Wikipedia:Reference desk/Science

Wikipedia:Reference desk/headercfg

August 23

What is Lanalool?

I see this crazy sounding substance in more and more shampoos and conditioners. What is it? And where does its name come from? --24.249.108.133 03:14, 23 August 2007 (UTC)

Are you sure you spelled that right? Lananool has no ghits.Whoops, mispelled it. Someguy1221 03:20, 23 August 2007 (UTC)

Lanalool does, but I'm still unsure exactly what the diff is between that and linalool. --jpgordon^∇∆∇∆ 03:57, 23 August 2007 (UTC)

I don't know what it's fashionable to put in shampoos these days, but maybe you mean lanolin? --Anonymous, August 23, 2007, 03:50 (UTC).

See Acetylated lanolin alcohol (aka Lanalol). -- MarcoTolo 04:04, 23 August 2007 (UTC)

No, I mean Lanalool. I'm quite familiar with Lanolin, silly. --24.249.108.133 19:40, 23 August 2007 (UTC)

I'm not trying to be obnoxious, but you're sure it's "lanalool"? Linalool (with a i) is "one of the most frequently encountered floral scent compounds".[1] -- MarcoTolo 20:02, 23 August 2007 (UTC)

sun and moon simultaneously visible

When the sun and moon are simultaneously visible, how do they appear to people on the other side of the world?

Literally on the other side of the world, i.e., a full half-rotation away? It would be night time, and a very dark night, as there'd be no moon visible. --jjron 08:39, 23 August 2007 (UTC)

Only half a rotation? What about a full one?  :) --Bowlhover 15:18, 23 August 2007 (UTC)

No! Ignore jjron! If it's dawn for me - then someone on the exact opposite side of the earth will be seeing a sunset. So it is certainly possible. There will be some difference in the relative position of the sun and moon because of parallax. This is most noticable during a solar eclipse. The amount of the eclipse is different depending where you are on the surface of the earth. Some places are seeing the moon precisely aligned with the sun (a total eclipse) - other places nearby (a couple of hundred miles away) see the moon slightly overlayed on the sun (a partial eclipse) - and further away still, a few thousand miles away, the moon is just off to the side of the sun (no eclipse at all). SteveBaker 11:52, 23 August 2007 (UTC)

This is the summertime, so if it's dawn for you in the United States (5:30 a.m.), it would be a hot late-afternoon somewhere in China (5:30 p.m.). But it would be nighttime in Australia at the point exactly half a world away, both in latitude and in longitude. Their time would also be 5:30 p.m. but it's winter for them right now; thus the day is shorter.

The same applies with the Moon, except there's a two-degree paralax error that SteveBaker mentioned. The actual parallax error will be smaller if one observer isn't exactly half a world away from the other. --Bowlhover 15:16, 23 August 2007 (UTC)

No! Oh come on guys - THINK! Forget about summer/winter, day/night, USA/China/Australia, whatever! Just take a near-perfect sphere - hold it up in the light of an object that's a very long way away (like the Sun for example) and you'll see that exactly half of the sphere is illuminated. Take one point that's right on the edge of the shadow - now find the point on the opposite end of a line through the center of the sphere - and guess what? It's right on the edge of the shadow too. PLEASE! Simple geometry! Hence if the sun is rising at one point on the surface of the earth then the sun is setting on the exact opposite point. QED.

Now, you may try to argue that the sun isn't infinitely far away and hence slightly less than half of the sphere of the earth is illuminated by it - but that's not true because the sun isn't an infinitely small dot - it's a large disk. Hence the some fraction of the suns disk is definitely visible from two opposite points on the earth at some point during sunrise/sunset. Now you're going to think to argue that the earth isn't a perfect sphere - but the error is of the order of 20km - 0.3% which isn't going to make enough difference to matter. Additionally, refraction of light through the atmosphere actually bends the suns light somewhat into the dark side of the planet - which prolongs both sunrise and sunset somewhat - so in fact, more than half of the earth can see the sun at any given time. SteveBaker 17:29, 23 August 2007 (UTC)

How did sunrise/sunset come up? haw haw pun. I thought he was asking about when you can see a white "ghost" of the moon in the daylight sky.. the answer would be maybe under the best of circumstances a person on "the other side of the earth" - I don't think he means literally 180 degrees, rather just generally on the dark side - could see a sliver of the moon. See this top down view. http://img212.imageshack.us/img212/1687/moonvz3.png --froth^t 22:17, 23 August 2007 (UTC)

No! Ignore SteveBaker! ;) His answer deals only with the extreme conditions at sunrise and sunset. My original answer, and Froth's answer above, deals with the 98% of the time (I don't want an argument on the exact percentage) when it's not sunrise and sunset. Surely that's what the original questioner meant. The sunrise/sunset issue is simply an addendum to this. --jjron 23:07, 23 August 2007 (UTC)

WHAT!? When did the OP mention that it couldn't happen at dawn? In fact, if the question has meaning, the OP must have been talking about dawn/dusk since it's the only way for it to happen. Then YOU flippantly (and utterly incorrectly) suggested that the OP was asking a stupid question (when in fact, it's a perfectly reasonable question) - when I corrected you, Bolhover claimed I was talking nonsense - so he also had to be corrected. And now you are pathetically trying to change things around to make it sound like your first comment was valid. Froth's answer is also nonsense - the OP specifically said "When the sun and moon are simultaneously visible" - so OP was not talking about anyone on the dark side (duh!). So, my answer (which said - precisely - that people on the exact 'other side of the world' when 'sun and moon are simultaneously visible'...can see the sun and moon in different relations to each other in the sky. I answered the actual question that was asked - not some other question as you guys did - and without invalidating what the OP specifically asked for. What's more, I went the extra mile and corrected your collective errors...and I'm in trouble?!?! Bah!  :-) SteveBaker 00:31, 24 August 2007 (UTC)

Hmmm, OK...

1. Now, who said the original question said it couldn't be at dawn? All I said was that without further clarification the logical assumption is that they're asking about the 98% of the time when it's not sunrise/sunset. Now perhaps they did only want a sunrise/sunset answer, but that's nowhere in the question, and has not been clarified any further.
2. I neither flippantly nor incorrectly said the original question was stupid - you're the only one who's mentioned that.
3. Bowlhover might appreciate you getting his name right.
4. I don't know about other users, but I feel that some of your comments are verging on personal attacks, e.g., saying my answers are pathetic. This is not the first time I've noticed this type of behaviour directed towards other users. I would thank you to desist with these actions.
5. Time to cut down on your tirades, and accept that you're not always right, and don't have a monopoly on giving answers. This is not the SteveBaker Reference Desk, it's the Science Reference Desk. --jjron 09:43, 24 August 2007 (UTC)

Ummm, one can see both sun and moon at other times than just dawn and dusk..... (runs away and hides). DuncanHill 00:36, 24 August 2007 (UTC)

You're completely right DuncanHill. It's only in SteveBaker-land that the moon and sun are only ever both visible at sunrise/sunset ;) . --jjron 08:56, 24 August 2007 (UTC)

Don't forget that special circumstance which allows people to see the Sun and Moon not only at the same time, but also in the same space! At this time, the other side of the world is indeed in a dark night (and generally experiencing quite high tide). Laïka 09:59, 24 August 2007 (UTC)

[edit conflict] SteveBaker must be considering the case where the sun and full moon are simultaneously visible. --Allen 10:02, 24 August 2007 (UTC)

Let me try to summarise:

• Most of the time the Sun is not simultaneously visible from two fixed antipodal locations on the Earth - it will be day at one location and night at the other.
• There are two short periods that are exceptions to this - around sunrise and sunset the Sun (or at least part of its disk) may be simultaneously visible at two antipodal locations.
• Similar considerations apply to the Moon - most of the time it will not be visible simultaneously from two fixed antipodal locations. There may be short periods around moonrise and moonset that are exceptions to this generalisation - although the relative neareness of the Moon to the Earth may rule this out too.
• So the only possible times that the Sun and the Moon could both be simultaneously visible from two fixed antipodal locations (even if only in theory) would be when moonrise or moonset conincide with sunrise or sunset i.e. when the moon is close to conjunction or opposition. Gandalf61 10:37, 24 August 2007 (UTC)

Looking back at OP's question, "When the sun and moon are simultaneously visible, how do they appear to people on the other side of the world?"

I don't think the question is asking when or where would one be able to see both sun and moon at 2 opposite positions are earth. The question asks when you can see both sun and moon at the same time, what does the sky look like at the exact opposite position on earth. Seeing both sun and moon can happen most time of the day. I was able still able to see the moon at around 11:30am in chicago during mid-fall. MOST of the time the opposite side wouldn't see either object. But during early sunrises or late sunsets (given you can still see both moon and sun), the other side may be able to see either one or both sun and moon.192.53.187.183 15:25, 24 August 2007 (UTC)

I agree- gandalf's answer is useful but not what the OP was looking for. If one of the antipodes sees the sun and moon simultaneously, what would the other see? Not, "under what circumstances would two antipodes both see the sun and moon simultaneously" --froth^t 16:24, 26 August 2007 (UTC)

Megapixel equivalent of eye

Had a discussion today about the sensitivity of the human eye versus digital camera sensors, VDUs, photographs, etc. We were trying to work out a megapixel equivalent of the human eye. I reckon I came up with a reasonable solution, my friend reckoned I was hugely underestimating. I won't give our figures at this stage, as I'd be interested to see what others come up with independently. What do you think? --jjron 08:35, 23 August 2007 (UTC)

You might want to check out the article on the Eye#Acuity, since it does cover this. Also, keep in mind that the density of photoreceptors differs in parts of the retina, as well as the type of photoreceptor (rod or cone), so comparing the megapixel resolution of a digital camera (which has a constant density across the whole width) to an eye is bound to have problems. -- JSBillings 11:37, 23 August 2007 (UTC)

There are some subtle issues that make direct comparisons with a digital camera tricky:

• The eye has more resolution in the center of its field of view than the edges.
• The edges of your retinas are more sensitive to motion and less sensitive to colour than the center of the field of view.
• Your eye continually vibrates back and forth so that each "pixel" samples the scene in different places which greatly increases the effective resolution for still scenes - but doesn't help much for moving scenes.
• There is the matter of being able to see brightness changes with maybe 4 to 6 times more precision than colour changes.
• All sorts of strange adaptations happen in low light conditions that trade "image quality" for night vision ability.
• We have a continually variable lens on the front end of the eye. This means that those (however many) pixels are sampling a different amount of the world when we are focussing at long distances than at short distances. Because this adjustment is continual and unconscious, it can result in a perception of higher resolution for things closer to the eye than at long distances.

So you just can't come up with a single meaningful number. Do you count the motion due to the vibration of the eyeball? Well, you should if you were deciding the resolution you should print a photograph (say) - but you probably shouldn't bother when planning a movie theatre that's going to show mostly fast-moving pictures. Should you count the monochrome 'pixels' at the edges of the eye? Well, again - "it depends" - those pixels are really good for attracting your attention to potential dangers sneaking up on you from the sides - but terrible at (say) reading a book. That vibration of the eye to improve resolution tends to vanish when you are extremely tired (or sick or drunk) - which is why you may get blurry vision under those circumstances. Black and white pictures can be seen with much, much better resolution than (say) red and green pictures. Switch your Windows colour scheme to red text on a green background and see how long you can stand it! Red and green are about the same brightness - so only your low-resolution colour sensors are helping you out...which makes vision much more blurry than for black and white text.

The whole question is a bit dubious...there just isn't a 1:1 comparison between our eyes and a digital camera. But if this information is not to to be used to settle an argument (or worse still, to win a bet!), I'd say this: In the flight simulation business (where I used to work) we would consider a graphics display of something like 6000x4000 resolution over a 60 degree arc to be roughly "eye limiting resolution" - ie there is no point in making the display sharper than that because the human eye would be unable to see the improvement. So - very, very roughly, 24Mpixels is about it. However, this is a tremendously variable thing and I wouldn't want to be held to that number under all circumstances. SteveBaker 11:41, 23 August 2007 (UTC)

I say roughly 100-200 MegaPixels. Something like 17320 x 11547 digital camera capturing images at 80 times a second. 202.168.50.40 22:25, 23 August 2007 (UTC)

I'm a bit doubtful about that. Suppose we go with (roughly) a 60 degree field of view...at normal reading distance (say 30cm) you'd be able to resolve an object that is 0.3/17320 = 1.7 x 10^-5 meters across. That's 17 microns - you'd be able to see some of the larger bacterium if your eyes were that good. I don't think so. SteveBaker 00:17, 24 August 2007 (UTC)

Hmmm, well the width of human hair ranges from 18 to 180 µm, with an average value of about 80 µm. I personally have no problem seeing a normal human hair from 30cm. Now I may not be able to resolve the very smallest/thinnest ones at that distance, but it's certainly not as absurd as you are trying to suggest. --jjron 08:30, 24 August 2007 (UTC)

Firstly, how do yo know you can see the finest hairs? After all, if you can't see them you won't know they are there! People have very, very fine hairs on some parts of the body. Maybe you can only see the thicker ones. 180um is no problem - you can see that with just 1Mpixel. Are you telling me you can see bacteria? I'm saying that 24Mpixels is reasonable and 100 to 200Mpixels is not. 24Mpixels is only 4x the 'area' resolution of 100Mpixels - just half the linear resolution. So I wouldn't be so surprised if you could see a 34um hair - but I'm pretty darned certain you can't see a single bacterium at 5cm - let alone 30cm. SteveBaker 18:18, 24 August 2007 (UTC)

OK, thanks for answers given so far (no kidding there's lots of complexities to it, I never said the sensitivity of the eye could be directly stated in megapixels; and get down off your high horse, whoever it is that's up on it...sheesh! It's a thought exercise for crying out loud. I thought my original question was pretty clear on that.). Anyway, for the record the answer I proposed was just over 100 megapixels per eye, based essentially on the number of photoreceptor cells. My friend thought it would be more likely in the gigapixel range. Since then though I have also noticed the article on the optic nerve says that the nerve itself contains only 1.2 million nerve fibres, indicating that the retina preprocesses the image before sending it to the brain. This would probably impact the effective sensitivity, i.e., what would get to the brain would not actually be the maximum possible figure that the eye could theoretically detect. Therefore my figure may be too high for the reality of the situation, and what our brain can actually detect may be closer to the figure given by SteveBaker from his practical experience, or possibly even less. Any other thoughts still welcome. --jjron 08:29, 24 August 2007 (UTC)

The optic nerve doesn't transmit pixels - or anything remotely like pixels. It's sending higher level things like "There is a vertical line 20% across from the left and it's moving at such-and-such speed" - the idea that our brain is fed a bunch of pixels is very far from the truth. Hence, you can't deduce anything whatever about resolution from examining the number of nerve fibres. (And even if it was sending pixels - I'd point out that my antenna connects to my TV with just two "fibres" - video and ground - that tells you nothing whatever about its resolution!) SteveBaker 18:18, 24 August 2007 (UTC)

Just noticed this in the eye article - equivalent resolution. Interesting. One calculation gives 81 megapixels, but goes onto to say that the area of sharp vision gained from the fovea is closer to just 1 megapixel. --jjron 08:42, 24 August 2007 (UTC)

Yes, it's an interesting question and odly - one I too was recently thinking about - I wanted to know how many megapixels an EVF would need to be as good as or better than the viewfinder in a SLR - i got 10,000 x 10,000 to be better - 100Mpixels - so I would agree with the 81megapixels figure above .87.102.79.29 13:12, 24 August 2007 (UTC)

where is the sun in google sky?

hi, on google earth "sky" mode.... I cant find the sun (it hasnt gone out has it?)

also how old are the pictures of earth and how often are they updated?

TIA —Preceding unsigned comment added by 91.105.76.65 (talk • contribs) 7:47, 23 August 2007

The images used in Google Sky were collected from telescope images, which don't include the sun. Like the images in Google Earth, they aren't "live" images, but come from archives of images collected by different agencies around the globe, some more frequent than others. Google answers the question of the age of the images in their Help section. -- JSBillings 14:19, 23 August 2007 (UTC)

Now that I think of it, I'm surprised that Google hasn't included high-resolution imagery of the Sun in it's Google Sky, with the option of turning it off. After all, it is a star in our sky. Maybe I'll suggest it. -- JSBillings 14:23, 23 August 2007 (UTC)

Why don't telescope images include the sun?! My telescope can view the sun jus-- I CAN'T SEE!!! AUUUUGGGGGH! :) --Mdwyer 05:15, 24 August 2007 (UTC)

They do have telescope images. They were mostly taken during sun elcipse to get rid of the intense glare. I'm sure it can also be done with some sort of filter though...

Recovering wet electronics

If the interior of a simple electronic is wet, should I dry it until it works again, or slightly longer to ensure no additional water remains? I'm keeping a previously-wet (still wet?) device warm right now with a hair blower even though it became functional half an hour ago. --Bowlhover 14:54, 23 August 2007 (UTC)

Water will rarely destroy electronic devices when there is no electricity running through them. However, it can leave corrosive and/or conductive deposits on the electronics when it dries. For that reason, you should dry the electronics and then clean them (I use rubbing alcohol). -- Kainaw^(what?) 14:58, 23 August 2007 (UTC)

You should probably avoid using a hair dryer to keep the device warm, since it'd probably produce a static charge, plus, heating the electronics can damage the components. Try a normal table fan. -- JSBillings 15:50, 23 August 2007 (UTC)

It sounds like this ship has sailed, but if it happens again, you shouldn't even attempt to turn the device back on until it is completely dry. kmccoy (talk) 16:56, 23 August 2007 (UTC)

Yep - exactly. The best procedure is:

1. Turn off the power, pull out the batteries - as fast as possible! Seconds count!
2. Dab off as much of the liquid as you can with something absorbant like a paper towel. Don't wipe it because you'll spread water from wet areas into dry areas.
3. If the liquid has 'stuff' in it (like a sugary drink for example) - then you may need to wash the stuff off. If so, use distilled water - not tap water. Don't use any detergent or soap...just plain water...and definitely don't used bottled mineral water (the minerals are what we're trying to avoid by using distilled water).
4. Leave it to dry SLOWLY - don't apply heat - don't blow air over it. You'll want to keep it somewhere not too cold - but don't deliberately heat it up.
5. Only after many days - when it's UTTERLY dry - in all the little nooks and crannies - try turning it back on again.
6. If it totally doesn't work - you can try using some of that oily stuff they sell in car parts stores for displacing water from car electrical systems. I've never had any luck with it - but some people claim it worked for them. Definitely a last resort though.

It's a crap shoot though - sometimes it survives - othertimes not. My favorite keyboard died of a diet coke overdose and couldn't be revived - my inkjet printer works just fine after a friends child dumped about a half pint of sticky orange juice inside! I'd never have believed it would still work after I had to pull out soggy paper - and re-wash with fresh, distilled water several times to get rid of the stickiness that pervaded every crevice of that mechanism! SteveBaker 20:01, 23 August 2007 (UTC)

Nobody actually said why to wait until there is no possibility of a drop of water remaining before starting it. The reason is that a drop of water can create an arc and short-circuit the electronics, which will likely cause permanent damage. StuRat 21:18, 23 August 2007 (UTC)

It's not just arcs. What you're really trying to avoid by instantly removing all power and batteries is the movement of ions. For example, you don't want to see all those nasty little chloride ions (from salts) migrating into the guts of the electronics where they'll rapidly murder everything.

It's on this point that I disagree with one bit of SteveBaker's advice: once I'd rinsed away any sticky stuff, I'd use mild heat and/or plenty of air motion to try to dry the circuitry as rapidly as possible. But keep mindful of the idea of mild; lots of electronics won't think well of you above 70°C (the top end of the "commercial" temperature range).

And yes, like so many of you, I rescued something. In my case, it was a TV that was given a drink of egg nog one New Year's Eve; I ended up mechanically removing a lot of the congealed nog the next day.

Atlant 23:10, 23 August 2007 (UTC)

Further to Steve's advice, while I agree that distilled water would be better than tap water to wash away a drink, I'd certainly do it with tap water if I had nothing else available. If the drink dries up in place, it will surely produce more residue than the tap water. --Anonymous, August 23, 22:10 (UTC).

The main reason to chop the power ASAP is because the water connects bits of electronics to other bits of electronics in ways that they were never designed to be connected! Who knows what that might do? Lots of chips are very sensitive to (for example) being driven with negative voltages. Shorting out the power supply ought to just blow a fuse - but these days, fuses cost money - so cheap power supplies are designed to just fail instead. Shorting out a resistor could result in too many volts going to the next device along the chain. Shorting a capacitor could shove a huge spike of current through something down the line - or cause the capacitor to discharge a stored charge suddenly, which might well wreck it. It's unlikely you could get to the power switch fast enough to stop any of those things happening where the circuits are already wet - but water spreads out fairly slowly so if you can cut the juice within just a few seconds, you are definitely improving your chances. The reason to prefer distilled water is that it's less corrosive than water with minerals in it - and also it doesn't conduct electricity anywhere near as well (although you aren't going to turn the thing back on until it's utterly dry - so maybe that doesn't matter. You need to avoid applying a lot of heat to the electronics as they dry because warm water is more corrosive than cold water - and most electronics don't like being overheated (eg with a hair drier). SteveBaker 17:48, 24 August 2007 (UTC)

This thread has prompted me to innovate Dweller's Ref Desk thread of the week award, and I hereby give the inaugural award to those who contributed here. Congratulations. --Dweller 13:00, 24 August 2007 (UTC)

What? No cookies? No barnstar-of-refdesk-goodness? No massive cash prizes? Not even a teeny-tiny penguin to put in the top-right corner of your user page? Where's the incentive here?! :-) SteveBaker 17:36, 24 August 2007 (UTC)

First, shake off any loose drips, then leave to drain (on a draining board) for say 30 mins. If you have a switched on dehumidifier, place the electronics in front of its output and leave there for for 24 hrs. After this time it should be safe for you to reapply power to the circuit. If you have an A/C unit set to dry/cool, this should also work. I have performed this on circuit boards from a TV. Worked perfectly afterwards (the picture ,however, was not noticeably cleaner)--88.109.139.255 18:43, 25 August 2007 (UTC)

The Federal Puke Ray: How does it work?

The government is working on something called a puke ray. http://www.theregister.co.uk/2007/07/27/dhs_chunder_cutlass/ The article claims it just uses light. Anyone know any more about it? I would like to try to build my own. Juanita Hodges 21:29, 23 August 2007 (UTC)

Mythbusters claimed an infrasonic beam could affect the intestines of a person. It did not work when they built it. It would work by shaking the contents loose! Graeme Bartlett 22:35, 23 August 2007 (UTC)

Wasn't there some research done (by the Soviets?) at some point into creating a 'gay beam' and a 'make them shit their pants' beam? --Kurt Shaped Box 22:39, 23 August 2007 (UTC)

I seem to recall the KLF getting hold of some American experimental kit and exploding a cow using sound waves some time ago. DuncanHill 22:43, 23 August 2007 (UTC)

Brown note? Capuchin 06:36, 24 August 2007 (UTC)

On a more serious note, I see we have a Less-lethal weapons article, with some interesting links from the see also section. DuncanHill 22:50, 23 August 2007 (UTC)

• I would guess that one way to do it would be with microwaves: since they (when focused right & all that) heat up water molecules, they should be able to cause serious damage to a gastrointestinal system. --M@rēino 23:01, 23 August 2007 (UTC)

How come it's a "federal" puke ray? I think each state should have its own. ◄Zahakiel► 23:10, 23 August 2007 (UTC)

How absurd. Next you'll be suggesting that each individual state administration should be privy to the records of the CIA's dream-stealing psychoelectronic satellites and the recordings from the microdot cameras hidden in that eye on the back of a dollar bill... --Kurt Shaped Box 23:22, 23 August 2007 (UTC)

Say, are you running for president on 08? ◄Zahakiel► 23:32, 23 August 2007 (UTC)

The news article appeared to claim it was by light, not sound. My neighbors' car stereos already are a sonic attack that cause me so much pain and naseau I nearly puke, but the article said this was with light. Juanita Hodges 01:10, 24 August 2007 (UTC)

Could they be showing the victim sickening images? Also a flashing light at a customized rate around 15 Hertz could cause some interesting effect on people including epileptic fits. Graeme Bartlett 11:47, 24 August 2007 (UTC)

I thought it might be flashing. They did claim there was this specific frequency they hit that did bad things. The TV, computer monitor stuff, etc. is all just red, green, blue stuff and maybe blacks and whites. The sun and light bulbs are all white-yellow variations usually. So it could be a specific frequency of light people don't see. Juanita Hodges 18:11, 24 August 2007 (UTC)

Remember the Sick Sticks in Minority Report? One touch and you'd lose your lunch! I could see a nausea induced weapon if it upset your inner ear and made you dizzy (like sea sickness). Not sure how lights would make you sick unless you were wearing VR goggles and your environment was spinning out of control --24.249.108.133 20:46, 27 August 2007 (UTC)

Which animals sweat?

Horses and humans perspire. Dogs and pigs don't (much). Is there some common thread or selective pressure that makes some animals sweat and others not? Which other animals sweat? Thanks! --Sean 23:11, 23 August 2007 (UTC)

The body surface-to-mass ratio might have a hand in that. If the animal is too large to efficiently siphon off heat, the skin is as good a place as any to get rid of the excess. ◄Zahakiel► 23:19, 23 August 2007 (UTC)

There was an article on sweat not long ago in the New York Times Science section titled "sweatology" or something like that. The basic drift of it as I understood it is that humans are actually pretty unique in this regard, and our copious, full-body sweat glands are among the reasons we can tolerate so many climates. One of the other interesting facts in the article is that while human internal temperatures can regularly be lowered without too much ill effect (hypothermia, but there are some professions where that occurs all the time), but if you raise the internal temperature by just a few degrees you get delusional and often quickly die. Ergo the importance of sweat glands, etc. --24.147.86.187 23:42, 23 August 2007 (UTC)

The lack of thick body hair on humans makes sweating work better. The question should really be why horses sweat. It does seem to cause them problems, as a horse that runs hard in cold weather gets soaked with sweat, then gets cold when it stops running. Perhaps being bred by humans has increased their tendency to sweat, as humans are likely to ride them hard (for which sweating helps to keep them cool) and then keep them warm (say in a barn with a blanket on them) and provide water. Thus, those which sweat profusely were more likely to survive with humans than they would on their own. StuRat 00:24, 24 August 2007 (UTC)

That happens with humans too - they always tell you that in arctic conditions, it's essential not to over-exert yourself to the point where you start to sweat because the moment you stop exercising, you die. SteveBaker 15:22, 24 August 2007 (UTC)

The article Sweat says that "Primates and horses have armpits that sweat similarly to those of humans." -- WikiCheng | Talk 06:15, 24 August 2007 (UTC)

One source states pigs can only sweat 3% the volume we can. Bendž|Ť 08:08, 24 August 2007 (UTC)

August 24

Weak bosons

Can a W⁺ or a W^- emit a Z⁰ I saw this in a list of fundamental interactions but it seems to violate conservation of angular momentum. So how does this work? Thanks, *Max* 01:05, 24 August 2007 (UTC).

Yes, it's possible, and no, it doesn't violate conservation of angular momentum. In order to fully understand how such things work, you must master the Table of Clebsch-Gordan coefficients, no easy task. It's somewhat arcane, but basically this table tells you all the ways that angular momentum vectors can be summed in quantum mechanics. In this case, you want the entry under j₁=1, j₁=1. This means that you have two things that both have angular momentum 1: the W and Z in the final state. Now we need them to add up to a total j=1: the W in the initial state. The entries for m₁, m₂, and m tell you the z component of these three spins. You can ignore the first table there, since it's for j=2. The second and third tables tell you how the state of the final W and Z relate to the initial W. --Reuben 05:41, 24 August 2007 (UTC)

I don't really understand it, but thanks for telling me it's possible. Also, I noticed that my list left out a W decaying into leptons of different generations. Is this just an oversight (they also forgot quarks emitting gluons)? Thank you *Max* 13:31, 24 August 2007 (UTC).

You could also think of the angular momentum as classical. If you put the two final spin vectors along edges of an equilateral triangle, then they add up to the third edge, which has the same length (that's how spin 1 + spin 1 = spin 1). Quantum mechanically the idea is the same, but the mathematical formalism looks very different. There's no simple vertex for W -> leptons of different generations. You can have W -> charged lepton + neutrino, and then the neutrino's flavor oscillates. --Reuben 19:33, 24 August 2007 (UTC)

Wouldn't it be sensible if Nature made us all hermaphrodites?

In a species that reproduces sexually, half of their numbers – the males – do not give birth, but continue to compete with females – who do give birth – for the available food. Wouldn’t a hermaphroditic species have all the benefits of genetic mixing that comes via sexual reproduction, while doubling the number of its members who are capable of becoming pregnant, and thus placing the survival of the species on a firmer footing? And yet no animals more advanced than some lizards are hermaphroditic. Myles325a 04:06, 24 August 2007 (UTC)

And tell us why there does NOT exists any species whose individuals CANNOT impregnate themselves but can impregnate other individuals. 202.168.50.40 04:43, 24 August 2007 (UTC)

(OP myles325 back). Don't understand what you mean. Humans are a species whose members CANNOT impregnate themselves, but who can impregnate others. Maybe you could rephrase your point without the use of double negatives. They can be confusing. Myles325a 05:23, 24 August 2007 (UTC)

When you say 'species' how far are you willing to go? Outside of the animal kingdom, there are a large number of species that have both sexual parts, but cannot impregnate themselves. Think flowers. --Mdwyer 05:12, 24 August 2007 (UTC)

(OP myles325 here). My question was simply why hermaphroditism is not found amongst the "higher" animals, when it is notionally so sensible. I don't understand your point at all. Myles325a 05:23, 24 August 2007 (UTC)

As far as I know, the offsprings produced by mating of different individuals (of the same species) are more robust. Genetically the farther the mating individuals are, the better. -- WikiCheng | Talk 06:13, 24 August 2007 (UTC)

One possible answer, although this is all speculation, is that it provides an easy division of labour. While you think men are competing for food without giving birth, in humans (traditionally anyway) it is the men who are hunting for food while the women raise the children. This system provides a safe environment for child raising and allows men the freedom to hunt. A hermaphrodite species would have to look after a baby while at the same time hunting or gathering, hardly a safe environment for a child. In some species the relationship is more equitable, for example in penguins, the males keep the eggs warm while the females hunt for months, and the men lose much of their weight doing this. The females return, after hatching, take over the job of warming the baby, while the males go off hunting for a long time and this continues. I assume you meant hermaphrodite but not self impregnating, so I don't know if the two sex solution may provide increased competition benefits as well? Cyta 07:17, 24 August 2007 (UTC)

As far as that goes, don't hunter-gatherer societies usually have the women (and children) gathering as well as raising the babies, while the mature men only hunt? So it's not so much of an advantage as you might think. 86.141.89.213 13:23, 29 August 2007 (UTC)

Except that sexual differentiation goes back WAY before humans, way before even division of labor. You can't figure out the origins of sexual differentiation by looking at humans; that's why people like Darwin tried to think about it by looking at animals where the advantages were less obvious to the naked eye (like barnacles and orchids). (And in any case, be aware that speculating on the evolutionary roles of human sexes is a scientific and political minefield. Characterizing men as just "hunters" and women as just "baby raisers" is overly simplistic, and such "naturalistic" explanations often end up enshrining the worst of contemporary social mores and gender roles.) --24.147.86.187 11:35, 24 August 2007 (UTC)

Sorry I didn't intend to offer an evolutionary explanation for gender with my human example, just an example of why it might not be sensible for nature to make us all hermaphrodites, as the original questioner suggested. As for political and scientific minefields, I like to keep the two seperate. And while I appreciate your point on not misusing science to influence politics, I won't avoid what I think is a reasonable "naturalistic" explanation in order to fit in with the "best" of contemporary social mores and gender roles. Cyta 12:59, 24 August 2007 (UTC)

I'm not implying you should embrace political correctness, I'm just implying that if you haven't really taken any serious time to think about gender roles then you should try to avoid speculating wildly on their "natural" origins. I don't claim to know enough about them to sort out the "natural" components or not (and there are surely some there), but I know that I don't know enough to do so with any success at all, and so I avoid speculating. (Put in more religious terms, I am a naturalistic-gender-role agnostic, not an atheist or a true-believer.) --24.147.86.187 00:47, 25 August 2007 (UTC)

OK well I don't consider my speculation wild, although as I admitted in my original post, it is just my speculation. It makes sense to me, that, hunting being a dangerous activity, babies should not be brought along, so someone has to stay home and look after them. Men are on average, faster and stronger and would make better hunters. I can't see any reason why women can't gather as well as men though. And atleast for the first few months of life, there is the obvious advantage that women can breastfeed! None of these things of course apply in the modern world. If I never speculated I'd never answer any RD questions, so I will continue to do so with disclaimers. Cyta 07:02, 27 August 2007 (UTC) ps Simon A's evolutionary answer below seems a much superior one to mine anyway.

Don't worry about it. The idea that men and women were not designed for different purposes (either by God or at random, thank you Darwin!) is scientifically nonsensical. The key idea to keep in mind is that there is no evidence we are confined to operating within these purposes (besides the obvious ones, of course, until some truly sadistic biologist finds a way to allow men to bear children). Someguy1221 07:12, 27 August 2007 (UTC)

I'm not worried at all, I have confidence in my opinions! I have to say I'd be happy to stay home and look after my future kids if necessary, but I am eternally grateful I will never have to go through the pain of childbirth! Cyta 08:23, 28 August 2007 (UTC)

[Edit conflict]

Myles, first of all: Beware of group selectionism. It is the not that uncommon fallacy in thinking about Darwinian evolution to assume that a species will thrive if its characteristics is of benefit for the species. Evolutionary selection only acts on the level of individual organisms (or even of single selfish genes). Now, I'll try to speculate a bit on the reason: Imagine a higher hermaphroditic species and assume that one individual has, due to some mutation, lost the functionality of its female reproductive apparatus. (Let's say the the organ simply got too small and does not work properly.) The individual hence does what it (or now rather: he) can do best, namely impregnate other animals. Given that it costs much more time to grow an egg or even allow an fetus to develop in a womb than to simply inject some semen, our mutated animal uses its time quite productively to spread it genes and the new male-only form will flood the species's gene pool. This results in over-abundance of male mating partners, which requires those of the hermaphrodites who choose to act as females to choose their partner carefully in order to not waste time on bad gene material (which would cause their gene-line to die out, see sexual selection). This renders being female a full-time job, where producing male genitalia is only a waste of energy, and so, a dimorphic species arises. In lower organisms, it seems to me, the disparity in the energy costs of producing eggs and semen is not that large yet, and hence, the advantage of this division of labor does not yet outweight the opportunity cost of not having the flexibility to perform both roles, and hence hermaphrodites occur. (Note, by the way, that many fish retain this flexibility: they can change their sex when needed. Also, observe that unisexuality and bisexuality seem to be quite on equal footings in plant sexuality) You may also like our article on evolution of sex. Simon A. 07:28, 24 August 2007 (UTC)

Sharks have been known to reproduce asexually, but why this is rare is explained in the article. Bendž|Ť 08:14, 24 August 2007 (UTC)

I presume that this is why (in higher species where the cost of child bearing is greatest) the females have evolved to demand often ridiculous adaptations in males. A male bower-bird doesn't have to suffer the 'cost' of producing gigantic eggs and keeping track of the young - which would suggest that the males would out-compete the females for food and such. To counter that, the females have evolved a strategy which requires the males to collect all sorts of junk - carefully arrange it into a bower and do complicated (but ultimately meaningless) dances to attract them. This disadvantages the male to level the playing field when it comes to hunting for food. Many male animals have to produce brightly coloured plumage/fur/scales in order to attract females. This puts them at a terrible disadvantage when it comes to hunting or hiding from predators - but it's the price of doing business...so they bear it. In humans, there is good evidence that females prefer the 'reliable type' of men who are going to stick around and share the cost of child rearing - rather than running off with other women. Females who make this demand are more likely to produce viable young that live to reproduce - so from the male's perspective, it's worth the price. This balances out the disparity of energy costs to the point where the advantage of being a male reduces enough that there is a reasonable population balance. SteveBaker 15:16, 24 August 2007 (UTC)

I've always thought the most enlightening example of gender distinction in animals to be the rotifer. The males can't eat or swim like their female counterparts, and merely twirl around trying to reproduce until they starve to death. Make your own conclusions as to what that means about us guys ;-) Someguy1221 20:56, 24 August 2007 (UTC)

Hermaphrodites have the problem of self-fertilisation which can be disadvantegous in some circumstances. Yes there are other ways to avoid self-fertilisation but seperating your sexes is one of them. I'm not saying this is the reason simply pointing it out as a possibility. Also note that while seperate sexes allows the division of labour it doesn't mean it necessarily has to be genetic or have a strong biology basis. The very existance of seperate sexes allows a division of labour and there could be only a minor genetic and biological basis amplfied by other factors. Finally note on the politics, it's highly questionable whether the existance of a biological and/or genetic basis for the division of labour implies it must be preserved. There is likely a biological and genetic basis for violence particularly among competing males but it doesn't mean it's okay for men to beat each other silly in the opinions of most people Nil Einne 23:16, 27 August 2007 (UTC)

Don't get caught up on the division of labor angle, people...our ancestors (going from early homonids to waaay back to the first mammals) didn't have high levels of hermaphrodism, and widely variable divisions of labor. The simple answer (as to why we're not all hermaphrodites) is that modes of reproduction are inherited down the tree of life and only drastically change if some selective pressure can act on available mutant phenotypes. That is, there would have to be some level of hermaphrodism in a species, and that would have to be selected for to establish itself, allowing such a shift to occur. There's no evidence that hermaphidism would be an "improvement" that would be selected for (in fact, they often have fertility problems) and there are some distinct advantages to regular ol' sexual reproduction that might be "bad" to lose.

Finally, remember that evolution is not (no matter how much Michael Behe wants) subject to external design, and doesn't create a mythical perfectly-adapted species design but rather a currently-most-well-adapted-to-the-present-niche-requirements-given-the-history-of-genetic-diversity-within-the-species-and-an-element-of-randomness design. — Scientizzle 23:29, 27 August 2007 (UTC)

It's important to keep in mind that evolution only builds on what came before. The most primitive organisms that reproduce sexually (and presumably the earliest ones as well) had no gender distinctions. It likely came about that sperm and egg, or the most primitive version thereof, was more advantageous for some ancient ancestor of ours than identical reproductive cells. Now look at human hermaphrodites for a moment. They are rare primarily because testicles and ovaries are derived from the same base organ in devoloping embryos, but those few that exist have never been documented to have functional ovaries and testicles. This is largely because the differing sets of gene activity necessary for bringing each set of sexual organs to maturity are incompatible with each other. It's possible that for some ancient ancestor of ours, it was simply easier for the oganisms devolopment to seperate processes of creating distinct reproductive cells between different organisms, and thus the creation of genders. Now, as to where division of labor actually came from, it's important to realize that there are a great many organisms that reproduce sexually for which there is no division of labor, and those for which there exists no form of society within which to divide the labor. It's possible that any division of labor was an emergent property of human genetics, not directly coded for by our genes. It may have been advantageous for early humans for men to do anything dangerous, not because they're better at it, but because they're pregnant and breastfeading somewhat less often, and an individual man is less significant to the survival of a small group than an individual woman. But it is the nature of division of labor as an emergent property (at least in the absence of any convincing evidence otherwise) that should give us pause when we begin thinking in terms of what gender roles are "supposed to be." Someguy1221 01:09, 28 August 2007 (UTC)

Geometry of complex

I want to know the geometry of potassium trioxalato aluminium trihydride complex?

[K⁺]₃ [Al(C₂O₄)₃]^3- Potassium trioxalatoaluminium complex has 6 coordinate aluminium with oxygens bonded to Al (can be chiral)

I can't see how the 3 hydrogens can be incorporated - have you missed a bit of the name - or can you give more details (eg its synthesis)...87.102.79.29 13:21, 24 August 2007 (UTC)

This link http://classes.uleth.ca/200401/chem2810a/lecture_15.pdf page 91, first set of diagrams, last (rightmost) diagram shows Iron (III) trioxalato complex which has the same structure as the aluminium complex.87.102.79.29 13:27, 24 August 2007 (UTC)

Colour question (related to one above)

How many colours should I be able to distinguish on a monitor - eg what's the 'bit equivalent' of the eye - and is 24bit colour beyond what the eye can percieve in terms of hue..87.102.79.29 13:51, 24 August 2007 (UTC)

This is another question that comes up a lot...and once again, a clear, simple answer is impossible because our eyes simply don't work like a digital camera:

• The eye is very sensitive to brightness variation - but much less sensitive to colour. Our eyes work in Red+Green+Blue+Brightness, not Red+Green+Blue like a TV set, a computer or a digital camera. Interestingly, there is a lot of work out there on RGB+Brightness displays (they are called 'RGBS' or 'RGBE' depending on who you read). Many modern computer games work in RGBE and convert to RGB at the last moment inside the graphics card (I do this stuff for a living!).
• In a computer monitor, the voltage sent to the monitor is directly proportional to the number used to represent it - so 8 bits per colour gives you 256 equally spaced voltages - however TV and LCD monitors aren't very linear - so equal changes of voltage do not produce equal brightness changes. In order to correct for this, computers and such have to perform a trick called 'gamma correction' which re-maps the numbers from a linear-voltage to a linear-brightness. This process causes a loss of precision over some of the brightness range - so the 8 bits you thought you were getting is more like 6 bits over the mid-range brightnesses. Cameras do similar tricks. Our eyes are also non-linear. We can tell the brightness differences between dark things much more easily than between bright things - so you can't directly compare bits-of-computer-colour-resolution to bits-of-human-eye-resolution...it's just not an apples-for-apples comparison.
• The eye is vastly more sensitive to green (and to a lesser extent, red) than it is to blue. However, in computer graphics, we tend to use the same number of bits for all three colours. We can easily see MUCH more than 256 brightnesses of (say) green - so 8+8+8=24 bits is simultaneously more bits of blue than we really need - and not enough green bits. The choice of 8 bits per component for computer graphics, etc is more because of the limitations of the display than of our eyes.
• Our eyes have all sorts of sneaky tricks for grabbing more light - by adjusting the amount of light let into the eye through the iris - and by releasing chemicals that sensitize the retina after you've been in the dark for maybe 20 to 30 minutes. So in a dark place - with dark-adapted eyes, you can see very dim things indeed - but you can't simultaneously see very bright things because as soon as a bright objects enters your line of sight, it erases your dark-adaptation and you don't get it back for another 20 to 30 minutes. So whilst 'instantaneously', 8 bits might be enough - over the entire range of your vision from something as bright as the sun down to something as dim as a candle a couple of miles away, you'd need maybe 24 bits for each of red, green and blue!
• Our 'resolution' is better in terms of brightness than in terms of colour - so for very small objects, colour doesn't work very well. You could imagine using fewer bits of colour for drawing text than for (say) cartoons.
• We are very good at spotting changes in colour - but less good at absolute colours. If you take two swatches of colour and place them a couple of inches apart on a grey background, you can only distinguish differences in the colours when they differ by maybe one or two percent. But if you place the two colours next to each other, then under the right circumstances (muted room lighting - brightly lit colour swatches, etc), you can see a change between the two of maybe 0.02%
• Our brains are designed to recognise the shapes of objects from subtle differences in shading. This is how you can tell the difference between a sphere and a flat circle. But we're pretty astoundingly good at that. Using subtle differences in lighting, we can look at a cylinder (which is just a shaded rectangle on our two-dimensional retinas) and tell whether it has a circular cross-section or a slightly oval cross-section. Remarkably, we can do this using shading cues that have less brightness difference than the smallest brightness differences we can recognise when comparing side-by-side colour swatches. This suggests that our eyes produce 'better' quality images than our brains actually need so that much of that precision is lost when performing unimportant tasks like comparing colour swatches - but which is fully utilised when deciding on the shape of a roughly cylindrical object. This makes sense from an evolutionary standpoint because telling which of two apples is the ripest to a precision of one part in a thousand is definitely overkill - but estimating the cross-sectional area (and hence the strength) of a branch whilst swinging through the trees might well be a life-or-death kind of a thing.

So, the disappointing bottom line is the same as for your last question...we don't really have a way to come up with a good number. The number that's used most often is 12 bits of green, 11 bits of red and 9 bits of blue...but that's by no means a "correct" answer. SteveBaker 15:03, 24 August 2007 (UTC)

Thanks - that was a long and good answer87.102.75.201 15:21, 24 August 2007 (UTC) (I didn't ask the previous question - just to be clear and prevent any confusion)87.102.75.201 15:51, 24 August 2007 (UTC)

Oops! My bad! SteveBaker 16:42, 24 August 2007 (UTC)

Thanks from me, too. I raised the question on the Computing desk (someone else copied it here) because I created an image containing all 2**24 colors (see the top entries here) and found that I cannot distinguish some adjacent colors no matter how much I blow it up. —Tamfang 21:15, 24 August 2007 (UTC)

True - I've tried similar things with long bands of colour varying by one unit. I couldn't see the join - it looked continuous- but I didn't look at every combination; specifically the green colours which I now know I should have been checking..87.102.6.217 22:11, 24 August 2007 (UTC)

But read what I wrote above. Unless your monitor gamma is set up perfectly - and even if it is - and room lighting conditions and that your eye is more sensitive over some of the bit range than others...it's inevitable that there will be some regions and some sets of conditions where you can't see single steps. The best region to see single bit variations is with a properly gamma-corrected monitor in a dark room - looking at only dark shades of colour. That (wonderful!) 4kx4k fractal with all 2²⁴ colours is great - but it puts light colours next to dark ones so it's hard to get a total screenful of dark colours. When I worked in flight simulation, we'd draw a night sky as a subtle blend from some kind of soft glow at the horizon to total black at zenith. In a darkened flight simulator cockpit, it was easy to see single bit steps in brightness - and it was impossible to fix with 8+8+8 bit graphics - so I know for sure that 8 bits isn't enough under all conditions. But this isn't a simple thing - eyesight is very complicated with lots of interacting phenomena. Even under controlled conditions, the amount of time you spend in darkness or how tired you are - all of those things interact. SteveBaker 20:47, 25 August 2007 (UTC)

Scary Movie

Hi, I've recently watched a scary movie about vampires n that sort of stuff... yeah, i know I shouldn have done so , but what's done is done... the problem is that I'm really scared now I know this may sound stupid, but is there a way to stop being scared? I've tried pushin it out of my mind but in vain... Thanks.

Maybe watching Buffy the Vampire Slayer would help?87.102.75.201 15:55, 24 August 2007 (UTC)

Or a humorous webcomic like Scary Go Round or Chopping Block. -- BenRG 01:42, 28 August 2007 (UTC)

I remember getting really scared after watching "The Ring" alone. I tried watching spongebob to counter the effect. :D

Yes, read the How to be saved instructable. That should do the trick. Either that or make it worse. Clem 17:05, 24 August 2007 (UTC)

I've always found that reciting the Litany against fear helped.  :) -- JSBillings 18:04, 24 August 2007 (UTC)

Just remind yourself it's a movie. Maybe after watching a scary movie, watch Scary Movie (a parody of scary movies). Juanita Hodges 18:08, 24 August 2007 (UTC)

I've done the same thing numerous times. The thing to remember is that the vast majority of the time you are afraid of what you don't know. For instance, you are afraid of a dark room because you don't know what is there (i.e. a vampire or werewolf). You could also be afraid of water because you don't know what's under you (i.e. a hungry shark). Of course, your assumption is that these creatures' intentions are to kill you or otherwise commit unspeakable harm to you. The point is that you don't know, which is what you really fear. It's not a huge help, but it gives me some comfort to put it in perspective. --204.23.231.181 18:35, 24 August 2007 (UTC)

Don't be scared. I mean, if the vampires are going to get you, you're not going to be able to do much to stop them. ;-)

Personally I find scary things less scary once I know how they work. Look up how they did the special effects for the movie. Once you see a few "behind the scenes" photos of the actor looking like a doofus it'll be easier to think of it as a staged production. After I saw The Ring (I don't watch very many scary movies) I took some time to look up all of the "scary" death scenes, which are really scary because they are flashed really quickly on the screen in the movie. Once I got a good long look at them and how the special effects were done I didn't worry so much anymore. --24.147.86.187 00:53, 25 August 2007 (UTC)

I still can't bear to look at any shots from The Ring. What did help is that I saw the movie Underworld right afterwards; it is another horror movie, but one where the protagonists have more direct abilities to confront their enemies. That might help. Eran of Arcadia 18:56, 27 August 2007 (UTC)

Next time listen to what mummy and daddy say and don't watch a movie you're too young to watch :-P Nil Einne 14:06, 25 August 2007 (UTC)

If rational reasons don't work, think irrationally. Scared vampires will get you in the night? It's okay; vampires can't enter your house unless you invite them in. Vampires can't go near any sort of cross. Vampires fear books and so can't go within 20 m of one! Decide the rules, then use them in your favour. Skittle 13:10, 29 August 2007 (UTC)

Salt in processed foods

Is it possible that there might be so much salt in a processed food that if you ate it without having any water to delude the salt that the salt content would actually be enough to kill you? Clem 17:01, 24 August 2007 (UTC)

Well LD50 of table salt is about 3g/kg body weight - so if you weigh 50-100kg you'd need 150g to 300g of salt to give you a 50/50 chance of survival.

That's about 10kilograms of corned beef.. (22lb) That said you could make yourself pretty sick by just eating a lot less .

You'd probably gag first before you eat enough.87.102.75.201 17:32, 24 August 2007 (UTC)

Since 1kg of seawater contains 35g of salt - if you weighed 50kg, your LD50 is 150g of salt - you'd only have to drink 5 liters of seawater. That's still an awful lot - but it seems like you could maybe do it. But processed food isn't ever even close to being that salty. SteveBaker 20:12, 24 August 2007 (UTC)

(OH! ...and of course, the LD50 dose is the dose at which half of the subjects die - at good proportion of people would drop dead with a lot less than the LD5- amount.) SteveBaker 20:14, 24 August 2007 (UTC)

I dont know how true this is but i thought the thing that killed you was that you drunk too much water after consuming too much salt? Tiddly-Tom 00:24, 25 August 2007 (UTC)

Per the point several people have made, the LD₅₀ is the median lethal dose. Of more interest perhaps is the LD_Lo which according to [2] is 1000mg/kg in humans. I.E. 50g of salt may be enough to kill a 50kg human. Nil Einne 11:50, 25 August 2007 (UTC)

Could try Dead Sea water. bibliomaniac15 Prepare to be deleted! 01:23, 27 August 2007 (UTC)

So one could die just by drinking 2 glasses from the dead sea ? Interesting --81.67.15.32 18:43, 28 August 2007 (UTC)

Editing Wikipedia telekinetically

I think I read about a kind of advanced, artificial limb that just came out that is designed such that the user can move his/her fake arm just by thinking about it. I think this is prety cool (does someone have a link to that an article about this, btw?). I'm wondering what other types of machines we'll eventually be able to operate just by thinking about their use... Are there other examples of this technology? In the future, could I, for example, edit Wikipedia articles just by thinking about the edits I'd like to make?--The Fat Man Who Never Came Back 18:07, 24 August 2007 (UTC)

You may be thinking of technology similar to this. This company (article) claims to have developed technology which allows players to control video games with their mind. I've read news articles about similar technology in the past but I can't find any of them - sorry — Matt Eason ^{(Talk • Contribs)} 18:14, 24 August 2007 (UTC)

There have recently been a lot of studies about brain waves which have produced experiments using these brain waves to control mouse movement, prosthetic movement, etc. I would suggest you do a google search on brainwave experiments, brainwave studies, or brainwave control. I'm sure you will get many sites on it. To be clear, these experiments use a "cap" of sorts that fits on your head and it connected to whatever device you want to move, it isn't telepathy as we think of it in science fiction. --204.23.231.181 18:46, 24 August 2007 (UTC)

Yes, this stuff exists - but it's not at the level of you thinking "I really wish such-and-such would happen" - and it magically happens - you either have to make a peripheral nerve do something (eg by trying to move an amputated arm) - or in some implementations, you concentrate on modifying your alpha brain waves, which is something you have to learn to do with biofeedback techniques. Either way, we're a long way from being able to think words and have them appear on the page. These are at best fairly slow one or two bit binary inputs. There is plenty of scope for improvement on this though. I suspect the worst part will be in getting electrodes that can be worn comfortably and easily and which don't have to be positioned too precisely. Failing that, we need implantable technology and medical ethics being what it is, I don't think doctors will be routinely implanting brain probes into perfectly healthy individuals. It's possible that in the future, you'll have to take a trip to some country with less medical ethics than in (for example) the USA in order to get your bio-implant widget implanted. The real problem then will be getting it upgraded every few years as the technology improves. SteveBaker 19:22, 24 August 2007 (UTC)

For the sensors to be precisely positioned, they do not need to be implanted in the brain. In the skull would also do the trick and would be a much less tricky operation. Actually, the sensors need only be 'anchored' this way and don't have to be in the skull. All the electronics can then be at the surface. Maybe that would require shaving the head and maybe wearing a whig, but that's hardly a medical issue and I'd be willing to do this if it really gave me direct mind control over electronics. DirkvdM 08:03, 25 August 2007 (UTC)

Some early work on this was done by Miguel Nicolelis, who gave a monkey the ability to control a computer game. An extremely simple one, but it proves the principle. Given that it's a fairly unobtrusive experiment, I wonder why he didn't use a human (such as himself).

Similar work is also done with pilots controlling planes through thought. DirkvdM 08:03, 25 August 2007 (UTC)

Unobtrusive? Did you read the article you linked to "He and his colleagues implanted electrode arrays into a monkey's brain that were able to detect the monkey's motor intent and thus able to control reaching and grasping movements performed by a robotic arm". If you consider that unobtrusive I guess you can volunteer for the next human trials but I'm guessing Miguel himself didn't. BTW, this sort of thing has actually been done in humans [3] [4], not surprisingly in people who had a good reason for being willing to take the risk. Oh and I just found we have a surprisingly detailed article Brain-computer interface Nil Einne 14:05, 25 August 2007 (UTC)

Running On Water

I am aware that there are several species that are able to traverse the surface of water. Plumed basilisk seem to be able to do with speed that counteracts their low weight, while water striders rely on the hydrophobic nature of their legs to beat surface tension. My question, however, is not a biological one, but more in the realm of physics. How fast would a human being need to run to run on water? If you know of some forumlae that can provide the answer, you need but provide it - I am capable of plugging in numbers. If you choose to run the numbers yourself, choose any arbitrary variables that please you (for instance: mass, weight, surface area of foot, etc) as long as you state what variables you assumed at what value, and that they are within human norms. I am fully aware that it is not possible, and that there are likely a number of complicating factors. Let them trouble you not. :) Thanks. -- Sapph42 18:25, 24 August 2007 (UTC)

You can barefoot ski at ~35 mph, according to the article. --Reuben 18:34, 24 August 2007 (UTC)

I'm assuming this takes advantage of hydroplaning, which is hydrodynamically very different than running on the surface. Its a good start, though. Thanks. -- 69.255.155.141 18:57, 24 August 2007 (UTC)

Well, let's think about this. As you push one foot into the water, you are displacing water out to the sides. That requires a force to be applied to the water - which will operate to counteract your weight. The ikky snag is that as you pull your foot out of the water, you have to suck back enough water around the sides to fill in the hole you left. At first thought (and I confess I've spent about 20 second on this one so far!) I suspect those forces are about equal - meaning that you could obviously push yourself up out of the water by stamping down very hard - but in pulling your foot up for the next 'stamp', you'd pull yourself back down into the water to the same degree. So I think a simplistic "running very fast" kind of thing can't work. But maybe with some kind of extreme speed (now purely hypothetical) - you could be trying to make the water move faster than the speed of sound in water - and then maybe something interesting and non-linear might happen. Hmmm - tough. The Plumed basilisk can only do this for a relatively short distance - it's possible that it's feet sink slightly deeper into the water with each step - which is about what you'd expect to happen - but the shape of it's feet maybe minimise the losses so it can stay up for much longer than we might expect. If it could run on water indefinitely (or at least until it got tired) then maybe we'd have to say there was a way for humans to walk (or run!) on water. Hydrodynamics is a tricky subject though - I could easily be way off base on this one. SteveBaker 19:32, 24 August 2007 (UTC)

My initial thought is that the only way this could work and avoid the force/counterforce problem you outline is if the surface is never breached. Is there a minimum response time for surface tension, below which no contact will break it? If so, a sufficiently fast stride could circumvent your objection. Further, in the case of the Plumed basilisk, if it could move twice as fast, would it be able to travel twice is far? If so, regardless of non-linear affects, could a supersonic basilisk travel miles? -- Sapph42 20:24, 24 August 2007 (UTC)

Surface tension is far too weak to have a measurable effect on something the size of a human. It's not a matter of speed. I've had some revised thoughts about this. As your foot strikes the water, the space it wants to occupy is full of water - so if your feet sink into the water (say) an inch - then a volume of water equal to the area of your sole times one inch deep has to be moved out to the sides. In so doing, it accellerates from a standstill to some speed that's determined by how fast your foot comes down. Since force equals mass times accelleration, in order to get a force that's enough to support your weight under gravity - you'd have to move the water out of the way with an accelleration that's proportional to your weight divided by the mass of the water you are displacing. If you displaced (say) 1 liter and you weigh 100kg - then you're going to have to push the water out the way with an accelleration of about 100g's! That's very fast...but in principle you could do it. So for as long as you are pushing your foot deeper and deeper into the water, you are not sinking. But there comes a point where that foot is down as far as it will reach - so you have to stamp with your other foot WHILST PULLING THE FIRST FOOT OUT! But to get your foot out of the "hole" it made, the water has to flow back in beneath it - and if your two feet are moving at the same speed, it seems likely that the upward force required to pull the water back in would be pretty similar to the downward force you get by stamping down on the water. I guess the saving grace here is that when you push down, you are trying to raise the depth of the water slightly - so you are also lifting water upwards vertically. Gravity opposes that so you can apply a bit more force to overcome it. When you pull your foot back out, gravity is helping the water to flow back underneath again - so maybe you have more water resistance in the foot that's going down than you do on the one that's moving up. That tiny amount of difference might be enough for a very light creature with proportionately large feet. Those basilisk guys are small - and skinny with big feet. Since the weight a creature has to support increases as the cube of it's height and the area of it's feet as only the square of the height - the amount of water displacement - as a fraction of weight gets worse the bigger you are. Perhaps that explains how the basilisk does so well at this? SteveBaker 20:54, 24 August 2007 (UTC)

Bored physicists to the rescue. From The Physics of Superheroes by James Kakalios: "The density of water is much greater than that of air - water molecules are in contact with one another, while there are large open spaces between air molecules. . . . [F]or the Flash, when running in top of the water's surface, this is a good thing. Just as someone is able to water-ski if he or she is towed at high speed, the Flash is able to run faster than the response time of water molecules. As his foot strikes the water's surface at speeds greater than 100mph, the water is not able to move out from underneath his boot fast enough and instead forms a shock front, similar to the shock front that forms in front of a supersonic airplane." -- Sapph42 22:33, 24 August 2007 (UTC)

I think that's an unnecessarily exotic explanation. I just point my -- um, that is, the Flash, yeah, that's the ticket -- just points his feet. He leans forward and pushes against the water at an angle with his forward foot. He slides the back foot backwards out of the hole in the water; this requires very little force because he doesn't have to move any water out of the way, except what sticks to the foot. --Trovatore 06:50, 25 August 2007 (UTC)

It's an easy question to answer; the only variable you need to control is the temperature. Just get the water down to around -20C for a while and it should be solid enough to walk, run, and skate on. Matt Deres 14:48, 26 August 2007 (UTC)

Space-time continium

Hi, im writing a science fiction story which involves a device that is able to look back in time, problem is i can't describe how it works because i don't know. I think it would be something to do with the space-time continium, but i'm not sure, i've already checked wikipedia for information, so i was hoping you could give me some info on how such a device could work. Thanks for taking the time to read this. (I would also like to thank everybody who has taken the time to provide answers for my question).

Best regards Sci-fiGOD2k7 18:51, 24 August 2007 (UTC) Sci-fiGOD2K7

A popular idea I've seen in a lot of science fiction is to take advantage of the Multiverse theory, and to view an alternative universe that is identical to our own, only that it is 20 years younger (or whatever time you want to look at). -- JSBillings 18:54, 24 August 2007 (UTC)

Look at info on pages like black hole and event horizon. Looking back in time is what we do all the time. What you see is not happening right now. It took time for light particles to bounce off stuff and then hit your eye. So, seeing far into the past simply means having some old light particles around to catch a peek at. -- Kainaw^(what?) 18:55, 24 August 2007 (UTC)

Or if something less scientific appeals to you, perhaps this device could access the Akashic records.--Shantavira|^{feed me} 19:17, 24 August 2007 (UTC)

Merely looking back seems maybe possible. Firstly, all the information about what was happening back then may not have been lost (talking about a scifi plot rather than reality here). Suppose a book slid across that table an hour ago. The energy of it's motion got turned into heat - perhaps some amazing scifi gizmo could examine the energy present in the world now - and track that backwards in time to someplace in the past. Not possible in reality for all sorts of thermodynamic and heisenburg-ish reasons - but maybe a good writer could make it seem plausible! Alternatively - if we don't have to look back into time before the creation of the technology, it could merely be recording where things in the world are right now - and replaying them later. In a sense, a VCR does what you ask. It's a spooky device that lets you watch TV from the past! A camera and a VCR lets you see into the past. So a device that recorded MUCH more information than a camera and a VCR could record EVERYTHING that happened. Maybe a ubiquitous array of sensors made out of nanotechnological 'dust' and sprayed from the air over everything and everyone - recording in massively complex nanotech memory and replayed via some kind of holistic network which allows you to broadcast a command for any mote of dust that was around 10 years ago at this location to please return data to me. But that limits you to not seeing further into the past than the invention of the machine. Most of the hypothetical relativistic/black-hole/wormhole time-machine contraptions that people come up with would have the same restrictions - but my way is a lot more do-able in reality. To actually see far into the past - before the invention of a machine to do it is exceedingly dubious. Parallel universes (as far as we know) are undetectable and cannot communicate information to us - so they don't really help - although if you are prepared to bend science enough, you could argue for it.

Do me a favor though. If you write this story - think about this: If you have a machine that can see back in time, it also has to be able to see different locations in space too - the earth is orbiting the sun - if you look back at the spot you are at right now, but 6 months ago - all you'll see is vacuum - because the earth was a long way away back then! So your device has to be able to look at any place as well as any time. If it lets you look back (say) 1 millisecond ago - but anywhere in space - then it's able to spy on anyone right now! It would be a tremendously useful instrument because we could (presumably) use it to explore the bottoms of the oceans - or the innermost parts of the earth's core. If the device were cheap enough so that (for example) a major newspaper publisher could afford one, you just know that nobody would have ANY privacy anymore. Forget being able to see into the past! Seeing any place here in the present would be an earth-shattering thing. SteveBaker 19:54, 24 August 2007 (UTC)

This is the plot for an old Isaac Asimov story. The government suppresses the technology because it allows someone to spy on anybody. Delmlsfan 02:31, 25 August 2007 (UTC)

I thought it measured the trajectory of neutrinos.. it's a pretty stupid idea. Based off of "if you know every particle's location and trajectory then you know the future".. of course it's impossible to define exactly where a particle is at quantum size, and it makes even less sense to try to pull off that calculation with only a miniscule data set --froth^t 04:05, 25 August 2007 (UTC)

There's a fairly famous old story on this premise, "E for Effort" by T. L. Sherred. Damon Knight revisited it, in a mellower key, in "I See You" (1976?), which i think assumed a sort of slow light. —Tamfang 21:56, 24 August 2007 (UTC)

I want to thank people for helping me with this matter, as its driving me nuts. My original idea was that it was a system of satellites all hooked up to a quantum computer, and the satellites were somehow able to look back in time, but i'm not sure how this would work. Thanks again, Sci-fiGOD2k7 22:30, 24 August 2007 (UTC)

I'm a big fan of this kind of 'hard-core' scifi - and in my view, I'll allow any story writer ONE ridiculously impossible invention providing that:

• It's self-consistant (like with what I said about it being able to see any PLACE as well as any TIME) - if there is a glaring inconsistancy - it'll bother me through the entire book!
• That all of the implications of the thing are properly explored.
• That it's actually necessary for the plot.

What I hate is when some device is postulated - and I find myself saying "But if you had a thing like that - why wouldn't you use it like this?!?" - or "Why did the author need to invent such a thing when the story would have been just the same with more reasonable technology". So I'd be happy to read a story where you handwave the details of why some quantum effect in a satellite allows you to look into another place at another time - so long as you tell me about the consequences of using it for spying on your boss one second in the past (or whatever). (I'm also trying to remember another story based around the "machine that looks into the past"...something to do with investigating the history of Christopher Columbus...I don't recall. SteveBaker 01:05, 25 August 2007 (UTC)

A looking-back-in-time machine

At right is a real-world device that once looked 13 billion years back in time. --Sean 01:10, 25 August 2007 (UTC)

I remember an Isaac Asimov short story had such a device. I can't remember if it had much explaination. Basically someone came up with the theory. The device was invented and under the control of the world government science ministry. They controlled the information about the device that was release. They did regularly release 'discoveries' from the past. Then a history professor got annoyed when his proposal to study something never received any attention and enlisted a student to help him (illegally) make a device. The student accepted but after a while realised that the government had been bullshitting as the device couldn't look back that far as it got more blurry the further back you go. The professor's wife found out about the device and was very interested. The professor himself lost interest because 1) It couldn't study what he wanted to 2) His wife wanted to look at their dead daughter which was bad because a) It was unlikely to be beneficial for her well being to keep look at her dead daughter b) He was a smoker and was afraid he may have been responsible for the fire that killed his daughter. The government meanwhile found out and was watching the involved parties with their version of the device. They professor intervened and tried to get the student to stop making the device. The government joined in and pointed out the reason they'd been protecting the device was because it completely destroy society as it would destroy privacy; as the past is basically the present. Unfortunately it was too late as the student had already given his research to his uncle who had then given it to the press and the government had not noticed the uncle's involvement so had not watched him. Anyway the point of my retelling here was to concur with SB. If you want to include such a device you have to think of the implications it will have. I mean there's already enough of Britney and Paris in the media without "watch Britney drinks a glass of water" or "watch Paris try out 3 dresses before deciding just to go naked (everyone's already seen her naked anyway)". Unless you take the easy way out and do the opposite Asimov's device, it can't look into the near past but only the far past. But this makes far less sense to me... Nil Einne 12:55, 25 August 2007 (UTC)

In fact, on the theme of implications, doesn't the story conclude that the whole reason for the interfering government and broken, fragmented academic system was to prevent this machine being built? The 'evil' government was just trying to protect everyone from the implications of progress. Completely unlike the Philip K. Dick (I think) short story where the man creates a time/space-viewing-portal thing in order to pass the exams that only robots have previously passed and get a job in government... But I digress. Going only far back in time is more like 'The Ugly Little Boy' (or whatever it's called, also by Asimov) isn't it? It could work. Personally, I wouldn't try to explain it properly; just have your characters accept that it works, and keep it consistent. Skittle 22:54, 28 August 2007 (UTC)

Yes I think it was the reason for the intefering government (or it may have just been to stop this machine and whatever else that may come along with similarly very nasty implications in some regards). Definitely the government person said something about how people like you always think about how bad the interfering government but fail to consider perhaps what they're doing is necessary and good. As for the Ugly Little Boy, was that one a physical limitation? Or was because they weren't just looking back but actually intefering and things tend to balance out in the end over time but if you go to close (or steal a famous person or whatever) they might not. Nil Einne 21:51, 30 August 2007 (UTC)

I have thought of what i want the device to be, a series of satellites linked to a powerful earth based quntum computer. The device can look a far distance back in time and as its a system of satellites it can look any where on earth. But i have a problem, as im not sure how i could get it to look back in time, does anyone have any ideas to how it could look backwards through time, because personaly i'm no good with the whole spacetime thing, but i was thinking it could use a series of light cones to look through a closed time like curve, but im not sure how it would do this and if it would work (in a fictional stand point). So if anyone has any ideas of how this would work i would love to hear them. Thanks for all answers past and future

Sincerly Sci-fiGOD2k7 16:29, 25 August 2007 (UTC)

A large mirror placed 2 light-years away - coupled with a really powerful telescope - would allow you to see exactly four years into the past. But as with all such devices, even if you launched it at some insane speed, close to the speed of light, it would take more than two years to get to the right place and by the time the light reflected from it got back to our telescope, it would be another two years - so the machine would only be able to look back to points in time AFTER its initial creation. This does seem to be a fundamental limitation of all such contraptions. SteveBaker 22:06, 25 August 2007 (UTC)

Also, the diffraction limit implies that you wouldn't be able to see very much. At visible wavelengths, with a mirror and telescope both as large as the entire Earth, you wouldn't be able to resolve any feature smaller than about a kilometer. You can get much better resolution much more economically by taking some photographs locally and looking at them four years later. -- BenRG 22:07, 30 August 2007 (UTC)

You can't really look back in time. All you can do is make inferences about the past based on surviving relics, like old light or old neutrinos or old manuscripts. We can only see the cosmic microwave background because it's right here, right now; if it weren't, we couldn't see the early universe no matter how hard we looked. Your device can only work if there's some hitherto unknown phenomenon that records information about the past in some locally recoverable way. -- BenRG 22:07, 30 August 2007 (UTC)

Okay, so what if somebody traveled to the past would there be any way for the device to lock onto them from the present? Sci-fiGOD2k7 18:30, 31 August 2007 (UTC)

I suppose it depends on what mechanism you've introduced to allow time travel. In general, if people can time travel somehow, I suppose a mechanical probing device could also travel back and forth in time relaying messages. -- BenRG 14:19, 1 September 2007 (UTC)

user knowledge

I have developed an indicator circuit to display the status of a Hall sensor. A friend says the user of the device it is in will not buy it because it is diagnostic tool only a technician would find of any value. I contradict saying that knowing is far better than not knowing regardless of whether the knowledge is useless of over your head. Who is right? Clem 20:54, 24 August 2007 (UTC)

I'd say you and your friend are right, whereas the user is wrong, and you might want to adapt to the user. As you say, for a completely rational person, more knowledge is always good. Your user, however, might find it intimidating or something, because he does not understand it. I did a similar thing at the supermarket the other day. I was going to buy ham, but there was too much to choose from so I ended up buying nothing! Stupid of me, but that's what I did. —Bromskloss 21:38, 24 August 2007 (UTC)

Perhaps a compromise is in order. I agree that displaying something all the time which the typical user won't understand would be annoying to them. Instead you could have them hold some combination of buttons down to get the status of the Hall sensor. That way, the user won't be annoyed by it, but techies can still get the info if they want it. StuRat 03:42, 25 August 2007 (UTC)

Good idea. An on/off switch. Clem 22:45, 26 August 2007 (UTC)

Maglev technology & Meissner Effect/Flux trapping

I know about the Japanese maglev system that uses superconducting coils for efficiency in its EDS system, but why has no-one tried using the Meissner and flux-trapping effects demonstrated by super-conductors (below their critical temperature) to create a stable maglev platform? The technique has been demonstrated on 'toy' maglev trains, videos of which can be found on YouTube ie. http://uk.youtube.com/watch?v=rfUWDYm0ewI

Would such a design not be favourable over both electrodynamic (EDS) and electromagnetic (EMS - eg. Transrapid) suspension, EDS requiring the movement of the train to create the levitating force, and EMS being naturally unstable and requiring a computer control system?

Or are there technical limitations that I am unaware of? For example can this method carry the weight of a laden train?

Thanks, Jonaboff_talk

22:41, 24 August 2007 (UTC)

Just an idea. I believe the superconducting property vanishes in the precense of too strong a magnetic field (right?). Carrying a full-size train would require a stronger magnetic field than carrying a toy. Perhaps it would be too strong. —Bromskloss 23:01, 24 August 2007 (UTC)

It would be a matter of price. A superconducting coil in the train is one thing, but making hundreds of kilometers of superconducting track would exceed the budget of the train company. The material costs on the order of $100 per gram, or $100,000,000 per ton. Graeme Bartlett 23:16, 24 August 2007 (UTC)

A minor note—the toy shown uses conventional (albeit fairly powerful) magnets in the track. The only superconductor in the toy is aboard the train. Of course, sufficiently powerful permanent magnets for such an application would also be quite costly. I'm not prepared to comment on whether it would even be possible to scale up such a system to operate at hundreds of kilometers per hour and with cars weighing tens of tons. TenOfAllTrades(talk) 13:09, 25 August 2007 (UTC)

I'd say Graeme is right. No chance to make such a large installation superconducting. The largest device build so far to my knowledge is the Large Hadron Collider: The 30 kilometre circumference ring is kept at liquid helium temperature to be able to use superconducting magnets. Simon A. 08:39, 25 August 2007 (UTC)

It there any reason why you have to use low temperature superconductors? Most maglev systems in development using superconductors are using 'high' temperatures ones cooled by liquid nitrogen Nil Einne 12:58, 25 August 2007 (UTC)

As Ten said, only the bogeys of the train would be superconducting, the track would be ferromagnetic. Do the superconductor effects only work with permanent magnets, or could electromagnets be used?

I also have a feeling that the $100 per gram estimate is a little high, that puts it at around £50, right? I can buy a kit like the one shown in the video for little more than £100, and the superconductor block weighs much more than 1 gram.

Thanks, Jonaboff_talk

14:05, 25 August 2007 (UTC)

I'm not 100% sure if I understand the difference between what you're proposing and what's be done but, are you sure this has never been attempted? What about the Southwest Jiaotong University, China test (see Maglev train). Our article has limited information but there is more information in various journal articles. Nil Einne 14:46, 25 August 2007 (UTC)

The Southwest Jiaotong University, China maglev is actually exactly what I meant by the sounds of the article, I'm not sure why I haven't noticed that in the article? I'll check the history, see how recently the section was added. Thanks anyway. My point still stands, that it seems strange to me that this approach isn't more popular, when it eliminates the problems of stability, power failure, does not require wheels etc.

On a side note, does anyone know if electromagnets can be used in such a system, or can only ferromagnetism achieve these effects? Is there a physical difference between electromagnetism and ferromagnetism besides the source?

Thanks, Jonaboff_talk

15:45, 25 August 2007 (UTC)

It's actually been there for quite a while (unless it was removed and re-added). I researched maglevs a bit a while back and it was there then. Check out the talk page for comments I made, it was there when I made them. However I don't and didn't have access to the journals which talk about it so I couldn't update the article (and it's probably over my head anyway). There is actually surprising little information I could find in more general publications other then an occasional PR from the China side which doesn't generally provide much useful information. I do recall that there is some controversy in Germany recently over whether some of China's recent work on maglev trains may have been 'borrowed' from the Shanghai maglev but the 2000 thing is I presume mostly home grown (well as homegrown as anything in China is). Nil Einne 21:55, 30 August 2007 (UTC)

August 25

Mountain height limit

I recall learning about a height at which mountains 'melt' their base, implying a hard limit on the physical height of mountains (on earth, etc). Is this true, and can anyone find details? Thanks :) --Quiddity 00:50, 25 August 2007 (UTC)

Regarding erosion... Angle of repose. —Preceding unsigned comment added by 138.29.51.251 (talk)

There are a few limits you can put on the size of a mountain, depending on exactly what failure mode you're interested in. It turns out that there are different things keeping mountains up: some are effectively floating, some are totally unstable and start to sink as soon as nothing is building them up again... the article at isostasy has some more information. Here's a paper where the author estimates the maximum height of a mountain: How high can a mountain be? by P.A.G. Scheuer, J. Astrophys. Astr. 2, 165 (1982). This primarily considers the failure mode where the mountain simply falls apart. As you make the base wider and wider, it's possible to make the mountain taller and taller. The paper also describes an odd "tower" of blocks that can be arbitrarily tall. There might also be a largest mountain that can be statically compensated, but I'm not sure about that. I don't think that melting as such should be a problem. You have to go all the way to the outer core to get liquid. It's more a matter of overstraining the material until it breaks. --Reuben 06:51, 25 August 2007 (UTC)

To elaborate on Reuben's point, the outer core starts at a depth of several thousand km, whereas mountains grow up to heights of several km or at most tens of km if you measure from the deepest sea trenches instead of the sea surface. However, I imagine there would still be some effect, even if it is not the most decisive. Also, some volcanoes (which are mountains of sorts) arise at hot spots, where the crust is much thinner. DirkvdM 08:28, 25 August 2007 (UTC)

So we know that for most substances, the melting point decreases with increasing pressure - so at what pressure does rock melt at (say) 20 degC ? Once you know that it should be a simple matter to discover the answer to this question. Sadly, I don't know how to find out that first answer. SteveBaker 21:13, 25 August 2007 (UTC)

A minor quibble—the melting point of most substances increases with increasing pressure, not decreases. One of the few materials for which this isn't true is water, resulting in the unusual, negative slope of the solid-liquid boundary on its phase diagram. TenOfAllTrades(talk) 03:07, 29 August 2007 (UTC)

I don't know if "melting" is the right model, but that's the basic reason why Olympus Mons is on Mars, and could never exist on earth with its greater gravity. Gzuckier 15:15, 27 August 2007 (UTC)

Monounsaturated and Polyunsaturated Fats

Hi, I've learnt that mono- and poly- unsaturated fats are beneficial to one's health, yet which is more important or more beneficial? I don't mean totally cutting out the other, but I just wanna know which is better. Thanks

There was a time in living memory when the conventional wisdom was, the more double bonds, the better; polyunsaturated fatty acids were considered to have better properties as regards preventing plaque accumulation in the arteries. I'm not an expert on this, but I believe the mainstream thinking has changed, and nutritionists think that most people would be well advised to increase the proportion of their fat intake that consists of monounsaturated fatty acids such as those found in olive oil and peanut oil (while reducing their total fat intake overall). Supposedly the polyunsaturates are more likely to cleave at the double bonds forming dangerously oxidative free radicals.

But you never know. These guys change their story a lot; five years from now we may be hearing something different. One exception to the "polyunsaturates bad" current conventional wisdom is that people are considered to require a certain intake of omega-3 fatty acids for proper brain function. --Trovatore 06:28, 25 August 2007 (UTC)

regarding heat

I understand that as an electron goes down an energy level it will release a photon or cause the atom or impart more kinetic energy to the atom. Could you please explain how this kinetic energy is imparted?

It still happens by a photon being emitted, but the photon is absorbed by a neighboring atom. Some other effects also come into play. When the photon is sent out it carries some momentum, and the atom moves off in the opposite direction to compensate. The photon is lowered in frequency or energy to compensate. Another way is that energy is shared amongst several atoms. One way to visualize it it to imagine the activated atom to be larger, and it suddenly shrinks or changes shape. If it is attached to other atoms in a chemical bond, it will shake around all the atoms involved disapating the energy. Graeme Bartlett 22:12, 25 August 2007 (UTC)

thanks

bird blood

Hello, if birds have hollow bones how do they synthesise blood ?Boomshanka

I asked the same question a while ago. turns out that bird bones aren't really hollow at all. They have air pockets, but apperently they also have bone marrow the synthesize new blood cells. PvT 17:07, 25 August 2007 (UTC)

Anyone who's sucked the marrow out of a chicken bone has seen it first hand. It's also worth noting that flying birds don't seem to have a lot of blood. I've hit birds with my car windshield, and it was all just feathers and grey guts with little or no blood. --Sean 12:20, 26 August 2007 (UTC)

Toxicity of unrinsed dishes

In the Netherlands (and in the UK, it seems) many people do not rinse the dishes after washing them. Washing-up liquid has a link to a suggestion that that is no problem if the right concentration was used, but I doubt that that happens often (most people use way too much, especially in the US). So is any remaining washing up liquid on the dishes a health risk? Btw, I once heard that swallowing pure washing-up liquid is unhealthy because it makes your intestines stick together, but that's a different thing. DirkvdM 06:22, 25 August 2007 (UTC)

Not in the short term - apart from the taste the small amounts should have no ill effects

In the long term - who knows? Myabe you'll just have a nice clean intenstine!87.102.84.56 12:59, 25 August 2007 (UTC)

It would depend on the composition of the dishwashing detergent used. Since it's not normally intended for human consumption, they may put things in which are somewhat toxic (not highly toxic, mind you). If you consume a substantially larger quantity than they expect, you may suffer from health issues. Of course, my observation is that food contaminated with even tiny quantities of dishwashing detergent is so unpalatable that I can't eat it anyway. This is why you should clean dishes in the organic way (have your dog lick them clean). StuRat 16:58, 25 August 2007 (UTC)

Disclaimer: this is my opinion, and I'm a very opinionated person.. I'll never understand people who don't rinse their dishes. It's like taking a shower and leaving the shampoo in your hair. Rinsing not only removes the detergent leftovers, but it's also an important part of the actual cleaning process. After all, the whole point of detergent is to make the grease come off. The grease will indeed come off the plate and attach itself to the soapy water, but if it isn't rinsed off, then you effectively haven't cleaned the dishes at all. Oh well.Nimlhûg 20:32, 25 August 2007 (UTC)

Exactly, that's what I tell people too. It's the rinse that counts, the soap or whatever is just an aid. I once saw in a hospital how the floor was 'cleaned' by applying a detergent solution (what do you call that?) and then simply sweeping it up again. No rinsing. That's just redistributing (most of) the dirt and adding toxic stuff to it. In a hospital! But a lot of people do that, more than with the dishes.

Anyway, it may be clear that I always rinse, but since a lot of people don't (including my mother) I wondered what the health risks might be, if any. And might washing up liquid be designed with this in mind? DirkvdM 06:13, 26 August 2007 (UTC)

While the thing about the hospital doesn't intuitively sound great, it strikes me as possible that things are not quite as bad as they sound. The "toxic stuff" may well be the point. There are actually two components to washing things -- mechanically removing nasty stuff, and chemically/physically killing it. The balance between the two depends on the context -- those "hand sanitizer" things you see people using a lot these days rely entirely on the second modality. Antibacterial soaps are a separate thorny issue; some people are worried about triclosan getting into the water supply, and about bacteria becoming resistant to it. --Trovatore 16:49, 27 August 2007 (UTC)

It also has to do with how much wash water is left on the dish to evaporate. If your dishes were reasonably hydrophobic and you set them vertically to drain and air-dry, the rinsing step might not make much difference because there might be very little wash-water (and its detergent) left on the dish anyway. By comparison, if the dishes were hydrophilic and/or you set them down horizontally with a puddle of dirty, soapy wash water standing in them to evaporate away, then your results would be quite different. But I'm American, so I'm a rinser.

Atlant 11:47, 27 August 2007 (UTC)

Spherical Magnet?

Why is it impossible to repeat a simple bar magnet onto a sphere at an angle that's perpendicular to the tangent of the surface so that whole of outside have one pole while the whole of the inside have the other pole? --antilived^{T | C | G} 07:15, 25 August 2007 (UTC)

I haven't made the calculation, but perhaps if you added together all their magnetic moments they would sum up to zero? —Bromskloss 10:48, 25 August 2007 (UTC)

I'm not sure that it is impossible - why do you think so (excluding the difficulty gluing the thing together).87.102.84.56 10:56, 25 August 2007 (UTC)

My Physics teacher said so, because of "the field lines would intersect the magnet itself". However is there any other explanation on why is it impossible (or not)? --antilived^{T | C | G} 12:14, 25 August 2007 (UTC)

There's this thing with that the magnetic field should be divergence free ($\nabla \cdot \mathbf {B} =0$), that is, there are no magnetic monopoles. The discussed spherical magnet, however, would have such a monopole in the middle, from which the field lines would originate. —Bromskloss 12:25, 25 August 2007 (UTC)

That would have to be a perfectly made example though - if there were gaps between the magnets there would be no problem.?

(Secondly what if Maxwell is just wrong - does the spin of a neutron not represent a magnetic monopole??)87.102.84.56 12:55, 25 August 2007 (UTC)

If there were gaps, the magnetic field inside would leak out there and cancel the outside field and we would no longer have a magnet. Spin would correspond to a magnetic dipole, I guess. —Bromskloss 16:48, 25 August 2007 (UTC)

Surely if there would be gaps the situation would be just one of having N magnets all arranged about a point - erm - so they would still function as magnets.?

Actually I don't get the original poster's physics teachers response "the field lines would intersect the magnet itself" - say I take a rectangular bar magnet and force (literally) 11 other similar magnets around it (not all N-S alligned) - then the magnetic field lines might be forced inside the magnet - with possible demagnetisation.??

MY ANSWER TO ORIGINAL POSTER I think to be honest your physics teacher has 'dodged the question' - though to be honest I'd like to dodge it also - it's a complicated situation really. And the answer depends on whether there are gaps between the magnets (Ithink) and also has to take into account the possibility of some demagnetisation near the centre due to the concentrated magnetic field.

If you could do it - with specially 'wedge' shaped magnetic peaces then it would be interesting to consider if the thing you would have made is effectively a monopole (from outside). I'm guessing some demagnetisation would stop this happening due to the highly concentrated field lines..87.102.84.56 18:16, 25 August 2007 (UTC)

I remember reading somewhere that mathematically a sphere with uniform density has the same gravitational pull as it would if it was all compressed into a point in the center. Because gravity and magnetism both obey the inverse square law, the same applies to a magnetic monopole. If you had a larger sphere that was a northern monopole, and a smaller one that was a southern one, and you put the smaller inside the larger so they shared the same center (effectively making the magnet you described), from anywhere outside the sphere it would be the same as if they were both in the same point in the center, where they'd counter each other out. In short, the southern magnetic field emanating from the center of the sphere and the northern field emanating from the outside would be the same everywhere outside the sphere and counter each other out. Get it? — Daniel 18:43, 25 August 2007 (UTC)

Yes - thats right - though I'd expect a very weak residual field from the magnets.

I don't know if you'd be able to explain what happens to the 'magnetic field lines' in the case where 'cone/wedge shaped magnets' make up a perfect sphere - (you answered question 1 pretty well - just hoping) - I think they must go through the magnets so there must be some blanking as well?87.102.84.56 18:56, 25 August 2007 (UTC)

Let's just take Maxwell's laws to their natural conclusion. $\nabla \cdot \mathbf {B} =0$. From this, we know that the same number of magnetic field lines enter the sphere as leave it. Further, let's just look at the wedge shaped magnets you'd need to make such a sphere. The same law holds for them, the same number of magnetic field lines entering the north end emanates from the south end. I'd imagine that in a realisticly constructed sphere, you'd have magnetic fields leaving the magnet (in standard magnetostatics, the field lines leave the south end, and enter the north end) through gaps between the wedges, and re-entering across the wedge surfaces. Now, if you could have a flawlessly spherical and uniform magnet, well, let's turn to electrostatics. The laws governing electrostatics and magnetostatics differ only due to the absence of magnetic monopoles. However, if such things existed, magnetic monopoles would interact with one another exactly as electric charges do (except the left-hand right-hand rules get switched somewhere, this has been a while for me!). So, one "monopole" spread over the surface of a sphere, and an equally strong but opposite monopole in the center. From Gauss's law, the monopole on the surface creates a magnetic field outside the sphere identical to one that would be created if it were concentrated at the center of the sphere. Since electromagnetic fields obey superposition quite perfectly, the two poles cancel out completely everwhere outside the sphere, and your long sought after spherical magnet is completely dead. Someguy1221 20:34, 25 August 2007 (UTC)

I think is worth noting (with reference to the later part of your argument) - that the field due to a spherical surface charge is not exactly the same as that of a point charge centred at the sphere centre - there's a (small difference) - which varies with distance... (that difference depends on the nature of the 'field' variation with distance and of course if the field is a vector or scalar quantity matters as well)... 87.102.84.56 21:16, 25 August 2007 (UTC)

Meaning that the spherical magnet is not dead (possibly very weak) but with a <literary effect>unmistakeable feeble pulse</literary effect>...87.102.84.56 21:21, 25 August 2007 (UTC)

That arises from the failure of the assumption that the charge can be uniformly spread over the surface. If it could be, the magnet would, literally, be completely dead on the outside. But since electrons have finite distance between them, this is not the case. Someguy1221 21:35, 25 August 2007 (UTC)

No the effect still arises when the charge is uniformly spread on the surface.87.102.23.4 00:36, 26 August 2007 (UTC)

I'm confused, why? Someguy1221 01:06, 26 August 2007 (UTC)

Consider the gravitational effect from a point mass M

and the gravitational effect from a evenly distributed spherical surface with total mass M (gravity follows the same inverse square law as electrostatics yes?)

The functions of field/force are very similar at great distances

But differ fundamentally - the field is given by a different equation for each case.

You'd need to work out the field due to a distributed mass/charge around a spherical surface as a function of distance - probably you'll end up with a function with two integrals - you don't need to be able to do the integration to show that the function is not the same as the 1/r² that comes from a point mass/charge. (this may be a maths desk problem)

Because the two functions are different - subtracting one from the other results in a non zero field (in fact there is a surface where the field is zero - but everywhere else it is non zero) - in fact the field changes sign. 87.102.23.4 01:16, 26 August 2007 (UTC)

(the gaussian law holds when r (the distance) is greater than R (the radius) r>R but is not 100% correct at finite distances - there is a minute error - which is much more noticable when r approaches R - in fact when r=R the field becomes infinite just as it does when r=0 with a point charge. Gausses law is an approximation - that's why I said that the noticable effect would be 'very feeble' - this is especially true when r>R because the approximation is very good.87.102.23.4 01:25, 26 August 2007 (UTC)

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elesph.html#c3 gives the approximations for field according to gauss inside and outside the sphere - note for inside a sphere of radius R the field according to gauss is Qr/4pie₀R³ - not the same as a point charge - I can't find a link to a more detailed analysis right now but can explain if if needed.87.102.23.4 01:33, 26 August 2007 (UTC)

Your own link states, if I may quote: "The electric field outside the sphere (r > R)is seen to be identical to that of a point charge Q at the center of the sphere." Their equations for both inside and outside the sphere are trivial applications of Gauss's law. Someguy1221 01:46, 26 August 2007 (UTC)

I linked just to show that a different equation exists (under guasses approximation) for r<R - there is under gausses approximation - a discontinuity at r=R - this is not the same as being 'identical to a point charge' because for a point charge there is no discontinuity at r=R. How exactly do you explain gausses equation for the field inside the sphere

Qr/4πє₀R³ (inside the sphere) compare Q/4πє₀r² for a point charge?

in terms of a point charge?87.102.44.85 10:54, 26 August 2007 (UTC)

It's actually completely consistent. The example given was that of a sphere whose charge is uniformly distributed through the entire sphere, not just the surface. If you accept that charge distributed across the surface of the sphere creates no electric field within the sphere, then at any point inside the sphere in the example, the charge you are "exposed to," in a sense, is proportional to the cube of your distance from the center. So, as you move out from the center, the apparent point charge increases in magnitude as r³ while the field strength/charge ratio remains proportional to 1/r², yielding the linear relationship Qr/4πє₀R³ (where R is the radius of the sphere, constant). At r = R, the two equations give the same result, there is no discontinuity. Someguy1221 22:24, 26 August 2007 (UTC)

In the example you gave originally "So, one "monopole" spread over the surface of a sphere, and an equally strong but opposite monopole in the center. From Gauss's law, the monopole on the surface" and in the example linked (which isn't connecting unfortunately) the charge was on the surface - I've underlined those parts that refer to the monopole/charge being on the surface. It looks like you don't know this.

You're analysis above is just wrong( the first part). The second part you have just turned into words what was stated in the equation. There is discontinuity in terms of the first and other differentials. If you want to discuss this further can you start a new question because we are getting very far away from the original magnets problem.87.102.45.106 12:01, 27 August 2007 (UTC)

Quoting from your source, again "The electric field of a sphere of uniform charge density and total charge charge Q can be obtained by applying Gauss' law." This is a common problem to be found in any introductory physics text book. Someguy1221 03:31, 29 August 2007 (UTC)

This is all because, from a mathematical perspective, Gauss's law and Coulomb's law are actually identical. The only difference is that Gauss's law does not inherently imply that the electric field of a point charge is radially symmetric, so you must make this assumption (which everyone does). Someguy1221 22:29, 26 August 2007 (UTC)

Note - gauss's law inside the sphere surface is mathematically different from coloumbs. Please be careful when you say things like 'mathematically ... identical'87.102.45.106 12:01, 27 August 2007 (UTC)

Guass's law still produces the same predictions. The electric fields of static charges predicted by Coulomb's law are always always always (i'm not sure I can emphasize this enough) identical to those predicted by Guass's law. The two can actually be derived from one another, provided you asume the obedience of electric fields to the superposition principle and the radial symmetry of the field about a static point charge. Someguy1221 03:31, 29 August 2007 (UTC)

Bacteria in human mouth vs. at the end of the digestion process

I know in some species like the kimono dragon their mouth has so much bacteria that it's what kills people and not their bite, so they may even have worse bacteria in their mouths than at the end of the digestion process (rectum). But what about humans who have bad breath, tooth decay, and that white-yellow film on their tongue from bacteria... how much, how deadly, etc. is that bacteria to the bacteria at the end of the digestion process? mouth (human) is a brief article that says nothing of this. Juanita Hodges 07:18, 25 August 2007 (UTC)

Very little bacteria survives the beginning of chemical digestion in the stomach—the low pH (high acidity) pretty effectively kills most bugs. Intestinal flora are usually quite different from the stuff in your mouth.

Meanwhile, the toxicity of komodo dragon saliva depends partly on the bite; it's not just the saliva by itself. By puncturing your skin, pathogens in the komodo dragon saliva get a free pass into deeper tissues and (potentially) your blood. While your mucous membranes and skin are (somewhat) resistant to many nasty things, most of the rest of your body is more poorly defended against pathogens. (This is one of the reasons why gastrointestinal perforation is so serious—the normally harmless and helpful bacteria in your gut get spilled out into the abdominal cavity, where they cause massive infection.) TenOfAllTrades(talk) 18:33, 25 August 2007 (UTC)

How bad are the human mouth bacteria compared to intestinal bacteria? Juanita Hodges 22:07, 25 August 2007 (UTC)

When placed where they shouldn't be, intestinal bacteria are generally worse. Someguy1221 01:48, 26 August 2007 (UTC)

Can human mouth bacteria be deadly or infectuous in the wrong place? Juanita Hodges 02:26, 26 August 2007 (UTC)

Depends how far along the road to decay the mouth is. If there's an actual infection with bacteria chewing away at the gum tissue, you can correctly imagine that those bacteria will be more than happy to chew away at your arm tissue or foot or whatever as well. This is the basic reason why people with pacemakers for instance have to be careful with dental surgery because those serious bacteria could enter the blood stream and infect the wiring to the pacemaker, etc. Regular tooth-cavity bacteria, not so much. Their big trick is turning sugar into cement, which is not that handy for infecting a puncture wound. Also, scientists currently are beginning to doubt the komodo dragon story, and theorizing that maybe it's a real toxin they secrete. Other reptiles get pretty good mileage out of the poison-bite trick, of course. Gzuckier 15:10, 27 August 2007 (UTC)

Camera emulating the human eye

In a question hereabove, SteveBaker says the human eye uses a combination of colour and brightness detection, a technique also being developed for monitors under the name RGBS or RGBE (note that RGBE is about something different, although related). I had previously thought of making a camera sensor that way. Put a layer in front of the colour sensor that does two things - measure the brightness and darken according to the brightness. Thus, the light passing through it to the colour sensor will be of equal brightness and the colour sensor needs only detect the colour. The idea is that if you split the two functions they can be more precise at what they do - more detail in brightness and shadows and a higher colour depth. Also, performing a more limited task means it can be done in a smaller area, so the pixels can be packed closer together, so the resolution (and with it the pixel count) goes up. Does this make any sense? DirkvdM 07:38, 25 August 2007 (UTC)

After a couple of reads .. yes... You get higher dynamic range (in the overall image) - a pixel seeing bright light can get a good exposure without being overexposed (whiteout) at the same time as a pixel getting low light can also get a good exposure - makes sense..

As for the second part "Also, performing a more limited task...." I'm not sure I agree - wont the pixels just be the same size as normal?87.102.84.56 11:01, 25 August 2007 (UTC)

I seem to remember a vaguely similar system - were there are four sensors - rgb and intensity - the intensity sensor controls the sensitivity of the rgb sensors electronically though - possibly this was in a fuji camera 'ccd' can't remember more though.87.102.84.56 13:39, 25 August 2007 (UTC)

One problem I see is that the time it would take for the first layer to darken wouldn't be enough to block the light from hitting the second layer. With flash photography, perhaps a double flash could be used, where the first flash darkens the first layer and the second flash is used for the second layer. Another problem might be that the first layer would refract light and cause a fuzzy image. The closer the two layers are to each other the less of a problem this would be. StuRat 16:46, 25 August 2007 (UTC)

Someone said something about pixels. This isn't to increase the number of pixels, it's to increase the accuracy of the color in each pixel. Why is it red green blue and brightness instead of hue sat and lum? I know one of those is brightness. — Daniel 17:04, 25 August 2007 (UTC)

It's hard (maybe impossible) to build a 'hue' detector without building it from a set of red, green and blue detectors. Hue is a measure of where on the rainbow spectrum you are - so you'd think it would be a measure of light frequency or something - but then we have 'hues' like Magenta (purple) which is a mixture of red and blue that doesn't ever appear as a single frequency of light. Alternatively, we have the colour humans call 'yellow' which is really one of two totally different physical phenomena. It's either pure light of a frequency somewhere between red and green - or it's a mixture of pure red and pure green. Humans can't tell the difference - but a frequency-measuring-sensor would have to do so in order to produce realistic colours. The concept of 'hue' as we describe it only works for creatures like humans who happen to have red, green and blue sensors. So when you are making a camera, the simplest and most realistic thing to do is to emulate the human eye - producing the exact same artifacts as the human eye does. Hence, our cameras have the exact same problem (that they can't tell the difference between the two kinds of yellow) as we humans do. So RGB is here to stay - adding intensity sensors would perhaps be useful though. SteveBaker 21:25, 25 August 2007 (UTC)

I'm not sure I follow. I'm not suggesting to eliminate the rgb sensor, just present it with a light that is always equally bright, so it can focus more on its own task and thus be better at it. The image at the top of Munsell color system is rather illustrative. I want the first sensor to measure the brightness and 'equalise it' for the second sensor, which then measures hue. Now I wonder how chroma is measured. Or does that go with hue? DirkvdM 07:24, 26 August 2007 (UTC)

The colour system you are talking about is Hue/Saturation/Value (HSV). Hue is best descriibed as 'where on the rainbow you are' - all shades of red through bright red to dark red and including pinks have about the same hue. Saturation is the distinction between red and pink - or blue and 'baby blue' - it's the amount of 'colour' in the colour so to speak. Value is brightness. HSV is a useful way to pick colours if (for example) you are worrying about colours that look good together, concepts of contrasting shades are easier to understand in HSV than in RGB - but there is relatively simple math to convert one into the other and back again. There are many different variations on the HSV theme though. So your idea for the sensor is to normalise the brightness of the incoming signal so that the RGB sensors are operating at higher brightness levels. Essentially, that's what RGBE/RGBS does - it decouples the overall brightness of the signal from the sensitivity of the RGB number range. But whether you can come up with a sensor that physically implements RGBE is a tougher question - as far as I know, all existing high-dynamic-range systems work by taking pictures at a range of different exposures and merging the results. SteveBaker 13:32, 26 August 2007 (UTC)

Ah, that last bit sounds interesting. A disadvantage of that method is that you need to expose several times, which means longer exposure, which becomes a problem at low light and/or a fast moving subject. My system requires only one single exposure with two sensors, the results of which are then combined. Sounds better, doesn't it? If it can be implemented, that is. DirkvdM 18:50, 26 August 2007 (UTC)

Stu, you say the first layer might not react fast enough. But I forgot to mention that the idea is that it takes its measurement-energy from the light. It's sort of like how an analogue film works - the silver halide grains that get hit by light darken and I assume they do that by absorbing the light energy. The idea is that this layer does that too. Since it does this by absorbing the light energy, the reaction is instantaneous. But it also needs to measure the light intensity. Maybe that could be done after the photo is taken, by letting the layer 'leak' its energy and measuring that.

But I just realise this might require wiring in front of the sensor, which is not a good idea. Maybe it could be a mirror that sends the image to the side, where the colour sensor is. There's another thought - why don't we have newtonian cameras? I'll make that a separate question. DirkvdM 07:24, 26 August 2007 (UTC)

Are you sure that reaction is "instantaneous" ? I don't know enough about it to say, but don't many such reactions involve electrons staying in one shell for a fraction of a second, then jumping to another ? StuRat 22:31, 26 August 2007 (UTC)

Maybe the darkening of photographic film is indeed not instantaneous, but in retrospect that might not be a good comparison. What counts is that the energy is taken out of the beam of light. Letting an electron jump to a higher energy state sounds like a good (the only?) way to do that. And maybe the falling back could then be measured somehow. But I now realise that this will probably not let through light of equal distribution. More likely, it will let light through at a fixed percentage of the incoming light. So the brightness is still measured, but the rgb sensor behind it will still have to deal with variable light intensities, and the idea was to be freed from that so the sensor can be made better at colour measurement.

Just in case that last bit needs clarification, think of different scales used for different weights - a very precise scale that weighs to the precision of milligrams will not be able to withstand the weight of, say, a car. A multimeter also has different 'scales' for different inputs, for similar reasons. DirkvdM 07:32, 27 August 2007 (UTC)

WHAT HAPPENS DURING MULTIPLE PERSONALITY DISORDER?

PLEASE LET ME KNOE THE PATHOPHYSIOLOGY OF THIS DISORDER I HAVE CHOSEN THIS TOPIC FOR MY SEMNINAR PRESENTATION AND SO I NEED THE HELP OF ALL THOSE WHO STUDY PSYCHIATRY SPECIALLY PLEASE STRESS ON WHAT HAPPENS TO THE BRAIN

Firstly, using all caps is not a very good idea, as some people may construe your statements as disrespectful. Secondly, Wikipedia is an encyclopedia, have you read our article on multiple personality disorder? Splintercellguy 09:15, 25 August 2007 (UTC)

Yeahhhhhh, using all caps when discussing mental health...? It makes me wonder about the poster's own mental stability. =/ Not a good combonation! --24.249.108.133 20:50, 27 August 2007 (UTC)

WHAT HAPPENS TO THE BRAIN DURING THE DISSOCIATIVE IDENTITY DISORDER?

i AM GOING TO DELIVER A SEMINAR ON THIS AND SO I NEED THE HELP OF ALL PSYCHOLOGISTS NO WEBSITE CLEARLY MENTIONS THE PATHOPHYSIOLOGY OF THE BRAIN AND SO I IMMEDIATELY NEED THE RELATED INFORMATION PLEASE MAIL ME IF POSSIBLE <e-mail removed>

See my response for your other question. Splintercellguy 09:16, 25 August 2007 (UTC)

Oh yeah, it's not a good idea to publicly post your e-mail, it's an invitation for spam. Splintercellguy 09:53, 25 August 2007 (UTC)

21 grams

Does the life force in humans have a discernible weight? - Kittybrewster (talk) 11:01, 25 August 2007 (UTC)

Well there isn't any tangible thing as a "life force" in modern medical science. "Life" itself is defined very differently by many different people, but generally speaking it is often considered to be processes which decrease entropy. These processes can have no independent weight of their own, and indeed are not independent from the functioning of the organism itself. Think of a wind-up toy—would you say the winding of the spring (we'll call it the "mechanical force") has a discernible weight, or was even something physically different from the toy as a whole? --24.147.86.187 12:08, 25 August 2007 (UTC)

Actually ... in 1907 Duncan MacDougall measured the weight of a soul and found it to be 21 grams. However, I think you'll find few people today that believe that the life force in humans has a discernible weight, and there is no scientific rationale to support such a belief. --Ed (Edgar181) 14:28, 25 August 2007 (UTC)

I think you you need to define what a life force is and try to prove it exists. What exacttly was he measuring? --72.202.150.92 18:41, 25 August 2007 (UTC)

Weigh someone just before they die - then again afterwards - the difference (if the experiment is done carefully enough) will certainly be zero. There is simply no such thing as 'life force' in modern science. SteveBaker 21:59, 25 August 2007 (UTC)

The air in your lungs has a weight. If on dying the ribs and diaphragm relax, the chest cavity would collapse slightly and expel some air; probably just over 0.5 litres, which would weigh about a gram, so the mass of the body would decrease slightly. The studies into the mass of the soul were fatally flawed for a number of reasons, though: people dying of terminal diseases tend to be moving quite a bit which can interfere with scales, it is very difficult to work out whether someone is alive or not with late 19th century science (even more so to do it without disturbing the scales), and of course, as the body dies, sweating, breathing and respiration will all decrease the total mass. Laïka 23:42, 25 August 2007 (UTC)

The air in your lungs is at the same pressure as the surrounding air, and therefore has the same density. It contributes to your body's mass, but not to its weight as measured in the normal way with air surrounding it. --Anon, August 26, 2007, 16:23 (UTC).

If you give any credence to the thoughts of naked space vampires, you may want to see Lifeforce (film).

Atlant 11:52, 27 August 2007 (UTC)

Actually, actually, if you wind up a spring or something similar, it does weigh more! Bizarre, huh? --Waldsen 21:59, 31 August 2007 (UTC)

Hooke's law and its integral

If Hooke's Law is $F=-kx\,$, why is its integral $U={1 \over 2}kx^{2}$? Shouldn't it be $U={-1 \over 2}kx^{2}$, although it gives rubbish results? Why does the negative sign suddenly disappears when it's calculating energy instead of force? --antilived^{T | C | G} 12:23, 25 August 2007 (UTC)

I think you should see it as follows. Your $F$ is the force the spring exerts on your hand, which compresses the spring. Your hand, however, exerts the force $-F$ on the spring, and this is the force you should integrate (since this is the force acting on the spring, transferring energy to it). —Bromskloss 12:30, 25 August 2007 (UTC)

So we are not actually integrating Hooke's law to get the energy formula? Shouldn't that be changed in the articles to reflect that? --antilived^{T | C | G} 12:34, 25 August 2007 (UTC)

You're probably right. Of course, it's not a very big thing so a short note would be enough. —Bromskloss 12:38, 25 August 2007 (UTC)

No,no - not right the energy equation is the integral - but the force (opposing) is in the opposite direction to the movement - hence the change of sign - maybe the article needs clarifying.

But the force needed to move the spring is kx not -kx since it is in the opposite direction to the force the spring makes itself - (make sense or not?)87.102.84.56 12:46, 25 August 2007 (UTC)

—Bromskloss has it right.

Work is force x distance. The force exerted by the spring is -kx The force needed to move the spring therefor is kx. Hence the change of sign.87.102.84.56 12:48, 25 August 2007 (UTC)

OK now a new problem comes up. If W = F × D, then isn't W = kx² only? Where does the 1/2 come from? --antilived^{T | C | G} 05:56, 26 August 2007 (UTC)

Work equals the integral of force with respect to distance. Normally this would just be force times the distance co-directional with the force, but for a spring, the force is not constant, but rather is directly proportional to the distance, so you must take the integral of the force this time. The integral of kx with respect to x is kx²/2. Someguy1221 06:16, 26 August 2007 (UTC)

Yea I know that, but I'm wondering WHY is it the integral of force? Why isn't it just a product of manipulating several other formulae like many others? --antilived^{T | C | G} 06:24, 26 August 2007 (UTC)

Well, if you'll accept that the force at a given instant, multiplied by the distance traveled over that instant equals the energy transfered in that instant...This only works for non-infintesimals if you use integrals, as integrals are infinite sums of infintesimals. If I'd remembered my physics better, I could derive for you the relationships from Newton's laws, but that's a few years in the past. The simplest I can put it, short of that, is that simply combining formulae algebraicly doesn't yield every possible physical relationship. Newton created the calculus for the primary purpose of answering physics questions that were beyond contemporary mathematics. Someguy1221 07:43, 26 August 2007 (UTC)

Mains adapter

I just bought a digibox and the mains adapter that came with it was small and surprisingly light, only about 50gm, almost as though there was nothing inside the box, but it works just fine (12v DC from 240v AC). They are usually up to ten times heavier than that. Is this some new technology?--Shantavira|^{feed me} 12:43, 25 August 2007 (UTC)

Digiboxes don't use much power and electronic things are getting more and more energy efficient - so maybe it just has a much smaller transformer than you were expecting?

Alternatively a wholey electronic power supply - (no transformer) could be made - which might be lighter.

I expect the former though - what is the rating of the power supply?87.102.84.56 12:51, 25 August 2007 (UTC)

12w.--Shantavira|^{feed me} 12:55, 25 August 2007 (UTC)

mmmh (I've got one of those too and it is very light) - a web search confirms what I used to think - that a conventional 12va transformer weighs much more about 125g at least...87.102.84.56 13:04, 25 August 2007 (UTC)

It sounds to me like this is a switching power supply and you're thinking of more traditional transformer based power supplies... Switching power supplies are hardly 'new technology' for example they've been used in computers for a long while. However it's perhaps only recently that they've began to become common as replacements for more traditional transformer based 'power brick' type mains adapters. Most mobile phone adapters nowdays are switching ones I presume because of the weight and universal use advantages Nil Einne 13:08, 25 August 2007 (UTC)

Edit: I also noticed this from the above article "In early 2006 even very low power linear regulators became more expensive than SMPS when the cost of copper and iron used in the transformers increased abruptly on world markets." It seems likely that in 10 years time, people will be asking 'why is this old power adapter I found so heavy?' Nil Einne 13:10, 25 August 2007 (UTC)

The article says switching power supplies are more efficient. So they may have been cheaper from the beginning, but alas people usually only look at what something costs now, not in the long run, which is what really matters. If people would wisen up in this area, that might just 'save the world' (climatologically speaking). Or at least it would help. (Of course it becomes totally irrelevant if you occasionally use a car when you don't need to - not to mention gas guzzlers.) DirkvdM 07:44, 26 August 2007 (UTC)

+ & - chargged metals

I am running an inhome experment and would like to use the maximum differencial in possitively and negatively charged metals. Is there an oppisit to isatobe 235, or a less radioactive metal? Is there isatobe 100 and an anti-100? A 50 and anti-50, anything? Can you stear me in the rite direction? Thanks, Gods— World Changer161.51.11.2 13:44, 25 August 2007 (UTC)

Um what? Isatobe 235? You mean Uranium-235 (uranium isotope 235? Um little hint. If you're planning a 'in home' experiment you want to consider elements you can actually obtain easily. Also I don't quite get what your doing. Are you trying to make a Galvanic cell? If so take a look at Standard electrode potential (data page). However personally I would recommend you steer away from anything which produces hydrogen flouride. Nil Einne 13:50, 25 August 2007 (UTC)

Not sure +3 is the usually max charge on a metal as found in Aluminium, maybe you were thinking of electronegativity and electropositivity?87.102.84.56 13:53, 25 August 2007 (UTC) If so gold and lithium would probably be your choices..

There is as far as I know no thing as an 'opposite to isotope 235' or an opposite to an isotope that can be got.87.102.84.56 13:56, 25 August 2007 (UTC)

It would help if you told us more..87.102.84.56 14:09, 25 August 2007 (UTC)

Sacrificial Anode - Aluminium

I have read that aluminium forms an oxide coat that prevents it from oxidising and hence is it quite unreactive. Yet I have been told aluminium could be attached to those drilling stations in the ocean to protect the iron from oxidation. Doesnt the oxide coat prevent this?

What you have been told may or may not be true - I've no idea - but it's a possibility.

The alkaline nature of sea water will tend to dissolve the aluminium oxide - so yes I imagine that aluminium could be used as a sacrificial anode..87.102.84.56 14:04, 25 August 2007 (UTC)

From Galvanic corrosion " Boats and vessels that are in salt water use either zinc alloy or aluminium alloy. If boats are only in fresh water, a magnesium alloy is used. "87.102.84.56 14:07, 25 August 2007 (UTC)

So are you saying the Cl- ions play a factor in this? And why would you use an alloy instead of pure Al? Thx58.107.237.74 15:13, 25 August 2007 (UTC)

The use of an alloy is probably for ease of welding and structural integrity. Nimur 15:44, 25 August 2007 (UTC)

The Cl- ions may help dissolve the Al, but the pH of the sea water is important too.87.102.84.56 16:32, 25 August 2007 (UTC)

I tried rubbing soft aluminium and zinc on different steel structures at the seaside, there was less corrosion compared to an untreated structure. So aluminium does work to some extent.Polypipe Wrangler 00:11, 29 August 2007 (UTC)

Fused NaCl

What does fused mean? (This is at Downs Cell in the diagram) but there is no explanation. Note it says "The electrolyte is sodium chloride that has been fused to a liquid by heating." can someone explain further? Phgao 15:27, 25 August 2007 (UTC)

I think it's a strange usage of the term to mean "melting." I might venture to say "incorrect usage" of the term fusion, which in chemistry and thermodynamics usually means the transition from liquid to solid (latent heat of fusion, for example). In this sense, the molecules "fuse" close together to form a solid phase (not to be confused at all with nuclear fusion, a totally different process). However, Wikipedia is edited by users from many locations, and some regions tend to use dramatically different terminology from the stuff I learned in school in the US. Nimur 15:47, 25 August 2007 (UTC)

It's not incorrect. I admit it's a little con--wait for it--fusing, though. This is one of those words that's its own antonym, like "cleave". I think there's a name for such words, but I forget what it is. --Trovatore 03:31, 27 August 2007 (UTC)

Though 'fused' usually means to us 'set solid' in this case it means melted - it's a standard chemistry term - (search for 'fused salt' if you want to check) Note electrical fuses melt when they fuse..87.102.84.56 16:26, 25 August 2007 (UTC)

Specifically 'to fuse' just means 'to melt' - to be pedantic fused ice is water.87.102.84.56 16:30, 25 August 2007 (UTC)

Just to confuse things 'fused' can also refer to substances that have been melted. Such as fused magnesia.87.102.84.56 18:03, 25 August 2007 (UTC)

Recharging a Lone Ranger atomic bomb ring

Oh boy oh boy. I got a pair of Lone Ranger atomic bomb rings, one of which is in good condition that I won't mess with, one of which is basically just the spinthariscope component and so I don't mind playing with it a bit.

I'd like to "recharge" it. I gather than the original alpha source was polonium-210.

I imagine that "recharging" it basically will come down to figuring out how to open up the isotope chamber, cleaning out the old stuff (now long since decayed into lead), and putting in a new isotope source.

My question is: what sort of radioisotope should I go with? I know that Po-210 was used because it had a high level of activity, and thus would produce more exciting flashes, but its short half-life (138 days) means that to keep it running at a reasonable level I'd have to "recharge" it once a year. Seems like a pain. If I could find something a little less active, but with a better half-life, that might be more ideal. The only site I know of to get radioisotopes seems to only offer Po-210 as its alpha emitter, so I might be stuck with that.

Could I use the Americium-241 sources in a smoke detector? Am I right in thinking that the only way to get a comparable number of alphas as from the original Po-210 source would be to have much more of it? (Obviously I can't get too comparable, as—if I understand half-lives correctly—that means I would need hundreds of times more.) Is it worth trying, since the half-life is a lot longer and the sources are a lot easier to get a hand on?

My next question is: is this even reasonably a good idea? Obviously exotic radioisotopes can be quite toxic though I imagine I am not going to want to be using more than a speck and my understanding of strong alphas is that as long as it doesn't get inside me I should be okay (skin will stop the alphas easily). If I got a needle source of Po-210 from that site, and made sure not to, say, eat it or inhale it, would it be safe to put inside the ring?

If I am totally backwards on any of this please let me know. I'm no physicist and no chemist. --24.147.86.187 15:36, 25 August 2007 (UTC)

I wonder if the interior of the chamber is filled with inert gas (or possibly even vacuum)? If so, opening the case to replace the radiation source would vent the chamber. I suppose, since alpha particles have a mean free path of a few centimeters in air, and this thing is pretty small, that this is a total non-issue. Nimur 15:55, 25 August 2007 (UTC)

Sounds like a bad idea to me. First, even though the skin may stop the radiation, it may do damage to the skin in the process, which might potentially cause skin cancer down the road. Second, handling such material without risking inhalation or ingestion requires specialized equipment and training. In other words, "don't try this at home, kids". StuRat 16:18, 25 August 2007 (UTC)

I agree bad idea - see http://www.hse.gov.uk/laU/lacs/42-6.htm what the article reveals is that "less radiotoxic alternatives have replaced radium in radioactively luminised articles such as tritium (3H) or promethium-147 (147Pm)" - these are beta emitters - I imagine they would still activate a scintillation device?

The major hazard here is inhalation of any dust when cleaning it out, amongst the others - I wouldn't go scraping out a fire sensor or what ever unless I had a device that would keep any dust away from ME. Thinking about glove boxes, breathing filters - note also that the materials used may be harmless when contained in their devices but when exposed can be really bad - this for instance applys to radioluminous watch dials which are consider safe? but if you break the glass it's a case of forget it - and don't even think about touching it - 2mm of glass provides a lot of protection - which out that you could expect 'burns' on your skin.

Specifically all this work needs to be done with tools eg pliers - don't even think of doing it if you would need to manipulate the things with your hands.

I know that there is a lot of 'scare' about radiation - but inhalation of any radioactive dust can be a very serious problem.

See http://www.bhi.co.uk/hints/poison.htm "The hands of the watch or clock should be scraped while immersed in oil and the scraper left submerged in the oil to prevent the particles entering the air being breathed."87.102.84.56 18:34, 25 August 2007 (UTC)

I really wouldn't try this at all.87.102.84.56 18:51, 25 August 2007 (UTC)

Well, obviously I don't want to be handling raw materials here. Am-241 in a smoke detector comes in an insoluable dioxide form inside a gold matrix. I would just be transferring that bit into the ring; I find it unlikely that it would be a significant health hazard, no? Anyway I would not be handling this with my bare fingers in any case.

Cleaning out the existing material is probably the toughest bit. What exactly is the existing material at this point? Po-210 decays to a stable element of lead (Pb-206), which doesn't sound all that dangerous. After 60 years there should only be 1.57 * 10^-48 of the original material left, according to my calculations; I find it hard to believe that this would be a significant amount. I'm also suspicious that the Po-210 was originally in a form that would be prone to be a health hazard if messed with, since it was distributed in children's cereal, but I'm well aware that making assumptions about the safety standards of the past is a losing game!

Anyway, I don't say that to be contrary, but some of the concerns above don't seem to be to be very tailored to this particular situation, and some strike me as being a little uninformed (e.g. replacing it with tritium, for which there is no way in hell I'd be able to get it into such a ring without very sophisticated tools, or the concern about skin cancer from brief contact with a tiny amount of a relatively weak alpha emitter, which is no real threat at all). --24.147.86.187 18:57, 25 August 2007 (UTC)

Yes - it's not 100% applicable - and the Po is in an insoluble form - but what bulk form does that dioxide come in - as a beed or powder - if it was me I'd like to know before opening the gold case.

If it's insoluble you could then make the transfer under water - which does give you additional safety. I deliberately ere on the side of caution here. The radiation (alpha or beta) from an unshielded source can burn you - (unrelated to radiation poisoning as such) - although it would be little more than a 'tiny speck of hot ash' in magnitude.87.102.84.56 19:33, 25 August 2007 (UTC)

The Americium in smoke detectors comes on a little disc, according to this fellow. It'd be nice to know exactly how it is put together, though, because the disc itself is too big to fit in the ring, obviously. The more I think about the cleaning aspect the more I think it is probably a non-issue—there's going to be for all intents and purposes no radioactive material left inside the ring, it is all going to be lead, yes? --24.147.86.187 23:00, 25 August 2007 (UTC)

I read (but can't find the source now) that the Am (don't know if the metal or oxide - think the oxide) is rolled into a very thin gold sheet - i guess that the AmO2 becomes embedded in the gold, as I remember another thin metal sheet is rolled onto this (too thin to stop the alpha particles), there was also a silver? thicker backing and some other metals plates involved - so what you should have is effectively a sandwich of AmO2 between gold - the rolling probably fuses the gold/silver sheets so it shouldn't be separable.. Apparently 0.2mg is the very approximate amount involved, another site says they detected 2000 alphas per second using some sort of counter?87.102.23.4 00:22, 26 August 2007 (UTC)

Here http://www.madehow.com/Volume-2/Smoke-Detector.html

The process begins with the compound AmO2, an oxide of Am-241. This substance is thoroughly mixed with gold, shaped into a briquette, and fused by pressure and heat at over 1470°F (800°C). A backing of silver and a front covering of gold or gold alloy are applied to the briquette and sealed by hot forging. The briquette is then processed through several stages of cold rolling to achieve the desired thickness and levels of radiation emission. The final thickness is about 0.008 inches (0.2 mm), with the gold cover representing about one percent of the thickness. The resulting foil strip, which is about 0.8 inches (20 mm) wide, is cut into sections 39 inches (1 meter) long.

87.102.23.4 00:28, 26 August 2007 (UTC)

http://www.rampac.com/certificates/1030036.PDF shows a structure for a laminate.

87.102.23.4 00:32, 26 August 2007 (UTC)

And the average amount of radiation is 1 microCurie. http://www.epa.gov/radiation/sources/smoke_alarm.htm87.102.23.4 00:34, 26 August 2007 (UTC)

Polonium 210 has been in the news quite a lot over the past year or so since it was used to murder an ex-Russian spy in the UK. What we can learn from that is that Polonium (in very, very small quantities) is insanely toxic if you ingest it or breath it in. But in general, the radiation it produces is stopped by a few centimeters of air or a sheet of paper - so it can be handled safely - with suitable precautions. So once inside the ring, it ought to be pretty safe - but getting it in there safely is going to be tough. The most likely way would be to buy one of those antistatic brushes that photographers use that contains polonium 210 in tiny quantities embedded in a matrix of more inert stuff. Whether the spintharoscope in the ring would be able to detect it - I don't know. At any rate, you ought to go to United Nuclear - those guys will sell you all manner of radioactive samples - and spintharoscopes and whatever else you are likely to need. SteveBaker 21:45, 25 August 2007 (UTC)

It is toxic, yes, but not in the quantities that you can buy on the internet, and not in the forms that you can buy on the internet. Big differences there. Notice that Litvivenko was killed with 50 mCi of Po-210; United Nuclear sells it in 0.1 μCi amounts — a difference of four orders of magnitude! The median lethal dose is still over two thousand times more than you could buy online. So again, I think we're maybe drawing on the wrong associations here, letting our imaginations get a little out of control with all of the scary imagery that surrounds all things nuclear... --24.147.86.187 22:48, 25 August 2007 (UTC)

Sorry - yes, the impression I was trying (and evidently failing) to convey was that the tiny amounts you get in antistatic brushes and from United Nuclear are safe - they wouldn't be sold so freely otherwise. But in much larger quantities, this is nasty stuff. The main point is that the radiation is stopped by your skin before it can do any damage - but if it gets inside your body, it can cause nasty problems (in enough quantity). However, we don't know how much was in the original ring - and we don't know how sensitive the spinthariscope inside the ring was (or indeed still is). It might be that larger quantities are needed to make the ring work - and attempting to make larger quantities (eg by buying a heck of a lot of photographer's brushes and refining the resulting stuff would be a very bad idea indeed. Back in the 1940's, this kind of stuff was not at all well understood and some pretty lethally dangerous products were made before we realised the long term consequences of radioactivity. Note however that Polonium 210 has a pretty short half-life (about 4 months) - so even if our OP sucessfully recharges the ring, it's likely to stop working again after a year or two - and the activity of any "polonium" you do buy may be critically dependent on how old it is - Po₂₁₀ turns gradually into boring old lead and stuff that's a year old has about 1/8th as much active ingredient than 'fresh' Polonium straight from the reactor! But, as I said before, I strongly recommend the United Nuclear web site - they have tons of safety information and will sell you reasonable quantities of several radioactive elements. SteveBaker 13:13, 26 August 2007 (UTC)

Something that concerns me in this whole discussion is the liability of manipulating radioactive materials or telling people to manipulate them to put them in what is clearly a toy, however expensive and collectable a toy it has become. There is a likelihood of such a ring or toy in the future being in the hands (or on the finger) of a child, and of it making its way into said child's mouth. So do not go there. Keep the ring as a collectable. Do not start scraping radioactive material off of something, whether it is the spinthariscope ring, a smoke detector, or an old radium watch dial. It is bad enough when children are harmed by swallowing magnets. Now on to playing with asbestos, mercury, lead, and other 1950's science experiment hazards. Edison 15:07, 27 August 2007 (UTC)

Please - don't go nuts over this. The radioactivity from polonium 210 is blocked by single sheet of paper for chrissakes! You can buy Spintharoscopes with radioactive sources in them in most museum shops and other educational toy outlets - all we're talking about is recreating something like that (although it's far from clear that the original Lone Ranger ring was that safe). [5] for example. SteveBaker 23:58, 27 August 2007 (UTC)

Fields of science

What field of science begins with the letters "Q", "J", "W", and "Y"? Thanks68.78.73.144 16:36, 25 August 2007 (UTC)

Quantum theory Algebraist 17:12, 25 August 2007 (UTC)

Homework question? lol Jonaboff_talk 19:37, 25 August 2007 (UTC)

Yes. please help.

Searching the lists turns up nothing obvious under j,w,y - maybe you'll have to get creative? eg Jungle science - the scientific study of jungles?87.102.84.56 20:02, 25 August 2007 (UTC)

Jupiterean studies, Yttrium chemical science, wastewater science, wetland science, wavelets? (ideas from http://www.dmoz.org/Science/J/)??87.102.84.56 20:06, 25 August 2007 (UTC)

This list might help http://www.daviddarling.info/encyclopedia/alphindexy.html Yeast studies?87.102.84.56 20:08, 25 August 2007 (UTC)

Wet chemistry? Laïka 20:14, 25 August 2007 (UTC)

Jungian Psychiatry? I don't think it's science, but a lot of people do. -Arch dude 01:33, 26 August 2007 (UTC)

See Special Pages (top left) > All Pages (Special:Allpages) and fill in those letters. No, sorry, that hardly narrows it down. DirkvdM 07:53, 26 August 2007 (UTC)

W and Z bosons ? (At least it satisfies the w... Nimur 17:59, 26 August 2007 (UTC)

You could go with Quaternary studies for Q Mac Davis 19:13, 27 August 2007 (UTC)

Elasticity and Strain

The elasticity of a string is its property to resist any deformation when a force is applied. So is it that an elastic string will have a greater strain value than a relatively non-elastic string ... ??? or is it the other way round ???

Please enlighten.

Probably you should read Deformation, Strain (materials science) and Elasticity (physics) - at least the first bits.

The answer is yes - and not the other way round - an 'elastic' string strains/stretches more than a less elastic one for a given weight/force- strain is given by the amount of stretch.87.102.84.56 20:14, 25 August 2007 (UTC)

Animal intelligence testing

Have any intelligence tests been devised that will give meaningful results, on the same scale, for both human and animal subjects? NeonMerlin 20:34, 25 August 2007 (UTC)

The days, at the most technical level, intelligence is usually considered to be a uniquely human concept, but our efforts to investigate the non-human animal equivalent is detailed at Animal cognition. Some of the more simple tests - that we use in testing human children, for example - are also used in animals. You might also see Comparative psychology. Rockpocket 21:42, 25 August 2007 (UTC)

There are plenty of tests - but they tend to be of a qualitative rather than quantitive nature. We have discovered (for example) that Chimpanzees and Dolphins can recognise 'self' - they recognise that the animal they see in a mirror is themself - but that dogs and cats can't do that. Grey parrots can learn the concept of numbers and can count to at least five. Dogs can learn to understand 500 words of English - but have no concept of grammar or word order. But intelligence tests that come up with a distinct number are likely to be impossible. Even IQ testing amongst humans is considered a very dubious science since it's very easy to allow cultural or age biasses to creep in. So I think the answer is a definite "NO!". SteveBaker 21:52, 25 August 2007 (UTC)

But you have to admit, it'd be rather enjoyable if you could confidently say, "My friend, I have quantitative, scientific proof that you are stupider than a hog." --24.147.86.187 23:56, 25 August 2007 (UTC)

Surely animals have intelligence. At least, I define it as the ability to solve problems and learn (the other traits the article mentions, reasoning, planning, abstract thinking, comprehension of ideas and language are all subsets of those two, if you ask me). And all animals can do those two things to some extent. For example, you could put a fence (of finite length) between a dog and a bowl of food. Stupid dogs will run into the fence and start barking in frustration. Intelligent dogs will walk around the fence. I once saw that done with two dogs at the same time. The stupid dog didn't even pick up the smart dog's solution. And that is another intelligence trait. For sheep dogs there are problem-solving contests called sheepdog trials (as shown on BBC), which can qualify as intelligence tests. The dogs are presented with a new situation and have to decide what to do (much the same way in which hunting animals do), possibly under the direction of a shepherd's whistle, which qualifies as language. The herding tests may be fairly standardised, but there are also other tests, where the dog has to follow a course and overcome obstacles they have never seen before. You can actually see them think, standing in doubt about what to do next. A stupid dog wouldn't even understand it was being tested.

However, the question was for a test that can be used for different species, and that would be trickier. Even among humans, there are different tests for different levels of intelligence. So one test for different types of intelligence seems impossible. Of course, it gets even more difficult for the 'lesser species'. Such as plants. Can they be said to have intelligence? DirkvdM 08:08, 26 August 2007 (UTC)

If you choose your own definition of intelligence, then surely they do. Rockpocket 05:08, 27 August 2007 (UTC)

May I politely suggest that sheepdogs are comparatively intelligent but in a limited way. They have a very strong instinct to herd other animals but this ability should not necessarily be assumed to be intelligence. Having watched sheepdog trials on TV it is very clear that the skill of the shepherd in signalling to and guiding his dog or dogs is of paramount importance. When dogs have no contact with the shepherd they frequently herded the sheep in a random way, showing little knowledge of the point of the competition. Richard Avery 09:12, 26 August 2007 (UTC)

I assume that is because they haven't been trained to do that. If they were, an interesting test would be to see how well they would do compared to humans - so dogs without the help of humans and humans without the help of without the dogs. I wouldn't be surprised if dogs would perform better, and that is what I meant with 'different types of intelligence'. Overall humans may be more intelligent (and certainly in tests designed for humans of course), but at specific tasks other animals might perform better. But of course we don't design such tests, as intelligence tests, that is, because we perform worse, so we think that that isn't intelligence. And that is a central problem here. We define intelligence based on what we are good at, so of course other animals are then by definition less intelligent. We've got a bad case of intellectual parochialism. We're human chauvinist pigs. :) DirkvdM 19:17, 26 August 2007 (UTC)

The difficulty and controversy of quantitative intelligence testing of humans has not yet been solved. Our article IQ explains the various criticisms of standardized testing. In my opinion, this boils down to a philosophical question - does "absolute intelligence" exist at all? If so, how can we effectively probe it with standardized testing? If not, what qualities do we generally associate with intelligence? Once these issues are definitively settled in humans, it will be easy to extend the concepts to other creatures, bridging the natural language gaps and so forth. Until then, we will have to use operational definitions with limited scope (such as "time to complete a mouse maze") as a metric for intelligence. Nimur 18:07, 26 August 2007 (UTC)

Yes, nicely put Nimur. I guess without defining what we mean by intelligence (with all its connotations and variations) comparing the intelligence of different species is a problematic excercise. Hey, Dirkvd that's a big tough on the pigs :)) Richard Avery 10:30, 27 August 2007 (UTC)

The root of the problem of intelligence testing is that we don't have a solid definition of what the word means. We originally (I believe) used the term to mean "those intellectual capabilities that man has but animals lack" - we named our own species "Homo Sapiens" (thinking man) as if no other animal has that ability. That definition would mean that all animals would have to score a zero on any true "intelligence test" because if any of them ever managed to score higher, we'd have to admit that the test wasn't testing intelligence at all.

But over the past 50 years or so, we've learned a lot more about animal intellectual capabilities and it's getting harder and harder to draw a line. We have dolphins and chimps who we have proven to have a sense of 'self'. We have all sorts of animals that make and use tools. When I was in high school in the 1970's, we were taught that only Man uses tools - in the 1980's that only Man makes tools - now, we've quietly abandoned the whole tool thing because we've found that even some really small and "stupid" fish make and use tools. In the early 1990's my son was taught that only humans have 'language' - but that's indefensible in the face of things like the lowly cuttlefish's visual 'language' and interpretations of whale 'song' in which personal names seem to make an appearance. Now we have gorillas who can not only learn sign language but also teach it to their children.

We'd probably claim that only humans have written languages - but then we'd be in trouble because plenty of human societies never developed it. Math is similarly problematic. There are human tribes who don't have words for numbers higher than three - yet we have a grey parrot who can clearly understand quantities as high as five.

One by one, things that separate us from the animals are being shown to be quantitative rather than qualitative. We use MORE tools, MORE language and have MORE "intelligence" than the animals. So now, we have to ask ourselves what intelligence is - because it's clearly not "what we have but animals don't have".

Worse still for our definition of 'intelligence' is that a lot of people dislike getting a low score on IQ tests (because it gives them no way to avoid thinking of themselves as "stupid") - so we start insisting that they have "different kinds of intelligence". So I hear that dancers (some of whom might maybe score low on a conventional IQ test) ought to get extra credit for their 'kinesthetic' sense, and that someone with a great memory should score some extra points for that too. That dilutes the meaning of the word - for unhelpful reasons of political correctness rather than as a result of scientific investigation.

We also want a score that allows some kind of absolute measure of intelligence that's irrespective of age or educational level - but it's becoming increasingly obvious that our brains change as a result of learning and that age most definitely is a factor. But without a solid definition - we'll never come up with a scoring system. With the rise of 'political correctness' - it's even less likely that such a measurement can be made without upsetting a lot of people. We dislike anything that discriminates on the basis of the way we were born - so you are in trouble if you try to measure that exact thing with an IQ test.

So it's a bust. The best science can do is to invent a new word and start over with the whole messy business. SteveBaker 17:46, 27 August 2007 (UTC)

I agree with SB et al here. Given that there is no real way to reliably measure the intelligence of humans the issue of animals doesn't really come into the equation. Unless your definition of intelligence is the ability to do IQ tests which nowadays isn't a very popular definition (what's the point of your ability to do a standardised test particularly when that test is supposed to be measuring an inate ability but you can in fact learn to do better on such tests). Somewhat OT but the funniest thing about IQ tests is how people get so worked up about male vs female difference even though the original IQ tests in fact standardised males and females seperately so the average for both should have been 100 Nil Einne 00:32, 28 August 2007 (UTC)

Yeah, that's a good point. I once heard about an IQ test on which women scored higher than men (or the other way around, not sure), which was for that reason rejected. So we don't make a standard and then measure with that. Instead we design the standard to give us the results we want. So we might also design a test on which animals don't score at all. Until we find an animal that does score, upon which we could redesign it again to suit our expectations. So we're not measuring reality, but what we want it to be. DirkvdM 06:20, 28 August 2007 (UTC)

I agree with a lot of what SB wrote above, but with one reservation. It's clear (to me, at least) that there legitimately are different kinds of intelligence and different modes for expressing it. One of the bases of intelligence is the ability to solve problems, but there are many many different kinds of problems to be solved. Solving a Rubik's cube takes a kind of intelligence; composing aesthetic works of art takes a kind of intelligence; discerning which example doesn't fit X pattern takes a kind of intelligence. While you can see that they're all part of the problem solving set, someone good at one of those things may not be any good at the others. It's oddly incongruous that we're willing to label both Mozart and Einstein as geniuses, but only one of them is deemed "intelligent". Matt Deres 20:46, 29 August 2007 (UTC)

Maybe you just pointed out the difference between genius and intelligence. :) DirkvdM 06:38, 30 August 2007 (UTC)

Of some relevance perhaps is this recent study [6] Nil Einne 10:49, 7 September 2007 (UTC)

liquid pressure

Is it possible, as it is with a gas, to cram an ordinary cup of water into a half-cup sealed container with enough pressure? If you dive a mile under the ocean and seal a flask of water, then return to the surface and open it, will it gush out of its container like a geyser? If you go down to the floor of the ocean with 6 sheets of metal and some really strong tape, and you construct a watertight box around yourself, will the water inside still be at high pressure or will the metal take the strain? What if you run a hose from your box up to the surface and keep it clear of water, but the box is still filled? --froth^t 21:57, 25 August 2007 (UTC)

Water's compressibility is very tiny compared to any sort of gas; the sort of question that you're asking is addressed on this external site. Working from those figures, the pressure at six miles depth should be about a thousand atmospheres, giving a decrease in volume of about five percent. In other words, it would be a very short-lived geyser.

If you wanted to keep that pressure inside a metal box, you're going to need something stronger than tape to hold it together. A thousand atmospheres is about fifteen thousand pounds (nearly eight tons) per square inch.

It is possible to increase the density of water by a factor of two, but you need absurdly high pressures to do it. This page has diagrams and details of all the exotic ices that are formed at extremely high pressures; to get water down to half it's normal volume, you'd need pressures closer to a million atmospheres. It also wouldn't be a liquid at that point; it would be an unusual type of ice. TenOfAllTrades(talk) 22:26, 25 August 2007 (UTC)

Here's an interesting bit of trivia. If water weren't compressible, sea level on Earth would be about 40 meters (130 feet) deeper, and the Earth would have about 5% less uncovered land area as a result. TenOfAllTrades(talk) 22:28, 25 August 2007 (UTC)

[EC] For the water flask: No. Fluids are said to be incompressible. If you compress gas the pressure to the walls increases because the density has increased and the particles now hit the wall more often. In a fluid, the particles are so close to each other that you cannot compress them more without forcing them into a crystal. Of course, water is not exactly incompressible, but you need huge pressure to just compress it a very tiny bit. There is no longer proportionality between volume and pressure. For the metal box: Yes, one can construct a metal box that is able to withstand the water pressure from outside and keep atmospheric pressure inside: it's called a submarine. Usually, submarines are filled with air and sailors and torpedoes and all this, but if you insist, you can also fill them with water. (Ok, before someone corrects me: A military submarine is not built to take the pressure at the deep ocean floor, but there are Bathyscaphes). Simon A. 22:32, 25 August 2007 (UTC)

Just a minor nit here: It's liquids that are (almost) incompressible, not fluids. A fluid, technically, is either a liquid or a gas (anything that flows, which is the etymological root of "fluid"). --Trovatore 03:12, 27 August 2007 (UTC)

Wikipedia needs a bit of work on the different forms of ice, and could do with an ice phase diagram. There are no articles on ice II IV V VI VII VIII X XIII or XIV! Graeme Bartlett 22:41, 25 August 2007 (UTC)

Thanks for the answers so far but I think you've missed the main thrust of my question. If you build a metal box around yourself at great depth, will there still be crushing pressure from the water above? Or will the box take the pressure and the water inside have pressure of surface water? Basically I mean like if you seal gas in a container then it retains its pressure, but if you seal high-pressure water in a container so that there's no longer a mile of water on top of it is it still high pressure? Do you see what I'm saying? Let me put it another way.. some guy puts on some super strong diving suit and dive down a mile underwater. He takes off his suit and promptly dies from the crushing pressure. The next guy comes along and has the idea of taking a sheet of metal to hold above his head, hoping that it'll hold up the massive column of water above him. He braces it between some rocks and crawls underneath, then takes off his suit. He's crushed too because the pressure "gets in" from the sides. The next guy decides to totally protect himself from the pressure above by taking down 6 sheets and building a box around himself. Now the gigantic column of water above him is supported by the box, and his body doesn't have to try to push back. Right? That's my question- would it work? Or would it act like gas, and retain its pressure? --froth^t 00:17, 26 August 2007 (UTC)

Your talking about a sealed box that the diver goes down in right (made of super tape that doesn't break) - like a submarine? The answer seems to be yes - because the box he's in isn't crushed or compressed - neither is he?

Or did you mean he builds the box when he's really deep - in which case the box will contain water under pressure when he builds it around him and he'll be crushed.

Or? 87.102.23.4 01:40, 26 August 2007 (UTC)

The original question - build a box/bottle down below and bring it up - as it is raised the pressure from within the box gets greater and greater - if it's opened at the top and it's kept its shape then - yes - water will come out ( a bit) as it expands.

If you build the box at deep pressure the water inside will still be pressureised.

If you take a pipe from sealed box up to the surface - nothing changes - the column of water above the box causing the pressure is the same height.87.102.23.4 01:45, 26 August 2007 (UTC)

I agree with the last guy;

1. if you build a sealed box underwater, the pressure inside when you seal it will be the same as the pressure outside.
2. if you run a hose to the top, as long as the top of the water inside the hose is at the same level as the top of the water outside the hose, the pressure in the box will be at the same pressure as outside. if you pump the water out of the hose until the top of the water is at the top of the box and the rest of the hose is full of air, the pressure in the box will be at atmospheric pressure, plus whatever extra atmospheric pressure you get for being that further down. Odd but true; the height of the water in that hose, even if it's like 1 mm in diameter, governs the pressure in the box. Gzuckier 14:56, 27 August 2007 (UTC)

Accents

This is a strange one, but since it concerns the brain it presumably belongs here. One night several months ago I stayed up all night, drank espresso, and watched episodes of QI. I must have watched every episode. The strangeness began when I went to class in the morning, having just watched the last episode about thirty minutes earlier. Every background voice sounded British or Irish to me. I will explain. Every vocal sound I overheard was analyzed as if it had been spoken by a Briton or Irishman - not at the level of words, but at the level of phonemes. I would be unable to say what was being said. If I listened closer, the effect would vanish. Also, certain phonemes would disrupt the effect, and the American accent would return fleetingly. Also, the effect was less apparent when the overheard voice was one familiar to me. All other background voices appeared to fluctuate between English, Scottish, or Irish. People with non-American accents, such as speakers from India, were no exception. Once I had some sleep, the effect waned, but it was another ten hours or so before it had vanished altogether. It has not happened again. I strongly suspect caffeine and/or lack of sleep was the root cause, but I was just wondering if this effect is known to psychiatry, if it has a special name, etc. Thanks! Bhumiya (said/done) 22:37, 25 August 2007 (UTC)

When I listen to a single voice for too long, my internal voice starts immitating that voice. A.Z. 01:38, 26 August 2007 (UTC)

You say the effect disappeared when you listened more closely. That suggests difficulties in concentration, which could easily have been caused by a lack of sleep. However, that doesn't explain this specific effect. In line with what AZ said, if you expose yourself to something long enough, you will start to expect that in your surroundings and pick up any hints of it and amplify those. So any 'English' traits' in what you heard in the pronunciation of those people would take the overhand. Similar to the effect of walking out of a movie theatre and seeing the world in the perspective of the sort of movie you've just watched. DirkvdM 08:31, 26 August 2007 (UTC)

Perhaps the experience described is akin to what happened to me when I lived for several months in a French-speaking city: if someone spoke English to me when I wasn't expecting it, I sometimes didn't understand it; I only recognized that it made no sense in French. —Tamfang 07:34, 27 August 2007 (UTC)

Haven't heard this one before but the opposite has been seen: "Foreign accent syndrome (FAS) is a rare speech disorder characterized by the appearance of a new accent, different from the speaker's native language and perceived as foreign by the speaker and the listener. In most of the reported cases, FAS follows stroke but has also been found following traumatic brain injury, cerebral haemorrhage and multiple sclerosis.", so it's not altogether surprising that it would go this way as well.

So you're proposing that watching British televison causes brain damage? :) GeeJo ^(t)⁄_(c) • 19:44, 30 August 2007 (UTC)

Prozac and Weight Change

I was wondering what Prozac does to cause weight loss and weight gain in some people. Is it from a change in appetite or does it have to do with something else? Which is more common? Weight loss or gain?

Prozac is a psychoactive drug. "Weight loss" and "wieght gain" are terms usually used to describe human behaviors. Prozac can have major effects on human behavior. I cannot cite any specific studies, but I I would guess that any effect on weight is a secondary effect. For example, Prozac is apparently used to treat bulemia nervosa. -Arch dude 03:54, 26 August 2007 (UTC)

I don't know either but I think the answer is easy to guess. Change in appetite is a very common effect in depression. I suppose everybody knows people who start eating a lot when they are depressed or stressed or whatever, and other people who eat less and less in such times. So, given that our appetite is so much coupled to our mood, shouldn't it be obvious that any mood-influencing drug changes appetite and hence over time body weight? Simon A. 10:28, 26 August 2007 (UTC)

Yes many depressed people tend to eat more to comfort themselves and gain weight, but many also gain weight rather then lose weight when taking prozac. I don't think the answer is that easy.

I gained thirty pounds while taking Prozac in 1996, and forty more over the next two years. During that time I had no acute depressive episodes, and they came back when I stopped gaining weight, or vice versa. Draw your own conclusions. —Tamfang 07:37, 27 August 2007 (UTC)

August 26

Psychology

I am currently in grade 12 and thinking of entering the field of psychology, specifically criminal psychology and I was wondering what route I should take regarding schooling. And what schools in Canada would be best? 75.154.106.228 04:47, 26 August 2007 (UTC)

Don't make hasty decisions, just because you think CSI or Criminal Intent or whatever it is on TV these day is cool doesn't necessarily mean it's true (if you are one of the millions of 'kids' that decide your career on TV programmes). --antilived^{T | C | G} 05:54, 26 August 2007 (UTC)

Don't condescend. He/she's a senior in high school and asked a well-directed question, I think we can afford to take it seriously. Anyway CSI is all about forensic investigation, not criminal psychology, if I recall, so if you are going to cast aspersions about his/her motivations, you might as well get the reference right! --24.147.86.187 13:05, 27 August 2007 (UTC)

I have not made this career choice because of shows on TV I have never watched any of the CSI shows or anything like that. I have done extensive research on this career, and chose it because it interested me.

You'll presumably want a general sciences background, with perhaps some pre-law stuff thrown in. Keeping your education focused on fundamentals will afford you the greatest flexibility later on. As for schools, I personally would go to University of British Columbia, as it's a great school in a world-class city. --Sean 19:47, 26 August 2007 (UTC)

I don't think there's anything wrong to having a goal for your education to a specific goal career — we can't all be generalists, and most people who graduate from undergrad these days have so inspecific of skills that they can't do anything without an additional year or two of education. Unfortunately I don't know the specifics of what that particular career requires, and I'm averse to just speculating on it. My recommendation would be to find a university with a criminal psychology program (even one you are not planning to go to) and try to contact someone there for advice. Someone "on the inside" will be able to give you good advice as to what sorts of backgrounds are more desirable, what level of education is normal for a practitioner (does it require a master's degree?), and what universities have good programs for that sort of goal. --24.147.86.187 13:03, 27 August 2007 (UTC)

Two general routes to becoming a shrink; one via MD one not. If you don't have an MD, you're not allowed to prescribe drugs, which is kind of a big part of the biz these days. But, not everybody is cut out for med school, for sure. They have to send patients out to an MD to do the drug prescribing and periodic monitoring and so on. Anyway, something to think about when you're sort of thinking through your plans. Gzuckier 14:48, 27 August 2007 (UTC)

• The MacLeans survey might help (most of it requires a subscription, sadly). --M@rēino 17:24, 27 August 2007 (UTC)

You might want to seriously consider something fairly local since it'll likely be cheaper and easier for you. I'm not a Canadian but I would assume most Canadian schools/universities are fairly decent from a general perspective. For a more specific perspective some might be better then others but often the student matters more then the university. As for what route, I would suggest you speak to a career counsellor in your current school and probably one in some of the prospective universities as well. The fact that you have a specific goal in mind makes it a lot easier since a lot of people have no idea. Also, you can likely find information on the university websites. Finally since your job is likely to be with your law enforcement, you might want to contact them for advice and particularly see if you can get in contact with someone working in the field to try and help you decide whether it's really the job for you (they can likely offer you advice on universities and stuff too). Nil Einne 00:51, 28 August 2007 (UTC)

Actually on second thought you don't really have to be working with law enforcement that much. You work could be more in the academic area so you could try talking to someone in that area too Nil Einne 00:59, 28 August 2007 (UTC)

Newtonian camera

Would it be possible to make a camera (lens) that uses the same principle as a newtonian telescope? I imagine it could be done simpler, with a mirror behind the lens (if any) that reflects the light to the side, where the sensor then should be. That would be a way to make the camera flatter, a solution to a substantial practical problem, especially with the better lenses, which are always too bulky to always carry around. Actually, come to think of it, why aren't photo cameras made the way film cameras are, with the lens at the narrow end? That would also get rid of the sticking out lens. Actually, some cameras are moving in that direction, but why don't they take the final step? DirkvdM 09:09, 26 August 2007 (UTC)

partial answer - newtonian telescopes don't make very good zoom lenses...that said some lens do utilise mirrors - Catadioptric systems

traditionally photo cameras were that shape because of the shape of the negative+film roll..

For maximum stability of a camera holding it with two hands helps - it could be argued that the classic shape is better for two hands holding than a cine-camera shape?87.102.44.85 10:41, 26 August 2007 (UTC)

It's actually quite difficult to make a 'fast' Newtonian reflector – that is, one with a small focal ratio that will fit in a short tube – that produces good images. Consider the workhorse zoom telephoto lens on my camera. It gathers light through an opening 72 mm across, and focuses it onto a film plane only about 150 mm away. In that length, I also get all the optics I need to focus, control my depth of field, and zoom the apparent focal length from 28 mm to 80 mm. In contrast, a typical Newtonian reflector will tend to have a length that is at least four to six times its diameter (and often quite a bit more). The highly curved mirror needed for a short body is costly and hard to manufacture precisely. The particular aberrations associated with the Newtonian optics (particularly coma) are also worsened with short focal ratios.

Telescope manufacturers have adopted (at least) three strategies to deal with this. 'Slower' optics with longer focal lengths relative to the telescope's diameter reduce the effect of the aberrations, but at the cost of a longer instrument. In astronomy, ignoring the problem is actually often an acceptable solution—stuff in the middle of the field is bright and sharp, and any weirdness can be confined to material off at the edges. Finally, telescope makers have started to add lenses to reflecting telescopes: catadioptric systems. It's that final solution that most often appears in the world of non-astronomical photography. Nevertheless, it's still only used where the cost and weight of glass lenses would be prohibitively high. TenOfAllTrades(talk) 11:23, 26 August 2007 (UTC)

Mostly agree - but.. (note not technically a newtonian - but still a reflector) consider this http://www.zenit-camera.com/rubinar_1000_lens.htm a 1000mm lens - note the short length to width ratio (especially when compared with the equivalent 'glass' lens).. also consider the reduced weight (not such a big factor nowadays with plastic lens) - I just wanted to pick up on that "length that is at least four to six times its diameter" bit - newtonians can be better than glass in this respect due the 'folded' nature of the light path.(and can get very wide for good light collection..

OK I admit I'm just trying to sell this lens (also available in other fittings!).87.102.44.85 13:14, 26 August 2007 (UTC)

You need to be careful with your terminology—while all Newtonians are reflectors, not all reflectors are Newtonians. All commercial (as opposed to home-built) reflecting camera attachments will contain lens elements as well as reflecting elements, both to correct the aberrations of the basic Newtonian design and to greatly reduce the length of the instrument. The focal ratio caveat obviously doesn't apply to catadioptric systems.

Finally, you can't 'fold' the light path in a Newtonian system down to much less than its focal length. The closer the secondary mirror is to the primary's surface (and the further it is from the primary's focal point) the larger the secondary needs to be to capture all of the light. This, in turn, increases the size of the central obstruction, reducing the telescope's light-gathering ability. TenOfAllTrades(talk) 14:39, 26 August 2007 (UTC)

Interesting - looks like I meant a Schmidt-Cassegrain telescope or similar - in my ignorance I assumed it would be considered just a variation on the newtonian - thinking all mirrored telescopes/lens were newtonians. Oops!.87.102.11.213 16:51, 26 August 2007 (UTC)

My oops. When I said newtonian telescope I meant reflecting telescope. So the title should read 'reflecting camera'. DirkvdM 09:23, 27 August 2007 (UTC)

87.102.11.213, you said that reflective telescopes don't make very good zoom 'lenses', but I get the notion that the opposite is true (or did you mean that reflective telescopes have a limited range of zoom?). They're very good at zoom (after all, that's what telescopes do) and are much more portable than comparable lenses. But I just realise there might be another problem here if the secondary mirror is in the path of the light, as indicated by the macro-limit of the Zenit 'lens' linked to by you. In a telescope that mirror being in the way doesn't matter too much because the objects are huge and far away, so it will only affect the overall light intensity. But for objects closer by there is a more serious problem. Take macro photography. If the object is small and only a cm away from the camera then its light might be completely blocked out by the secondary mirror. That is an extreme example, but for objects not that close but still close the 'blockage' of light would still be unevenly distributed. Does that make sense and from which distance would it no longer be a (serious) problem?

That would be solved by not having the secondary mirror in the path of the light, but I remember from a previous thread here that that would cause more problems in constructing the primary mirror. Then again, maybe economics of scale might solve this if the cost is largely in the development of the technique and the production of the machine that makes the mirrors. Telescopes are never mass produced, but cameras are. Once you have a (polishing) machine that can make this type of mirror then the production of each individual mirror would not be so expensive, so it's just a matter of how many you can sell. Right? DirkvdM 09:23, 27 August 2007 (UTC)

Re - zoom - by zoom I meant the ability to change the focal length. I never heard of a 'zoom' telescope as such, but I know different eyepieces can change the magnification - is that the same.. Otherwise I agree the other points. I think the question is (in the case of a camera) why use mirrored optics in preference to lenses - especially when the abberations due the the second mirror are avoidable with a lens system..?87.102.45.106 11:45, 27 August 2007 (UTC)

disclaimer I'm no optics expert - it's probably the thing I know least about - I think you DirkvdM should ask a new question about the reasons why we are not using newtonians in cameras - I'd be interested to see a proper answer. 87.102.45.106 12:10, 27 August 2007 (UTC)

stepped transmission

why geometric progression of speeds is preferred in stepped transmission systems? thank you210.212.24.7 09:55, 26 August 2007 (UTC)

you mean like gear ratios 1:1,1:2,1:4,1:8 etc?

a geometric progression gives a wider range of gear ratios than a linear progression cf 1:1,1:2,1:3,1:4

So that enables both slow crawls and high speed driving.

There may another reason I've missed?87.102.44.85 11:42, 26 August 2007 (UTC)

It's not just automatic transmissions, the gear ratios (reverse, 1st, 2nd, ...etc) for four manual transmission cars I've owned recently are:

• 1963 Austin Mini (37hp): 13.66, 13.66, 8.18, 5.32, 3.77
• 2003 BMW MINI Cooper S (165hp): 11.13, 11.42, 7.18, 5.40, 4.40, 3.66, 2.99
• 2005 BMW MINI Cooper S (172hp): 11.94, 12.79, 7.79, 5.65, 4.61, 3.83, 3.13
• 2007 BMW MINI Cooper S (178hp): 11.78, 12.06, 7.77, 5.41, 4.15, 3.46, 2.97

All of them have the property that the difference between consecutive ratios reduces by smaller and smaller amounts as you get into higher gears. I believe this is because they wish to move the optimum shift points closer and closer together (in RPM terms) so that the car may be kept running within narrower and narrower torque bands - allowing you to employ more torque at higher speeds when air resistance becomes a significant factor. They also seem to have been chosen to provide efficient cruising at typical speed limits. If you look at the differences in gear ratios between 2003 and 2005 - and note that the 2005 model had just 7hp more than the 2003, you can see that careful selection of gear ratios to match small engine changes is sufficiently important to car manufacturers that even a 4% engine performance improvement warranted redesigning the gearbox! This tells you that there is a lot of science going into picking those ratios. SteveBaker 12:48, 26 August 2007 (UTC)

Building a wall or fence to block traffic noise

A noisy road has been built about 70 metres away from my house. I was wondering if I could reduce or remove the traffic noise by building a wall adjacent to my house so that I would have a small enclosed courtyard area that was open to the sky yet comparatively quiet.

The main determinant of how silent the courtyard would be, I think, would be the noise coming over the top of the wall and diffracting into the space beyond it. Thus even though below the height of the wall, you would still hear noise because of the sound waves diffracting from the top of the wall. Does anyone know how to calculate this effect? A taller wall would be better, but I'd like to estimate if an acceptable height of wall (say two metres) would still reduce the noise enough to be worth building.

I'd be grateful for any practical ideas about how to reduce the noise - for example trellisses that may reduce noise by acting as diffractors and creating destructive interference of the sound waves. Thanks. 80.2.200.132 10:33, 26 August 2007 (UTC)

I can't give you an equation - but can confirm that a wall (taller than you) will significantly cut the noise.

The other methods are pretty much as you describe - anything that can absorb a sound wave - anything solid - trees may help.

A wall would definately be 'worth building' the sound reduction effects would be significant. A hedge or row of trees would also help - pines grow fast and tall.87.102.44.85 11:46, 26 August 2007 (UTC)

This page says: A noise barrier can achieve a 5 dB noise level reduction, when it is tall enough to break the line-of-sight from the highway to the home or receiver. After it breaks the line-of-sight, it can achieve approximately 1.5dB of additional noise level reduction for each meter of barrier height". I've also seen rows of fast-growing cypress trees that are very dense, nice to look at, and apparently good for noise abatement. --Sean 12:08, 26 August 2007 (UTC)

My first guess would be that trees (especially the thick cypress variety) would form a better sound barrier than a brick or concrete wall. The trees will block the line-of-sight as effectively, but will muffle the sound better. Also, they can grow to very tall heights, which has been empirically shown (as above - 1.5 dB per meter of height) to reduce the noise significantly. Nimur 18:16, 26 August 2007 (UTC)

• Another way to reduce noise is rubberized asphalt. If this is a new road built near existing houses, your community might be able to force the use of a surface of rubberized asphalt. --JWSchmidt 00:04, 27 August 2007 (UTC)

There are many street-noise blocking walls where I live. They are 12-15 feet tall, corrugated steel walls. Very ugly, but work well. -- Kainaw^(what?) 00:23, 27 August 2007 (UTC)

I've studied sound breaking and pretty much what you'd need is a really dense, solid wall with lots of mass. Brick and concrete probably. Traffic noise is often low frequency so the wall would need to be a ways into the ground (I think--anyone know for sure??) and then I know it'd need to be high and pretty fully surround your home at least in the noise's direction. Traffic noise is worst as loud engines and loud car stereos. Juanita Hodges 01:34, 27 August 2007 (UTC)

This question has been asked before, last year I believe. Alas I don't know of an easy way to search for that. But 'the answer' I believe was a plant-barrier. This might have the added advantage that you will be allowed to make it taller than a wall. For an obvious reason - it's not as ugly. I don't know how the costs would compare, especially if you don't want to wait and want to plant big trees (with plants below them). DirkvdM 09:31, 27 August 2007 (UTC)

You'll want to wait for winter when plants are dormant for a bio-solution, but a fence of living willow would work. You can use a species that grows at a rate to match your need. Bendž|Ť 09:42, 27 August 2007 (UTC)

I strongly support the tree idea, as well, for acoustic, aesthetic, and environmental reasons. One caution is to use evergreen trees, not deciduous, as bare trees wouldn't provide much sound protection in winter. Another idea is to create an earthen berm, possibly with bushes and trees on top:

     /\
    /  \ TREES/BUSHES
     || 
   +----+
   |    |
 +-+    +-+
 |  BERM  |
-+        +-

StuRat 02:09, 28 August 2007 (UTC)

Or maybe one of those wooden fences with thin 'planks' woven through them. Horribly bourgeois, but you can have climber plants cover it. DirkvdM 06:28, 28 August 2007 (UTC)

Unidentified disease of Marigold

I have a marigold plant. It was flowering really well. Suddenlty one day I saw cobweb like stuff had developed on the flowers. On close inspection I saw small dot like white things moving in that web. This web is more like a thin veil of cotton rather than a web actually. I wasn't sure what to do so I banished the pot to the fire exit and closed the window. I did not want my other plants to get whatever it is and I thought sun might be helpful. I live in NY but am used to a more tropical weather garden. The questions are:

What is this disease? Is it harmful to other plants or to humans? How do I cure it?

Some added information: It rained heavily and the plant was soaked. I brought it indoors so that it is not harmed by the cold rain. It remained indoors for 4 days before it developed this thing. --Kaveri 13:59, 26 August 2007 (UTC)

Sounds like red spider mite. Easy to get rid of if you spray with water mist daily. (Or possibly mealy bug.)--Shantavira|^{feed me} 15:25, 26 August 2007 (UTC)

I agree, red spider mite. They love hot, sunny, dry places so giving them a fine water spray once or twice a day will certainly control them. Check your other plants because these little monkeys can spread round a greenhouse at the speed of light. Richard Avery 10:13, 27 August 2007 (UTC)

Uh oh, looks like we're going to have to augment our disclaimer: no medical, legal, or horticultural advice! :-) --Steve Summit (talk) 17:35, 27 August 2007 (UTC)

lenses

Can't seem to find a page on 'lens manufacture' other than history of lensmaking. Is there one? I'm thinking specifically on how plastic and glass lenses are made (cast, then ground ??) rather than lens design.87.102.11.213 16:55, 26 August 2007 (UTC)

Float glass details the process of float glass, but I think this is not the common procedure for small lenses. We seem to have the historical perspective well-represented, but I can't find much on modern lensmaking either. Nimur 18:19, 26 August 2007 (UTC)

????Does "ref desk collaboration of the week" still exist - if so I'd like to put this forward. Where is it. I've also made a requested article thing as well..87.102.11.213 19:23, 26 August 2007 (UTC)

Lenses are ground into the desired shape. One problem with the grinding of large lenses is that gravity deforms them to a significant degree, so that changing their orientation or the strength of the gravity field (say by launching them into space) between production and usage can cause significant distortion. StuRat 01:59, 28 August 2007 (UTC)

Acoustics

When, say a trumpet plays a note, and then a piano play a note of the same pitch, what is the difference between the sound waves that the two instruments make that allows us to distinguish between them? Imaninjapirate^{talk to me} 17:31, 26 August 2007 (UTC)

The second,third,fourth etc harmonics differ. Overtones is probably the easier/better article to read here and both give you the answer.87.102.11.213 17:37, 26 August 2007 (UTC)

Also you are listening to different waveforms. See the various articles linked from that one, some of which have samples of what different waveforms sound like. The only thing the two notes have in common is their wavelength.--Shantavira|^{feed me} 17:45, 26 August 2007 (UTC)

It's worth noting (as it's not in the article waveform) that the waveform consists of the (wavelength) fundamental frequency plus all the overtones or harmonics - bringing all three articles together.

Effectively the presence of harmonics or overtones is means that the 'note' consists of multiple pure tones - there are multiple notes being played simultaneously when a piano key is pressed - the note (on the musical score) corresponds to the first harmonic.87.102.11.213 18:07, 26 August 2007 (UTC)

Also, "imperfections" in each instrument (such as breathy noise in the trumpet) result in non-harmonic elements of the sound spectrum. You might want to investigate psychoacoustic perception, which is an ongoing research topic. Nimur 18:22, 26 August 2007 (UTC)

Then there is also the rate of attack and decay (how quickly the sound reaches max volume and how quickly it ends), which tends to vary by instrument. A grand piano, for example, will have a slower decay rate than an upright piano. StuRat 22:13, 26 August 2007 (UTC)

And the technical term for it is timbre. Confusing Manifestation 22:26, 26 August 2007 (UTC)

And Stu is referring to the adsr envelope (at least, that's the simplified model used in electronic musical instruments). Note that during attack, the pitch may also be different. DirkvdM 09:37, 27 August 2007 (UTC)

Also, the relative amplitude of the overtones can change with time. Also, some partials can be more or less out of tune (as per the 7th on a piano).

In truth, this question is being asked backwards! There is almost nothing the same between the acoustic waveform of a trumpet and a piano playing the same note. Just about all you can say is that the majority of the energy present in the sound is delivered at some specific frequency for most of the duration of both notes. All else is up for grabs and will be different. It's interesting that our brains are able to discern any similarity between the two notes at all! I suspect that some aspect of the way we percieve sound is responsible for that - but I'm no audio expert. My domain is in the world of light and eyes - and our ability to see hundreds of shades of red as all being fundamentally more or less the same "colour" is perhaps a similar ability. If so, it's an artifact of the approximate way we percieve such things ("It's a bug - not a feature!") SteveBaker 16:30, 27 August 2007 (UTC)

I'd say it's rather different for light. Calling different shades of red red is a linguistic thing - we can't have a name for every discernible shade. And perceiving a band of similar colours as one colour is a matter of lack of precision. But picking out the frequency of a note is more like a mathematical thing, probably some fourier analysis. Also note that we designed the instruments to make those notes. Non-living nature rarely produces them and then usually only a vague hint of a note. We put nature in a straightjacket to make it produce pure notes. So it's not so much that there was something there for which we developed a sense, but we had this sense for which we manipulated nature, so it would produce something for us to perceive. DirkvdM 06:39, 28 August 2007 (UTC)

The tiny hairs in the Cochlea are each tuned to a different frequency - the hairs that vibrate the most will be those tuned to middle-C - and those exact same hairs will vibrate for both the trumpet and the piano. The other hairs that respond to the overtones will also vibrate (differently in the case of piano and trumpet) - but those aren't "shouting the loudest" as the information goes to the brain. If we concentrate on the biggest signal from the cochlea - we'll hear the piano and the trumpet "playing the same note" - if we pay attention to the lesser signals, we'll hear the more subtle tonal differences between the two instruments. Our eyes only see at three different frequencies (unlike our ears which can hear all frequencies within our audible range) - but the result is the same. When the red sensor shouts the loudest - we can see that pink and red are varieties of the same thing. If we concentrate on 'overtones' from the green and blue sensors then we can tell that there are a variety of shades and brightnesses of 'red'.

I agree with you that orangy-red and red don't differ in the same way that a trumpet and a piano playing middle-C differ - an orangy-red would be analogous to an out-of-tune trumpet. But the difference between a bright red and a pinkish-red is very similar. The fourier series for pink has a peak at 'red' and 'overtones' of blue and green. But we still think of 'pink' as being 'a kind of red' - we don't imagine it to be 'a kind of green' even though there is plenty of green in there. This is not dissimilar to the idea that the overtones of a trumpet and in a piano being relatively unimportant to our hearing it as a middle-C.

SteveBaker 15:06, 29 August 2007 (UTC)

If a tree falls in the woods, does it make a sound?

answer the question!!!!--arab 20:56, 26 August 2007 (UTC) —Preceding unsigned comment added by TerrorSonghai (talk • contribs) 20:56, 26 August 2007

If a tree falls in a forest — Matt Eason ^{(Talk &#149; Contribs)} 21:05, 26 August 2007 (UTC)

And this entire discussion, from June 30. Without doubt, sound is produced. Nimur 21:54, 26 August 2007 (UTC)

Without doubt? That's not the answer. The answer depends on what kind of question you are really asking, as the normal one requires qualification to be precise. --24.147.86.187 22:00, 26 August 2007 (UTC)

Not really. Nobody was able to come up with any kind of reasonable version of the question in the June 30th discussion that produced a tree that falls in a forest without making a sound. The nearest anyone came (IMHO) required a redefinition of the word "sound" in a way that fits no dictionary definition. What do you think is unclear? SteveBaker 23:47, 26 August 2007 (UTC)

OK, I made many comments that I removed now. Science simply cannot answer any question, including this one, as the article on science correctly states. A.Z. 03:11, 27 August 2007 (UTC)

This thread is at grave risk of turning into the kind of debate which the reference desks frown on, but: this last is of course nonsense. Science can answer many (if not most) questions, and it can answer them to an arbitrary degree of accuracy. There are, to be sure, untestable philosophical questions which science cannot answer, and it's also true that "an arbitrary degree of accuracy" is not synonymous with "absolute accuracy". But if science can't answer anything, then how is it we're not all still living on nuts and berries? —Steve Summit (talk) 03:42, 27 August 2007 (UTC)

I'm sorry, but I do not know if we are living on nuts and berries. I do not know absolutely and unquestionably that a berry or a nut have ever existed. If you can't realize that science is nothing, and that it doesn't make you know nothing and that no truth comes from it, you are just fooling yourself. A.Z. 03:44, 27 August 2007 (UTC)

Yes, yes, it's fun to play the I-can't-prove-that-all-of-observable-reality-isn't-a-figment-of-my-imagination game. We've all played that game before. But if you want to cure disease or feed the masses or travel faster than you can walk, it's not a useful game to play. The "practical everyday purposes" which you seem to be pooh-poohing are (for practical everyday purposes) the only purposes that matter. Scientific truths may not be isomorphic with philosophical truths, but neither one has a monopoly on the concept of truth.

To A.Z.: This will be my last post in this thread. To everyone else: I apologize for prolonging a philosophical debate on this science desk. —Steve Summit (talk) 03:57, 27 August 2007 (UTC)

I profoundly disagree with you. I'm not playing a game, and I'm sorry you're mocking me. Believing in science is like believing in the Bible. You don't know if there are masses, you don't know if there is food, and that does matter. I feel really sorry to see a question that does matter being mocked here, and philosophers who are just people that don't have a blind faith in science or the Bible being called pathetic. You should admit that no, you don't know if a tree makes a sound or not when it falls, either in the forest or in front of you. I think we should feed the masses and live our practical ignorant everyday life, and I belive there should be science, but I won't pretend to know truths, and pretend I'm not ignorant. A.Z. 04:07, 27 August 2007 (UTC)

Here's the problem for the "nothing can be proven to be real" folks. If nothing were real outside of your thoughts then you could simply cease to interact with this phoney world. So shut off your sensory inputs and just sit inside your mind and all should be well. The trouble is that after you have thought a significant number of thoughts (what we scientists would describe as "a few hours of time passing"), your "fake" sensory devices are going to start making some alarmingly real demands on your thoughts. You'll find that you get sleepy, hungry and thirsty. There is simply no way to shut out those demands no matter how unreal you believe them to be. So whether or not these things are real, you have to act in pretty much every way as if they were. If the demands of food and sleep were illusions brought about by our senses - why are your thoughts so utterly dependent on them? If you go for 48 hours without sleep - you'll find your "inner thoughts" become very hard to keep on track...which would be a surprising thing if the real world were utterly illusionary. So the value of an unprovable (and unfalsifiable) hypothesis such as yours drops to zero within a surprisingly short period of time. The "real world" (as I would prefer to describe it) is 100% compelling - you can't shut it out no matter how hard you try. Time passes in your mind at a rate not too dissimilar to the real world - you can't count to 100 in your head (or think 100 interesting thoughts or...whatever) without at least (say) half a minute or so passing in the real world. Increasingly, we scientists out here in the real world can tell (in the form of various brain scanners) approximately what's going on in your 'inner thought world' - we can see regions of your brain relating to vision light up when you think about pictures and regions related to reasoning light up when you think about math problems. In an increasingly real sense, I can compare what's going on in your mind with what's happening in mine - and find some sharp correlations. So your personal 'inner world' is also increasingly able to be viewed from within my personal 'inner world' - and as far as can be discerned, they work the same way. So what is the point (other than to annoy Steve Summit - which, I agree may be entertaining!) in holding the bizarre view that the outside world is fake and your thoughts are all there is - when the reverse seems to be the only thing that actually works for you? You have absolutely no evidence for the view that your inner world is all that there is and that the real world is faked - yet there is a mountain of evidence that says the opposite. If all of that evidence was out here in the 'real' world - you'd have some grounds for regarding that evidence as illusionary - but it's not - some of the evidence for the existance of a real world exists inside your inner world. Your absolute inability to keep your inner world from turning to thoughts of food, drink, sleep, etc as the real world places demands on it reveals evidence that is totally independent of your senses. Sure the 'feeling' of hunger is a sensory input from your stomach - but if it were illusionary, you could have it not affect your inner world...but you just can't do that. Try this: Try counting to 100,000 in your head without getting hungry. If the world were illusionary, you'd be able to do it...you can't. You just can't. Ergo, the real world is...real. QED. SteveBaker 16:21, 27 August 2007 (UTC)

[response to now-deleted prior comment referring to our article on Science]

While the statement, "Science does not and can not produce absolute and unquestionable truth" is certainly true in the context of the philosophy of science, it's profoundly misleading in the context of everyday life. If you've heard that scientific truths aren't absolute, you can easily conclude that (say) biblical truths are just as good as scientific ones. In a way, it'd be really great if we could publicly claim that scientific truths are absolute.

For everyday purposes, saying that scientific truth is not absolute is like saying that falling trees do not produce sound, or that the sky is not blue, or that 1+1=3, or that gasoline doesn't power automobiles, or that heavy objects fall faster than light ones, or that death from cholera is inevitable, or that easy transmutation of lead into gold might be possible tomorrow. —Steve Summit (talk) 03:31, 27 August 2007 (UTC)

But the tree question couldn't care less about everyday life. It's a question about truth, not a ridiculous question about whether your recorder will record something if you place it next to a tree that is about to fall. And, yes, I admit not to have a clue about whether the sky is blue. When I say it's blue, I'm assuming everyone knows that's just for practical everyday purposes. A.Z. 03:38, 27 August 2007 (UTC)

If you take the view that you cannot trust your senses then you have deeper problems. It's not just that you have to doubt that the tree makes a sound - you have to say that the words "tree", "fall", "forest" and "sound" are completely neutral audio signals that your senses are feeding to you with no verifiable meaning whatever. You don't know that you read the question correctly (or at all) or that you did in fact answer it. You don't know whether you are reading what I wrote - you don't even know that anything exists. If that is indeed your belief - then why are you trying to answer this question? In any not-believing-ones-own-senses situation, the question may never have been asked.

The truth is that the question (like everything else we do or say in the real world) is merely shorthand for: "If 'trees' (defined as the following bundle of possibly-illusory sensory inputs....) existed in the way our senses depict them - and if one 'fell' (defined as...) in a manner subsequently seemingly revealed to our senses but not reported directly to our senses at that time..."...and so on for about another four pages. The answer is: "If all of those things were hypothetically true then the answer would be (with many, many more caveats) - Yes!"...which is all you can ever answer about any question on any topic. The point being that you have to understand that the question is wrapped around with all manner of unwritten caveats and assumptions about the real world existing as perceived - and it is implied and understood that your answer should strictly be wrapped in the same unwieldy bundle of linguistic torture. If you accept the question under those terms then the answer is unquestionably "Yes" under those same terms. If you don't accept the question because you refuse to accept those layers of implied meaning then why are you answering it? If the sound of the tree might not exist - then neither might the question be about trees in forests at all - so you can't have a valid answer either way. SteveBaker 18:38, 27 August 2007 (UTC)

Actually in a number of ways you can't trust your senses. I'm not referring on the level of religious zealots who refuse to believe in science but simply that they have numerous limitations and a lot of things things are subjective in ways we often don't realise. I'm not saying this to be contrary and I suspect SB realises this, simply pointing it out for the general reader. Any philosophy of science book is likely useful to get an idea of the limitations of observation, one that I've read before and found good is What is this thing called science? by A.F. Chalmers. Nil Einne 22:34, 27 August 2007 (UTC)

That 1+1=2 is an absolute and unquestionable truth, not discovered by science. A.Z. 03:42, 27 August 2007 (UTC)

I don't know about that. It's (essentially) an axiom built into mathematics - and math (done that way) happens to be useful. But there are other ways that don't come out with that. Suppose you did all of your math in logarithmic domain or perhaps if math were invented by creatures who lived their lives moving at speeds close to the speed of light relative to each other and who learned to add velocities, times and masses using the Lorentz transform: 1c+1c doesn't equal 2c, it equals 1c. Sure they'd have to come up with some new, fancy representation for counting apples - but then we had to go to quite a lot of trouble to bend our math to do relativistic stuff that would come naturally to them. That doesn't make either their or our math 'wrong' - it just doesn't apply. Just as we say that the three angles of a triangle add to 180 degrees - that's not true in a severely warped gravitational field and beings who lived in proximity of a black hole would never have believed what Euclid had to say. It's not entirely obvious that every imaginable culture would see addition of integers as particularly useful. We can imagine beings who can only count to three (one, two, three, many) - who would have an entirely different arithmetic system. 1+1=2 and 1+2=3 but 2+2=many and 2+3=many. Also 2-1=1 but many-1=undefined. You would say that 1-1=0 was also an absolute, unquestionable truth - but the ancient Greeks had an entire system of arithmetic that didn't even contain the concept of zero. You could come up with an entire self-consistent (but not very useful in our world) set of mathematics based around denying our basic rules of arithmetic - in which 1+1=2 would not be quite the slam-dunk you think it is. SteveBaker 18:08, 27 August 2007 (UTC)

Besides, in most axiomatizations of basic arithmetic, 1 + 1 = 2 isn't an axiom (although something closely related, such as 2 = succ(1) in Peano arithmetic, may be taken as the definition of 2). For an example of how one might go about proving it while constructing arithmetic based on axiomatic set theory, see Principia Mathematica#Quotations and particularly this image there. (Ps. What all that old-fashioned set-theoretic notation in the image basically says is that, given two disjoint sets of one member each, their union has two members. Addition is later defined based on the union of sets.) —Ilmari Karonen (talk) 00:23, 29 August 2007 (UTC)

To the Original Poster: the answer to your question is, "yes". (Why do you ask?) —Steve Summit (talk) 02:56, 27 August 2007 (UTC)

The answer is yes. Those kids at the Humanities desk may tell you something different, but here we value objective reality and empirical verifiability. Unless you ask the quantum people, who will likely disagree as to whether the falling tree even hits to ground... Plasticup ^T/C 03:31, 27 August 2007 (UTC)

Sound of a bong bubbling* *Cough* Wow, like, you guys just totally blew my mind. 24.22.163.169 06:58, 27 August 2007 (UTC)

This requires the true definition of the word "sound" in a way that newer dictionary nolonger use. According to Webster's new international dictionary published 1931 2620 pg. Definition "Sound": 3. To Speak; utter; express "audibly". Now Rare. Definition of audibly which is an adv. form of "Audiblo" its definition is "Audiblo"- Capable of being heard. Not the word capable, as in if present or not present! key. it will be capable of being heard., it is capable of being heard even if no one there. Key word capable so it someone happens to be there it can be heard but does not require someone to be there, then it would be heard, not just capable.... Sound waves being produced,, case solved!!! Q.E.D. --Aaron hart 09:50, 27 August 2007 (UTC) so the ansuer is yes no matter how you twist your modern definitions......

Like in any debate, the person who defines the terms wins the argument. -- JSBillings 10:22, 27 August 2007 (UTC)

Answer=yes.87.102.45.106 13:19, 27 August 2007 (UTC)

How do you demolish a skyscraper?

What is the normal non-terrorism way to demolish a skyscraper? Mapper of the streets 22:54, 26 August 2007 (UTC)

Tall buildings are typically demolished using excavators. Controlled implosion has been used on buildings ~40 stories tall, although the danger and environmental hazards make this a non-prefered method of doing it (and this would imaginably be impossible in sufficiently dense urban areas). The tallest building ever demolished (not by terrorists) was only 47 stories tall. See also, demolition, high-reach excavator. Someguy1221 23:13, 26 August 2007 (UTC)

Explosives are planted in the base of the tower and then the tower falls vertically rather than on its side. It takes a lot of planning to get a tower to fall vertically. Juanita Hodges 23:25, 26 August 2007 (UTC)

Occasionally, buildings are dismantled piece by piece, in sort of the reverse order they were built. I watched this being done to the top floor or two of a building in Seattle that was being remodeled, and the same thing is currently and notably being done to the damaged Deutsche Bank building next to the WTC site. Presumably manual dismantling is more timeconsuming, more expensive, but less disruptive than either explosive demolition or excavator demolition. —Steve Summit (talk) 02:55, 27 August 2007 (UTC)

It is also noticeably less exciting. Plasticup ^T/C 03:33, 27 August 2007 (UTC)

Well, except for a couple of recent incidents at the Deutsche Bank building. :-( —Steve Summit (talk) 03:37, 27 August 2007 (UTC)

You can find a very good article on building_implosion at [7] -- WikiCheng | Talk 04:11, 27 August 2007 (UTC)

If you're (understandably) worried about the building falling to its side during demolition, think about the New York WTC (the terrorist thing you refer too, I presume). Both those towers fell straight down, despite the fact that they had been hit violently in the side. I can imagine that skyscrapers are even designed to fall like that if explosive demolition is so much cheaper than excavator demolition. Btw, funny that you specify non-terrorist. Loads of skycrapers must have been demolished (makes me wonder - how many?) and only once by terrorists. But the images have been repeated on tv so often that indeed I also instantly thought of the New York WTC when I read the header. We've been brainwashed. :) DirkvdM 07:13, 27 August 2007 (UTC)

A lot of people say there were explosives planted in the twin towers and people heard explosions at the base of the towers, too. Juanita Hodges 11:05, 27 August 2007 (UTC)

That would of course be the controlled demolition hypothesis. Worth noting is that – aside from a tiny minority of conspiracy theorists – it is widely acknowledged as bunk. Beware the 'major events must have major causes' trap in human psychology: [8]. TenOfAllTrades(talk) 13:27, 27 August 2007 (UTC)

You might enjoy David Macaulay's book Unbuilding, in which he descrbes the hypothetical dismanteling of the Empire State Building.

Atlant 12:00, 27 August 2007 (UTC)

The lesson the twin towers does bring is how relatively easy it is to bring buildings down more or less vertically. In that case, both essentially unplanned collapses happened fairly close to vertically. Demolition experts who are trying to achieve this kind of effect ought to be able to produce it on demand. One wonders how much thought about the ultimate demolition of the building goes into the original design process. Are architects inadvertantly making buildings that are going to be costly to demolish when the time comes? SteveBaker 15:49, 27 August 2007 (UTC)

Don't mean to brag, but I already said that. :) DirkvdM 19:09, 28 August 2007 (UTC)

Twin towers spilled debris out all over the place, presented a major health hazard, and rained concrete on the city. I doubt it is a good model for how things ought to work, demolition-wise. It superficially came straight down (under the massive weight of the top bits of it) but it was nowhere near a model for a safe demolition, and if you look at the footage/pictures you can see that there is a tremendous plume of materials as the buildings comes down (i.e. Image:South WTC Collapse.jpg). --24.147.86.187 18:22, 27 August 2007 (UTC)

Ok, so I definitely wasn't bragging. :)

A way to prevent this debris-damage is to make the building sag in the middle first, so the outer walls collapse inwards. Don't know how well this would work for skyscrapers, though.

But this brings me to a reply to TenOfAllTrades: A respectable Dutch tv programme, Zembla, debunked a lot of those 'conspiracy stories', but when they showed the film of the imploding adjacent CIA building (which was much smaller) to the major Dutch demolitioner he instantly said that that was without a doubt a controlled demolition job - it sagged in middle first, just the way demolitioners do it, and that couldn't possibly have happened in an uncontrolled collapse. Which fits in with the idea that the CIA knew about the attacks beforehand and decided this provided them with a nice excuse to 'counterattack' 'rogue states'. The collapse of their own building supposedly got rid of evidence. It was also oddly already evacuated before there was sufficient reason to do so. And after it became apparent that there was something wrong with those flights, normal procedure was not followed - they should have been instantly intercepted, but were left free to finish their 'job'. And there's more evidence pointing that way, I believe. DirkvdM 19:09, 28 August 2007 (UTC)

Btw, all references to this appear to have been removed from Wikipedia. They used to be somewhere, but I can't find them anymore. All there is is debunking of controlled demolition of the twin towers, but that's not the main issue, as I understand it. I wouldn't be surprised if the CIA started those stories themselves - create a lot of confusion with bull stories to distract from the real issue. DirkvdM 19:21, 28 August 2007 (UTC)

August 27

Noise reduction history

What 'playback only' audio noise reduction techniques were available in 1989 in the US? IE how did they go about reducing tape hiss in those days?--88.110.232.152 04:24, 27 August 2007 (UTC)

Dolby noise reduction systems were quite common in 1989, but they are not "playback only". I'm not sure there are any reasonable techniques for reducing tape hiss on playback only. Since tape hiss occurs across a very broad frequency range you can't really reduce it without also reducing everything, signal as well as noise (I could be wrong, perhaps there are some Magical Algorithms out there I haven't heard about). Still, it's best to take noise reduction steps at the recording stage. Pfly 05:59, 27 August 2007 (UTC)

On prerecorded tapes at that time dolby B was common.87.102.45.106 11:34, 27 August 2007 (UTC)

The playback-only techniques that are commonly used depend upon having a "moment of silence" from which one can deduce the various noise sources in the system (hiss, turntable rumble, etc.). One way it is done is to take the Fourier transform of the noise and decide how much noise is in each of the frequency bins. The normal (non-silent) signal is then run through the transform and any frequency bin that has about the same energy as was present in the noise sample is just dropped (zeroed out). The signal is then inverse-transformed back into an analog waveform and voila!, some of the noise has been removed.

Other techniques look for discrete events like "clicks" and "pops"; the real sound source is muted during these events and inferences are drawn (again, often using the Fourier Transform) as to what the sound would have been had the click or pop not occurred.

Back in 1989, it would have been a possible but expensive proposition. Nowadays, you can buy reasonably-priced software for your PC or Mac that will do all of this automagically (e.g., Sound Soap).

Atlant 12:07, 27 August 2007 (UTC)

thanks you. l am aware of the modern spectral subtraction techniques such as is used in Cool Edit etc. I have a reissued CD digitally remixed in 1989, where they say on the sleeve note that they have managed to remove most of the tape hiss (caused by too low a recording level) on the original master tape. What noise reduction technique are they likely to have used? (BTW is not low pass filtering as the upper frequencies are OK) Oh yeah, and why would they keep the very low amplitude and refrain from eqing the tracks back to something acceptable?--88.110.232.152 13:53, 27 August 2007 (UTC)

Plants Water Purifacation

How plants can discern the particles of substances and elements , with what special characteristic of them?Flakture 07:42, 27 August 2007 (UTC)

As a general answer, the process is based on similar concepts in both plants and animals. Membrane transport proteins are generally sensitive to the charge and size of molecules and ions. Proteins can also be "designed" to take advantage of chemical characteristics of target molecules (ie, the propensity of oxygen to bind to iron in hemoglobin). Someguy1221 08:08, 27 August 2007 (UTC)

Proteins can also be evolved to take advantage of chemical characteristics of target molecules (ie, the propensity of oxygen to bind to iron in hemoglobin).--Funnyguy555 21:49, 28 August 2007 (UTC)

Photon duality

--Aaron hart 11:30, 27 August 2007 (UTC) An Old subject but could someone please explain the current theory of partical duality. I thought I had it figured out, "Transformes from energy to matter for a brief instant durring an interaction. Durring the interaction I thought that when it existed as matter is speed was <<C then back to energy propegating through space time at C. Like the particles in a accelerator that result from a smash, these particles exist as mass and in an electromagnetic field spiral and pop into energy Likewise in space-time particles are continually popping from energy fluxuations to matter, then back to energy!., not nececerrially the pairs just similar....--Aaron hart 09:25, 27 August 2007 (UTC) ANY IDEAS From top Physicist giving up secrets that are well kept. Has it been proven that photons always travel at c, is it possible that durring an interaction velcity is <C since it interacts and transforms into mass, then imidiatly back??? Just wondering I mean is anyone really sure at this time??--Aaron hart 10:18, 27 August 2007 (UTC)

You have a very distorted idea of what matter and energy are. The interactions you think you are talking about, transformation from matter to energy, is actually not this at all. The interactions you speak of are transformations from waves to particles. Light never slows down below C when it interacts with something, and it never stops being energy (the "m" in E=mc^2 is not matter, but mass. A lot of people think that mass and energy are two very different things that can simply be interconverted, but their distinction is actually quite non-apparent in high-energy physics. A photon of "pure energy" has a measurable mass, that given by E=mc^2, and an atom holds within it the energy calculated from E=mc^2, using its measured mass. If you remove through chemical interaction some measurable amount of energy from an atom, it actually weighs that much less as well, even though you removed no particles from it). Now, what it means when light turns from a wave into a particle is that it goes from having no definite position to having a definite position (it's a very difficult concept to wrap your mind around that an object can actually not have a position. The wave the photon is said to be is a sort of map of the probability that you will find it at any particular point at a given instant in time. The very important idea to keep in mind is that before the photon interacts, it isn't actually anywhere! It has no position before it interacts, merely a probability of being found at each point in space). Now, as to what's going on in those particle accelerators is that a pair of particles, typically those generally associated with matter (ie, protons) are smashed together, and interactions that can be described only by quantum mechanics (these interactions are impossible to understand, no point trying to explain them) transform the proton into new particles. As for the particles popping in and out of existence in space time, there are two sources for these. Some are photons or or something else transforming into another type of particle, and then back. Others just, well, pop out of nowhere. These are called virtual particles. They don't actually require any energy to pop into existence, they just do. You can't detect them unless you supply them with energy somehow, but that's another story. But back to the energy/mass/matter thing. Matter is typically used to describe "that which is tangible" (atoms and their constituents). Energy, well, I have no way of explaining that one. You can read energy if you like. The most basic physical idea is that energy is a property of all particles that is conserved (the total amount of it in the universe never changes) in all possible detectable interactions, but is not a measurable physical property like mass. And mass, of course, is merely that which has inertia. I'm sure my answer will not satisfy you, please ask more, and do consider taking introductory quantum physics when you enter college (if you haven't already). Someguy1221 10:25, 27 August 2007 (UTC)

About light dropping below C, while the waves of light can do very funny things indeed, and appear to speed up or slow down, the most basic answer is that photons cannot ever change speed. This is not something to be proven or disproven, but rather it is a mathematically necessary property of photons derivable from the fundamental laws of physics. Someguy1221 10:26, 27 August 2007 (UTC)

Yes I worded it rather incorectly I did mean waves to particles which I meant to refer to as mass. Now my question is how can a photon have mass when only massless waves can travel at the speed of light? Yes I did mean that the waves convert to particles of a mass with the equivalent energy. I also knew that when chemicals interact exothermically they lose the mass equivalent to their evergy, Is this not a form of mass to energy, and could it not similary be waves to energy and energy to mass, and back. could some of the mass be changed to energy, in a wavelike packet? But the part I am interested in is the mass leaving the molecules when energy leaves, is this itself not a transformation as I have proposed?!, is not energy from a exothermic reaction transmitted as a photon? Also The particles poping into existance being photons does this not support my theory. Also I tought this was from energy fluctuations in space time......--Aaron hart 10:58, 27 August 2007 (UTC) p>s> I really appreciate someone with your calaber repling to me thoughts.

Also I was refering to energy to mass, or wave to particle the mass being equivalent to the energy of the particle. It has been a while since I have studied any of this, and quite a while since I have thought of any of it, it started to interfear with my being quote "a normal person" sorry--Aaron hart 11:30, 27 August 2007 (UTC)

I'll try to answer the new questions point by point. To say that only massless waves can travel at the speed of light is not entirely correct. The relativistic equation for kinetic energy (γ-1)m where "m" is the measurable inertial mass of the particle at rest shows that a particle with non-zero rest mass requires an infinite amount of energy to move at the speed of light, since γ = ∞ at the speed of light. This is not to say that photons have no mass, and in theory this is measurable by their gravitational influence (I can hop over to one of my labs right now and measure their momentum easily enough, but this may not satisfy you). Simply all of their mass resides in what is defined as their kinetic energy. Now, back to this mass to energy bit. Firstly, I'll declare that a particle is actually a special case of a wave. If you are concerning yourself with waves that represent a potential particle's probable position in space, then an actual particle can be thought of (ignoring a tad bit of physics at the moment) as nothing more than a Dirac delta wave. Further, one can think of energy and mass as abstract mathematical properties of waves, calculable from the use of mass/energy operators if the wave form is known. Now, an atom is a wave, or rather a superposition of many waves representing the numerous particles that can be found within. The waves have a calculable mass, and therefore energy. When what you normally think of as "pure energy" is extracted from the atom (this can be through emission of a photon or as causing something else to speed up) the wave forms will change in some way. The new wave forms, while describing the same potential particles, will have a different calculable mass/energy. Sometimes it's very easy to ascribe to some nature the type of energy one is dealing with, ie, kinetic energy, thermal energy, photonic/phononic energy, gravitational/electrical potential energy, etc. When you're dealing with a static system, like a lone atom, for example, it's very hard to ascribe the location of the energy, and we generally shrug it off and say that it's all just mass. But in truth, the "energy" is merely a calculable property of the wave functions describing that atom, and this point of view happens to work for all other forms of energy as well. This is all simply to say that classical views of the distinction between mass and energy somewhat collapse in the presence of quantum mechanics. Now, to the last question, the nature of any possible "energy fluctuations" in space-time is largely a matter of interpretation of the meaning of vacuum energy. But if you prescribe yourself to believing that particles pop into existence, then by quantum mechanics, as hard as it may be to swallow this, they didn't actually come from anything. They just start existing, and very quickly stop existing. Now unfortunately I must go to bed, but I'll be back in about 8 hours. Someguy1221 11:29, 27 August 2007 (UTC)

measurable inertial mass of the particle at rest this is where I believe it is a particle, sice it acourding to quantum mechanics it can never be at rest. Also I don't completly believe in Quantum Mechanics, Is it not based on we can not know the position and the velocity since we have to interact with it, which messes with the velocity. But this is only due to scientific measurement, not actuall fact. In fact Relitivity states the Big bang began at a Singularity, Impossible for Quantum Mechanics, but only by our measurments, thus I believe it is basied upon an unkonwn, which is unkown to observers but not God. Thus I believe in singularities, and sure it stands up to evidence, since we are observing the phenomenon, thus it fits. From our observation.--Aaron hart 11:52, 27 August 2007 (UTC) P.S. thank you

It is actually a very good question you bring up, and a common and key misunderstanding of quantum mechanics. We are often taught in high-school or introductory college-level chemistry classes that Heisenberg's uncertainty principle prohibits us from knowing the simultaneous position and momentum of a particle at a given moment in time to greater than a specified accuracy. What we normally aren't told is that it is not our inability to measure these quantities, or our inability to measure one quantity without disturbing the other (that one is only partially true. After measuring a particle's position, applying the momentum operator to the new wave function of the particle, now something like a Dirac delta, will show a very large range of probable values). Rather, the uncertainty in a particle's position/momentum arises from the fact that it doesn't actually have a single defined position and momentum. This is a very alien concept to classical physics, and why it is a common misunderstanding. As I said in above posts, the wave function, through the application of operators, gives the probability of the particle having any given position, momentum, or energy. Before the measurement is made (any arbitrary event whose outcome depends on the particle's position/momentum/energy), the particle exists only as this wave, and occupies no actual position in space. And so, from a quantum perspective, it is not that there is a limit to what we can know about the universe, but rather there is a limit to how much information can actually exist in the universe. As to the singularity thing, Quantum doesn't forbid the existence of a singularity, it merely can't explain it. But neither can relativity. Someguy1221 19:22, 27 August 2007 (UTC)

I misunderstood, I thought that a particles position and momentum could not both be measured at the same time, and that this was a conciquece of the observation. Also I don't understand how something with mass can travel at the speed or light, You site rest mass, but this is the total energy of the particle, which can not exist at rest. I just don't seem to get the concept; a particle with rest mass traveling at the speed of light, has all of its matter or more correctly mass converted to energy (i.e. electromagnetic wave), then when it interacts I believe it is possible however short lived, to transfer from energy back to mass, to interact. Then the mass transfers back to a EM wave, due to its unstable form, (being so small). Which I think all has to do with the properties of Space-time. I am most likely way off, but it makes sence to me, and it is very hard to relate in words. Note, I did not think Physicist completely understand Photon Duality at this time; only theorys with mathmatical formulas that all fit nice and neat (for the observer)--Aaron hart 21:48, 27 August 2007 (UTC)

You're right on the very last point, quantum mechanics was only ever meant to make predictions of the outcomes of experiments, nothing more. Although this has been the nature of science since Newton, moving away from attempts at providing an antiquated sense of satisfaction in explaining natural phenomena. Just a couple more points I'll repeat and/or throw in: a particle that has non-zero rest mass cannot travel at the speed of light, as this would mathematically imply infinite kinetic energy. As for photons interacting, I think all that I can say is that one can find a time-dependent wave function that describes the interaction. I've even said before, and I'll say here, if one is actually trying to solve a QM problem, it's best to ignore why any of it works, and just accept it (darned good predictions come out of it). Someguy1221 21:48, 27 August 2007 (UTC)

Thank you for your time and patience, I learned much from you, but still wonder about the natural phenomenon; and what actually takes place, but I am over 30 so I guess I should give it up. Again thank you for your time--Aaron hart 04:32, 28 August 2007 (UTC)

(Being 30 is no excuse - there are plenty of 60 year old physicists!) The problem is that you are trying to think about what "actually takes place" - implying that there is some 'classical' event going on behind the math that you simply don't understand. It's not like that at all. The reality is that all of this weird quantum stuff is what "actually takes place". Fundamental particles are indeed simultaneously particles and waves - they really don't have a well defined position or momentum - masses and time compression really does happen when objects move fast. That is literally how the universe operates. The only reason we find that strange is because we've evolved and educated ourselves in an environment where we only see and interact with slow moving macroscopic objects. This idea of 'classical' Newtonian physics is simply not how things really are - it's merely a shorthand for producing approximate answers for questions that relate to our slow moving macroscopic lifestyle. SteveBaker 11:58, 28 August 2007 (UTC)

Yes, I do believe something actually takes place, but I don't know if anyone understands it beyond mathmatical derivations from partial differentals of the wave equation. I do not believe it is a classical event, though I believe photons have simultanious mass/momentum, it is just impossible to observe, or measure. I believe that Heizenberg basied his uncertanty principle on the interaction durring observation. While Debrolie and Schrodinger used mathmatics alone, my question is did they do this to fit the observations; "this may be an ignorant question, but I am curious." And to be honest I prefer modern physics to classical newtonian, since it is more accurate and really makes more sence, I can use the equations just fine, I just wish to know what actually takes place!. I realize this may be of no concern for finding the outcome of situations, but it would be beautiful to know how particles actually interact in space-time.--Aaron hart 14:17, 28 August 2007 (UTC)

How things 'actually' happen is something that's unknowable though - two fuzzy clouds of probability approach each other - and some short (but fuzzy) amount of time later a number of differently fuzzy probability clouds come out the other side. We can't look more deeply into it than that because whatever we prod and poke the system with to examine it changes the answer...which we couldn't measure precisely in the first place. We're beyond the point where we could make progress by observing what happens and writing it down. Nowadays we have to theorize what the larger scale effect of some quantum scale event might be if it works like this rather than like that - then think up some kind of devious experiment to show that happening. Annoyingly, these experiments require greater and greater energies - resulting in exponentially more expensive equipment. The great hope of using string theory for answering these questions suffers from this exact problem. It is beautiful, elegant and has great explanatory powers - but it's unable to predict anything that we can test - so whilst it may well be right, we can't tell whether it's true or not. In the end (if we buy into string theory), the universe appears to be the result of the mathematics of probability wave packets and the more carefully we look, the less there is to see. SteveBaker 19:15, 28 August 2007 (UTC)

Riverstone pebble tiles

Hi, under composite materials I have found the above product, which I require for my knitchen worktop. Problem is I cannot find any reference to a maker, where can I source this? MMany thanks <email address redacted>

^{Email address removed — Matt Eason (Talk &#149; Contribs) 11:01, 27 August 2007 (UTC)}

Do you mean like this http://www.alibaba.com/catalog/10880060/River_Stone_Natural_Stone_Stone_Tile_Cobble_Pebble.html or http://www.ecvv.com/offerdetail/I1424081.html ?87.102.45.106 13:14, 27 August 2007 (UTC)

Thanks, close but I need a uk supplier any thoughts?

Try searching for "riverstone pebble tiles" and restrict your search to the uk - google allows you to do this. eg http://ww.google.co.uk/search?hl=en&q=riverstone+pebble+tiles&btnG=Search&meta=cr%3DcountryUK%7CcountryGB —Preceding unsigned comment added by 83.100.251.36 (talk) 06:31, August 28, 2007 (UTC)

True open circuit- calculation

How does one achieve a true open circuit (at RF) at the end of a piece of 50 ohm coaxial cable (or other sort of line) bearing in mind that the impedance of free space is always 377 ohms? Is it possible, or must one always have some radiation from the line end?--88.110.232.152 13:41, 27 August 2007 (UTC)

ie since :$\Gamma ={Z_{L}-Z_{S} \over Z_{L}+Z_{S}}$, is it true that gamma can only be a maximum of (377 -50)/(377+50) = 0.7658? as opposed to the ideal of 1?

A very good question, and I'm disturbed that I can't get my thought in order to answer it myself. My intuition tells me that if you enlarge the cable (keeping its impedance constant, of course) so that the centre conductor and shield are far apart, the situation would be more close to the ideal open circuit. Then again, you know how intuitions can be. Please, can someone help out here? —Bromskloss 19:23, 27 August 2007 (UTC)

I suspect that the 377 ohms is irrelevant in this case, but I can't be certain. At a guess, it's because the sequence of impedances is 50R-open-377R and not 50R-377R, so the wave is reflected from the "open" condition at the end of the cable and never sees the 377 ohms of free space beyond.

I can more easily tackle the OP's conclusion, because a simple ETDR experiment shows that an open-circuited cable has a reflection coefficient close to 1. See Figure 11 in LeCroy App Note 016 for an example. --Heron 19:32, 27 August 2007 (UTC)

Ah! but how close? cant be closer than 0.7658--88.111.124.125 20:44, 27 August 2007 (UTC)

So you didn't look at the example I linked to, then. The example I linked to above shows a gamma of at least 0.95, as nearly as I can judge from the waveform. --Heron 19:12, 28 August 2007 (UTC)

Yes I did look at your link. It gives the same response as it does on my oscilloscope. My Q was how the hell can it be better than the 0.7856 predicted by theory. Some other responses are starting to answer this question--88.109.90.214 22:45, 28 August 2007 (UTC)

OK to help anyone pursuing this line of inquiry, I quote from the article on coaxial cable:

• The characteristic impedance in ohms (Ω) is calculated from the ratio of the inner (d) and outer (D) diameters and the dielectric constant ($\epsilon _{r}$). The characteristic impedance is given by $Z_{0}={\frac {138}{\sqrt {\epsilon _{r}}}}\times \log({\frac {D}{d}})$.

Certainly a lower source impedance would make a better o/c, but still not perfect. Is perfection possible/--88.110.52.40 19:35, 27 August 2007 (UTC)

On the topic of electromagnetic radiation from an open end of a coax it can happen, but the coupling to free space is very low, and unless the coax diameter is comparable to the wavelength the escaping radio waves will be minuscule. The reason is that the radial arrangements of fields cancel out at a distance. I will see if I can find a formula for this. Graeme Bartlett 22:39, 27 August 2007 (UTC)

So you are saying less than 10% of the incident power leaks out the end of the cable-- is that correct?--88.111.187.180 22:50, 27 August 2007 (UTC)

Much less that 10%. 0.01% would be more typical. Graeme Bartlett 06:18, 28 August 2007 (UTC)

The leakage is proportional to the area of the coax between the conductors, and to the square of the frequency. Graeme Bartlett 22:48, 28 August 2007 (UTC)

That's an excellent question! You made me think, and almost had me convinced. I don't think it's true, though. The reflection coefficient is really close to 1. Why? The formula you gave is specifically for a resistive load that terminates the cable. If you hook up a resistor to the end, that's what you get. But the 377 Ohms of impedance of free space is not a resistive load! Of course, you can't measure 377 Ohms of resistance across an open circuit. Therefore, the simple formula is not applicable. --Reuben 06:44, 28 August 2007 (UTC)

Indeed. I filled a whole notebook with uglier versions of the reflection coefficient equations (practical, empirical, and theoretical equations). There are boatloads of "special case" treatments which you can find in a good textbook on circuit or antenna theory. Nimur 16:53, 29 August 2007 (UTC)

toothpaste

does toothpaste ever expire? thanks.

The Chicago librarians who researched this question say yes. [9] --Sean 14:27, 27 August 2007 (UTC)

reaction machenism

conversion of suger to 2,5-dimethlyfuran with complete reaction machanism

• Check your spelling; I believe you mean 2,5-Dimethylfuran. The reference materials on that page should answer your question. --M@rēino 17:28, 27 August 2007 (UTC)

I looks like you might be thinking of a method with Hydroxymethylfurfural as an intermediate- that page has a lot of useful mechanistic infomation (on the production from sugar).87.102.85.15 17:32, 27 August 2007 (UTC)

Telescope Physics

I know how a telescope works, however, I am a little shady on the physics of light travel and a telescope. It's fairly simple when you talk about seeing a couple of miles away with binoculars as you are seeing what is happening right then. What I don't get is when astronomers look into space billions of light years away. I understand that light travels at approx 186,000 miles per second and so what is being seen happened billions of years ago. So the question is when you look through a telescope are you simply pin pointing an area of the sky as though it were a 2-dimensional image? So the more closely you can pin point an image, the farther away from earth you can see? If I were able to take an extremely high resolution picture of the sky would I be able to see as far away with the telecope? --Beckerj99 18:25, 27 August 2007 (UTC)

Your picture needs to be both high resolution and high sensitivity, as the images of distant objects will be very faint - but the basic answer to your question is "yes" - see Hubble Deep Field, Hubble Deep Field South and Hubble Ultra Deep Field. Gandalf61 18:40, 27 August 2007 (UTC)

Awesome, I always thought that was the case, but couldn't find an article specifying it. Thx!!

Earths magnetic pole swapping

Does anyone know thy from time to time, the earths magnetic poles swap from N to S.--Aaron hart 21:30, 27 August 2007 (UTC)

Geomagnetic reversal#Causes. Someguy1221 21:50, 27 August 2007 (UTC)

Thank you, from now on I will search before I ask, It was very interesting. It has been bothering me for years. Two thumbs up for Wikipedia..--Aaron hart 14:33, 28 August 2007 (UTC)

Time dilation at the speed of light

Does time dilation become infinite at the speed of light? If so, then does time pass for light? 69.150.209.13 22:18, 27 August 2007 (UTC)

time dilation becomes infinite for light. No time passes from the point of view of light. So it is emitted and absorbed at the same time, (in its own reference frame), even when it crosses astronomical distances between galaxies. Graeme Bartlett 22:45, 27 August 2007 (UTC)

composite material, kitchen work top made of clear resin and white pebbles

Were can I source this product?

Try your local hardware or DIY store perhaps. Or stores used by builders if they serve you. Given than you're provided zero information about where you live (I'm guessing the US but who knows) we can't help more. Nil Einne 22:40, 27 August 2007 (UTC)

Again a search engine is your friend "pebble resin tile" into any generic search engine will produce results eg http://www.google.co.uk/search?hl=en&q=pebble+resin+tile&btnG=Search&meta=cr%3DcountryUK%7CcountryGB (same poster for UK as above?) gives multiple choices - is that ok?83.100.251.36 06:42, 28 August 2007 (UTC)

August 28

When is the best time to change gear in a manual car?

In the question Wikipedia:Reference_desk/Archives/Miscellaneous/2007_August_18#transmissin_output_torque_.3D_engine_power, User:SteveBaker talked about obtaining the best 0-60 time in his Mini Cooper S by shifting to keep the engine at it highest torque output. I notice SteveBaker answers alot of questions on the reference desk so I have been reluctant to ask, but I can't work it out for myself -- Why is gearing ignored in his answer?

For example, I created some tables using these gear ratios I found on the net for a Mini Cooper S:

1st Gear 11.450
2nd Gear 7.181
3rd Gear 5.397
4th Gear 4.407
5th Gear 3.656
6th Gear 2.986

According to the graph he linked, in first gear the engine at 5500 RPM would be creating 150 ft-lbs of torque and turning the wheels at around 480.35 RPM (5500 RPM / 11.45) with 1717.5 ft-lbs of torque (150 ft-lbs * 11.45). If we shifted up now, the engine would be running at 3449.39 RPM (480.35 RPM * 7.181) and producing still around 150 ft-lbs of torque but our torque at the wheels has dropped to 1077.15 (150 ft-lbs * 7.181). Had we have stayed in first gear to nearer the redline, say 6500 RPM we would have been making only 140 ft-lbs at the engine but 1603 ft-lbs (140 ft-lbs * 11.45) at the wheels.

Help! Where am I going wrong?

Alan 78.32.138.240 00:12, 28 August 2007 (UTC)

I think what you say sounds good. As far as I can tell, you are correct. —Bromskloss 06:31, 28 August 2007 (UTC)

What you are missing is that if you stay in 1st gear for longer than I would, your torque in 1st is dropping rapidly as the RPM's increase - so whilst you'd be getting more torque in 2nd after you shift at redline, you'll have lost ground over someone who shifted earlier. SteveBaker 11:47, 28 August 2007 (UTC)

By my basic understanding, acceleration is determined by force at the wheels, force at the wheels is given by engine torque * gear ratio. Even if torque dropped to 130 ft-lbs at the flywheel, 130 * 11.450 is still more then 150 ft-lbs * 7.181. Maybe my confusion is coming from the use of the word torque for both "flywheel torque" and "driving wheels torque". Also see [10] which is linked from the article on Torque, specifically the section "A Simple Example" where he shows that by changing from 3rd to 2nd even though he produces less flywheel torque, it results in more force at the wheels. Alan. 78.32.138.240 12:29, 28 August 2007 (UTC)

Really? Decreasing torque as a result of staying in gear is OK, if shifting would have given you even less torque. (I assume shifting is instantaneous, as I believe we all do.) —Bromskloss 12:01, 28 August 2007 (UTC)

mathematically speaking: plot rear wheel torque vs car speed in all gears. you will get a bunch of peaks, one for each gear; but what's important is where the descending tail end of each gear crosses the ascending front end of the next gear. obviously, that's the shift point, in mph. in real life, you have to allow for a drop in rpms while shifting, so run it a bit higher. Gzuckier 15:57, 28 August 2007 (UTC)

That is exactly what I did and from 0-60 I can see no point where the Mini Cooper S generates more torque at the wheels in a higher gear (lower ratio) before hitting the redline. I am admitedly very much a beginner when it comes to automotive engineering but my theory is that, as the Cooper S is supercharged it has a very flat torque curve through-out the RPM range much like a naturally aspirated engine with a higher displacement - coupled with it's wide gear ratio means the curves do not overlap. Although if SteveBaker has had his Mini Cooper S on a drag strip I cannot argue with empirical evidence. Alan. 78.32.138.240 16:50, 28 August 2007 (UTC)

For 'drag strip' read 'nice, level, deserted freeway on-ramp'! I used an accellerometer to measure 0-60 times. Please bear in mind that mine is not a 'normal' MINI Cooper'S - its got a bunch of 'go faster' stuff, so my torque curve doesn't look like the one in that article. Also, in practice, an awful lot depends on how fast/smoothely you shift and how quickly the engine will drop RPMs as you shift - and (not least) whether you can keep a close enough eye on the tachometer while remaining on the road! It took months of practice and a computer program that I wrote to simulate the entire process in order to get the best 0-60 time out of my car - and without an accellerometer, you can't measure your times accurately enough to know whether you are getting better. SteveBaker 19:02, 28 August 2007 (UTC)

For what it's worth, I've used an accelerometer (A Perfmeter Pro I think it was called), but I'm not sure I have a lot of confidence in their accuracy. The one I used depended on being perfectly level when the car is sitting there. But, a hard launch will jerk it around, possible causing it to move off-level, which could skew results for that run. I suppose as long as you confirm that it's still level once you've stopped, maybe this problem is reduced. But, to my knowledge, car magazines for example don't depend on such devices, presumably because they're willing to put in the cost and effort for more accurate means of measurement. But, maybe a typical accelerometer is plenty accurate for casual usage as long as it's used correctly. Mine was pretty easy to use incorrectly, tho. Friday (talk) 19:08, 28 August 2007 (UTC)

Mine's a G-Tech Pro - it compensates for being level because you tell it when you are stationary and it measures it's slope at that point. It seems to survive the worst jerks I can give it with my MINI - it beeps when it thinks you're at 60mph - and that agrees well with my GPS's speed estimate (but not with the car speedometer - which like most cars is deliberately off by a couple of mph). But in any case, I'm not looking for absolute numbers - just "did I do better than yesterday", and since I used this same freeway on-ramp (on my way to work after dropping my kid off at school - every day for many months) - all of the slope issues and other variables ought to cancel out. The things that don't cancel out are things like ambient air temperature (which affects the car's performance noticably) and the amount of gas in the gas tank (which is a not-inconsiderable weight difference in such a light car as the MINI). SteveBaker 21:24, 28 August 2007 (UTC)

katydids/diet

Your entry on katydids reports that larger, predatorial katydids have been known to eat small children. This is a joke, yes? My son, Andrew, is worried. Thanks for your clarification. —Preceding unsigned comment added by 72.133.249.135 (talk) 03:31, August 28, 2007 (UTC)

That was vandalism. Interestingly enough, added by an IP address registered in Wisconsin, same as yours! Someguy1221 03:51, 28 August 2007 (UTC)

It is ashame that someone would alegedly lible a reputable person, did they think it was funny, or a joke, "yes"., I don't find it funny.--Aaron hart 14:29, 28 August 2007 (UTC)

Apparently, not a lot of people think about the consequences of their actions, unfortunately. x42bn6 Talk Mess 15:44, 28 August 2007 (UTC)

Laser

So, we've all heard of those handheld green laser pointers that can burn through paper, but would shining a "normal" laser pointer through a telescope of magnificvating glass make it as powerfull (ya know, like when you do it with the sun?) 82.198.250.72 14:55, 28 August 2007 (UTC) 82.198.250.72 14:55, 28 August 2007 (UTC)

Probably not : a lens focuses the rays from the sun onto a point - but in the case of a laser there is really only one ray. That single ray does have width however so it will be possible to concentrate the narrow cylinder of light onto a point - in fact people have done this - creating flashes at the focus point (in air) where the atoms or whatever are heated very hot and ionised.87.102.90.8 15:16, 28 August 2007 (UTC)

I've never heard of this being done with a normal laser pointer (1mW) but it might be possible if focused enough. If you want to do this, you'll have to widen a lot your beam (because otherwise you'll be limited by diffraction) and then refocus it. Then, you'll have problems with the quality of your optics. You can't make your calculations with ray optics, you at least have to consider gaussian beams optics or a full simulation taking into account diffraction. It's difficult to focus much narrower than 1 micron^2. Might be easier with a green pointer of equivalent continuous power because those ones are pulsed (passive Q-switch) so it interacts a bit differently with matter. --81.67.15.32 18:09, 28 August 2007 (UTC)

In my optics lab we used lenses to focus lasers very similar to those laser pointers (the only difference was that ours were more coherent) into fiber-optic systems. The typical width of a laser from such a pointer is 1 mm, but fiber optic wires we used were about 10 micrometers wide. The Gaussian nature alone prevented us from making it much smaller than a few micrometers wide, though. Someguy1221 03:00, 29 August 2007 (UTC)

XRF Bremsstrahlung Shape

I've done my homework on the wikipedia X-Ray Fluorescence Spectroscopy and Bremsstrahlung articles, as well as some others, but I can't seem to find any sort of equation for the Bremsstrahlung itself. I don't care how many parameters it calls upon -- I just need to find some sort of legitimate baseline that works better than a basic interpolation fit. Any ideas? 146.139.76.94 14:06, 29 August 2007 (UTC)

http://rkb.home.cern.ch/rkb/PH14pp/node16.html (any good? - didn't check!)87.102.90.8 16:16, 28 August 2007 (UTC)

Have you tried searching the web itself for "Bremsstrahlung" already?87.102.90.8 16:17, 28 August 2007 (UTC)

I appreciate the link - although I can't seem to get a fittable equation out of the one in integral format. I've tried googling a range of related search topics, but none of the results actually show how the background Bremsstrahlung was fitted. 146.139.76.94 14:06, 29 August 2007 (UTC)

I'm afraid I don't understand/can't explain bremsstrahlung fully, and nobody else here seems to be clued up on it..

In the link I gave - it seemed to cover bremsstrahlung for an electron in an atomic field - this is the behaviour you are asking about I hope..

Assuming the link was in the right subject area but not detailed enough maybe the maths desk could help you more?

You said "I just need to find some sort of legitimate baseline that works better than a basic interpolation fit" - did that mean you want an expression for the whole spectra, or do you just need a relationship between highest bremsstrahlung energy and electron X-ray energy (latter is much easier)

I'll try to help further if you wish. though I'm currently confused how conservation of spin (selection rules) can be made to fit with the spectra obtained..If you can explain that to me I might be able to have a go at deriving the equation myself for you. ("Hope Springs Eternal")87.102.18.14 14:39, 29 August 2007 (UTC)

I'm guessing that you have a real spectra and need a theoretical bremsstrahlung curve so that you can subtract it to get a clean baseline...?87.102.18.14 14:43, 29 August 2007 (UTC) (Note - if you are doing x-ray fluoresence won't you be measuring the electron energy and not bremstrallung photon energy? - though the two are closely related)

By the way it's possible to quite easily remove the bremsstrahlung hump without knowing its equation using simple analysis (on a computer) - and just leaving the peaks on a flat baseline - maybe this is all you need?87.102.18.14 15:51, 29 August 2007 (UTC)

Area of Earth one can see.

Just say I were in the middle of a flat ocean, and I look 360 degrees around myself, how much of the surface area of the earth will I be able to see as a percentage of the total area of earth, and as just a figure? Assuming perfect vision. Phgao 15:44, 28 August 2007 (UTC)

The horizon article is a good place to start. If you know the distance you can see, you can figure out the area of the sphere within that distance. The Mathematics Desk might be a better place to discuss the details of these geometrical calculations. DMacks 16:00, 28 August 2007 (UTC)

(ec)According to Horizon#Distance_to_the_horizon, the true horizon is only 4.7 km away for a person 1.7 m tall. (You may be able to see farther due to refraction dependent upon atmospheric conditions.) Thus you can see an area of 69.4 km². The surface area of the earth is 510,065,600 km². Percentage-wise that's tiny: 1.37 x 10^-5 %. -- Flyguy649 ^talk _contribs 16:02, 28 August 2007 (UTC)

For a perfectly spherical earth, I think the answer is exactly ${\tfrac {h}{2(R+h)}}$, where R is the radius of the earth and h is the height of your eye above the surface. This agrees with Flyguy649's number for the special case of h = 1.7 m. -- BenRG 16:25, 28 August 2007 (UTC)

BenRG messed up somehow - that can't be the right answer - if you increase R, the distance you can see gets smaller - that's not right. When I plug in the numbers, I wind up with about 1 micron as the distance to the horizon!! SteveBaker 18:51, 28 August 2007 (UTC)

The area you see increases, but the fraction of the total area decreases. BenRG's answer is dimensionless, so it could never have been the area itself. —Bromskloss 19:10, 28 August 2007 (UTC)

OH! I see, sorry I didn't realise BenRG was talking about the ratio of the area. That makes sense. My bad! SteveBaker 21:07, 28 August 2007 (UTC)

Now wait here. I'm getting something else. Did you neglect the curvature of the Earth at some point? —Bromskloss 17:59, 28 August 2007 (UTC)

Hmmm - let's derive this from first principles: Imagine a right triangle - one vertex at the center of the earth (C), another where your eye is (E), the third where your line of sight hits the horizon (H) where it is a tangent to the surface of the earth. The angle C-H-E is a right angle (because E-H is a tangent). The distance you can see is given by Pythagoras: (R+h)²=d²+R² (where 'd' is the distance you can see, 'R' is the radius of the earth and 'h' is the height of your eye above the surface of the earth). Rearranging, I get: d = sqrt((R+h)²-R²) which you can multiply out to give: d=sqrt(h²+2Rh) - Some people drop the h² part because it's negligable compared to 2Rh, so you wind up with d=sqrt(2Rh) - which is a reasonable approximation for small values of h. SteveBaker 18:43, 28 August 2007 (UTC)

(And plugging in the numbers - I get 4.656km for a 1.7m eye height - which is in good agreement with Flyguy649's answer). SteveBaker —Preceding unsigned comment added by SteveBaker (talk • contribs) 18:48, August 28, 2007 (UTC)

Sorry, I was wrong. I did it over again, and got exactly the same as BenRG, without any approximations. The area seen is $2\pi R^{2}h/(R+h)$, and if you divide by the area of the whole Earth ($4\pi R^{2}$) you get $h/(2(R+h))$. —Bromskloss 19:06, 28 August 2007 (UTC)

So you could see someone else of that height at almost 10 km away in the eye - assuming perfect vision. DirkvdM 06:13, 29 August 2007 (UTC)

How much of a difference does atmospheric refraction make? Could you see more of the earth if you were in a big desert (a hot one) than if you were at the antarctic (due to temperature gradients)? How much more? Capuchin 06:55, 29 August 2007 (UTC)

Yes - refraction through the air does extend the distance you can theoretically see by a small amount. Exactly at the horizon there is a deflection of about a half degree (at sunset, for example, when the bottom edge of the sun touches the horizon, in reality the sun is almost completely below the horizon and you can only see it because of diffraction). Translating this into extra distance is kinda tricky - but the difference isn't great. You can see a teeny-bit further at the poles than at the equator because the earth isn't quite spherical...but again, the effect is negligable. It's rather pointless to figure all of these subtle effects into the equation because you never have sufficiently perfect conditions for these things to matter - at sea, you are bobbing up and down - so your estimation of eye height is not accurate. On land, the ground is never flat enough for these calculations to have real meaning. The numbers we've already given are plenty good enough! SteveBaker 14:41, 29 August 2007 (UTC)

Pointless but interesting :) Capuchin 14:59, 29 August 2007 (UTC)

Hardly pointless! International treaties have been made and broken over such details as "how far into the ocean can I see from my watchtower?". How far from the coast is international water? Were these guys in sight of land or not? Modern GPS surely doesn't eliminate the problem, or else such incidents would easily be settled by consulting a hand-held display and pleasantly agreeing on coordinates. Nimur 17:02, 29 August 2007 (UTC)

Gull feathers - do they make better duvet filling than duck/goose/chicken feathers?

I was told this today by someone who used to make feather duvets. I don't know if she was joking or not but apparently, seagull feathers make the warmest duvet fillings of all - better than eiderdown. The only downside is that they're hard to gather and expensive (thinking about it, gulls have very thick coats, don't they?). Anyone have more info? I know some of the gull people here will be interested in this. --90.240.209.98 15:45, 28 August 2007 (UTC)

Generally down is better than feathers (in terms of warmness) I believe..You must have meant seagul down?87.102.90.8 16:24, 28 August 2007 (UTC)

Question - can it really be any better than any other 100% down filling?87.102.90.8 16:29, 28 August 2007 (UTC)

Good question. I wonder if the down of the gulls of the high Arctic (e.g. the Glaucous Gull) has superior insulating properties? Gulls are generally *very* hardy birds, so maybe there's something to it. Heh, I wonder if a penguin down duvet would be any good? --Kurt Shaped Box 16:37, 28 August 2007 (UTC)

It's possible, but you would need to research which particular species of gull, and you would need an awful lot of them. I've no doubt penguin down is also an excellent insulator when supplemented with a layer of fat.--Shantavira|^{feed me} 17:42, 28 August 2007 (UTC)

The person tasked with collecting the gull down has my deepest sympathy. They should get those bear bile guys to do it. --Kurt Shaped Box 21:50, 28 August 2007 (UTC)

experiment to determine planck's constant

hi

can someone suggest an experiment to determine planck's constant (apart from the common photoelectric effect one)? thanks. —Preceding unsigned comment added by 202.63.233.12 (talk) 15:54, August 28, 2007 (UTC)

Seaching the web for "planck constant determination" throws up several different methods eg http://ww.google.co.uk/search?q=planck+constant+determination&hl=en87.102.90.8 16:22, 28 August 2007 (UTC)

ANTI-GRAVITY WORKSPACE

This question is really aimed I guess for an Astronaut, being that they are a well documented breed of workhorse, I'm going to assume there is a wiki-individual that knows something to the matter. ?Being in an Anti-Gravity environ, the lack of stress on the body, what types of effects does this have on the mindframe of a worker?(can they work longer than 8 hours? is time an issue? on time off, do you still work just to do something? how much sleep is needed? who evaluates fatigue?) In the same sense of T.H.White's explanations on how things came to be from observations in the wild kingdom. I'm going to theorize the pressures of the battle regalia of Samurai/Knight class warriors. Pressures stressed on body, flare up a driving force to focus intently on whatever it is you are doing. Like all the mail a knight would have to wear, and his visibility from helmet visor, and/or Samurai scary mask, covers much of the face and vision., and yet the extreme warrior gets the job done. Or the today's and Victorian English Gentleman and Gentlewomen, with the extreme stresses on body with tight corsets and neckties. Putting pressure on a human body, the physical part, does in fact amplify the mental performance. And yet, the exact reverse, no pressure at all., hence my question on anti-gravity. This may fall under the catagory of Corporate Mass Psychology, there's a term for that, I just forgot what it was. Thank you. 216.100.216.5 16:57, 28 August 2007 (UTC)Jacob V

I've tried to parse your stream-of-consciousness "question", and have a couple comments. 1.) Astronauts work in zero (or near-zero) gravity, not Anti-gravity. 2.) Anti-gravity doesn't actually exist outside of theory and science fiction. 3.) The psychophysical problems with living in the Weightlessness article. -- JSBillings 17:23, 28 August 2007 (UTC)

Strictly, it's not even 'zero g' - there is almost as much gravity up there as there is down here. The correct term is 'free fall'. Astronauts and the craft they are in is falling - hence they don't FEEL the gravity. But it's definitely still there! The only time humans have truly experienced zero g was during the moon shots when the astronauts were at the exact point between earth and moon where the two gravity wells cancelled out...and even then, they were experiencing the force of gravity from the sun. SteveBaker 18:26, 28 August 2007 (UTC)

I would suggest also that the notion of encumbrance increasing effectiveness is flawed, at least as presented. A suit of armor doesn't make someone a better swordsman, it just makes him harder to kill. Additionally, much of the encumbrance you mention (such as corsets and neckties) contributes no meaningful weight, which is the only change when moving to weightlessness. A suit of armor is still incredibly restrictive when weightless -- just look at spacesuits! — Lomn 18:18, 28 August 2007 (UTC)

Plus, a lack of gravity does not negate mass's inertia. So, if you're wearing a half-ton suit of armor in space, you still need to be strong enough to get it moving and to slow it down, move your arms and legs. -- JSBillings 18:24, 28 August 2007 (UTC)

Our bodies evolved to work efficiently at 1g. I would expect there to be in almost all cases some deterioration to functions in any other environment without artificial support. Capuchin 07:40, 29 August 2007 (UTC)

As far as ability to work goes, microgravity is far better than no gravity. Microgravity makes heavy things easier to lift (although inertia does become an issue with really heavy items), but doesn't cause the annoyances of zero gravity, like not being able to walk and having your tools float away when you set them "down". While inertia can be overcome by moving massive objects extremely slowly, at some point it becomes too slow to be practical. StuRat 04:48, 30 August 2007 (UTC)

White House

Why is it called white house? Is it because they only allow white presidents? 211.28.78.74 18:02, 28 August 2007 (UTC)

Read the article White House before making ridiculous assumptions. -- Kainaw^(what?) 18:05, 28 August 2007 (UTC)

that article is incomplete. just says http://en.wikipedia.org/wiki/White_House#Naming_conventions which says nothing about the origins of name?

The article states (under Naming Conventions): "...it is also speculated that the name of the traditional home of the President of the United States may have derived from Martha Custis Washington's home, White House Plantation in New Kent County, Virginia...". It is my opinion that that is SOMETHING about the origins of the name. -- Kainaw^(what?) 18:14, 28 August 2007 (UTC)

Yes i did read that part, but it is speculation, which shouldnot be in there. You should remove it. I want to know the truth, what is the real reason. Why would you call it "white" house? Has it got to do with American Foreign Policy? 211.28.78.74 18:26, 28 August 2007 (UTC)

The phrase in the article is properly cited and there is no need to remove it. You are correct that speculation on the part of Wikipedia editors shouldn't be in articles, but this is not an example of such speculation. There is no conspiracy or secret agenda behind the naming of the White House. — Lomn 19:38, 28 August 2007 (UTC)

Given that when it was named, only whites were allowed to vote anyways, they would see no need to point this out. It is like referring to it as the "Human Palace" on the off chance great apes get the vote some day. Eran of Arcadia 19:53, 28 August 2007 (UTC)

Just a minor point of politeness -- I know you probably didn't intend it, but the analogy comparing Whites::Nonwhites and Humans::Apes is somewhat offensive. -- JSBillings 20:07, 28 August 2007 (UTC)

It seems fairly clear that Eran was refering to how people perceived things at the time, not how things actually are. Skittle 14:05, 29 August 2007 (UTC)

(de-indent) Not true, strictly speaking. While race was abolished as a condition for suffrage in 1870, many states permitted multiracial voting from inception. — Lomn 20:05, 28 August 2007 (UTC)

But don't forget the poll tax though Nil Einne 20:20, 28 August 2007 (UTC)

There were plenty of voting restrictions to be sure. However, "only whites were allowed to vote anyway" is flat-out false. — Lomn 20:47, 28 August 2007 (UTC)

After reading the article, it seems that they called it the "White House" just as another name amongst others, such as the "President's Castle", even before it was burned to the ground and rebuilt. Could it possibly be that it was called the "White House" because.... it was painted white? -- JSBillings 20:13, 28 August 2007 (UTC)

That question is as absurd as asking "Why is the Casa Rosada called like that? Is it because they only allow pink presidents?" Titoxd^{(?!? - cool stuff)} 20:15, 28 August 2007 (UTC)

While I'm not challenging the idea the question is absurd, to be fair no one ever really called themselves pink AFAIK (ever if many people are more accurately called pink then anything else) whereas people did and do call themselves white. So it's not really the same thing IMHO (but reread the first part of my response). Nil Einne 20:23, 28 August 2007 (UTC)

Yeah, but the original question was gasping at straws to make a political statement out of an insignificant fact... Titoxd^{(?!? - cool stuff)} 22:55, 28 August 2007 (UTC)

This question doesn't really have anything to do with science does it Nil Einne 20:24, 28 August 2007 (UTC)

The "urban legend" of its name [11] went that after the British burned it in 1814, it was stained black from the soot, and after it was rebuilt, it had to be painted white, so it came to be called the "white house." In truth, the stone it was built from was porous and tended to absorb moisture and spall during freeze-thaw cycles, so the exterior was painted white from the day it was built. Furthermore, after the celebrated burning, it was demolished down to the basement level except for parts of the south face, and rebuilt with new stone. It was first officially called the "White House" on presidential stationary during the Theodore Roosevelt presidency. Edison 02:00, 29 August 2007 (UTC)

It's a house. It's white. DirkvdM 06:14, 29 August 2007 (UTC)

One might go so far as to make the political interpretation that it is a house and not a palace because America is a Republic with a President, not an aristocracy with a monarch. Our presidents are private citizen and they live in a house. Nimur 17:20, 29 August 2007 (U

I think I agree to what Edison explained on how the "White House" name came about. By the way, Presidents are public personalities because they are public servants.

Yes, and many, including the current President, have thoroughly serviced both the US electorate and the world at large. StuRat 04:37, 30 August 2007 (UTC)

I don't think any more political statements are needed after the troll's initial question, but... please leave it to the "world at large" to decide whether they feel "thoroughly serviced"... --Ibn Battuta 23:24, 30 August 2007 (UTC)

Many have been. Whether they liked it is a different matter. DirkvdM 06:25, 31 August 2007 (UTC)

Does ice conduct electricity?

I ask because I work at a facility which has just purchased an AED. When using an AED, the victim must not be in a puddle, and must have as dry a chest as is possible. Our policy also includes moving victims off ice (we have an ice rink), which seems ridiculous if ice doesn't conduct electricity. – Mike.lifeguard | ^talk 19:50, 28 August 2007 (UTC)

But the thin film of water that forms when you place your feet over the ice, due to conduction and radiation, does conduct electric charges. Titoxd^{(?!? - cool stuff)} 20:17, 28 August 2007 (UTC)

Neither pure ice nor pure water conduct electricity very well - it's the stuff in the water that changes that:

• Ultra pure water: 5 x 10^-6 S/m
• Drinking water: 0.005 – 0.05 S/m
• Sea water: 5 S/m
• Ice: 6x10^-6 S/m

But ice is weird stuff and it conducts across surface defects rather than through the bulk of the stuff. Weird. SteveBaker 21:02, 28 August 2007 (UTC)

Unidentified Fixed Object

This

Can anyone tell me what this is?

I saw this thing under a light microscope at low magnification (something like 100X if I remember correctly). Some background if it helps: My friend and I were preparing a karyotype for fun. I collected some of his blood, went through the whole procedure, and I came across this thing on one of the slides. —LestatdeLioncourt 21:24, 28 August 2007 (UTC)

It looks vaguely like the cellulose skeleton of a plant cell wall but that is a guess. Graeme Bartlett 22:50, 28 August 2007 (UTC)

Well, it seems awfully hard to believe - but it looks suspiciously like a Stent of some kind. Quite how you'd manage to extract one from someone's blood stream is kinda hard to imagine. If that's correct then whoever you yanked this out of REALLY needs to seek medical help ASAP! SteveBaker 22:51, 28 August 2007 (UTC)

I agree that it looks man-made (like a stent). I would blame contamination from lab materials before assuming that something came out of your friend's bloodstream. -- Kainaw^(what?) 23:01, 28 August 2007 (UTC)

Can you estimate the size and describe the shape more? How does it appear to you when you fiddle with the focus? just describe anything that might not be obvious from the picture. -- Diletante 00:52, 29 August 2007 (UTC)

I'm not sure about the size, but if it helps those little dots here and there are T lymphocytes. By the way, I'm leaning towards the contamination theory; I don't really think this was acutally there in his blood. I'd just like to know what it could be. Aren't stents too big? I don't know if anyone noticed, but I find its membrane's pattern very interesting (you can see it most clearly on the right side). —LestatdeLioncourt 06:32, 29 August 2007 (UTC)~

It's really not clear from the description exactly how big this thing is. If that's a 100x magnified image and those dots are lymphocytes then this thing would have to be a fraction of a millimeter across - so I guess my stent suggestion is not it. It sure looks artificial though - but maybe there is some kind of natural structure that looks like this. Weird. SteveBaker 14:25, 29 August 2007 (UTC)

It looks vaguely diatomish to me. DuncanHill 19:25, 29 August 2007 (UTC)

I'd like y'alls to really work on this one more. You've got me wondering. If a Diatom of some sort, how does it live in the bloodsystem? t-cells, on attack? Could it be some sort of metalic crystalisation of sodiom of sorts? Or again the plant theory?-some bacteria of sorts? Come on people! bear down. Ask a scientist! --Jacob Vi am the kwisatz haderach 21:16, 29 August 2007 (UTC) —Preceding unsigned comment added by Specialagent777 (talk • contribs)

If this was "for fun," then what was your lab procedure? If you are working with a set of slides or cover slips that had previoiusly been used for diatoms and not scrupuluosly cleaned, or on a bench that was contaminated, or in a labe with some dust fo the right sort, this object might have gotten into you sample. My swimming pool filter uses "diatomaceous earth," which is essentially finely ground chalk and which (I guess) may have such structures in it. -Arch dude 00:10, 30 August 2007 (UTC)

Well the first part of the procedure (culturing) was carried out in an aseptic environment (it had better be, cuz it was in a blood-drawing room), but later on (centrifugation, hypotonic treatment, fixation, etc...) the chances of outside contamination was very high, because we were working in the same compartment that they were doing all the bacterial cultures in. The lab technician who was there said he hadn't seen anything like it in his 15 years of lab work, so I doubt it was due to contamination from the compartment we were working in. The slides were also brand new and previously chilled in a sterile cup. —LestatdeLioncourt 22:18, 30 August 2007 (UTC)

If you were 'shooting up' 'bad drugs' the 'product' might be 'tamped' with some 'white stuff' eg chalk - but then you'd know if you were doing that wouldn't you.. Seriously though (I HOPE) The probability of external diatom contamination is quite high - if for instance you - "use a lot of chalk"..87.102.14.233 08:27, 30 August 2007 (UTC)

Another suggestion is that it is the wing off an insect, perhaps a mosquito or fly. It is broken off on the lower end and complete on the upper rounded side. Initially I thought it must have been a cut out piece of seagull feather, but the line around the edge argues against this. Diatom occurred to me, but its nothing like the diatoms I have seen, that tend to have spikes on them. Graeme Bartlett 10:51, 30 August 2007 (UTC)

It doesn't look at all like a fly wing. (I've looked at very, very many!) At high mag, they have a regular pattern of "hairs" that all point in the same direction. And epithelial cells in general are hexagonal in shape (to maximize cell-cell contacts). Flyguy649 ^talk _contribs 13:58, 30 August 2007 (UTC)

Another thing is skin (reminds me of snake skin) - what exactly is the length of this thing? —Preceding unsigned comment added by 87.102.14.233 (talk) 11:11, August 30, 2007 (UTC) Also too big, plus (above) diatoms don't have seems (or do they?)87.102.14.233 11:14, 30 August 2007 (UTC)

The idea that it is a wing or scale appears to me to be based on the idea that the object is flat. The bad focus on the lower left and upper right indicate to me that this is more of a tube than a flat object. It isn't really even a round tube. It has rather sharp corners, making it rectangular. The roundness of the top isn't very round if you follow the edges up to it. It is nearly squared off as well - just appearing rounded due to the lost focus. -- Kainaw^(what?) 13:22, 30 August 2007 (UTC)

Could it be a thread or a bit of gauze? Some type of cotton fiber?--69.118.235.97 15:43, 30 August 2007 (UTC)

If you look very close it seems that it is woven, and that threads approach the edge from behind wrap around and continue to be woven. Could this possble be some new kind of blown celluloce cigarete filter???--Aaron hart 03:50, 31 August 2007 (UTC)

You know you need to quit...when you have cigarettes floating in your blood. Someguy1221 03:53, 31 August 2007 (UTC)

August 29

Chill

Hi, what is actually (ie biologically) happening when one feels a chill running through one's body, or back or whatever? Thanks —Preceding unsigned comment added by 218.250.156.40 (talk) 01:55, August 29, 2007 (UTC)

First, what causes it... This is caused by the sympathetic nervous system, which triggers the fight-or-flight response. It is normally caused by the perception of something requiring the body to prepare for a fight-or-flight response, but can also be triggered by a minor chemical imbalance. The imbalance is normally corrected immediately, but the sudden rush of endorphins and/or adrenalin can cause chills, sweats, and goose bumps.

Now, the chill... As explained, the body is in fight-or-flight mode. One of the responses is to constrict blood flow through much of the body (preparing to need a burst of oxygen-rich blood in a moment's notice). That constriction flows across the skin and is felt as a "chill". This is normally accompanied by the other responses, but can be a chill with no other responses when caused by an imbalance. -- Kainaw^(what?) 02:13, 29 August 2007 (UTC)

Thanks a lot! —Preceding unsigned comment added by 218.250.157.77 (talk) 01:41, August 30, 2007 (UTC)

Hollow moon

Is it true that the moon is actually hollow? --124.254.77.148 02:33, 29 August 2007 (UTC)

See Hollow moon. There are various advocates of this theory - eg. [12]. But I doubt that most terrestrial scientists take it seriously. -- JackofOz 02:39, 29 August 2007 (UTC)

Yes, Mighty Mouse ate all that delicious green cheese. Clarityfiend 03:50, 29 August 2007 (UTC)

If the moon were hollow, then:

1. The moon would long ago have collapsed into the hole in the middle - and we'd be looking at a solid (albeit smaller) moon.
2. There is no known mechanism for a large hollow body to form. What we know of planetary formation would not permit that.
3. We have measured the vibrations of the moon from the impact of discarded a lunar lander crashing into it. The resulting seismic signals show a solid moon.
4. The moment of inertia of a hollow sphere is wildly different from a solid sphere. Careful measurement of the moon's moment of inertia clearly prove that the moon is quite solid.
5. The mass of the moon is easily measured from it's gravity. If it were hollow, the material which the skin of the moon would have to be made of would have to be insanely dense.

This is a really obvious nonsense theory. Why do people have to keep coming up with these things? Are the mysteries that we REALLY have not interesting enough for them?

SteveBaker 15:24, 29 August 2007 (UTC)

Perhaps it's because the real mysteries take the form of "Why doesn't the zero-point energy of the vacuum cause a large cosmological constant?". You can see how "the moon is hollow!" could hog the limelight. --Sean 19:35, 29 August 2007 (UTC)

Moon's moment of inertia

So, how has the Moon's moment of inertia been determined? It's not as if we could just apply some known force and measure what happens. --Anonymous, August 29, 2007, 20:08 (UTC).

Well...that's not exactly true.

I only know that the rotational inertia of the moon has been measured because hollow moon says so. But if I was an astronomer given the task of doing this I'd note that the moon is almost exactly tidally locked to the earth (ie the same face of the moon faces the earth all the time). That means that theoretically, the length of a lunar day and a lunar month ought to be identical. Yet we know that the duration of the moon's orbit is slowly increasing. As the orbital speed changes then the moon's rotation has to change to compensate for the orbital speed change. We know the size if the force that's doing that (the gravitational forces of earth and moon) - so we could measure the rate at which the orbital speed and rotational speed are changing (which ought to be fairly easy to measure since Apollo dropped laser reflectors onto the moon). So a known force (the tidal force) is being applied and we can measure what happens. But that's speculation. I don't know how they actually did that - I'm relying on Wikipedia (Dangerous!!) SteveBaker 21:38, 29 August 2007 (UTC)

Here is how they proposed to do it in 1977. SteveBaker 21:44, 29 August 2007 (UTC)

Well... it is exactly true. The tidal force isn't something "we" apply.

Regarding the first answer, you're talking about measuring the extent by which the change in rate of rotation speed lags behind very small changes in the orbit. I find it hard to believe that enough precision would be available th atway. As to the second answer, only the abstract of that article is available online free. It apparently refers to measurements based on effects of the orbit on a lunar orbiter. But that ought to be impossible; because the gravitational fields of a hollow sphere and a solid one of the same mass are identical, it would seem that such an experiment could only detect departures from spherical symmetry, not the distribution of mass by depth. I must admit that to having no idea what is meant by "C ₂₂ gravity harmonics", though. --Anonymous, August 29, 22:18 (UTC).

The Moon is is tidally locked, but it still oscillates with a motion called libration. This oscillation would depend, I think, on the Moon's moment of inertia. -Arch dude 23:52, 29 August 2007 (UTC)

(Update) Ah, yes. A quick google for moon libration inertia gives a lot of papers that show that libration is used to measure inertis, and that are measuring things that are several orders of magnitude more subtle than a hollw moon would be. -Arch dude 00:00, 30 August 2007 (UTC)

Aha. I was thinking of libration only in terms of the apparent motion due to the difference between the essentially constant speed of revolution and the varying speed of the moon in its orbit, but that also causes a change to the angle of the tidal force, and that causes a real motion, and there we go. Thanks! --Anon, August 30, 02:15 (UTC).

I also wondered how the moment of inertia is measured by fine observations of satellites in lunar orbits. Surely a hollow shell would be indistinguishable from a solid moon as far as Lunar Prospector is concerned! Without having done the homework, I think it must work something like this: the moon's librations depend on its mass distribution in several ways. The amount of torque depends on how asymmetric the moon is, and the angular acceleration is the torque divided by the moment of inertia. You can see the librations from Earth and make very fine measurements without leaving home. But if you don't know how much torque is causing the librations, you can't calculate the moment of inertia. So you need the satellites to tell you how lopsided the moon is, and therefore how much torque is acting on it. That probably dominates the uncertainty on moment of inertia. (Just to repeat, this is an educated guess - my university doesn't seem to have an online subscription for reading those papers either!) --Reuben 02:40, 30 August 2007 (UTC)

The moment of inertia of a hollow sphere is quite different from a solid one - even if their masses are identical. For a uniform solid sphere it's 2mr²/5 and for an infinitely thin spherical shell it would be 2mr²/3 - for something which is hollow but not infinitely thin, it's somewhere between those two limits. So there is a huge difference in the two - even with fairly poor precision one would be able to tell the difference between the two. As noted in NASA's 'moonfacts' the measured moment of inertia is about 1% less than theory would suggest for a uniformly solid sphere. (A hollow sphere would have more inertia than a uniformly solid sphere. That means that not only is it solid - but it's also denser in the center than it is at the surface. SteveBaker 04:00, 30 August 2007 (UTC)

Are you responding to my post? I don't disagree, but I don't see how that relates to the question of how satellite tracking is sensitive to moment of inertia. --Reuben 06:51, 30 August 2007 (UTC)

Vision improved?

Something really weird happend yesterday. I went to the eye doctor and he told me my vision improved and its rare but he's seen it before in people that have improved their health (I went from 205lbs (30% bodyfat) to 165lbs (about 11% body fat) but I have never heard of this, is it really possible? I didnt believe it either at first but he gave me new contacts and I see very well with them. —Preceding unsigned comment added by 76.167.145.55 (talk) 04:03, August 29, 2007 (UTC)

Note that nothing said here may be taken as medical advice. Sudden worsening of vision has sometimes been found due to a high blood sugar from adult onset Diabetes [13] , [14],[15] , and with improved blood sugar levels, the vision has sometimes improved, if the vision changes were due to the effect of high sugar causing swelling of the clear tissues in the front of the eye (as opposed to the more permanent effects on the retina). Weight loss due to diet and exercise can lead to improved blood sugar levels. In any event, congratulations on having vision improvement rather than vision detriment. Edison 17:31, 29 August 2007 (UTC)

(to Anon) My vision has improved slightly in one eye over the past number of years enough that my prescription is off in an old pair of glasses. So you aren't unique here! Flyguy649 ^talk _contribs 21:44, 29 August 2007 (UTC)

Near-sightedness (myopia) is common in the young, and far-sightedness (presbyopia) is common in older people. Thus, it's fairly common for those who are near-sighted in their youth to see their vision improve slightly with age. This happened to my brother, he was slightly near-sighted, then his vision was perfect for maybe a month, now he is slightly far-sighted.

Another possibility is that it's just an inability to measure your vision accurately. Since they rely on the "which one is better" method, and I usually can't really tell between two adjacent settings, I might pick the worse setting of the two one time and the better setting of the two the next time, even though there was no real change. StuRat 04:18, 30 August 2007 (UTC)

In that situation, I tell the optician that I can't tell the difference. In fact, they usually phrase it as 'Which is better? 1, or 2? Or are they the same?' at my place. After all, no point in giving a potentially wrong answer to that sort of question. Skittle 14:31, 30 August 2007 (UTC)

My optometrist measures my prescription with a machine (that you look in with a picture of hot-air balloon in it) and then confirms it with the "which is better" - which is also for astigmatism correction. Flyguy649 ^talk _contribs 13:27, 30 August 2007 (UTC)

Germans then and now

This is more of a historical-biological question. Are the physical characteristics of today's German people any different than that of their 11th century ancestors? I know some Germans that have dark hair, brown eyes, and very tan scan. I realize that not all Germans are tall with light skin and blue eyes, but I'm sure some sort of change had to take place over the course of a millennia. I guess it also depends on what area of Germany you choose and what the staple diet of the people was at that time. If they were underfed for example, they would be shorter because of a lack of protein and vital nutrients required for healthy growth. However, this is just a generalized question. --Ghostexorcist 07:25, 29 August 2007 (UTC)

((Probably an archeologist would be a good person to ask (or an anthropologist) - ie someone who studies skeletons of 15th century germans - maybe such people hang out on the humantities desk - I suggest you ask there as well..87.102.18.14 11:50, 29 August 2007 (UTC)))

I think geography is important more because of interbreeding with neighboring people. Those in northern Germany would tend to resemble Swedes, Danes, Finns, and Norwegians (blonde hair and blue eyes), while those towards the south would tend to resemble the French and Italians (dark hair and eyes). StuRat 04:08, 30 August 2007 (UTC)

I don't know much, but it's a fact that they were shorter. I'm not sure these are facts, but at least rumor has it that Frederic the Great, when recruiting his famous soldiers (the "Potsdam Giants" - in German simply "lange Kerls" = tall guys) only from people that were 1.80m (5"11') or taller, had some trouble finding enough (capable) people. Well, the population was also smaller, but still I don't think you'd have any trouble finding men of +1.80m in Germany nowadays. (No guarantee that this story is true, it's just hearsay; but the different size of people in the Middle Ages is an often talked-about fact; also see the linked article.)

What you're mentioning about dark hair, brown eyes, and tan scan, however, seems more of a genetics question. So apart from emigration of specific types and from immigration (not in extreme numbers since the 11th century... if you disregard the 20th century which has greatly changed the German population), the regional differences that you mentioned are important. Northern Germans come generally closer to the stereotype (tall, blond, blue-eyed - think of stereotypes about the Dutch or Scandinavians) than do South Germans, and I would speculate that this was even a bit more true before mobility increased dramatically in more recent decades and through WWII - though one can hardly stress enough that even in the North, the stereotype is far from being true in general. (For current numbers, this article might tell more, but it's not for free... But google tells us that "In Germany, among 6000000 school children only 31.80 percent had both blond hair and blue eyes..., while of the 75377 Jewish children 42 percent were of the ..... As the percentage of blond types among the Germans in Prussia is very high ..." - so, judging by the context, these may be figures from the 1930s). Happy googling... --Ibn Battuta 23:57, 30 August 2007 (UTC)

Biros!

Here's a stumper for you all. At work I enjoy using many different colours of biro. I have found that while the blue and black ink biros write well, the red ones don't write quite as well, and the green ones very rarely work. Why is this? Is it a different viscosity of the ink? Out of 4 green biros from 2 different batches, I have only just got 1 to write at all, and it doesnt write very well. Capuchin 09:08, 29 August 2007 (UTC)

Could it be that green is not a popular coulour, and that the biros sit around for ages on the shelf before you use it? Perhaps exceeding the shelf life. The same could apply for red. I noticed that no one steals a red pen, but the blue and black pens disappear fast. Blue and black are far more popular and would have a faster stock turnover rate. Graeme Bartlett 09:13, 29 August 2007 (UTC)

I'll snoop around and check tomorrow morning! :) Capuchin 09:56, 29 August 2007 (UTC)

I vote for Graeme Bartlett's explanation. The other point I'll note is that water-based pens (such as Biros) often write poorly on xerographic copies or printouts, owing to an overall fine coating of hydrophobic plastic toner materal on the printout. But I've never known that malfunction to be color-sensitive.

Atlant 11:39, 29 August 2007 (UTC)

This problem varies from make to make surely?87.102.18.14 11:41, 29 August 2007 (UTC)

Yes there are some good quality pens around that work. Also some workplaces have more problematic pens than others. The kind of workplace that buys 10000 biros at a time can have problem with aging biros. And the fine point pens seem to blockup more easily than the coarse tipped pens. Graeme Bartlett 14:49, 29 August 2007 (UTC)

I assume you refer to Ballpoint pen rather than the felt-tip variety. Except for the most expensive name-brand ones, they always seem to stop writing long before the ink is used up. I have tried the time-tested method of scribbling them back and forth on scrap paper while muttering (usually ineffective), using centrifugal force by whirling/flipping them like an old mercury fever thermometer (often effective) and applying heat to the tip (rarely effective but often satisfying). The centrufugal force method might be more effective if the pen were attached to a motor to allow more effective centrifuging of the ink, forcing fresh ink around the ball to flush out the dried ink, but of course there is the likelihood of the attempt producing a line of sprayed out ink on anything within range (been there, done that), and/or a pen/projectile flying loose and causing injuries or damage. This has been discussed at Answerbag.com: [16]. [17] suggests storing biros vertically with the cap on, and running the tip across an eraser to force the stuck ball to roll and to clean the dried ink off the ball. Edison 17:18, 29 August 2007 (UTC)

erm had you tried licking the tip? - re wetting the dry ink? (I'm finding it difficult to resist advertising my favoured biro brand - which of course work down to the last mm of ink)87.102.18.14 18:17, 29 August 2007 (UTC)

(US readers may not appreciate that 'Biro' is the name of a company that makes cheap ballpoint pens. They have had such a longstanding dominance of the market that many people in the UK call all ballpoint pens 'biros' no matter who makes them.) SteveBaker 21:22, 29 August 2007 (UTC)

Except there is no such 'biro' firm, which an internet search confirms, perhaps you meant...87.102.14.233 08:22, 30 August 2007 (UTC)

In other words, a genericized trademark. Titoxd^{(?!? - cool stuff)} 06:48, 30 August 2007 (UTC)

Not a company Steve, but the inventor, László Bíró. The company you're thinking of is Bic, but is not where the name comes from. I forgot to look this morning. I will try to remember tomorrow! Capuchin 08:32, 30 August 2007 (UTC)

Could it be the reason red and green pens "are shit" is because nobody needs red and green pens. It's a sort of reverse reasoning which perhaps someone could tell me the name of..87.102.14.233 09:55, 30 August 2007 (UTC)

I'm not sure this works for "biros", but at least for regular fountain pens (which are much better for the environment anyways, if you excuse me saying so) black and blue ink are in fact different, with the black ink eventually jamming the pen (I think the culprit was soot, but may be completely wrong). I don't think it would happen in the short lifetime of a "biro", but since we're not talking about the difference between black and blue anyways - there's at least a slim chance that some other ingredient would just jam the pens faster. I lean towards the simple explication of the expiry, though. --Ibn Battuta 00:04, 31 August 2007 (UTC)

Speedy Than Light

I read somewhere that Hawkings had discovered thermal radiations thats coming from Black Holes. Black Holes are huge masses that wont even let light go away from it. So does it mean that the particles in "Hawking's Radiations" has velocity more than of light ?

Oasa 11:33, 29 August 2007 (UTC)

No, the photons are generated exterior to the event horizon from vacuum fluctuations (This is a simplified explanation, but is an intuitive way to look at it). See Hawking Radiation. Capuchin 11:43, 29 August 2007 (UTC)

If you are interested in faster than light phenomena, check out faster-than-light and the theoretical tachyon. Capuchin 11:57, 29 August 2007 (UTC)

These particles are not travelling faster than light. The black hole's event horizon does prevent things that are moving no faster than light (that is to say: "everything") from escaping. What's happening here is that there is a peculiar process happening throughout the universe where (even in a complete vacuum) a particle and it's anti-particle may spontaneously pop into existance for no particularly good reason (See Pair production). Generally, this is irrelevent because they collide and cancel each other out shortly afterwards. However, if one of those particle pairs happens to pop into existance close to the event horizon of a black hole then before they get to annihilate each other, one of the two particles may stray across the event horizon while the other does not. This prevents them from cancelling each other out. Hence, one particle (like maybe an electron) shoots off into space (which it can do without travelling faster than light since it's already outside of the event horizon) - while a negative particle (a positron perhaps) falls into the black hole. This effectively results in the black hole "emitting a particle" - whilst simultaneously losing a small amount of mass. Seen from a distance, it's just as if the black hole is emitting random particles while gradually 'evaporating'. This is explained quite well in Hawkin Radiation. It's only a theory though - it's not proven and many cosmologists are skeptical about it.

(What I don't understand is why we don't get a random mix of (say) electrons and positrons being emitted - which would still cancel out. Also, if the black hole is absorbing a random mix of particles and antiparticles - how come it 'evaporates'?)

SteveBaker 14:16, 29 August 2007 (UTC)

For the evaporation, the article explains it quite well (although oversimplified): "In order to preserve total energy, the particle which fell into the black hole must have had a negative energy (with respect to an observer far away from the black hole). By this process the black hole loses mass, and to an outside observer it would appear that the black hole has just emitted a particle.". As for the still cancelling thing, i'm not sure that there's any reason for the emitted particles to come into contact and annihilate is there? Capuchin 14:21, 29 August 2007 (UTC)

Yeah - I already read that. It says it's true - but I don't understand why. Why couldn't it be the particle with the positive energy that fell into the black hole (resulting in the hole gaining mass and Hawking radiation being negative energy)? This would allow a black hole to grow by 'devouring the vacuum'! Energy would still be conserved. Personally, I'd expect it to be entirely random whether the particle or the antiparticle that fell into the hole - resulting in (on average) no net loss or gain to the mass of the hole - and the resulting radiation would be a random mix of positive and negative particles - which would (presumably) annihilate each other almost immediately. The result of which would be: No Hawking radiation - no black hole evaporation. If those particles and antiparticles didn't annihilate each other - then Hawking radiation would be a random mix of particles and antiparticles - but the black hole would not evaporate.

So why the asymmetry between particles and antiparticles? Why does the antiparticle get swallowed by the black hole in preference to the positive particle? SteveBaker 15:15, 29 August 2007 (UTC)

There's no asymmetry between particles and antiparticles: both come out. The asymmetry is between positive-energy and negative-energy particles of all types, including both electrons and positrons. Positive-energy electrons and positrons (and everything else) tend to escape, while negative-energy ones tend to fall in. There's no connection between having a positive or negative energy, and being a particle or antiparticle. --Reuben 16:54, 29 August 2007 (UTC)

OK, so Someguy1221 made a good point (and then self-censored it!): that story about a pair of particles, one with positive and one with negative energy, is itself quite suspect as an explanation for how Hawking radiation works. In fact, it might even be totally bogus. It is the most common non-technical way of explaining Hawking radiation, and if I remember correctly, Hawking himself uses it in A brief history of time. I can't claim to understand the "real" version, but I think I know enough to answer Steve's questions.

• The possibly-bogus explanation involves negative-energy particles going in and positive-energy particles coming out.
• There's no particular correlation between negative/positive energy and particles/antiparticles.
• Particles and antiparticles come out in equal numbers (it's a perfectly thermal distribution, so you can write a partition function).
• This last point remains true even in the "real" treatment.

Here's a paper if you want the "real" version: [18]. I only skimmed part of it; it's good, but this is not light reading. --Reuben 17:49, 29 August 2007 (UTC)

Surely the positive/negative energy particle explanation is an outdated one from Dirac hole theory. They can only exist for a short time due to the Uncertainty Principle. The reason we may see more particles than antiparticles coming out is that antiparticles will annihilate with the many particles that make up the universe, giving off photons. As to why the universe has more matter than antimatter, that is another, much more difficult, question. Cyta 09:28, 30 August 2007 (UTC)

That might be a reasonable explanation for why Hawking radiation would consist almost entirely of regular particles and photons - but it doesn't explain why the black hole would gradually 'evaporate'. Ingestion of more 'negative energy' than positive seems like the only way that could happen and I don't understand why that asymmetry would exist. SteveBaker 14:13, 30 August 2007 (UTC)

What effect do creatine supplements have on insulin levels?

What effect do creatine supplements have on insulin levels? Creatine affects insulin levels but I'm not sure exactly how. Up or down. Can it cause diabetes or other problems? Also what impact does this have on blood sugar level? --Gosplan 11:55, 29 August 2007 (UTC)

Creatine supplements#Safety states that there are no known problems associated with the supplements, except possibly muscle cramping. Algebraist 13:03, 29 August 2007 (UTC)

Note that if you are looking for medical advice, people on Wikipedia are not qualified to give it: Wikipedia:Medical disclaimer -- 21:34, 29 August 2007 (UTC) —Preceding unsigned comment added by 72.33.121.200 (talk)

Network subscribers in South Africa

Hey Wikis, i was wondering if any one could tell me how many subscribers are listed on the mobile networks in SA(Vodacom, Cell C,MTN,Virgin Mobile etc)I have already searched on wiki so thanks for that info....Also what would you consider to be luxury features on a cellphone and which are a basic needs. Any added info on this topic would be appreciated! Crazypinkster 12:32, 29 August 2007 (UTC)

For me, I consider these to be basic features:

1) Having a directory of names and phone numbers with the ability to both call those numbers and display those names when a call is received (a version of Caller ID).

2) Phone should display the number of minutes/days remaining before it goes dead.

3) Should save a list of missed, received, and sent calls (dates, times, and names/numbers).

4) Should hold a charge for a long time and recharge at home or with the cigarette lighter in a car.

5) Cell phone should take and store phone messages. Ideally these should be stored right in the phone, as opposed to making you call some number to get your messages, but that would only work if you had free incoming calls.

6) Good reception everywhere I need to use it.

7) No "roaming" charge.

8) Silent ring (vibrate) option.

9) No ability for the government to track you down by your cell phone (it should be anonymous).

10) Callers should have to enter a code number (which I've previously given them) after dialing the phone number, or it should ignore the call. This would prevent drunken bastards from calling me at 3 AM unless I actually know them. (Alas, my phone lacks this feature.)

Unimportant to me:

1) Games.

2) Multiple ring tones.

3) Being small enough to fit into a wallet.

4) Color screen with fancy graphics.

5) Camera (I have a real digital camera).

6) Speaker phone (nice idea, but it's going to drain those batteries too quickly).

7) Not having any buttons (the iPhone).

8) Internet access (I don't want to squint at the Internet through a 2 inch screen.)

9) Text messaging (how is getting sore fingers by typing in hieroglyphics better than talking ?).

Unfortunately, to get most of the important things, I had to accept some of the unimportant things. I have a Motorola V170 with a Tracfone plan; not perfect, but fits my needs fairly well. I live in the US and don't know if either of these is available in South Africa. StuRat 03:41, 30 August 2007 (UTC)

• Although the two are related, there is a difference between what your cell phone is able to offer and what your cellular network is able to offer. This is what confuses me about the OP's question: Are you asking about basic/luxury needs on a cell phone with regard to the networks, or in general? For example I don't know of any cell phone that takes a voice message on the phone itself, usually voicemails / messages happen when the call diverts back to the network (because your phone is off / out of range / you didn't answer it) and then the network puts the call through to your voicemail bank, plays your customised message (if applicable) and records a message, then, according to your account's settings will notify you of a message by sending an SMS/text.
  

• Another example is the storing of SMSs/texts on the phone instead of the SIM card - some phones do this, others don't, and the phone's that do will usually have a setting.
  

• South Africa's networks are actually great. There is a bit of a fuss that it's "So expensive" - and yes, when comparing the costs around the world South Africa's telecoms don't fair very well; but having compared the networks in South Africa and the networks in Australia, I'd have to say South Africa's are absolutely gold. Almost none of the networks in Australia have free voicemail (compare with South Africa where they all have free voicemail). In South Africa on Cell C you can recharge your credit for as little as R5 (approx. $USD0.65), on Vodacom for R12 (approx. $USD1.80) and the credit doesn't expire for at least a month - compared with Australia where almost all minimum recharges are $AUD29.00 (approx $USD24.00) (There are some exceptions, such as a $AUD10.00 (approx $USD7.00 recharge with Optus where the credit lasts for 7 days!). As far as I know, all networks in South Africa don't charge you to check your balance, and it's always easy to do such as punching in '#101*' - compare with Australia where you get charged for this on certain networks -- and you have to call a hotline to get the information
  

• Strictly speaking, originally, "basic" functions of a cellular network and cellular phone was to simply be able to make and receive calls much like you would on a landline phone - it "rings" when somebody calls it, and you can also pick it up and dial a number. Of course this evolved, and you could store contacts on it. This evolved to being able to store more information on contacts, and of course ring tones evolved. ... Flash-forward to the future, and now phones do a whole host of functions: GPS navigation, graphics, games, internet functionality, cameras (something I'm very critical of with phones), etc. I would still rate all of those as "luxuries", but as technology develops the market will become to dictate that a phone should have certain things as basic functionality - for example it would be 'bad' if a phone would only allow you to store 7-8 SMS/texts (consider the Nokia 3310 that used only store about a dozen) - now phones store hundreds of SMS/texts. There also used to be phones that were only compatable with certain 'bands' of network range, and now most phones are 'dual-band' and are more compatable with reception.

• But to answer what network capabilities are considered "basic" and which are considered "luxury", I'd like to think that checking your balance for free should be considered basic, voicemail should be considered basic (I'll compromise and say "even if you have to pay for it"), SMSs should be considered basic, call diverts are basic, etc.<br /.

• I hope this has been of some help
  
• Rfwoolf 04:11, 30 August 2007 (UTC)

• According to this article released 29 August 2007 MTN has 13 412 000 subscribers in SA, and 48.2 Million altogether in Africa.
  

I haven't managed to find anything recent on Vodacom and Cell C or Virgin. Rfwoolf 04:30, 30 August 2007 (UTC)

I'm a bit of a minimalist when it comes to phones. The number one feature I looked for in my present phone was the shape of the charger socket! All of my previous three or four phones - along with those of my family - have failed because the weird multi-pin charger socket wore out and the phone wouldn't reliably recharge. My present phone has lasted longer than any previous phone I've owned because it has a 'conventional' Barrel connector. So - the nature of the power connector has become my #1 requirement on a new phone! SteveBaker 14:03, 30 August 2007 (UTC)

Helium Baloons

How many helium baloons would i need to take off or glide with, if i had them attached in clusters around my armpits and the back of my heel? (kinda the same pose in the cartoon where that boy flies with the snow man )(You know the one....) —Preceding unsigned comment added by 81.76.125.193 (talk) 15:17, August 29, 2007 (UTC)

42 weather ballons full Gzuckier 15:57, 29 August 2007 (UTC)

Well considering im a 16 year old weighing no more than 10 stone ( unlike the 33 year old, truck driver) it should be significantly less... also how can i avoid air fines (bearing in mind i live about 10 miles from cottesmore airport) where would i get the weather baloons, and where would i get a parachute, in england *cough* nanny state *cough*? answers appreciated ... —Preceding unsigned comment added by 78.144.55.130 (talk) 17:24, August 29, 2007 (UTC)

If you seek manned flight, I recommend the safer, slower process of becoming a certified pilot. This way, you will learn the appropriate regulations that will prevent harm to yourself and others. The process can take as little as a few weeks or months, depending on how well you progress. Remember - aviation rules are not only there for your safety, but for the safety of others. Imagine if your lawn-chair-balloon contraption interfered with a commercial aircraft flight - you would be personally responsible for endangering other people. Do not violate local laws by operating an unregulated aircraft. Nimur 17:32, 29 August 2007 (UTC)

See Cluster ballooning. It's more dangerous than you think, so you're pretty much on your own figuring out how to do it. —Keenan Pepper 17:43, 29 August 2007 (UTC)

Ah, you see, the nanny state is everywhere, not just the UK. But seriously this sounds like a bad idea. A fall from 20 feet could kill you as would a strike from a Greater Black-Backed Gull (see below)Richard Avery 17:59, 30 August 2007 (UTC)

Bear in mind if you do this in the US in particular in or near a no fly zone you might find some fighter jets heading your way. And if you're near commercial aircraft, particularly if you're wearing a rucksack or you look foreign well let's just say you may find you trip rather short and the landing far faster then you had planned (of course you may already be in pieces so you won't care) Nil Einne 22:04, 30 August 2007 (UTC)

odd question - spin inversion

If a proton, neutron, or electron is isolated in space (ie no magnetic or electric fields) then the energy of the two spin states is equal (I'm assuming the answer to this is yes)

1.Is the spin here considered to be undefined (eg a 'supposition of states' or whatever language term used to describe 'unknown until tested') or is a particles spin fixed even though the energy between states is zero.

2.If spin inversion occurs the energy change is zero, but the spin change is 1 - does this mean that a photon of energy 0 is emitted - does this count as a non event?

3.(ignore depending on Q.1) If the spin IS fixed - what rules govern spin inversion here - is there a rate of inversion, is it allowed or forbidden.87.102.18.14 15:42, 29 August 2007 (UTC)

It would be in a superposition of states, and if there is no field, then the distribution should be equal. In order to check the spin, you would need to probe the particle, which would typically require an applied magnetic field. The spin can't really invert until it has been determined in the first place (so what you describe in (2) is a "non-event"); detection of any emitted energy would mandate that the spin is first measured (i.e. an applied field). Nimur 17:28, 29 August 2007 (UTC)

You have to be careful here. A spin-1/2 system can't be in an equal superposition of all spin states; every possible state vector describes some definite spin axis (see Bloch sphere). On the other hand, a spin-1/2 system described by a density matrix can be in a spherically symmetric state, namely 1/2 times the identity matrix.

Regarding the original poster's second question, a free electron or proton can't emit a photon (or any other particle) without violating the conservation of energy-momentum. As you say, the energy of the emitted particle would have to be zero. -- BenRG 21:24, 29 August 2007 (UTC)

You think there is a spin axis?? (like a direction in space?)?87.102.14.233 08:59, 30 August 2007 (UTC)

Hm? Yes, there's a spin axis. Electron spin is described by a spinor, which points in a particular direction like a vector does. -- BenRG 21:34, 30 August 2007 (UTC)

I thought it merely had value - are you sure? I mean it's easy to quote articles.213.249.232.202 06:16, 31 August 2007 (UTC)

What I mean to say is that given that the spin can be either 'alligned' or 'opposed' to the field (since it is quantised) a concept of direction is irrelevent. It is the field itself which has a direction. Do you agree?213.249.232.202 07:21, 31 August 2007 (UTC)

It's tricky to talk about this because of the lack of a good ontology for quantum mechanics, but the following is true: Any wavefunction describing an electron spin system can be interpreted as a direction (ray) in space. If you do a Stern-Gerlach measurement along the axis of the ray, you'll find the spin to be pointing in the direction of the ray with probability 1. If you measure along a different axis, you'll find one of the two axis-aligned states with probabilities related to the angle between the measurement axis and the ray. To put it in purely operational terms, when you prepare a spin system you choose a particular spatial direction, and when you measure it you choose an axis, and the transition probabilities are a monotonic function of the angle between the two. -- BenRG 11:22, 31 August 2007 (UTC)

Discouraging collared doves from my bird table?

I got a bird table for my garden a few months ago (I don't only just feed the gulls any more!). One problem though - I have way too many collared doves coming down and eating way too much birdseed. As well as being easily capable of devouring a 10lb bag of seed in two days, they also chase the other garden birds away if they approach the table. These critters look cute, sweet and innocent but they have an aggressive streak towards smaller birds - and they'll even drive the magpies and crows away. Just about the only bird that isn't phased by them are my great black-backed gulls, which have absolutely zero interest in eating seed in the first place. They're seriously worse than the starlings when it comes to being mob-handed, winged hogs.

Does anyone know of a way that I might discourage the doves from feeding in my garden? I don't want to shoot, poison or otherwise kill anything - and I don't want to stop feeding the birds. Is there such a thing as a 'dove proof' feeder I can hang on the table? --Kurt Shaped Box 17:37, 29 August 2007 (UTC)

You can certainly invent complicated feeders that birds have to hang upside down from (or something difficult like that) which would discourage birds like doves that can't do that. You could also devise something where the perch that the bird stands on to get at the food is a counter-balanced lever that closes a door and shuts off access to the food to any bird that weighs more than the counterweight - this could be used to shut out large birds and let the smaller ones have access to the food. You could make a large clear plastic cube and put the food inside - then cut holes as entrances and exits that are too small for a dove to get into. SteveBaker 19:38, 29 August 2007 (UTC)

You have black backed gulls? Why not stop feeding those FEARSOME PREDATORS, let them get hungry and angry, then let them deal with the doves for you? —Preceding unsigned comment added by 84.65.105.7 (talk) 20:32, August 29, 2007 (UTC)

No! It's worse! These are GREAT black-backed gulls. SteveBaker 00:29, 30 August 2007 (UTC)

That's quite funny - the thought of these gulls actually motivating themselves to hunt, that is. If I stopped feeding them, they'd just go and hang out near the house of the next 'gull friendly' person on the street. Or they'd rip open my rubbish bags. A lot of people on my street like the seeing the GBBGs feeding up close - just look at the general size and impressiveness of them!, so they tend to be somewhat 'pampered'. --Kurt Shaped Box 09:27, 30 August 2007 (UTC)

Is this a very roundabout seagull question? >:|      :) --froth^t 22:05, 29 August 2007 (UTC)

(It has seagull in it...I think it counts.) SteveBaker 00:29, 30 August 2007 (UTC)

or you could make a protective cover out of what we call 'chicken wire' or 'wire netting' in the UK. You can buy it in several different sizes. I would think 2 inch holes would allow the little birds in and keep the bigger birds out....sorry for stating the obvious. On a slightly related ornithological note, we had no collared doves in the UK in the 50s then a few were brought over from the US for a private aviary and now we are similarly plagued with the damn things. Do they taste good? Richard Avery 17:53, 30 August 2007 (UTC)

I'm in the UK too, dude! :) While cute, the collared dove is very, very annoying. I don't mind the screeching of nesting gulls outside my bedroom window, the chattering of magpies or the warbling of an overzealous song thrush early in the morning - but that constant, repetitive 'coooo coooo cuk' from the doves goes right through me like a dripping tap. It's worst in the summer when it starts getting light at 4am - there's no way I can sleep through that racket. I figure that if they were good to eat, they'd be finding their way into pigeon pies (wot? no article???) - which they don't seem to be. --Kurt Shaped Box 18:08, 30 August 2007 (UTC)

The American Dental Association made a vaccine to Streptococcus mutans and then patented it and sat on the patent so ensure dentists stayed in business???

My dentist told me that in dental school a professor claimed that in the 1950s, the American Dental Association made a vaccine to Streptococcus mutans and then patented it and sat on the patent so ensure dentists stayed in business. I've asked him about it and tried to find information confirming if this was true or not. Google only finds that some people are working on a vaccine. The Streptococcus mutans article's is vague on the idea of a vaccine and it's one source on that is some website that's unviewable unless you pay them a lot of month first. Juanita Hodges 18:30, 29 August 2007 (UTC)

If they patented it in the 1950s, that patent would be expired now. The patent would have always been public and whatever it covered would have long since become unprotected as well, so anyone (drug company, private or university researcher, etc) could work on making it. That's the whole model of the generic-drugs business—patent protection is quite limited and once something is patented it soon becomes free-for-all. DMacks 18:40, 29 August 2007 (UTC)

I would add that taking out a patent on something is in no way proof that it actually works. You can patent the most outrageous concepts whether true or not. People have FAR too much respect for the patent system. It's perfectly possible that this guy did indeed patent this - but that doesn't prove that a usable vaccine has ever existed. SteveBaker 19:32, 29 August 2007 (UTC)

A shame, since otherwise I'd be getting to work in a British Rail flying saucer. GeeJo ^(t)⁄_(c) • 19:03, 30 August 2007 (UTC)

A patent is a bargain that society makes: you tell us how to do something neat, and we'll give you a temporary monopoly on making money off of it. There is no way to sit on a patent indefinitely, since that would break the inventor's side of the deal. You can try to get an extension, but not for 50+ years. For that, you need copyright. --Sean 19:46, 29 August 2007 (UTC)

And even then, copyright is not infinite. Well, at least not yet. Titoxd^{(?!? - cool stuff)} 19:49, 29 August 2007 (UTC)

Trademarks, on the other hand, are infinite as long as they are still being used. But we digress. And please do not take this as legal advice! --Anonymous, August 29, 20:08 (UTC).

The pitiful article, Caries vaccine, points out that researchers are still working on a vaccine against tooth decay. It would be important to point out that although decay is still a very common problem treated in dental offices, you still have gum disease, root canal issues, trauma, cancer, and replacement of teeth that dentistry would still need to address even in the event of a 100% effective vaccine. ;) And those are the first things that come to mind. There are still many other problems. Thus, I, myself, am not too worried about dentistry staying in business. - Dozenist talk 00:05, 30 August 2007 (UTC)

Along that same line, there is actually a vaccine out for dogs now for periodontitis. It covers three different Porphyromonas species (see Porphyromonas gingivalis for the human version of the bacteria). --Joelmills 02:48, 30 August 2007 (UTC)

There is this article. As I recall, the biggest hurdle was the transfer of the bacteria by sharing glasses/kissing etc. Since you'd need a prescription to get the bacteria, you'd be giving it out illegally, or some other nonsense. In any case that is a place to start. I also did a Google search for "tooth decay bacteria genetic modification", and got some hits about modified sugar cane and other things along those lines. --Cody.Pope 10:19, 30 August 2007 (UTC)

Wind data

I'm looking for any sites with quantitative data I can use to show relationships between geographic features and/or seasonal variation with changes in wind speed. Any links would be appreciated. --Sopoforic 20:21, 29 August 2007 (UTC)

Google Search turns up some geographic sites on wind erosion? Might be of help SGGH ^speak! 21:14, 29 August 2007 (UTC)

Yes, but those are more geographical features created by wind than wind created (or channeled) by geographic features, although they both effect each other, I suppose. StuRat 03:05, 30 August 2007 (UTC)

this pdf also seems to have soem figures SGGH ^speak! 21:14, 29 August 2007 (UTC)

Well, I don't know about the World, but for the Great State of California, here's a place I drive by every now and again, their site with wind reports, http://www.energy.ca.gov/wind/overview.html --Jacobi am the kwisatz haderach 21:28, 29 August 2007 (UTC)

August 30

EFFECT OF ATMOSPHERIC PRESSURE ON BODY WEIGHT

I'M ON A DIET. SOMEDAYS I KNOW THAT I HAVE EATEN NOTHING AND YET MY WEIGHT HAS STILL GONE UP --ONE TIME IT WAS 5 LBS OVERNIGHT. A FRIEND SAID THAT ATMOSPHERIC PRESSURE OR BAROMETRIC PRESSURE CHANGES CAN AFFECT THE RESULTS OF MY STEPPING ON THE BATHROOM SCALE. IS THIS TRUE? AND IF SO, WHY? —Preceding unsigned comment added by Gtigue (talk • contribs) 00:37, August 30, 2007 (UTC)

If atmospheric pressure goes up, your apparent weight will be slightly less, because of buoyancy. Emphasis on slightly -- there's no way this is the real issue you're seeing. But your scale will be somewhat variable, so it could show your weight as higher when it's not. Or you might have drunk water. Or you might have forgotten about a snack. --Trovatore 00:47, 30 August 2007 (UTC)

Slight differences in foot positioning can affect cheap scales. Try weighing yourself 5 times per session (just step off and back on), and take the average. If you are still seeing a significant overnight increase in your weight, you might be a somnambulist.  :) --Sean 01:19, 30 August 2007 (UTC)

There are a lot of factors that can change the reading on scales. You can weigh different at different times of day, depending on how much water you've drunk recently, whether the scale is placed on a hard or soft surface, what you're wearing, whether the planets are aligned (ok that's only going to have an effect of a fraction of a gram, no matter what the astrologers say), and - this might be what your friend was thinking of - humidity. If you have a mechanical scale, especially a really cheap one, it may be possible for high humidity to affect the inner workings in such a way that the reading changes. So, the best way to get reliable weighings is to (a) buy a good quality, possibly digital scale, that is fully enclosed, (b) weigh yourself at the same time of day every time, wearing a similar amount of clothing, (c) try to make sure your eating and drinking habits are regular enough that you won't have drunk a litre of water before your weighing one day and not the next. Confusing Manifestation 01:41, 30 August 2007 (UTC)

I agree with humidity. I had just such a cheap spring scale that would vary by 5 lbs depending on the humidity. One clue that it was "sticking" was that the needle would go back and forth maybe 10 times before it settled on a reading when the humidity was low, but only once or twice when humid. Also, a change in barometric (atmospheric) pressure frequently goes along with a change in humidity, so your friend wasn't wrong. StuRat 02:03, 30 August 2007 (UTC)

The weight of air pushing down on the top of the scale is absolutely huge, 14.7 pounds on every square inch - that's probably more than a ton on the whole top surface of the scale! However, that same force is pushing on the bottom of the scale's cover too. And it's there even when you're not standing on the scale, so any effect from air pressure should simply be zeroed out. Even though you may not often think about it, the air weighing down on you from above is actually very heavy! --Reuben 02:16, 30 August 2007 (UTC)

No, not quite zeroed out. The air around your feet is under slightly higher pressure than the air around your head. This creates a slight net upward force, equal to the weight of the chunk of air that would have occupied the space where your body is, if your body weren't there. See Archimedes' principle for details -- haven't looked at that article but that's where it should be. --Trovatore 02:21, 30 August 2007 (UTC)

Right - that's a small but nonzero effect too. According to atmospheric pressure, air at sea level is about 0.08 lb / cubic foot. A human is a few cubic feet [19], so each of us displaces a weight of air of order 1/4 pound. Not big, but that's far more than I expected! --Reuben 02:33, 30 August 2007 (UTC)

According to this site: [20] "The lowest sea level air pressure ever recorded was 870 mb (25.69 in.) in the eye of Typhoon (Tip) over the Pacific Ocean, whereas the highest sea level air pressure ever recorded was 1084 mb (32.01 in.) at Siberia associated with an extremely cold air mass." That's about 24.6% higher at the maximum air pressure using the min air pressure as a base. If we multiply that by Reuben's 1/4 pound figure, we get around 1/16 pound differential in your weight from the highest atmospheric pressure to the lowest. The air pressure in your bathroom won't vary nearly as much, so air pressure alone can't explain a 5 lb diff. It's off by well over a factor of 80. StuRat 02:47, 30 August 2007 (UTC)

On another note, eating nothing at all for a day is not generally considered an effective way of losing weight, for a variety of reasons. Skittle 14:11, 30 August 2007 (UTC)

Gecko feet

Just read about Geckos and their sticky feet. Since their feet are so sticky, why don't they get totaly clogged up with dirt and lose their stickyness? -OOPSIE- 02:40, 30 August 2007 (UTC)

Perhaps they use the slug method and constantly ooze more slime, leaving the old "clogged up" slime in a trail behind them. StuRat 02:53, 30 August 2007 (UTC)

Gecko feet do not use a sticky slime to generate their stickiness, instead they have "a network of tiny hairs and pads on their feet which produce electrical attractions that literally glue the animals down. With millions of the hairs on each foot, the combined attraction of the weak electrical forces allow the gecko to stick to virtually any surface." [21] [22] I expect small dirt particles do not interfere with the Van der Waals forces between the gecko's seta and the surface of adhesion. Rockpocket 06:12, 30 August 2007 (UTC)

The setae somehow self-clean, but the mechanism is still a subject of current research [23]. --mglg_(talk) 21:08, 30 August 2007 (UTC)

Thank you! -OOPSIE- 03:48, 31 August 2007 (UTC)

Physics

What is Radio Frequency Identification? —Preceding unsigned comment added by Beta alpha (talk • contribs) 07:32, August 30, 2007 (UTC)

Just look it up! Radio-frequency identification. —Bromskloss 07:52, 30 August 2007 (UTC)

Hunger related

What is the scientific term used to describe the condition when a person chooses not to eat and their body comes to a point where it no longer triggers us to let u snow we are hungry? - Pastor Jon--JacksonParkBC 12:18, 30 August 2007 (UTC)

symptomatologically, this is known as anorexia. Tuckerekcut 12:46, 30 August 2007 (UTC)

That's a more general term, though. I'm more familiar with what the OP's asking in terms of thirst. At first, you experience sensations of thirst, but after a certain level of dehydration, your body "gives up" on trying to notify you that you need water. I was always taught that if you're not thirsty (and circumstances suggest you should be), that can mean that you're extremely dehydrated. Anyway, I can imagine a similar situation with hunger. jeffjon 13:28, 30 August 2007 (UTC)

Spider Web

In regards to this link,

http://www.cnn.com/2007/US/08/30/spider.web.ap/index.html

What species of spider is this? Are there any spider species that work together with other species? --WonderFran 13:52, 30 August 2007 (UTC)

If the entomologist in the article can't identify them through the pictures, I doubt anyone here can. However, there is a social spiders section in the Spider article. -- JSBillings 17:07, 30 August 2007 (UTC)

This past spring there were quite a number of smaller versions of this phenomenon covering hedges alongside roads to the north of Salisbury, (UK). Those webs were made by the larvae of some species of moth that lived on the leaves of the plant it had covered as a form of protection from predators. I think they might have been tent moths, Lasiocampidae, although several other species spin webs. But in whatever case that is one huge infestation. Richard Avery 17:39, 30 August 2007 (UTC)

Time period for the deposition of calcium carbonate in Italy.

I have written the following footnote for a book I'm working on using information gleaned from Wikepedia.

The pure-white stone mostly associated with the word “marble” is the result of the metamorphism of pure limestone (calcium carbonate, whose origin was the deposition of the shells of marine organisms 65–100 million years ago). The heat and pressure in the metamorphic process usually destroys the fossil remains. This marble was used in Roman interiors and works of art. The most common Roman “marble” was travertine, a precipitate of carbonate minerals often aragonite but at times calcium carbonate. It has not undergone metamorphism and is often yellowish with visible embedded fossils. The stone blocks of the Coliseum are of travertine. The Latin name for the rock was lapis tiburtinus because of the large deposit quarried at Tibur (Tivoli).

The info for the time period of the deposit of calcium carbonate was from an article on the formation of chalk in England. Would this period also include the deposition of calcium carbonate in Italy? 69.201.141.45 14:04, 30 August 2007 (UTC)Linnaeus Shecut

(I just wanted to pick you up on a sentence you gave above - "..travertine, a precipitate of carbonate minerals often aragonite but at times calcium carbonate.." - aragonite is a form of calcium carbonate so.. you could just omit the "..but at times calcium carbonate.." - did that make sense.?

as for your main question - until someone else answers - I think it's best to say not neccessarily - the cretacious period is named after the chalk that formed at that time - but that doesn't mean that carbonates weren't produced in earlier aeons - that said - I've no idea.87.102.14.233 15:15, 30 August 2007 (UTC)

HOWEVER from the article "The Cretaceous is justly famous for its chalk; indeed, more chalk formed in the Cretaceous than in any other period in the Phanerozoic" - so it's a good bet that the chalk is cretacian - but I suppose it depends where it's found and at what depth...213.249.232.26 19:14, 30 August 2007 (UTC)

NOTE a web search for "marble formation italy" suggests that liassic is a common age quoted for the date of formation. —Preceding unsigned comment added by 213.249.232.26 (talk) 19:02, August 30, 2007 (UTC) UK chalk I believe formed in the cretacious - however it's up to you to discover whether the liassic date refers to the laying down of the sediment OR the partial metamorphosis to marble (disclaimer I'm not a profesional geologist)213.249.232.26 19:05, 30 August 2007 (UTC)

As suggested, the age range of various marbles and limestones in Italy can be large. The Carrara marbles are Jurassic but there are probably plenty of other ages as well. The lapis tiburtinus travertines are quite young - around 100,000 years [24]. The mineral name for the other crystalline habit of calcium carbonate (apart from Aragonite which as mentioned is also calcium carbonate) is calcite. Also note the correct spelling of Cretaceous. Cheers Geologyguy 19:37, 30 August 2007 (UTC)

geography/cartography issue, example included

I needed coordinates of the topmost easternmost, etc., points of a country, I used those specified in the article on the respective country. Here's what I get.

OK, there's an offset or something of some 40 km.

But, I get that it's not uncommon to specify this (i.e., coordinates of the northernmost esternmost, etc., points of a particular country) in literature dealing with this. I was wondering if anyone knows of some website or something that would have reliable information. I'm actually not sure how do I google this. Alternative methods of putting territories into boxes and getting the coordinates of the sides of the box would be even greater appreciated. 354d 16:09, 30 August 2007 (UTC)

Is it possible that one source is including the terratorial waters around the country and the other isn't? If the numbers in the article included the oceanic terratory and the map that you laid into that box did not - then there would be an error of around this much Perhaps there is some teeny-tiny island that belongs to Latvia that you didn't include in your map. This seems a very 'iffy' way of getting things to line up right. SteveBaker 19:01, 30 August 2007 (UTC)

I doubt there are territorial waters included cause they're like 200 km or something idk and it has no islands. Actually as I look at it there's some distortion - the top part's offset less than bottom - the overlain map appears to be somehow bigger although google maps is supposed to scale it.

The solution might be pulling the contours of the country from a snapshot of google maps (since it apparently has different projection) and somehow fitting the original map in there. Actually yea I thought earth is round and google maps have cylindrical projection - there has to be distortion.

No I'm wrong - there has to be a built-in "google-maps-pptimization" cause specifying a polyline for instance involves specifying real life coordinates and google maps dispalys it correctly so that's def not relevant. 354d 06:31, 31 August 2007 (UTC)

but anyway the coordinates in the wikipedia article are very crude or something. It would be cool if there was some google-maps-optimization function somewhere, but guess I have to ask this on google earth forums.

anyway any authoritative source on "country lies between ... and..." coordinates would be appreciated. 354d 05:01, 31 August 2007 (UTC)

Bachelor of Science in Engineering vs Bachelor of Engineering

I have a BSc in Engineering, my work colleagues have a BEng. We are trying to figure out what is the difference between the two and if one is better than the other. —Preceding unsigned comment added by Pebbles82 (talk • contribs) 16:12, August 30, 2007 (UTC)

If the degrees are from different schools, there may be no direct comparison. Schools may choose their own nomenclature. You might look under accreditation guidelines to see if both schools are accredited - if so, they must meet certain minimum requirements. If it's boasting rights you seek, why don't you compare number of classes you had to take? That will clearly settle which of you had more requirements in college; but of course there is always room for subjective interpretation. You might also look into Philosophy of education - our article details some of the different viewpoints about quantity and quality of coursework. Nimur 16:33, 30 August 2007 (UTC)

We also have Bachelor of Engineering and Bachelor of Science articles, but you should be aware that regional and school variations may supersede information in those articles. Nimur 16:35, 30 August 2007 (UTC)

I don't think there is any kind of formal distinction. Lots of British universities award 'BA' (Bachelor of the Arts) degrees for science subjects - whilst others award the 'BSc'. There is no significance in that beyond tradition. I would expect the same to be true of a BEng versus a BSc. To know which is 'best', I think you'd have to look at the quality of the institution that awarded it. In the minds of most employers, a 'B-anything' from Harvard, Yale, MIT or whatever trumps a 'B-whatever' from some of the lesser colleges - even if the name is the same. SteveBaker 18:35, 30 August 2007 (UTC)

Not certain here, but I think that by 'lots of British universities' you mean 'Oxford and Cambridge': certainly that isn't common practice here in Britain. Algebraist 23:28, 30 August 2007 (UTC)

Are those really the only ones? Well - I guess it could be - my two friends who have BA's in science subjects both went to Oxford and my BSc comes from Kent - so that fits the facts. But anyway - there is no special significance to that beyond tradition. SteveBaker 01:20, 31 August 2007 (UTC)

SOAP Notes

HI,

I am a speech-language pathologist with the current position of instructor/clinical supervisor at Southern Illinois University. I am teaching our graduate students how to write a SOAP note note this semester. I found your definition great for doctors, however, SOAP notes for other professions (ours, counseling, etc.) are a little different as to what goes into each section. It would be great to see different examples pertaining to other fields that utilize SOAP notes.

Thank You, Shawna Pope

—Preceding unsigned comment added by 131.230.22.145 (talk) 16:34, August 30, 2007 (UTC)

Email removed to prevent spam - Nimur 16:36, 30 August 2007 (UTC)

Simple Object Access Protocol? Sorry, I guess you meant a SOAP note. I have to say, in the engineering fields I work with, there's not much room for subjectivity. If, for example, I am diagnosing a circuit error, I simply record the appropriate characteristics (voltage, current, pin diagrams, etc. for example). This pure objectivity is, by design, a part of the philosophy of engineering (with good reason, in my opinion - though this point may be debated). I've often wondered if biology and the social scientists could improve dramatically if they would work a little harder to remove subjectivity from their world-view; but I recognize that those disciplines address very different types of problems. Maybe this question should defer to someone in a different area... Nimur 16:44, 30 August 2007 (UTC)

The article should be enough for any provider-patient relationship. First, let the patient explain his or her problem. Then, the provider gathers information on the patient through any tests the providers deems necessary. Then, the provider assesses the problem(s) that need treatment. Finally, the provider prescribes a plan for treatment. -- Kainaw^(what?) 16:58, 30 August 2007 (UTC)

Shawna: Are you saying that you understand what is needed for a SOAP Note in your profession and that you wish our article covered that? Or are you perhaps saying that you don't understand how a SOAP Note would look for your profession? From the way you phrased your question and the fact that you are an instructor - I presume that it's the former and that you are simply pointing out a flaw in our article. If that's the case, then could I plead for you to write up whatever is missing and add it to the article yourself. Wikipedia only exists because people who know the subject material write about it - the contributions of a professional in the field (such as yourself) would be greatly welcomed. SteveBaker 18:27, 30 August 2007 (UTC)

Time, space and the universe.

Hi there, my question is simply this :- Assuming the universe is exactly 13.7 billion years old, if you had a telescope capable of looking back 13.7 billion yrs and 1 minute, would you actually see the big bang happen? ( Also assuming you were pointing it at the right point in space ). I can fully relate to " looking back 10 billion yrs " but seeing the big bang happen ( all be it with a super telescope ) is perplexing me. I hope someone can answer my question. Many thanks. Symon. —Preceding unsigned comment added by Gun dog 1 (talk • contribs) 17:20, August 30, 2007 (UTC)

The problem is that the big bang wasn't just a teeny-tiny dot somewhere in an infinitely empty space that kinda exploded and tossed out matter in all directions. It was the fabric of space and time itself that was a dot (a 'singularity' to be more exact). So the curvature of the universe was infinite and there was literally nothing other than the singularity itself...no 'outside'. So you couldn't be looking from 'outside' of the big bang and watch it going off like a stick of dynamite. No matter which way you look, you are looking towards the big bang. Worse still, time itself started with the big bang - so there is no 'before'. You could look back to (say) one nanosecond after the Big Bang - but space would be so screwed up that I'm not at all sure there would be things like photons flying out from it. Using specialised instruments mounted on satellites, we can see the Cosmic microwave background radiation which formed about 300,000 years after the Big Bang - that's pretty amazingly close to the beginning of time and space (compared to 14 billion years anyway). We could theoretically look back to within 2 seconds of the Big Bang by examining the Cosmic neutrino background - but neutrino's are insanely difficult to detect and a typical neutrino "telescope" is something that lives in a deep mineshaft and has a couple of swimming pools worth of dry cleaning fluid in it and can detect a couple of neutrino's every month. This is not the kind of instrument that's going to give you much in the way of a photograph! So, no - you can't watch the Big Bang going off. SteveBaker 18:17, 30 August 2007 (UTC)

Further to SteveBaker's response, the reason we need neutrinos or something to see further back is that before c. 380,000 years after the big bang, the universe was so hot and dense that it was opaque to photons (see Cosmic background radiation#Features) Algebraist 18:22, 30 August 2007 (UTC)

We can see artifacts of the expansion and the inhomogeneity of the early universe - see W map. Nimur 19:19, 30 August 2007 (UTC)

A question as this, you may enjoy an authors take on timeline and understanding of beginnings and ends. Gabriel García Márquez' One Hundred Years of Solitude. Note the studying of the Melquíades Parchments. --i am the kwisatz haderach 19:50, 30 August 2007 (UTC)

Stephen Hawking wrote 'A Brief History of Time' - it is a very approachable book on this subject and was actually a best seller when it was first published. SteveBaker 01:17, 31 August 2007 (UTC)

Colored water on plants

What is the effect of colored water on plants such as daisies or roses? —Preceding unsigned comment added by 71.166.60.75 (talk) 19:35, August 30, 2007 (UTC)

This is commonly used to give artificial color to flowers. Some dyes will be absorbed by the plant and show up in the flowers, others will not. -- Kainaw^(what?) 22:59, 30 August 2007 (UTC)

And some dyes spread relatively evenly through the flowers while other remain concentrated around the veins. StuRat 03:28, 31 August 2007 (UTC)

Looking back in time

Hi, i wanted to know that if you had a powerful enough telescope could it look back in time to places on Earth, more specificly could it be programed to look back to a certain time period on Earth, e.g may 2000. If so how long would it take and how would it work.

Thanks Bailster2k7 20:30, 30 August 2007 (UTC)

If you had a sufficiently powerful telescope, yes, you could look at Earth circa 2000, although you would have to be 7 light years from Earth. It would take at least 7 years to get 7 light years from Earth, so even if you left right now, by the time you got there you'd only be able to look at right now. Further, the telescope would only be able to see the light coming in, "at-the-moment." So, if you have situated it 7 light years from Earth, it will always be seeing what happened on Earth exactly 7 years prior. Someguy1221 20:47, 30 August 2007 (UTC)

Check out the discussion on the space-time continuum just up the page. — Lomn 21:15, 30 August 2007 (UTC)

Of course, if there was a mirror 3.5 light years away from Earth, sufficiently large and facing the right way, then you could use the super-telescope to view things in the mirror. --Anonymous, 21:57 UTC, August 30, 2007.

I suspect that nicely polished large mirrors in space are unlikely...although I suppose that it wouldn't be beyond the bounds of possibility to find some light path that passed close to two or more massive objects, say neutron stars or black holes, whereby you could receive some photons in your telescope that originally came from the Earth in the past. The problem being that this path would likely be short-lived due to the changing relative positions of these objects and the Earth - and I suspect that you'd receive only a very tiny proportion of the photons due to the accuracy needed to get any to return back to the Earth. Also, I suspect the nearest things massive enough to deflect the light sufficiently would give a very long light-path of at least several thousand years.Richard B 23:07, 30 August 2007 (UTC)

We had this in answer to another question a few days ago. Basically, there is no way to see further back in time than the day you launch your mirror - and even then, you'd have to launch it at the speed of light. Of course if you launched your mirror - waited a few hundred years to get a few lightyears out there - then you'd be able to look back to a point a few years in the past...but not before the day you launched the mirror. There would doubtless be practical problems with making a large enough mirror and steering it so it would still be looking at the earth as the earth goes around the sun...but I guess this is a thought experiment. It would be cheaper and easier to stick a bunch of cameras into orbit with video recorders hooked up to them...the result would be pretty similar. SteveBaker 01:12, 31 August 2007 (UTC)

Think about this - "seeing into the past" is going to be a lot like using Google Maps (many of those photos are a decade old). SteveBaker 01:14, 31 August 2007 (UTC)

You are separated from your past self on earth by a time-like interval, so there is no mechanism consistent with modern theory that would allow you to view your past self (regardless of where you travel to before setting up your hypothetical telescope). Nimur 01:31, 31 August 2007 (UTC)

Flies in the dark

What happens if you switch off the light while a fly (or some other insect which is usually active during daylight) is still flying around? Do they crash into the nearest wall? Can they instantly switch to some type of "night vision" (if so, how?)? At least some insects do seem to see rather badly at night. Or let's just assume it's really pitch black. Do they fly more cautiously? Do they have a way of "extending their legs, so they'll land instantly on whatever they touch"? Or what happens? ... Thanks, Ibn Battuta 23:02, 30 August 2007 (UTC)

• It's an interesting question, but I note that houseflies will routinely fly at full speed into a glass window pane with no obvious ill effect. --Sean 01:19, 31 August 2007 (UTC)

• Agreed, I see no sign that they watch where they're going even during the day, they just bounce off the walls until they find something they can eat or something eats them. Sort of Roomba logic. StuRat 03:22, 31 August 2007 (UTC)

I can imagine that they could sense a difference in air movement near a surface. So maybe they slow down very quickly (flies can change course extremely fast) and don't quite hit the wall/window at full speed. However, being very small makes them light, which means the momentum and therefore the force exerted on their bodies can't be very high. Being small also means they can withstand more force. So maybe they wouldn't even need to slow down. DirkvdM 06:40, 31 August 2007 (UTC)

Titration and pH meter/indicator

What did chemists use to determine pH of chemicals before the electric pH meter was invented? Seeing how determining the pH of chemicals are very important, the instrument that measures it has to be accurate. —Preceding unsigned comment added by 128.163.224.103 (talk) 23:30, 30 August 2007 (UTC)

Why, litmus paper! I remember it well :D. I didn't even know there was an electric pH meter SGGH ^speak! 23:48, 30 August 2007 (UTC)

I've never seen an electric pH meter, but when I did A-level chemistry, most titrations were done with phenolphthalein: it doesn't have the range of litmus, but it's not bad for locating the acid/base changeover fairly precisely. Algebraist 00:19, 31 August 2007 (UTC)

See pH indicator for more useful chemicals. Algebraist 00:22, 31 August 2007 (UTC)

But aren't those methods not accurate in terms of getting the exact number? In other words, they're merely approximations. In acid/base calculations, such as the Henderson Hasselbach equation, and in doing titrations doesn't the exact pH need to be known? 128.163.224.103 00:54, 31 August 2007 (UTC)

There was no way to get an exact (accurate) number, before the electronic pH meter. All you could do was approximate based on calculations. Even using the most sophisticated derivations of the Henderson Hasselbach Eqn, there is a level of error that can't be accounted for. Ionic shielding and activity coefficients try and compensate, but there is no replacement for using a pH meter.Mrdeath5493 01:25, 31 August 2007 (UTC)

Mythbusters

On Mythbusters last night they tested using a grappling hook shot from a moving car onto a stable structure to make fast 90 degree turns. When they used a steel cable rated for 15,000 pounds, it broke. How much pressure would actually be on a cable going from a car to a structure at 30 miles per hour making a 90 degree turn? 68.231.151.161 23:40, 30 August 2007 (UTC)

By pressure I assume you me force? F=M*A?? At the time the cable became taught, acceleration was zero to thirty miles an hour (I think) which is 48 280.32m/s/s if the cable goes taught over one second. But without the mass of the car, and the time it took for the cable to get caught, I don't know if it can be worked out. I predict that I am about to be proved wrong though! :D SGGH ^speak! 23:47, 30 August 2007 (UTC)

I think they said the weight of the car was 7000 pounds. —Preceding unsigned comment added by 68.231.151.161 (talk) 00:41, 31 August 2007 (UTC)

We'd also need to know the length of the cable. Someguy1221 00:46, 31 August 2007 (UTC)

Yep - we sure would. We need the centrifugal force - but to calculate that, we need the length of the rope...which we don't know. F=mw²r - but we don't know 'r' (the radius) and to calculate w (the rotational velocity) given only the 30mph linear velocity, we also need the radius. Since w is inversely proportional to r, the final force is proportional to 1/r. So if we guess the radius wrong by a factor of two, we'll be off by a factor of two when we work out the force on the rope. Can't calculate it...sorry! I'm kinda surprised the force was that great though - if a 7,000lb car broke a 15,000lb rope - that's a lateral force of 2g's...this surprises me because my tricked out MINI Cooper takes turns like that at around 30mph without resorting to ropes and it can only manage about 1g of lateral. I guess that turn was tighter than it looked. SteveBaker 01:03, 31 August 2007 (UTC)

No need for angular momentum formulas; for circular motion a = v²/r. If a 7,000-pound car (Is that right? What was it, an SUV?) exerts 15,000 pounds force on the rope, we have a = 15/7 gees = 21 m/s². And v = 30 mph = 13.4 m/s, which gives r = 13.4²/21 m = 8.55 m = 28 feet. The radius needed to produce the same force in the rope is proportional to the car's mass, so if a the car weighed say 3,000 pounds they'd have to have tried a rope only 12 feet long.

I haven't seen the episode; could the turn they tried have been that tight? If not, I'd guess that the rope was not capable of supporting its rated force when it was applied suddenly. That seems possible intuitively but I don't know if it's likely in terms of materials science.

--Anonymous, 01:34 UTC, August 31, 2007.

It was a tight turn, probably well under 2 car lengths, meant to be tighter than one could do with a car alone. Also, since they were doing it without the aid of the steering system, there would be an additional substantial force created by the friction of trying to drag the tires sideways. 76.225.157.167 07:28, 31 August 2007 (UTC)

Fourth dimension

Have just been reading this article, and am finding it really difficult to wrap my head around. I can understand all the other universe expansion, theory of relativity things (was always very good at physics) but I'm hoping someone can give me a simple analogy for the Fourth dimension.I'm looking at my monitor, it has an "arrow" for up (height) and arrow away from me (depth) and an arrow running across my (width). With time as the Fourth dimension, does this mean it has another arrow pointing somewhere else representing this progress of the monitor through time (progressing along with me)? If so, where is this arrow pointing? The "time-vectors" of all objects must be the same length otherwise we would all be jumping through time at different speeds? what?! huh? Help! SGGH ^speak! 00:17, 31 August 2007 (UTC)

Thinking of time as a fourth dimension is very hard to wrap one's mind around. Instead, try to imagine time as the third dimension in some imaginary 2 dimensional universe. In this universe, everything is only described as width and depth, there is no height. Imagine also that this universe is finite in size, shaped like a square. You are looking at it now. Any given moment in this universe can be captured in a 2 dimensional image of the universe, like individual frames of a video. But instead of playing the frames continuously to observe the universe in motion, stack the frames on top of one another. You have now introduced height, where height is time. Any particle that remains motionless is a straight, vertical line in in your 3D space-time. If an object is in motion, it will trace out a more complex curve through this 3D space-time. If you slice out any cross section of this space-time, you have captured for yourself a freeze-frame of the universe in a given moment. I hope that gives you some guidance. Someguy1221 00:31, 31 August 2007 (UTC)

that is actually really helpful, thankyou! So in essence, time's 4th dimension is the 3D universe "stacked" ontop of itself for each frame? And the movement of these complex 3D shapes would produce some very complex curves indeed if you managed to link them all together dot-to-dot and view the universe kind of... "side on" if we use that 3D square model of yours. So in theory, as height in your 3D model has a vector and a direction, time has a vector and a direction? Does this mean time has a direction of travel that is relative to length width and depth? If an object could somehow move through the frames quicker than other objects, would it have a larger vector? Or have I extended your model too far? I'm basially asking if time as a front, like your length and width and depth has finite ends, is an object at the end of its "time" at all times because it is in the present, just as the edge of my tv screen is at the end of its length/width/depth? SGGH ^speak! 00:48, 31 August 2007 (UTC)

I'm not sure how to answer all of those, but I'm sure someone else will come along soon. Time is always pointing straight up in the example I provided. The directional change is in the total "space-time" vector. As for the "ends" of a particle's extent through time, the only ends would be wherever the particle is created or destroyed, otherwise it will continue on through the time dimension (unless time itself ends at some point). You may be interested in reading Minkowski diagram, a scientifically rigorous method of diagraming 2D space-time. Someguy1221 01:06, 31 August 2007 (UTC)

The traces of a 4-dimensional object in three-space are solids. It's possible for a single 4-dimensional object to create multiple solid objects as the traces in 3D, just as a single 3D object (say an octopus) can create multiple 2D curves (cross sections) in any 2D plane. StuRat 03:12, 31 August 2007 (UTC)

It's worth noting that there are different types of "4 dimensional space" - spacetime mentioned above is one, another is simply the addition of a fourth orthogonal axis to the 3 (length )dimensions most people experience - see Fourth dimension. These are often called 'einsteinian' and 'spatial' fourth dimensions respectively.213.249.232.202 06:06, 31 August 2007 (UTC)

"Most people"? Are there cases of people who think they live in a 4D world? Does WP have articles on them? Aaadddaaammm 09:05, 31 August 2007 (UTC)

"...the 3 (length )dimensions most people experience " 3, three...????????213.249.232.202 09:46, 31 August 2007 (UTC)

Sadly, almost everyone seems to fail to understand what 4 dimensional space means. Maybe an elementary course in linear algebra could help, but, in the meantime, don't panic: 4 dimensions means having "4 variables" in which to store information, nothing more, nothing less. Living in a world of 4 dimensions means we have 4 variables attached to every object in our universe, 3 for what we call "space" altogether and one for time. We could imagine a world of 12 dimensions too, just think of having 3 for space, one for time, one for its angular momentum, another for its favourite football team... --Taraborn 10:38, 31 August 2007 (UTC)

Blood Sugar Dropping

Why does blood sugar drop in normal people sometimes and cause them to get dizzy and sometimes faint? I thought when you blood sugar drops and you dont eat, you start breaking down fat. How come the same people dont have the same problem when they exercise? —Preceding unsigned comment added by 76.167.145.55 (talk) 03:13, 31 August 2007 (UTC)

Please see hypoglycemia, Neuroglycopenia, and maybe even Idiopathic postprandial syndrome. In short, while most of your body can burn other fuel sources, your brain really doesn't like to (I haven't figured this one out yet, but Wikipedia claims it is not fully understood). Someguy1221 03:39, 31 August 2007 (UTC)

Gauss's law

Another person seems to think that the field due a point charge Q at distance r (due to coloumb inverse square law) is exactly the same as the field due to a evenly distributed charge of Q on the surface of a sphere (of radius R) when r>R. Exactly the same! Can someone else help persuade them that gauss's law is only an approximation to the field when r>R, (and maybe at the same time show that the approximation becomes better as r/R increase..). (Or maybe you'd like to do the opposite!)213.249.232.202 06:37, 31 August 2007 (UTC) ((Comment added after: I'm assuming here that Gauss's law should be consistent and derivable from Coloumb's law))213.249.232.202 07:29, 31 August 2007 (UTC)

Have you seen the article Gauss's law? No approximations there. It can be derived exactly from a starting point of an inverse square field strength function. And yes, the electric field outside a spherically symmetric system is identical to that of a point charge located at the origin. (In fact, this can occur even when an inverse square law doesn't apply, such as in general relativity.) Confusing Manifestation 06:56, 31 August 2007 (UTC)

Have you considered that the charge on the outside of the sphere (relative to the line joining the centre of the sphere and point of measurement) is at an angle to that line - and therefor (due to the circular symmetry about that line) the effective field (due to the charge on that circular band of the sphere) is reduced by a factor of cos(angle between line and points on sphere)? - this means that the true field is always less than the field given by gauss's law (except at infintity). That is the approximation.213.249.232.202 07:19, 31 August 2007 (UTC)

If you want to prove the equality of the predictions using Coulomb's law, be prepared to write out pages and pages of calculus (you also neglect that some charges are closer or further than the center. A charge being closer than it should has a greater effect on its field at your location than its being further away). But please note that Gauss's law was not derived from Coulomb's law, it was derived from the divergence theorem (proof here (not the original!)). This is pure math, based on arbitrary vector fields. Coulomb's law describes a vector field, so Gauss's law applies. If you seriously doubt this, I truly suggest you pick up an introductory vector calculus book for a more detailed proof (I have been seperated from my own temporarily, or else I would read to you from that). Someguy1221 07:52, 31 August 2007 (UTC)

Actually, I see that Shell theorem has a nice proof (that Gauss's law and Coulomb's law agree) of this for gravity starting from Newton's law of gravitation (just swap the constants to turn it into coulomb's law). (Oh, and it definately took me a lot more calculus to do my own proof! I think it never occured to me to use law of cosines...) Someguy1221 07:57, 31 August 2007 (UTC)

Well, well, well I really owe you a debt of gratitude for finding me shell theory. Excellent! I haven't checked it thoroughly but it looks like it simplifies the integration a lot - MANY THANKS! (To you and Newton)

However looking at the integration

$F_{r}={\frac {GMm}{4r^{2}R}}\int _{r-R}^{r+R}{\frac {r^{2}+s^{2}-R^{2}}{s^{2}}}ds={\frac {GMm}{r^{2}}}$

There seems to be a problem since

ʃ r²+s²-R²/s² ds = ʃ (r²-R²/s² + 1) ds

Which equals [s - (r²-R)²/3s³] and evaluates to:

between r+R and r-R

2R - (r-R)/3(r+R)² + (r+R)/3(r-R)² ?

Not giving the same result as in the text, have I made a mistake?213.249.232.202 08:33, 31 August 2007 (UTC)

Your notation is unclear but:

$\int _{r-R}^{r+R}{\frac {r^{2}+s^{2}-R^{2}}{s^{2}}}ds$

= $\int _{r-R}^{r+R}{\frac {r^{2}}{s^{2}}}+1-{\frac {R^{2}}{s^{2}}}ds$

= $(-{\frac {r^{2}}{s}}+s+{\frac {R^{2}}{s}})|_{r-R}^{r+R}$

= $(-{\frac {r^{2}}{r+R}}+r+R+{\frac {R^{2}}{r+R}})-(-{\frac {r^{2}}{r-R}}+r-R+{\frac {R^{2}}{r-R}})$

= ${\frac {R^{2}-r^{2}}{r+R}}+2*R+{\frac {r^{2}-R^{2}}{r-R}}$

= $R-r+2*R+r+R$

= $4*R$

Which matches the quoted result. Dragons flight 09:00, 31 August 2007 (UTC)

Ah yes thanks. (made a mistake)213.249.232.202 09:05, 31 August 2007 (UTC)

Moths.

Kind of similar to the fly question above. At night, moths esspecially more than any other bug are attracted into my room with the light on. They are attracted directly to the light and fly around it and try to get as close to the light source as possible. Do they do the same during the day? Just try to get as close to the sun as possible? Or is the sky luminous enough to turn off this behavior? What exactly is the advantage of seeking out light? Capuchin 07:06, 31 August 2007 (UTC)

See Moth, especially Moth#Attraction to light. Moths are typically nocturnal, so they don't see the Sun, and they navigate by the Moon, so artificial lights confuse them. Confusing Manifestation 07:10, 31 August 2007 (UTC)

Gaussian_surface#Spherical_surface

Quote " It is immediately apparent that for a spherical Gaussian surface of radius r < R the enclosed charge is zero: hence the net flux is zero and the magnitude of the electric field on the Gaussian surface is also 0"

I think this is not quite right - especially in terms of wording

To my thinking it is immediately apparent that the field at r=0 is zero. However if r<>0 but r<R then the field is non-zero - this is not what the article says. Should there be a change of wording or a disclaimer of the variation from reality?213.249.232.202 07:36, 31 August 2007 (UTC)

Quite right, actually. See above, and see Shell theorem for proof (the same as Coulomb's law, just swap the constants). Someguy1221 07:57, 31 August 2007 (UTC)

While "immediately apparent" might be a bit generous, the field IS exactly zero everywhere inside of a spherically symmetric distribution. This can be proven mathematically and is the whole point of the shell theorem. 76.225.157.167 08:05, 31 August 2007 (UTC)

See talk 2 sections above for my questions about shell theorum.213.249.232.202 08:40, 31 August 2007 (UTC)

phenomena-defying gravity

I visited a unique place near Nairobi,a town in Athi River area,we were taken to a hill by locals where they poured water on the steep road.Instead of water going down,it went upward.I put our car in netural,instead of going down it went up the hill.It is a phenomena.

Where can I get the explanation.How can I search Wikipedia?

Best regards.

Nizam Khalfan —Preceding unsigned comment added by 202.163.98.109 (talk) 08:45, 31 August 2007 (UTC)

It's usually explained as being an optical illusion - ie it looks 'up' but that's just due to the lie of the land. Many places like this exist - see Gravity hill for more details.213.249.232.202 08:59, 31 August 2007 (UTC)

You could add your place to the list now under Gravity hill#Locations.213.249.232.202 09:02, 31 August 2007 (UTC)

Really Odd Insect

My husband and I drive a truck over the road and have the opportunity to see some really odd and amazing things sometimes. This trip was no different.

While at the shipper this past Tuesday afternoon in West Valley City, Utah, I saw this "thing" crawling around under one of the customers vans. Upon closer examination, this "thing" was an insect of some kind and I would very much like for someone to give me some help on finding out what it was.

It was about 2 1/2 to 3 inches long, had an orange head, black pinchers or jaws (whatever you want to call them), six legs and its body was black and white striped.

I have been all over the internet looking for this thing and while I refused to allow it in the truck with me, I would still like to know what it was and whether or not it was dangerous. (yes we let it live)

Is there anyone who can help me with this and tell me where i can find the information on it and what it is?

Thank you

--Dyanna1 09:05, 31 August 2007 (UTC)

Did you take a picture we can see (but note, I have no idea, but don't know much about bugs, sorry)? --Cody.Pope 09:57, 31 August 2007 (UTC)

Black and white spinner

Do we have an article on those discs colored with a black and white pattern and when you spin it you see colors? I just got a similar effect while scrolling through a pdf file. Would like more info on the effect - I can't remember how it works. Also, would the two effects be related, I have a clumsy old CRT monitor on this PC and wouldnt be surprised if the effect I just saw was down to some sort of moiré patterning and difference in response times. Capuchin 10:50, 31 August 2007 (UTC)

We have an article on Benham's top - is that what you mean? DuncanHill 10:58, 31 August 2007 (UTC)

That's the one I was thinking of, but maybe a version a little less complicated than the picture here. Fechner color seems to describe exactly what I was seeing with the text. Very strange. Capuchin 11:03, 31 August 2007 (UTC)

I strongly recommend following the link to an interactive version from the Benham's Top page - more optical illusions than you can shake a stick at! DuncanHill 11:23, 31 August 2007 (UTC)

That's the one I was thinking of! The one with the sets of three lines! Capuchin 11:25, 31 August 2007 (UTC)

Hmm, on second thought, playing with that interactive one, the black lines appear colored, whereas the effect I was seeing was far more blurry, more of a kind of faint rainbow behind the text. Capuchin 11:28, 31 August 2007 (UTC)

The Membrane Cell for NaOH Production

Hello! I read that in the Membrane Cell there is a "Semipermeable Plastic Membrane" which seperates the solutions of ions and products. It allows positive Na+ ions to migrate through to react with OH- to form NaOH, yet it prevents the OH- and Cl- ions from passing through. ie. It allows +ve charged ions to pass, yet blocks negative charged ions. I am wondering what material this is, how it works and whether wikipedia has any detailed infomation on it. Thanks! —Preceding unsigned comment added by Phgao (talk • contribs) 11:44, 31 August 2007 (UTC)

It partially depends on the concentration gradient. You might check out active transport versus passive transport, and things like sodium potassium pumps. --slakr^(talk) 11:48, 31 August 2007 (UTC)

Another one: osmosis, which is basically passive transport/diffusion but with movement of only water. Also, if you're interested in an all-encompassing, practical example, you might check out action potentials, as they're how neurons in your brain communicate. --slakr^(talk) 11:52, 31 August 2007 (UTC)

You know, on third thought, I completely misread what you originally posted, LOL. You were asking what the semi-permeable membrane could be made of. A practical example is dialysis tubing, which is, in essence, a semi-permeable membrane used in real-world kidney dialysis. Sorry 'bout that. --slakr^(talk) 12:02, 31 August 2007 (UTC)

No problem, when I first read what you wrote, I was wondering... So these tubings allow +ve ions to pass while blocking -ve ions? Can you explain why that occurs? —Preceding unsigned comment added by Phgao (talk • contribs) 12:05, 31 August 2007 (UTC)