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January 2

Cutting the carotid artery

What is the best course of action to take if one cuts his carotid artery by accident, until the emergency teams arrive? -- Leptictidium (mammal talk!) 00:41, 2 January 2008 (UTC)

For most people, the brain can be supplied with blood from one carotid, so I'd suggest compression below the cut, plus trying to block/close the wound might be a good idea. For disclosure, I'm not a doctor, nurse, or paramedic; I'd like to see what one of those people has to say. -- Flyguy649 ^talk 00:49, 2 January 2008 (UTC)

I'm not a doctor or anything, either. Our first aid article does not deal specifically with that injury. A Google search indicates that the first aid treatment for a severed carotid artery is a secret, at least on the internet. I managed to find a quiz for lifeguards that suggests lying down and applying pressure both above and below the cut. The pressure above the cut is to prevent air getting sucked in.

Bear in mind that there are several arteries called "carotid" (common, external, and internal) and that they occur in pairs, one on either side. Also, the common and internal would be hard to cut without cutting a lot of other important stuff, so I would imagine that a simple lacerated one of those would be a freak occurrence. --Milkbreath (talk) 01:43, 2 January 2008 (UTC)

To be clear, I meant that the brain can be supplied with blood by one intact left or right (common or internal) carotid artery. It would likely be the common carotid artery that would be severed, although the external carotid could also be severed; the internal carotid is generally quite deep and there would be a lot more damaged than just that. Even with a cut to the common carotid, there would likely also be damage to the internal jugular vein, if I remember my anatomy right. -- Flyguy649 ^talk 05:07, 2 January 2008 (UTC)

BTW I presume if you do call up an emergency team when this happens, say on a phone, they will be the best one's advice to follow. Obviously this doesn't help you if you don't have a phone and someone else has to go and get the emergency team but anyway...Nil Einne (talk) 06:44, 2 January 2008 (UTC)

Been watching Sweeney Todd (2007 film), eh? :-) —Steve Summit (talk) 02:53, 2 January 2008 (UTC)

Are not the answers here in contravention of giving medical advice and should be removed? SpinningSpark 01:33, 5 January 2008 (UTC)

Discussion about deleting a question should be conducted not on the desk itself but on the talk page. I have started one there about this question. --Milkbreath (talk) 02:52, 5 January 2008 (UTC)

zookeeper physics question

Hey It`s Me THE PHYSICS MAGAZINE GUY.I`ve got some questions for you.

A zookeeper devises a rubber-gun to shoot food to a monkey who is too shy to come down down the trees. If the monkey does not move,should the keeper keeper aim above,at or below the monkey. If the monkey lets go of the branch at the instant the keeper,shoots the food,should the keeper aim above,at,or below the monkey in mid-air. —Preceding unsigned comment added by 71.249.146.168 (talk) 01:26, 2 January 2008 (UTC)

See the Trajectory page to solve what looks very much like a homework question--TreeSmiler (talk) 02:23, 2 January 2008 (UTC)

Assuming the gun is designed properly, you always aim at that target. You adjust the sights for distance, wind, and target movement, then you aim at the target. -- kainaw™ 03:29, 2 January 2008 (UTC)

Only a homework question could be so divorced from reality. Is the monkey supposed to catch the food or what? Surely it's more practical to build a platform in the tree, and put the food on the platform. However, the monkey will come down from the tree when it gets hungry enough. There is no way it is going to sit there and starve when it can just climb down and grab the food.--Shantavira|^{feed me} 13:43, 2 January 2008 (UTC)

If the muzzle velocity is significantly high, the short time of flight will make gravity negligible (this would be a "linear approximation" or "straight line" trajectory model, instead of a more accurate parabola). Since you're surely already neglecting air resistance, why not neglect gravity as well? In such a case, the food might seriously harm the monkey. (Why are we shooting food at monkeys?) A slower muzzle velocity would invalidate this approximate solution, though, since the curvature of the trajectory would be too significant to ignore as the food accelerates (falls) towards the ground. Nimur (talk) 13:50, 2 January 2008 (UTC)

Given that the point of the problem is to illustrate the behavior of falling objects (the primate and the bullet), neglecting gravity would diminish the pedagogical value of the exercise. -- Coneslayer (talk) 18:16, 3 January 2008 (UTC)

The poster has previously asked questions here, asserting that they come from a physics magazine called Physics Weekly. I don't have this magazine to confirm, but I would suggest assuming good faith and taking him at his word that he's not cheating on his homework. It seems plausible to me that the magazine questions would resemble homework problems in their style. -- Coneslayer (talk) 14:12, 2 January 2008 (UTC)

Ha the second scenario is a trick question. The answer is to aim straight at the monkey since the instance the bullet "food" is fired, the monkey start dropping, so both objects will accelerate downwards because of gravity at the same time. So unless the muzzle velocity is slow enough that the "food" will reach the ground due to gravity before it reaches the monkey, it will always hit the target dead on (whether a monkey has such good reflexes though, is a better question). --antilived^{T | C | G} 06:03, 3 January 2008 (UTC)

I still say it is all a trick question. By "aim", it implies that you have sights. Sights are designed so you always aim at the target - not above or below it. It doesn't matter if the target is close, far, moving, or still. You adjust the sights and aim directly at the target. Now, if the question asked "Do you adjust your sights to raise the muzzle or lower the muzzle?" it would be completely different. Then, you can consider the muzzle velocity, movement of the monkey, and ballistic curve (as well as wind resistance). -- kainaw™ 17:52, 3 January 2008 (UTC)

A physicist's gedankengunsight does not have these adjustments; when the gun is "aimed" at the target, the axis of the gun barrel will intersect the target. If real-world firearms do not obey this convention, it is merely because their users are not as adept at physicists at doing real-time mental corrections to the aimpoint.  :-P -- Coneslayer (talk) 18:03, 3 January 2008 (UTC)

For what it's worth, I've never heard of anyone (when using an actual gun) try to adjust the sights for target movement. For longer distances where bullet drop is a concern, sometimes yes, altho it's quite common to just adjust the point of aim instead. Friday (talk) 18:12, 3 January 2008 (UTC)

Then, you've obviously never talked to anyone who went to military training for long distance sniping. The first rule of aiming is that the crosshairs (we actually said 'dot', not 'crosshairs') must be centered on the target. No "Kentucky windage" was allowed - which is what they called aiming away from the target to adjust for wind or movement. -- kainaw™ 18:22, 3 January 2008 (UTC)

I suspect it's a military vs civilian thing. Unless you have a rangefinder and a way to measure the wind between you and the target, trying to make an exact adjustment to the scope is still a matter of guessing. Also, how in the heck do you use sights to compensate for a moving target who may stop or change direction at any time? Seems like it'd be too slow. I've never known a hunter to adjust their sights in the field. Do you always have to reset the sights to some zero position when you're done, to avoid having to remember how you set them last? Seems like a lot of trouble for no real benefit. Friday (talk) 18:28, 3 January 2008 (UTC)

To be brief, since we're off-topic, the sights do zero out easily. I calculated range by seeing how many football fields I'd have to run (since I played football for many years). Wind just took time. There are many hours of training in calculating distance and wind before any real shooting. Movement does change. However, most things that need to be shot at long range do not jump all around. They move in a rather straight line. I think a big difference is the distance. I didn't even get a scope until I was shooting over 500 meters. Then, 800 meters was the normal distance. When I went deer hunting, we were shooting at 20-30 meters. -- kainaw™ 18:40, 3 January 2008 (UTC)

FETs

1. What is the advantage of n-channel JFET? The only reason I can think of is higher electron mobility compared to holes.
2. In MOSFET, the pictures show the Inversion Layer Being pinched of at a distance from the Drain. So how can the device conduct? The inversion layer formation provided carriers for it in the first place right? What happens to the carriers at the pinched end? Do they travel along the surface? —Preceding unsigned comment added by 59.93.32.233 (talk) 05:06, 2 January 2008 (UTC)

Found on JFET article, An electric current flows from one connection, called the source, to a second connection, called the drain. A third connection, the gate, determines how much current flows. By applying an increasing negative (for an n-channel JFET) bias voltage to the gate, the current flow from source to drain can be impeded by pinching off the channel Is it correct? Doesn't majority carriers flow form source to drain? So the paragraph is correct only for p-channel right? 59.93.26.127 (talk) 07:02, 2 January 2008 (UTC)

You might find DIBL helpful for your second question - the drain can induce a strong lateral field and "suck" electrons over the nonconducting "gap." Remember that "conducting" and "nonconducting" are only relative terms. Nimur (talk) 11:31, 2 January 2008 (UTC)

1. n-channel and p-channel indicates how the gate must be biased. One does not have any advantage over the other unless by design/manufacturing.
2. The gate controls the size of the inverstion layer. You can see from the picture that by changing the size of the layer, you change the size of the conducting path thereby changing the conductivity. Electrons flows from the S thru the layer to D.

Your follow up question refers to a JFET which has a depletion layers. This layers prevent electrons from flowing therefore the bigger the layers, the less conductivity between S and D. See Field Effect Transistor for more info. The majority of current does flow between S and D. Compared to this, the current from gate is insignificant. You may also want to see Bipolar Junction Transistor where S, D are similar to E(mitter), C(ollector) and gate is B(ase). Basic operation of any transistor is little current out of gate (or base) controls a larger current from source and drain (or emitter and collector). NYCDA (talk) 22:17, 2 January 2008 (UTC)

Note that "pinchoff" is a technical term, and does not mean "pinched closed." When an FET is operating in the pinchoff region, the channel will dynamically change its geometry to maintain a relatively constant current under changes of Vds. In other words, the channel is still open during "pinchoff," it just starts acting differently than it does when in the "resistive" region at much lower values of Vds. --Wjbeaty (talk) 23:32, 2 January 2008 (UTC)

Yes it seems Bill is correct again! [1]

--TreeSmiler (talk) 23:22, 3 January 2008 (UTC)

high tension lines or transmission lines and archival photos of "galloping" lines

Any archival video or photos of transmission lines or high tension wires "galloping"? sean —Preceding unsigned comment added by 75.73.162.109 (talk) 07:52, 2 January 2008 (UTC)

Video [2]--TreeSmiler (talk) 10:18, 2 January 2008 (UTC)

Resonance has some related video and animation links. Nimur (talk) 11:34, 2 January 2008 (UTC)

Hydrogen ion

I have studied in school that when an atom looses or gains electrons, to obtain the nearest noble gas' configuration, an ion of that element is formed. But in the case of Hydrogen the nearest noble is helium with electronic configuration of He(2) Thus Hydrogen gains one electron to achieve that configuration. Thus the Hydrogen ion becomes negatively charged.

But How is it positively charged????????? —Preceding unsigned comment added by 202.179.79.132 (talk) 15:49, 2 January 2008 (UTC)

What you've described is called hydride (H⁻), and it is one of the two possible ions of hydrogen. The other (perhaps more common) ion of hydrogen, H⁺, is sometimes called a hydron (a word I've actually never heard before; most chemists just say "proton"). A H⁺ ion has no electrons at all; it's just a bare nucleus. The nuclear charge is +1, and there are no electrons to cancel it, so the overall ion charge is also +1. —Keenan Pepper 16:27, 2 January 2008 (UTC)

The explanation that the original questioner mentioned regarding noble gases is a simplification; ions try to obtain a stable electron configuration. Often, the best stable state mimics a nearby noble gas valence shell, but this is not always the case. In the case of H⁺, it is easier to lose a single electron than to attract one. The rules which govern stability of electron configuration are extremely complicated, so a lot of simple versions such as the "octet rule" exist; however these are at best "approximate" and do not always apply. Nimur (talk) 16:31, 2 January 2008 (UTC)

This probably counts as a lie-to-children, but you can think of hydrogen as being halfway between two "noble gases" - helium, and vacuum (not that I've ever seen vacuum classed as a noble gas, but I think it technically would fit at least some of the definition). So it can go either way. Confusing Manifestation(Say hi!) 21:36, 2 January 2008 (UTC)

One could also think of a free neutron as a noble gas with valence 0 (an unstable isotope of the vacuum, natch). Of course, the lack of nuclear charge and surrounding electrons causes the neutron to behave rather differently than "proper" atoms, even of noble gases; in particular, it has no Coulomb barrier to prevent it from fusing with other nuclei. But yes, the whole octet rule is a gross simplification, and breaks down rather badly e.g. with the transition metals, which often can exist as several different types of ions. —Ilmari Karonen (talk) 22:07, 2 January 2008 (UTC)

It's probably worth mentioning that unless you're talking about high-vacuum gas phase conditions, the H⁺ ion really doesn't have an independent existent. While it is energetically favorable for hydrogen atom to give up its electron to form "H⁺", the naked proton is not stable by itself, and rapidly latches on to any available lone pair of electrons. For example, in water, a water molecule can dissociate to form OH^- and H⁺, but the H⁺ immediately latches onto a lone pair from another, adjacent water molecule to form a hydronium ion. The hydrogen ion is thus able to fill its "octet" by borrowing the lone pair electrons from the oxygen. Similar things happen in other solvents, where free H⁺s don't really exist by themselves, but get passed from one lone electron pair to another. -- 128.104.112.236 (talk) 23:08, 6 January 2008 (UTC)

January 3

Using the IUCN Red List

Hello, I've been struggling for half an hour with the Red List home page[3] trying to decide whether or not Prosthechea cochleata var. triandra is endangered, since it concerns the article I have just created concerning that subject. Could anyone who is familiar with that website (since I understand Wikipedia relies mostly on it for endangered species classification) help me search or search and tell me what they consider it (Least Concern, Vulnerable, etc.)? --♦♦♦Vlmastra♦♦♦ (talk) 00:11, 3 January 2008 (UTC) Edit: Let me be more specific: My message was:

No results were found for the criteria you specified:

• Text search: Prosthechea cochleata var. triandra
• Modifier: Exact phrase
• Search in: Whole database
• Results type: Standard
• Taxa: Species

If these are correct, then the species you are searching for may not be in the database.

I changed the database, taxa, modifier, etc. extensively, to no avail. Taxa should be listed whether or not endangered (and in that case as Least Concern) so I don't think this means it isn't endangered, and since P. cochleata var. triandra has been considered endangered elsewhere I imagine it has been reviewed by the IUCN. I would like to use this source, so any help will be appreciated. I assume that I am not searching correctly because common genera such as Cattleya and Paphiopedilum were similarly unlisted, and I know for a fact that Paphiopedilum rothschildianum is endangered. --♦♦♦Vlmastra♦♦♦ (talk) 00:28, 3 January 2008 (UTC)

You can set the modifier to "Starts with" and enter the genus to see if any species of a given genus is listed. A number of Paphs are listed but not P. rothschildianum. There seem to be no Cattleyas or Prosthecheas listed. Alternatively, use the "expert search" which allows you to drill down through the hierarchy of taxa, e.g. Kingdom PLANTAE, Phylum TRACHEOPHYTA, Class LILIOPSIDA, Order ORCHIDALES, Family ORCHIDACEAE, Genus Paphiopedilum, etc. Bear in mind that "only" about 40,000 species have been assessed. William Avery (talk) 12:42, 3 January 2008 (UTC)

And also, just for plants, it may not have been assessed since 1997. See http://www.iucnredlist.org/info/faq#technical-1 William Avery (talk) 13:34, 3 January 2008 (UTC)

I had already tried the expert search, but, thanks anyways... I guess it was just wishful thinking. 40,000 species is of course a massive number, but when actually looking for a particular species, those numbers seem limiting. By the way, I meant P. sanderiana was endangered for a fact (although I understand P. rothschildianum is known only from three two sites, since one burned down recently). I notice P. sanderiana is also missing.--♦♦♦Vlmastra♦♦♦ (talk) 05:55, 4 January 2008 (UTC)

Body shape and structure

What, exactly, gives us (and other organisms for that matter) their shapes and structures? Why does every person (well, almost every person) have a nose in the middle of their face, two eyes, their arms where they are, all of their kidneys and other organs virtually the same shape and location, etc... I know its in the DNA, but could that answer be elaborated on? Thanks. --71.117.37.108 (talk) 03:34, 3 January 2008 (UTC)

If you don't know of it first see evolution.--Dacium (talk) 04:27, 3 January 2008 (UTC)

See also developmental biology, a whole scientific field devoted to these issues. --JWSchmidt (talk) 04:43, 3 January 2008 (UTC)

Another article that may be of interest is morphogenesis, which is the process by which our body forms shapes and structures. One of the most important genes in forming shapes and structures in the right place are the Hox gene family, which are turned on at different places along the length of a developing embryo thereby patterning the body plan. The pattern laid down by the Hox genes then turns on other genes which in turn start processes that form organs and structures. Its a very complex system in humans and we are a long way from fully understanding it, but by altering genes in animal models (especially fruit flies) and seeing the absence of wings for example, we begin to find the important genes and how they work. Rockpocket 04:57, 3 January 2008 (UTC)

Focal distance and light intensity (camera question about f-stop)

According to the f-stop article, a 135mm lens and a 100mm lens at f/4 transmit the same amount of light to the focal point despite the aperture being larger in the 135mm lens. How can this be? Something about a longer focal length reduces the amount of light that reaches the focal point but I don't see why this should be. When light is diverging from its source, I can see why being further away from the source would lead to a reduction in observed intensity but when the light is converging to a point I expect that the more light you begin with, the more light you have after converging. ----Seans Potato Business 12:03, 3 January 2008 (UTC)

Essentially true for point sources (such as a star), but most photographers are concerned with extended sources. Imagine using the 100mm lens at f/4 to take a picture of a white square (like a piece of paper). On the film or sensor, it images to a 10x10mm square. Switch to the 135mm lens at f/4, and, yes, more light is collected from the paper, but now it's spread over 13.5x13.5mm on the film or sensor. The exposure for a given pixel on the sensor, or "tiny patch" of film, is exactly the same. This is what matters for photographic exposure, not the total number of photons collected over the whole area of the white square. -- Coneslayer (talk) 12:47, 3 January 2008 (UTC)

Is it possible to make a 135mm lens that focuses down to a square of 10x10 instead of 13.5x13.5mm? Also, what if I had an SLR and swapped between 135mm and 100mm lenses - since the CCD is fixed in size, this madness will lead to either incomplete coverage of the CCD (wasting pixels of a 13.5x13.5mm CCD) or spilling picture off the edges of the CCD (so the outer parts of the image are not captured because the CCD is only 10x10mm (or whatever size it is)). ----Seans Potato Business 13:54, 3 January 2008 (UTC)

I think you misunderstand. I'm talking about the size of a particular object in the image, a sheet of paper. Not the coverage of the lens (how much of the CCD it illuminates). If you switch to a different focal length, of course the image of the piece of paper changes size on the sensor—that's why we use different lenses, so that we can control the size of objects that we image (a long-focal-length lens to make things big—like a small bird far away, or a short-focal-length lens to make things small, and encompass more of the scene—like a landscape). If your subject fills the frame with a 100mm lens, and you switch to a 135mm lens, why would you complain about it "spilling picture off the edges"? Why did you switch to a 135mm lens if you didn't want that to happen? -- Coneslayer (talk) 14:03, 3 January 2008 (UTC)

lol. 'Cause I don't know what I'm doing? *drops camera* - I understand it now. Thanks :) ----Seans Potato Business 14:08, 3 January 2008 (UTC)

Don't drop it—keep playing with it, so you get the hang of this stuff! You might check out Ansel Adams' The Camera (ISBN 0821221841) for a good explanation of photographic optics. It's not as warm and fuzzy as today's "Everything for Dummies" books, but is probably OK for the sorts of people who read this Reference Desk. -- Coneslayer (talk) 14:26, 3 January 2008 (UTC)

Lens focusing by eye

I was wondering, if I hold a glass lens in behind a window to the outside world and a piece of paper behind the lens, the focal length of the lens should be equal to the distance between the lens and the paper when the image is in focus. In actuality, however, wont there be some ability of the lens in my eye to compensate for poor focusing of the image, thereby creating a small range of paper-glass lens distances for which the image appears in focus? You might argue that, if this is the case, you can just take the middle of the range, but that assumes that the eye can focus from "neutral" (where the image on the paper really is in best-possible focus) to an equal extent in both plus and minus directions? ----Seans Potato Business 14:03, 3 January 2008 (UTC)

First, the statement that "the focal length of the lens should be equal to the distance between the lens and the paper when the image is in focus" is only true for a simple lens. For a complex lens like most photographic lenses, it's not really true. Second, if you're forming the image on a surface, like a sheet of paper, or the focusing screen of an SLR camera, your eye doesn't matter. The image formed is like ink on the page of a book. With something like binoculars or a telescope, you're not forming the image on a surface—you're looking at the "aerial image". In this case, you can compensate (to some extent) for the instrument's focus with your eye's focus. -- Coneslayer (talk) 14:08, 3 January 2008 (UTC)

When you talk about simple and complex lenses, is it that a simple lens focuses to a single point whereas a photographic lens must focus to a square? —Preceding unsigned comment added by Seans Potato Business (talk • contribs) 14:12, 3 January 2008 (UTC)

No, that's not the distinction. The simplest lens exists only in physics classes, like a spherical cow. That would be the "thin lens" that magically bends light, but has no thickness. You can see how that makes it easy to measure the distance from the object to the lens, and the lens to the image. A real simple lens is one that has only one element (piece of glass), like a magnifying glass. If you take a magnifying glass, you can see that you can produce an image of a light on a sheet of paper. If your light is big (like the overhead fluorescent fixture in an office, or a table lamp with a shade at home), you will see that it's not just covering a point—you can see the full shape of the fixture. A complex lens, like a camera lens, has multiple elements, in order to improve the quality of the images it produces (see aberration (optics)). First of all, they're big, which makes it unclear how, exactly, you would measure the distance from the lens to the image (from the front of the lens? middle? rear?). Second, many of them are of a retrofocus or telephoto design, which completely removes the direct relationship between lens-to-image distance and effective focal length. -- Coneslayer (talk) 14:21, 3 January 2008 (UTC)

I think the original poster's statement about "the focal length of the lens should be equal to the distance between the lens and the paper when the image is in focus" is only true if the objects you're projecting onto the paper are at "infinity" (+/- a smidge, of course). For closer objects, the relationship between the paper and the lens must shift. The lens of your eye is different because its curvature can be shifted by the muscles of your eye, changing its effective focal length.

Atlant (talk) 16:46, 3 January 2008 (UTC)

Yes, the distance from the simple lens to the image is only equal to the focal length if the object being imaged is very far away ("at infinity"). Otherwise, the distance from the lens to the paper increases according to the thin lens formula. -- Coneslayer (talk) 16:52, 3 January 2008 (UTC)

If I understand correctly, you're asking if the lenses in your eyes can compensate for a blurry image projected onto a piece of paper, or, for that matter, printed on one. They can't. If you focus exactly on the image, it will look however blurry it is. If you don't, it will look blurrier. The best way I can think of to explain it is that once the image is projected onto the paper, the information about which way the light came from is lost. — Daniel 20:15, 3 January 2008 (UTC)

Excessive emotional responses

Children seem to be more aware of and responsive to their emotions, sensations and feelings. E.g. they laugh / cry more readily. Why is this and is there a term or article about it? Is it a lack of something or too much something? - CarbonLifeForm (talk) 14:39, 3 January 2008 (UTC)

Bear in mind it is a very complex process of going from being a child to becoming a fully developed adult, especially in regards to the amount of nervous branches in the brain in this case. Everyone has a fear of the unknown, and a child who has learnt little with be more easily overwhelmed by what they experience than an adult would, because they haven't seen a lot of it before. As far as I know there is no article on children's emotional development, but for further reading you could use this site: Erikson's Eight Stages of Development Cyclonenim (talk) 14:50, 3 January 2008 (UTC)

Children have a more labile affect. MrRedact (talk) 14:53, 3 January 2008 (UTC)

What is this object?

Can someone identify this object (two pictures are below). It is made of metal, it is almost as big as a football. It is about 8 inches high. I could get more measurements of it and weigh it, if that would help.

photo 1 photo 2 Bubba73 (talk), 16:02, 3 January 2008 (UTC)

It looks like a meteorite to me. Is that speculation consistent with the object's history?

Atlant (talk) 16:41, 3 January 2008 (UTC)

I think it looks like a clinker. (Altho, we don't have much of a good article on the type of clinker I mean.) I found something similar as a kid and thought it was a meteorite too. Friday (talk) 16:50, 3 January 2008 (UTC)

(To me, it seemed awfully large to be a clinker, although battling that one would certainly do the old man proud!)

Atlant (talk) 19:33, 3 January 2008 (UTC)

Well, the thing I found as a kid which I was told was a clinker (meaning, basically, a big rock-like cinder) was probably about football sized. I always assumed the cinder explanation was right, but I suppose I have no way of knowing this for sure. A couple older people I showed it to seemed to think it looked like a normal thing they had seen before. It looked like a bunch of rock and/or metal, all melted together, and full of weird holes. Friday (talk) 19:47, 3 January 2008 (UTC)

Looks like an ironstone concretion - basically a weathered rock like sandstone where the iron in it has become concentrated along joints or fractures. It is common for such concentrations to be sub-circular, as the iron sort of filters out from a central point. Cheers Geologyguy (talk) 16:55, 3 January 2008 (UTC)

I agree. It looks very much like one. There are such "things" around here (Southern New Jersey). I say "things" because they aren't really rocks. Ours are formed straight from sand, not sandstone. They are surprisingly heavy and can be any size. Some of them even form pipes or tubes. --Milkbreath (talk) 21:05, 4 January 2008 (UTC)

Try breaking it open. If you succeed show us a photo of the inside. Theresa Knott | The otter sank 17:29, 3 January 2008 (UTC)

I don't think there is any way for me to break it open - it is very solid. My father thought it was a meteorite, but I don't think it is. This one and a larger, similar one were both found in a hole in some river sand in south Georgia. I haven't seen anything quite like them around here, and I don't know of any local industry where they would be waste products. I haven't checked its magnetic properties, but it seems to be iron. I think it is unlikely to be a meteorite, since two of these were found in a hole.Bubba73 (talk), 18:17, 3 January 2008 (UTC)

I bet if you try a magnet on it, you'll find it is not magnetic. The metallic iron-looking stuff is not iron, per se, but iron oxide, the result of weathering. Cheers Geologyguy (talk) 18:48, 3 January 2008 (UTC)

Iron oxide not magnetic? [[4]]--TreeSmiler (talk) 01:50, 4 January 2008 (UTC)

Sorry, magnetite is an iron oxide that is magnetic, but this is probably not magnetite. I think it likely that the iron oxides in this rock are hematite, limonite, goethite and the like, none of which are magnetic (at least not attracted to a magnet). See also Bog iron. Thanks for nudging me to make the clarification. Cheers Geologyguy (talk) 01:55, 4 January 2008 (UTC)

It appears that Goethite becomes magnetic in a reducing flame. Is this one test that could be done on a small sample?--TreeSmiler (talk) 02:22, 4 January 2008 (UTC)

You would need a blowpipe and alcohol burner to do it right - the times I tried such tests were abysmal failures. Takes a pretty delicate touch. Cheers Geologyguy (talk) 15:54, 4 January 2008 (UTC)

In case any readers are puzzled by the blowpipe reference, we have an article at Blowpipe (tool). DuncanHill (talk) 15:58, 4 January 2008 (UTC)

A hole like someone might dig for a fire? I still think it's a cinder. Friday (talk) 18:54, 3 January 2008 (UTC)

It was a deep hole - 6 or 8 feet. It was hard for them to bring them up. I think it is far too heavy to be a cinder. Bubba73 (talk), 19:49, 3 January 2008 (UTC)

Looks like clinker (furnace waste) especially because of the black glassy bits.Polypipe Wrangler (talk) 08:09, 7 January 2008 (UTC)

OK, but what kind of furnace or factory? There is no furnace that I know of near there. Of course, it could have been carried a long way and discarded there, possibly. Bubba73 (talk), 03:13, 8 January 2008 (UTC)

ISO setting verus shutter speed

If you go here and scroll down to the example pictures, Film_speed#Digital_camera_ISO_speed_and_exposure_index... where they say they change the "ISO setting", do they mean they changed the film inside the camera? If not, what is the difference between the ISO setting and the shutter speed? --Seans Potato Business 16:14, 3 January 2008 (UTC)

Digital cameras don't have film inside. --LarryMac | Talk 16:19, 3 January 2008 (UTC)

To expand on that a little... The only way to change the ISO sensitivity of a film camera is to open it up and put different film inside. The sensor of a digital camera, on the other hand, is capable of acting like film of several different ISO sensitivities, so you can change it at the push of a button. (I think it changes the gain of the internal analog-to-digital converter). —Keenan Pepper 16:27, 3 January 2008 (UTC)

(ec) The 'shutter speed' is simply the amount of time the film (in a film camera) or image sensor (in a digital camera) is exposed to light when taking a picture. 'Shutter speed' and 'exposure time' are synonyms. It's easier to hold the camera steady for a short exposure than for a longer one, and moving objects in the scene will be less blurred. Longer exposures will be required for dimly-lit subjects (indoors, night shots, etc.).

The 'ISO setting' on a film camera is a mechanism (usually a knob) that lets you dial in the sensitivity of the film. (You may also see 'ASA setting' on older cameras; it does the same thing.) The camera needs to know how 'fast' or 'slow' the film is that has been loaded so that it can calculate appropriate exposure times. 'Faster', more sensitive films require shorter exposure times but also tend to appear grainier and have poorer colour saturation.

For a digital camera, one (obviously) can't change the film. Instead, the ISO setting adjusts the sensitivity of the sensor that captures the images. Once again, choosing a higher ISO setting (more sensitivity to lower levels of light) allows one to set a shorter exposure time, but this comes at a cost of 'noisier' images. In principle, a scene shot at ISO 100 and an exposure time of 1 second should be of equal brightness in the recorded image as the same scene shot at ISO 1600 and an exposure time of 1/16 of a second. The former image will be more prone to motion blur, while the latter will be grainier (film) or noisier (digital). TenOfAllTrades(talk) 16:30, 3 January 2008 (UTC)

So the difference in brightness observed in the example in that article, is due to disparity between the ratio of the two ISO settings and the ratio the shutter speeds? Ideally, shouldn't the photographer, if they intended to use those photos in that article, have used a 1/5600 shutter speed (perhaps not possible on the camera used) in order to show the similarity? --Seans Potato Business 17:19, 3 January 2008 (UTC)

Yes, it would absolutely be better (for the clarity of the article) to do as you suggest. The camera used has a fastest shutter speed of 1/4000 second, so shooting at 1/5600 would not be possible. However, shooting at a smaller aperture would have made it possible to do what you suggest. At f/8 (one stop smaller), the shutter speeds would have been 1/175 and 1/2800. -- Coneslayer (talk) 17:26, 3 January 2008 (UTC)

One could, if it wasn't considered "dishonest", take a copy of one photo, maybe change it ever so slightly, and then say that it is the same subject with both shutter speed and ISO changed by the same ratio? Alternatively, if it's not too much hassle, perhaps you could take suitable photographs? I don't yet have a suitable camera. --Seans Potato Business 01:02, 4 January 2008 (UTC)

Yeah, maybe I can do it this weekend. I have a Pentax K10D that will do the trick, and it's fairly noisy at ISO 1600. Usually, that's not such a good thing, but I guess for this application, it is. -- Coneslayer (talk) 01:10, 4 January 2008 (UTC)

Thanks, Coneslayer. No, SPB—'doctoring' a photo to show a specific effect is definitely 'dishonest'. It's the sort of thing that gets academic types suspended or expelled (if students) or fired and blackballed (if faculty). TenOfAllTrades(talk) 15:17, 4 January 2008 (UTC)

Yeah, but I'm not suggesting it to support scientific research! I would never! I simply suggested it for educational purposes and don't think it's nearly as immoral... --Seans Potato Business 18:06, 4 January 2008 (UTC)

But we're an educational resource. (At least, we're trying to be.) Faking the data and lying to our readers isn't really a business we want to get into. Besides, are you sure that you would add the correct type(s) of noise to the image? Not all noise is created equal, and understanding it (and simulating it) properly is a non-trivial task. (Compare shot noise, salt and pepper noise, Gaussian noise, thermal noise....) TenOfAllTrades(talk) 19:08, 4 January 2008 (UTC)

I don't think lying is inherently bad. People do it all the time. You ask someone if lying is bad and they scream "YES!!", but then I ask what's Santa Clause? It's a lie! People lie all the time in some perfectly moral (and immoral) ways. I think it's the malicious intent behind a lie that makes it bad. If I was educating a class of children and needed to illustrate a point, my focus would be on the ideas that they walked away with, not how I managed to get those ideas across. The technical issue that you raise is however quite valid, I suppose. Do noise patterns vary between cameras? --Seans Potato Business 00:33, 6 January 2008 (UTC)

Coneslayer: I already uploaded photos for the article; the photos were taken using my Nikon D40x DSLR at ISO 100 and ISO 3200. If your photos are more encyclopedic, feel free to replace my images with them. --Bowlhover (talk) 19:33, 5 January 2008 (UTC)

(Thanks for updating the images) Was your camera mounted on a tripod? If so, why the blur on ISO 100? --Seans Potato Business 00:24, 6 January 2008 (UTC)

No, I didn't mount my camera on a tripod. I wanted to use motion blur to show the exposure time is longer on ISO 100 than on ISO 3200, since motion blur is the only reason not to shoot at the lowest possible ISO. --Bowlhover (talk) 03:12, 6 January 2008 (UTC)

What about noise? We were expecting a crisp ISO 100 and noisy 3200. --Seans Potato Business 11:37, 6 January 2008 (UTC)

indian resources on iron

tell about all indian resources of iron —Preceding unsigned comment added by 210.89.50.190 (talk) 17:42, 3 January 2008 (UTC)

Do you mean: "Where is iron being mined in India?" -- kainaw™ 17:56, 3 January 2008 (UTC)

By googling "indian resources of iron" I got this link [5]. Maybe that's useful. --Taraborn (talk) 08:55, 5 January 2008 (UTC)

Falling Leaf

Is there a name for the side to side motion a leaf makes when it is falling to the ground? --Juliet (talk) 19:56, 3 January 2008 (UTC)

I don't know that there's a particular name for it, but it looks like someone's studied it. (It looks like they call this particular motion "fluttering". I don't know if other people would associate that word with this specific motion.) -- Coneslayer (talk) 20:01, 3 January 2008 (UTC)

I am writing a presentation

Can you please answer a couple questions for me please? —Preceding unsigned comment added by 207.69.139.157 (talk) 22:25, 3 January 2008 (UTC)

Maybe. Ask specific questions on specific topics (after having searched wikipedia yourself to get your feet wet, obviously) and we'll see what we can do. DMacks (talk) 22:36, 3 January 2008 (UTC)

Kidney in hagfish

I'm confused as to what "type" of kidney an adult hagfish has? I guess it's safe to assume that at the larval stage it's a pronephros, but does it change to a mesonephros at a later stage? Wikipedia says that pronephros is an active organ in the adult hagfish and my book (Introduction to Chordatezoology by J. M. Jørgensen) says that in 'some' hagfish the pronephros will turn into a bloodcreating organ, 'like' mammalian bone marrow, thus making it an active organ but not the active kidney? And I've always been told that all "higher" chordates (so everything other than urochordates and cephalochordates) develop a mesonephros, however i've also been told that only amphibians and fish have a mesonephros as the adult kidney, so which is it? 80.63.191.67 (talk) 23:23, 3 January 2008 (UTC)

Battery effect

I know from radio-controlled models that if you empty certain rechargeable batteries (I'm pretty sure it is nickel-cadmium batteries) in a short time until the model won't drive or fly any more, then wait a few minutes, then the batteries can be used again for driving/flying for a short time. It may appear as if the battery would recharge itself partially. I think this effect is due to the thermochemistry of the discharge reactions, i. e. they lower the entropy (and lower the enthalpy, else the reaction wouldn't occur at all) so that the chemical equilibrium is shifted towards the charged state at higher temperatures. Any further thoughts on this? Icek (talk) 23:28, 3 January 2008 (UTC)

Maybe the cells cool down causing a lowering of their internal resistance giving you more current capacity when you re energize? See Nickel cadmium--TreeSmiler (talk) 23:36, 3 January 2008 (UTC)

But the article claims the opposite - "This meant that as the cell temperature rose, the internal resistance fell". Icek (talk) 22:26, 4 January 2008 (UTC)

Yes well spotted. I missed that bit (with it being hidden away in the 'disadvantages' para.) Im not sure if its true though as there doesnt seem to be a ref to that effect and i have not heard of it before.--TreeSmiler (talk) 01:57, 5 January 2008 (UTC)

I'm fairly sure this is the surface charge (an electrical charge stored in the metal of the battery, similar to that of a capacitor) that you're encountering: the chemical reactions that drive the battery run at a limited rate, and when you've nearly drained the battery, they can't go fast enough to generate a usable voltage/current. If you let the battery sit, however, the reactions will keep running until they rebuild the surface charge, which gives the appearance of a partial recharge. --Carnildo (talk) 00:24, 5 January 2008 (UTC)

Flash evaporation of a solution

If you were to flash evaporate a liquid with a solid dissolved in it, e.g. sugarwater, would the solute not have time to crystallize and just turn into an extremely fine powder? Would it be separated into individual molecules? Would it matter of the solute was disassociated, e.g. saltwater? — Daniel 23:51, 3 January 2008 (UTC)

Did you see the paragraph on Spray drying therein? Your conclusion is right, you will get a fine powder. With sugar if you do it slow enough you will get a supersaturated syrup which could make a sticky foam that gums up your system. The ions in a disassociated ionised soltion will make the effort to recombine into a salt powder. You want get a plasma of sodium and chloride ions unless you do it at an extreme temperature! Graeme Bartlett (talk) 03:33, 4 January 2008 (UTC)

How fine will the powder be? It seems like spray drying would result in crystals forming in each individual droplet, and result in a powder that isn't as fine as would be created with flash evaporation. — Daniel 07:44, 4 January 2008 (UTC)

As the first few words of the article will tell you, flash evaporation is partial. It will leave you not with a powder but with a cooler, possibly supersaturated liquid. --169.230.94.28 (talk) 17:05, 4 January 2008 (UTC)

January 4

Bike mechanics - removal of rear sprocket (single speed - no cassette)

My bike has internal hub gears. The time has come to replace the rear sprocket but I don't know how. I need to remove something. Here is a picture to illustrate the situation. You can see the sprocket, a tube coming from the center (the gear changing pin goes in there) and a big, thick (1cm), round metal thing keeping my sprocket in place against my will. Can anyone identify that metal thing and advise on its extraction? Thx. in advance ----Seans Potato Business 00:58, 4 January 2008 (UTC)

This may be what you need [6] Spinningspark (talk) 10:56, 4 January 2008 (UTC)

What I have is a 'snap ring' and it should be removed with a screw driver (I needed two and a pair of pliers...). There's a picture available here. --Seans Potato Business 21:47, 4 January 2008 (UTC)

Strategic Defense Initiative ("Star Wars")

I would like to know if the theory of "laser beams" from orbiting satellites with the capability of shooting down missiles is even slightly plausible, and if yes, how so? No, I don't plan to build one, I'm just curious as to how it is done, and what exactly the "laser beam" consists of.SDI

EWHS (talk) 13:37, 4 January 2008 (UTC)

You should read the article you linked to: Strategic Defense Initiative. Short opinion/speculation: yes, it's certainly plausible that a space-based laser could shoot down a missile; no, it's not plausible that this could ever win in an arms race against anti-SDI countermeasures. Also check out Boeing YAL-1. --Sean 13:48, 4 January 2008 (UTC)

Thank you. EWHS (talk) 14:19, 4 January 2008 (UTC)

There were a few "laser" plans. Most were just big, conventional lasers. One which got a lot of attention (because it was later discovered to have been vastly oversold) was the x-ray laser, where the x-rays released by a nuclear bomb would be channeled into specific directions. Anyway, the problem with SDI—and all missile defense—is that the economics of it are not very good. It is always going to be cheaper to send up counter-measures than it is to shoot them down; it is always going to be much easier to attack with missiles than it is to defend against them. And even if one did get a reasonably good missile shield in place, the existence of it alone would change the threat landscape quite a bit (e.g. instead of shooting a missile, an enemy would try to smuggle the weapon in, or just do something else). At the moment the US spends a HUGE amount of money on a technology which may or may not ever work as advertised, but even if it does work it only is one small thing in an overall landscape of threats. Personally I think the money could be better spent elsewhere. --24.147.86.187 (talk) 16:24, 4 January 2008 (UTC)

Here's one: not satellites from space but American Airlines is participating in tests of anti-missile lasers installed in commercial airliners link. These are used to confuse shoulder-fired missiles, not destroy ICBMs but show the targeting systems be workable. Rmhermen (talk) 14:37, 7 January 2008 (UTC)

What is the difference between Nernst equation and Nerst's equation?

--78.145.168.125 (talk) 14:18, 4 January 2008 (UTC)

I think the latter was a mistake (misspelled, not a great article). I've changed it to a redirect to the former. -- Coneslayer (talk) 14:35, 4 January 2008 (UTC)

Amazonian insects and fruit for identification

Greetings,

I went to the Amazon Rainforest and took plenty of pictures for Wikipedia. Unfortunately I couldn't identify some of the insects I saw, so I ask for your help. In addition, you're asked to identify or at least classify the yellow fruit locally named Pitabao (or Pitabau). Its flesh has a smooth texture, tasting a bit like Eugenia uniflora, and its seed is expectedly bitter. Thanks, Lior (talk) 14:41, 4 January 2008 (UTC)

• 
  Who am I?
• 
  A particularly annoying big moth
• 
  Same moth
• 
  A butterfly also found in southern Brazil
• 
  A huge tree ant
• 
  Unidentified wasps emerging from an unidentified tree
• 
  The same wasps with a better look on the tree
• 
  Pitabao tree
• 
  Pitabao fruit - whole, peeled and consumed

The "pitabao" look like a palm fruit, possibly Bactris gasipaes. However, your fruits look too small for that species.--Eriastrum (talk) 17:34, 5 January 2008 (UTC) Oops! My bad. I failed to look at your photo of the tree, which is not a palm! It looks like it belongs to the Melastomataceae, because it has three prominent veins on the leaves.--Eriastrum (talk) 17:41, 5 January 2008 (UTC)

How much gas can a candle burn?

Imagine I had a gas cooker with four burners inside a kitchen with the standard gas ventilation measures. If I lit a candle in the kitchen before turning the gas on, and then opened the gas to all four burners at maximum rate;

• would the gas eventually build up in great quantities and explode

• or would the candle burn the gas quicker than it can build up?

I'm not going to commit suicide by blowing myself up or anything, I'm just wondering if the gas explosion in the film Hot Fuzz is possible or just artistic license. Thanks for your answers. -- Leptictidium (mammal talk!) 14:58, 4 January 2008 (UTC)

There would be an explosion once the gas-air mixture reached the candle flame in the critical proportions. The further away from the source, the greater the quantity of gas and the bigger the bang. The candle burns its wax, not the gas.--Shantavira|^{feed me} 15:27, 4 January 2008 (UTC)

Yup. And if the gas burns at all without blowing out the flame, then the fire will travel back from the candle through the gas-filled air and then just burn at the source of the gas. In other words, if there isn't a big enough explosion from the gas reaching the candle to blow out the fire, then you just end up with flame burning at the source(s) of the gas. -- HiEv 23:54, 4 January 2008 (UTC)

I would expect that even if the candle was extinguished... --Seans Potato Business 19:12, 6 January 2008 (UTC)

But a small explosion could put out the flame entirely, so then the gas would just leak without burning. -- HiEv 01:47, 10 January 2008 (UTC)

Gluing plastics together

What's a good glue for gluing plastics together? Super glue doesn't work. 64.236.121.129 (talk) 15:15, 4 January 2008 (UTC)

Not all plastics can be glued. You need to know exactly what you are trying to glue. Then have a look at this chart.--Shantavira|^{feed me} 15:33, 4 January 2008 (UTC)

Depending on the plastic and application you might consider welding it together too. --BozMo talk 12:55, 5 January 2008 (UTC)

Yes indeed, with plastic welding rods.--Shantavira|^{feed me} 17:08, 5 January 2008 (UTC)

Speed of Light

I think that Einstein held that nothing can travel faster than the speeed of light, yet his famous equation states that mass is the equivalent of energy times the speed of light squared. How can one logically square the speed of light in the "real" world? —Preceding unsigned comment added by Lasummrs (talk • contribs) 17:31, 4 January 2008 (UTC)

By multiplying it by itself:

$c^{2}=(299792458~{\rm {m/s}})(299792458~{\rm {m/s}})=8.98755179\times 10^{16}~{\rm {m}}^{2}/{\rm {s}}^{2}$

Seriously, I don't understand the question. It sounds like you're assigning some tangible meaning to "squaring the speed of light" that it doesn't have. It's a mathematical operation. It absolutely does not imply that anything is moving faster than the speed of light, if that's what you're getting at—after you square c, it doesn't even have units of speed anymore. -- Coneslayer (talk) 17:44, 4 January 2008 (UTC)

Note that you square the speed of light in a very equation that tells you you cannot go faster than the speed of light! (see Lorentz factor, which makes it pretty clear that v can never exceed c). As for why squaring the speed of light is so important—the speed of light as a fundamental constant in the universe, and so its no surprise that there is a mathematical relationship between it and many other things related to mass and energy. Doing mathematical manipulations to the speed of light does not itself violate anything—the only problems come in when you try to make a velocity larger than the speed of light. It's a specific constraint. --24.147.86.187 (talk) 19:04, 4 January 2008 (UTC)

1 kg m²/s² is the amount of energy it takes to move an object one meter against a force capable of accelerating one kilogram by one meter per second in one second, thus e=mc² converts between units of mass and units of energy. It has nothing to do with speed or any physical process. — Daniel 19:31, 4 January 2008 (UTC)

Einstein wasn't the first to say that the speed of light is constant. According to Speed_of_light#Special_relativity: 'From the work of James Clerk Maxwell, it was known that the speed of electromagnetic radiation was a constant defined by the electromagnetic properties of the vacuum (permittivity and permeability)'. AndrewWTaylor (talk) 20:14, 4 January 2008 (UTC)

It's worth pointing out what Einstein and earlier researcher's wording actually was. It was not accepted or postulated that the speed of light was constant; rather, the common expression was something along the lines of "the speed of light has the same measure no matter how you measure it," which is what was literally apparent from Maxwell's work. It's a minor distinction, but it's important in that you don't need to assume the speed of light is constant to derive special relativity. You merely need to assume the validity of the laws of physics in all inertial reference frames (and some other random stuff, depending on how nitpicky you are). Someguy1221 (talk) 20:24, 4 January 2008 (UTC)

Thanks for the clarification: I suspected I was on shaky ground with my comment... AndrewWTaylor (talk) 20:57, 4 January 2008 (UTC)

Even more specific, you can say "the speed of light is independent of the speed of that which emitted it", which is obvious if you think of light as being a wave in a medium—the speed of any wave in any medium is independent of the speed of its emitter (it only feels conceptually awkward when you start thinking of it as a particle or as a wave without a medium). --24.147.86.187 (talk) 04:08, 5 January 2008 (UTC)

The idea that light is a wave in a medium is the "luminiferous aether" theory. However, empirical evidence such as the Michelson-Morley experiment shows that the speed of light is also independent of the motion of the observer, which rules out any theory that involves an aether-like medium. Gandalf61 (talk) 08:32, 5 January 2008 (UTC)

"Rules out" might be a bit strong. It's evidence, to be sure, but not entirely dispositive -- you can argue that the Lorentz contraction, by a convenient coincidence, distorts our measurements in a way that just happens to exactly cancel the effects you'd see from the aether. Philosophically less satisfying, maybe, but it predicts the same observations. --Trovatore (talk) 08:51, 5 January 2008 (UTC)

And unfortunately for Lorentz, his hypothesis didn't account for time dilation. And then we get the Lorentz transformation, which just works a whole lot better. Someguy1221 (talk) 17:20, 5 January 2008 (UTC)

Sure, but the point is still the same. There could be an aether (read: preferred frame of reference), and it just so happens that the behavior of yardsticks and clocks conspire to prevent us from detecting its influence. It's not ruled out in principle that the question could someday come up again in a way that is experimentally distinguishible--perhaps there's some sort of interaction, as yet undiscovered, that does not behave in an (apparently) frame-independent way, and that could identify for us the preferred frame. --Trovatore (talk) 21:50, 5 January 2008 (UTC)

One question, though: Could you ever replicate general relativity with an aether theory? I've never been able to do it. Someguy1221 (talk) 08:00, 6 January 2008 (UTC)

Hey, I didn't claim there was a medium, I just said it makes things conceptually easier when thinking of light as a wave (so much so that physicists were kicking and screaming about getting rid of it because it made things conceptually bizarre—where else does one have a wave without a medium?), and in understanding why people accepted without really worrying about it that light acted in a certain way in the pre-Einstein years, that's the way you've got to think about it. And I'm sure Trovatore knows this but that's exactly where the Lorentz contraction originally came from: Lorentz's ingenious fix to preserve the aether in the face of Michelson-Morley. We now, like Einstein, find the idea of an indetectable aether philosophically unnecessary (if it is indetectable, why postulate it?), but we still use the ingenious fix. Funny how history works, no? --24.147.86.187 (talk) 17:22, 5 January 2008 (UTC)

Temperature data archives

Is there a website or database somewhere where I could find daily maximum and minimum temperatures for different locations in the united states, going back at least twenty years? Ideally something where the data could be easy sifted through (i.e. in an excel file or access database)? Thanks —Preceding unsigned comment added by 66.162.50.98 (talk) 20:29, 4 January 2008 (UTC)

Try http://www.ncdc.noaa.gov/oa/mpp/freedata.html —Nricardo (talk) 02:15, 5 January 2008 (UTC)

Photography: closing aperture

Here is a diagram. In the first part, we see what might go on inside a camera aimed at a guy with a hat. When the aperture is closed (second part) in order to limit the amount of light that enters, doesn't that mean that the outer regions are not captured by the camera? --Seans Potato Business 20:43, 4 January 2008 (UTC)

That diagram is erroneous. For a simple lens, which is what's shown, the aperture stop would have to be located at the lens, not behind it. It does not have the effect of reducing the field of view. Rather, for a simple lens, it would have the same effect as making the lens diameter smaller. It would collect less light, and produce a fainter image. (Remember that the diagram is not showing all rays. There's a ray from the subject's head through every point on the lens. Likewise, there's a ray from the subject's feet through every point on the lens. Placing an aperture stop, or making the lens smaller, just means that fewer rays get through—not that part of the scene gets cut off. In the extreme limit, the lens becomes a pinhole camera.) -- Coneslayer (talk) 20:54, 4 January 2008 (UTC)

You might also compare the aperture opening of a camera lens with the iris of a human eye. Notice that when you go from a dimly-lit space to a brightly-lit one the field of view of your eye doesn't change, even though the pupil diameter changes by a factor of five or more. TenOfAllTrades(talk) 21:15, 4 January 2008 (UTC)

Oh, that's great - thank you both! I blame whoever is responsible for AQA A level physics specification... I always said to my teacher that our diagrams didn't make sense (since I figured that light in all directions from any point to all points on the lens just as you explain... in the end I just had to memorise the diagrams without really understanding them :( ----Seans Potato Business 21:52, 4 January 2008 (UTC)

Actually, it is OK for the aperture to be positioned away from the lens, as long as it is the only aperture in the system. Specifically, as long as the lens itself is large enough that it does not act as an aperture (i.e. the edge of the lens does not cut off any ray (from any point within the intended field of view) that wasn't going to be cut off by the other aperture anyway). If you have more than one aperture in a system, you get vignetting: a darkening and eventually cutoff of the edges of the field of view. --mglg_(talk) 22:53, 4 January 2008 (UTC)

January 5

Dawkins' Selfish Gene on sex

I am reading The Selfish Gene and I'm having some problems understanding a particular argument, on page 44 paragraph 2 Dawkins writes

A gene 'for' sexuality manipulates all the other genes for its own selfish ends. So does a gene for crossing-over. There are even genes--called mutators--that manipulate the rates of copying errors in other genes. By definition, a copying error is to the disadvantage of the gene which is miscopied. But if it is to the advantage of the selfish mutator gene that induces it, the mutator can spread through the gene pool. Similarly if crossing-over benefits a gene for crossing over, that is a sufficient explanation for the existence of crossing-over. And if sexual, as opposed to non-sexual, reproduction benefits a gene for sexual reproduction, that is sufficient explanation for the existence of sexual reproduction.

I don't undertand how crossing-over or inducing mutation can benefit any gene, much less the genes responsible for the those particular behaviors. What am I missing? -- Diletante (talk) 04:10, 5 January 2008 (UTC)

Crossing over means that there can be many different neighbors from the gene pool for any particular allele. This is good since it is more likely to survive selection if it has desirable neighbors and crossing over makes this more likely. David D. (Talk) 05:49, 5 January 2008 (UTC)

Would it be correct to say that crossing over can increase the fitness of the organism and therefore the fitness of the gene for crossing over? -- Diletante (talk) 18:02, 5 January 2008 (UTC)

As regards to the inducing mutation example, have a look at genetic hitchhiking, I believe it explains a mechanism by which a mutator gene could selfishly propagate itself. Hope that's what you're looking for. Azi Like a Fox (talk) 12:53, 5 January 2008 (UTC)

I am still a bit confused on the paragraph I quoted but I can understand the mutator gene example now after reading that article. I know I am going to have to re-read the chapter a few times. -- Diletante (talk) 18:02, 5 January 2008 (UTC)

Jet injector

Are these painfree or at least noticeably less painful than needles? Google results seem to contradict . --Taraborn (talk) 08:50, 5 January 2008 (UTC)

A hygiene conundrum

I have an uncle (who's a little nutty, although fairly smart) who has this theory that he refuses to use the blow-dryers in public restrooms (you know those things on the walls that blow hot air air and sounds like a 747 taking off?) because he argues that they just recycle the dirty air in the washroom and puts all these nasty bugs on your hand. What he does is just leaves his hands wet and let them dry off by themselves. I contend that that is insane, because all air is filled with dangerous stuff that sticks to a wet hand, and it is in fact safer to not wash your hands at all than to leave them wet (a fact which I first found out about in a Slate Explainer). So he shouldn't wash his hands at all. Of course, this means that the blow-dryer also is a pretty bad way to dry your hands (since it uses air), but I argue that it least it is really hot and that the warmers inside kill a bunch of the bugs, unlike normal air.

And here we are at the standoff: assuming that regardless of safety, you really want to wash your hands after using the toilet (to get off the urine, and all), what is safer at a public restroom without paper towels: using the blowdryer, or letting your hand dry off by itself? 83.250.203.75 (talk) 09:16, 5 January 2008 (UTC)

Just wipe your hands on your pants. Nobody has time to wait for the blow dryer to do its work. SpinningSpark 11:11, 5 January 2008 (UTC)

Your uncle's reasoning is completely absurd. However, the only time I've used a blow dryer in a public restroom was once that I had my pants wet. --Taraborn (talk) 11:33, 5 January 2008 (UTC)

Using a hand dryer is almost definitely more hygenic then simply let your hands dry naturally (note it isn't just the air your pick up germs from, you're likely to be touching a number of surfaces with your wet hands potentially including the toilet door) and you may very well touch your wet, contaminated hands to your face greatly easing transfer of whatever you've picked up. There is some comparison of paper towels versus hand dryers on the wikilinked article (with paper towels usually coming across as more hygenic). (These have mostly be from studies relating to best practice in a hospital context where there is far greater concern.) On the whole, most comparisons have concentrated on the economical & environmental efficiency side of things (which hand dryers usually winning there, [7] and [8] seem to be the best for that area) although there's a lot of dubious research and claims from either side. BTW, just an educate guess but wiping your hands on your pants is probably more unhygenic then either suggestion but still probably better then leaving them wet in most cases. Of course, the biggest problem with hand dryers is that most of them take too long (there are apparently some new ones which are a lot faster but I've never seen them) and so a lot of people don't use them or at least don't use them for long enough. Of course most people don't really wash their hands properly either (if you take a look the recommended practice)... P.S. does your uncle hold his breath from the moment he enters the toilet? Nil Einne (talk) 14:00, 5 January 2008 (UTC)

Also worth noting is that the air from the drying is quite hot; most bugs don't like being heated up and dried out. While it's no substitute for an autoclave cycle, a hot air dryer will certainly take the wind out of most critters.

Of course, I like the paper towels because I can use them to open the washroom door after I'm done. About half of all people don't wash their hands regularly after using a public washroom, and the first thing they touch after doing their business is the door of the washroom. By the same token, if I'm using an older hot air dryer that doesn't come on automagically, I press the button with my elbow. TenOfAllTrades(talk) 15:20, 5 January 2008 (UTC)

Am I the only one who dries his hands by running them through his hair? Two birds with one stone is how I see it--dries my hands and keeps my hair neat. --Trovatore (talk) 21:55, 5 January 2008 (UTC)

Backcrossing

MyD88-/- mice were generated as described and backcrossed for 9 generations on an H-2d (BALB/c) background. - what's the backcrossing necessary for? --Seans Potato Business 20:15, 12 December 2007 (UTC)

When generating knockout mice, it's generally necessary to mix two different strains of mice. Backcrossing is used to reduce the genetic components of one of the founding strains. — [[Scientizzle 21:16, 12 December 2007 (UTC)

Here is an ugly graphical representation. After several generations of backcrossing, one can assume that the only non-BALB/c DNA in these mice is from the regions flanking the knocked-out gene — Scientizzle 21:21, 12 December 2007 (UTC)

That's great; thanks. So you only need to perform backcrossing when you have the knockout in a different genetic background than the one you want? Would it not be simpler to have performed the knockout in the genetic background in which you wanted it in the first place? Are some backgrounds in some way easier to use for producing knockouts? --Seans Potato Business 22:07, 13 December 2007 (UTC)

The formation of a genetic knockout mouse is moderately complex. A genetically modified embryonic stem cell of strain 1 is placed in the developing blastocyst of strain 2. In order to determine the efficacy of the implantation (and to plan subsequent breeding), it's useful to produce a chimera of strains with different coat colors. There's more information at Knockout mouse. — Scientizzle 22:22, 13 December 2007 (UTC)

But the diagram you link to uses three different strains. One cell type endures the knockout and is put into a blastocyst of another type. They then try to get the transgene in a C57BL/6 background by "backcrossing". If they (the scientists involved) had used C57BL/6 cells in the first place, they could put those cells in the same blastocyst as before, breed with a C57BL/6 mouse, and just like that, all the black offspring are heterozygous for the knockout and fully C57BL/6; no backcrossing necessary. --Seans Potato Business 13:30, 15 December 2007 (UTC)

As far as I can tell that is what this diagram shows. The founder is a chimera of C57BL/6 (abbreviated as B6) and 129/Sv cells and it is backcrossed to C57BL/6 mice. That is just two strains. However, you don't put B6 cells into a B6 blastocyst, because then its is much more difficult to identify which offspring are chimeric. Typically need your null allele to be incorporated into the DNA from a strain with a different coat colour, since this is the way you can identify your founders (129 mice are white, and B6 mice are black - chimeric mice will be a patchwork of white and black). So at N1, the first backcross, you will select mice that have one allele that is B6 and the other has to be the null allele, which is on a 129 background. Thus, at that point, you will have a 50/50 mixed genetic background. Rockpocket 19:35, 21 December 2007 (UTC)

Having a coat color chimera allows for a greater simplicity in creating a knockout strain--the chimeric progeny of a successful incorporation will be obvious, they're adorable little multicolored animals with the coat colors of both the recipient cell and the donor cell (the cell w/ the altered DNA). Those that have the color type of the donor in higher ratio, and especially if that coat color is found near the reproductive organs, are more likely to be heterozygous for the target mutation in their germ cells, which is the key. The progeny of those animals become your F1 generation if germline transmission is received. Because raising animals is expensive, and genotyping a new mutation can be difficult/expensive/time consuming, these shortcuts make it simpler to produce a strain.

One note--the mice I've been involved with ususally only use two strains, 129/SvEv cells injected into C57BL/6J, then further backcrossed onto C57BL/6J, for example. Why one would use three strains, I don't know...but using only one strain would cause large difficulties...it would be effectively impossible to determine the efficacy of any blastocyst implantation; one would be left with attempting to test every possible F1 pup for the genotype of interest. — Scientizzle 20:35, 21 December 2007 (UTC)

But aren't you assuming that the coat colour is linked to the chromosome holding the knockout? In reality, they will probably separate, being on different chromosomes, leaving a mouse with grey colour but homozygous positive (no knockout), indistinguishable from a mouse that has the same colour and is heterozygous.

Scheme:

Chimeric + White =

Grey hetero

Grey hetero + White =

Light grey hetero and light grey homo +ve

--Seans Potato Business 23:07, 21 December 2007 (UTC)

No.

1. DNA-altered ES cell from gray-coat-colored strain added to developing blastocyst of a black-coat-colored strain.
2. Resulting offspring are chimeric: stripes & patches of black and gray. The level of gray coloration is suggestive of the extent of the expansion of the altered cell into the various tissues, including the germ tissues.
3. Those mice are crossed with black mice. Those offspring will only be heterozygous for the mutation if their chimeric parent's germline cells were derived from the altered (gray) stem cell. Coat color may be, at this point, genetically independent of the mutation, as you suggested. (But! pups of variable color--half completely black and half of the litter completely gray--are suggestive of gray-type DNA in the germ cells, so that's usually a good sign.)
4. These putative F1 mice are then genotyped...and the rest is history.

The key to the whole process is that the genetically altered stem cell must end up as a progenitor to germline cells in order for the whole scheme to work. Mixing coat colors is a way to measure that efficacy. I'm not saying this is the best way to do it, but it is why it's done. If one only uses C57 cells in C57 embryos, one cannot easily know if any step (incorporation of ES cell, expansion of that cell into relevant tissue, inheritance of said cell's coat color phenotype) along the way, until genotyping the F1, has worked. — Scientizzle 23:59, 21 December 2007 (UTC)

Okay, I understand it. I'll try to make a nice SVG diagram for the article. Here's a method that I think would be better though; it requires approximately eight genotypings but no backcrossing. Is it flawed?

1. Transduce C57 cells and insert in 129 blastocyst
2. Cross chimera with C57 mice
3. Black offspring are heterozygous
4. Cross black offspring
5. Genotype approximately four males and four females to find one double negative of each type.
6. Breed as much as you like. They're all fully C57 background and so no backcrossing required. --Seans Potato Business 09:52, 22 December 2007 (UTC)

Sorry Sean, your scheme doesn't look too good. #3 is wrong because, unless the mutation of interest is on the same chromosome as the coat color gene(s), one cannot assume that the black offspring are the hets. In fact, if unlinked, black offspring have same odds of heterozygosity as non-black.

The backcrossing is necessary because any het F1s would, by definition, have ~50% 129 strain DNA. (The chimera parent has a mostly C57 body, but must have 129 sperm or eggs in order to contain the mutation.) Each F1 het would have a different profile of C57 and 129 DNA, too, so crossing them could make offspring that are between 0 and 100% genetically 129. Continued backcrossing against C57 +/+ animals reduces, each generation, the amount of (mutated-chromosome-unlinked) 129 DNA by 50%, until only the region of the altered chromosome is non-C57. This is important because different inbred mouse strains can have wide variability in many important features, including behavioral measures, drug metabolism, cancer development, etc. — Scientizzle 20:53, 22 December 2007 (UTC)

Okay, I messed up on the first scheme, but I'm not through yet!

=== Revolutionary Nobel-prize-winning method ===

1. Transduce C57 cells and insert in 129 blastocyst
2. Cross chimera with mouse of C57 background
3. 50% of black offspring are heterozygous - genotype approximately two males and two females to find one heterozygous of each gender
4. Cross heterozygous black offspring
5. 25% of offspring are homozygous negative - genotype approximately four males and four females to find one homozygous knockout of each gender
6. Breed as much as you like. They're all fully C57 background and so no backcrossing required

Stats to achieve two homo.neg. in required background: Total crossings = 2, total genotypings: 12

=== Standard Leading-brand method ===

1. Transduce 129 cells and insert in C57 blastocyst
2. Cross chimera with mouse of C57 background
3. 50% of not-black offspring are heterozygous - genotype approximately two mice to find a heterozygous negative mouse
4. Cross heterozygous negative with mouse of C57 background
5. Offspring are all about 75% C57 and 50% are heterozygous - genotype approximately two mice to find a heterozygous negative mouse
6. Repeat steps 4 and 5 10 more times to achieve mice with 99.98% C57 genome and genotype approximately two male and two female mice to find one heterozygous mouse of each gender
7. Cross these two mice to achieve 25% homozygous knockout mice with 99.99% C57 genome - genotype approximately four males and four females to find one homozygous knockout of each gender

Stats to achieve two homo.neg. in required background: Total crossings = 13, total genotypings: 32

Am I right in my understanding of the backcrossing procedure and/or my assertion that reversing the roles of the C57 and 129 mice is a sound suggestion? --Seans Potato Business 16:10, 25 December 2007 (UTC)

Not really. Your idea of reversing the roles of C27 and 129 is flawed because of the dominance relationship of alleles of the tyrosinase gene. The Tyr⁺ allele is dominant to the Tyr^- allele. 129 mice are Tyr^-/- which makes them albino. C57 mice are Tyr^+/+ which makes them melanic. At step 2, all the offspring from the cross will be melanic (either Tyr^+/+ or Tyr^+/-) Therefore there is no way of knowing, by looking at the offspring from step 2, whether the transgene went germline in the chimera. As Scientizzle notes above, the key to the whole process is that the genetically altered stem cell must end up as a progenitor to germline cells in order for the whole scheme to work, your suggestion does not help us determine whether that step has occurred. Rockpocket 05:34, 29 December 2007 (UTC)

Thinking about this further, I fear I have given you misleading information. While my points are correct in reference to the original 129/SvJ strain, it turns out that typical 129 available mice today are actually from a congenic substrain called 129/Sv-Sl/+,+^p,+^c. The coat colour in this mouse is from a mutation at the Steel locus, giving the mouse a "steely" white/grey colour. Importantly, this is dominant to the C57 Steel allele, so if one were to use this substrain then my criticism is no longer valid. However, there is another technical problem, and that is that pretty much all the embryonic stem cells lines widely available (in which you need to make your knock-in/out) are from the 129 strain. Again, there are a number of technical and historical reasons for this. If you could get adequate C57 ES lines, then I think your strategy would work. However, as with most revolutionary Nobel-prize-winning methods, you are not the first to think it up - the Gene Targeting Facility at the University of Virgina already offer this service using their own source of C57 derived ES cell lines. [9] Rockpocket 09:33, 29 December 2007 (UTC)

Okay, thanks for the insight. I've made a schematic for the backcrossing article. Comments? --Seans Potato Business 14:11, 1 January 2008 (UTC)

I don't see anything at that link, I'm afraid. Rockpocket 03:06, 2 January 2008 (UTC)

Apparently you need to click on another link to get to the actual file. It confused me for a while, too, since the page you get at first looks just like a typical parked domain.

Anyway, the picture seems basically correct (and rather funny, too) to my untrained eye. It's somewhat confusing though — I had to look at it several times to figure out which mouse was the offspring of which mating. Perhaps it would be better to use more whitespace, and to draw an explicit family tree with lines connecting each mated pair and pointing to each of their offspring. —Ilmari Karonen (talk) 17:24, 2 January 2008 (UTC)

Here is Mk II. Is it any better family-tree-wise? Do you still think it needs white space, and if so, between which elements exactly? Your input is valuable and appreciated. ----Seans Potato Business 00:38, 3 January 2008 (UTC)

Yes, that's definitely better. —Ilmari Karonen (talk) 23:40, 5 January 2008 (UTC)

That's weird...we answered this question on Dec 12th. What's it doing back here again? The OP's signature is even from Dec 12th. SteveBaker (talk) 21:04, 21 December 2007 (UTC)

Sean brought it back for round 2... — Scientizzle 21:09, 21 December 2007 (UTC)

RockPocket brought it back for Round 3 now? Are we attempting to make this the thread that never dies? Should we give it its own subpage? ;-) Nil Einne (talk) 08:53, 29 December 2007 (UTC)

Not me. This is Sean's baby. Rockpocket 08:57, 29 December 2007 (UTC)

Ooops sorry then, I thought it was you who brought it back with your response but I guess Sean brought it back because he'd received no response Nil Einne (talk) 09:08, 29 December 2007 (UTC)

Aha! I hadn't tracked it down, but this explains why the RD archiving script has been complaining on and off for the past month or so about an "orphaned" entry from December 12 that it declines to archive because it's out of sequence. (Lord knows what the poor script will do now that the beleaguered orphan has wandered into a completely different year...) —Steve Summit (talk) 14:08, 5 January 2008 (UTC)

• Final round! I just want feedback on whether my diagram is fit for use or needs tweaking. --Seans Potato Business 13:50, 5 January 2008 (UTC)

No I'll kill myself if this thread ends! (j/k) Nil Einne (talk) 14:01, 5 January 2008 (UTC)

Three minutes into the fourth round... K.O.! Any comments re: my diagram at backcrossing should be directed to my talkpage. Thanks for all the explanations, everyone! --Seans Potato Business 19:09, 6 January 2008 (UTC)

Is cannabis good for you?

In order to settle a dispute I have with User:Pundit over Cannabis Culture magazine as a source for the article on Chocolate Thai, I request that anyone address the question: Is cannabis good for you? It's important because the claim was made by one of the editors of Cannabis Culture magazine in this forum thread, suggesting they're not a reliable source on anything, including cannabis. Zenwhat (talk) 16:35, 5 January 2008 (UTC)

Isn't this pretty much impossible to answer? Is morphine good for you? Yes, if you're in a lot of pain it can surely help, but... Well, you get the point. What exactly are you asking about, the health benefits of smoking pot? ;) Aeluwas (talk) 16:45, 5 January 2008 (UTC)

Let me add that I don't think this question is in any way relevant to our dispute. I myself do not smoke marijuana and I believe the health risks (especially in case of asthmatics) are bigger than the benefits. But I think that this kind of a question is only for each of ourselves to ask and no poll can help. Pundit|utter 16:47, 5 January 2008 (UTC)

I'm asking: Is there any reliable evidence to suggest marijuana may have negative health effects? The editor of Cannabis Culture magazine strongly said no. They literally said, "Cannabis is good for you," as if it were a vitamin or essential nutrient. They appear to push fringe theories about Cannabis and I'd like to confirm this.Zenwhat (talk) 17:01, 5 January 2008 (UTC)

I am pretty sure you can find both information on general negative effects (AFAIK possible increase of allergies) as well as long-term influence on psyche (I recall an article I read in New Scientists or something like that). But in the question as you ask it I would assume the thesis is not that there are no negative effects, but rather that the positives are bigger. In any case, the question is so subjective that we all can answer it to ourselves, as Aeluwas pointed out (health is not the universal value to many people and some prefer e.g. pleasure - it is difficult to define "good" in this respect). Pundit|utter 17:10, 5 January 2008 (UTC)

Jogging is good for you, unless you slip on ice. Democracy is good for you, unless you elect a moron. Medicine is good for you, unless something goes wrong. Water is good for you, unless you are drowning. "X is good for you" is not a rigorous statement by itself, it can't be easily evaluated and can't be the sole basis as to whether a source is good or bad. --24.147.86.187 (talk) 17:28, 5 January 2008 (UTC)

Pundit: That's my point. There is conflicting research. The idea that inhaling tar -- even if it's cannabis tar -- is "good for you" is absurd. Specifically, THC may have some medicinal and therapeutic effects if used in a certain way, as prescribed by a doctor, but it is not a vitamin and excessive recreational use of cannabis is likely unhealthy. As I said in that thread, even if THC is an anti-depressant, the recreational use of anti-depressants is widely acknowledged by Psychologists to be mentally unhealthy. They dispute that claim and endorse recreational use of cannabis as being beneficial to health, which seems to violate WP:FRINGE. According to them, everybody should smoke weed because "Cannabis is good for you." Zenwhat (talk) 17:34, 5 January 2008 (UTC)

Sure, you're right. It is just, as I wrote to you before, that in NRA publications you will also see a glorification of possessing guns, although independent research may show that having a gun increases the statistical likelihood of being shot. Also, I think what they're doing is reporting ONLY good sides of cannabis - just like Men's Health recent article on why is drinking beer good for health (and their objective was not to go into negatives). Nevertheless, just "being good for someone" is a vague category and not possible to evaluate scientifically for or against. Pundit|utter 17:38, 5 January 2008 (UTC)

Zenwhat, using a single line of such an ambiguous and unrigorous nature as a way of trying to discredit an entire publication as a reliable source is absurd. The line doesn't imply that the editors are unaware of potential health detriments nor does it imply that they think it is a vitamin or that "everybody should smoke weed". You're being a little silly here in your zeal to discredit a source, especially since you are not taking your claims from the source itself but a forum post made by one of the individual editors. (I honestly don't know if they are a good source or not, but this is not the way to determine it.) --24.147.86.187 (talk) 19:27, 5 January 2008 (UTC)

Dear anonymous editor, don't call your opponents silly. It is a personal attack and in some cases qualifies for blocking. Also, consider registering an account - it is much easier to talk with somebody known at least from their nickname and edits history. Pundit|utter 22:30, 5 January 2008 (UTC)

Opponents? We're all here to build the wiki, not to slug things out. This isn't a forum. 24 merely pointed out that you seem to have got a bit carried away in your zeal to discredit a source, and have strayed into saying some rather silly things. That is not in any way a personal attack. (Oh, and many of us around here know 24 from their IP and edit history, but I would personally find your comments unpleasant even if I were not familiar with the person they were aimed at) Skittle (talk) 23:17, 5 January 2008 (UTC)

If you read the discussion above, which I'm assuming you didn't, you'd see that it would be quite hard for me to be zealous in discrediting a source, as I was the main opponent of Zenwhat. "Opponent" is a typical term used in academic discourse for a person taking a different (opposing) stance (read the definition). Saying that somebody is a little silly is a personal attack and is a personal remark, rather than a remark about a statement. I disapprove of such behavior. In the same time I humbly accept your judgment of my comment as being silly, but I don't think such a judgment as yours is particularly constructive either. Of course, any user has a right to remain anonymous. I don't think it simultaneously means that registered editors should be disallowed to encourage IP users to register. You may want to read why is it a good idea to log in. Pundit|utter 14:27, 6 January 2008 (UTC)

Now you're being silly. If saying someone is acting silly is a personal attack, then we're not going to get very far. The thrust of my argument had nothing to do with whether someone was being silly or not, incidentally. And I've edited on here for a lot longer than you have (almost four years, if you can believe it!); I log in when I need to. I should probably get a bumper sticker that says "My Other Account is an Admin" but that'd be a bit silly, no? ;-) If you're around here long enough you'll probably get to the point where you want to log out too. :-) --24.147.86.187 (talk) 21:27, 6 January 2008 (UTC)

Perhaps you have trouble recalling what you wrote. You were not describing an action, but a person, and you should know there is a difference. Calling an argument silly is just a bad rhetoric practice. Saying that a person is being silly is close to an insult, and definitely does not enrich the argument in any way, while may be unpleasant for the other party. Although I agree with the argument you made, I still disapprove with your way of addressing Zenwhat. I realize that being civil is sometimes difficult and, as an administrator on another project with some experience I honestly admit that it is occasionally hard for me as well. But recalling your big experience to justify the manner of speech in which you're calling your fellow editors silly (Merriam-Webster: weak in intellect : foolish b: exhibiting or indicative of a lack of common sense or sound judgment) is working against you - I would expect more civility from an experienced editor than from a newbie. And if you really are an administrator in the project, as you suggest (and which I doubt a little, for I can't see any reason why would an admin be ashamed to reveal his/her identity) then you should serve as an example to other editors. The fact that you have edited Wikipedia longer than me is something I very much respect and have in high regard. But respect is also something that bases more on behavior, than just on time. Pundit|utter 23:34, 6 January 2008 (UTC)

Can you see how silly you're being? You just spent 250 words trying to discuss my usage of the word "silly". You've devoted over 450 words to this particular topic so far. That's silly. Lighten up! :-) Collaborative projects go down the tubes when people spend more time talking about how to have a discussion rather that just having the discussion itself. --24.147.86.187 (talk) 01:56, 8 January 2008 (UTC)

I devoted all these words not to discuss your usage of words, but perhaps to encourage you to civilize yourself, you know, just a little :) But you certainly are right that there are better things to do. Your usage of smileys was enough to lighten me up, so have a good night and see you around ! Pundit|utter 05:20, 8 January 2008 (UTC)

The reference desk is not a soapbox. This question is not rigorous and depends entirely on the individual interpretation of "good." Nimur (talk) 01:19, 6 January 2008 (UTC)

No, it is definately not good for you. As well as causing psychosis, it is more carcinogenic than tobacco. See this page and the links to the right: http://news.bbc.co.uk/1/hi/england/cambridgeshire/7153698.stm (Its not illegal just because governments or the police are simply mean, is it?) 80.0.105.180 (talk) 19:56, 7 January 2008 (UTC)

Extend my antenna

My radio doesn't pick up a signal very well. Can I just attach a long wire to the radio's extendable antenna and drop it out my window? or attach it to my window screen? In general, will connecting more metal to my antenna improve matters?

Thanks! --Mike 17:32, 5 January 2008 (UTC)

Theory says "no", but I wish I had a nickel for every time reality made a monkey of theory (often there are too many variables). Try it. There is no way it can harm your radio. If the signal gets stronger, then great. By the way, inside or outside will make little difference, usually. --Milkbreath (talk) 18:33, 5 January 2008 (UTC)

The extendable antenna on most radios is for FM, and extending it to a great length will probably not increase the clarity of reception. A shortwave band receiver or AM receiver might benefit from a longer antenna if you have a way to attach it to the appropriate antenna terminal. Edison (talk) 20:22, 5 January 2008 (UTC)

An antenna increases the gain for a particular (range of) frequencies in a particular direction.

If you contect the wrong antenna, you will degrade the signal. If you connect the right antenna you will enhance the signal. If you are working at random, you wiil almost ceartainly degrade the signal instead of enhanceing it. To answer yojr question, we need the following information:

• transmissiion band
• polarization
• your location
• &location of the transmitter.

A properly-designed antenna system can add more than 40dB to your link budget. -Arch dude (talk) 01:23, 6 January 2008 (UTC)

There are such things as random wire antennas. Anyway, whatever theory says, I have had good experiences with improving marginal FM reception with the simple addition of a very long wire to the antenna. Then again, I've also had surprisingly good results from the addition of a coat hanger and assorted kitchen utensils, tweaked and repositioned until reception was adequate. It was an ugly kluge indeed, but it did make the difference between static and music at the time. —Ilmari Karonen (talk) 00:44, 7 January 2008 (UTC)

If you want to improve the reception of a specific frequency, you can size the antenna according to the equation & diagram at Dipole antenna to optimize for just that frequency, without significantly worsening other frequencies. jeffjon (talk) 13:35, 7 January 2008 (UTC)

Orbital planes

Our solar system has a bunch of things going round the sun, all on the same (ish) 2D plane. Is is possible, and theoretically viable for life given right conditions, for a system's planets to not be all in a 2D plane but all over the place at all kinds of degrees up/down, a bit like the basic atom icon? Lady BlahDeBlah (talk) 18:08, 5 January 2008 (UTC)

Well, who knows what may be possible, as we only have one example, we can't draw any firm conclusions. However, the view is that such a system would be too unstable for life to be likely. Planets interacting with each other would cause huge changes in their orbits and consequently huge changes to their environmental conditions. It is even possible that a planet could be thrown out of the system altogether. I have seen this question discussed in New Scientist and elsewhere but I could not immediately find an article that directly addresses it. However, you will see from the Planetary habitability article that life needs a reasonably stable planet (or so it is thought). You might want to look at the Extraterrestrial life article also.

SpinningSpark 18:39, 5 January 2008 (UTC)

We don't only have one example; we have eight planets all aligned to each other. They're even rotating the same direction around the sun. This would be extremely unlikely if there wasn't a reason for it. Of course, it's probably possible that something like another star passing nearby could throw all the planets out of whack, and I suppose you could get a whole lot of dwarf planets the same way we got Pluto.

We do only have one example of abiogenesis, and thus don't really know what it takes for life to begin. Any unlikely things about earth could just be because it's required for intelligent life. We do know that life can evolve to survive most anything you can throw at them, so the planets would definitely be viable for life, but there's no guarantee they can start it on their own. — Daniel 18:55, 5 January 2008 (UTC)

What is that reason? Why couldn't Mars be above us, Venus far below and to the right and Jupiter perpendicular? Makes kid of an artistic 3D sense in my head, but I have a habit of fudging the laws of everything mentally before I hit the proverbial roadblock. I tried to find it and it's a bit...baffling. Lady BlahDeBlah (talk) 19:03, 5 January 2008 (UTC)

Any rotating gas cloud that undergoes gravitational collapse will tend to flatten into a disk. This is a consequence of the conservation of angular momentum coupled with internal friction. The planets (and most everything else) formed out of such a disk so they can be expected to all lie in roughly the same plane and be travelling in the same orientation. Dragons flight (talk) 19:17, 5 January 2008 (UTC)

(edit conflict answering Daniel) I meant one example of life, not one example of planet. I know the system described is highly unlikely for astrophysical reasons but I was trying to answer the question as put. I think my point was there is no long term viability, so as you say, life is unlikey to evolve there. But if something was to visit, sure it might be ok there for a while at least. SpinningSpark 19:07, 5 January 2008 (UTC)

By long term viability, do you mean life that gets there would die out? As I said before, life can survive a lot. — Daniel 20:48, 6 January 2008 (UTC)

It seems to me that harmful interactions between planets are less likely if orbital inclinations vary widely! — Even if there's no primordial disc, I imagine the system would tend to converge to a plane through exchanges of angular momentum; though that raises a question: why do globular clusters (which contain the oldest stars) exist? —Tamfang (talk) 07:43, 7 January 2008 (UTC)

Gravity and planetary bodies

Are there any instances, and is it theoretically possible, for two roughly equally sized planetary bodies to orbit around each other? Say, two planets as they orbit their star or two satellites as they orbit their planet/moon? As well, if it is possible, what gravitational implications would occur to the planetary bodies and any satellites orbiting them? -67.34.186.30 (talk) 19:01, 5 January 2008 (UTC)

Certainly; this is the case with Pluto the dwarf planet. It's called a Binary system. Daniel (‽) 19:15, 5 January 2008 (UTC)

(edit conflict) Yes, in fact the Earth and Moon are near enough to each other in size to be considered a double planet by some rather than a planet and moon. The gravitational effect would be what the moon does to us - tides. Saturns moon Janus has another interesting variation (possibly what you meant). It shares an orbit with the moon Epimetheus. One slowly catches up with the other over time. This does not result in a collision as you might expect. What happens is they orbit each other for a brief while until they have exchanged orbital positions. This results in what was the faster one now becoming the slower one. What was the slower one now chases the other around the entire orbit until it catches up and the whoe thing starts over again. SpinningSpark 19:22, 5 January 2008 (UTC)

Thank you very much. -67.34.186.30 (talk) 19:53, 5 January 2008 (UTC)

Asteroid 90 Antiope is remarkable in that its two members are nearly equal in size (and rather big). —Tamfang (talk) 07:55, 7 January 2008 (UTC)

Sex

Which sex positions are most and least likely to result in pregnancy, assuming there is a difference? --67.185.172.158 (talk) 21:13, 5 January 2008 (UTC)

Well oral and anal sex tend to be ineffective at creating babies. Dragons flight (talk) 21:26, 5 January 2008 (UTC)

1 where the semen doesn't enter the cervix. Neal (talk) 21:51, 5 January 2008 (UTC).

A Google search turned up this site recommending the missionary position for maximum chance of pregnancy: [10]. I can't vouch for the website, but their logic seems sound. --Allen (talk) 22:42, 5 January 2008 (UTC)

My searches also suggest the missionary position or entry from behind (i.e. doggy position, n.b. in case it isn't obvious this means vaginal entry) are rcommended[11] [12] [13]. However an important point as mention in some of the sources is whether it has any real relevance. Sure it may increase chances of conception but by how much? 2%? In reality it's probably better to concentrate on being comfortable, enjoying the sex and mutual pleasure since this may very well in itself increase the chance of conception (improved arousal and many other factors combined) and it may also increase the frequency the partners have sex (which of course increases the chance of conception too) and will probably end up having a far greater percentage change in the likelihood of conception. If a couple is really having problems conceiving, they probably should see a specialist who will be able to discuss ways to increase fertility and I strongly suspect the position won't be a big consideration Nil Einne (talk) 08:44, 6 January 2008 (UTC)

One thing that's important to keep in mind here is that, while strictly speaking the answer doesn't change depending on its purpose, the way to think about the answer does change. If you're trying for a baby then every percentage point of improvement is all to the good; if a pregnancy would be a disaster then relying on a small difference in probability is a terrible plan. That's probably the reason that organizations trying to keep the public informed on such matters shy away from this topic -- they don't want to promote the idea that woman-on-top counts as a birth control method. --Trovatore (talk) 23:48, 5 January 2008 (UTC)

One that starts with you and/or your sleeping partner in the chemist buying some good-quality condoms is a effective position for not getting pregnant. Use a condom in the right way and the chance of pregnancy is very low. May I recommend the birth control pill too (although that won't protect against STIs)? -- _{Escape Artist Swyer} ^{Talk to me} _{Articles touched by my noodly appendage} 00:45, 6 January 2008 (UTC)

Solo masturbation is the most effective sex position for avoiding pregnancy Nil Einne (talk) 08:31, 6 January 2008 (UTC)

There is a mention of this question in the Sex Positions article although not terribly informative, it does debunk some myths. SpinningSpark 12:13, 6 January 2008 (UTC)

The varied colouration of Feral Pigeons...

I was just been reading this article, which was recently added to our Feral Pigeon article as a reference when the thought stuck me - could another reason that Feral Pigeons have never reverted to their ancestral 'classic' Rock Pigeon colouration be that the various shades of browns, greys and whites and differing plumage patterns that we see on our street pigeons (which the article supposes would single out the birds to predators, as compared to the original colouration) are not particularly any more or less noticeable from the air against the varied backdrop of the city vs. the original colouration? After all, the plumage patterns and colours evolved in the 'classic' species in order to camouflage it in a very specific *and* very different environment. Any thoughts? --Kurt Shaped Box (talk) 22:59, 5 January 2008 (UTC)

This would presume that there are enough predators of pigeons in cities for there to be a selective pressure in colouration. I'm not aware of there being any significant predators of urban pigeons (which is why there are so many of the little bastards). My professional opinion would be that it is a result of a combination of selectively bred birds polluting the natural colour morph, combined with genetic drift of pigment genes, because there are few natural predators that would select against them. Rockpocket 09:07, 6 January 2008 (UTC)

I know that various hawks prey on feral pigeons - to what extent, I'm not entirely sure (any idea how common urban hawks are, in general?). Interestingly (to me), whilst the feral pigeons still retain a fear of urban birds of prey (and scatter as soon as they notice one in the sky), they never seem to see it coming when an urban gull decides that it would like some fresh meat. It's not a widespread thing (it may only be the odd individual gull that bothers to hunt when discarded human food is so readily available) but the pigeon will happily continue sauntering around and pecking at the ground - until the gull is literally stood behind/next to it and ready to seize it by the throat and shake it to death. --Kurt Shaped Box (talk) 17:39, 6 January 2008 (UTC)

January 6

Gear Math

Is there a way to rig up a mechanical system so one gear, which is spun by something, causes another gear to spin only when it changes speed? That is, to differentiate one gear's motion and put the result in another one? Black Carrot (talk) 03:09, 6 January 2008 (UTC)

I am probably misunderstanding your question, but it appears that you want one gear to spin. Another gear will be connected to it through some sort of device. When the first gear changes speed, the second gear moves. As long as the first gear maintains the same rotational speed, the second gear remains stationary. This is what a tachometer (as well as a speedometer) does. Normally, we use a little stick that rotates around a marked dial to show that the speed has changed, but you could replace that with a gear that turns one way or the other when the speed changes. -- kainaw™ 03:16, 6 January 2008 (UTC)

Agreed. I believe that the usual way a tachometer works is by spinning a magnet inside a copper cup, causing the latter to twist against a spring. This is an example of the Hall effect. Bovlb (talk) 05:02, 6 January 2008 (UTC)

Actually, it's an example of eddy current-induced drag.

Atlant (talk) 22:46, 6 January 2008 (UTC)

That's not really mechanical differentiation, though - it uses an electromagnetic interaction property which provides the derivative with respect to time. Nimur (talk) 20:41, 6 January 2008 (UTC)

Yes, there is. Edison (talk) 05:05, 6 January 2008 (UTC)

The flyball governor?

Atlant (talk) 22:46, 6 January 2008 (UTC)

I believe the great mechanical analog computers of the early- to mid-twentieth century (in particular various differential analysers) had both integrators and differentiators, so presumably the answer is yes. —Steve Summit (talk) 01:39, 7 January 2008 (UTC)

The core component of a mechanical differential analyser is the wheel-and-disc integrator, invented by James Thomson, brother of Lord Kelvin. The way this device works is described here. Its principle is quite straightforward - the disc rotates at a constant speed (in the simplest applications); the wheel is moved radially across the disc so that its contact point with the disk is at a distance y(t) from the centre of the disc; the distance turned by the wheel (assuming no slipping) is then proportional to $\int y(t)dt$. A practical implementation presents various difficulties, such as ensuring that friction between the wheel and the disc is sufficient to turn the wheel smoothly without slipping, but not so great that it affects the turning speed of the disc. Gandalf61 (talk) 11:58, 7 January 2008 (UTC)

Flavour Sense Perception?

Im really confused about what flavour actually is. As far as i understand it's formed from mainly the sense of smell and taste but also others. So is it just a combination of sensory impressions/can flavour be seen as a seperate sense perception at all? If only the smell of a substance were perceived (say), what would be the qualitative difference between the flavour and smell of that substance, if any? Where is it interpreted in the brain as opposed to smell, taste etc? If I hold my nose when I eat bad food will the taste be less intense64.230.97.161 (talk) 06:17, 6 January 2008 (UTC)?

Flavour is the combination of taste and smell. As far as I'm aware there is no part of the brain dedicated to flavour rather it is just the combination of the two perceptions. Haven't you ever smelled something without eating it before? If you've had a cold and a blocked nose, you may have a rough idea of what eating without smell is like. did you read flavour? Nil Einne (talk) 08:29, 6 January 2008 (UTC)

(ec) Flavour can be thought of as the qualitative summation of olfaction and gustation. Each of the senses can be used to detect a chemical independently, giving you the smell and the taste, respectively (certain drugs, for example, can inhibit your ability to smell or taste without effecting to other). While we often think of flavour as being mostly taste, in fact smell plays a pretty important role, as anyone with really bad nasal congestion can tell you when when they are eating a nice meal. Thus there is a qualitative difference between the flavour and taste of that substance. Its also worth noting that there are only 5 basic tastes, but there are many hundreds of different receptors in the nose to detect smells, so while the taste plays an important role in determining the gross flavour, the subtleties are encoded by the smell. Again, this is why food tastes bland with a bad cold.

As Nil Einne notes, there is not a distinct brain region for detecting flavour, but there likely is a region where the projections from the olfactory bulb converge with neurons from the gustatory system to encode flavour. The very little is known about how and where "cross-talk" occurs between different sensory systems, but this is likely to be an area of research in the future. Rockpocket 08:55, 6 January 2008 (UTC)

The holding my nose for bad food thing was more of a joke but the way I read your comment RockPocket does this mean that the taste of the food will remain the same with or without smell, but without it will lose its flavour, which doesn't intensify the taste of the food but adds a different kind of sensation altogether?70.49.136.117 (talk) 21:32, 6 January 2008 (UTC)

Yes, the taste will remain the same, and the flavour will not be lost exactly, but will be different and less "flavorful", because the smell contribution to determining the flavour will be missing. And yes, smell does add as a different sensation. There are experiments you could do where feed similar tasting things to people while they hold their nose. They may not be struggle to determine the difference between then because the subtle difference in flavour is actually perceived by the nose, rather than the taste buds. Rockpocket 21:46, 6 January 2008 (UTC)

Immunoprecipitation(IP)

Hi, can anyone tell me which method to detect and analyse protein protein interaction provides quantitative data? Ie. , regarding the strength of the binding. —Preceding unsigned comment added by 165.21.155.114 (talk) 08:28, 6 January 2008 (UTC)

Wikipedia has an article on this subject here. SpinningSpark 12:19, 6 January 2008 (UTC)

Did the answer need to be a variation of immunoprecipitation or will some other assay suffice? ----Seans Potato Business 12:23, 6 January 2008 (UTC)

If so, see immunoprecipitation. --JWSchmidt (talk) 15:36, 6 January 2008 (UTC)

Quantitatively measuring the 'strength of binding' of two proteins is another way of asking how to measure their dissociation constant, or K_d. Our article (unfortunately) doesn't yet discuss the many, many methods that may be used to measure this constant. You might find some useful hints, however, if you look up Scatchard plots on Google. (Again, our own article on the Scatchard equation is a bit thin.) TenOfAllTrades(talk) 16:32, 6 January 2008 (UTC)

Baby Dolphins and Fur?

I've heard that baby dolphins (calves) are born with a layer of fur that they lose after a few days. Is this true? And are there any photos of calves with fur available to see on the Internet?

Thank you for your help,

--91.104.10.242 (talk) 10:10, 6 January 2008 (UTC)

No, and no. Though they do have some blubber. Fur wouldn't be of any use to them. Maybe you are thinking of seals.--Shantavira|^{feed me} 15:36, 6 January 2008 (UTC)

According to this site dolphins have "a few scattered bristles [of hair] about the lips or often present only in the young." Think outside the box 11:14, 7 January 2008 (UTC)

When is the on average coldest day each year in the northern hemisphere?

I dislike winter and look forward to and internally celibrate the day of earliest sunset. Another celibration day would be the day which is, on average, the coldest day of the year. Does anyone know when this is? I would calculate it myself but have been unable to find suitible historical temperature data for past daily temperatures that would not take several hours to prepare for use. (Note that even though averaging the temperature of each calendar day for past years for one particular geographical point could still give a noisy 'signal', fitting a curve to this data should allow estimating the day which is the minima). I'd also be interested in what the hottest day is, and when these occur in the southern hemisphere also. Thanks 80.0.126.128 (talk) 16:13, 6 January 2008 (UTC)

Hottest weather follows longest day says that "the hottest or coldest weather lags behind the summer or winter solstice by about a month or two." Earth and Sky also has several articles that talk about the earliest sunrise. Hope that is somewhat informative. -- Diletante (talk) 18:11, 6 January 2008 (UTC)

As far as I'm aware there's no average day, it depends on the area. You could I presume resonably easy work out the average day for your area by taking a look at the mean daily temperatures for your area over a period of say 100 years or whatever is recorded Nil Einne (talk) 18:56, 6 January 2008 (UTC)

"I would calculate it myself but have been unable to find suitible historical temperature data for past daily temperatures that would not take several hours to prepare for use." 80.0.133.83 (talk) 23:34, 6 January 2008 (UTC)

As it would (several hours) for most anyone else. hydnjo talk 02:12, 7 January 2008 (UTC)

The coldest day would certainly be different depending on where you are—altitude, water, latitude, and terrain would all affect it. The northern hemisphere is a big place, so you couldn't even come up with a perfect average, because you'd have to limit the number of samples. But poking around in the internet seems to put it sometime in middle to late January, which surprises me; I'd always thought February was worse, but maybe that's just because I'm that much more sick of winter by then. If you want to plan a party, you could do worse than to hold it on January 14, St Hilary's Day, which, according to the Bablake weather station in Coventry, England, is the coldest day according to folklore. --Milkbreath (talk) 16:19, 7 January 2008 (UTC)

Thank you, your link to Bablake station gives details of a typical year: Warmest day of the year 28th July; Warmest night of the year 28th July; Coldest day of the year 16th February; Coldest night of the year 20th February. From http://bws.users.netlink.co.uk/typical%20year.htm I expected the coldest day to be in January, and where I live spring seems to begin on Valentine's Day on the 14th. February: apparantly I was mistaken. There is however almost a 6 month gap between the coldest and hottest day - it is out by about 12 days I think. I have downloaded some other historical data from the site and will be looking to see if I can estimate the average coldest calendar day myself. 62.253.48.92 (talk) 19:14, 7 January 2008 (UTC)

eyes above mouth

why do animals commonly possess eyes above the mouth? ie: what is advantageous in this. are there examples to the contrary? (the part of the nose seems clearer: smells waft up into the nostrils to be identified before ingestion) 3170s228 (talk) 17:39, 6 January 2008 (UTC)

it occurred to me immediately after asking that food & saliva would tend to gravitate downward & mess up your vision. I'm still curious about alternate explanations & examples. 3170s228 (talk) 17:42, 6 January 2008 (UTC)

It's good to be able to maintain vigilance while eating. It would be disadvantageous to have your view blocked while you were eating allowing predators and rivals to sneak up on you. Generally the higher your eyes are, the more you can see. -- Diletante (talk) 18:05, 6 January 2008 (UTC)

The "eating" function of the mouth is the beginning of the digestive system, which goes down. As species become increasingly cephalic, why have the mouth move up past (and throat go around?) the eyes, which are primarily just an extension of the brain? DMacks (talk) 21:19, 6 January 2008 (UTC)

Perhaps I should make the keen observation that food is often on the ground. Mac Davis (talk) 23:46, 6 January 2008 (UTC)

Another keen observation would be that most organisms move forwards to collect this food (wriggling on their belly), and primitive organisms (along with many others) are most interested in making sure they're in the dark (my favorite flatworm). Thus, it makes sense to have the mouth at the front, and the eyes "on top." If the worm evolves to stand up one day, it would just be easier for the eyes to remain above the mouth. Someguy1221 (talk) 16:06, 7 January 2008 (UTC)

I can't imagine a situation in which it would advantageous to have your eyes below your mouth. You'd inevitably be blocking your view while eating. What would the benefit be? If something has only strong detriments and no strong benefits, it's not going to be favorably selected for, obviously. --24.147.86.187 (talk) 01:11, 8 January 2008 (UTC)

Old cartoon mocking Mendeleev's system

Hello,

my chemistry teacher once told us that Mendeleev was mocked by some scientist in his days because of his proposed periodic system. The reason would have been that he had "dumpster groups" in his table, certain sets of elements that he had just put together because he didn't know where else to put them. My teacher claimed that they even made cartoons depicting Mendeleev sitting in his own dumpster, surrounded by elements, mockingly suggesting the question" what other elements will he put in there?"

Does anyone know more about this? Seeing such a cartoon would be very nice! Thanks! Evilbu (talk) 19:56, 6 January 2008 (UTC)

Hmm... I've never seen it, though I'm no expert on Mendeleev. You might try e-mailing this guy—he wrote the most definitive biography of Mendeleev and he's a really nice guy at that. He has at least one cartoon about Mendeleev in his book though it is related to his appointment in the Russian Academy of Sciences. --24.147.86.187 (talk) 21:14, 6 January 2008 (UTC)

January 7

DIY electric quadricycle

As my final year electronics project I've been thinking about making an electric quadricycle that looks like a skateboard with a box below it and 4 very over sized wheels. However, I'm having some questions on the feasibility of this, and I would appreciate any input or other examples of similar projects.

1. I want to reduce the mechanical components to the minimum so I'm thinking about putting the motor and a epicyclic reduction gear inside the wheel assembly, eliminating the drive train. Is this a good idea? Or should I really reconsider having one huge motor and lots of shafts? I've found a motor suitable for this use but I don't know where to find the epicyclic reduction gear nor suitable wheels. The ones on Jaycar are like the Lego ones and I really doubt it can take that amount of torque. Does anyone here know where to find these things in New Zealand, or if that's really hard, Australia?
2. Aside from the drive train the other mechanically complex part is the turning. Will driving the motors at different speed (ie. faster on the outside wheels and slower on the inside wheels) work in real life, or do I need to actually rotate the wheels?
3. I want the vehicle to have similar performances to a bicycle, and according to Human-powered transport "The average "in-shape" cyclist can produce about 3 watts/kg for more than an hour (e.g., around 200 watts for a 70 kg rider)", so do 4 of the above-mentioned motors (1 in each wheel) offer enough power?
4. Can I do regenerative braking with that motor? What would I need for a regenerative braking circuit?
5. The planned range for this vehicle is somewhere between 1-3 hours (assuming 10km/h, 10-30km). That makes 200Wh at 12V, but normal lead acid batteries are too heavy for this use. Where can I get NiMH or Li-ion battery packs at this size?

Also, any other suggestions on reducing the complexity or the cost are also welcome. --antilived^{T | C | G} 00:00, 6 January 2008 (UTC)

Why not go overboard and a use a motor on each wheel? You could use that for directional control as well.--TreeSmiler (talk) 01:24, 8 January 2008 (UTC)

I am planning to use a motor on each wheel, which is basically what question 1 is about. Does varying speed of the wheels on the different sides work satisfactorily or will it put a lot of wear on the tyres or something? --antilived^{T | C | G} 10:05, 8 January 2008 (UTC)

Parasites

How do they survive inside bodies? 138.217.145.45 (talk) 08:29, 7 January 2008 (UTC)

Lots of different ways, but generally by attaching to tissue (sometimes under the skin, in the gut or the bloodstream) and getting the nutrients they need to survive from the host. Ones that live inside bodies are called endoparasites. An example is hookworm, which live in the small intestine and suck blood to survive. Rockpocket 09:14, 7 January 2008 (UTC)

Sun

Is the Sun part of any constelation? 138.217.145.45 (talk) 11:50, 7 January 2008 (UTC)

No. See List of constellations. --Sean 12:51, 7 January 2008 (UTC)

Strictly speaking, the sun might be part of a constellation for a civilisation living on another planet, orbiting another star in a solar system different from ours. However, at this point it's mere speculation, as we haven't contacted them yet in this or any other matter. --Ouro (blah blah) 13:05, 7 January 2008 (UTC)

Constellations do not necessarily consist of stars that are relatively close together: they have significance to us because of the 'shapes' they make in the night sky. To observers on a planet in another part of the galaxy there might be no apparent pattern at all; indeed it might never be possible to see all the stars of Orion, say, at the same time from any point on the surface of the planet. AndrewWTaylor (talk) 13:19, 7 January 2008 (UTC)

That's right. By definition, constellations can only consist of fixed stars.--Shantavira|^{feed me} 15:11, 7 January 2008 (UTC)

Another question- how close to our solar system would another species have to be to be able to see our sun without a telescope? 70.162.25.53 (talk) 02:56, 8 January 2008 (UTC)

By "another species", do you mean "another species that just happens to have eyesight identical to human beings, on a planet whose atmospheric transmission and night-sky brightness are identical to a dark site on earth"? If so, we can subtract the sun's absolute magnitude of 4.83 from the faintest apparent magnitude these "aliens" can see of 6.5, for a distance modulus of 1.67. That works out to a distance of about 21.5 parsecs. Call it 20 pc in round numbers. -- Coneslayer (talk) 03:17, 8 January 2008 (UTC)

K shell

hello, I wanted t ask that why do we name the first shell of quantum atom model,"K" (principal quantum number 1)? max6 —Preceding unsigned comment added by Max6 (talk • contribs) 12:38, 7 January 2008 (UTC)

• Electron shell says Barkla labelled them with the letters K, L, M, etc. The origin of this terminology was alphabetic, so it sounds like he just started at K arbitrarily. --Sean 12:55, 7 January 2008 (UTC)

It suggests to me that he thought there might end up being more shells before K, and he wanted to leave a lot of room (which is a rather modest thing to do). But I don't know—often such details in the history of physics are not easy to document because after getting repeated 50 times over it is hard to find out what the so-called "seminal paper" was that launched it, because the scientists themselves often just repeat such things without referencing the original. (In some rare cases this is true and the original is consulted for many years—like Einstein's 1905 papers—but in most cases, especially with experimental physics, this is not so, and just results get reported.) --24.147.86.187 (talk) 01:36, 8 January 2008 (UTC)

Science

What is the best method, other then heat, to melt ice????????? —Preceding unsigned comment added by 72.186.80.145 (talk) 15:12, 7 January 2008 (UTC)

You can't melt ice without heat. The physical process of melting requires that the ice be absorbing heat. Someguy1221 (talk) 15:51, 7 January 2008 (UTC)

Well, you could add something to the ice that lowers its freezing point. This is why they salt the roads in the winter in many places, for example. Friday (talk) 15:53, 7 January 2008 (UTC)

OK, unless you're cheating like that :-p Someguy1221 (talk) 16:00, 7 January 2008 (UTC)

Doesn't that still involve some heat? Or can salt be dissolved and absorbed by solid ice? APL (talk) 16:10, 7 January 2008 (UTC)

The mechanism by which salt lowers the freezing point is that water molecules at the solid/liquid interface are constantly moving from one state to the other, but when you add salt, water in the liquid state attaches to it and is then unable to move back to the solid part. Therefore, I imagine that you would need at least some amount of water on the ice's surface to allow salt to melt it. --Sean 17:54, 7 January 2008 (UTC)

But by your own argument, there's always some amount of water at the surface, so it always works (as long as the temperature's not lower than that of salt water, of course). —Steve Summit (talk) 22:59, 7 January 2008 (UTC)

I know you can boil ice by putting it in a vacuum chamber, so you can probably melt it by controlling the pressure more carefully. Black Carrot (talk) 16:52, 7 January 2008 (UTC)

Unexpectedly, you can melt ice by increasing pressure - see regelation. Gandalf61 (talk) 16:55, 7 January 2008 (UTC)

Yeah, that's supposedly what makes skating possible, though there's no mention of it at the article on regelation. --Trovatore (talk) 23:06, 7 January 2008 (UTC)

• With good reason: that's a myth. See under Ice skating#How it works, last paragraph in the section. --Anonymous, 03:48 UTC, January 8, 2008.

Extreme pressure ends up heating things, just think of those pressed penny machines (or Elongated_coin. Unless that counts as heat. --Omnipotence407 (talk) 03:32, 8 January 2008 (UTC)

Question on salt and excercise

What happends if you take in a large ammount of salt and then do training? —Preceding unsigned comment added by Bastard Soap (talk • contribs) 15:21, 7 January 2008 (UTC)

We're not well equipped to give medical or training advice. All I would recommend is, don't go trying to exceed the recommended intake of salt unless directed by a medical professional. See also Salt#Health_effects for the relevant section of our article. Friday (talk) 15:51, 7 January 2008 (UTC)

Cells

Plant cells have cell walls but animal cells do not. Why do animal cells not hav cell walls? —Preceding unsigned comment added by Stylin99 (talk • contribs) 15:44, 7 January 2008 (UTC)

Cell walls are quite rigid, which wouldn't be beneficial for anything that planned on moving a lot. Instead, those animals that actually needed the rigidness they lacked by not having cell walls evolved various forms of skeletons and exoskeletons. For the purpose of an animal, these are atually superior, as they afford rigidness where such is needed, and allow the rest of the organism to remain flexible. Someguy1221 (talk) 15:57, 7 January 2008 (UTC)

Microscope

1.Who is the first person that invented microscope and when it is invented? Can anyone tell me more about Anton van Leeuwenhoek's microscope and Roberts Hooke's microscope? —Preceding unsigned comment added by Stylin99 (talk • contribs) 15:51, 7 January 2008 (UTC)

The article about microscope may help you here. It doesn't look long in history, but it at least mentions Hooke's version. His own article has a bit more. Friday (talk) 15:59, 7 January 2008 (UTC)

We do have a Timeline of microscope technology, and the bulk of the history appears in the Optical microscope article. Someguy1221 (talk) 16:01, 7 January 2008 (UTC)

I have added a little more at Wikipedia:Reference_desk/Miscellaneous#Microscope. By the way, it's a good idea to ask a question on only one desk - that way, the answers can all be in the same place, which is easier for everyone to follow. DuncanHill (talk) 16:02, 7 January 2008 (UTC)

why does a comet leave atrail behind it?

why does a comet leave a trail behind it? —Preceding unsigned comment added by 195.229.236.212 (talk) 16:35, 7 January 2008 (UTC)

You may want to read our comet article and if this doesn't answer your questions, come back here again.

Atlant (talk) 16:37, 7 January 2008 (UTC)

Are you referring to a comet's tail? That's not exactly its trail. --Ouro (blah blah) 16:58, 7 January 2008 (UTC)

(longer answer without pun) A comet will leave a trail (its tail aside for now) because it could shed its material, primarily rock and ice because that's what they're composed of, or other material (like hydrogen or water) that it would expel by means of jets which some comets possess. Should the comet not be caught in a stream of solar, interstellar or other type of cosmic wind, the trail would be pointing in the opposite to the direction it's travelling in. The tail, now, could be a type of trail that's not pointed this way but away from the source of the wind it's caught in (the simplest and easiest example to observe would be a comet passing by the Sun with its tail pointing away from it). Right? --Ouro (blah blah) 17:08, 7 January 2008 (UTC)

If the comet sheds rocks they don't just stay were the comet was when they were shed, but they continue to orbit the sun (due to their inertia). The orbits of the fragments would be slightly different from the comet's orbit. After many orbital periods, the rocks will be distributed along the comet's orbit, and we will see meteor showers if Earth passes the comet's orbit. Icek (talk) 06:17, 8 January 2008 (UTC)

Falling from an aircraft into the sea

In a James Bond film the hero falls from an aircraft without a parachute. This made me wonder: 1) What is the greatest height you could fall into the deep sea from, and survive? 2) Not really a science question, but has anyone ever been suicidally crazy enough to leap from a plane without a parachute, and be handed and put on a parachute from another skydiver in mid-air? Thanks. 80.0.105.180 (talk) 19:36, 7 January 2008 (UTC)

Multiple people have survived jumps off the Golden Gate Bridge. So, you have to go higher than 746 feet. I'm not sure how many popular jumping spots there are that are higher than that. -- kainaw™ 19:58, 7 January 2008 (UTC)

From watching MythBusters, it seems to be completely dependent on multiple factors, including density of the water, entry, velocity, etc. But as Kainaw said, people have survived jumps of the Golden Gate Bridge. So it would depend on the height of the plane as well. I recall something about a person surviving a mile-high fall from a plane on land...I'll research that and repost. EWHS (talk) 20:04, 7 January 2008 (UTC)

Checking parachuting, a common parachuting height is 13,000 feet. That is much higher than 746 feet. Of course, there is a point at which you'll reach terminal velocity and it won't matter how much higher you are when you jump. I don't know what that altitude is. -- kainaw™ 20:09, 7 January 2008 (UTC)

According to terminal velocity the max speed that a person would hit the water in the safest manner (feet first, arms crossed tight, and head back) is 200mph. So, this becomes a question of water density. How dense can the water be to survive a 200mph impact? -- kainaw™ 20:12, 7 January 2008 (UTC)

According to this, you can survive a 10560 feet (2 mile) fall over land. EWHS (talk) 20:17, 7 January 2008 (UTC)

There's a pretty important difference between what is typically non-fatal, versus what someone might occasionally survive by extraordinary luck. Friday (talk) 20:41, 7 January 2008 (UTC)

A quick note on the Golden Gate: 746 ft isn't really the metric most commonly associated (that's height from the top of the tower). Rather, most jumps are made from the bridge span, which has a clearance of 220 feet.

Anyway, regarding terminal velocity: I think it's more accurate to go with what the slowest TV for a human is, as one could fall in that position and then shift to preferred landing position late enough that you don't then fully accelerate to the higher TV before impact. Some handwaving suggests that 175-200 meters is sufficient fall distance to reach 210 km/h (the TV article suggests that ~195 km/h is the slowest somebody could fall). — Lomn 22:03, 7 January 2008 (UTC)

Oh, and as for the last part (getting a parachute mid-air): I have no idea if it's been documented, but it's certainly achievable. Skydiver teams do mid-air rendezvous as a matter of course; handing off a parachute (sans most of the safety straps) or buckling onto someone with one isn't much more difficult. While I might characterize it as "crazy", I wouldn't call it "suicidal". — Lomn 22:08, 7 January 2008 (UTC)

Note that those operations are very dangerous, as skydivers can reach extremely high horizontal speeds. I read one account where two divers whacked into each other so hard, one guy's leg was torn off! --Sean 00:04, 8 January 2008 (UTC)

Vesna Vulovic managed 33,000 feet without a chute! Also, read this *hilarious* essay; it's awesome. --Sean 00:04, 8 January 2008 (UTC)

Vesna may not have had a parachute, but she was strapped in a section of the fuselage, which limited the velocity she reached before striking the ground. I have descended safely from such a height myself, in an airplane fuselage (but an intact one). Not comparable to a human without chute or plane. Edison (talk) 01:47, 8 January 2008 (UTC)

Robert Langdon in Angels and Demons fell from a pretty good height if i remember correctly. Though he did have a tarp. --Omnipotence407 (talk) 03:37, 8 January 2008 (UTC)

Going without orgasm for a long time

If I do not ejaculate for several days, my testicles become painful. I wonder how men in environments where ejaculation is not possible, such as in the Apollo spaceship or in a submarine, cope? Don't they have sex on the mind all the time to the exclusion of everything else, and pernament erections? 80.0.105.180 (talk) 20:09, 7 January 2008 (UTC)

As strange as it may seem, persons aboard spacecraft and in submarines don't -always- have sex on the mind. They are trying to run some of the most technologically advanced machines in existance, of course. Erections only come from arousing thoughts, etc. (excluding "morning-woods" and the likes). If their minds are wholly focused on something else, such as piloting the Apollo spaceshuttle, then it is unlikely they will have "perpetual erections" and therefor will feel no need to ejaculate. —Preceding unsigned comment added by EWHS (talk • contribs) 20:16, 7 January 2008 (UTC)

If your testicles become painful, you should see your doctor about it. Masturbation isn't necessary and going without it should have no harmful consequences (other than perhaps boredom, I guess). Think of monks. —Keenan Pepper 22:09, 7 January 2008 (UTC)

Sounds like its possible the OP could be suffering from a case of blue balls. Constant erections and no climax may result in that particularly painful situation. An ejaculation or a cold shower would probably make it stop hurting. [THAT WAS IN NO WAY MEDICAL ADVICE; GO SEE YOUR DOCTOR FOR A PROPER DIAGNOSIS] Also, accomplished astronauts and scientists have already gone through their hormonal teenage years (not to say that they are never horny anymore), and probably have more important things on their mind than constantly thinking of sex. --71.98.28.243 (talk) 22:16, 7 January 2008 (UTC)

Huh? At what age are you supposed to stop thinking about sex constantly? I'm well beyond my hormonal teenage years and I guess that I still think about sex approximately every couple of minutes... ;) --Kurt Shaped Box (talk) 22:34, 7 January 2008 (UTC)

I'm pretty sure that if they're *really* desperate, then there's one of those 'it's not gay if...' 'loopholes' that covers submariners and astronauts. EDIT: Anyhow, they have women under the sea and in space now, don't they? ;) --Kurt Shaped Box (talk) 22:37, 7 January 2008 (UTC)

Indeed, for pain in your testicles, see a G-D doctor right fast. Beyond that, bear in mind that the plural of anecdote is not data (and the singular of anecdote is definitely not data) but it's rather hard to go more than about three months without an orgasm (at least for postpubscent males) - your body has a tendancy to just go ahead and do it without your permission anyways. Cheers, WilyD 22:55, 7 January 2008 (UTC)

Sorry to say that painful testicles is a medical condition and you should see your doctor. We cannot answer medical questions here.--TreeSmiler (talk) 23:45, 7 January 2008 (UTC)

Hydrogen peroxide solution still good?

I know that H202 breaks down somewhat over time, but I don't have a sense for how rapidly this happens. I have a two year old bottle of 30% H2O2 that has been refrigered since receipt. I intend to use in converting formic acid to performic acid. From a practical point of view, do you think this bottle of H2O2 is still good, or should be replaced? It is cheap, but there are shipping charges and of course I'd have to wait for it. ike9898 (talk) 20:36, 7 January 2008 (UTC)

If you're in a chem lab, there's an easy way to tell. Just add a little manganese dioxide to a sample of the H₂O₂ and measure the volume of oxygen gas evolved. You can determine the concentration of peroxide from that. —Keenan Pepper 22:04, 7 January 2008 (UTC)

H2O2 decomposes spontaneously as it says here Hydrogen_peroxide#Decomposition--TreeSmiler (talk) 23:54, 7 January 2008 (UTC)

But unfortunately the article doesn't say how fast. Another issue: It confuses me that the article says that lower concentrations decompose faster - shouldn't the decomposition rate be proportional to the square of the concentration since the reaction requires 2 molecules of H2O2 to collide? Icek (talk) 00:42, 8 January 2008 (UTC)

Its variable:

The rate of decomposition is dependent on the temperature and concentration of the peroxide, as well as the pH and the presence of impurities and stabilizers. Hydrogen peroxide is incompatible with many substances that catalyse its decomposition, including most of the transition metals and their compounds. Common catalysts include manganese dioxide, and silver. The same reaction is catalysed by the enzyme catalase, found in the liver, whose main function in the body is the removal of toxic byproducts of metabolism and the reduction of oxidative stress. The decomposition occurs more rapidly in alkali, so acid is often added as a stabilizer.

--TreeSmiler (talk) 00:53, 8 January 2008 (UTC)

Nonetheless it would be nice if we had some data for a nearly pure H2O2 and water mixture, at a common temperature, in a common inert container. Icek (talk) 04:32, 8 January 2008 (UTC)

energy efficient houses

How does a energy efficient house (E.E.H) helpp stop air polution? What bad and good things does a normal US house do to the enviornment such as light polution? What bad and good things does a normal US E.E.H do to the enviornment? What types of things give off VOC's that are used in houses and what things give off the most VOC's? How much VOC's does the average US house give off and how VOC's does the average US E.E.H give off?

thanks —Preceding unsigned comment added by 76.235.160.188 (talk) 21:25, 7 January 2008 (UTC)

molds and organisms

how do the structures of the slime molds differ from those of cellular organisms —Preceding unsigned comment added by 72.147.252.127 (talk) 21:57, 7 January 2008 (UTC)

If you haven't checked it out already, slime mold has relevant information. — Scientizzle 22:02, 7 January 2008 (UTC)

Whiskers

I've been told that the whiskers on cats are approximately as long as the cat is wide. This makes sense, seeing as they like to go in narrow, tight places and would need to judge as to whether they could fit or not. So my question is HOW the heck to the whiskers grow to that specific length? How do they "know" when to stop growing? Thanks. --71.98.28.243 (talk) 22:10, 7 January 2008 (UTC)

I don't think it's true. My cat's whiskers are quite a bit longer than she is wide. Deli nk (talk) 22:16, 7 January 2008 (UTC)

Actually, according to this site, "The whiskers are roughly the same width of the cat, so he can put his head in a small area and determine if the rest will follow. Interestingly, if you cat gets overly chubby, he loses this ability, since the whisker length is determined by genetics, not by how fat the cat is."

Conversely, this site claims that "If a cat gets quite fat and resembles a barrel, at least some of those whiskers will grow longer in response to the added girth."

What I don't understand is how do the whiskers (or genes or whatever dictates length) "know" when to stop growing? What allows them to "know" the girth of the cat, therefor dictating the length of the whiskers? --71.98.28.243 (talk) 22:33, 7 January 2008 (UTC)

Whiskers grow from modified hair follicles, which have a life cycle of three hair growth phases. A number of different genes are known to be involved in regulating growth, these include Insulin-like growth factors and fibroblast growth factors and Transforming growth factor beta (TGF-β). The exact interaction of genes that tells the hair to stop growing is not yet known, to quote a review on the subject: [14]

Why does the [growth] cycle end when it does? Is this due to the fact that a limited number of mitoses of the transit amplifying cell population becomes exhausted? Or, is it due to a change in the paracrine factor milieu, such as to the accumulation of growth inhibition and proapoptotic agents, or to changes in activities of perifollicular mast cells and macrophages, or to a combination of all of the above? The unknown signal, either inherent in or delivered to the follicle, causes the cycling, deep, portion of the follicle to involute at a surprisingly rapid rate. This phase, catagen, is a highly controlled process of coordinated cell differentiation and apoptosis, involving the cessation of cell growth and pigmentation, release of the papilla from the bulb, loss of the layered differentiation of the lower follicle, substantial extracellular matrix remodeling, and vectorial shrinkage (distally) of the inferior follicle by the process of apoptosis.

Rockpocket 23:19, 7 January 2008 (UTC)

Thanks Rockpocket, I'll try to mull this one over and figure it out. This is a bit more advanced than my normal biology homework ;) --71.98.28.243 (talk) 00:04, 8 January 2008 (UTC)

It is quite wordy. Let me try and translate. The authors speculate about a few explanations for how the hair knows how to stop. They suggest it could be because:

• Some of the cells that are involved in producing the whiskers - the so called transit amplifying cells - can only divide a certain amount of times before they stop. When they stop dividing, they can no longer produce enough material to drive whisker production and so the whisker stops growing.
• There is a steady accumulation of signaling proteins being produced by surrounding cells to tell the whisker cells what do to, signals that tell the whisker growing cells to stop growing and begin to die could be released slowly, however eventually enough of them will accumulate so to over-ride the "grow" signals and the hair stops growing.
• Certain types of cells around the follicle get more active and basically start killing the whiker growing cells.

These are all good hypotheses about how the whisker stops growing, but the question then because what genetic factors regulate these processes to co-ordinate the whiskers to be the correct length. That is yet to be worked out. Rockpocket 03:03, 8 January 2008 (UTC)

Three big cocks!

Okay, now that I've got your attention...

I happened to be observing a flock of chickens today (my grandma's window in the old folks' home looks out onto someone's garden) when I noticed that amongst the 20 or so hens, there were three (very large) fully-grown cockerels happily coexisting amongst them. Okay, so if one got a little too close to another, there'd be a little bit of beak lunging and bickering (as happens constantly with my beloved gulls) - but on the whole, they seemed to be getting along rather well.

Now, I remember someone stating here on this desk that it is impossible to keep more than one cockerel per flock, as they would undoubtedly fight one another to the death at the first opportunity. The garden was in no way large enough for each cock to have his own territory either - all the birds were intermingling.

Question - how do you think that the owner managed to stop the violence? Would it make any difference if the birds were siblings? --Kurt Shaped Box (talk) 22:57, 7 January 2008 (UTC)

• It's common to keep one rooster intact to lord over the flock, while any others who hatch are caponized, which makes them less pugnacious, not to mention fatter and tastier. --Sean 23:53, 7 January 2008 (UTC)

Not in the UK (where I am), according to that article... --Kurt Shaped Box (talk) 23:57, 7 January 2008 (UTC)

unknown disorder

Hi there, can a psychologist or a scientist figure out what type of problem I have? the problem is that when the holidays are over, I feel like i not ready to go to school and night before, I start crying and I can't sleep because I have nightmare, and I feel sad throughout the school day because whenever a teacher assigns a group work, I feel sad or nervous that I start to sweat because whenever kids in my class hear "group work", they think of their friends and I don't have any friends and I started to have this problem since I was in Grade 11. I hate group work and another problem is after school, I start to cry for five minutes and I don't know why I start to cry and I cannot sleep properly. It usually happens during the rainy days I usually have this problem for three days. Once again, what type of problem do I have? Please answer my question. —Preceding unsigned comment added by 76.64.53.193 (talk) 23:21, 7 January 2008 (UTC)

You need to go see your doctor about this (or get your mom to arrange it), as you may be suffering from depression.--TreeSmiler (talk) 23:50, 7 January 2008 (UTC)

Could be seasonal depression. —Tamfang (talk) 02:31, 8 January 2008 (UTC)

January 8

Cells

Plant cells have cell walls but animals cells do not. Why do animal cells not have cell walls?--Stylin99 (talk) 02:10, 8 January 2008 (UTC)

See Cell Wall. From this article and some intuition, it seems that differing evolutionary niches that plants and animals inhabit make their differing cell membrane structure advantageous to each group. Plants are generally stationary, whereas animals generally move around. Therefore a cell wall that provides rigidity and stiff structure to an organism is advantageous for plants which must stay in one place and endure stresses. A rigid cell wall structure is not advantageous for animals however, since they generally must move around rapidly to avoid stresses. -Bmk (talk) 02:21, 8 January 2008 (UTC)

Cells

What is the function of cell membrane?--Stylin99 (talk) 02:27, 8 January 2008 (UTC)

See cell membrane and in the future, typing your terms in the search box at the top left will save you time. ----Seans Potato Business 03:01, 8 January 2008 (UTC)

Annihilation - energy of photons from electron-positron interaction

Some lady says that a positron and an electron annihilating each other yields two 511 keV photons, but surely the energy that the electron and positron had at the time of interaction also comes into play? (even if it's negligible, that should be stated rather than pretending it doesn't exist) ----Seans Potato Business 03:00, 8 January 2008 (UTC)

We have an article called Electron-positron annihilation. See the "high energy state" section. Depending on the context, it may have been proper for her to leave out. What happened? Black Carrot (talk) 03:09, 8 January 2008 (UTC)

Rail Guns

From what I can understand the main problem with rail guns is the damage done to the rails upon firing. What I want to know is there any reason stopping a system or device that could in essence "reload" the rails every couple of shots? Thanks DTWATKINS (talk) 04:22, 8 January 2008 (UTC)

Nothing but time and space. Rails are big, so if you need to swap them after every two or three shots, you can't fire for very long. Frequent swapping also means you can't keep up a constant rate of fire: if you need to fire four shots to take down four incoming missiles, but the rails wear out after three, you might not get the new set of rails ready in time to hit the fourth. For long-range artillery, where you can have a machine shop next to the gun to re-surface the rails, it might not be a problem, but for anything else, it is. --67.185.172.158 (talk) 10:07, 8 January 2008 (UTC)

Carbon black

I've noticed that soot is a super excellent water repellent. In a survival situation and except for mistaking it for mold would there be any problem with using carbon black to waterproof clothing? 71.100.12.59 (talk) 06:10, 8 January 2008 (UTC)

Square-cube laws

The size of ground vehicles such as tanks is limited by a square-cube law: the mass of the vehicle increases as the cube of the size, while the available ground area for supporting the vehicle only increases as the square of the size. Is there a similar square-cube limit on the size of ships? --67.185.172.158 (talk) 10:01, 8 January 2008 (UTC)