy to remove given their target market Nil Einne 23:40, 10 July 2007 (UTC)

Supposing that we were to accidentally create a black hole on earth...

What would an observer on the ground actually see during the minutes before the whole planet was torn apart and consumed? I remember seeing a dramatization of the event on some 'end of the world'-type documentary some time ago. As I recall, everything within thousands of miles of 'ground zero' immediately ignited, then collapsed into a swirling vortex of energy within seconds (with the BH at the centre). All over the rest of the world, gigantic thunderstorms raged, winds of several hundred mph battered the surface and the horizon glowed white. --Kurt Shaped Box 22:27, 8 July 2007 (UTC)

What one sees would depend a lot on the mass. A very low mass black hole, which would presumably be the only kind we might "accidentally" create, would evaporate via Hawking radiation and pose no threat to the Earth. You see some sort of flash as it disintegrated, if you were looking at it. The other issue is that even Earth mass black holes would be very small. The Schwartzschild radius of the Earth is ~1 cm. At that size, and even if you could feed it would a continous stream of matter moving near the speed of light, it would take ~100 million years to force a volume the size of the Earth to fit through a surface area as small as the event horizon of the black hole. A micromass blackhole, i.e. something say the mass of a mountain, could well take longer than the remaining life of the solar system to eat the Earth. In other words, you might not see much of anything in your lifetime. Dragons flight 23:00, 8 July 2007 (UTC)

Depends on the mass of the thing. Look at it like this: The gravity field of a black hole is no stronger than the thing it's made of.

So I guess the worst case would be if we took the largest thing we can imagine that's handy and nearby - suppose we could take the entire moon and maybe "accidentally" turn it into a black hole using who-knows-what weird science (tsk, tsk - these scientist are so careless!). Well, that wouldn't do much - the moon-sized black hole would continue to orbit the earth - suckinging in microscopic amounts of gas...we'd hardly even notice! But I guess we're asking about a black hole on the surface of the earth. If the moon-sized hole were somehow brought to the surface of the earth...now THAT would be the kind of apocalypse you have in mind. The black hole would have the same gravity as the moon - except you could get much closer to it than you can get to the real moon. The moon has a radius of 1700km - so at 1700km from the black hole, it would be attracting with the force of 1/6th of a g - enough to collapse buildings maybe - but not directly dangerous. At 800km, we're up to 2/3rd of a g, at 400km, we're looking at 2.6g, at 200km, 10g, at 100km, 40g...there isn't much that can withstand a force of 40g - so the hole that a moon-sized black hole would immediately dig would be a few hundred kilometers across! Since nothing can support a moon-sized black hole - it would immediately fall towards the center of the earth - it would fall towards the center of our planet - gaining speed as it did it - then oscillate back and fourth within the earth carving out massive tunnels. The planet would rapidly hollow out from the inside out until the mantle would not be strong enough to support the weight - then the earth would collapse inwards - all in slow motion. It would take a long time to fall that far!

But for a much smaller black hole, nothing much would happen. If you took 1000kg of matter and made a 1000kg black hole - it wouldn't exert any measurable g-force at one meter - you car weighs more than that - and it doesn't exert much gravity a meter away! The hole it would burrow in the earth might only be a tiny fraction of a millimeter across. It would still fall to the center of the earth - probably weighing a little more by the time it got there. But then it might eat out a hollow area in the middle a few centimeters across - but it's gravity would be pretty pathetic - but it's not exerting enough force on the earth's liquid iron core to excavate a huge cave - it might take thousands or millions of years for it to accumulate enough mass to be really dangerous to us.

If you made a black hole out of 1kg of stuff - the hole it would drill might be of the order of the diameter of an atom - at which point you wouldn't ever know it was there.

SteveBaker 23:27, 8 July 2007 (UTC)

Really? I smell original research.... Nimur 00:51, 9 July 2007 (UTC)

That moon mass black hole is only 200 microns across. While 40g may seem like a lot, it's not really from a structural prospective, it would take ~3000g to pull apart a 1 m^3 slab of rock with a typical yield stress of 100 MPa, further the ability to pull things apart depends of the difference in force between the two ends on object. The end result is that you have to be within 500 m to break rock, and much much closer to actually be consumed because of the very small surface area. Dragons flight 00:37, 9 July 2007 (UTC)

In total, there is not enough experimental evidence with close-up black holes to say for sure with any kind of certainty. There's going to be lots of speculation, artistic license, and mishmash theories of classical and quantum and relativistic effects; but since we have no prior experience it is all speculation (no matter how rigorous the math may be, who knows if our models would break down in unforeseen ways?) Nimur 00:54, 9 July 2007 (UTC)

Thanks for all your answers, guys - interesting reading. I appreciate the time you must've taken to figure all that out. So, is there any scientific substance to the oft-seen-in-scifi 'shockwave' that is formed when matter (be it a star, planet or the drive of a spacecraft) is forced to collapse down into a black hole? What the hell is that supposed to be anyway (other than a convenient method of destroying the entire alien fleet)? --Kurt Shaped Box 05:08, 9 July 2007 (UTC)

Let's say it's not entirely unfounded. The reason a star collapses is because it requires less energy to be scrunched up as small as possible, and things tend to want to be in the lowest energy state possible (big simplifications and lies to children here, but a reasonable approximation). For most matter, though, the force causing the matter to collapse is counteracted by other forces - the normal electromagnetic repulsion between atoms, the pressure of expelled photons in the case of a star, and Fermi energy / "degeneracy pressure" when you get to white dwarves and smaller. When the matter finally collapses into a black hole, the excess energy gets expelled quite violently. It's possible (and in the case of stars, pretty much de rigeur) for an inner core of matter to collapse into a black hole, and the surrounding matter to get blasted out in a big shockwave. Whether this happens when you reverse the polarity on your photon drive is another question entirely. Confusing Manifestation 06:32, 9 July 2007 (UTC)

Expanding on SteveBaker's answer, if we assume a microscopic black hole, starting from rest at the surface of the Earth and experiencing no friction, then it will describe simple harmonic motion about the centre of the Earth, with a period of about 84 minutes - see here. So it takes a quarter of a period - about 21 minutes - to reach the centre of the Earth. Which is quicker than I thought it would be. The actual path traced by the black hole relative to a fixed point on the surface of the Earth will be some sort of complicated 3D rosette, due to the Earth's rotation. Gandalf61 08:52, 9 July 2007 (UTC)

A moon sized black hole would produce very little spaghettification (imagine a piece of plasticine or blue tack being stretched unevenly - now imagine the plasticine is a car or a building!) at any reasonable distance; given that rock breaks at 100 megapascals, in order to shatter the 1 metre cube, it would have to placed closer than 500 metres to the black hole (back of envelope). Laïka 22:36, 9 July 2007 (UTC)

Yeah - the tidal effects of the moon couldn't pull a rock apart at those kinds of distances - but for sure it could bodily rip it out of the ground and suck it in in one big lump if it's close enough. If that's not convincing enough to you - think about the oceans. If they are experiencing 1g downwards from the earth and 1/6th of a g sideways because the black hole/moon has just been formed in a lab on the coast 1700 kilometers away - then it's going to be like the ocean was suddenly sloping at an angle of maybe 10 or 20 degrees to the "vertical" (I'm too tired to work it out the exact angle - sorry!) - so ALL of that water will immediately rush "downhill" towards the black hole with speeds and violence that would make a normal tsunami look like a ripple in pond by comparison! All of the water on the earth would rush towards the black hole - but the hole is by now falling (with a 1g+ accelleration) whilst burrowing a large hole through the earth as it goes. Of course the atmosphere would do the same thing - so there would be violent winds - and depressurization of areas even quite far from the hole. Of course the black hole itself isn't going to stay there because it's falling through the earth - eating out a tunnel as it goes. Worse still, the earth's spin is going to be wildly destabilised by the abrupt appearance of this large mass on one side of the planet. The end would be rapid and spectacularly violent - I'd guess that people living a long way from the hole might survive a few minutes - but they're gone for sure in an hour. As the black hole 'eats' things - it'll be emitting hard gamma and X-ray radiation - that's no fun either.

I think the important message here is NOT that a black hole is automatically a death dealing monster - it's pretty clear that small black holes are harmless - and (as others have explained) will eventually evaporate due to Hawkins radiation. No the message is that if something with a lot of gravity ends up someplace where it's not supposed to be - the damage will be unimaginable. A moon-massed black hole would hardly be less damaging than a moon-massed lump of moonrock - or a moon-massed bag of feathers - gravity is gravity. SteveBaker 01:22, 10 July 2007 (UTC)

You may want to check out Large Hadron Collider#Safety concerns and work your way from there. This sort of accidental black hole theory (and other catastrophic events) has been consider re:the LHC and I believe other particle colliders. The majority think the probability of any catastrophic event occuring are extremely remove for a variety of reasons. But there is a minority which thinks that the risks need to be considered better. Nil Einne 23:46, 10 July 2007 (UTC)

I have to pass on a story that shows similar 'issues' to the accidental creation of a dangerous black hole. When I worked at Philips Research labs in Surrey, England they worked in a building - part of which went back to around the 1930's. That was the time of Ernest Rutherford et al. Early days for theories of the atom. They had been smashing particles together following Rutherfords lead and later got into the atom smashing craze. However, it was clear that since they were doing research - they had no idea what would happen as a result of some of these experiments. They wondered whether widespread - or even apocalyptic - destruction might ensue. Rather than not do the experiment, they opted to dig a 20' deep basement, line it with a foot of concrete and had a motorized foot-thick slab of concrete that slid over the entrance stairwell to block it while experiments were going on. All of that was still there in the glass-blowing workshop as late as the 1980's. But what amazes me was that they had NO IDEA what would happen - and yet still went ahead with it. They clearly weren't at all certain that nothing would happen - or they wouldn't have bothered with all the concrete. It's very interesting to muse about their motives and expectations! SteveBaker 00:36, 11 July 2007 (UTC)

I once remember seeing a documentary on the Discovery Channel (so take it with that proviso) about the Manhattan Project where it was stated that some of the scientists involved had serious concerns that detonating an atomic bomb would initiate an unstoppable chain reaction that would 'burn off' the earth's atmosphere! Apparently, at the Trinity test, there was more than one person crossing his fingers that the device wouldn't work *too well*. --Kurt Shaped Box 00:58, 11 July 2007 (UTC)

I sometimes like to muse to myself that any 'unforeseen incident' that leads to the unleashing of 'forces beyond our control' and 'that which cannot be undone' may be the one thing that finally gives us a definitive answer to the question of the existence of a higher power. Sitting back as a neutral observer and leaving us to exercise our free will and make our mistakes is one thing - but what happens when we perform an action (i.e. accidentally obliterating the planet, killing everyone and everything through bad science) that interferes directly with His grand design for us? Now *that* is when I'd expect to see intervention... :) --Kurt Shaped Box 01:21, 11 July 2007 (UTC)

I thought what we had to worry about was Quarks or something, tearing the planet apart? But then, I was more paying attention to the large banks of computers in the background than what duh science man sed. --L^augh! 12:58, 12 July 2007 (UTC)

I think you're thinking about Quantum vacuum collapse... http://www.exitmundi.nl/vacuum.htm ...yeah - don't do that. That would be "A Bad Thing". This article has several similar dire warnings from one scientist to another: http://www.kressworks.com/Science/A_black_hole_ate_my_planet.htm SteveBaker 14:37, 12 July 2007 (UTC)

An insect to identify

File:Insect to be identified.jpg

What is this?

Butterflies have two pairs of large wings, dragonflies two pairs of equal-sized slender, transparant wings. At the banks of the Soča river, near Bovec, Slovenia, I have seen several of the beautifully coloured kind of insect depicted to the right. It has dark blue-black wings with white spots, slender like a draginfly's, but seemingly only one pair. The body has a prominently yellow-coloured ring, and I think that I've seen one with an additional blue ring. What is this? TIA. Simon A. 22:48, 8 July 2007 (UTC)

The rear wings are simply smaller; you can just make out their outline, and this is a day flying moth, Syntomis phegea, family Ctenuchidae (syn. Syntomidae). There's not much on here in wp, but googling gets you plenty. Bendž|Ť 17:34, 9 July 2007 (UTC)

P.S. we could use the photo in an article if you rename it. Bendž|Ť 17:37, 9 July 2007 (UTC)

Thanks, Bendž. It's a pity that the vacation is aleady over; otherwise I could now check out the seperation between the fore- and hindwings when used in flight. But if I think of it: the wings of butterflies also merge into each other, so that the division gets hard to make out. Say, how have you figured out the species? Did you just happen to know, is it common where you live, or could you recognize the family from general features and then used a classification book? For the picture: Go ahead and use it. How do I rename it? Or should I move it to Wikimedia Commons? Simon A. 06:03, 10 July 2007 (UTC)

Just googled for it and the Dutch Wikipedia has a pretty nice picture, nl:Melkdrupje. Simon A. 06:05, 10 July 2007 (UTC)

It is the most common species of the family but we don't get them in Britain so I didn't know it. No, I simply opened my Collin's field guide on the plate with its picture. A case for wikipedia as the product of infinite monkeys. Bendž|Ť 09:36, 11 July 2007 (UTC)

Butterfly with spotted compound eyes

A butterfly with spotes in its compound eyes

In the hope that my previous question already caught the idea of any professional or amateur entomologists roaming the Reference Desk, I ask a second one: I took the photo to the right at more or less the same location, again at the banks of the Soča near Bovec, Slovenia. When looking at the photo on my computer screen at maximum zoom, I was amazed to note a funny detail: The wings' colouring pattern, dark brown markings on amber background, seems to continue onto the butterfly's compound eyes. Two questions arise: (a) Is it common for butterflies to have coloure eyes? (ii) Given that wing colours are produced by scales tinted by thin film interference or pigments, how can a compund eye have the same colours although it does not have scales? Simon A. 23:24, 8 July 2007 (UTC)

Insects can produce pigments in their eyes, just like anywhere else. See the image at Drosophila_melanogaster#Model_organism_in_genetics for some variations of eye pigmentation in fruitflies, for example. --mglg_(talk) 03:51, 9 July 2007 (UTC)

Good point, thanks. Simon A. 15:30, 10 July 2007 (UTC)

July 9

Political views of Scientists

Obviously scientists (defining scientist however you want) have a broad range of political beliefs. However taking all scientists, how do you think their views compare to the general public in their country. ie More conservative or liberal in social policy?, more left wing or right wing economically? More religious or aethiest than the general public? etc.

Over the earth or over first world countries?

I'll presume you mean the U.S. and PhD scientists. More liberal in social policy. More capitalist economically. More religious than the general public. --Tbeatty 01:57, 9 July 2007 (UTC)

Presume the U.S if thats where you are Willy turner 02:19, 9 July 2007 (UTC)

Of course you should use a scientific approach regarding the answer to this question! Note the distinction between correlation and causation. Also note the exceptions to the general trends. And finally, evaluate whether your initial criteria are valid to begin with (is "liberal/conservative" a good way to measure political affiliation and belief?) Nimur 02:03, 9 July 2007 (UTC)

liberal/conservative is one way. feel free to answer the question with regards to any other measure of political beliefs you like Willy turner 02:19, 9 July 2007 (UTC)

I would vote for less religious than the general public. More sceptical of everything. Aaadddaaammm 02:05, 9 July 2007 (UTC)

Surveys support your view, with practitioners in the "hard sciences" being far less religious than the claims of (at least) the American public at large.

Atlant 16:49, 9 July 2007 (UTC)

Thats what i would have thought. Willy turner 02:08, 9 July 2007 (UTC)

In fact, it is fairly well established that US scientists are much less religious than the general US public, and that this difference becomes dramatic if one restricts the comparison to those top scientists that are members of the National Academy of Science. 169.230.94.28 02:17, 9 July 2007 (UTC)

One thing that is distinctive about good scientists is that they have open minds until they see proof. This tends to make conventional political distinctions hard for them to make. Democrat/Republican, Left wing/Right wing...these are statements of a belief in a bundle of policies. To pick two issues at random - traditionally, in the USA, Republicans are anti-abortion and pro-guns - Democrats are pro-abortion and anti-guns. A scientist can't simply fall into one demographic or the other. A scientist has to examine the issues - and may well decide that they are pro-abortion and pro-guns (for example). Taken over dozens of issues, this will result in someone who probably sides mostly with the views of one side - but may be very extreme on the opposite side for other views. On the whole, I think most scientists tend to be "left of center" in a majority of their views, wildly leftist on others and wildly rightist on yet others. The whole idea of "joining a club and mindlessly promoting all of their views" is an anathema to most of us. SteveBaker 02:53, 9 July 2007 (UTC)

Spot on, SteveBaker. Well summarized. Nimur 18:45, 9 July 2007 (UTC)

If the interface of science and politics is something that interests you, Chris Mooney's The Republican War on Science is an essential read (or just wait for the upcoming documentary). As SteveBaker says, scientists tend to be less ideological than the average member of the electorate, and thus harder to pigeonhole in such broad strokes. So while scientists, as a group, are probably on average somewhere left-of-centre on their personal politics, the perception as scientists as overwhelmingly and actively liberal is no more than a political tactic. Indeed, painting politically unconvenient research as junk science and policy friendly research (usually from industry) as sound science has become remarkable common in the US, and is extensively by the Bush administration to justify forming policy against the scientific consensus. Indeed Karl Rove sums this up best with his definition of a Democrat as, "somebody with a doctorate." Rockpocket 03:26, 9 July 2007 (UTC)

On the other hand Newt Gingrich is an advocate of increased federal funding for basic science research. I have heard him on NPR and he sounds genuine about this issue. Rove really said that quote? :eyes rolling: David D. (Talk) 03:32, 9 July 2007 (UTC)

A bit of an aside, but an interesting one all the same, Mooney addresses Gingrich in Chapter 5 and acknowledges,

... Gingrich presents a condundrum. On one hand [he] presided over an era of stunning congressional science abuse. And yet Gingrich is no anti-intellectual rube. Far from it: he holds a PhD, taught environmental studies and has a reputation as a science fiction fan and ardent technophile.

Indeed since leaving congress he has actually proposed tripling NSF funding. But despite that he set the stage for the politicization of science in modern US politics by dismantling the Office of Technology Assessment, which used to provide objective analysis of scientific and technical issues for Congress. The OTA was a agency of stellar international repute. When it was trashed Lord Kennet commented that "the leading technological state in the world should have abolished its own main means of democratic assessment left us [The British] aghast." So why did Gingrich dismantle it? So he could bring in his own "experts" that provided the requisite analysis that backed up their preferred policy. For example, in 1995 the Gingrich Congress heard "scientific integrity" hearings into whether CFC's were linked to stratospheric ozone depletion. By then the scientific consensus was all but unanimous in accepting this (infact later that year Mario Molina and Sherwood Rowland received the Nobel Prize for their work in demonstrating it). Who did Gingrich bring in to provide "objective analysis of scientific and technical issues" in place of the OTA? Fred Singer and Sallie Baliunas, two of the few high profile skepticsof global warming. So Gingrich's Congress was pretty much the architect of a free market for science expertise: they demanded experts that told them what they wanted to hear and the OTA wouldn't supply that, so they found scientists who would. The result, which persists to today according to William Schlesinger, is that politicians "go to the table with their hired guns and beat on each other for a while, and there is never an agreement and nothing happens - and CO2 continues to rise." Rockpocket 07:06, 9 July 2007 (UTC)

I think you need to define what religious is. I think if you define it as regularly attending church, you'll find they are more religious. This is a demographic thing. Most likely educated, upper middle class, white male with 2.5 kids, etc, etc. This screams regular churchgoer without ascribing to any particular belief. There is more to religion than creationism and there are religions that don't adherently preach creationism like some fundamentalist churches. In fact, Vatican observatories are some of the most respected in the world and the chruch spends a large amount of money on scientific research. --Tbeatty 03:51, 9 July 2007 (UTC)

And you present this theory, in the face of actual studies to the contrary quoted above, based on which reliable sources? — Preceding unsigned comment added by 169.230.94.28 (talk)

And what studies were those? Religious is more than a belief in God. Also, the study comparing scientists belief over time when both the term "scientist" and the nature of science has changed so drastically is not quite valid, is it? Certainly not as a an answer to the question comparing scientists to the general population. --Tbeatty 04:24, 9 July 2007 (UTC)

Since you appear to be from the US, I was assuming that you were aware that around 44% of the US public claim to attend church regularly, according to many polls like this one [22]. In the above survey, 72.2% of top scientists professed "personal disbelief" in God , and another 20.8% professed "doubt or agnosticism". For these scientists to be "more religious" than the general public, using the regular-churchgoing criterion that you suggest, would require that all the believers, all the agnostics and doubters, and almost a quarter of the outright disbelievers would have to attend church regularly. Is this really what you believe? 169.230.94.28 05:26, 9 July 2007 (UTC)

Creationism Questions

Firstly, how do creationists explain how plants and fungi and protists (and everything else alive at that time) survived the flood? There are indeed many living things that would survive a forty-day flood, but there are some that would not. The bible only mentions animals going on the ark. Also, does anyone recall whether the bible mentions the depth of the water? This would have a large impact on the survival of photosynthetic creatures.

Secondly, I have studied the "exact proportions" (according to the bible) of the ark that god commanded Noah to build, and I doubt that two of every species of animal would fit on something of that size.138.87.213.224 02:20, 9 July 2007 (UTC)

The first one could be answered by an evolutionist too- what we see now are the surviving plants. The second one would probably get you two answers- an apologist saying you shouldn't take it literally, and someone who's dead set in their ways telling you that it was a miracle, or some such --L^augh! 02:32, 9 July 2007 (UTC)

Your questions are addressed at Noah's Ark#Biblical literalism and the Ark. Specifically, the apparent conundrum is usually explained by the fact that the Ark contained representatives of "created kinds" rather than species known today. This belief has spawned the pseudoscientific discipline known as "Baraminology". Rockpocket 02:33, 9 July 2007 (UTC)

Asking the science desk how creationists explain this is not likely to end well! Since creationism is about as far from science as it's possible to get - it's unlikely that many of them are here to answer your question. It goes deeper if you want to get picky - how do you feed all of those animals for 40 days? Particularly since a good fraction of them only eat other animals. Where did the water come from? Where did it go to? How come we don't see any evidence of a world-wide layer of sediment? When the dove returns to Noah with the olive branch - we have to ask ourselves what Olive trees had survived 40 days underwater. If it rained freshwater - then the level of dilution of the oceans required in order to get the water depth up to the top of Mt.Everest would kill most saltwater plants and animals - if it rained saltwater - then ditto for freshwater lifeforms. The questions and obstacles that a sceptical mind can throw into the path of this rather nice childrens' story are truly endless. However, if you believe in a being with literally unlimited powers - then no story is falsifiable. All a creationist has to say is "God arranged it so it all worked out using his magical abilities" - and you can't take the argument any further. Any hypothesis that includes such a being is unfalsifiable - and the whole of science, engineering, history and anything else humans have done becomes irrelevent. SteveBaker 02:39, 9 July 2007 (UTC)

This is the nature of faith. God can certainly fit two of every creature on the Ark if you have faith. The fact that YOU can't fit two of every creature in the ark answers another question :). Ask a scientist how life was created from molecules and amino acids and the answer will be a faith based answer of sorts saying that science can answer that question someday. Science answers a lot of questions. And with each new answer comes two new questions. Science doesn't diminish the concept of God, rather the complexity that science reveals actually makes God more intricate. Think of what science has done to the scale of God. In about 300 years, God has gone from the creator of 1 planet at the center of the Universe to the creator of a Universe with billions of galaxies that contain billions of stars. The universe has expanded from 8 light-minutes to 10 billion light years. God has gone from Earth-Air-Fire-Water to molecules, atoms, quarks and strings. And just think of the rules system he has created that we are just unravelling. --Tbeatty 04:04, 9 July 2007 (UTC)

You bring up an excellent point, which brings up one of my beefs with organized religions; they are still struggling with "science", ca. like 1920. As a "seeker after truth" in whatever form it may come, I'm disappointed that they haven't got much to say regarding quantum mechanics, DNA, the Big Bang, dark energy and dark matter, the expanding cosmos, and the now burgeoning catalog of extrasolar planets. Gzuckier 18:48, 9 July 2007 (UTC)

Here is a pretty decent attempt at a literalist justification. But for the real creationist student, what the (amateur) reviewers are calling a "tour de force" that answers "the folly of Ark critics, many with science doctorates" and puts the "Darwinian fundamentalists" in their place [23], may I present to you: Noah's Ark: A Feasibility Study. Rockpocket 04:19, 9 July 2007 (UTC)

The Bible neglects to mention that God made all the animals 2 inches tall and miraculous made them not need to eat or poop for 40 days. If you choose faith, that's about as good an answer as any other. There is no scientific basis for understanding the ark, and it's not really reasonable to expect one. Filling in the details is basically always going to be an exercise in creative writing. Dragons flight 04:37, 9 July 2007 (UTC)

If we are to believe that God created the entirety of all that is in six days, then is it really that much of a stretch to believe that he could somehow fit 2 of every animal onto a ship for 40 days? --Kurt Shaped Box 05:17, 9 July 2007 (UTC)

I'm not really interested in this question but just wanted to point out that it was only the unclean animals that went in by twos. The clean animals and the birds got to be collected in sevens. (Genesis 7:2–3.) Not a lot of people know that.--Shantavira|^{feed me} 07:33, 9 July 2007 (UTC)

"God can certainly fit two of every creature on the Ark if you have faith." How? does he make the animals smaller, the ark bigger, or what? 80.169.64.22 18:12, 9 July 2007 (UTC)

Yes, yes and yes. ;) --Kurt Shaped Box 18:17, 9 July 2007 (UTC)

If you want to start nitpicking biblical literalism, Project Gutenberg's King James Bible is a good free free electronic reference. There are also many many many other bibles on Project Gutenberg for your viewing and comparison. With a modern computer, diff, and wiki technology, I think there's a lot of interesting details you can come up with in comparative biblical study. Nimur 18:54, 9 July 2007 (UTC)

I tend to think there really was a great flood, but not one that covered "all the Earth". After all, how would they have known it covered all the Earth, as they could only see for a few miles in each direction ? The giant flood which formed the Black Sea is a good candidate. The ark may have indeed contained a few farm animals useful to restart life once they found their way to dry land, but certainly not every animal, much less every life form on Earth. See Black Sea deluge theory. StuRat 06:35, 10 July 2007 (UTC)

That's a fine theory - and I'm pretty sure that the same Black Sea event is what several religions are talking about in their flood stories too. The impossibility of a truly global flood - combined with the fact that all of the animals from other continents would not be needed if the flood was a purely local event suggest that local flooding is a much more possible thing. If Noah just needed sets of the animals he knew about from (say) 30 miles around his home - then perhaps a couple of dozen species might well have done the job and a boat that could truly have been built in those times could have contained the animals plus sufficient supplies for a month or two at sea. But from a religious perspective, the very moment you let yourself start modifying what the bible says - you've left yourself open to the question of whether you modified the right words. An alternative view is that Noah "SAID" all of these things happened to him - when in reality they didn't - you can come up with a bunch of ways to change the story and make it work - the only problem with most bible stories is when we're expected to take them literally. A few years ago, I actually sat down and read the King James bible from cover to cover - and as a work of fiction, it's really not all that bad. There are lots of plot holes and inconsistancies - and it's not exactly compelling literature the whole way through - but if you read it as if it were a sci-fi book - there are some good short stories tucked away in there. SteveBaker 00:22, 11 July 2007 (UTC)

Spring Flowers

Spring flowers from my garden

I actually am seeking a peer picture review in hopes of finding someone who knows what this flower is. I planted it last summer but for the life of me cannot remember what its name. I've been told that it's some type of carnation but I'm not sure. I think it's a good photo to be included in an article once I find out what the flower's name is. - AutoGyro 02:34, 9 July 2007 (UTC)

Comments:

• Looks like Sweet William to me. David D. (Talk) 03:35, 9 July 2007 (UTC)

(why is this transcluded onto the ref desk from Picture peer review?)

• Yup, go ahead, rename as "Sweet William Dwarf" (reference: [24]) and add it to the article. Bendž|Ť 17:52, 9 July 2007 (UTC)

100cc,250cc,500cc

What does CC imply in the knowledge of bikes?

Cubic centimeters of cylinder displacement.169.230.94.28 04:24, 9 July 2007 (UTC)

A cubic centimeter is .001 liters (1 milliliter). A 500cc bike is a 0.5 litre engine to compare it to car engines standard sizing. --Tbeatty 04:37, 9 July 2007 (UTC)

Argh, I was beaten to it! While we're on the topic, what're generally suggested usage ones? I know I've heard that generally beginners should have less than 150cc, but that more experienced riders will want more, but what're the guidelines on that? --L^augh! 04:40, 9 July 2007 (UTC)

1 cubic centimetre (of volume) is the definition of 1 milliliter.

or

1 cubic decimetre (of volume) is the definition of 1 litre.

202.168.50.40 04:56, 9 July 2007 (UTC)

It is a general understanding that higher the CC, more powerful the engine is. In India, most of the bikes are of 100cc and that is what the beginners use. I don't think there are any guidelines for this. It is just that beginners may not be able to handle something which is very powerful and hence a lower CC is recommended -- WikiCheng | Talk 09:32, 9 July 2007 (UTC)

In most states of the USA, you do not need a special license for bikes with 49cc or smaller engines. Larger than that requires a motorcycle permit and/or a vehicle driver's license (with regional variation from state to state). Nimur 18:57, 9 July 2007 (UTC)

In New Zealand you can drive a speed restricted (50 km/h) 50cc with an engine output of 2KW or under scooter (moped) on any license (including car) [25]. People on a learner's or restricted motorcycle license can only drive a 250cc or under motorcycle [26]. Nil Einne 23:19, 10 July 2007 (UTC)

Tox Screens

What are tox screens (and what is the appropriate article)? They mention them frequently in CSI and Scrubs. ALTON .ıl 05:50, 9 July 2007 (UTC)

Forensic toxicology may be what you're looking for. --Kurt Shaped Box 05:55, 9 July 2007 (UTC)

I believe that means screening (testing) for the presence of toxic chemicals. StuRat 06:23, 10 July 2007 (UTC)

4-legged insect

we have found a 4-legged insect in our house, it crawled across the floor and entered a reclining chair, we knocked it out and it jumped back in, so it seems to have jumping powers, it does not appear to have wings, the body is small compared to its legs, kind of like a spider, it even crawled like a spider, the color is dark brown and does not seem to have any patterns. if anybody knows of a species like this let me know, i searched on the internet and the best thing i could find goes to biblical references. anyways i appreciate any help anyone might have

thanks, david

Hello David. I'm afraid there are no insects with 4 legs. All insects have 6 legs (one pair per segment). Perhaps your creature has another pair of legs that are much smaller than the others, or that have become adapted to other purposes (See here for example? Though I suppose someone might have pulled one pair of legs off an insect, thereby giving it the appearance of a four legged creature. Rockpocket 07:58, 9 July 2007 (UTC)

A spider which has lost four legs in the gladiatorial pits? Seriously, losing half its legs sounds a trifle excessive, but when I lived near a forest I would regularly encounter insects and spiders missing one or two limbs. -Eldereft 08:06, 9 July 2007 (UTC)

I once watched a 5-legged spider walking along without obvious difficulty, and wondered: would it travel so well if the lost legs were all on one side (leaving 4+1 rather than 3+2)? —Tamfang 00:23, 10 July 2007 (UTC)

Headcrab? --Reuben 08:33, 9 July 2007 (UTC)

Make sure it is not a tiny intelligent alien. Edison 03:35, 10 July 2007 (UTC)

There is a spider (with 8 legs, of course) which keeps it's legs together in pairs, thus looking like it has 4 legs. I don't recall the name. StuRat 06:14, 10 July 2007 (UTC)

Babies

Chances are it will look something like this. Beyond that is mere speculation. Rockpocket 17:21, 9 July 2007 (UTC)

Hi, my partner and I are curious about what our baby boy or girl will look like.

Myself:

• Born in the Philippines
• 5 Foot 7 Inches
• Black hair
• Dark brown eyes

My Partner:

• Born in Australia
• 5 Foot 4 Inches
• Dark Blonde Hair
• Blue Eyes

I understand that that this is a pretty general question, but if anyone could point me in the direction of some information that may be able to assist. Something we could send in photos.

I look forward to hearing from you.

Dave

This will depend on a lot of factors- what they eat (both your wife and your baby), how long the pregnancy is, if it's your child or not, your bloodlines, which side of the dice some things fall on, and many, many, many obscure genes that govern a lot of things. If you really want pictures, you'll just have to get an ultrasound, or wait. Alternatively, there are some photo booths that will mix your faces together, although it's nowhere near an accurate representation --L^augh! 08:55, 9 July 2007 (UTC)

L - as the question appears to be about genetics and biological inheritance, I don't understand why you start your list with "what they eat". Apart from extreme examples involving drugs or alcohol, how does diet during pregnancy affect the appearance of the baby ? Can you elaborate ? Gandalf61 10:59, 9 July 2007 (UTC)

Diet will affect height - a well-nourished child will grow taller than its identical twin who has been less well fed. DuncanHill 11:28, 9 July 2007 (UTC)

Yep, as well as weight. I imagine a mother that eats more will have a heavier baby, and a baby that eats more than normal will definitely gain weight. --L^augh! 20:49, 9 July 2007 (UTC)

The simple one is eye color. If you have double brown allelles, which is common in that part of the world, your children will have brown eyes as this is dominant, though not necessarily as dark as yours. Hair and skin color are more likely to blend and appear intermediate (though I do know one half-asian woman who is naturally a darkish blonde). Dragons flight 09:10, 9 July 2007 (UTC)

Since you are both relatively short, your children are likely to be so, too. I'd expect girls to be around 5 foot 3 and boys to be around 5 foot 7, with say a 90% chance of being within 6 inches of those marks. Note that this assumes you've both attained your maximum genetic height. If either of you are still growing or had your growth stunted for some reason, then your children should be taller, assuming they reach their maximum genetic height. StuRat 06:02, 10 July 2007 (UTC)

You're ignoring regression to the mean which indicates that shorter-than-average parents will have children taller than them and taller-than-average parents will have children shorter than them. Of course, we need to know more about their genetic subpopulations to really know which category they fall into. Donald Hosek 14:30, 10 July 2007 (UTC)

Weather patterns

What is the Ninio effect (mentioned on the met office as La Nina - with an accent on the second n)? Happens in the Pacific Ocean and affects climate.

El Niño-Southern Oscillation? Someguy1221 15:41, 9 July 2007 (UTC)

La Niña is the opposite of el Niño: the opposite phase of the southern oscillation. --169.230.94.28 17:56, 9 July 2007 (UTC)

Correct, and here's the link: La Niña. StuRat 05:53, 10 July 2007 (UTC)

Thanks for the help, great link, cheers. S

Circuit assistance

Hello Reference Deskers. I'm currently working on a scientific experiment, and I've been placed in charge of circuitry. Unfortunately, I have no electrical engineering background.

Anyway, I have several devices (loads) connected in parallel to a 15VDC power supply. A few of them require the full 15V, but the rest can handle less. Each of them requires a current ranging from 20mA to 300mA.

Now, each of these devices is supposed to light up a green LED if powered on, and a red LED if switched off (or broken). I kind of have an idea of what to do (involves a few transistors and resistors), but I'm wondering what you guys think.

Thanks! — TheKMan 17:51, 9 July 2007 (UTC)

First off, make sure every LED has a current-limiting resistor, especially if you're thinking of driving it with the 15 volts! This can be done, though it will reduce the total life of the LED (usually). LEDs can be driven off much lower voltage. Next, read up on pull-up resistor and pull-down resistor, which you can use to turn the LED "on" or "off" by default. There's ten million ways to arrange the LEDs that would satisfy your needs... let me know if you have specific issues or need detailed schematic assistance. Nimur 18:38, 9 July 2007 (UTC)

I think I would put a low-value resistor in series with the +15 V line to each load, enough to give a drop of a few millivolts when the load is drawing current. The low side of the resistor would go to the input of a comparator. The other input of the comparator would be supplied with a reference voltage from a potential divider fed off the +15 V rail. The output of the comparator would drive the LED. This should be easier for a novice to work with than trying to use individual transistors. Anybody have a simpler solution? --Heron 19:19, 9 July 2007 (UTC)

For clarity, redraw the circuit with multiple load branches and with the switch separate from the load. Naturally it will have to be further elaborated to show the LED circuitry. It concerns me a little that you say the different devices need different voltages. You should be able to have current-operated comparators controlled by the voltage across a relatively small sampling resistor in series with each load as mentioned above. Because the current draws differ so much in each branch , you may need separately adjusted comparator circuits to drive the LEDs. You might consider placing them in the gound (negative) leg of each branch to make the circuitry simpler, so that a chip with multiple comparators might be used more easily than if each sampling resistor was at a different positive potential. Edison 19:40, 9 July 2007 (UTC)

Colour of matters

What's the cause of the colour of matters in microscopic view, and probing it among the particle.Flakture 21:10, 9 July 2007 (UTC)

I believe color at the atomic level is related to the energy of the various electron levels (the s, p, d, and f orbitals within each electron shell). The energy quanta absorbed or given off when changing electrons from one level to another each correspond with a particular frequency and wavelength of light, and hence color. StuRat 05:45, 10 July 2007 (UTC)

It's the same as for other objects you can see with your eyes - couloured lighting and pigments absorbing light. When you magnify a lot you can see coloured diffraction rings or pieces of rainbow around small objects. This is because of the wave nature of light, and that red is longer wavelength than blue. GB 05:51, 10 July 2007 (UTC)

Unless you are talking about color charge in quantum chromodynamics, in which case "color" is just a whimsical metaphor to simplify the bookkeeping. -Eldereft 07:20, 10 July 2007 (UTC)

There does come a point with microscopes of high magnification where the wavelength of visible light is just too long compared to the sizes of things you are looking at. This is why we have electron microscopes to make pictures of the very smallest things. Pictures taken in an electron microscope don't have real "colours" because the very concept of that is meaningless at those small scales. SteveBaker 00:05, 11 July 2007 (UTC)

When Electricity currents in the metals ...

What's the influence of current electricity on the size of metals? and why?Flakture 21:09, 9 July 2007 (UTC)

The size/shape of a block of metal affects current (resistance, actually, and current indirectly). See resistivity for diagrams and equations. Nimur 21:07, 9 July 2007 (UTC)

Many (all???) metal expand when heated. Elctricity passing through any metal other than a superconductor dissipates heat, in an amount equal to the current squared times the resistance. Heat cause the metal to expand, a tendency which is called thermal expansion [27]. The sagging of power lines when they are heavily loaded on a hot day is an important example of this: if they sag too much they touch trees and there is a prolonged outage. (Sag may also involve the matal softening and stretching under the tension due to gravity) Perhaps others can explain why metals expand when heated. Edison 03:34, 10 July 2007 (UTC)

Aluminum Carbonate

A question came up on CarTalk (this past weekend's rerun) about the chemical symbol for Aluminum Carbonate. Tom (and the chemist who had called in with another problem) thought that it was Al₂CO₃, although looking stuff up, it seems to me that it should be Al₂(CO₃)₃. Google searches turn up nothing, nor is there a wikipedia article on this substance (which apparently has some medicinal use). Anyone have the correct answer? Donald Hosek 21:09, 9 July 2007 (UTC)

• Rx for Al₂(CO₃)₃, the apparent correct formula (from what I can find). — Scientizzle 22:20, 9 July 2007 (UTC)

It appears that Aluminium Carbonate may not actually exist - [28]. I googled using the British spelling, which brought up lots of links. DuncanHill 22:28, 9 July 2007 (UTC)

Are you sure they did not mean Lithium carbonate? This is a very powerful psychoactive compound used for treatment of depression and severe mental illnesses. I was not able to find Aluminum Carbonate at Fisher or other chemical suppliers, so if it does exist at all, it is not commonly commercially available. Nimur 23:31, 9 July 2007 (UTC)

This is from the first search result on aluminum carbonate

Aluminum is a naturally occurring substance. Aluminum carbonate is the carbonate salt form of aluminum designed for oral ingestion. Aluminum carbonate is used to treat the symptoms of increased stomach acid in conditions such as heartburn, acid reflux, acid indigestion, sour stomach, and stomach ulcers. Aluminum carbonate is also used to treat, control, or manage high levels of phosphate in the body. Aluminum carbonate is also used with a low phosphate diet to prevent the formation of phosphate urinary stones.

I'm pretty sure that it's a different substance from Lithium Carbonate based on the pharmaceutical use. Incidentally, a google search on Al2(CO3)3 turns up a number of indications that this is, indeed. the correct formulation of Aluminum Carbonate. Donald Hosek 23:43, 9 July 2007 (UTC)

This site from a chemical supplier [29] gives C₂HO₆Al as the formula.

They're the only site that gives that formula (doing a google search on C2HO6Al). Trying permutations of H, Al and (CO₃)₂ doesn't appear to give anything more. Digging a bit deeper, although there does appear to be a salt which is as above, the medical aluminum carbonate is, in fact, an "aluminum hydroxide-carbonate complex" which is medical in its use according to New and Nonofficial Drugs, By Council on Drugs (American Medical Association) Published 1963 Lippincott Donald Hosek 01:11, 10 July 2007 (UTC)

Renewable energy capacity of the planet

Say we covered all areas of the planet that were sunny enough with solar power equipment, all areas that were windy enough with wind turbines, etc, for all the different renewable energy sources there are. Would the total amount of electricity generated be as much as is currently generated by all methods for the whole planet. ie with current technology is there enough renewable capacity to meet current demand for electricity? Willy turner 21:15, 9 July 2007 (UTC)

There is more than enough renewable energy on the Earth to supply all the world's energy needs, but you're talking about a huge investment. Think solar panel farms the size of Kansas. 151.152.101.44 22:13, 9 July 2007 (UTC)

Sunlight, collectively, contains about 10,000 times the energy that humans consume. The potentially capturable wind energy is about ~7 times what humans consume. It is physically achievable to power the world on renewables, but it would require a major economic, industrial and political effort to make it happen. Dragons flight 23:31, 9 July 2007 (UTC)

If you really want to collect energy, I suggest a Dyson sphere. -- JSBillings 19:07, 10 July 2007 (UTC)

Yep - there is more than enough energy coming from the sun to power all of our needs. The problem is mainly the cost of putting enough solar panels/windmills out there. It's just not a reasonable cost...unless of course you believe that we are killing our planet - then any cost is justifiable. However, even with "free" energy, if we trap more sunlight - turn it into electricity then turn the electricity into heat - then we're lowering the albedo of the planet - and that too may have consequences...especially if we have this big CO2 blanket preventing that heat from radiating out into space. Using windmills to extract energy from the wind cannot be without consequences to the weather. There is literally nothing we can do that'll have no effect whatever because extracting energy for our needs is driving the net entropy of the system...and that means more heat. Whether the effect we have is significant or not is the key question. What we really, truly need is to use less energy - and to do that to a sufficient degree probably means reducing our population drastically. SteveBaker 23:59, 10 July 2007 (UTC)

Speed and energy

I am having a somewhat thought experiment I don’t have any scientifically answer on.

If you are in motion, does tossing (or shooting) an object while you are in motion, cause the object to move faster than you, without any extra energy compared to tossing while not in motion.

It’s important to know that I do not think of a closed environment, like inside a bus or a spaceship that are in motion. It must be outside, like on the back of a pickup truck or something like that (this also includes with other matter and in a perfect vacuum). I am also wondering what will happen if I supposedly am travelling at the speed of light, and then shot a bullet. Will the bullet then go faster than speed of light?

--82.196.221.117 21:20, 9 July 2007 (UTC)

Question one is a bit vague. If you toss an object ahead of you (ignoring things like air resistance), then it will move faster than you in that direction, regardless of your speed. Further, the object moves at the same speed relative to you regardless of your speed relative to anything else. You can throw a ball at X speed standing still or at X+Y speed (relative to the ground) if you are moving at Y. This is the normal everyday ignore-relativity answer.

Question two gets into relativistic stuff. For one, you can't be traveling the speed of light. The question as stated is meaningless. But suppose you travel 5 mph below the speed of light, and can throw a ball 50 mph? What then? Yay, relativity! In your frame of reference, you might as well say that you are standing still and the world is moving around you. The ball appears to travel away at 50 mph in whatever direction you throw it. To an outside observer who sees you moving at almost-but-not-quite-the-speed-of-light, the ball travels ever-so-very-gradually-faster-or-slower than almost-but-not-quite-the-speed-of-light (depending on if you threw it ahead or behind) but in no frame of reference does anything exceed light speed. — Lomn 22:20, 9 July 2007 (UTC)

The only difference between being in a closed environment (like a schoolbus) and the back of a pickup truck is that in the latter case you have wind in your face. As far as special relativity is concerned, there is no difference. And how much energy it seems to take differs based on what reference frame you are observing from. As far as the thrower is concerned, it takes the same amount of energy no matter what inertial reference frame he is in, except for what resistance he will face from the wind. As for whether the ball can break the light barrier, no. You can't reach the speed of light to begin with, so at best you would speed up to 99.9999...(ending somewhere, not repeating forever) percent the speed of light and then throw it. Now again, from your perspective, this is the same a throwing a ball while "stationary" (stationary, velocity, it's all relative). From someone else's perspective, the ball is merely going very slightly faster, by the relativistic velocity addition formula. 151.152.101.44 22:25, 9 July 2007 (UTC)

To get into the first question a bit more - before you throw it, your rock or whatever is moving at the same speed as the rest of the truck (let us assume that your buddy is a cautious driver who maintains a constant non-relativistic speed and makes no turns). If you toss it straight up (impart a vertical momentum), its motion along the road is unaffected. Ignoring air resistance for the nonce, it looks to you like the rock goes straight up and falls. To the friendly roadside vegetable-monger, the rock traces a nice parabola with constant horizontal motion and constant vertical acceleration. At slow speeds this can be a fairly decent approximation, as demonstrated by my high school physics prof. using a small cart with a spring-loaded launch tube to toss and catch a ping pong ball while in motion. Turning air resistance back on, the rock is subject to a backwards force since the surrounding air will generally not be moving with the same velocity as your buddy's truck. Still, a gentle lob of a full can of beer out the window is, so I am reliably informed, quite sufficient to transform a common roadsign into a frothy dented mess. I am not clear on the energy part of your question, but kinetic energy explains the v² relation and might help. -Eldereft 08:03, 10 July 2007 (UTC)

What causes ice cubes to stick, like your tongue to a pole?

Exactly what force(s) cause partially melted ice cubes to stick to each other so quickly and so strongly, or your tongue to a metal pole in wintertime? (I'm assuming it is the same force(s).)

It's simply the freezing of water. If an object well below the freezing temp of water, like an ice cube or pole, comes into contact with liquid water, it causes that water to freeze to the object. Are you asking why water ice adheres to solid objects ? StuRat 01:37, 10 July 2007 (UTC)

Does Regelation play a part? -- JackofOz 01:44, 10 July 2007 (UTC)

Regelation may be the answer to ice cubes sticking together (but the article itself expresses some doubt, due to the enormous pressure required to melt the ice) but tongue sticking to a metal pole is for a different reason. It is just that the water content on your tongue gets frozen, binding the tongue and the pole. The same thing happens if you wet your finger and touch the pole. If the water film on your skin is thin enough (to freeze at the contact of the pole), then your finger will stick to the pole. -- WikiCheng | Talk 04:41, 10 July 2007 (UTC)

The surface of your tongue isn't smooth!

I think the reason that tongues are especially vulnerable is that they have a large surface area due to all of the little Papillae (taste buds) - so you aren't just talking about a smooth surface (like skin) that could just slip off of the ice - you're freezing all of those tiny bumps into the layer of ice - posing a significant mechanical problem. Also, for skin, the blood pumping through the finger (or whatever) will melt the ice that's in contact of the skin - making it relatively easy to come un-stuck. I don't think there is enough (or indeed any) blood flow through those buds to allow them to melt their own way out of the ice. SteveBaker 23:47, 10 July 2007 (UTC)

July 10

Question about UV light danger

I was looking at a fume hood today with a germicidal (UV) light on. While the light is concealed from view, the purple light reflects out of the hood. I was wondering, can the UV light reflect off of the walls and floor of the chamber in any sufficient intensity to present a health hazard? The interior of the hood is made of stainless steel. I know that the glass shield will block most UV passing through it, but it is typically half open. And as for a possible health hazard, I am basing this on the possibility of spending anywhere from minutes to hours a day in front of it (I make sure to spend only seconds a day out of paranoia). Everyone who works here, including several doctors, say "Just don't stickaa your hands inside with that light on." But I'm still curious. 151.152.101.44 00:53, 10 July 2007 (UTC)

You can get the bulb's emission spectrum from the manufacturer. You can probably get the reflection characteristics of the stainless steel from the respective manufacturers. In any event, you should have access to a separate instrument that can directly measure the UV spectrum at various locations at your workstation. Until you have these objective measurements, any general advice is meaningless. Nevertheless, here is some general advice: Do not look at the germicidal bulbs directly. To a first approximation, treat the bulbs and their reflections as you would direct solar radiation: do not look at it directly. -Arch dude 02:17, 10 July 2007 (UTC)

How about wearing glasses which block UV, as a first approximation to safety? You can get an anti-UV clear coating on normal glasses. You certainly do not need the UV to see by, because our eyes are insensitive to it (unless the yellowish lens has been removed due to cataracts, in which case the retina can see nicely by UV). Then maybe rub on some UV blocking suntan lotion. (Who needs a melanoma?) Does the school/lab have an industrial hygienist? Measuring UV and checking it against government standards would be his job. Edison 03:24, 10 July 2007 (UTC)

I work with UV lasers. Germicidal mecury lamps emit UV-C, a type of ultraviolet light not found in the sunlight reaching the Earth's surface, and are specifically designed to break down DNA. As a result, for the same amount of energy, the light from germicidal lamps is many many times more carcinogenic than what you will find in sunlight. I would never place exposed skin under a germicidal lamp. Prolonged exposure will also result in sunburn symptoms or eye inflamation. The good news is that UV-C is easy to block. It will be blocked by ordinary glass or plastic. Normal safety glasses are more than adequate at these wavelengths (no need for special "UV" filters, which generally target UV-A/B). Sunscreen is not designed for UV-C and depending on the active ingredients may not offer any protection. For moderate durations, latex gloves plus long sleeves would be adequate if one must work under a germicidal lamp. As for reflections, UV-C will reflect off of many shiny metallic surfaces the same as visible light (though a higher fraction is absorbed than visible light), so if the purple glow is bouncing out under the hood, then so is the UV and it is a potential safety risk. If your hood has a cover/window that can be closed, it really should be when the lamp is on. How large a safety risk will depend on a variety of details of your setup, but I would not want to work in front of it for extended periods. Dragons flight 04:44, 10 July 2007 (UTC)

Dragons flight, if you'll forgive me, I've added a Wikilink to your reply.

Atlant 12:46, 10 July 2007 (UTC)

Somewhat OT but I heard of someone who got sunburnt from the UV light use for visualising a gel electrophoresis (the open one, used for cutting the gel etc). IIRC, he was wearing glasses or a face mask and gloves so those areas were fine but his arms got sunburnt. He was working with a large quantity and didn't take adequete protection. Back on topic, I was thought to always to what Dragons flight said. Close the cover and then turn the light on. Of course, if you need to do some work with it on, this obviously wouldn't be possible Nil Einne 23:03, 10 July 2007 (UTC)

How is the frequency response of an acoustic transducer determined?

How is the frequency response of an acoustic transducer determined? If it is done empirically by measurement, there must be a way to generate an acoustic test signal of precisely known power — without using the transducer under measurement. You could use a pre-calibrated transducer to calibrate the test signal, but that transducer must have undergone calibration before. At some point, you must stop reducing the calibration of one transducer to that of another. How is this problem (meaning frequency response measurement) solved in practice?

See Microphone in the section "Measurement microphones." 2oth century methods included the pistonphone, which mechanically moved a piston a known distance in a known space to create known pressure variations up to 250 Hz. A diaphragm could be electrostatically moved by high frequency alternating current to create pressure variations. AC electrical current could produce pressure variations in the "thermaphone." Certain types of microphones were thus calibrated with the pistonphone and used as lab standards. Now there is the "reciprocity method" which uses microphones which can either receive an acoustic signal and produce an electric signal, or receive an electric signal and produce acoustic waves. This is discussed at [30]. See also [31] and [32]. Edison 05:44, 10 July 2007 (UTC)

Water Retention

My doctor just gave me a medicine and he said it will cause my body to retain water while I am on it (two weeks). I already look fatter in the stomach area with the same diet and exercise. Does water retention look the same as weight gain from fat? If I were to gain 3 pounds of fat on my stomach, would it look the same as retaining the same amount in water?

Firstly we have to say Wikipedia does not give medical advice. If you are concerned about the side-effects of any medicine, talk to your Doctor or pharmacist. That said, in terms of appearence, yes, water-retention can look similar to weight-gain from fat. DuncanHill 09:44, 10 July 2007 (UTC)

induced paranormal experiences

Do we have any articles on the possibility of inducing paranormal experiences by engineering the lighting/dimensions/layout of a room? I remember hearing about a study that showed some kind of link. Also if you know about any other articles that are in the area of the psychology of paranormal experiences, I'd be interested in that too. Capuchin 08:19, 10 July 2007 (UTC)

I don't believe there is scientifically-reproducible evidence that paranormal experiences exist. Therefore, scientifically speaking, the experiences are invariant under room configuration. However some configurations may allow for non-paranormal factors (such as non-verbal communication) to influence the perception of an event. I'm not sure whether there are non-scientific articles on the topic. — RJH (talk) 15:32, 10 July 2007 (UTC)

Possibly Capuchin was asking whether apparent paranormal experiences could be engineered, and if there had been work in this area. That's how it reads to me, anyway. I recall reading very recently (why can I never remember where?) that some percentage of the UK population reported having had a paranormal experience, but that the less educated you were, the more likely you were to claim it was a ghost. The more educated you were, the more likely you were to claim it was a religious experience. I suspect I read it in a printed source. Hmm. Anyway, there are quite a few studies into the psychology of 'paranormal' experiences, but it does seem to be hard to find articles on them here; perhaps I just haven't found the right category yet. Theres Religious and physiological views of near-death experiences, but it doesn't look like a very good article. I'd expected to find stuff in [[Category:Forteana]], but I can't see the sort of thing I think you're looking for. Sorry :-( Skittle 16:27, 10 July 2007 (UTC)

Sorry for misunderstanding then. — RJH (talk) 19:52, 11 July 2007 (UTC)

The acoustics of the room could enable/enhance infrasound, which has been known to make people feel spooked out. --TotoBaggins 16:33, 10 July 2007 (UTC)

It can be done with direct brain stimulation. -Eldereft 03:43, 11 July 2007 (UTC)

See also Angular_gyrus#Out-of-body_experiences. -Eldereft 03:49, 11 July 2007 (UTC)

Skittle, you're quite right about what I am looking for. I remember watching a tv show (or part of a show) where they had set up a room of a specific size/shape at a museum or exibition of some kind. People would go in and sit in there for 5 minutes, and would often come out the other side claiming to have had a paranormal experience in there. I don't think they were providing any kind of stimulus. Looking through the infrasound article, the 18Hz resonant frequency of the room would be a good way to create it. Capuchin 08:13, 11 July 2007 (UTC)

how do you get rid of the smell from dried starfish?

I bought some dried starfish from a tourist shop to use as decoration, but the smell coming off them is so repulsive. how can i get rid of it, will it fade with time? and could i use sodium bicarbonate, as this is reknown for neutralising bad odors? has any one ever solved this problem?

I would suggest making sure that it is thouroughly dry should help - leave it in the sun outdoors for a few hours. Don't get it wet - they can go mushy, and will start to decompose, smelling even worse. I have seen a suggestion online that you soak it in 70% isopropyl alcohol, but have no experience of this. DuncanHill 10:08, 10 July 2007 (UTC)

70% isopropyl alcohol is 30% water, so presumably would wet it. --TotoBaggins 19:48, 10 July 2007 (UTC)

I'd have thought that would depend on whether the starfish is more or less than 30% water. I'd imagine (though I do not have a source) that an undried starfish would be much more than 30% water. What percent of this particular dried starfish is water, I do not know. Skittle 18:20, 11 July 2007 (UTC)

"Your Face Will Stick Like That!"

If someone continuously wipes their nose so that it is mushed into a "pig nose" shape... or holds it that way to make a stupid face... is it possible for the nose's shape to be altered (permanently or short-term?

• Yes. --jpgordon^∇∆∇∆ 14:37, 10 July 2007 (UTC)

Not sure. I do know that extremely vigorous laughing can cause your face to temporarily be stuck in a smile , I'd assume due to contractions of the muscles. I imagine long term damage nearly impossible though, unless, say, your process scrunching up your nose also includes a sledgehammer to the face, or you bind your nose to grow like that from a young age, such as the old feet binding practices in asia --L^augh! 14:45, 10 July 2007 (UTC)

Possibly, but my intuition says you will have better luck with continuous pressure, an ill-fitting muzzle or somesuch. See lip plate and body modification for some other ideas. -Eldereft 04:33, 11 July 2007 (UTC)

• Artificial cranial deformation allowed for reshaping of the skull, so I'd imagine it's possible with the softer nose cartilage. — RJH (talk) 19:52, 11 July 2007 (UTC)

Question, re: Archaea taxonomy

A few questions, please!

1.) If Archaea is a domain (or sometimes a superkingdom), then why do so many systems refer to Crenarchaeota as a phylum (though some do refer to it as a kingdom)? I personally don't like skipping levels, but maybe there's a good reason to skip over Kingdom.

2.) Some references list the phyla (or kingdoms) of Archaea as: Crenarchaeota and Euryarchaeota; some also include Nanoarchaeota and/or Korarchaeota. Would you think that, if Nano and Korar are not listed as phyla/kingdoms, then their species are currently included in Cren or Eury?

3.) Isn't there some organization that "decides" taxonomy? If not, how is it taught in schools? Just depends on the textbooks' POV?

(Please forgive if my questions are lame, I'm a tech writer, not a biologist.)

Reenie15:12, 10 July 2007 (UTC)

PS, I clicked on a link to ask a question; now it looks like I'm making a comment. I have a reference question!

I'm no biologist - but isn't it the case that Archaea have been moved around in the taxonomy over the last few years (decades)? Maybe you are just comparing sources that are current with books that are somewhat out of date? SteveBaker 23:37, 10 July 2007 (UTC)

Steve: the domain/kingdoms have changed much in thepast 30 years. I'm interested in how to find a consensus on this, if there is one!

There is no one organisation, but taxonomist follow strict Nomenclature Codes. Cladistics have come a long way and is now a more exact science thanks to molecular techniques. I know little about the archaea, but if Nano and Kor are omitted, everything under them is omitted: unless included in the other phyla (probably the case as they couldn't be placed anywhere else). This is a part of the age old lumpers and splitters debate and is very tiresome. Bendž|Ť 09:53, 11 July 2007 (UTC)

Communication in Behavioural Science

Can you critically analyse the place of silence in communication. Mabel

Yes, but your teacher probably wants you to do it. alteripse 15:21, 10 July 2007 (UTC)

Certainly. ... ... ... ... ... ... Clarityfiend 15:58, 10 July 2007 (UTC)

I certainly can. I might use Calvin Coolidge as an example. Edison 18:08, 10 July 2007 (UTC)

Depending on your particular "take" on things, you might want to see our articles on either dead air, Morse code, or 4′33″. The fortress of the Soundkeeper in The Phantom Tollbooth might also prove interesting to you.

Atlant 19:49, 10 July 2007 (UTC)

Nil Einne 22:35, 10 July 2007 (UTC) (sic)

Sure you can. If I tell the following joke:

Knock knock. Who's there? The interrupting sheep. The interrupting sh Baaaaaaa!

I must be careful not to leave too much silence in my performance or the joke falls flat. Timing is critical to much of humor and drama alike. Timing is merely the presence, absence or duration of silences. A poor performer might have silences of the wrong duration or clever use of an appropriate pause can stretch the humor or the drama of the moment. That's certainly a topic for critical analysis. SteveBaker 23:35, 10 July 2007 (UTC)

old dog dilemma

My old Irish setter is 15 which makes her venerable.Her original vet(now retired)administered seven years of delvesteron heat suppresants before retiring,and earlier this year the dog had three mammary tumours removed.She recovered amazingly well,but the new young vets refuse to give delvesteron.Trouble is,dog's now in season(over a month),lovesick and pining for a mate. Vet says hysterectomy. I say how can more hormones hurt now?She surely doesn't have much more than a year to live-however dirty the drug,can it matter now?usually she is happy,lively,sociable,no joint problems.This is an ethical problem.Help!

We can't give medical advice, so I'll just say "go see a different vet". --TotoBaggins 19:51, 10 July 2007 (UTC)

Did you speak to your vet about why he or she refused to give the drug? I see from the factsheet that delvosteron is associated with mammary hypertrophy. This would likely be the cause. Given your dog has already had mammary tumours, it would seem a bad idea to prescribe such a drug. If the tumours were removed and your dog recovered well, why do you assume she only has a year to live? Somewhat OT, but why didn't you spay her rather then take the risk and expense of an unspayed dog with hormone treatement? Nil Einne 22:23, 10 July 2007 (UTC)

Dog#Lifespan_and_old_age says midsize dogs live (on average) 13 or 14 years - it's reasonable to assume that a 15 year old Setter might not live much longer - especially if her health is already on the decline. SteveBaker 23:25, 10 July 2007 (UTC)

But that's average. Admitedly the dog was not spayed so it's lifespan may be below average since I presume the average is for all dogs and sterilised animals tend to live longer (I presume the hormone therapy helps but it not as beneficial as complete sterilisation). Nevertheless while I'm not going to say you shouldn't expect the dog might not last much longer, I don't think you should expect the dog to die in a year or less either especially when it's in apparently good health. IMHO, it would still be better for the poster to at least talk to their vet first, with an open mind and try and get an understanding of why the vet recommends his/her current course of action. If after doing so, and having carefully considered what's been said, you still feel your course is best, think carefully why and try to explain to the vet in these terms. You may find he or she will be much more receptive when you have carefully considered the recommendations and explain why you want to take a different course. Indeed, you may find in doing so you'll be able to convince the vet. If not, he or she may at least recommend you seek a second opinion. If none of this works, you can obviously still seek a second opinion even without your vet recommending it. Perhaps you've already done or this but from the way you phrased the question it just sounds to me like you've made up your mind without really bothering to consider what's been suggested and have just tried to convince the vet to do it, I apologise if I'm wrong. This is likely to be a problem since if the vet, as is hopefully the case has strong ethical reasons based on his/her medical knowledge for feeling his/her course is the best course then when you don't bother to consider the recommended course and instead try and convinice your vet without having considered the course and perhaps without even sufficiently explaining why you feel your course is best (which may be difficult if you haven't heard properly thought about the vet's recommendation) then the vet is understandably going to be concerned and may be unwilling to go against what he/she feels is best. I'm not saying the vet has to be right, simply that IMHO it's wise to properly consider what the vet recommends and why first if you haven't already since there's a good chance he or she has reasons you aren't aware of. Nil Einne 00:31, 11 July 2007 (UTC)

(Vetinary advice != Medical advice : the Wikipedia rules don't apply here) I'd agree that this is a case of 'doing the least harm'. Find another vet who will do what you want. One of our dogs has bad arthritis in all four limbs (he's a VERY large dog) and he finds it hard to walk. The vet pointed out that in the absence of a cure, we must either euthenise the dog or manage his pain - but the continuous dosage of painkillers it takes to get a 150lb dog over this much pain is going to damage his kidneys within a year. Well, they get him up and about and chasing squirrels again - better a year of that followed by death from kidney failure than death now - and better that than years of pain. Losing a dog is a horrible thing - do whatever it takes to make it easier. SteveBaker 23:25, 10 July 2007 (UTC)

Never harms to get a second opinion in any case. I had a budgie with a massive tumour in his abdomen - the first vet I saw said that it was inoperable and that euthanasia was the only option. Not happy with this, I went to another vet who examined him and said that he was prepared to perform the (albeit very high risk of death on the table) op. I figured that if the bird was going to die anyway, then it might as well be during an attempt to fix him that just *might* work. As it turned out, he was pretty much back to normal a couple of days after the op and he lived for another six years. --Kurt Shaped Box 23:34, 10 July 2007 (UTC)

I agree with Steve that keeping a dog comfortable at that age is the most important thing, and if the choice is between putting a very old dog through a fairly major surgery and giving a shot that may or may not cause problems in the future, then ethically a vet has some leeway. I assume you are in Europe since delvosteron is not available in the U.S., and I don't know if they have different laws pertaining to drug use than we do here, but it is much different for a vet than an M.D.: a vet can ethically do something that may sacrifice the patient's health in order to keep it comfortable (euthanasia being an extreme example). However, I will say that I disagree with Steve's assessment of Wikipedia:Medical disclaimer. I don't see why that wouldn't apply to veterinary medicine just as much as human medicine (well, maybe not just as much, but still we shouldn't say "do this to your dog", or "give this medication to your goat"). --Joelmills 23:40, 10 July 2007 (UTC)

Agreed. Don't want anyone coming back at us with lawyers in tow, angry that "WP told me to give this to my expensive pedigree dog and now my dog is dead!". --Kurt Shaped Box 23:48, 10 July 2007 (UTC)

The medical rule is primarily because it's illegal to practice human medicine without a license in most jurisdictions. There is no defense against bad advice causing people harm - we're certainly allowed to give car maintenance advice - "WP told me to put this in the tank of my $100,000 BMW and now my car is broken!". Offering vetenary advice is far less likely to be injurious to our readership. If we omit to tell someone to tighten up the wheel nuts after changing a tyre (or if there were just merely a typo in the torque wrench setting we advised them to use) then they may well die as a result. If we had to protect against all of these things, we'd be unable to give any advice whatever. SteveBaker 05:08, 11 July 2007 (UTC)

Well, we have whatever protection is provided by the various disclaimer notices linked from every page. These include both a Medical disclaimer and a more general Risk disclaimer that says "None of the authors, contributors, sponsors, administrators, vandals, or anyone else connected with Wikipedia, in any way whatsoever, can be responsible for your use of the information contained in or linked from these web pages". The guideline that prohibits medical advice on the RDs is an additional (and sensible) prevention measure around the most potentially dangerous area of advice. Gandalf61 07:36, 11 July 2007 (UTC)

As I understand it, disclaimers are not legally binding in all circumstances. After reading about some of the insane lawsuits that people bring that actually make it to court, I don't doubt that someone will eventually try to sue WP (or a particular user thereof) over a broken car, or suchlike. --Kurt Shaped Box 09:24, 11 July 2007 (UTC)

On further consideration and reading, I agree that veterinary advice should be OK here, since pets are essentially seen as property by the law. My advice is to see a different vet until you're satisfied with either the treatment or the explanation of why the treatment is not possible. I definitely agree with SteveBaker that it's better to potentially shorten the life of the animal in order to avoid having it live with pain. Dogs live in the now. Disclaimer: I have 4 dogs, but have not yet had to deal with any end-of-life issues; I'm still in denial that they'll die at all. :( --TotoBaggins 14:05, 11 July 2007 (UTC)

Interestingly, I see that the reference desk header now says "Do not request medical, veterinary or legal advice. Ask a doctor, veterinarian or lawyer instead." Has it always said that, or did that somehow come out of this discussion? Either way, I don't think that anything that has been mentioned in this discussion really constitutes veterinary advice. Nobody is giving dosage information or offering to write a prescription. --Joelmills 03:16, 12 July 2007 (UTC)

Never mind, I saw the answer over at Wikipedia:Reference desk/Miscellaneous#Why cant medical advice be given here?. --Joelmills 03:28, 12 July 2007 (UTC)

Microwave of Doom

How dangerous is the radation inside of a microwave after the signal has gone off that you can take your food or whatever out? How long after the microwave stops doing it's thing is it dangerous to be exposed to it (i.e. opening the door and sticking your arm in..or putting your face really close)? If someone is in the habit of opening the microwave door during operation, could the amount of radiation from that eventually be damaging?

Microwaves are a form of light. As such they move at the Speed_of_Light. Therefore it doesnt take very long for them to bounce around inside the microwave oven before they are absorbed by the food you are heating. Since the Magnetron automatically turns off when you open the door, an insignificant amount of radiation would be able to reach you. Also understand, the all microwaves do is heat things up, so even if you could get your arm into a microwave and turn it on, it would burn you due to heating the water in your body, as opposed to damaging your DNA which would happen if you were exposed to higher energy light radiation, X_rays or neutron radiation, Gamma_rays. -Czmtzc 17:14, 10 July 2007 (UTC)

Things being heated = higher rate of molecule movement... if this is going on inside your body, would that be an issue?

Yes - look at what happens to a piece of meat when you put it into an oven. That is heating - and that is bad for a live human. Batmanand | Talk 17:28, 10 July 2007 (UTC)

The Microwave oven#Controversial_hazards article has more information about some of these hazards. In summary, you've got more to worry about radiation from your cell phone than a standard microwave. -- JSBillings 19:04, 10 July 2007 (UTC)

Note that that cell phone you hold next to your head puts out 300X the permissible leakage of a microwave oven. I'm not saying it's dangerous, I'm just saying if I were to get worried about microwave radiation, I'd start with the big end and work down.Gzuckier 15:27, 11 July 2007 (UTC)

Body composition

A general ball-park figure is fine. What percent of the human body is water? Thanks. (JosephASpadaro 17:27, 10 July 2007 (UTC))

60-78% Batmanand | Talk 17:29, 10 July 2007 (UTC)

Also, check out this page: Body water. Hope that all helps. Batmanand | Talk 17:30, 10 July 2007 (UTC)

Thanks. You gotta be kidding me? So, if a person weighs 200 pounds, up to 160 pounds of that is merely water? And there is only 40 pounds "left over" for organs, bones, tissue, muscle, fat, etc.? (JosephASpadaro 20:34, 10 July 2007 (UTC))

Bear in mind that a large part of the weight of tissue, organs, muscle, fat, etc (perhaps not bones) is itself water, so "water vs everything else" isn't really a list as you describe it. — Lomn 21:06, 10 July 2007 (UTC)

Not quite. Consider that the individual cells that make up your organs are much like water filled sacks of protein, lipids, and other biomolecules (some arranged into neat little organelles, of course). 151.152.101.44 21:09, 10 July 2007 (UTC)

This seems surprising in part because it's hard to believe that something that's 70% water is anything other than a puddle on the ground! But consider this - a cucumber is 96% water. This large and very solid seeming object is basically just slightly impure water! One of our regular help desk contributors has the Wiki username 'Ugly bag of mostly water'...which is a fair description of most of us. SteveBaker 23:08, 10 July 2007 (UTC)

... sans the "ugly"? (JosephASpadaro 23:16, 10 July 2007 (UTC))

The mythical beautiful wikipedian exists? Nil Einne 00:45, 11 July 2007 (UTC)

Every Wikipedian is beautiful, in his or her own way ........ -- JackofOz 01:40, 11 July 2007 (UTC)

A human body is just a big concentrated jello mold, on one level of abstraction. That's one reason they use gelatin for ballistics testing, for instance.Gzuckier 15:25, 11 July 2007 (UTC)

How to Make Someone Feel Something Without Touching Them

Can anyone explain why this trick works?-How to Make Someone Feel Something Without Touching Them--Foljiny 17:53, 10 July 2007 (UTC)

No evidence was provided that it does work. Edison 18:05, 10 July 2007 (UTC)

I'm sure it'd make me feel annoyed. -- JSBillings 18:39, 10 July 2007 (UTC)

It looks (at first glance) like a combination of at least two factors... the expectation of contact and the movement of eye muscles as the subject tries to focus on the object almost-touching them on the forehead. If this works with the individual's eyes closed, then something else is going on :) ◄Zahakiel► 19:53, 10 July 2007 (UTC)

It probably touches the small hairs on their foreheads, which would cause them to feel a sensation without anything touching their skin.

My brother hates it when I do this to him. I don't think I'm touching any hairs on his forehead. I think it's mostly what Zahakiel says, that there's an expectation of contact. If my brother closes his eyes, he feels nothing. —Bkell (talk) 00:13, 11 July 2007 (UTC)

I haven't got past Step 1: "Retrieve a pencil or use your own finger and retrieve another person". What does that mean in English? -- JackofOz 01:33, 11 July 2007 (UTC)

Obtain a pencil *and* a human for the experiment? --Kurt Shaped Box 01:40, 11 July 2007 (UTC)

This trick does not work. As Bkell mentioned, if the subject closes his eyes, either he will not feel the effect or he may feel that tingling sensation even if there is no pencil near his forehead. It is the expectation. -- WikiCheng | Talk 05:45, 11 July 2007 (UTC)

Step 4 says to "Gently shake, vibrate the pencil back and forth and the person should feel a strange sensation." I would think that the person/victim is feeling little air currents in front of those sensitive little hairs. --JDitto 02:52, 12 July 2007 (UTC)

Noon and the middle of the day

Is there a day (= one of the 365 or 366 slices of the year) where noon falls exactly in the middle of the day (= the period of time between sunrise and sunset)? For example and hypothetically speaking, if the sun rises at 0700h and sets at 1700h then noon (1200h) falls in the middle. Is this possible concerning midnight (0000h) too, ie falling at exactly the time between sunset and sunrise? (cubic[*]star(Talk(Email))) 18:16, 10 July 2007 (UTC)

The article Noon explains this pretty well. Noon is the middle of the day, when the sun is highest. Due to Standard time (Time zones), Daylight saving time, and other things, "clock noon and solar noon hardly ever coincide", but they can and do. If one lives close to one's time zone's central meridian and it isn't currently daylight saving time, solar noon and clock noon should be about the same, if I understand it right. Pfly 18:30, 10 July 2007 (UTC)

You might also enjoy our article on the Analemma (which shows the oscillation of the sun in the sky vis-a-vis a fixed clock-time of day).

Atlant 19:57, 10 July 2007 (UTC)

Yes, four times a year. The article you want to read is Equation of time. The equation of time (which is not an equation but a function) is the difference between true local time and mean local time, and the article explains the rest nicely. Simon A. 19:59, 10 July 2007 (UTC)

I think you mean up to four times a year, depending on location. If you are more than a degree and a bit from your time zone's central meridian, then you probably won't get any. More than a third to a half of a degree away and you might get this happening twice a year. But these might only be approximately in the middle of the day, i.e. on the time zone's central meridian, you might not get the equation of time exactly equal to zero at precisely noon, but that could be being pedantic?

Yes, yiu caught me. I first wanted to write: True local time equals mean local time four times a year but then realized that the questioner asked about zone time, not mean local time. To lazy to dive into this subtlty I decided that the Equation of Time article explains this well enough. Simon A. 07:09, 11 July 2007 (UTC)

To be really picky, at every point in time, the day is either getting longer (if we're between the winter solstice and the summer solstice) or shorter (if we're between the summer solstice and the winter solstice). Hence, if 1200h falls exactly halfway between sunrise and sunset, then it will not correspond precisely to solar noon, the point in time when the sun is highest in the sky! For example, if the day is getting longer, then the period from sunrise to solar noon will be slightly shorter than the period from solar noon to sunset. Someone with an actual background in astronomy should either agree or disagree with me. —Bkell (talk) 00:10, 11 July 2007 (UTC)

That's true, but I'll talk about "local solar noon" here for convenience. Everything I say is true both for local solar noon and for the midpoint between sunrise and sunset, although those do not exactly coincide.

The thing is that at some particular location, the clock time of local solar noon time on successive days might be 11:59:25, 11:59:39, 11:59:54, 12:00:09, 12:00:24, for example. So it does hit 12:00 if you only measure time to the minute, but not exactly 12:00:00 -- but how close it comes is essentially random. It might exactly hit 12:00:00 once ever few years. But if you measure time to the millisecond, you might have to wait a few thousand years before local solar noon was exactly at 12:00:00.000. And if you measure to the microsecond, a few million years.

But all that's for a specific location. If you move west a mile or so (assuming mid-latitudes; the exact distance depends on your latitude), you're still in the same time zone, and now the local solar noon is 6 seconds later. So in this example you do get 12:00:00. And if you want to measure the time to the millisecond and get 12:00:00.000, you just have to measure the distance with corresponding accuracy. So it is true that there are places where the local solar noon occurs at noon by the clock, if you measure to the second: they just aren't the same places each time it happens. And if you measure to the minute, then it happens in lots of places.

There are also places where it never happens, because their local zone clock time the clock time in their particular zone is based on a longitude meridian too far from the place. For example, some decades ago France switched to using time zone UTC+1 (which is local mean time for longitude 15°E) in winter and UTC+2 (30°E) in summer (daylight saving time). But France actually extends from about longitude 5.25°W to about 8.25°E. 15 minus 8.25 is 6.75 degrees, which corresponds to 27 minutes of time, and the equation of time never gets to values that large. So in France they never have local solar noon at noon by the clock. There are several other parts of the world where the same thing is true (they choose to use the same zone time as another place, or a zone time closer to that of another place than they might, for political/economic reasons), notably including large parts of China and Alaska. And daylight saving time can also make it impossible for clock noon to be local solar noon during that part of the year. --Anonymous, July 11, 2007, 00:12 (UTC).

A note on terminology. When discussing time, the word 'local' indicates that we are talking about the time as specified by the sun viewed from the current place. 'Zone time' is the time we usually use. 'Local zone time' is hence a confusing oxymoron even though 'local time zone' sound reasonable. Furthermore, true local time is defined as the time given by a sun dial, i.e. whenever the sun passes through the meridian (in astonomy, the meridian is the thought line from the south point on the horizon through the zenith to the north point), it is by definition 12:00 h true local time. The time from true noon to true noon is not exactly 24:00:00 h (i.e. sundials are clock with varying speed), and this is why we define a mean local time to allow clocks run at constant speed. The mean local time a zero longitude is defines as GMT. Simon A. 07:09, 11 July 2007 (UTC)

On the first point, thanks; I've corrected my wording above to avoid the confusion. As to "true local time", I don't think this is a commonly used name for this concept. I think "local solar time" is what I usually see for it, although Wikipedia's Solar time article goes with "apparent solar time". --Anon, July 11. 22:30 (UTC).

Stomatal Density and Transpiration

Is it correct to assume that the relationship between stomatal density and the rate of transpiration is such that as the stomatal dessity increases, the rate of transpiration also increases. How is this explained, and is this true for all species of leaf? Thanks, 86.142.230.63 20:59, 10 July 2007 (UTC)

astronomical device

I am trying to find the name of a divice thats similar to a mobile with planets on but mimicks the position and rotation of the in relation ot the sun the name of the developer and its modern nameor the device if possible.

An Orrery is what you are looking for. DuncanHill 21:45, 10 July 2007 (UTC)

July 11

Big red insect

I was having dinner when I suddenly heard a buzzing noise from the kitchen. I went to inspect, and it turned out to be this large insect struggling to fly through the pane of glass in the kitchen window. I helped it out, and it flew straight for the dew covered rose bush, presumably to drink water. I rushed to get the camera, and I was able to take this picture. I did not have a ruler handy, but it might have been as large as 4 cm in length, which is exceptional for Norway. Does anyone have an idea what species this is? -GSchjetne 00:33, 11 July 2007 (UTC)

It could be an Elephant Hawk-moth (Deilephila elpenor). ---Sluzzelin talk 05:48, 11 July 2007 (UTC)

Reactivity of Chrome plating to Hydrocarbon fuels

I was wondering if anyone knew how reactive hydrocarbon fuels (ranging from jet fuel all the way to mogas) reacts with chrome plating?

history of hygiene

Hi - not sure if this is a humanities or science question. In the articles on hygiene, pasteurisation, etc, there is mention that medieval europeans bathed, but no mention why - did they believe dirt carried disease? If so, I'd love it if someone could point me to a medieval text where this is set down.

Thanks,

Adambrowne666 01:58, 11 July 2007 (UTC)

I don't know the answer to this, but I hope that at least some medieval and ancient persons valued not smelling bad. Someguy1221 02:22, 11 July 2007 (UTC)

Hello, Adam! Indeed, I recall reading that sweet fragrances were appreciated in courtly love. Bathing was also a social act, fun, and felt (and feels) good. Here are two links that might help you a bit: Tubd-a-Scrubd, bathing and cleanliness in the Middle Ages. ---Sluzzelin talk 06:00, 11 July 2007 (UTC)

Our article on hygiene has an, albeit short, section on history. So short, in fact, that it fails to mention, Ignaz Semmelweis, the Austrian physician who revolutionized hospitals by showing how dramatically survival rates in hospital raise if staff adheres to rules of hygiene. Before him, your chances of catching a deadly disease in a hospital and dying there may have been higher than getting cured from your original problem. Simon A. 07:14, 11 July 2007 (UTC)

Thanks, all, for your generous answers. As I often do, I posed the question in completely the wrong way. The thing is: I'm writing a bit set in 1650 France, where a badly wounded guy is about to be treated by a surgeon who wants (for reasons we need not go into here) to plaster his wounds with filth. I want the wounded guy to resist the whole idea - but would he have? Did people have any idea that dirt + wounds = problems? (In my desperation, and knowing people in the renaissance were less interested in bathing than in medieval times, I thought I'd have my character hark back to some medieval medical text that commends cleanliness for open wounds, and get around it that way - hence my previous question.) Sorry about this - hope I'm making sense here.

Adambrowne666 07:37, 11 July 2007 (UTC)

Hippocrates, like the Sumerians before him, had the right idea, advocating avoidance of suppuration, and treatment by cleansing with wine, applying a bandage, and then pouring wine on the bandage. It was Galen who screwed up, and pontificated that the formation of pus was essential for wound healing. I'd suggest looking at Theodoric Borgognoni of Cervia (1205–1298), who opposed Galen's idea of laudable pus, and proposed instead attention to control of bleeding, removal of contaminated or necrotic material, avoidance of dead space, and careful application of the wound dressing. Perhaps your wounded guy could have studied him, or harkened back to Hippocrates. But Galen was orthodoxy, and his (erroneous) principles governed treatment generally for fifteen centuries: until the late 19th century. Other names to look at would be Henry of Mondeville, Casare Magati, and Paracelsus - though Paracelsus was in his advocacy lucky rather than perspicacious. - Nunh-huh 08:17, 11 July 2007 (UTC)

Wonderful answer, thanks so much! - I love 'laudable pus'; might even end up as the chapter titleAdambrowne666 11:16, 11 July 2007 (UTC)

Anaconda migrations

The movie Anacondas: Hunt for the Blood Orchid is about a group of giant anacondas (from South America) congregating in Borneo. Ignoring the plausibility of an anaconda deciding to swim across the Pacific as far as Borneo, would it be possible for the animal to make such a journey? 69.77.205.206 02:29, 11 July 2007 (UTC)

I doubt it - anacondas are river snakes, and probably would not survive prolonged immersion in salt water. They would be continuously exposed to direct sunlight, and would likely be unable to feed for the duration of the voyage. While snakes can go weeks (months?) between meals, they typically do not exert themselves continuously during this period. -Eldereft 05:22, 11 July 2007 (UTC)

Moreover, what would they drink? Batmanand | Talk 08:17, 11 July 2007 (UTC)

Fish like Rainbow Trout are Euryhalines, which means they can live in salt and fresh water. They actually go through a metabolic change to be able to do so. As far as I know, River Anacondas are not Euryhalines, so they'd die as soon as they entered salt water. -- JSBillings 11:34, 11 July 2007 (UTC)

Apparently some amazingly far animal transplants have occurred when critters have ended up on floating mats of vegetation that took them across the oceans. An anthropologist speculates here that Homo floresiensis might have ended up on Flores that way, so presumably a snake could as well. This isn't the sort of deliberate migration you're talking about, though. --TotoBaggins 16:38, 11 July 2007 (UTC)

That's the way new species get to islands - it doesn't seem too impossible given enough time. Anaconda is sitting sunning himself on a tree limb (think HUGE tree!) - on the opposite limb of the same tree is the mate of a rival anaconda. There is a storm - the tree snaps and falls into a river - it floats downstream into the ocean with two anaconda's (one already pregnant) - it takes a month or two for the current to wash it over to Borneo - meanwhile maybe they eat seabirds - but a snake can live that long without food or water. They wash up on the coast of Borneo - momma-snake gives birth, then mates with the male - now you don't have a whole lot of genetic diversity - but your growing anaconda population maybe won't be too inbred by the time another anaconda washes up on the beach 50 years later. It could certainly happen...and it this kind of story must have happened tens of thousands of times in history in order for remote islands to have their own odd-ball species. SteveBaker 02:20, 12 July 2007 (UTC)

But, Borneo could have been populated by animals from neighboring landmasses. South America is very, very far. I don't know if it's plausible for a snake to float on a branch across the largest ocean on the planet... Nimur 02:27, 12 July 2007 (UTC)

Sure - Borneo is going to have a lot more animals from close-by places than it's gotten from South America. So I think the creation of a viable colony of anaconda's on the island is possible - plausible even - it's just very, very unlikely. But one assumes that anacondas have been around for a good few million years - there might have been a hundred instances per year of tree+anaconda ending up in a river - so even if the odds of one making it across the pacific is only one in a million, it'll have happened a hundred times throughout history. But this is a movie - it doesn't have to be a common occurrance - it just has to be borderline-possibility. The deeper question is why the movie script writers felt compelled to set a story about anacondas in a place where there aren't any! SteveBaker 14:24, 12 July 2007 (UTC)

I would think it's because they didn't do any research and/or confused anacondas with pythons. Vultur 15:49, 12 July 2007 (UTC)

Something of eyesight & light!

While we are slightly able to see the road during nights (even without street lights) why can't we able to see the same if a vehicle focusses light on our eyes? I can't explain better than this! I think you understood the issue! Temuzion 04:38, 11 July 2007 (UTC)

The pupils of the eyes dilate and contract to allow more or less light into the eye. They dilate in the dark so you can see better, and contract in bright light to prevent damage to the retina from excessive exposure to light. And so, your pupils contract in response to the bright light from the car, and your eyes no longer receive enough light to make out the road. Someguy1221 04:42, 11 July 2007 (UTC)

Worse still, our pupils can contract to shut out bright light quite rapidly - but they dilate again only rather slowly after the bright light goes away. Worse still, the chemical Rhodopsin acts on the cells in the retina to make them more sensitive to dim light. When a bright light hits the retina, the rhodopsin washes out almost instantly to reduce light sensitivity - but sadly, it takes 30 minutes for the rhodopsin to recharge and get you back to maximum light sensitivity. So, critically, even after the oncoming car headlight passes, you still have trouble getting back your night vision - some of it returns within a few seconds - but your best night sensitivity can take a half hour to return! SteveBaker 04:53, 11 July 2007 (UTC)

We have an article on that effect, called Night blindness or "Nyctalopia". Nimur 07:22, 11 July 2007 (UTC)

That articles appears to be about something else, actually. Someguy1221 08:22, 11 July 2007 (UTC)

It's not night blindness at all. Our eyes can only see differences in brightness of 3 orders of magnitude (x1000) within the field of view. Car headlights are much more than 1000 times brighter than the moonlit street. The pupils adjust for the brightest areas, to protect the retina, making the dim ones indistinguishable. Bendž|Ť 10:07, 11 July 2007 (UTC)

I think "Bendzh" has striken the right tong..! B'caz the answer was clear & straight & ofcourse my doubt was completely clarified with it.. I wonder why someone are pondering over the night blindness issue.. it was totally an unrelated subject here.. Finally I thank everyone for their valuable contributions..! Temuzion 04:08, 12 July 2007 (UTC)

Another factor can be scattering within the eye. The strong rays of light from the bright source can be scattered to produce a small amount of illumination over other parts of the retina, and wash out the images of fainter objects. Scattering could be produced by an early-stage cataract or by suspended particles inside the eye (floaters). The severity of this effect would vary from person to person. --Prophys 12:19, 12 July 2007 (UTC)

Cloning

What is the difference between Cloning and Artificial Insemination ?

See Cloning and Artificial insemination, basically cloning is recreating an organism using its DNA, while artificial insemination is simply combining gametes artificially. Artificial insemination will produce similar offspring to ones that are produced normally while cloning will produce identical copies of the parent organism. --antilived^{T | C | G} 06:56, 11 July 2007 (UTC)

Artificial insemination requires a male and a female parent, while cloning only requires a single genetic "parent." Nimur 07:23, 11 July 2007 (UTC)

Whoa!

I was just reading a post on my work's forums about how it doesnt automatically correct for DST, and I was thinking "hmmm, wouldnt it be easy to add such a function to automatically correct for it like other forums do?". And POW, featured article is daylight savings time. More than a little creepy.

What's the proper term for this? Confirmation bias? Capuchin 07:56, 11 July 2007 (UTC)

The root of all superstition is that men observe when a thing hits, but not when it misses.

— Francis Bacon

Bendž|Ť 10:12, 11 July 2007 (UTC)

Synchronicity? Or just coincidence?--Shantavira|^{feed me} 13:29, 11 July 2007 (UTC)

Similar to Bendzh's note, coincidence is to be expected. Amazement should be at a lack of coincidence. -- Kainaw^(what?) 13:31, 11 July 2007 (UTC)

I'd say that rather than "confirmation bias", a closer match would be observer bias (the same reason that people believe that they can psychically control streetlamps by walking under them); it would only be creepy if you'd spent yesterday chatting about building of the World Trade Center, and the day before that dicussing the Ebionites... Laïka 22:32, 11 July 2007 (UTC)

Yes, i'm completely aware that this is perfectly explainable by statistics, don't worry about that. Thanks for the links :) Capuchin 07:56, 12 July 2007 (UTC)

how hard

am not sure if its a medical or not question but how hard does a penis have to be to know ur ok.the other part is hard but the head is a bit soft.is it ok.before u have sex.am 24 and am not sure if am impotent or just beoing stupid.its hard but i tried sleeping withing a prostitute and it kept bending.

I think the quality of your erection is something that you should discuss with your doctor. Splintercellguy 09:01, 11 July 2007 (UTC)

If she displays no resistance to a second round, then your impedance is nothing to worry about. Oh sorry, wrong question! --TotoBaggins 16:16, 11 July 2007 (UTC)

Coconut Husks and Water absorption

My son science project is to establish whether coconut husk absorbs water or not ? Anyone has the reference ? Scientific explanation, absorb or not ? Thanks.— Preceding unsigned comment added by 60.54.53.151 (talk)

The articles Coconut and Coir might be helpful. DuncanHill 11:59, 11 July 2007 (UTC)

I'm no expert - but I strongly doubt it because:

1. A coconut contains 'coconut milk' that would leak out and evaporate if the husk could soak it up.
2. The reason the coconut tree has evolved this massively protected seed case is so that coconuts can float on the ocean from one island to another and thereby spread. If they soaked up water, they wouldn't last for long before sinking.

SteveBaker 14:15, 11 July 2007 (UTC)

I don't see how finding the answer online wil help your son with his project... I suggest your son buys a coconut, slices it such that only the husk is remaining and puts it in a measured amount of water for a certain amount of time (being sure to prevent any evaporation of water). Then after a certain time, remove the coconut husk and measure the amount of water remaining. Any difference will show any net absorption (or desorption). He can also weigh the husks before and after to confirm the result.

Steve, I'm thinking that perhaps the husk is protected from the milk by the flesh inside the coconut (that seems to be where the milk is located when you open one up, interior to the flesh)? Similarly this would protect them from water ingression when floating, still leaving a hollow inside and keeping them afloat? I don't know whether the husk does absorb water but your reasoning isn't solid enough to rule it out. Capuchin 14:59, 11 July 2007 (UTC)

A good starting place would be to decide on a precise definition of the word "absorption. Rubber is not known as absorbent, but a mesh bag full of shredded rubber would certainly pick up some water in Capuchin's experiment, as would a rubber sponge, of course. It's hard to imagine the fibers on a coconut husk not doing the same. --TotoBaggins 16:28, 11 July 2007 (UTC)

Electrical

what is the difference between resistance and impedance?

The articles Electrical resistance and Electrical impedance may help, but they are written in rather a technical manner. DuncanHill 12:46, 11 July 2007 (UTC)

Sometimes a dictionary is more helpful than an encyclopedia. My Oxford Concise defines impedance as "the total effective resistance of an electric circuit etc to alternating current, arising from ohmic resistance and reactance".--Shantavira|^{feed me} 13:35, 11 July 2007 (UTC)

Yes, that's basically it. Resistance describes how strongly a circuit resists the flow of direct current whereas impedance describes how strongly a circuit resists the flow of alternating current at a specified frequency. Note that for "pure resistances" (imaginary devices that have no capacitance or inductance, just resistance), their impedance at any frequency is the same as their dc resistance.

Atlant 16:18, 11 July 2007 (UTC)

Re:Black Hole(s) Vs. Black Hole(s)?

What would happen if a black hole with a force and density of x were to meet another black hole which is far more powerful then it? Will they annihilate each other? Or will the stronger one suck in x? And what will happen if black hole x meets another that is more or less x's power? --Zacharycrimsonwolf 13:24, 11 July 2007 (UTC)

It is all theoretical at this point in time. It is my understanding that the theory of black holes merging is accepted by more people - which doesn't necessarily mean it is correct. I googled for a paper I read a while back. I found this link to a news article about it. I don't know if the article is good or not. -- Kainaw^(what?) 13:35, 11 July 2007 (UTC)

The two will merge, and outside the immediate vicinity of either original black hole (where the local gravity of one dominates that of the other), there won't bNimur 15:30, 11 July 2007 (UTC)e any change from a gravitational standpoint (neither the total mass nor center of mass changes appreciably). There's nothing special about "force" or "density" to this question; it's just two objects colliding. The interactions of their accretion discs (if present), however, would likely be spectacular. — Lomn 13:41, 11 July 2007 (UTC)

The Black hole article states that black holes are a result of individual stars collapsing. So, if, if, a pair (or more) of supergiant stars collapse and form black holes around an area, will they merge as well? --Zacharycrimsonwolf 13:56, 11 July 2007 (UTC)

Sure - the two would approach each other and pretty swiftly spiral around faster and faster until they smoosh together ("smoosh" - it's a technical term - right?!) ...subject to all of the weird relativistic stuff about event horizons and time dilation that make it tough to describe what happens when a black hole devours anything. I suppose it's possible that they might somehow get into stable orbits around each other - so you'd get a kind of 'binary black hole' - but I doubt that could be stable for very long. The black hole article correctly states that a hole initially forms from the collapse of a single star - but it can and will absorb all sorts of other stuff in order to grow - so it will ultimately have 'eaten' many more stars, planets, gas clouds, photons, other black holes...you name it. SteveBaker 14:11, 11 July 2007 (UTC)

Compact binary systems are never completely stable because they emit energy in the form of gravitational waves, causing them to spiral in to each other at an increasing rate. I'm doing a summer internship for LIGO and we just had a talk about these things, which are likely to be the first recognizable signals that LIGO hears. There are actually three kinds of binary inspirals being searched for: neutron star-neutron star, neutron star-black hole, and black hole-black hole. The inspiral phase is relatively easy to model, because you can use Post-Newtonian expansion, but when the two objects get close enough to be in the nonlinear strong-field regime of general relativity, different numerical models give very different results. We know exactly what the GR equations are, but we don't know how to solve them correctly for this complex and violent situation. After the two black holes merge, the resulting larger black hole is distorted from the stable spherical shape, so it emits more gravitational waves in a "ringdown" phase.

In 5-10 years, Enhanced or Advanced LIGO will probably hear the gravitational waves from one of these things, and then we'll be able to say in much more detail what actually happens. Won't that be exciting? —Keenan Pepper 18:49, 11 July 2007 (UTC)

I'm rooting for LISA. If they ever build it, that is... Someguy1221 22:08, 11 July 2007 (UTC)

This page has an animation of two neutron stars merging and forming a black hole. Sorry I couldn't find an animation of two black holes merging. —Keenan Pepper 18:57, 11 July 2007 (UTC)

---

Ooo...okay. Nice stuff, black holes. Anyone can recommend nice snapshots of them? Thanks, Steve, Lomn, and Kainaw. Cheers!!! --Zacharycrimsonwolf 14:16, 11 July 2007 (UTC)

Snapshots? They're kind of... you know... black. Capuchin 14:26, 11 July 2007 (UTC)

Artist impression - not photo.
(Not a photo, but not an artist's impression either. It is a computer-generated distortion of a measured all-sky image, based on calculations of the bending of light by gravity in the vicinity of a black hole.mglg_(talk))

I don't think we have good enough telescopes to image black holes - partly because none of them (as far as we know) are nearby and partly because they are...black...kinda like space is black! What you'd see would be a very small black circular region with some wild distortion of the background stars in the region just outside of that...as in the artistic impression over here =====>

The huge secondary energies that the black hole is emitting in gamma and X-rays as it swallows stars, etc might in turn cause nearby gas clouds to glow in visible light - so there might be some noticable effects because of that. There are lots of nice artist impressions out there - but no decent photos as far as I'm aware. SteveBaker 14:33, 11 July 2007 (UTC)

Just looking at that picture, would there really be a black circular region? surely light would be lensed to this area of the detector. Capuchin 14:52, 11 July 2007 (UTC)

Once again, artistic license in an astronomical photo... I don't think I need to rant about it this time. Nimur 15:20, 11 July 2007 (UTC)

Okay, I can't resist. My biggest complaint is not with the speculative physics, nor the gross misrepresentation of gravitational lensing... (I have seen several images of actual black hole gravitational lensing and none are this ... "gigantic circle of black in the middle.") But what irks me most about this photo is the total absence of CCD noise in the black hole region. Throughout the rest of the photo, the starry background is punctuated by a sort of fuzzy background noise, which is almost certainly due to the thermal effect of the camera sensor. So are we to believe that the black hole is so powerful that it sucks the thermal noise out of the center of the camera? I think I'll just conclude by saying that taking artistic license with a scientific subject is walking a fine line. Nimur 15:25, 11 July 2007 (UTC)

Just so you know I'm not blowing smoke, here is an actual scientifc photograph of gravitational lensing from UC Davis Cosmology Group. It may be less dramatic, but its scientific accuracy is far more inspiring than the other image. Nimur 15:30, 11 July 2007 (UTC)

The image description says that this is a technical simulation too, but under the implausible observing conditions of a 10 solar mass black hole at only 600 km distance from the camera. At that distance, I suppose a hole may well look hole-like, and the lensing effects be severe. Dragons flight

Agree, that image is pretty useless. Why is it at the top of black hole? — Laura Scudder ☎ 16:49, 11 July 2007 (UTC)

I think that the black disc (the hole itself) is realistic, whatever the image's other flaws. I can't see a mechanism for a spherically-symmetric hole to cause a light ray to leave it in such a direction as to appear to come from the body of the hole, since any such ray in the other direction would fall in. --Tardis 18:32, 11 July 2007 (UTC)

You have to take lensing into account. Imagine light rays going around the black hole on all sides and being bent, so that they eventually come together again (i.e. focus) at your eye. They can go around, not through. By the way, there are also counterintuitive effects that can't be understood in terms of tracing rays of light. If you block the sun with a circular disc, you can get a bright Arago spot right in the center of the shadow! --Reuben 18:53, 11 July 2007 (UTC)

I'm aware of lensing, thanks. But for light to appear to come from within the black hole's "disc" (just the section of your sky the event horizon subtends) and yet not come from the hole (obviously impossible), it must start on some other course that intersects a point between you and the hole (but does not intersect the hole!) and then be somehow bent away from the hole onto the line from that point to your eye. I don't see how the hole can do that. As for diffraction effects, I tend to believe that the spatial distortions near the hole would decohere the starlight, but I could be wrong. --Tardis 23:16, 11 July 2007 (UTC)

You're right. Sorry, I hadn't thought through your point clearly. I suppose that leaves only Hawking radiation and any diffraction effects (probably not significant here). --Reuben 14:59, 12 July 2007 (UTC)

Some links: a video of gravitational fields during a black hole merger (done by actual scientists); an article about the video; an article about using the violence of black hole collisions to detect gravitational waves. --TotoBaggins 16:13, 11 July 2007 (UTC)

The video seems to be a bit different from the image above, doesn't it? I mean, in the movie, there is no apparent bending of light around the holes. —Bromskloss 16:30, 11 July 2007 (UTC)

I believe the stuff in the video is supposed to represent gravitational fields, rather than bent light from behind the objects. --TotoBaggins 17:56, 11 July 2007 (UTC)

Yes, there seemed to be some fields there. What I was thinking of, however, was that the still image and the movie must have used different methods to project the three-dimensional space onto the screen. The still apparently follows light rays, which seems natural enough. The movie must use some other method (perhaps equally natural). It would be nice if someone could sort these things out. —Bromskloss 18:05, 11 July 2007 (UTC)

The two visualizations treat space differently because they are trying to illustrate very different things. The still image is specifically illustrating how light rays are bent by the gravitational field, by distorting a photograph of the sky. The video simulation is trying to illustrate gravitational waves. It would be extremely confusing, and thus less useful, if it tried to distort the view of those waves like the still image does. Instead that movie is apparently (I'm guessing here, but it is a pretty obvious guess) produced using a purely spacelike projection. This is what you would see if the speed of light were somehow made infinite for purposes of your vision, so that your vision follows spacelike paths instead of lightlike ones, and you were at rest with respect to the center of mass of the black hole pair. You can see a less compressed version of the movie and read about it here. Returning to the still image, you can read more about it, and see other stages of approaching a black hole, here, and read about the ray paths involved here. Note that the calculation (for the still images) was made for observers that were at rest with respect to the black hole, which would require extreme amounts of rocket power when this close to the event horizon, for a black hole as small as they assumed. An observer that was free-falling into the hole, from having been at rest at great distance, would see a different view (he would be traveling at a significant fraction of the speed of light at that point, so the apparent angle from which photons hit him would be different because of the different reference frame, just like runnning in the rain makes the raindrops hit your front more than if you stand still). --mglg_(talk) 19:53, 11 July 2007 (UTC)

Wouldn't the light travel along the same paths even if its speed changed? —Bromskloss 20:11, 11 July 2007 (UTC)

Yeah, that was not a very useful thing for me to say, since the impossibility of faster-than-light light makes it hard to be sure what I meant. Let me formulate my guess this way instead: I think they

1. Picked the distant-observer space-time coordinate system that coincides with the standard, non-relativistic, Euclidean one at large distance, and in which the center of mass of the black holes is at rest. (For a single black hole, such a coordinate system can be extended to the event horizon, where it breaks down because the radial direction becomes timelike. I imagine it works similarly with two well-separated black holes, but what happens at near-merger I have no idea).
2. Then treated that coordinate system as a normal, non-relativistic space in which vision occurs along straight lines.

Which is just a complicated way of saying that they ignored the bending of light by gravity. --mglg_(talk) 20:46, 11 July 2007 (UTC)

I sort of understand what you say, it sounds good, but I can't follow it quite all the way. What other "straight lines" are there than the geodesics, which light follows? —Bromskloss 13:11, 12 July 2007 (UTC)

Someone said way up above that the mass doesn't change substantially in a collision between two black holes. I don't have a reference but I don't think that's true. As I recall, a very substantial portion of the invariant mass of the combined system is released in the form of energy, as gravitational waves. --Trovatore 22:13, 11 July 2007 (UTC)

I attendent a lecture from Kip Thorne a couple years ago, and he stated a predicted 10% mass loss in a collision between two large black holes. Don't ask me for a paper to cite or anything, though. Someguy1221 22:23, 11 July 2007 (UTC)

The atmosphere of gas giants (a hypothetical question)

Would it be theoretically possible for a gas giant to have a liveable atmosphere similar to Earth's? That is to say, oxygen/nitrogen, active hydrosphere, nice fluffy white clouds and so on? 58.7.181.129 17:15, 11 July 2007 (UTC)

No. Oxygen and nitrogen are both denser than the hydrogen and helium that make up the body of the planet, so they would sink down to the core and stay there. Keep in mind that gas giants have no definite surfaces. —Keenan Pepper 18:31, 11 July 2007 (UTC)

Maybe the question could be rephrased - is it plausible to have a gas giant composed of nitrogen and oxygen (instead of hydrogen and helium?) The answer is, no again, because hydrogen and helium are the only gases that exist in sufficient quantities to form a gas giant. See planetary formation. Nimur 18:53, 11 July 2007 (UTC)

In other words, once a planet reaches a size large enough that it's escape_velocity is high enough to prevent hydrogen and helium from escaping, very quickly hydogen would accumulate until H2 was the predominant element in the atmosphere. (Because hydrogen is the predominant element in the universe) -Czmtzc 19:23, 11 July 2007 (UTC)

What if, by some freak chance, there was no hydrogen or helium in this particular sector of the universe? Or if the planet was specifically engineered to be composed of oxygen and nitrogen by an alien race or something? Would it still operate in basically the same way as a regular gas giant? 58.7.181.129 10:02, 12 July 2007 (UTC)

We're now entirely outside the realm of what could naturally exist, but yes -- an appropriate mass of oxygen could form a gas giant, and at some altitude, the pressure is likely to be livable. Extending an active hydrosphere is yet another unsupportable-but-vaguely-plausible possibility, so why not. You may be interested in checking out Larry Niven's The Integral Trees. — Lomn 14:22, 12 July 2007 (UTC)

...and the sequel The Smoke Ring - both great mind-stretching Sci-Fi by the way! The premise of those books is a toroidal gas cloud surrounding a neutron star (IIRC) with some other planets orbiting nearby to keep the ring together. The gas cloud is made of breathable air - and it contains plants and animals - plus some humans who have been stranded there for a few dozen generations. Forests take the form of gigantic puff-balls of vegetation, there is water in the form of large, spherical 'ponds' that contain fish that float freely around the toroidal 'world'. It's fun to read because these people are living in an essentially zero-g environment. The life cycle of the 'integral trees' is fascinating. I think it's pretty sure that this couldn't work in reality - but the story is good enough that it doesn't really matter. Someone should make a movie based on these two books - it would be AWESOME. SteveBaker 16:42, 12 July 2007 (UTC)

Vacuum blimp

Would it be theoretically possible to make a high-lift blimp type device by enclosing a relatively perfect vacuum in some sort of sealed aerogel? I'm thinking that the total displacement would be pretty significant compared to the weight of the vacuum (negligible) combined with that of the aerogel (roughly eqivalent to an equal volume of air) and the sealant (maybe about the weight of a normal dirigible skin). The only questions really would be whether or not the aerogel would be strong enough to withstand the pressure while sustaining a vacuum (obviously not alone, as it is porous), and whether the difference in lift between it and helium would be worth the cost of manufacturing the aerogel/evacuating the chamber of air. 65.96.237.245 20:46, 11 July 2007 (UTC) Theonewhoclimbs28

It would be theoretically possible, but aerogel is both expensive to make, and somewhat brittle. -Czmtzc 20:47, 11 July 2007 (UTC)

The least-dense aerogels reported so far have a density (after the air is evacuated from them) of about 1 mg/cm³. (The density of a 'functional' aerogel that could be used in the application you propose would be higher; you correctly note that the aerogel would have to be sealed against vacuum, adding weight. In addition, I suspect that these record-setting aerogels lack the mechanical strength to hold up against a full atmosphere of pressure.)

The density of helium is a shade less than 0.18 mg/cm³ at 0 °C, and even lower at higher temperatures. So for now, even a state-of-the-art vacuum aerogel would have less lifting capacity than an equivalent volume of helium. Indeed, given that the sea-level density of air is about 1.2 mg/cm³, it may not be possible to create a sealed, mechanically stable vacuum aerogel with a positive buoyancy at all. TenOfAllTrades(talk) 21:02, 11 July 2007 (UTC)

How about a vacuum bubble constructed by covering a loose aluminum frame with lightweight plastic? Building some sort of vacuum blimp feels possible to me, though obviously a substantial technical challenge with little practical advantage. Dragons flight 21:10, 11 July 2007 (UTC)

For purposes of light-than air travel, "helium is almost vacuum"! The buoyancy of a balloon or blimp is proportional to the density difference between the air outside and the gas (or vacuum) inside. Since the density of helium (molecular weight 4) is already a small fraction of that of air (molecular weight about 29), buoyancy would not change very much if the helium were replaced by vacuum. (To be explicit, it would increase by a factor of 29/(29-4), or about 16%.) The negative effect on buoyancy from the added weight of any conceivable vacuum vessel would almost certainly overwhelm the small improvement gained from replacing helium with vacuum. And most (3/4) half of that same buoyancy improvement can be achieved in a much simpler way: by replacing helium with hydrogen, which is "even closer to vacuum" (molecular weight 1 2), and also much cheaper than helium. That would not require adding any weight to the balloon, except for a large No Smoking sign... --mglg_(talk) 21:34, 11 July 2007 (UTC)

Yeah, but a bouyant vacuum bubble would just be cool.  ;-) Dragons flight 21:38, 11 July 2007 (UTC)

Minor quibble in an otherwise good analysis: hydrogen molecular weight is 2. DMacks 21:43, 11 July 2007 (UTC)

Of course. Thanks. --mglg_(talk) 21:45, 11 July 2007 (UTC)

Remember to take into consideration that the gases (both Hydrogen and Helium) are pumped at higher pressure than air so the real world buoyancy would be less. --antilived^{T | C | G} 22:35, 11 July 2007 (UTC)

This actually amounts to an almost trivially small difference. The internal pressure of a modern airship is at most a few inches of water over the ambient air pressure, resulting in a difference in gas density of less than one percent. Much more important is the change in gas pressure (and therefore density) with altitude. In going from sea level to 300 meters (1000 feet), you lose 4% of your pressure. At 3000 meters (10 000 feet) your pressure is down 30%. TenOfAllTrades(talk) 01:32, 12 July 2007 (UTC)

People definitely under-estimate the power of atmospheric pressure! Ten tonnes on every square meter! Just think of a 1 meter cube acting as a vacuum balloon - think how much structural steel you'd need to prevent the ton of pressure acting on the top - plus the ton pressing up from beneath from crushing it flat! Could you even consider building something that strong that weighs less than a cubic meter of helium?! The thing that would maybe make it possible would be to go BIG! The force you have to withstand from air pressure is proportional to the area of the craft - but the amount of air you displace is proportional to the volume. If you double the diameter of your 'balloon', you'd quadruple the surface area (quadrupling the pressure) - but you'd octuple the volume - so you'd have eight times the available material with which to withstand that pressure. So I suppose the answer is to build something GIGANTIC! SteveBaker 00:12, 12 July 2007 (UTC)

Unfortunately, Steve, scaling up (or down) doesn't help. Consider two cases:

1. If the buoyant object is supported by something that fills its volume (like a solid block of aerogel, or some framework of braces), that structure has a yield strength with dimension force/area, i.e. pressure, so the ratio of this yield strength to the atmospheric pressure it must support does not change with size. Therefore the required yield strength, and thus density, of the gel or framework does not change with size. The weight of the aerogel or framework is then proportional to volume, just like the buoyancy is, so effective buoyancy per volume unit does not improve with increasing (or decreasing) size.
2. If the buoyant object is instead supported by a rigid shell, the force it needs to support is proportional to area, i.e. to radius squared, but the cross section area of shell that must support it (consider the equatorial cross section) is proportional to radius (all right, circumference) times shell thickness. As we increase size, therefore, shell thickness must increase in proportion to the radius. And the area of the shell is of course proportional to radius squared. Therefore the weight of the shell increases proportionally to radius cubed = volume, as does the buoyancy, so effective buoyancy per volume unit does not improve with increasing or decreasing size in this case either. Sorry.

(p.s. This is the same reason why it is hard to find a good way to store pressurized hydrogen gas for automobile use: scaling some storage scheme up or down in size doesn't change the vessel weight required per volume of gas, at a given pressure.) --mglg_(talk) 00:45, 12 July 2007 (UTC)

Hmm - well argued! Yep - I think you're right. Oh well - there had to be a reason nobody ever seriously considers this kind of thing. Thanks for the correction! SteveBaker 02:04, 12 July 2007 (UTC)

"Nobody ever seriously considers these sorts of things" is a bit misleading, eh? Somebody had the idea to build a GIGANTIC BAG and fill it with helium, hydrogen, or just plain hot air. Somebody even went to the trouble of doing the math for it! And somebody believed it might actually work, and stuck to the crazy idea long enough to build it. The same train of thought can be said for manned space flight, submarines, and a whole host of other wacky ideas that could have catastrophically failed in ten million ways. Somehow, an idea gets trivially considered, and sometimes seriously considered, and finally it becomes reality. Nimur 05:07, 12 July 2007 (UTC)

If you'll permit me to synthesize several recent Reference Desk questions, imagine for a moment a sphere of completely-reflective foil. Within this sphere is a vacuum, but we will introduce an enormously bright pulse of light. The radiation pressure keeps the sphere pressed-out against the air pressure and because the foil is completely reflective, the light keeps bouncing around and the foil is not ablated by the enormous luminous flux.

What do you thing? Could it work? ;-)

By the way, I'm pretty sure we've discussed vacuum blimps before on the Reference Desk.

Atlant 12:52, 12 July 2007 (UTC)

As we've explained a couple of times before - the idea of trapping light inside a big reflective sphere doesn't work because no mirror is ever 100% efficient. Even if it's 99.99999% efficient, the light would be absorbed due to that 0.0000001% absorbtion rate - and given the speed of light - that would happen in a tiny fraction of a second. But in any case, for photon pressure to move something (like the foil of your sphere) takes energy - and it would have to be a truly amazingly bright burst of light to have enough energy to 'inflate' your balloon against air pressure - but that energy would very rapidly diminish due to absorbtion by the balloons' reflective inside layer. The idea is interesting - but perhaps light is the wrong thing to use. Maybe you could have a vast array of baseball pitching machines at the center of some giant zepplin-like balloon - they would toss baseballs at the inside of the balloon anytime it looked like collapsing - with some kind of machine to pick up the lost balls and recycle them...but that wouldn't be a very 'smooth' mechanism...oh but wait, maybe something smaller than baseballs...pingpong balls...atoms maybe? ...and then you wouldn't need the pitching machines - you could just use brownian motion...and that brings us right back to filling the balloon with gas - which is exactly what we do. SteveBaker 14:11, 12 July 2007 (UTC)

The key word in my suggestion was (after the intro) the first word: "imagine". Here in thought experiment land, we can have perfectly reflective foil, perhaps made from unobtainium ;-).

Atlant 15:18, 12 July 2007 (UTC)

Well, I was completely with you on the 'thought experiment'...right up to when you asked: What do you thing? Could it work? ;-). At that moment, you crossed the line from 'thought experiment' to 'would it work' - and the answer is "No" for unobtainium-related reasons! SteveBaker 16:34, 12 July 2007 (UTC)

Sure it would work, in thought experiment land. As discussed above, buoyancy improves when switching to lighter particles, so photons, which lack rest mass entirely would be the ultimate choice. (How's that for an article title: Quantum limited ballooning?) To lift a 100 kg person we would need a balloon volume of 83.3 m³; to fill this with photons to one atmosphere of radiation pressure would require a total photon energy of 3*pressure*volume = 25 MJ, over something like 18 ns (=diameter/c), for a pulse power of 1.4 PW. This is within a modest factor of what the National Ignition Facility is supposed to output, so once you have built your unobtainium balloon, the NIF people should be able to fill 'er up for you in a few pulses. Of course, you'd have to to make part of your unobtainium mirror electrically switchable, to get the photons in, but your fictitious-materials dealer should be able to help you with that. The total weight of the photons would be about 275 ng. Happy flying! --169.230.94.28 18:24, 12 July 2007 (UTC)

vortex force decline

Hi Does anyone know the rate of decline or force delivered by vortex rings? For example if a vortex ring can deliver 20 kgs per square inch of pressure when launched from 10 meters, how much more would it deliver from 5 meters? that sort of thing

Robin

It's certainly characteristic of vortex rings that they lose very little energy as they move away from the source - but it's going to be hard to say how much. I'm pretty sure it would be a highly non-linear thing. They travel for a ways with almost no losses - then something catastrophic happens and they fall apart very soon after. I hope we get a good answer - I'd like to know this too! SteveBaker 00:02, 12 July 2007 (UTC)

Pressure Points

Is there a name given to the condition whereby a person does not experience pain, like most people normally would, when having pressure applied to a pressure point? --80.229.152.246 21:09, 11 July 2007 (UTC)

One such condition is congenital insensitivity to pain with anhidrosis. The inability to feel pain is analgia; "congenital analgia" is a synonym for congenital insensitivity to pain. - Nunh-huh 21:53, 11 July 2007 (UTC)

Sorry, but that's not what I am looking for. Thanks anyway, especially seeing as it shows me I need to be clearer. The person I know whom this does affect does feel pain just as much as anyone else I know, it's just that they don't feel increased pain on pressure points like most people do. I.E. poking him hard on a pressure point is just the same to him as poking him on a normal point. --80.229.152.246 21:58, 11 July 2007 (UTC)

After reading the Pressure point article, I have to wonder if maybe the term pressure point isn't well defined. I know when I grew up it was quite popular for kids to press on the point in other kid's collar bone to cause pain, and it simply didn't work for on me. Maybe this person just has a different body configuration such that the pressure point you are using isn't as effective. Or maybe, as I suspect, the whole idea of Pressure points is pseudoscience. -- JSBillings 12:15, 12 July 2007 (UTC)

Surely someone must mention our article on the Vulcan nerve pinch?

Oops, too late! Well, how about Radiculopathy ("pinched nerve") instead?

Atlant 12:56, 12 July 2007 (UTC)

Cactus

I have a catus, "Opurtia Cylindrica", a native of Chile i believe. Does anyone possess one? I need to know how to best look after it.

I found this cahed page which may be helpful [33] DuncanHill 23:33, 11 July 2007 (UTC)

That would be Opuntia. --jpgordon^∇∆∇∆ 00:33, 12 July 2007 (UTC)

120 glasses of water!? Aaadddaaammm 02:36, 12 July 2007 (UTC)

Wha? That's only 7 or 8 gallons (approx 28 L). Geesh. ~ hydnjo talk 03:42, 12 July 2007 (UTC)

If you have it in a pot or outside, whenever you need to water it just soak it thoroughly. Exact water measurements are not necessary. Just make sure you don't water it too often or not often enough. I've killed cacti by going both ways. Sifaka ^talk 06:55, 12 July 2007 (UTC)

July 12

Record Player Sound

I have a copy of the same album on both CD and LP, and I noticed that the LP plays at a slightly higher pitch. The LPs and record player are in good condition, and I couldn't find an explanation at gramophone record. How can the higher pitch be explained? -- Sturgeonman 00:52, 12 July 2007 (UTC)

• Are you sure your gramophone is at the exact right speed? --jpgordon^∇∆∇∆ 00:55, 12 July 2007 (UTC)

Some record players have a stripey disk at the center of the turntable. This is designed so that if it's spinning at the right speed - under a regular room lamp (not a florescent), it will appear to be dead stationary. You can use that to verify that all is well with your turntable. But it certainly sounds like it's spinning a teeny-bit too fast. Most halfway decent turntables have a fine speed adjustment somewhere. I suppose it's just possible that when they recorded the LP, they speeded the master tape up a tiny bit so that they could fit the track onto the limited space on the LP...but I really doubt that. SteveBaker 01:56, 12 July 2007 (UTC)

Steve, why not a florescent lamp which I would have thought to be more "binary" than an incandescent lamp and thus show "strobe" effects more distinctly, no? ~ hydnjo talk 02:36, 12 July 2007 (UTC)

See phosphors and persistence of such to find answer. --Tugjob 02:57, 12 July 2007 (UTC)

I would have thought that the stroboscopic effect was more on target. ~ hydnjo talk 03:10, 12 July 2007 (UTC)

With regard to "ordinary" (presumably incandescent) lamps versus fluorescent lamps, nonsense. Maybe in the 50Hz world the flicker from an incandescent lamp is adequate to look at a strobe disk, but in the 60Hz world, you'll have a very hard time; the peak-to-trough variation in an incandescent filament just isn't deep enough. A fluorescent will give much better effects, especially if you recognize that the light is quite bluish when the arc is active and redish when it's just the phosphors glowing. But the strobe of choice is definitely a neon lamp or light-emitting diode powered from the mains through a rectifier (so it's only on a maximum of 50% of the time). This will give you very clear readings of the strobe disk. When turntable contained built-in strobes, it was almost always just such a neon lamp (with or without the rectifier).

Then again, how accurate is your mains frequency? While it's usually very accurate over the long-term (so electric clocks read correctly), you may find noticeable variations over the short term.

Atlant 13:04, 12 July 2007 (UTC)

Everything you say is OK - right up to the point where what I said is 100% true. Record turntables DO have those disks and they DO work perfectly well with incandescent lamps. Some florescent lamps work OK - some don't - it depends on the type of ballast circuitry they use. To be on the safe side - use a filament bulb - because even though they don't produce a deep modulation - it's plenty good enough for adjustment of a turntable (I used to be a volunteer DJ at a local hospital radio station - and I worked in student radio when I was in college - I've done this a bazillion times, under both 50Hz and 60Hz room lighting). You're right about small variations in mains frequency - but the errors are very small compared to the fairly poor precision of a typical turntable deck motor. At any rate - that is what you get with most turntables - a strobe that works off mains lighting. High end 'professional' decks often have a crystal clock to automatically adjust the speed - so they are every bit as accurate as CD players - but we may deduce that our questioner doesn't have one of those or we wouldn't be having this debate. SteveBaker 13:42, 12 July 2007 (UTC)

Ahh, you're speaking of electronic ballasts. Well, for the low-end (consumer-grade) ones that I've examined so far, the bulk-storage capacitor isn't large enough to store enough energy across a half-cycle of the mains to prevent all flickering, but I'll grant you that point; I was only thinking of old-style magnetic ballasts.

Atlant 15:11, 12 July 2007 (UTC)

Regarding the pitch, I can confidently say that the gramophone player is turning a bit too fast. I am equally confident that there will be a small knob / lever to adjust the speed. Regarding the stroboscopic effect, the stripey disk Steve mentioned must be having the strobe effect built-in. (Like a stripey disk spinning under a stationary disk with stipey holes in it such that you need to look at the spinning stripey disk thru the holes). This would work under an incandescent lamp but would not be very accurate under a florescent lamp (because of a bit of inherent strobe effect). I am supposing this because Steve seemed very confident :-) -- WikiCheng | Talk 04:17, 12 July 2007 (UTC)

Ahh, I get it! The "effect" requires pretty much a steady light as the "built-in" observation scheme depends on it. My bad as I was stuck on the strobe effect of the external florescent light which would indeed screw-up the intended effect. Sorry :-( hydnjo talk 04:32, 12 July 2007 (UTC)

?? I'm a bit confused here. High quality turntables that were around when I was young usually had a series of white stripes around their rim - in fact, usually 3 rows, one for 33 rpm, one for 45 rpm and one for 78 rpm. I seem to remember that the machines usually had an inbuilt light source close to the stripes, and the light source was modulated, probably in synch with the mains power supply, so that the speed was right if the appropriate row of stripes appeared stationary. (The design would vary between countries with 60 Hz and 50 Hz mains supplies). Also, incandescent lights tend to show less strobe effect than fluorescent tubes because their thermal time constant is longer than the persistence of phosphors; hence some people find the flicker of fluoro tubes more distressing than the flicker of incandescent lights. I don't see how a strobe effect with one spinning disk and one stationary would work, without some time-dependent reference illumination. --Prophys 12:39, 12 July 2007 (UTC)

Right - some decks have them around the rim instead of in the center. (Come to think of it - the ones at the last radio station I worked in were like that). My own (ancient) Technics deck has them in the center which is not as convenient because you can't see it with the record on there and the stylus down. Since the stylus must add a bit of drag, calibrating the turntable with the record actually on there would presumably be the most accurate method. I haven't seen one with a light source actually mounted onto the deck - that would be handy - but incandescent room lamps work just fine - I used an angle-poise lamp at the radio station. SteveBaker 13:42, 12 July 2007 (UTC)

While we're at it, why don't the turntables just adjust the rotation speed themselves? It must have been many years since the electronics needed were too bulky to be worth it. —Bromskloss 13:52, 12 July 2007 (UTC)

Some did (with crystal oscillators or what-have-you. But folks, especially high-end audio folks, like to have things to tweak. My AR turntable simply had a synchronous motor so it was as line-locked as the stroboscope would have been.

Atlant 15:07, 12 July 2007 (UTC)

The wattage of the incandescent bulb you use will affect the degree of 60 hz modulation. I have found that 100 or 200 watt bulbs appear to take longer to reach full brightness or to dim than say 30 watt bulbs, whose filament has less thermal inertia. A neon bulb is ideal, and a normal flourescent is better than an incandescent. The powerline frequency does vary slightly, generally running slightly slower when the system is heavily loaded (like on a hot afternoon) and then slightly faster in the middle of the night to "catch up" any synchronous clocks. The frequency usually varies by only a few hundredths of a hertz, but the clock time (which is the frequency integrated) sometimes gets 30 seconds or so behind. The frequency variation should be way too slight to affect the heard pitch. It is always possible that in making the record, with the various steps of copying and editing analog tapes,or earlier wax master discs, there could be noticeable pitch variations. I learned that old time jazz musicians did not really play in the bizarre keys the records seem to be in; it was speed variation in the production of the records. In these cases, you should tune the record to concert pitch by making the record play slower or faster. Analog tapes, wax recordings, and even the cutting of master ciscs for the stamping process, were not guaranteed to be at perfect speed, since the usually were at the mercy of the powerline frequency, which probably had far greater speed variation in bygone decades. A sidenote is that DVDs of American TV programs may play 4% faster in Europe and other places with PAL TV systems, with a corresponding increase of 2/3 of a semitone in pitch, because of 25 frame/second projection there and 24 frame/second projection in the US. The film being over 4% sooner could be a "feature" rather than a defect" if the film is lousy. But PAL TV viewers will find that when they watch a film in the theater it will have 24 frame projection and the pitch will be correct. Some of the latest DVD players are able to show films on PAL systems with correct pitch. [34]Edison 16:10, 12 July 2007 (UTC)

Sorry to interrupt discussion, but Jpgordon was right- the turntable was a tad fast, and I was able to adjust it. Thanks --Sturgeonman 17:39, 12 July 2007 (UTC)

Fates worse than death in nature?

I personally have sympathy for a cockroach at the hands (mandibles?) of the emerald cockroach wasp - and the male anglerfish. So, does anyone know of any other (worse?) examples of dark, lingering, skin-crawling nastiness that the creatures of the land, sea and sky may be subjected to by cruel, cruel nature? --Kurt Shaped Box 00:53, 12 July 2007 (UTC)

Hey, I thought the male anglerfish has it pretty good - permanent female companionship and free food! Vultur 15:53, 12 July 2007 (UTC)

At the cost of his life and very existence as an individual. I *could* make a parallel to marriage here - but I'm not going to... --Kurt Shaped Box 15:59, 12 July 2007 (UTC)

Dunno for sure but what is the seagull's favorite breakfast? ~ hydnjo talk 02:01, 12 July 2007 (UTC)

Round here, a gull's typical breakfast will include one or more of the following: kebab meat, cold chips, pizza, half-eaten burgers, Chinese/Indian food, vomit. Basically whatever the staggering drunks drop in the street on the way home after the pubs close... --Kurt Shaped Box 16:03, 12 July 2007 (UTC)

Since we don't know for sure what's the experience of death we can't really compare them can we? --antilived^{T | C | G} 02:33, 12 July 2007 (UTC)

Ahh, but there's always Imagination which was what I think Kurt was mining for (even though he asked "....does anyone know..." ). ~ hydnjo talk 02:42, 12 July 2007 (UTC)

Well, if you consider magnifying glasses natural... --L^augh! 02:53, 12 July 2007 (UTC)

Ouch! ~ hydnjo talk 03:05, 12 July 2007 (UTC)

'Ribeiroia ondatrae trematode' in its lifecycle, enters into frog's tadpole, induces the growth of additional limbs and immobilizes it so that a crane could make a meal of this frog. Since the frog could move nowhere, it starves and lays there until its death(either by starvation or by being a meal). All this is done to make sure that the trematode enters into the crane where it produces the eggs. — Preceding unsigned comment added by 220.227.179.5 (talk)

Check parasitoids, these are parasites which eventually kill their hosts after a usually long and gruesome process. Or you could have your parasite-infected pulsating eyes ripped off repeatedly by birds, like this brain-function-altered-by-parasitic-worms snail... http://www.youtube.com/watch?v=EWB_COSUXMw Sifaka ^talk 06:45, 12 July 2007 (UTC)

Omarska? Well, humans, even if inhuman, are part of nature, too. 84.160.198.39 18:46, 12 July 2007 (UTC)

Heat transition with colour

How does the colour of somthing affect how hot the water inside it is? — Preceding unsigned comment added by 210.54.194.29 (talk)

If you're asking how the color of a container of water affects the temperature of the water, this was recenctly discussed at the reference desk, and the archive is here. If this is not what you mean, you'll have to be more specific. Someguy1221 07:44, 12 July 2007 (UTC)

insulation affecting current

HI.... i wanted to do an extensive project on electricity and i thought of something. When i take a normal conduucting wire with a plastic insulation on it, and connect it in a circuit, does the insulation affect the current carrying capacity of the wire? i mean to say in one case if i apply a potential to it and suppose with the help of an ammeter find that lets say 10 amps of current is flowing through it....and in another case if i take the same conducting wire but this time without the insulation coating, will more current flow? like does the insulating material affect the current conducting capacity of the wire? i know we might get a shock if there was no insulation....but is this phenomenon possible? will more current flow? and if it will then how can i design an elaborate practical experiment...i mean for my project i need to take experimental readings and collect the numeric data....so how do i design the circuit?

This was asked a week or so ago. It is extremely complicated. However, there are many reasons why insulation reduces the current-carrying capacity of the wire for high current levels. At normal current levels, the insulation has no noticeable limitation. -- Kainaw^(what?) 12:03, 12 July 2007 (UTC)

If it is a good insulator, there will be no change in the current carrying capacity. But if the insulator is not good enough (if it is partially conducting), then insulating a conductor will effectively increase the cross sectional area of the conducting surface and hence this will reduce the resistance, thereby increasing the current. Kainaw... I am curious to know how the insulator reduces the current carrying capacity? Can you point me to any article on the wikipedia / web ? -- WikiCheng | Talk 12:18, 12 July 2007 (UTC)

I think the idea is that the insulation melts if it gets too hot and in that way puts a limit on how much current you can draw. Also, but I'd guess this is less important, since the insulation insulates the wire thermally as well, the wire gets hotter than without it. —Bromskloss 12:43, 12 July 2007 (UTC)

It also matters whether the electrical insulation also acts as thermal insulation. If it does, the copper conductor will run warmer (for a given current flow) and the conductor will change its electrical resistance. So yes, when carefully analysed, the insulation does affect the current flow in the wire even before the insulation bursts into flames.

Atlant 13:11, 12 July 2007 (UTC)

You should really check back through the archives for the full discussion - but in brief, the other point is that the insulation has additional properties in preventing cross-talk between adjacent wires where higher frequency signals are present. SteveBaker 13:22, 12 July 2007 (UTC)

I forgot that part of the previous conversation. It really matters what you plan to use this for. If it is for power, then we are discussing thermal insulation. If it is for data transfer, we are discussing electrical insulation. However, both schools of thought came to the same conclusion - the current carrying capacity (regardless of signal interference) is only affected by insulation when you are handling extremely high currents - in which case the wire heats up and becomes resistant to current. Insulation makes the wire heat up faster. -- Kainaw^(what?) 13:30, 12 July 2007 (UTC)

Brrrr

I was searching for information on different methods of Cold adaptation in plants & animals. I couldn't find exactly what I was looking for but did find articles such as Cryobiology (meaning 1), Psychrophile, Arctic_ecology#Plant_Adaptations, Cold hardening, Hibernation etc. Basically I'm not so interested in methods of keeping warm so much as ways that organisms keep alive, reproduce etc when they are cold for long periods. Maybe there's a more specific term for this that I'm unaware of? JMiall₰ 13:46, 12 July 2007 (UTC)

I just queried our library periodical catalog for "cold hibernation" and turned up two interesting articles about survival and reproduction in animals that spend long periods of time in cold hibernation. None of them are available on the web. Try checking a university library. -- Kainaw^(what?) 13:50, 12 July 2007 (UTC)

As far as I know, the principal effects of low temperature are 1) slowing down chemical reactions in general 2) the growing of ice needles that will destroy the cell membranes mechanically and 3) the change from liquid to solid state that inhibits the transport of molecules cross the cell. Additionally, many enzymes have a temperature optimum and will not work efficiently above or below. Item 1 does only affect the time scale. Item 2 is deadly but can be avoided by dehydration or by substances that lower the freezing point of water or prevent the freezing into needles. (See trehalose.) 3 without 2 need not be deadly as such but prevents any metabolism, making life impossible while in this state. 84.160.198.39 18:36, 12 July 2007 (UTC)

Baffling Bananas.

I had this banana and i pulled the little sticker off of it. i didn't eat it and the place where i left it was really sunny. after a few days, the whole banana was black, save for the place where the sticker had been. what would cause that place to remain normal banana colored?

Complete guess here. I would suppose most of the blackening would be caused by evaporation of water. This wouldnt be able to happen in the place where the sticker was, due to the thin film of glue that was left behind. Other processes of outgassing would also be inhibited. Bacteria would be unable to attack the glued area? I'd love to be proved wrong on this if I am wrong, though. (I'm not exactly knowledgable about food spoilage). Capuchin 14:39, 12 July 2007 (UTC)

I believe the answer lies in polyphenol oxidase, an enzyme that causes the browning of fruits. It requires oxygen to convert phenols to quinones (which turn into melanins--these have antibacterial, anti-fungal and other protective benefits for the fruit--which are dark in color). The sticker (and perhaps residual glue after removal) would have prevented the enzyme's activity. — Scientizzle 15:41, 12 July 2007 (UTC)

"If the black box is the only part of the plane that survives the crash, then why don't they make the WHOLE PLANE out of the black box?" Of interest, this patent idea would use this principle. - CHAIRBOY (☎) 16:19, 12 July 2007 (UTC)

So if they coated the entire banana with this glue stuff they'd last longer? Nah - I have an alternative theory. Perhaps the banana had gotten enough sunlight to be close to turning black - except where the sticker was. When you peeled the sticker off, the area beneath hadn't yet been exposed to sunlight - so it wasn't yet ready to turn - while the rest of the banana had already had enough sun to be close. I prefer this to the "thin layer of glue" hypothesis because the glue is likely to be pretty transparent - where the sticker was not. SteveBaker 16:22, 12 July 2007 (UTC)

So, why don't all bananas thus come covered in peelable glue-backed plastic? ;) --Kurt Shaped Box 16:26, 12 July 2007 (UTC)

The banana was indoors in a non-sunny spot before I accidentally left it out by the window, so I tend to think that it wasn't the difference in sun exposure time. Also, when I picked it up after a few days it was completely black (and mushy) except for the small Dole sticker shaped yellow patch. It was pretty cool to look at. I took a picture and hope to get that on here later.

That is to say that the side that was down on the windowsill would also be less black or not black at all if it were a matter of sun exposure.

chemistry

can any one say how many electrons are released from glycerol after oxidation???

GLYCEROL+O2(OXIDATION) ------>?????????

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. -- Kainaw^(what?) 14:07, 12 July 2007 (UTC)

I don't believe it... there's actually a template for it... 68.39.174.238 15:24, 12 July 2007 (UTC)

It isn't used nearly as often in the summer - most summer school kids don't appear to come here asking others to do their homework (which may be why they are in summer school). -- Kainaw^(what?) 15:27, 12 July 2007 (UTC)

I agree with the above. You should try to do your own work first. But, my suggestion is to figure out what the product of that reaction is. Then you could figure out your answer based on oxidation states or hydrogens gained/lost or etc...Eclipse45 18:54, 12 July 2007 (UTC)

Caffiene Overdose

How much caffiene can a person of average height and weight consume before it becomes potentially harmful. I heard that if you drink three or more Monsters it can cause heart palpitations and the like.

The caffeine article has lots of information about caffeine, including toxicity. DMacks 16:43, 12 July 2007 (UTC)

I prefer to believe the Futurama episode Three Hundred Big Boys when examining, for example, the effect of one hundred cups of coffee on a human, and I quote, "As the flames spread rapidly through the room, an agitated Fry, shaking violently from his massive caffeine intake, heads for the buffet table and drinks his hundredth cup of coffee. Fry enters a caffeine-induced state of hyperspeed, then rescues everyone at incredible speed and puts out the fire.". Fry is unharmed and shows coffee to be an excellent method of achieving hyperspeed. Lanfear's Bane