Wikipedia:Reference desk archive/Science/2006 June 1

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[edit] f-ing ipods

sorry to ask this here. i remember seeing some discussion about how these questions should be asked in the math section, but in that discussion, somebody said that the people in the math section don't write in normal english, so i'll stick to you guys. and yes, i did try all sorts of apple discussions, but nobody's answered the damned question, so: i bought a white 60 gig picture ipod a ways back, and it's worked beautifully for me for a year or two. my dad just got two black video 30 gig ipods as freebies, and he wanted me to put some music on them for him. but for some reason, itunes (and another program - yamipod - that i've got) wont recognize the new ipod. when i first plugged it in, apple downloaded some new software and asked me to restart. i did, and though neither program recognizes the ipod (in any usb port i've tried,) the computer recognizes it as a removable disk, and the ipod screen shows that flashy do-not-disconnect thing. so the computer and ipod seem to be speaking, but itunes just isn't recognizing it. what the hell is going on? i've rebooted several times, and renamed the removable disk drive. help? sorry if this is clearly the wrong place to post this question, but everyone else is completely useless

Have you tried deleting all your iPod software except for iTunes. Science is the computer help forum now. Those math guys don't know anything about it. — The Mac Davis] ⌇☢ ญƛ. 04:46, 1 June 2006 (UTC)
Have you tried resetting the iPod? You can hold down both the top and the bottom of the click wheel for a few seconds which should reset the iPod. (this works with mine which does not do video and I'm guessing that the video ones work the same) Also, when I originally got my iPod, for some reason it wouldn't work with the USB cable but the firewire cable worked fine. Maybe try switching ports/cables. Hope this helps... Oh yeah! Also, this month's issue of MacAddict has a cover story on the iPod. If my copy weren't at home right now (I'm at work) I'd look in there for you. Dismas|(talk) 05:13, 1 June 2006 (UTC)

yeah. none of that's worked, and the reset thingy isn't working, even if i hold up and down for a minute. is it possible that the problem has something to do with the fact that the freebie didn't come with a cd for itunes and whatnot. might there be specific updates and all that i'd need for this particular ipod?

This sounds like what was mentioned in an article I read today: Dodgy download riles iPod users. Basically, the latest version of the iPod Software which you just downloaded is buggy and causes iTunes not to recognise the iPod Nano. I know this is the iPod with Video but this sounds like the same problem. --Canley 08:17, 1 June 2006 (UTC)
Not sure whether this article might be relevant? Interesting anyway. --Shantavira 08:20, 1 June 2006 (UTC)
I have a 30gb picture iPod and I have run into a few problems along the way. I usually try (in this order) reset iPod (should return to Apple Logo to boot up), restart iTunes, restart computer, then if all else fails, use the iPod software to reformat the iPod. You may already be aware that the iPod probably shouldn't be renamed using the OS. It should only be renamed using iTunes. iPods can get very whingy if you don't do everything using Apple Software. Also, I am guessing that it doesn't like multiple different iPods in the same computer at the same time, ensure you plug them in at different times (and I would restart iTunes in between plugging them in, to refresh it). Just suggestions, don't know if it's been said/tried or works. --DanielBC 03:41, 2 June 2006 (UTC)

[edit] .tga

What's a program to open a .tga? Preferably something open source. A Clown in the Dark 05:43, 1 June 2006 (UTC)

I typed TGA in the search box, hit enter, and got this: Truevision TGA. You should be able to open TGA files with any decent image editing software - free ones? Try The GIMP.--George 06:27, 1 June 2006 (UTC)
IrfanView can view pretty much any image file once you've installed the plugins pack. It can't do much in the way of editing though. It's free as in beer, but not open source. the wub "?!" 08:52, 1 June 2006 (UTC)
ImageMagick supports conversion to and from Truevision Targa, and is free as in beer and free as in speech, + open source. –Mysid(t) 10:36, 1 June 2006 (UTC)
Isn't tga a common texture file for video games? Akin to bmp? — The Mac Davis] ⌇☢ ญƛ. 11:16, 1 June 2006 (UTC)
TGA is a common format in games because it's very easy to write a reader for it: the format is simpler than any of the more common formats such as PNG or JPEG. --Serie 19:25, 1 June 2006 (UTC)
Well I just need it to open up my screenshots from WoW. For some reason they're not BMPs, they're TGA.
Pretty sure you can get a plugin for it for Photoshop

No need, PS 7+ opens Targa Bitmaps as standard -- 82.42.72.5 23:44, 3 June 2006 (UTC)

[edit] Prompt supercritical masses don't "explode" - why

In discussions on the A-bomb, there is generally an argument being made that one has to use high explosives to get the prompt supercritical mass for explosion, otherwise the excursion will be terminated before a huge amount of energy is released. Indeed, when one looks at cases like the SL-1 reactor, which became prompt supercritical, there wasn't an atomic explosion (though there was a steam explosion, which had the good effects of removing the moderator).

The time constants for neutron propagation and fission look very small compared to the time constants for, say, vaporizing the moderator water. So what exactly are the mechanism that prevent a "simple" prompt supercritical mass from exploding?

(We have exchanged ideas but none seem very convincing.) David.Monniaux 21:06, 30 May 2006 (UTC)

What I heard was that the energy released effectively blows the supercritical mass apart enough that it is no longer supercritical. So, you have a bomb. You have 3 subcritical masses and bang them together. They release enough energy to move apart again. You have to blow them together with other explosives to get them to stick. This may be far too simple. Skittle 09:59, 1 June 2006 (UTC)
One of the best-known sources on nuclear weapons in the open literature is Carey Sublette's nuclear weapons FAQ. You can read his explanation here. His explanation is similar; basically, until the weapon is assembled into its final configuration, if fission starts the "neutron growth rate" (as I understand it, a proxy for the rate at which the nuclear reaction accelerates) will be lower than is optimal. Therefore, as Skittle says, the weapon blows itself apart before enough material has a chance to fission to get the full yield. IANAPhysicist. --Robert Merkel 10:56, 1 June 2006 (UTC)
That's pretty much it. In effect, a supercritical mass doesn't stay supercritical very long; the more supercritical it is, the faster it blows itself apart. The trick is in pushing it far enough above criticality and making it stay that way long enough that, when it does blow up, it does so in a sufficiently dramatic fashion. —Ilmari Karonen (talk) 11:15, 1 June 2006 (UTC)

Well, this goes back to the original question: the time constant for the exponential blowup in neutron flux is very little. This means that in a tiny fraction of a second, tremendous amounts of energy are released.

In comparison, the time for physical reactions such as turning moderator water into steam, or physically blowing up the supercritical mass, seem higher. It seems not so obvious that, physically, the reaction may actually have time to heat up the moderator or break up the fissile material before it really has released a lot of energy.

http://www.milnet.com/nukeweap/Nfaq4-1.html#Nfaq4.1.5.3 seems a good pointer indeed. David.Monniaux 22:49, 2 June 2006 (UTC)

Is it possible to construct a bomb in such a way so as to use some sort of filler(as only 3%-5% of the material gets fissioned)to make an efficient device without unfissioned material?

[edit] underwater

can we blow a balloon underwater?

If you mean using your mouth and lungs, it is possible, but more difficult than normal because the water pressure pushing in on the balloon is much higher than air pressure. If you used an electric pump you could definitely do it. --Canley 08:03, 1 June 2006 (UTC)
Yes, it's called a lifting bag, but it is filled with air using a pump. --Shantavira 08:26, 1 June 2006 (UTC)
Erm, really? I've always seen them filled (having never personally used one) by air from a scuba tank. Since they're open at the bottom, all you need to do is orient them vertically and blow off some air beneath them. The air bubbles will rise through the water, and enter the bag where they will displace the water inside, giving the bag positive buoyancy. — QuantumEleven 10:45, 1 June 2006 (UTC)

Let's forget about the possibility of drowning. Blowing a balloon under water using your mouth and lungs can be as easy as doing the same thing on land.

Imagine you're 10 m under water (1 extra ATM) and you have an air tank. The air tank is pressurized. The air from tank is depressurized before entering your mouth. So you inhale mildly pressurized air from the mouth piece. The air in your lungs is supposed to be 1 ATM higher in pressure when you're under water. You than remove the mouth piece and blow the air into the baloon. If you can do this under water, I think the balloon would still inflate normally. Maybe you need another diver to hold the mouth piece for you. -- Toytoy 12:17, 1 June 2006 (UTC)

I can tell you that it can be done, but it is harder than on land, if this is because of the extra preassure or that you are in water I do not know, and yes I have done it. Stefan 14:59, 1 June 2006 (UTC)
On land, your balloon does not float. Under water, your balloon floats. Other than conquering back pressure and the rubber balloon's surface tension, you need to displace water. This is difficult. -- Toytoy 16:26, 1 June 2006 (UTC)

No one needs to hold the mouthpiece for you, and the pressure pushing in the ballon is the same as the pressure pushing in your lungs, so the air you inhale will be in that pressure as well. The only problem to me seems to be to hold the balloon. Notice that if you fill the balloon with air at say 10m underwater, tie it, and release, it will blow up before reaching the surface because the pressure outside will decrease causing the air inside to expand. This is basic physics... and they teach it when you take scuba diving lessons. VdSV9•♫ 18:09, 1 June 2006 (UTC)

[edit] is this true?

i heard that the moon is moving away from the earth every year by 1.5inches and also that the rotation of the earth is slowing down so much that in the future a day will last 960hours. please tell me if this is true?

thanks

Yes, the first statement is true. Have a look at our article on moon. The distance increases 38 mm per year which is 1.5 inches. The Earth day lengthens about 15 µs every year, so that yes, when 225 billion years have passed, it will last 960 hours (assuming the speed of slowing stays constant). But on the other hand, the Sun is estimated to live for some 5 billion years only. –Mysid(t) 10:31, 1 June 2006 (UTC)
That 15 µs he said, that means microseconds, a thousandth of a second. — The Mac Davis] ⌇☢ ญƛ. 11:15, 1 June 2006 (UTC)
225 billion years!? only about 220 billion years after the earth has frozen as the sun died, been cooked as it turns to a red giant and destroyed as it all collapses. So basically, no, unless we find a way to engineer stars, the earths day will never reach 960 hours. Philc TECI 12:00, 1 June 2006 (UTC)
Correction, a microsecond is a millionth of a second.--Shantavira 11:58, 1 June 2006 (UTC)

[edit] science

why the burners of the gas are circular in shape??

Because it's easiest to get a uniform gas flow out of a circular nozzle. And a uniform gas flow makes for a nicely shaped, regular flame, which is a good thing. — QuantumEleven 10:42, 1 June 2006 (UTC)
That's why you want your flame blue or clear, instead of the cooler orange and yellow. The more stable and clean the flame, the better. — The Mac Davis] ⌇☢ ญƛ. 11:18, 1 June 2006 (UTC)

Would you buy a square pan ? (tssss) --DLL 20:51, 1 June 2006 (UTC)

Square pans do exist in Japan, for cooking eggs. --KJ 03:23, 2 June 2006 (UTC)
You beat me to that comment! --Ginkgo100 03:26, 2 June 2006 (UTC)
Do square eggs exist there as well? Conscious 05:42, 2 June 2006 (UTC)
If they're anything like square watermelons, they come from chickens in little glass boxes. — TheKMantalk 05:53, 2 June 2006 (UTC)
Well, the square pans are meant for "tamagoyaki." Tamagoyaki is made by cooking and rolling together thin layers of egg. (I've never made it myself, so I can't describe it properly.) Anyway, it's easier with a square pan that has perpendicular edges, and such pans are in use in Japan. Some Japanese tamagoyaki pans have a sloping far-edge instead. --KJ 10:16, 2 June 2006 (UTC)
And here's where I learned about square pans: Makiyakinabe. At Wikipedia, no less. :) --KJ 10:20, 2 June 2006 (UTC)

[edit] world wide web.

Where is all the information that we can access on on the web, stored?

On a wide range of servers. For example, Wikipedia is stored on the Wikipedia servers. If something happens to these servers, this can mean you can't access this information. At the same time, you can still access other information on other servers. The web isn't really a single thing, it is just a collection of connected servers. If you want to put something up on the internet, you either need a server that you keep connected or you need to find someone else who is happy to host your information on their server. The information doesn't just float in the ether, sadly. Skittle 09:53, 1 June 2006 (UTC)

Geographically, as its name states, the WWW is stored around the world. It is my understanding that a majority of servers is located in the United States or Europe, though. –Mysid(t) 10:22, 1 June 2006 (UTC)
Google also has a large chunk of the internet stored on RAM. [1] — The Mac Davis] ⌇☢ ญƛ. 11:20, 1 June 2006 (UTC)
Not to mention, there is the Internet archive. Skittle 12:31, 1 June 2006 (UTC)
Cyberspace, of course. --Shantavira 17:06, 1 June 2006 (UTC)
Google must have a hell of a lot of RAM. Wish I had that much to play with! --DanielBC 03:44, 2 June 2006 (UTC)
Might want to check out data center too (to see where most of those servers are kept) —Pengo 10:38, 3 June 2006 (UTC)
Server farm is worth a look, too. --Howard Train 04:03, 5 June 2006 (UTC)

[edit] GIF Compression

I've read in several places that GIFs are compressed better if there are areas of continuous colour. However, I also read that they use the LZW algorithm. This works on repeated strings, which don't necessarily need to be the same colour repeated but could be a repeated pattern of colours. A large block of colour would be compressed more thoroughly by an algorithm like the RLE.

Is this a mistake in my understanding of how GIFs work, in the authors of the web pages I'm reading, both or neither? can someone please explain to me why, when using an LZW algorithm, a block of identical colours is compressed best (if that is the case).

Thanks, JeffUK 10:53, 1 June 2006 (UTC)

When people talk about "continuous color" in connection with compression they are often contrasting it with continually varying color, as is found in photographs. Algorithms like LZW are fairly poor for photographs because there are few repeated patterns. It is more complex with GIF because it is limited to 256 colors anyway, and dithering effects can introduce repetition not found in the original, but still it's poor for photos, better for continuous color. Notinasnaid 11:27, 1 June 2006 (UTC)
So, their definition of "continous color" may well include RGBRGRGRGRGRG as well as RRRRRRRRGGGGGG, I suppose the chances of finding a _perfectly_ repeating pattern or a perfect block of one colour in photographs are equally slim. If I've understood this properly, thanks, if not, please correct me! JeffUK 11:33, 1 June 2006 (UTC)
From a quick pen-and-paper simulation of the LZW algorithm, I'd say that the number of codes in the output for a file of one solid colour looks like roughly the square root of the number of bytes. This is probably the best that LZW can do, given that you can't get any more redundant than a solid colour, so JeffUK's understanding is correct. GIF is optimised for speed and simplicity, so it always uses LZW, even though RLE would be more efficient in some cases. For GIF to choose between the two methods it would need to do an analysis pass first, which would slow it down. --Heron 20:09, 1 June 2006 (UTC)

[edit] Blend ratios in fabrics

what are the tests to determine blend ratio in blended fabrics? Like poly cotton for example how do we test how much cotton and poly is present in the fabric?

I think the company tells you. — The Mac Davis] ⌇☢ ญƛ. 11:36, 1 June 2006 (UTC)
I think that person wants to know how to test the fabrics for quality control. -- Toytoy 11:42, 1 June 2006 (UTC)
Or he wants to know just any post-processing way of determining the content of a blended fabric of unknown origin. Philc TECI 12:13, 1 June 2006 (UTC)
Or he wants to know whether someone is violating Leviticus 19:19. alteripse 15:59, 1 June 2006 (UTC)
Or he has deliberately made the wording of the question ambiguous in a calculated attempt to fool us all.... Philc TECI 17:38, 1 June 2006 (UTC)
If it's polycotton - you could try dissolving the cellulose and weighing what's left (the polyester) - (I think cotton is cellulose) as for other blends - don't know - some sort of 'chemical analysis'?HappyVR 17:48, 1 June 2006 (UTC)

[edit] Second

How do we know how long a second is exactly? especially if our fram of reference --the rotation of the earth is slowing? Are seconds getting longer? How did we origionally determine how to measure time objectively? And why is it called a "2nd"? 12.183.203.184 11:51, 1 June 2006 (UTC)

everything you asked in answered on Second, please search before asking. Philc TECI 12:04, 1 June 2006 (UTC)
A second has something to do with a hydrogen or carbon atom...I think. But it is set. It wasn't made up randomly.
You know, there's a reason we have articles about these things. It's not hydrogen or carbon, it's cesium. —Keenan Pepper 21:14, 1 June 2006 (UTC)

[edit] The Last Person on Earth who Used a Slide Rule to Design a Digital Computer

I want to know who was the last analog nerd on this beautiful planet. -- Toytoy 12:04, 1 June 2006 (UTC)

Brains are analog computers. so every nerd is analog :-þ Philc TECI 12:11, 1 June 2006 (UTC)
According to the article, there are those who still prefer the slide rule to a pocket calculator. Black Carrot 01:02, 2 June 2006 (UTC)
A slide rule can be far, far quicker for rough approximations if you know how to handle one. I still use one occasionally. Grutness...wha? 01:36, 2 June 2006 (UTC)
Wow... remarkable... I thought they stopped making them ages ago -- 82.42.72.5 23:52, 3 June 2006 (UTC)

[edit] Mother seagulls and their babies

Is it true that a mother seagull will fight to the death to defend her chicks from predators? --84.68.193.224 12:19, 1 June 2006 (UTC)

Just blunder into a seagull nest and see what happens... --Zeizmic 15:07, 1 June 2006 (UTC)
What does the mother gull do? Attack? --84.68.193.224 15:45, 1 June 2006 (UTC)

In general, success in breeding means that birds who choose fairly open nests must be ferocious in defending them. They will not go to the point of death, since that is not a formula for success. If you canoe up to a seagull nest, you will be bombed and pecked, and shouting 'owies' in no time. If you go up to a Canada Goose nest, you are risking broken limbs. When I was young, I once tried to return a baby bluejay to its nest. Owies! On the other hand, a sandpiper uses a highly concealed nest, and tries to passively lure the blunderer away. --Zeizmic 16:25, 1 June 2006 (UTC)

[edit] Where do seagulls sleep?

There are loads of seagulls in my town, yet I never see any sleeping around here at night. When it starts getting dark, I see them all taking to the air and leaving the town to go somewhere else. What sort of place do they usually go to roost/sleep? --84.68.193.224 12:20, 1 June 2006 (UTC)

Usually right Here [[2]]

Many animals sleep in such a way that they don't look like they are sleeping. The obvious examples are cows sleeping while standing up and sharks sleeping while swiming. Well, sleep says that many birds sleep while perched -- while others rest their brain one hemisphere at a time. -Quasipalm 13:23, 1 June 2006 (UTC)
It's pretty obvious when a gull is sleeping. It either stands up and naps with its head lolling or sits down with its head turned backwards. They all like to doze in the sun a lot during the day (read somewhere that they sleep on average 18 hours a day). What I meant was where do they all go at night? The seagulls spend all day hanging around in the city but as soon as the sun begins to set, they all take off en-masse in V formation and leave the city completely. There must be a place where the whole flock sleeps at night, far away from humans. --84.68.193.224 13:41, 1 June 2006 (UTC)
or sits down with its head turned backwards - see image:Aix galericulata2.jpg for an example of this. Raul654 13:43, 1 June 2006 (UTC)
Spectacular, I'd say. These aren't colourful. Sigh. -- Sundar \talk \contribs 13:48, 1 June 2006 (UTC)
I think some bird species sleep while in flight, as they often fly hundreds to thousands of miles at once. Andrew 18:05, 1 June 2006 (UTC)

[edit] Orbit Question

Would it be possible to connect an orbiting satellite to the earth with a cable or hollow cyllinder? It seems that if a cable/cylinder were connected, the points on the cable close to the earth would have to be moving very very fast for that point to stay in orbit, if it were not moving that fast, gravity would pull it towards the earth. So it seems to me like if someone connected the moon to the earth with a thin cable, the earth's gravitational field would pull it towards the earth. Is this correct? My reasoning here is that something close to the earth has to have a higher radial velocity than something further away. If they were forced to be the same via a cable... would the earth pull on the cable, and thus pull on the moon? 199.201.168.100 12:30, 1 June 2006 (UTC)

How about if the satellite were geostationary? Then it would be kind of a space elevator. Notinasnaid 12:40, 1 June 2006 (UTC)
Maybe that pulling would compensate for the slow increasing of the distance between Moon and Earth ;) (see Wikipedia:Reference desk/Science#is this true? above]]). –Mysid(t) 13:01, 1 June 2006 (UTC)
I have read something about Carbon Nanotubes under discussion to do this. I think a situation like this would result in a geostationary orbit as the cable would tend to pull the satellite into it unless some means is available for the cable to move its contact point in the earth around.
Exactly, so does that mean a space elevator or cable attachment to satellite would be impossible? 199.201.168.100 16:01, 1 June 2006 (UTC)
Ok, I did not bother thinking about the ideal situation where we would be able to make infinitely robust ropes, but in a concrete experiment we would have tidal force to mess things up (and notably breaking the rope). Cthulhu.mythos 16:39, 1 June 2006 (UTC)
But couldn't there be an engineering solution to compensate for the tidal effects, such as slackening or tightening the cable in response? ike9898 17:44, 1 June 2006 (UTC)
Steel cables certainly cant perform this, as when they are to long they break under their own weight, I don't know about carbon nanotubes strength to weight ratio, but I would have my doubts about them aswell, though I may well be wrong. Philc TECI 17:36, 1 June 2006 (UTC)
Remember end of the cable near the satelite has very little weight. ike9898 17:46, 1 June 2006 (UTC)
Yes, but in WW2 they used to hang cables from balloons to cut up the wings of the german night bombers. And these balloons had an upper ceiling, because if they went to high, the cable holding them down snapped under its own weight, and I doubt that these balloons went higher than the sattelites would. Philc TECI 19:31, 6 June 2006 (UTC)
The carbon nanotubes are supposed to be strong enough to do this, but I do not have in depth knowlege of this.
I just thought of something else. The angular velocity of a satellite varys inversely with the distance from the mass it orbits, right? This means a cable fixed to a certain spot on the earth will tend to drag closely orbiting objects to a slower velocity, which will cause them to drop to a lower orbit, the reverse would be true for distantly orbiting objects, it would try to whip them into a higher orbit. I think this would cause strain on the cable.
I believe that a careful engineering of any material could theoretically make up the cable. The trick is it has to change its thickness dramatically (exponentially?) to support the lower bits of the cable. In college we did a simulation and I think that a steal cable would have to be near a kilometer thick at the top in order to support itself (and elevator at any point on its length), whereas a carbon nanotube cable would only have to be a few centimeters at the top.131.243.163.45 22:01, 8 June 2006 (UTC)

[edit] Ph of Orange Juice before and after pasteurization?

Does the Ph of Orange juice change due to high temperatuture pasteurization?

In order to change the Ph level, the amount of acid (citric acid in the case of orange juice) would need to change and/or the volume of liquid would have to change. Proper pasteurization should not increase/decrease the acid contents and should not increase/decrease the liquid volume. --Kainaw (talk) 14:35, 1 June 2006 (UTC)
In theory the temperature might cause some chemical reactions to occur which will alter the acid/alkaline nature of the orange juice which will have an effect on the orange juice. I will bet there is a change, but I also bet the change is very slight.
That makes me wonder: How do they make "low acid" orange juice? It seems to have a similar flavor to regular OJ. --Ginkgo100 19:18, 1 June 2006 (UTC)
Many OJ companies add extra citric acid to give it a bite. Low acid ones may be using normal OJ without the additives. Also, some oranges have more acid than others - so it is probably easy to have a grove of low-acid oranges. --Kainaw (talk) 19:49, 1 June 2006 (UTC)
Or they just add something like calcium hydroxide. —Keenan Pepper 21:06, 1 June 2006 (UTC)
They add a calcium base and advertise it as having calcium, like Keenan suggests. Isopropyl 04:16, 2 June 2006 (UTC)

[edit] Night vision?

This site (an external link from night vision goggles) suggests that a piece of exposed camera film acts as a filter to enable a camera to see in the infra-red. Can this be true? If so, how does it work? --Shantavira 14:50, 1 June 2006 (UTC)

In my experience, almost all CCD cameras can see infrared light – just point a TV remote control to a video camera, press any button and see for yourself. I think the point in your link is to filter the visible light out, so that only the IR part is seen by the camera. Try the same in a dark room, with the IR lamp but without the filter (none will be needed as there is no light to begin with) and it will see in the dark, too. –Mysid(t) 14:58, 1 June 2006 (UTC)
Point your remote control to a digital camera. Press any button, you will see the IR LED's flash. Exposed film only acts as a visible light filter. I think they also covered the CCD or CMOS chip with a UV or IR filter material. If you know how to remove it and place it with a visible light + UV filter, you may have a nice near IR camera.
However, you may need to adjust your lens because these optical parts are engineered to focus visible light and minimize chromatic aberration. -- Toytoy 00:05, 2 June 2006 (UTC)

[edit] signals

why does the tv screen flashes when a nearby kept mobile rings.i know that the signals interfere bt how exactly does it hapen,thats not clear

Wave Interference is a good place to start. Just remember that in ringing, the mobile phone also needs to transmit back to the tower to indicate reciept of the call. Scienda 15:24, 1 June 2006 (UTC)

I would imagine it's the same reason why you get interference on loudspeakers when you make or receive a call on a mobile nearby. Andrew 17:59, 1 June 2006 (UTC)
From Time division multiple access: "A disadvantage of TDMA systems is that they create interference at a frequency which is directly connected to the timeslot length. This is the irritating buzz which can sometimes be heard if a GSM phone is left next to a radio or speakers." No, I don't understand that article either. Sum0 12:20, 2 June 2006 (UTC)

[edit] sds

just wondering the molar mass of sodium dodecyl sulphate (sds)?

288.38 g/mol according to sodium dodecyl sulfate. --Ed (Edgar181) 15:27, 1 June 2006 (UTC)

[edit] protease size

Any idea on the molecular weight of the smallest proteases? Working with a crude bacterial cell lysate, I am wondering if there is a molecular weight below which there are probably no proteases. ike9898 17:40, 1 June 2006 (UTC)

As of 1997, the smallest reported protease was 132 amino acid residues in length[3]; that's a molecular weight of about 14 kDa. It was found in the yeast Streptomyces caespitosus. I don't know what the smallest bacterial protease is, or if something smaller has been discovered. I'd be fairly comfortable assuming that there aren't any below 10 kDa.
Thank you! ike9898 20:58, 1 June 2006 (UTC)
I'm assuming that you're working on something where you can't just add one of the off-the-shelf protease inhibitor cocktails...? TenOfAllTrades(talk) 18:11, 1 June 2006 (UTC)
Yep. ike9898 20:58, 1 June 2006 (UTC)

[edit] Water loss in relation to leaf's surface area

A colleague of mine, a teacher, was wondering if it would be possible to calculate the amount of moisture lost by a plant through one of its leaves on an hourly basis, given the leaf's surface area, the local humidity, temperature, et cetera. She has taught her students frequently about how in the desert, plants have adapted to the harsh, dry environment by having leaves with minimal surface area; she has also heard and repeated some factoid about how the Hoover Dam loses some millions of gallons of water per hour due to evaporation. Since the children are in fifth grade, any sort of crude approximation, or hint about how to generate such an approximation, would be enlightening for them.

The teacher also has a two-foot long leaf from some healthy tree living near a creek in the Boston area; any information about what families of broad-leaved trees inhabit that region would be deeply appreciated.


Many thanks from your most humble and obedient servant,

--Doce

Transpiration, not just evaporation, is taking place. It is an active process, not a passive one like evaporation. The article will answer many of your questions, though. --Ginkgo100 19:20, 1 June 2006 (UTC)
Here is an idea. Take some cuttings with leaves from a plant, submerge them in a thin graduated vessel of water (like a graduated cylinder if that is available to you) and add a layer of light oil over the top. Measure the volume of the water and let the cutting sit for a while. Most of the water will be lost through the leaves of the cutting rather than the stem, and the oil will prevent water from evaporating from the surface of the water. Then at the end take a rough estimate of the leaves' surface area by cutting them up or placing them on a grid, tracing them, and making a crude guess. This won't work with thick succulent leaves. We did something like this in high school and it worked pretty well especially when the plants are under a hot lamp. Pick leaves that are relatively flat and large. Any kind of plant that lives in arid conditions (not riparian) would be a good choice for approximating a desert plant. Plants lose a good deal of water through stomata and many desert plants are CAM plants rather than C3 or C4 which means they only open their stomata at night, rather than during the day to decrease water loss. For best comparison results choose a CAM desert plant. C3 plants lose the most water I think on average. Sunflowers are C3 and other crops are as well. Sifaka talk 21:07, 1 June 2006 (UTC)

[edit] The moon and cheese

Is the moon really made out of cheese?

Only for people who ask 'cheezy' questions...
Check Google. --Serie 19:36, 1 June 2006 (UTC)
Define Cheese Sifaka talk 20:50, 1 June 2006 (UTC)

Well by "cheese," I think he/she means "uranium, thorium, potassium, oxygen, silicon, magnesium, iron, titanium, calcium, aluminium and hydrogen." schyler 22:50, 1 June 2006 (UTC)

Perhaps it's Chernobyl Cheddar. That would explain why it's always said to be green cheese... ;) —Zero Gravitas 02:49, 2 June 2006 (UTC)
Of course it is; see documentary evidence to the right. Melchoir 20:48, 2 June 2006 (UTC)

[edit] abdominal/tummy fat reduction techniques

What are some of the methods that have been developed other than liposuction to help in the reduction of fat from the body particularly in the abdominal/tummy area?

You could always use a big knife.
Diet and exercise techniques. Although it reduces the fat, it does not reduce the number of fat cells, just shrinks them.
There's no such thing as "spot reduction," meaning that weight loss techniques (diet & exercise) may reduce fat, but not necessarily in the particular area you want them to. Abdominal excercises will tone the muscles in that area, though. --Ginkgo100 19:24, 1 June 2006 (UTC)
Wouldn't long-term use of a tight corset reduce fat in the abdominal area? Also, there is always chemotherapy. The patients on it in our cancer center tend to lose a lot of weight. --Kainaw (talk) 19:47, 1 June 2006 (UTC)
They can just cut a load of flesh off. Not a joke, surgeons do it to some obese people, and specially to those that have lost alot of weight and have loose skin. Philc TECI 20:39, 1 June 2006 (UTC)

[edit] GREENHOUSE GAS

If carbon dioxide is more dense than air how can it rise through the atmosphere and form a 300metre thick "blanket" that raises the earth's temperature? If it does- what height above the earth's service is this "blanket"

I think the blanket sits right on top of the ground, because everything that produces CO2 is on the ground, and as you say, it's more dense than N2 and O2. —Keenan Pepper 21:11, 1 June 2006 (UTC)
Diffusion alone is sufficient to ensure that a totally static column of air would be reasonably homogeneous. But the mixing effect of wind (esp. convective currents) means that air is pretty much homogeneous all the way up. -- EdC 01:07, 2 June 2006 (UTC)
Are you certain of that? Black Carrot 01:10, 2 June 2006 (UTC)
Well, up to 100km (the turbopause), anyway. After that, in theory proportions should fall off as e-Mkh, where M is the molar mass of the gas. CO2, at less than 1.5 times the molar mass of O2, falls off that much faster. But it's not like you'd notice; there's nothing up there anyway.
Without mixing, supposing that air is mostly N2, with roughly half the molar weight of CO2, seeing as air pressure is ½atm at 5km, the partial pressure of CO2 would be ½ its sea level value at 2.5km, so 0.707 its sea level concentration. Not much of a "blanket".EdC
The concentration of CO2 is roughly constant throughout the homosphere, i.e., until about altitudes of the order of 80 km or so, except near the planetary surface where there may be significant variations in space and time, due to the proximity of sources and sinks of this gas. Turbulence (at the micro-scale) and weather events (fronts, waves at the macro-scale) are sufficient to mix the various gases and ensure a rather homogeneous relative atmospheric composition. Things can change drastically above that level, in what is known as the heterosphere. The altitude of the turbopause is not fixed or defined a priori, it can depend on location and season. --87.0.46.134 12:40, 4 June 2006 (UTC)

[edit] cancer treatment and research 1450-1750

I am looking for information related to the prevalence, attitude, understanding, and treatment of cancer during the time period 1450-1750. I think this is known as the early modern period. Any assistance would be appreciated.

Is this homework? I sense a lack of focus. You are asking several quite disparate questions about a broad range of diseases. An in-depth treatment sounds like a major piece of work. If that is what you are doing, and the problem is that you lack experience in browsing the internet, I suggest you start right here.
Google is an excellent tool for finding starting information. Hint: use Cancer as a search word, together with a term that you would be likely to find in the article you are looking for, and unlikely to find elsewhere, such as "century". If you add "-20th -20st", you will narrow it further down. The minus signs excude articles that contain 20th and 21st. Adding "History of medicine" (including the quotes) will narrow it further down.
A quick search yielded the following:
I cannot vouch for the quality of the sources.
If this is homework, feel free to cut-and-paste, but remember:
  • your teacher may be better at googling than you are.
  • your teacher has the advantage of being able to search for uncommon words or phrases that you have used.
Cheers, --vibo56 23:37, 1 June 2006 (UTC)

Thanks for the tips on browsing the internet. You are very perceptive. This was/is part of a homework assignment. I was doing some leg work for my 14 year old son. As a nurse I found the topic of some interest also. The hospital librarian put me onto the first site you mention. Apparently thru the 1500's the most common theory as to the cause of cancer was an excess of black bile. ( the bile I have encountered is yellow ) With the discovery of the lymphatic system this belief ended. Time, ability to do autopsis and the inquiring minds of many physicians " laid the foundation for scientific oncology during the 1700's. I have added this Reference desk to my favorites. I've found it fascinating reading, and the responses of the researches often amusing.Thanks again.

[edit] how to run a Monte Carlo simulation on a DEM using ArcGIS

Please, I would like to know how the Monte Carlo simulation techniques are used to evaluate the impact of DEM error on viewshed analyses.

CaPItAlizAtIoN eXISTs FOR a ReASoN. Black Carrot 01:04, 2 June 2006 (UTC)

Seriously, this question is probably too specific for the RD. Have you tried reading the fine manual? You might have more luck asking somewhere like the Arcgis desktop discussion conference. That said, if this is a homework question I doubt they'll do it for you either. --Robert Merkel 05:07, 2 June 2006 (UTC)

[edit] dental implant

Is a dental implant/crown always necessary? If a crown has been lost and is not replaced, would that have any long term effects or potentially bad outcomes for the jawbone, i.e., missing a tooth changes the structure of the tooth? Any advice or thought is appreciated.

Thanks.

The answer to your question very much depends on individual circumstance, and how you define "necessary". In the broadest definition of the term, replacing teeth that have been removed is not necessary-- life does carry on, albeit more unpleasantly, even when teeth are lost. However, there are consequences. Apart from the obvious functional and cosmetic virtues of the individual teeth, they provide more subtle benefits. A jaw full of contiguous teeth functions much like the stones in an arch-- teeth establish and maintain the position of their neighbors. Take one tooth out, and there is a gradual collapse in tooth position. The teeth forward of the lost tooth tip backward, the teeth posterior to the lost tooth tip forward, and the teeth opposing the lost tooth extrude into the newly available space. This tipping impacts negatively on dental health, since teeth are best suited to sustaining chewing forces directed parallel to their long axes. Tipped teeth incur damage to the tissues that surround and support their roots. Additionally, the progressive tipping of the teeth prevents them from properly buttressing the facial height, and the upper and lower jaws eventually assume positions that are closer to each other. This adversely affects facial appearance, as well as the ergonomic functioning of the jaw muscles, which must work at positions at which they lose efficiency. So-- is tooth replacement necessary? No, but it can often avert much more significant problems down the road, which are more difficult and expensive to manage.--Mark Bornfeld DDS 00:02, 2 June 2006 (UTC)
From personal experience, the horrors one might possibly encounter when teeth do not aline properly include extensive periodontal work, seemingly-endless TMJ-splint therapy followed by orthodontia. Two missing teeth I did not replace, or crown, caused more pain and cost more money than if I had known that teeth need each other to make alot of other facial parts work properly. Good Luck...--HafBrit 06:02, 2 June 2006 (UTC)

[edit] From Windows to Mac

By the end of the year I am planning on getting a new computer. I have always been fascinated by the beauty of Macs as opposed to PCs. The problem though is that in the past my dad has always bought new computers every 4-5 years for his office and puts in an order for me because it costs a lot less due to the bulk order. Now that I am going to buy a computer for/by myself, I definitely want a Mac because Windows computers crash (a lot) and all the other problems that windows encounters that Macs just don't. To get to my question, is there any new lingo I would need to learn, anything considerably different that would freak me out. I know when I switched from Internet Explorer to Mozilla Firefox it had a whole little help page for those in my situation. Like instead of refresh it's reload, etc. Maybe there's an article/web-page on the subject. Thanks. schyler 22:39, 1 June 2006 (UTC)

Apples website explains a lot. You could try starting at http://www.apple.com/getamac/ --JeremyA 22:47, 1 June 2006 (UTC)
Or google for "Mac switcher". The think most likely to freak you out: the thing may come with a one-button mouse (or with Mighty-mouse, which is only sort of a two-button mouse: the solution is to buy a mouse you're comfortable with. It'll take a while to get used to the way things look, but otherwise you should have no problems. - Nunh-huh 02:43, 2 June 2006 (UTC)
With your new mac, you won't have to do any hardware upgrades for a while (~5 yrs). What kind are you getting? For a right click, you hold down the control button and click, although you don't usually need to do a right click. Keyboard shortcuts are all instead of command, it is the apple key. On the Mac, Safari is much better to use than any other browser. — The Mac Davis] ⌇☢ ญƛ. 04:56, 2 June 2006 (UTC)
I got a Mac about a year or so ago, and if you're a halfway competent Windows user then Mac OS is no problem - you should be able to pick up the majority of functions in a week or less. Learn to use Exposé (Mac OS X) (the F9, F10 and F11 keys) and know that Command+Option+Esc is the Mac's Ctrl+Alt+Del. Sum0 12:13, 2 June 2006 (UTC)

Thanks much for both answers. That has been helpful and convinced me. It is what I thought too.

[edit] "Acess is denied"

Well I got a new computer recently, and I moved the old hard drive into an hd enclosure and hooked it up to my new computer. I wanted to transfer some of the files to my new computer, but since I forgot to uncheck the "make this folder private" option, it won't let me acess it. Is there anyway around this?

And btw, how can I change the save names on Battlefront 2 (for PC) without screwing up the game, since they all have names like "felucia0dbcf38a.rote" and "utapau0dc50e5b.rote" Wizrdwarts 22:58, 1 June 2006 (UTC)

If you are capable of doing this, you can connect your old hd into the place of your new one; if you have your old OS installed on that same disk, you then start your computer and access your old disk as before. Then you can change your file options. Otherwise, you can download some live Linux distro like knoppix and you should be able to access your data directly, as it should overgo Windows file properties. But in this case I think you'll have to manually remount your new hd partitions to read-write. Then you can copy your data to the new hd. Then you format your old hd and move them back. Hope this helps. Cthulhu.mythos 10:24, 2 June 2006 (UTC)
Unless the files are encrypted, there should be no reason you cant get at them within your current windows environment. Often this error comes from a lack of read/write permissions on a given folder. As the administrator user, simply open the properties of the folder in question and add privileges so you can access it. I have done this many times for users who want to recover 'inaccessible' files from old windows installations.
The "Make this folder private" checkbox is grayed out so I can't do anything with that. Wizrdwarts 01:03, 4 June 2006 (UTC)
Yes, you likely don't have permissions to uncheck it. That's where Knoppix comes in, as Cthulhu.mythos suggested. Knoppix is a "live" Linux distribution; in other words, you boot it off a CD/DVD, and it runs itself entirely in RAM, no need to install to hard drive. Since it is its own OS and has physical access to the hard disk, it can read any data on your Windows NTFS partitions, even those that you don't have permission to access on Windows. It might sound complicated, but it boots straight into a KDE graphical environment and is very good at detecting and auto-configuring nearly all types of recent hardware. It has thousands of software packages which would be helpful to you, quite a few of which help you connect to the Internet, or more importantly to your home network to transfer the files in question. It has CD burning software (I think) but if you only have one optical drive that's kind of useless since you've got the Knoppix disc in that drive. The main catch here is that you have to be prepared to download a 700 MB CD image or 4 GB DVD image. There are very good, fast torrents available, but there are also FTP and HTTP mirrors if you prefer. That's my Knoppix rant wrapped up for you. Regarding the Battlefield 2 save data, have you tried looking inside the files to see if the names are stored there in plaintext? -- Daverocks (talk) 09:50, 5 June 2006 (UTC)

[edit] USB

When I'm charging/updating my iPod on my PC (Windows XP), and someone turns it on standby, a little notification comes up and tells me that I am not using a hi-speed USB port when I come back from standby. It says that data transfer could be much quicker, and it gives a list of open hi-speed USB ports. I have repeatedly tried to connect it to one of these hi-speed ports, but I just can't seem to find them. Can anyone help me? Is there a difference between the symbol of a full-speed and a hi-speed USB port? Thanks--71.98.0.166 23:08, 1 June 2006 (UTC)

Microsoft Windows is a nagging OS. You can just forget about it and live your life happily. Nothing is going to burn your iPod or your computer. -- Toytoy 23:36, 1 June 2006 (UTC)
Yes, It gives you the (useless) notification even when there are no Hi-Speed ports on your computer at all.—Pengo 10:30, 3 June 2006 (UTC)
Control Panel -> System -> Hardware tab -> Device Manager -> Universal Serial Bus Controllers -> properties of your USB Universal Host Controller -> Advanced tab. Here you should find a checkbox that says "Notify me of USB errors" or "Disable USB error detection", I'm not sure which. Disable the error detection and this message should no longer pop up. You may have to do this more than once if you have more than one USB Controller listed (once for each of them). Bloodshedder 16:44, 7 June 2006 (UTC)

[edit] Shut up Microsoft Windows

I am using Windows XP. But I think these problems are in many other versions.

  • If I rename a file's extension (e.g. .htm → .html or .jpeg → .jpg), the system always alerts me, "DO YOU WANT TO DO IT, YOU MAY LOSE YOUR LOUSY JOB." Can I switch it off?
  • I turned off CD autoplay for all my drives. But from time to time, my system runs a CD-ROM's setup program without my consent. How do I fix it?
  • Sometimes when I finished updating my LEGAL COPY of Windows, a dialog box pops up and ask me to restart the computer. If I deny it, that nagging window pops up again again and again. How do I kill that process? Or should I use a pirated copy instead?


I hate billg@microsoft.com. -- Toytoy 23:46, 1 June 2006 (UTC)

Have you considered Linux? Black Carrot 01:09, 2 June 2006 (UTC)
Indeed, today is your lucky day because Ubuntu Dapper Drake was just released: http://www.ubuntu.com/download —Keenan Pepper 01:23, 2 June 2006 (UTC)
This is another time when I can endorse mac products!! http://apple.com/getamac/ — The Mac Davis] ⌇☢ ญƛ. 04:59, 2 June 2006 (UTC)
On a less exciting note, your third complaint has nothing to do with the legality of your copy. The update probably contained an upgrade to the kernel or some essential system service so you should restart as soon as possible. That happens with Mac and Linux too. When you get a new kernel, it doesn't actually run until you boot it up. —Keenan Pepper 05:13, 2 June 2006 (UTC)
Though there seldom is need for a kernel update on Linux, and after any other updates a reboot will not be needed. –Mysid(t) 08:03, 2 June 2006 (UTC)
Although if you've updated X, you'll need to restart it, which can be almost as disruptive as a full reboot. --Serie 18:49, 2 June 2006 (UTC)
Windows is particularly bad in that after you've chosen "no" you dont want to restart, it will ask again every 5 minutes until you've kicked the screen off the table and driven a knife through the computer case. I think you can drag the dialog into the corner of the screen, but I dont know a better way to stop it nagging for reset. I'd recommend Linux but I don't find it to be hassle free either.—Pengo 10:28, 3 June 2006 (UTC)
Instead of crazily advocating my OS of choice, I'll assume that you won't be swayed from Windows that easily, and try to give some tips on your problems. Unfortunately, Windows does like to nag. I renamed file extensions often and as far as I know, I never found a way to stop those confirmation messages. Regarding CD autoplay, are you sure you've turned it "off"? One way in Windows to manually stop Autoplay is to hold down the shift key as you load the CD in the drive. And with Windows Update, you can always turn Automatic Updates off through the Control Panel. But this'll stop you from getting much needed security updates, which you really do want if you don't want your machine to be compromised within 10 seconds. Hence the endless patch cycle that is Microsoft Windows. Deal with it, or switch to another better OS. What am I saying, any other OS is better than Winblows :P. Oh no, here I go with the Operating system advocacy again... -- Daverocks (talk) 10:03, 5 June 2006 (UTC)
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