Wikipedia:Reference desk/Archives/Science/2010 April 2

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April 2

Unknown squirrel species

I took this photo today of a squirrel on the grounds of the American Museum of Natural History in NYC -- it's sort of reddish and the bushiness of the tail is somewhat compressed dorso-ventrally. Doesn't look like an eastern gray squirrel to me -- any ideas? DRosenbach ^{(Talk | Contribs)} 00:32, 2 April 2010 (UTC)

Columbian ground squirrel perhaps? --The High Fin Sperm Whale 01:03, 2 April 2010 (UTC)

Looks to me like a thinner version of eastern gray -- in that it would be a tree squirrel. DRosenbach ^{(Talk | Contribs)} 01:09, 2 April 2010 (UTC)

the Columbian ground squirrel occurs in the western U.S., not the East. Rmhermen (talk) 04:23, 2 April 2010 (UTC)

Improvised teleprompter - looking for one-way mirror in UK

I want to make my own teleprompter and need to get the one way mirror glass. I live in the UK. My ebay searches aren't yielding anything except this privacy film - would that be likely to work, stretched over some clear acrylic? Proper teleprompter mirrors have an antireflective coating on the camera-side of the mirror.. not sure whether I can prepare such a surface? --78.151.30.114 (talk) 00:55, 2 April 2010 (UTC)

While I don't know whether you're right or wrong about the anti-reflective coating, I have a suspicion that you may have a misunderstanding of how a two-way mirror works (the proper name is two-way mirror, and that's also the name that correctly describes how it works). A two-way mirror reflects from both sides, and it lets light through from both sides. The reason you perceive it as a mirror from one side and a window from the other has to do with the relative intensities of the transmitted signal versus the reflected one. If you're on the bright side of the mirror, then the reflected signal is brighter (simply because there was more light to start with), and in your eye and/or your brain, it drowns out the signal from the dark side so that you are unable to perceive it.

(Sorry that I don't know where to buy it.) --Trovatore (talk) 01:03, 2 April 2010 (UTC)

• Both one-way mirror and two-way mirror are commonly used names, and they both make sense, so let's not be saying that only one of them is "proper". "One-way" makes sense because you can only see one way through it. "Two-way" makes sense because it behaves in two ways when seen from different sides. --Anonymous, 04:10 UTC, April 2, 2010.

No, one-way mirror is wrong, period. It should never be used. It encourages people to think that there is some directionality to the mirror. --Trovatore (talk) 07:46, 2 April 2010 (UTC)

There is directionality. The lighted side and the dark side. But you knew that. --Anon, 10:43 UTC, April 2, 2010.

And it does not "behave in two ways when seen from different sides". It behaves in exactly the same way. (Well, at least in principle -- in practice of course one side could be dirtier than the other or something.) This is a very key point -- if you don't understand that, then you don't understand the gadget at all. --Trovatore (talk) 07:49, 2 April 2010 (UTC)

It does. It allows you to see what is on the same side when you look into it from the lighted side, and allows you to see what is on the other side when you look into it from the dark side. The symmetry of the underlying mechanism is irrelevant to that fact. And you knew that too. Now please stop telling people what not to say. --Anon, 10:43 UTC, April 2, 2010.

I will not. People should not say one-way mirror. It makes people think that the device is directional, which it is not. On the bright side, you see a roughly equal mix of the bright image and the dark image. And on the dark side, you see a roughly equal mix of the bright image and the dark image. --Trovatore (talk) 17:35, 2 April 2010 (UTC)

It is directional, because it has a bright side and a dark side, which it relies on to work. (An ordinary window works as a one-way mirror, at night.) If it doesn't have the bright side and the dark side, it won't work, and therefore isn't a one-way mirror (or a two-way one, which is the same thing). 81.131.62.171 (talk) 02:47, 5 April 2010 (UTC)

It is not directional. On both sides, it gives you a roughly equal mix of the image from both sides. That's what it means for it to "work", and it does that even if the lighting is equal on both sides.

It is properly called a two-way mirror, because it acts as a mirror in both directions. An ordinary mirror works as a mirror in only one direction, and therefore would be the correct referent for the term one-way mirror. Of course you can't use that term that way because of the potential for confusion. --Trovatore (talk) 08:07, 5 April 2010 (UTC)

Yeah, but when you construct a box around the camera, there is little light on that side of the mirror, so it works (text is reflected from the screen while the camera receives light from the other side of the mirror). --78.151.30.114 (talk) 01:30, 2 April 2010 (UTC)

Actually from looking at the diagrams in the teleprompter article, I think the reason the audience (or camera) doesn't see the text has less to do with the relative illumination than with the angle of the mirror. A two-way mirror is essentially a beam splitter. The text is projected up at the mirror from below. Part of the image is reflected towards the speaker; the other half (or so) of it continues up to the ceiling. Essentially none of it goes to the audience, just because the audience is not in the right place to see it. --Trovatore (talk) 01:45, 2 April 2010 (UTC)

It is also called a "Half-silvered mirrot." Edmund Scientific always had them for sale. Random local glass stores also offered half silvered mirrors for sale. A simple piece of glass would also work nicely, as in the old "Pepper's Ghost" effect. Edison (talk) 04:19, 2 April 2010 (UTC)

I prefer the name "half-silvered mirror". It makes it clear that it reflects half the light and allows half of it through (roughly). Once you understand that, the behaviour of the mirror is obvious. --Tango (talk) 13:47, 2 April 2010 (UTC)

I think there is some confusion here over the type of teleprompter being used. The OP wants a teleprompter that allows someone to look into a camera while reading. I think Trovatore is thinking of the teleprompters people use when they want to read while looking at a live audience (the type Obama is (in)famous for using). I think they both use half-silvered mirrors, but in slightly different ways (although I suspect the second type may be less-than-half-silvered, since that will look better from the audience side and you can compensate by just using a brighter projector, the first type could also use a less-than-half-silvered mirror but there is less benefit since the two sides are lit different amounts). --Tango (talk) 13:47, 2 April 2010 (UTC)

Planetary rings

What is the cause of rings around Uranus?--79.76.175.65 (talk) 01:10, 2 April 2010 (UTC)

The same as the reason for rings around Saturn, Jupiter, and Neptune. When rocks and particles are sucked into orbit, due to centrifugal force, they flatten out. Shepard moons help 'herd' the rings into specific bands. You may also want to read Rings of Uranus. --The High Fin Sperm Whale 01:13, 2 April 2010 (UTC)

Poor hygiene?. --Jayron32 04:11, 2 April 2010 (UTC)

Is there no end to these pseudo funny comments about Uranus?--79.76.239.84 (talk) 02:58, 7 April 2010 (UTC)

What does Shepard have to do with moons? Or did you mean "shepherd moons"? 24.23.197.43 (talk) 05:51, 2 April 2010 (UTC)

Or even Shepherd moon. Mitch Ames (talk) 07:55, 2 April 2010 (UTC)

Also, the large planets all have many moons, and the gravitational interaction between them and the planet seems to prevent the rings from coalescing into additional moons. There are smaller planets with multiple moons (Mars has at least 2 and Pluto has at least 3), so perhaps there could be tiny rings there, but I'm not aware of any having been found. StuRat (talk) 13:10, 2 April 2010 (UTC)

Carbon dioxide accumulation

In various places it seems that it is the short duration of and accumulation or flow of enough CO₂ in low spots or ditches or even down a hillside slop and even flat ground to make impossible a breath of fresh air after 2 or 3 breaths that any air breathing life form has collapsed and within seconds to minutes succumbed and died even if air returned within 5 minutes and even if air was in reach of the life form if it stood on its toes or raised its head. This attests to the power of CO₂ to knock an animal out quickly but my question is if instead of Nuclear Winter caused by an asteroid striking Earth and killing everything an accumulation of CO₂ could be enough from burning matter and release by shock to have killed off most of the dinosaurs? 71.100.3.207 (talk) 02:30, 2 April 2010 (UTC)

Seems like it would take a lot of carbon dioxide to give enough blanket to enough area. "Everything" on the terrain can't be ditches:) More than just filling low areas and sweeping down hills, you have to get over hills to spread over a continent-sized region.. But certainly the situation has occurred on town-size areas. See for example Lake Nyos. DMacks (talk) 02:46, 2 April 2010 (UTC)

Agreed. My understanding though is that in the Permian-Triassic extinction event 251 million years ago, which was even worse than the mass extinction that killed the dinosaurs and is thought most likely to have been caused by enormous volcanic eruptions, there is evidence that high CO₂ concentrations played an important role in killing large animals. Looie496 (talk) 03:19, 2 April 2010 (UTC)

The phenomenon which raises this question is the strange accumulation of bone in some places as if they were all living int the same town and the dam broke sweeping them down river to accumulate in eddies and other spots. 71.100.3.207 (talk) 04:28, 2 April 2010 (UTC)

That's probably closer to the true explanation than carbon dioxide poisoning. After all, there are natural dams. We have beaver dams now, and, although they aren't large enough to cause that type of damage, perhaps some ancient creature did the same thing on a massive scale ? If not, there's still ice dams/glacial dams. You can also get flash floods from sudden rains, without the need for a dam to burst. Another source of floods is when a lake or sea is held back by rock, and that rock collapses. This can happen in a lake in a caldera, for example, and may also have allowed the Mediterranean Sea to catastrophically flood into what became the Black Sea. See Black Sea deluge theory. StuRat (talk) 12:53, 2 April 2010 (UTC)

This has been known in modern times; see Lake Monoun. Tonywalton ^Talk 18:28, 4 April 2010 (UTC)

For the actual condition that causes CO2-laden air to be unbreathable, see carbon dioxide poisoning and carbonic acid. Another cause of the Permian-Triassic extinction may have been hydrogen sulfide. ~AH1^(TCU) 23:42, 4 April 2010 (UTC)

Juicy nose

Why is my dog's nose so juicy? I would like to know where all this juice comes from, because sometimes it is so wet I am tempted to get a towel and dry it off. What causes all this juice? I'm not at all concerned about my dogs health; she is completely healthy, she just has a juicy, juicy nose! It's not dripping, like with snot it's just always cold and totally wet. I am wondering *where* this juice comes from. I'm not the only person in the world that has a dog with a juicy nose. I see them all the time. Thanks.70.245.24.14 (talk) 04:51, 2 April 2010 (UTC)

If you are concerned about your dog's health, you should take them to a veterenarian. Medical advice, even regarding animals, isn't reliable when it comes from random strangers in teh interwbz. --Jayron32 04:58, 2 April 2010 (UTC)

Did you miss the words "not at all"? --Anon, 10:45 UTC, April 2, 2010.

Dogs have all this juice on their noses to help them smell. This does not mean they are unhealthy. Regards, --The High Fin Sperm Whale 05:18, 2 April 2010 (UTC)

The High Fin Sperm Whale, thank you but where does the juice originate from? That is the nature of my question. Are there some sort of nose glands that produce this juice. 70.245.24.14 (talk) 05:26, 2 April 2010 (UTC)

The article mucus explains a bit about this. See also Mucous membrane and Goblet cell. --Jayron32 05:35, 2 April 2010 (UTC)

Google-ing "dog wet nose" gets tons of hits. One that I found interesting says that the role of the moistness is to help in evaporative cooling. Following some links, the main organ involved in this process seems to be the lateral nose gland. If you want the source for this info, try this article from Science. Other links say that the wetness comes from the dog licking their nose, which I can certainly believe, having observed my own dogs, but I couldn't find any primary sources on that one (not to mention the question of whether the licking is a cause or effect of a wet nose). --- Medical geneticist (talk) 11:46, 2 April 2010 (UTC)

I've always thought of most animal noses as inside-out relative to humans. That is, the portion that's inside and always kept moist on humans is outside (and inside as well), on dogs. This is likely part of their much better senses of smell. The glands that keep it moist are similar to our sweat glands. StuRat (talk) 12:37, 2 April 2010 (UTC)

Yes - and part of the reason for that appears to be to give them a better directional sense of smell. When all of the little detectors are up inside your nose, all you can really tell is which nostril the smell came through - but dogs (in particular) have a completely directional sense. SteveBaker (talk) 14:21, 2 April 2010 (UTC)

Anecdotally, it comes from their tongue. Dogs lick their noses, for olfactory (smell) and evaporative (cooling) benefit. After sleeping a dog's nose is often dry and warm. I suspect that's because dogs don't lick their noses while asleep. Some dog-health related websites identify dry nose as a 'possible' indicator of illness, but this is apparently a poor indicator since plenty of healthy dogs can have occassional or non problematic dry noses. Lastly, for comparison, compare dog noses to human lips... Ours stay moist from us licking them as well. 206.53.153.110 (talk) 13:09, 4 April 2010 (UTC)

Ah yes, the good old juicy nose. Forgive me, but perhaps a new juice could hit the market. To go with V-8, we could call it K9! 10draftsdeep (talk) 20:24, 5 April 2010 (UTC)

Electra hydraulics

For those who have a working knowledge of historic aircraft (especially those made by Lockheed): did the Electra 10-E have a hydraulic system (and I don't mean just the oleo-struts), and if so, what components did it actuate? I'm pretty sure the primary flight controls were all mechanical, as on all other aircraft at the time (AFAIK hydraulic boosters did not begin to be fitted to aircraft until after World War 2, and even then only to the highest-performance jet planes at first); my question is, was there anything else vital to the plane's safety (like flap controls, or landing gear retraction) on the Electra that was hydraulically powered? And no, in case you're suspicious, this has nothing to do with any fringe theories about Amelia Earhart's disappearance; it's for a novel that I plan to write some time in the future. Thanks in advance! 24.23.197.43 (talk) 06:31, 2 April 2010 (UTC)

Anybody? OK, I'll make it a fuel leak, then (or maybe an engine fire).  :-) 24.23.197.43 (talk) 04:48, 3 April 2010 (UTC)

drive

Sir, please send me the drive internal connection diagrams ie, IGBT, RECTIFIER,IVERTER etc

Thanking you sir, S.G.Rabbani —Preceding unsigned comment added by Sgrn70231 (talk • contribs) 07:01, 2 April 2010 (UTC)

Our inverter (electrical), rectifier, and IGBT articles contain circuit diagrams. StuRat (talk) 12:43, 2 April 2010 (UTC)

Tree color.

From my office window, I look out over an apartment complex which contains dozens of large, mature, deciduous trees. These appear to be of identical species (sorry - I'm clueless as to what species they are - but I don't think that matters). They are all more or less the same size (40 feet maybe). Presumably they were all bought from the same tree supplier on the same day and planted when the apartment complex was first built. So they ought to be pretty close to identical...possibly even genetically similar or perhaps identical if they were grown from cuttings rather than seed. I'd guess that they are of some fairly fast-growing species.

But they are all slightly different shades of green - some slightly yellowish, some subtly brownish, some are a really vivid almost "lime" green. They all seem pretty healthy though - the color differences are pretty subtle - they aren't brown as in "Autumnal", it's spring here in Texas and the leaves are all pretty new.

Given that everything else is the same (species, age, etc) I presume that this must be due to differences in soil chemistry, available sunlight and amount of water available.

It's also noticable that the color of all of the leaves of a particular tree are identical in color - even though some parts of the tree are in more or less permenant shadow between these large buildings and other parts are getting plenty of light because they are ten feet above the roof-line.

But (chemically) what is changing in the leaves? Is it just a matter of whether there is more or less chlorophyll - or is it the presence of different amounts of some other colorant?

I'm curious because I do computer graphics and I'm wondering about what might constitute a realistic range of randomized colors for otherwise identical trees - I'll probably end up just having one of our artists go and make an artistic choice - but it would be nice to actually understand what's going on. For example, if the differences are only in chlorophyll levels - then it's likely that only the amount of green is changing from tree to tree...but if it were wildly varying amounts of some reddish compound then the answer is different.

SteveBaker (talk) 14:39, 2 April 2010 (UTC)

I know that in aerial overflight imagery, the most common cause of coloration difference in vegetation is amount of water. This is especially detectable in infrared channels (also picking up amount of chlorophyll). You may be seeing variations of the water table or phreatic surface on a meters-scale level. Whether the quantity of water is a biological cause for a variation in chlorophyll quantity/quality is a question for a botanist... Nimur (talk) 15:33, 2 April 2010 (UTC)

(ec) The colour of leaves is determined by a combination of various pigments (such as carotenoids), including chlorophyll (those other pigments are what give the autumnal colours). There are also different types of chlorophyll, with slightly different colours (see Chlorophyll). Since it is currently spring, the difference could be due to differing ages of the leaves (young leaves are often yellower than old ones). If the trees get different amount of sunlight, they may be a few days ahead/behind each other. If that is the case, I would expect the differences to reduce over time - I suggest you take daily photographs and compare them. I would expect the soil to be very similar over such a small area (unless different plants had been grown there previously, I suppose). There could be differences in water, though. --Tango (talk) 15:35, 2 April 2010 (UTC)

(ec) I'd go with the amount of chlorophyll. Note that new leaves are often also a very different shade of green than last year's growth, so the ratio of new leaves to old would affect the overall color. And the percentage of new leaves could depend on water, sunlight, temperature, how many old leaves are retained, and many other factors. StuRat (talk) 15:38, 2 April 2010 (UTC)

Power lines compared to Overhead cables on train lines

Hi. I am trying to understand what differences there are between power transmission lines that are part of the power grid and power lines that you would find above an electrified train track. I imagine that the power lines are usually almost continuously transmitting electricity, but that overhead train lines are only doing so, when trains pass, and also that far power power passes down power transmission lines than overhead train line. I would also like to understand if the electromagnetic radiation from overhead train lines is at all comparable to the radiation from power transmission lines. Any help would be appreciated. Thanks GregB1968 (talk) 15:47, 2 April 2010 (UTC)

For the train, they use two power lines, one positively charged and one negative, so that no electricity should flow until the train completes the circuit. I suppose regular power lines are similar, with the appliances at the end being what completes the circuit. However, unlike the train case, the circuit is always completed by many thousands of appliances, so electricity is always flowing. StuRat (talk) 15:57, 2 April 2010 (UTC)

Our article on overhead lines explains their use for public transport / train systems. They may use mechanical schemes to keep them from breaking under the constant attachment of the train's electrical paddle or connector. Typically, they are higher voltage than the residential circulation lines; voltages vary anywhere from ~ 1000 volts (e.g., San Francisco Muni) to much higher (~ 10 kV in Germany. Sometimes, they also operate at a different AC frequency. Consequently, they have different power distribution and substation implementations; but otherwise, they are not very different from standard transmission lines. Nimur (talk) 16:13, 2 April 2010 (UTC)

Railway electrification systems usually use the tracks as the one "line" and the overhead as the other. Therefore, only when a train makes a circuit is power transmitted. Power for trams and light rails are typically 750 V DC, while mainline trains may be either DC (typically 1500 V or 3000 V) or AC (15 kV or 25 kV are the most common). With so high voltage, it is often not necessary to have a parallel feeding system, although unless the trains use a different frequency than the power grid (50 Hz in Europe; 60 Hz in North America), they can simply feed from the local grip at regular intervals. Arsenikk ^(talk) 17:11, 2 April 2010 (UTC)

Thanks for all the input, so far. There is a rail line near to my place of work (Hertford Loop Line) which seems to be 25 kV AC line. The power transmission article seems to suggest that power lines are usually greater than 110 kV. I am wondering what impact that has on electromagnetic radiation. Does the much lower voltage mean that there is much less radiation, and does the fact that there is only intermittent power transmission on the rail line, mean that there is only intermittent electromagnetic radiation (i.e. only during actual power transmission)? Thanks again for the help so far. GregB1968 (talk) 17:38, 2 April 2010 (UTC)

Stu also even if there no appliances or anything in use, most power lines are at such high voltages that if you touch just the positively charged line, electricity will arc across from the negatively charged one and through your body.--92.251.179.38 (talk) 18:31, 2 April 2010 (UTC)

One additional question on railway power. I once slept in room in Bremen an in the dark I could see a Cold cathode flicker each time a tram was passing. Next morning I checked and I saw that a steel cable, holding the isolated power cable, was attached to the wall in the room were I was staying. How does enough energy get into my room that a cold cathode is giving light. --Stone (talk) 18:58, 2 April 2010 (UTC)

It takes very little energy to make a fluorescent light flicker. StuRat (talk) 19:05, 2 April 2010 (UTC)

If the power is DC there is almost no electromagnetic (radio wave) leak. But there is a (stationary) electric and magnetic field around it. Are you referring to electromagnetic sensitivity? If you are, since it's fictional, I can't tell you if a railway power line is better or worse. Ariel. (talk) 19:11, 2 April 2010 (UTC)

Thanks Ariel. I would just like to understand if there is an electromagnetic field, even if there is not a train passing. I really don't understand electricity at all, but I think that the voltage of the cable is just the energy potential between two point, whereas the current is actually the flow of electrical energy. With transmission cables, I am guessing there is typically a current because there is usually always something drawing current from the grid, whereas with the trains, there is only current drawn when there is a train drawing power. What I am not clear on, is whether the electromagnetic field is caused simply by having a cable which is "live", or whether it is only when there is current drawn. I did read an article elsewhere that suggests there is a large electromagnetic field near the floor of many train carriages but, of course, that doesn't clarify whether the field is always there even if there is no train. Any more help appreciated. Many Thanks GregB1968 (talk) 12:51, 3 April 2010 (UTC)

Any charged object (like live DC electrical wires, even in an open circuit) will have an electromagnetic field around it. Your exposure to that field varies with the strength of the charge and (the square of) your distance from it, of course, but also the material between you and the charged object. Insulators provide some protection, but are not perfect. A Faraday cage (a mesh of conductors designed to cancel the field) is another way to block EM radiation. StuRat (talk) 15:19, 3 April 2010 (UTC)

Thanks Stu. So presumably the cables would be considered charged, even if no current is being drawn. Is that right? If I wanted to measure the field around a power transmission line, or an overhead rail cable, which kind of monitor would I use? I Googled electromagnetic detectors, and got this page - [1]. Of the detectors listed there, would an AC gaussmeter be the most appropriate (assuming that the cable in question was AC)? Thanks again GregB1968 (talk) 17:15, 3 April 2010 (UTC)

I failed to say that only DC electrical wires would have a charge in an open circuit, so I now added that up above. (In fact, I don't think AC wires would show a charge, even when electricity is flowing.) As for the meter, it sounds to me like you are interested in all types of electrical and magnetic fields and radiation, so you should probably get a general purpose meter. StuRat (talk) 18:37, 3 April 2010 (UTC)

Thanks. I read up a bit more on this [2], and what I read seems to suggest that there is an electric field when the cable is charged, but a magnetic field only when there is a current flowing (not sure if this varies between DC and AC). I wonder if this means that there would only be a magnetic field when a train passes, but an electric field all the time. I've got to say that I am getting more confused :) When people talk about an electromagnetic field, is that actually two fields (electrical and magnetic), or is it a magnetic field generated by an electrical source (i.e. a current passing through a conductor). Thanks again. GregB1968 (talk) 19:44, 3 April 2010 (UTC)

There are three fields here, and they are related but different. Electric, Magnetic, and Electromagnetic. Electromagnetic is photons, and radiates away from the conductor. Electric exists in a charged conductor (voltage, not current), Magnetic exists with current (current, not voltage). Electromagnetic exists in a changing field (of either type). (That's simplistic, but I hope accurate.) Ariel. (talk) 01:06, 4 April 2010 (UTC)

As far as physicists are concerned, electromagnetism is one fundamental force, with different manifestations. Thus, electricity creates magnetic fields and magnetism creates electric fields. StuRat (talk) 01:11, 4 April 2010 (UTC)

So would it be correct to say that, for DC with absolutely no current flowing, there will be only an electrical field (from the charge), but that for flowing DC and from AC (where some current flows most of the time), there will always be an electromagnetic field? And in the case of the flicker on a fluorescent light, I assume it is the high inductance of the choke that picks up the E-M field (a single flash when the current changes in DC, or a continuous 50/60 Hz flicker from a strong AC field). Would an old choke connected to a "mains tester" screwdriver serve as a very cheap E-M field detector? (I'll try it!) Dbfirs 08:32, 5 April 2010 (UTC)

MBBS 100% free scholarships

from where can i get 100% free scholarship for mbbs? —Preceding unsigned comment added by 117.102.16.126 (talk) 16:59, 2 April 2010 (UTC)

Are you referring to the medical degree? Your IP address says you are in Pakistan, is that where you want to study? --Tango (talk) 17:02, 2 April 2010 (UTC)

All medical schools in Pakistan use the Bachelor of Medicine, Bachelor of Surgery (MBBS) degree. Not sure how you would obtain a scholorship but usually such schemes are done directly by the medical schools (e.g. for very good grades at pre-medical level) or they are subsidised by a company in return for you working for them after the degree. Though the latter is rare for being a doctor, you may be able to find a research institution who could fund you if you find that you have exceptional ability and you sign an agreement to work for them post-qualification. Regards, --—Cyclonenim | Chat  21:43, 2 April 2010 (UTC)

How are proton beams created?

I've always wondered how proton beams for colliders, like the Large Headron Collider, are created. Are the beams exclusively protons? If so, what element is used for the protons? And how are the protons "separated out"?

Thanks —Preceding unsigned comment added by Spodeworld (talk • contribs) 17:39, 2 April 2010 (UTC)

I don't know for sure, but I would assume that they just ionize hydrogen using an electric field, which also serves to separate the protons and electrons. -- Coneslayer (talk) 18:11, 2 April 2010 (UTC)

There are lots of types of ion sources for linear accelerators. Unfortunately, proton beam in particular is a redirect to proton, which talks nothing about that topic. DMacks (talk) 18:26, 2 April 2010 (UTC)

We should probably get together and try to fix that. Theresa Knott | token threats 18:34, 2 April 2010 (UTC)

It's amazing that we have a Proton pack article but not a real proton beam article! --Mr.98 (talk) 00:55, 3 April 2010 (UTC)

Coneslayer is correct. Dauto (talk) 18:39, 2 April 2010 (UTC)

[3] states that they come from a Duoplasmatron. There they are created by a electron beam kicking electrons from a gas and the created ions are extracted by a magnetic field. Cern shows a bottle of hydrogen for the Linac 2 Pre-Injector --Stone (talk) 18:49, 2 April 2010 (UTC)

What would happen

What would happen if someone built an engine that propel a spacecraft at 1,079,252,851 km/h? Supposing we found some method of propulsion that could potentially provide the necessary power, and lets say it's travelling through a complete vacuum so it doesn't get blown all to hell by the friction, is there any reason why the spacecraft couldn't achieve that speed?--92.251.179.38 (talk) 18:25, 2 April 2010 (UTC)

That's a little bit faster than the speed of light so the answer is NO, it can't be done. Dauto (talk) 18:30, 2 April 2010 (UTC)

See special relativity Theresa Knott | token threats 18:31, 2 April 2010 (UTC)

You see this is what I was expecting. But obviously there's nothing stopping us from building such a propulsion system. What would happen as the craft neared the speed of light?--92.251.179.38 (talk) 18:33, 2 April 2010 (UTC)

As you accelerate the craft its energy increases which by the Einstein's formula E=mc² means its mass also increase making it harder and harder to accelerate (More inertia). To reach the speed of light you would need an infinite amount of energy which is not possible. Dauto (talk) 19:00, 2 April 2010 (UTC)

"obviously" ? Energy (speed) has mass (weight). So as you speed up the craft it gets heavier. In order to speed it up some more, not only do you have to speed up the original weight of the craft (called the rest mass), but also all the additional mass from the energy (called the relativistic mass, and don't for a second think this mass is fictional, or just a mathematical concept - it's totally real). The more you speed it up, the heavier it gets, the heavier it gets the harder you have to push to speed it up - but that very hard "push" uses a lot of energy, so it gets even MORE heavy from all that additional energy. The result is that when you hit the speed of light the mass becomes infinite, so no matter how hard to push, you just can't move it.

Well, you can't hit the speed of light, so it doesn't mean much to say the mass is infinite at the speed of light. The energy required to reach the speed of light (which you calculate as an integral) is infinite. --Tango (talk) 19:31, 2 April 2010 (UTC)

And why is it infinite?--92.251.142.219 (talk) 15:18, 3 April 2010 (UTC)

Here is the relativistic formula for the kinetic energy $K\,$ of a particle of mass $m\,$ moving at speed $v\,$.

$K=mc^{2}\left[{\frac {1}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}-1\right]$.

Where $c\,$ is the speed of light. Just plug $v=c\,$ in the formula and you will see that you get infinity. Dauto (talk) 15:37, 3 April 2010 (UTC)

Special relativity gives a good explanation of what happens—the mass of the craft increases, it starts to perceive time as being slower than other reference frames, its size gets smaller as viewed from other reference frames, and the energy needed to keep it going increases. You can't hit the speed of light this way, or go beyond it—the physics just doesn't work out. If you could get to it (which you can't), the end result would be that its size would be nothing, its mass would be infinite, and its perception of time would stop (if I understand it correctly—I am sure there is a more subtle way of saying those things). The faster-than-light article is a good discussion of why current science says it won't work, and gives some problems with making loopholes in current understandings as a way to get around this constraint. Our theories would have to be substantially wrong (or missing something huge) for this to work out. (Which is always possible, but you'd have to get your new theory to jibe with the rest of the observed data, which would be a non-trivial task! You probably aren't going to manage it!) --Mr.98 (talk) 22:05, 2 April 2010 (UTC)

time on the cross

What would be the average time of survival after being nailed to a cross by ancient Romans and the time of death? 71.100.3.207 (talk) 19:29, 2 April 2010 (UTC)

It depends on the details. See Crucifixion#Cause of death. --Tango (talk) 19:41, 2 April 2010 (UTC)

Assuming ideal conditions (hah!), ie no blood loss, toxic shock, torture, or extreme exposure to heat or cold, the limiting factor would probably be water, without which humans can rarely survive more than 3 or 4 days. All of the afformentioned factors would greatly increase perspiration, as well as general stress, so I'd estimate that the lower end of 2-4 days, though it could certainly be faster. Perhaps most cruel would be to offer or even force the consumption of water, which could extend this time period up to, again in "ideal conditions" as much as a few weeks, and possibly even longer with food, sterile conditions--i think I've said too much. Don't try it.68.171.235.139 (talk) 14:08, 4 April 2010 (UTC)

Note that in the story that is most familiar to us, the victim was given a wound in the side in order to make death come more quickly. Looie496 (talk) 19:17, 4 April 2010 (UTC)

My understanding of that particular story is that the victim had apparently died more quickly than was usual, and the wound was made to test whether death had actually occurred (as it had). The standard Roman procedure for hastening the death of a crucifixee was to break the lower legs, preventing them from taking body weight from the arms and thus bringing on suffocation (the usual cause of death, as per the answers below) more quickly. 87.81.230.195 (talk) 11:58, 5 April 2010 (UTC)

I must disagree with 68.171 about dehydration being the limiting factor for crucifixion survival time. This is because, when a person is suspended by his/her arms in a crucified position, the person's own weight puts an extreme stretching load on the muscles, tendons and ligaments in the arms/shoulders; this, in addition to causing excruciating pain, is also transmitted through the shoulders to the ribs, stretching the chest muscles and the diaphragm to the point where they cannot contract properly for exhalation. The victim must then haul himself/herself up and then forcefully contract the diaphragm and chest muscles in order to exhale (no easy task when the arm muscles are stretched out too), which leads to muscular exhaustion in a matter of a few hours at the very most. Once muscular exhaustion sets in, the victim can no longer force an exhalation, leading to death by asphyxiation long before dehydration becomes dangerous. FWiW the article mentions some people surviving crucifixion for up to several days, but I doubt it. 24.23.197.43 (talk) 01:55, 5 April 2010 (UTC)

that's also accurate, but it would depend on how a person was set and how their weight was supported. 206.53.157.72 (talk) 02:20, 5 April 2010 (UTC)

Normally, when someone was being executed by crucifixion, he/she would be tied or nailed to the cross by the wrists, with the arms stretched out to the sides -- this ensured that the stretching load would be transmitted to the ribs. If, on the other hand, someone was hanged by the wrists with the arms pointing straight up, this would not in itself be fatal, just excruciatingly painful and permanently crippling (which is plenty bad enough as it is). BTW, when St. Andrew was crucified, they hanged him on a cross that was X-shaped, so his arms were stretched up and outward at an angle -- would that be fatal by itself? 24.23.197.43 (talk) 05:44, 5 April 2010 (UTC)

Tougher than grass

Is there any plant, capable of being mown, that would stand up to be parked on by cars more than grass does? Thanks 89.243.36.35 (talk) 20:16, 2 April 2010 (UTC)

What you need is to put things within the grass like the link that follows this. a Sustainable Urban Drainage System. Basically a sort of cross-hatch rubber/plastic layer that grass can grow through (amongst other things) that allow the main weight of the vehicle to be carried by that, allowing the grass to flourish. - http://www.tensar.co.uk/contents.asp?cont_id=306&cont_type=3&page_type=CT ny156uk (talk) 21:21, 2 April 2010 (UTC)

(Just Added) Or Grass Pavers (search on google and you'll find loads of companies). ny156uk (talk) 21:22, 2 April 2010 (UTC)

Those rubber things look ugly, I've seen some. I'm still looking for some plant that is tougher than grass, and which will survive being mown. 78.149.194.146 (talk) 13:49, 3 April 2010 (UTC)

Try this. And google "high traffic ground cover" for more. Ariel. (talk) 01:10, 4 April 2010 (UTC)

The fist sentence says "These groundcovers don't take as much rough play as grass...". StuRat (talk) 13:51, 4 April 2010 (UTC)

I know. But a negative answer is still an answer. Ariel. (talk) 17:47, 4 April 2010 (UTC)

The trouble is that there are solid biological reasons why grasses make the best lawns.

The "surviving being mown" part is an interesting issue. The reason that plants of the grass family survive being mown is that they evolved to cope with grazing animals. The specific adaptation that they have is that - unlike other plants - the growth happens at the base of the plant instead of at the tips. With most plants, you mow off the growing tips and the plant can't renew itself so it just ages and dies. With grasses, the plant is renewed from the bottom - so you can keep on mowing it - and it'll just keep on growing. So right there - you're in trouble. You need grass (or at least something else in that family...um...bamboo? Probably not!

Sorry - but I'm pretty sure you need those pavers with the holes that let grass grow up between them. If you do find another plant, it'll be in the grass family. I don't think anything else will work. (Maybe astroturf?!)

SteveBaker (talk) 03:17, 5 April 2010 (UTC)

The problem is that cars compact the soil too much and make it hard for roots to penetrate. Graeme Bartlett (talk) 08:57, 5 April 2010 (UTC)

I've always joked that we should have chives as our lawn instead of grass. It seems that no matter how little attention they get or what horrible conditions they're put in they still flourish more than every other plant. Never tried mowing them, although they do stand up to being cut and used for potatoes pretty well. Your neighbors would hate you though; I'm sure the smell would be incredibly strong. -Pete5x5 (talk) 15:49, 5 April 2010 (UTC)

Things like dandelions and daisies survive being mown, so its not just grasses. 92.27.160.94 (talk) 09:45, 6 April 2010 (UTC)

is it possible to get pregnant 6 days after (onset of) menstruation?

is it possible to get pregant six days after the onset of mensturation (ie first day being last sunday 1, mon 2, tue 3, wed 4, thur 5, fri - today- 6). thank you. 82.113.106.100 (talk) 22:37, 2 April 2010 (UTC)

Incidentally, doing a search on one's user name, only to find a misspelled instance of the word "menstruation", is a distinctly unpleasant experience. :-) StuRat (talk) 13:39, 4 April 2010 (UTC)

Yes. See my answer below. Theresa Knott | token threats 23:35, 2 April 2010 (UTC)

It may be worth noting that home pregnancy tests are relatively cheap and quite accurate if you follow the directions carefully. Your doctor can conduct a more accurate test. Not to state the obvious, but... sex is kind of designed to make women pregnant. That's what it's for. You should always assume that a woman might become pregnant because she almost always can get pregnant. Matt Deres (talk) 00:02, 3 April 2010 (UTC)

*Sarcasm* See Evolutionary purpose of sex...aww, red link. =( Ks0stm ^(T•C•G) 00:09, 3 April 2010 (UTC)

WHAAOE - try Evolution of sexual reproduction...close enough. SteveBaker (talk) 02:10, 3 April 2010 (UTC)

No longer a redlink--Patton123 (talk) 12:50, 3 April 2010 (UTC)

PREGNANCY

When is a woman ready to concieve after menstruation period?reproduction in human being —Preceding unsigned comment added by KENNEDY NEWTON (talk • contribs) 23:29, 2 April 2010 (UTC)

It's not an exact science, (if it were people would be able to choose exactly when to get pregnant) but see our article Calendar-based methods for rough details. Theresa Knott | token threats 23:34, 2 April 2010 (UTC)