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June 27

Neutron annihilation

What does neutron and anti-neutron annihilation produce? What particles? ScienceApe (talk) 01:06, 27 June 2008 (UTC)

Usually two gamma rays (or maybe pions?), but sometimes other stuff. Theoretically it could make anything as long as energy, electric charge, and a bunch of other things are conserved. Hold on and I'll try to look it up in PDGLive. —Keenan Pepper 01:27, 27 June 2008 (UTC)

Thanks, and while you look it up, if it produces pions, can you tell me if they are neutral or charged pions? ScienceApe (talk) 04:23, 27 June 2008 (UTC)

Take a look at annihilation and electron-positron annihilation. As Keenan says, products could be almost anything, depending on energy of collision, as long as energy, charge, momentum etc. are conserved. Enough rest mass alone in a neutron pair to produce a small zoo of particles, and if they have significant kinetic energy then the possibilities increase. Electron-positron annihilation article says that W and Z bosons have been produced by banging just electrons and positrons together with enough energy. Gandalf61 (talk) 09:05, 27 June 2008 (UTC)

I'm asking about a low energy interaction. A low energy interaction between an electron and positron will yield two gamma ray photons. I want to know what a low energy interaction between a neutron and antineutron will yield. ScienceApe (talk) 14:58, 27 June 2008 (UTC)

This document might be helpful (especially page 10). As in proton-antiproton annihilation, it's pions and not much else. Icek (talk) 18:52, 27 June 2008 (UTC)

Nose

Was there ever nose hair clippers before 1910? For people who had nose hair that was too long, what was the pattern and how long out of the nostril did it come out of? —Preceding unsigned comment added by 68.148.164.166 (talk) 04:28, 27 June 2008 (UTC)

It's a moot point. Nose hairs can still be trimmed with small scissors. ScienceApe (talk) 15:01, 27 June 2008 (UTC)

...and scissors have been around since 1500 BCE.--Shantavira|^{feed me} 16:25, 27 June 2008 (UTC)

Those who could afford it went to the barber, who could have used either scissors or a razor. Itsmejudith (talk) 16:21, 27 June 2008 (UTC)

Besides, man has always been equipped with fingers and a strong grip. Plasticup ^T/C 18:07, 27 June 2008 (UTC)

Man has also been equipped with fists that enable him to punch himself in the testicles if he so wishes. That doesn't make it a good idea. :) --Kurt Shaped Box (talk) 23:24, 27 June 2008 (UTC)

what is this formula?

PVU = Δ x Δ p >= h / (4 п) = h/2

(not the best rendering, the second H is supposed to be an h with a line towards the top) but maybe someone recongises it? A different but related question, what is the best way to search for formulas? I tried searching for PVU and for h/4 but didn't get much... I think PVU isn't the right thing there though ++Lar: t/c 04:37, 27 June 2008 (UTC)

Never mind, I found it. It's the Heisenberg uncertainty principle Uncertainty_principle and I think h-bar is Planck's constant and the answer to the second question is that if you do a search on google using delta X delta P, (symbolically) [1] it will find it ++Lar: t/c 04:46, 27 June 2008 (UTC)

Awww...

Repost - Black holes and Hawking radiation

[2]

I never really got a good reply, BenRG had a go, but self-admittedly wasn't sure. Any advances? Rixxin (talk) 08:59, 27 June 2008 (UTC)

Looking over the previous question, it appears the point is a case of understanding exactly what is meant by the rate of emission. Hawking radiation, as best I can tell, does not say that there is more radiation from a smaller black hole than a larger. Rather, the point is likely one of surface area to volume (if we consider volume to be defined by the event horizon, since that's where the radiation originates). Since volume is a radius-cubed function and surface area radius-squared, a small black hole will have a higher surface area to volume ratio than a large one. With volume being proportional to mass, and Hawking radiation proportional to surface area, that means a small black hole has a larger radiation to mass ratio than a large one. Thus, it evaporates "faster" taken as a unit (one black hole) even if it's evaporating less in a more absolute sense. — Lomn 14:03, 27 June 2008 (UTC)

Tell me if I'm wrong, but assuming that the event horizon is proportional to (or indeed, defined by) the Schwarzschild radius, which in turn is defined by the mass of the black hole, does the square/cube ratio explanation still hold up? I guess what I'm saying is, does the changing mass affect the Schwarzschild radius in a linear way, or not? I can see the equation on the Schwarzschild radius page, but I'm not sure how to do it!

Rixxin (talk) 15:04, 27 June 2008 (UTC)

The event horizon is the sphere whose radius is the Schwarzchild radius. The event horizon is based on the density of a body (radius and mass), but the Schwarzchild radius is based on the mass. By multiplicity, there is a linear relationship (mass is multiplied by two constants). If you have a graphing calculator you can enter in y=(G*1/c^2)x and substitute the real values for G and c to see the graph of the function. For future reference, if the variable is squared, cubed, etc, that's what makes it a square/cube relationship, etc. Mac Davis (talk) 18:01, 27 June 2008 (UTC)

That's great, cheers to you both, Lomn and Mac Davis. Rixxin (talk) 10:54, 28 June 2008 (UTC)

Cilia

Can cilia be found in the external nares?68.148.164.166 (talk) 09:55, 27 June 2008 (UTC)

Not in the first centimetre. Fribbler (talk) 17:26, 27 June 2008 (UTC)

Who is Celia? What is she? (Also: where is she?) —Preceding unsigned comment added by 79.76.191.71 (talk) 00:29, 28 June 2008 (UTC)

Pubic hairs

Removed reposted thread... the new addition is a description of the poster's symptoms, which is clearly a request for medical advice. -- Coneslayer (talk) 13:31, 27 June 2008 (UTC)

Options after completing MBBS

Usually, after completing MBBS, a person would choose courses like Scan reading (Radiology), Diabetis specialist or other things like Psychiatry or MD general medicine.

Is there any other options apart from those usual courses?

What should a person after completing MBBS should do to join companies like Pfizer to do research in that company? Or what are the options in biotechnology and bioinformatics?

If one should get job in biotechnology or bioinformatics after completing MBBS what should one do? —Preceding unsigned comment added by 59.92.107.26 (talk) 14:41, 27 June 2008 (UTC)

If you're interested in research, you're going to want to get an MD/PhD. Short of that, you're pretty much limited to medical practice. To do something like biotech or bioinformatics you should really get a bachelors in a science and then go for a PhD in that science...at least those are the most common routes. Strictly speaking, you could probably wind up in almost any career based on any training. Also, to do research with most pharmaceutical companies you're going to want a PhD in chemistry or biology (unless you want to be a lab tech, in which case a bachelors in either of those will do). As above, there are lots of different paths to the same career. But in my experience not much else really gets hired.

Also, you should really speak to a professor or doctor or something. They can give you lots of first hand advice. EagleFalconn (talk) 14:59, 27 June 2008 (UTC)

Or your university's careers service. Students and ex-students under-use such facilities. Itsmejudith (talk) 23:39, 27 June 2008 (UTC)

Videos of adults or adolescents with harlequin ichthyosis

Our article on harlequin type ichthyosis describes a few, rare examples where patients have survived into adolescence and adulthood. I was looking for a video on Youtube or elsewhere that shows an older survivor, but the only videos I can find are of babies. I also tried the links at the bottom of the Wikipedia article to no avail. I'm interested to know if they can move around, talk, etc.--The Fat Man Who Never Came Back (talk) 14:56, 27 June 2008 (UTC)

Harlequin_type_ichthyosis#United_Kingdom — I saw the documentary that they mention in the article and the kids could certainly move around and talk. Had it not been for the skin condition, you would not know them as separate from other children or adults. — CycloneNimrod ^talk?_contribs? 19:35, 27 June 2008 (UTC)

IIRC, adults with the condition don't actually look as bad as you might expect. I'd guess that the really horrific pics that people trick people into viewing on the internet are the more serious examples that are invariably weeded out by nature shortly after birth. --Kurt Shaped Box (talk) 23:18, 27 June 2008 (UTC)

Eating cancer cell

Do eating live cancer cells impose danger to human? I know gastric juice will digest incoming living cells.But, will some cells attach on the inner wall of oesophagus and try to invade adjacent tissues?

I suspect the chance would be slim. If anyone can find a correlation between skin cancer and incidence of oesophageal cancer in the same household, that might verify your question. But I doubt it, to be honest. — CycloneNimrod ^talk?_contribs? 17:01, 27 June 2008 (UTC)

I would expect eating one's own cancer cells to be dangerous if they somehow survived the digestive system. But I think someone else's cancer cells ought to be recognized as foreign and attacked by the immune system. --Allen (talk) 19:50, 27 June 2008 (UTC)

unless you are closely related, see Devil facial tumour disease and allograft diseases. Also of a concern is a possible viral infection from consuming cancerous tissue, see Carcinogenesis#Role of viral infections. --Dr Dima (talk) 20:27, 27 June 2008 (UTC)

In the case of canine transmissible venereal tumor, the cancer cells are "often if not always unrelated to the DNA of their host." So it seems that not being closely related to a vector does not necessarily make a host not susceptible. --71.162.249.44 (talk) 22:21, 27 June 2008 (UTC)

I hope there wouldn't be a human version of allograft disease. I think that will spread like wildfire.--Lenticel ^(talk) 22:51, 27 June 2008 (UTC)

Why do you think so? It wouldn't be more contagious than any other infection that is transmitted by body cells, i.e. much less contagious than super-light viral particles. Also, if you read the Tasman Devil disease article, the animals' immune system is compromised which wouldn't be the case with humans. --Ayacop (talk) 08:28, 28 June 2008 (UTC)

I was basing my opinion on the canine version. Well, we're a very sexually active species and cancer can erupt anytime. The animals are immunocompromised because they little biodiversity and this might also be the case in some isolated human culture/colony.--Lenticel ^(talk) 06:54, 29 June 2008 (UTC)

What is this spider?

Hi, please see Image:Mystery OR jumping spider.jpg. I apologize for the poor quality of the pictures - my camera doesn't take close-ups very well and this spider is about 7mm from the tip of the antennae to the tail. I've never seen any of these until this week, but I've seen three different ones in about a five-mile area this week. Two were on the exterior walls of 2 different houses, and another was in my living room. They were all seen in extremely NW Oregon. I'm curious what species/classification you can narrow it down to. I think it's a jumping spider because I've seen two of them jump around. Flayked (talk) 21:32, 27 June 2008 (UTC)

Yes it looks like a jumping spider alright. Could be male Salticus scenicus actually, but I wouldn't bet more than $1 on that ;) --Dr Dima (talk) 21:42, 27 June 2008 (UTC)

Salticus scenicus is a good candidate. So is Phidippus audax. Check out this link to some spiders found in Tigard, Oregon 161.222.160.8 (talk) 21:52, 27 June 2008 (UTC)

Cool, thanks a lot to both of you. I think I've narrowed it down to Zebra spider - the stripe pattern on mine matches that on the photo 161.222.160.8 linked to. The color marking pattern on the Phidippus audax is very different from mine (no noticeable stripes on legs, and zebra/tiger-like stripes, not the dot and semi-circle). Thanks again. I think what threw me off was the eyes - the spider was too small for me to really notice the "large eyes" which are supposedly characteristic of jumping spiders. Flayked (talk) 22:06, 27 June 2008 (UTC)

Gun and bullets

What sort of gun and bullets would it take to deliver a lethal blow to a personin a house who was sitting behind double glazed windows , closed venetian blinds and velvet curtains? BTW I'm not an assassin, I'm just interested in protecting myself!--79.76.191.71 (talk) 23:51, 27 June 2008 (UTC)

Colonel Moran would know, presumably ;) --Dr Dima (talk) 00:17, 28 June 2008 (UTC)

Assuming those windows aren't bulletproof, I believe just about any gun except maybe a paintball gun would do the trick. Paragon12321 (talk) 04:36, 28 June 2008 (UTC)

Really? A watergun? :-P But back to the main point, if you're referring to a single shot, my guess is even if accurately aimed at the head (which would be rather difficult behind closed curtains/blinds) some sort of 'light' pistol with low calibre ammunition (sorry I know next to nothing about guns) may not be enough for death if your lucky [I wouldn't bet my life on it tho ;-) ]. But since the first shot is going to break the windows I would concur it's probably enough with multiple shots presuming the target doesn't run away. And as I've already mentioned, it's going to be rather difficult to aim accurately at the very least you may need some sort of infrared vision sensot Nil Einne (talk) 06:47, 28 June 2008 (UTC)

Infrared won't work behind double windows (I've even doubts as to single ones). Remember those heat pictures of houses where windows are undifferentiated rectangles/heat leaks. --Ayacop (talk) 08:19, 28 June 2008 (UTC)

Glass is pretty opaque to (far) infra-red, I believe (that's why greenhouses work), so thermal imaging through even a single window pane would be very difficult. --Tango (talk) 15:19, 28 June 2008 (UTC)

June 28

Why is spitting in someone's face considered to be particularly offensive?

Whilst hitting or insulting another person are taken as offensive acts, what is it about spitting on another person in particular that can drive the victim into an immediate murderous rage?

At least where I'm from, it seems to be the unwritten rule that 'a man should not spit on other man under any circumstances' and that to do so is completely disgusting, reprehensible and dishonourable. If you insult or punch another man during a disagreement, you may end up in a fight. If you spit in another man's face during a disagreement, you *will* end up in a serious fight.

Based on my personal observations of life and people falling out over various things in my homeland, my general perceived severity of various insults is so (going from least offensive to most offensive):

• Dirty looks
• Personal verbal insult
• A punch/push
• Disrespect to property and/or woman
• An insult against one's mother
• Spitting in the face

Any ideas? Is this something instinctual/deeply-rooted in the human psyche? --Kurt Shaped Box (talk) 00:18, 28 June 2008 (UTC)

How would you like a gob of bacteria-ridden goop from someone else in your face? bibliomaniac15 00:20, 28 June 2008 (UTC)

Yeah, I assume it's the general taboo about unwilling exchange of bodily fluids, which people instinctively dislike due to diseases being spread that way. Spitting simply falls into that category in the same way as someone intentionally coughing on you, urinating on you, ejaculating on you, whatever. ~ mazca ^{t | c} 00:23, 28 June 2008 (UTC)

Not at all - but why would I find it more offensive than that same person punching me in the face? --Kurt Shaped Box (talk) 00:25, 28 June 2008 (UTC)

Because saliva is abject. Violence (perversely enough) is not. Most bodily fluids are in a special psychological category of grossness for (most) human beings that far outdoes any rational reason. --74.223.170.187 (talk) 02:10, 28 June 2008 (UTC)

In Ireland I remember old farmers sealing a deal by spitting on their hands before shaking (sealed with a spit, I guess) but spitting on another person would be deeply offensive there.Gaiatechnician (talk) 16:32, 1 July 2008 (UTC)

It's probably worth noting that this is likely to be a fairly culture-specific thing. I mean, you can say whatever you want about my mother, and unless you actually know my mother and are making a specific personal comment about her, it's not likely to mean anything to me other than make me aware of the fact that you're trying to offend me. Whether you tell me to go fuck myself or call my mother a whore, it's just noise, you know? It obviously won't make me happy, but that choice of subject matter won't make me any more angry. I think that generally speaking, this definitely goes for most of the people I know as well. I know that this definitely isn't the case in many other cultures. Likewise, if someone were to spit in my face, it would probably make me really, really angry simply because it's such a hostile thing to do, but I'd still strongly prefer it to a punch in the face. On the other hand, at least according to our article on spitting, the Maasai tribespeople spit on each other as a form of greeting and farewell. Personally, I think I'm gonna stick with shaking hands for the time being... -- Captain Disdain (talk) 13:03, 29 June 2008 (UTC)

That could explain something that I've wondered about. According to the Laws of the Game for soccer, "Spitting on someone" is specifically called out as an immediate sending-off offence (red card). I've wondered why that was necessary -- perhaps it's for the benefit of those for whom spitting is not an affront, to let them know that it is for many others?

--Danh, 63.231.163.123 (talk) 23:22, 29 June 2008 (UTC)

Cavy

What do you call a female cavy? a male cavy? Idle Jan (talk) 01:26, 28 June 2008 (UTC)

I assume you are talking about a Guinea pig. Our article uses "sow" for female, "boar" for male, and "pup" for young, here. Hope this helps. --Dr Dima (talk) 01:58, 28 June 2008 (UTC)

Heliostat

I have been trying to design a heliostat that is on equatorial mount with some sort of clock drive. And I think I have hit on a design that will eventually work. (It is on instructables.com). (Clockwork being simpler and potentially cheaper than throwing computer power at everything). I just got everything uploaded and then I was very surprised to find out that clock based heliostats are an old concept! They were used for many years by early scientists.

http://physics.kenyon.edu/EarlyApparatus/Optics/Heliostat/Heliostat.html shows a bunch of them.

and http://www.earlytech.com/common/show_image.phtml?Id=491390987&Item_Name=Heliostat+by+Silbermann+1843 shows how the geometry works. I confess that i do not understand it at all! So, it is too late for me and I will continue with my little design. Mine goes at 15 degrees per hour, but I think these old ones go at a different rate, either twice as fast or twice as slow as the sun appears to travel around the earth. So, anyone like to explain or just mention how the old scientific heliostats worked? On the heliostat page would be great. Thank you 24.69.192.200 (talk) 03:00, 28 June 2008 (UTC)

First of all, please do not ask for knowledge questions to be answered on article talk pages. The article talk is for discussing improvements to the article, this desk is the right place to ask questions.

The heliostat in that link needs to rotate at half the speed of the sun because it is trying to keep the direction of reflection constant. If you are just trying to keep a telescope or camera pointing directly at the sun then you need to rotate at the same speed. So it depends what you are trying to do, if you want to redirect the sunlight to a fixed point where you can use it to do work then 15^o/hr is going to be wrong.

Note that to track the stars (siderostat) it needs to rotate at a different speed to a clock because the earth is not rotating once every 24 hours with respect to the stars. The earth rotates in 24 hours with respect to the sun which is not quite the same thing. In one day, the earth has moved on 1/365th of its orbit around the sun and so needs to rotate a further 1/365th of a revolution in order to face the sun again. The siderostat therefore needs to run 1/365th parts per day slowfast (about 4 minutes) otherwise your photographs of the stars will be streaks instead of nice points. SpinningSpark 13:08, 28 June 2008 (UTC)

I made my first model http://www.youtube.com/watch?v=WRTX1S7PD-U and the principles seem to work. In this case, the mirror does not turn at all, but 2 pointers decide its angle as it pivots round its centre. One is pointed at where the light will go and one is pointed at the sun. (That one turns on the equatorial mount axis). I used 2 rubber bands to bisect the distance between the pointers and attached a post at the centre of the mirror to the bands. This seems such a simple method but I do not see it documented anywhere.Gaiatechnician (talk) 16:40, 1 July 2008 (UTC)

AC Power - Generation, Voltage and Current

I know that this might seem very basic, but it does not seem to be answered by the existing Wiki sections on AC power. The questions stems from an argument that you don't get electrocuted if you (are grounded) and touch the negative side of an AC power point.

There is also no basic explanation that in an AC (Alternating Current) circuit it also has Alternating Voltage. Most graphs show AC voltage varying in a sine wave pattern, with a graph that that has its X axis at 0 and the voltage varying equally to the positive and negative side. It seems to mean that the voltage in the AC system fluctates from +240 to -240v (Australian voltages). This doesn't seem correct to me - I though it fluctuated and its average (RMS) was +240V.

Could someone please explain how the electrical generator at the power station, ends up at 240VAC at my power point. And what the actual voltage graph, and current, looks like at: 1 - the generator 2 - the transmission lines 3 - the transformers 4 - my domestic power point.

Thanks. —Preceding unsigned comment added by 58.165.127.244 (talk) 04:36, 28 June 2008 (UTC)

There is no "negative" side to A/C power. In the US, there are "neutral" and a "hot" wires feeding typical 120V outlets. The neutral side is usually tied to ground at the service entrance, while the hot wire carries the A/C voltage sine wave. So in this case, coming in contact with the neutral wire will not likely cause injury, although I wouldn't bet my life on it. -- Tcncv (talk) 04:43, 28 June 2008 (UTC)

To better answer your questions: Power is typically generated and distributed as three-phase electric power. Because power is equal to voltage times current (amperage) while power loss during electric power transmission due to electrical resistance is proportional to current and not voltage, it is more economical to step up voltage and reduce current using transformers when transmitting power over long distances. As the power nears the consumer, transformers are again used at several points (electrical substations and pole top transformers) to step down the voltage to consumer levels. Also, while three phase power is used in most industrial and many business users, for residential use, the power is typically converted to single-phase electric power or split-phase electric power. For single-phase electric power, only one voltage is available to the customer. For split-phase electric power, two opposing AC voltage feeds are provided plus a neutral. One voltage (such as 120V in the U.S.) is obtained by using one of the hot feeds together with the neutral, while another voltage (240V in the U.S.) by using the two opposing hot feeds. If you follow the links above, you should find more detailed answers to your questions. -- Tcncv (talk) 05:28, 28 June 2008 (UTC)

To bring it back to your Australian case (or in my case, South Africa), what you have in your house is a Live, Neutral and Earth wire. Typically a sinusoidal voltage is supplied between the live and neutral. The neutral wire is grounded (connected to the physical earth) at some point where it comes into your house. Thus typically touching the neutral wire while you are in contact with the ground should be less lethal because there will be almost zero voltage across your body. DO NOT try this! More on the neutral/ground issue further on, for the time being let's deal with amplitudes and that sine wave.

The voltage at the live terminal is quoted as 240 V AC. First off the 240 is not the amplitude, it is actually the RMS value, and equates to the amplitude/sqrt(2) for a sine wave. The actual amplitude is therefore 240*sqrt(2)=340 V. More on RMS in a couple of sentences, keep reading. The signal does indeed fluctuate between +340 V and -340 V, thus the average value of the voltage signal is in fact zero. This is obviously not a useful quantity when talking about AC voltages, so how do we actually quantity the "magnitude" of an AC signal?

This is where RMS comes in. (p.s. if you how to do integral calculus you can actually derive this yourself which will give you good insight). How do we quantify usefully the magnitude of an AC signal in order to equate it to a DC signal of "equivalent size"? Obviously using the amplitude will give an over-estimate (the signal is only briefly at max amplitude), and obviously the average is zero no matter how high the voltage. The concept that is thus used is that of "equal POWER": what amplitude of AC volts does it take to generate the same amount of power in a load as a steady 1 volt DC signal. The answer turns out to be sqrt(2). Thus the convention when talking about "1 volt AC" is that you're talking about a signal of amplitude sqrt(2), because this 1 V AC signal does the same amount of work as a 1 V steady DC signal.

Let's derive the sqrt(2): given a 1 V DC signal placed across a 1 ohm resistor, how much power generated? well, going by P=V²/R gives 1 Watt. Now let's take an AC signal of amplitude A. What size of A gives 1 Watt dissipated? Now your voltage is Asin(2Πf*t) where f is 50 Hz for Aus I assume (but that's immaterial because we are working out the average power over 1 cycle of the AC wave). P = V²/R = A²sin²(2Πf*t)/1. Now we calculate the average power dissipated over 1 cycle of the AC wave. The average of the sin² term is 0.5 (do some trig to derive this if you don't know it already). Thus we have 0.5*A²=P=1 Watt which gives A=sqrt(2).

As to why we use RMS rather than just the amplitudes: well one of the applications of AC is obviously electrical power generation and distribution, in which case you have to know how much power is being produced and absorbed. Using the RMS values instead of absolute amplitudes makes it easier to work things out (you don't carry factors of sqrt(2) everywhere in teh calculations) and thus has become the convention.

Ok back to the neutral/ground issue. So the neutral is physically connected to the ground at some point where it enters your house. How is this useful? Well, it keeps the neutral close to ground potential so that if you come into contact with it you should receive a much smaller (possibly non-lethal) shock. Now, from beyond this connection point looking into your house nothing should be flowing through the earth conductor, thus you can put a very sensitive circuit breaker (called an earth leakage breaker) into the earth circuit at this point, and if any of your earthed appliances develops a short to the its internal earth wire there will be current in the earth wire and the breaker will trip to safely isolate the appliance (typically it actually breaks the path for ALL your plug sockets in the house). Zunaid©® 07:49, 28 June 2008 (UTC)

When wiring in a house breaks or is improperly installed, the neutral or ground wires can become energized at the supply voltage, and in such situations touching the neutral and ground wires could place the full supply voltage across your body, causing injury or electrocution. When everything is installed and working as designed, there may still be a few volts between ground and neutral at some points in the circuit, because of the voltage drop from load current in the neutral. A low resistance connection, such as a wire jumper from ground to neutral can carry very high current from this small voltage difference. Do not attempt the experiment. Edison (talk) 19:29, 28 June 2008 (UTC)

Evolution in Physics

In biology, evolution is presented as the major scientific cause of change in wildlife. But what about the other sciences ? I evolution was very significant, would't it be directly observable in nuclerar physics, astrononym, chemistry and the like ? 69.157.237.196 (talk) 09:20, 28 June 2008 (UTC)

Because, as you certainly know, living things consist of molecules, evolution is in fact a chemical phenomenon. It's just that people take the really complicated chemistry and call it biology. Also, as molecules behave to the laws of physics, in the same way evolution is also a physical phenomenon. On the other hand, the objects astronomy deals with aren't living things, and as evolution is a phenomenon of life, it won't apply to astronomical objects. --Ayacop (talk) 09:39, 28 June 2008 (UTC)

There is such a thing as evolution of stars etc but that is really a different subject.

Evolution as in darwinism etc relies on an objects ability to self replicate (see self replication) and mutate - as such it's pretty much confined to plants and animals.87.102.86.73 (talk) 10:31, 28 June 2008 (UTC)

Not quite, evolution occurs in all living beings. ScienceApe (talk) 22:42, 4 July 2008 (UTC)

I don't know why you'd think that something that pertains to one branch of nature would necessarily exist in others in any major way. There's no doubt that matter-antimatter annihilation exists in nuclear physics, but it doesn't exist anywhere else. There's no equivalent for special relativity in biology—I'm not sure what that would even look like. And there's no requirement that biological evolution exist outside of biology. --74.223.170.157 (talk) 13:09, 28 June 2008 (UTC)

Generally, all biology is complicated chemistry and all chemistry is complicated physics. Everything in biology or chemistry could, given the time, be linked to physics. However, not everything in physics can be linked to biology or chemistry. It only works one way. — CycloneNimrod ^talk?_contribs? 15:03, 28 June 2008 (UTC)

Evolution in the sense of changes through time from initial conditions does indeed occur in the hard sciences: that is what cosmology is. The processes that dictate how the changes happen are, of course, different from biological evolution. In fact, when looking at the universe today, or looking at the geology of our own planet, the only way you can make sense of it is to be aware of the historic evolution that occurred.--Eriastrum (talk) 16:00, 28 June 2008 (UTC)

Evolution occurs in everything. Because evolution means something changing over time. Our technology evolves. Our planet evolves. Stars evolve. Etc etc. It's not the same as biological evolution, but it's still evolution. ScienceApe (talk) 22:42, 4 July 2008 (UTC)

Medical diagnosis

Yes, I am looking for medical advice and treatment, but not here.

Here, I am asking a question about medical diagnosis.

I have been ill with the recurring symptoms of an infection for about three months now. It starts to endanger my job. The doctor tells me I won't get antibiotics unless I have at least 39 C temperature. He did a thorough and costly physical examination and came up with the result that all examined organs were healthy but that I probably had some kind of infection. (What a surprise for that lot of money spent!)

He did nothing that could lead to a diagnosis of what kind of infection I have, whether it's viral or bacterial. He even neglected to ask me if I had been to foreign countries recently. And I had similar experiences with other doctors in the past with other cases of diseases. It looks like they won't do anything useful until a disease has already done damage to the organs. (And yes, I am angry.)

Now the question: are there really no methods to diagnose the kind of an infection? What would they be, are there any plausible reasons why they are not applied, and, finally where can I get them (note this is asking about medical advice, not for).

Thanks 77.3.155.173 (talk) 13:57, 28 June 2008 (UTC)

I know that situation, and it's a good question. There are ways, however, to have a good guess (besides a post-mortem), for example by exclusion: you can ascertain it's not disease X if you don't have its typical symptoms; it can't be in organ Y because all the numbers concerning that organ are fine; and so on. Secondly, the symptoms you encounter at the moment should be a hint. Thirdly, you could try to apply natural antibiotics---for example, garlic will temporarily kill any bacteria in the stomach and many bad boys in the upper intestine: if you feel better after that, then you know. Make yourself informed, do (harmless) experiments.

There may also be special diagnostic tools that just aren't applied by doctors because they aren't known well enough, take too much time, cost too much. For years I read about methods to recognize diseases from the breath, but where is that stuff? The teams probably show a prototype, but the pharma boss decides against it, probably. However, it is possible to get a lot of diagnostics privately from laboratories, if you know what you're looking for, and are willing to pay for it. --Ayacop (talk) 14:18, 28 June 2008 (UTC)

Really good general diagnosticians get busy pretty quickly. They also have to explore and process a lot of information, which is time-consuming (and poorly compensated relative to other activities that require similar amounts of training, intelligence, and time). I anticipate that some aspects of the task will be automated soon - software could elicit symptoms and ask some pretty standard questions (like recent travel, as you point out) that would help a good diagnostician do a more thorough job. Sorry to hear about your frustrations - I hope things improve soon. Scray (talk) 19:02, 28 June 2008 (UTC)

There are tests for all kinds of bacterial and viral infections. Nearly all known bacterial/viral infections can be detected. It appears that you are in a country with nationalized health care (or worse, HMO-controlled healthcare). There are many studies on nationalized health care that point out the weakness of doctors not being able to go "off script" for special cases. As the doctor pointed out, he is not allowed to treat you for a bacterial infection until you meet the guidelines necessary to qualify for bacterial infection treatment. As such, he was basically telling you what to do. You need to return and tell them that you had a fever of 39C but took a fever reducer and a cold bath to reduce it enough so you could show up at the doctor's office. Then, he can treat you. It is important to listen to what the doctor says. He cannot say "Go home and come back complaining of a 39C fever." He can only say "I cannot give you antibacterial treatment until you have a 39C fever." -- kainaw™ 23:26, 28 June 2008 (UTC)

Well it's a bit more complicated. He told me that unless I had 39C a blood culture would be too insensitive. I'm well aware of antibiotic-resistance and that there is a 1:1 chance that the infection is viral and for the other 50% there is a good chance that those bacteria will not respond to general broadband antibiotics, so I see the need to know what those little critters really are. I explicitly asked him about PCR and genetic detection and he honestly could not tell me why this is not used for diagnosis. He obviously didn't know about ELISA either, this seems not to be part of the education. As I understand, a blood culture would only be positive if the disease is caused by bacteria (or other microbes, not viruses or poisons) and only if they proliferate in the blood, so infections where the microbes grow is specialized tissue could only be detected when they are so numerous that they penetrate into the blood stream.

I live in Germany where another reason for reluctant prescription is that each doctor has a limited budget for all his patients and has to pay the excess amount from his own earnings. I don't know if it would be perfectly legal to go abroad for treatment, and more, I don't know which countries allow a better and more effective treatment. And as for pretending fever, yes, I think that would work but, that's why they are becoming us a bread of liars and cheaterlings. 77.3.168.22 (talk) 08:39, 29 June 2008 (UTC)

The typical reason that a doctor is reluctant to prescribe antibiotics is to prevent the evolution of antibiotic-resistant microbes. For a more specific diagnosis you could call the doctor and express your concerns to him directly, or you could ask a specialist (if you are in the United States, look for somebody who is board-certified in Infectious Disease Medicine) for a second opinion. I hope you feel better soon. 69.140.152.55 (talk) 03:34, 29 June 2008 (UTC)

This whole exchange illustrates why there is a policy against medical advice here. The original question contains at least 4 false assumptions, none of which were pointed out or explained by any of the responders. Second, the responses contain numerous irrelevant, and not a few erroneous "facts". Finally, no one has provided a direct and accurate answer to the two direct questions asked at the end of the initial account. This is no better than an impromptu conversation among 6 strangers on a train. The inquirer is a fool to rely on this information to make decisions about his health and should have asked his questions of the one person who heard his whole story, had the training to sort out the facts, could have answered his questions accurately, and could be held legally responsible for the answer. 159.14.240.230 (talk) 13:26, 1 July 2008 (UTC)

You are welcome to give an answer to the question as well as to explicitly point out what you think were false assumptions of mine. When I saw that the whole thing would boil down to legal questions I removed the entire section but it was restored. 77.3.134.249 (talk) 18:20, 1 July 2008 (UTC)

I don't think any explicit medical advice has been given here. The answers are attempting to explain the methodology of the practice of medical diagnoses itself, in line with the original question which clearly states medical advice is not being sought. A discussion is however in progress at Wikipedia talk:Reference_desk/Science. Jdrewitt (talk) 20:40, 1 July 2008 (UTC)

EMF Transmission Dangers

Is there significant scientific evidence to support claims of health dangers from living in close proximity to electric power stations?70.58.154.222 (talk) 18:35, 28 June 2008 (UTC)

There have been studies which found statistical association between exposure to electromagnetic radiation from power lines, and studies which found no such association where one might have been expected, such as among power system workers. Biological stidies have found some effects of powerline frequency EMF on cells and tissues. Overall, the association with cancer or other ailments is far less clear than for ionizing radiation, asbestos, smoking, exposure to sunlight or exposure to several other well known health hazards. Research continues. Edison (talk) 19:23, 28 June 2008 (UTC)

Also see Electromagnetic_radiation_and_health#powertransmission. --Allen (talk) 00:48, 29 June 2008 (UTC)

Keep in mind that "hot topic" issues like this suffer from tremendous publication bias. Plasticup ^T/C 12:57, 30 June 2008 (UTC)

Interesting note: The example given in the publication bias article is about the supposed cancer risk of powerlines. Plasticup ^T/C 12:59, 30 June 2008 (UTC)

June 29

galaxy edge on

what do u mena by galaxy caught edge on ? i am only able to get the pics for my niew but not the explanation —Preceding unsigned comment added by 123.239.149.69 (talk) 08:24, 29 June 2008 (UTC)

There are many different types of galaxies, see Galaxy morphological classification. Now, edge-on is simply a term describing the inclination of the galaxy with respect to an observer on earth. If a galaxy is inclined 90° relative to the earth then you will observe the galaxy directly from the side, or edge. Jdrewitt (talk) 09:59, 29 June 2008 (UTC)

Here's some pictures:

edge on

from 'above'

as you can see galaxies are thin like a plate87.102.86.73 (talk) 10:19, 29 June 2008 (UTC)

Please note that the above pictures do not appear to be fully edge-on or fully face-on, although they are quite close. Perhaps the images below illustrate an edge-on galaxy and face-on galaxies with an inclination relative to the earth closer to 90° and 0° respectively.

• 
  An edge-on glaxy with an inclination of 90° relative to the earth.
• 
  A face-on galaxy with an inclination of 0° relative to the earth.

Jdrewitt (talk) 10:49, 29 June 2008 (UTC)

The "edge-on" picture shows lots of light coming from oval regions above and below the disc. A spinning disc shaped arrangement of stars could be reasonably stable, but why does light come from above and below the disc? Are there a significant number of stars in soupbowl shaped regions above and below the disc to create the apparent glowing clouds? If so, what keeps the gravity of the disc stars from pulling them into the disc? If the stars are in the disc and the light is being scattered, what is there to scatter the light in space? If dust, gasses, or small objects, then again why doesn't the gravity of the stars in the spinning discull in the surrounding matter? —Preceding unsigned comment added by Edison (talk • contribs) 11:57, 29 June, 2008 (UTC)

See galaxy - it answers these questions and more. PhySusie (talk) 12:17, 29 June 2008 (UTC)

The region you are referring to is the galactic halo which exists around spiral galaxies. Its shine is due to the stars and star clusters that exist in that region, but at much lower density to the main disk region of the galaxy. There is a lack of new material in the galactic halo and so there is no new star formation. The stars that exist in the halo have much different orbits to stars lying in the plane of the galaxy, and halo stars may pass through the disk and nucleus of the galaxy. See Galactic spheroid. Jdrewitt (talk) 12:53, 29 June 2008 (UTC)

Actually - I think this person is referring to the galactic bulge, rather than the halo. But the article referred to by Jdrewitt is a good one to check out. PhySusie (talk) 00:40, 30 June 2008 (UTC)

"apparent glowing clouds" suggested the halo to me, however, both answers are valid. Jdrewitt (talk) 08:35, 30 June 2008 (UTC)

Flying Mammals

Which is the only mammal that has no wings,cannot fly, but does fly? —Preceding unsigned comment added by 72.51.78.180 (talk) 12:43, 29 June 2008 (UTC)

Is this some kind of a riddle? It sounds to me that you already know the answer. Anyway, humans have no wings and are incapable of flight by themselves, but they still do a fair bit of flying by various means. -- Captain Disdain (talk) 12:48, 29 June 2008 (UTC)

Flying squirrels kind of match the question too. -- Aeluwas (talk) 12:51, 29 June 2008 (UTC)

Wait, this mammal cannot fly yet does? That seems like you've logically excluded all mammals. -- JSBillings 16:53, 29 June 2008 (UTC)

It sounds like it may involve some kind of word play - in which case, original poster, are you sure you've got the exact wording of the question? If not, there could be a vital clue missing. Confusing Manifestation(Say hi!) 23:01, 29 June 2008 (UTC)

As said above, this question is impossible to answer, as all mammals are excluded. —Preceding unsigned comment added by Sliver Slave (talk • contribs) 20:17, 2 July 2008 (UTC)

Medicine-Patella replacement.

Whilst looking at a page on the Patella, a sesamoid bone, I wondered whether replacing the Bone with something larger would be beneficial to jumpers or distance runners. The larger bone would create more leverage for the muscle which the primary functional role is knee extension. Obviously after healing and training, it may improve top speed for runners, like a high gear on a bicycle. Whereas jumpers, long or triple jumpers, might find it beneficial for their sport. However you look at it, controversial, cheating or whatever, do you think it possible?

The Patella [[3]]

Mike —Preceding unsigned comment added by 88.105.111.27 (talk) 12:49, 29 June 2008 (UTC)

I think you´d be hard pressed to find a runner who would undergo a risky knee surgery like that. Replacing the bone would require disconnecting all sorts of tendons and ligaments, reattaching them, then a long rehab which may not necessarily return all function to the limb. I guess it´s possible that it could work, but I think ít´s about as likely as a runner having his legs removed completely and replaced with prosthetics (which apparently can have some advantages over actual legs). You´d probably find Oscar_Pistorius#Dispute_over_prosthetics interesting. --Shaggorama (talk) 01:13, 30 June 2008 (UTC)

Human and agricultural uses of antibiotics, and the development of drug-resistant bacteria

Is it known how great the contribution of non-judicious human use of antibiotics is to the development of drug-resistant bacteria, when compared with the contribution of antibiotics use in animal farming? —Preceding unsigned comment added by 71.162.249.44 (talk) 12:58, 29 June 2008 (UTC)

Not to me, at least. But I suspect nobody really knows, but the uppers fear it and do everything to reduce the use of antibiotics for humans so they will still work when the important people like soccer players, stock bulls or politicians fall ill. 77.3.168.22 (talk) 15:36, 29 June 2008 (UTC)

Heh... "Important people like soccer players"? You make it sound as if they're more worthy of healthcare than anyone else... -- Aeluwas (talk) 16:03, 29 June 2008 (UTC)

I think 77* was being sarcastic, though unfortunately so. Antibiotic resistance, it seems to me, will harm people with less money disproportionately. Rich people will be more likely to have access to the few remaining effective antibiotics. (And by the way, the article I linked to has a section on use in animals, though apparently it's under dispute.) --Allen (talk) 16:13, 29 June 2008 (UTC)

Hey, yes, I am sarcastic. But soccer players really do get better treatment, so that proves they effectively are more important, at least for those people that decide who gets the real medication and who only get the dopes so they don't feel so much ill any more.

But are there any serious alternatives to antibiotics? Washing hands won't get you healthy again once someone else has sneezed his bacteria into you. And phages are natural vectors for genes, including those for antibiotic resistance. Unlike antibiotics they mutate and have a potential to get out of control. 77.3.168.22 (talk) 18:01, 29 June 2008 (UTC)

Well, no, there aren't serious alternatives to antibiotics... that's the whole point of fighting antibiotic resistance by discouraging overuse, right? --Allen (talk) 03:59, 30 June 2008 (UTC)

Inseminating Mars

If humans sent spaceships to nuke Mars with bacteria, would new life develop and would this new life eventually generate itw own atmosphere, allowing people to breathe easily ? 69.157.237.196 (talk) 13:53, 29 June 2008 (UTC).

This is indeed an area of great interest to scientists, and is studied and theorized about frequently. We have a nice article about it: Terraforming of Mars. Apparently the biggest problem currently is that Mars is waaaaay cold, so we'd need to heat it up considerably. The good thing is that once you get the heating process started, Mars can help along, since there is considerable quantities of CO₂ frozen at the poles. When it got warmer, that would be released into the atmosphere and help along the greenhouse effect. It's some sort of irony that the things that would make Mars more like earth is vast quantities of CFCs and CO₂.

After that it is done, the article says gives essentially your plan for continuing:

After the heavy dust-storms subside, the warmer planet could conceivably be habitable to some forms of terrestrial life. Certain forms of algae and bacteria that are able to live in the Antarctic would be prime candidates. By filling a few of the rockets with algae spores and crashing them in the polar areas where there would still be water-ice, they could not only grow but even thrive in the no-competition, high-radiation, high CO2 environment.

(I assume that this is what you meant, and not literally nuking the surface of Mars. That would probably not be the greatest plan for allowing life to spread). The article is fascinating, I highly recommend you read it. 217.213.153.218 (talk) 14:08, 29 June 2008 (UTC)

Starting out with electronics...

(not sure if this is more computing than science, but here goes...)

After seeing a bunch of guides and how-tos on the internet about how to easily program microcontrollers to control LEDs or build robots or do whatever (you know, MAKE magazine stuff), I've sort-of become intersted in learning this stuff. I'm great at computers, and I can develop in a number of different languages (including C, which I suppose is the language you'd use to program microcontrollers), and I have a deep understand how computers work. The thing is, I've always concentrated on the software side, I don't think I've ever in my life held a soldering iron in my hand. I know some of the theory behind electronics and basically how it all works, but I don't really know about this stuff in practice (When do you need a power-supply capacitor? How big does it need to be? Where do you put it? How big a resistor do you need not to fry stuff? And how do you read those colorful bars? And how do you solder without burning yourself and your stuff? etc.) I'm betting that out there there's a book for me, called "I'm a pretty smart guy and I want to try to build stuff but don't really know how" or something. Or maybe a website? Can anyone make a recommendation? Like, a beginners crash-course. 217.213.153.218 (talk) 13:56, 29 June 2008 (UTC)

I had similar motivations once. I did some research and decided to buy The Art of Electronics. I kind of fizzled out after a couple chapters, but that was my fault. The book seemed excellent. Hopefully someone who's actually finished a book will also respond :-). --Allen (talk) 15:59, 29 June 2008 (UTC)

Allen, you beat me to it with your recommendation for Art of Electronics. Another good one is Electronic Circuits and Applications by Senturia and Wedlock. But I'm not sure either of these books will teach the more-practical aspects of electronics (such as which end of the soldering iron to hold; I'm not sure about reading color codes, but Wiki's article is probably enough there). In the old days, Heathkit, Eico, and Knightkit were the best answers for learning the more-practical skills, but they're gone, of course. You can still buy kits of parts with a PC board from a few electronics parts shops (such as "You-blew-it", err, "You-do-it" Electronics in Needham, Massachusetts [4]). They can also sell you a soldering iron, electronic test equipment, and the like. (Soldering is like any other skill; practice makes perfect.)

It's gotten a lot harder to learn anything about electronics as a hobbyist; the prevalence of VLSI, very-fine-pitch parts, and surface mount devices has made the bar to entry much, much higher than when I joined the trade.

Atlant (talk) 17:17, 29 June 2008 (UTC)

This seems oddly fitting, since I learned many of my programming skills from The Art of Computer Programming (my dear parents gave me all three volumes my second year in high school; it is the best birthday present I've ever got). I can at least check them out from the library to see if they are what I want :) 83.250.202.36 (talk) 17:22, 29 June 2008 (UTC)

Someone in one of the electronics magazines a couple of years ago noted that electronics became a great hobby when the era arrived in the 1960's that you could build radios amplifiers and other gadgets using transistors and LEDs rather than vacuum tubes with high voltage power supplies. Breadboarding became cheap and easy. People built TVs, oscilloscopes, computers and even robots from Heathkit kits. Ham radio was a popular pursuit for tecchie. Then along came computers as a tecchie pursuit, with people programming them to do amazing things with BASIC programs. Large scale integration meant that there was not all that much soldering to do in building an electronic device. Websurfing seemed to replace ham radio to some extent. Then PCs arrived with less accesss to the lower level functioning and no BASIC. No more games to be typed into the computer from a monthly computer magazine and debugged so they actually worked. Just the running of applications and games. With the passing of the era of big chemistry sets, Heathkits, and other hands-on technology, there seems to be less interest and ability of those entering college today to understand the inner workings of the electronic and computer devices they use. So it is great to see someone interested in tinkering. You can approach electronics from a low technical level of perhaps experimenting with one of the larger Radio Shack electronic experimenter sets, and you can still buy lots of interesting kits from the electronics magazines. Community colleges offer some great courses in basic electronics that are less of a calculus fest than electrical engineering courses. Edison (talk) 19:15, 30 June 2008 (UTC)

Look for the evil genius series of books, like the title Electronic Gadgets for the Evil Genius or 53 High-Tech Pranks for the Evil Genius, Bionics for the Evil Genius (etc.) they all have introductions to electronics and stuff. While not exactly textbooks or courses in electronics, they make learning electronics an enjoyable activity. They have some really phenomenal projects, ranging in difficulty from absolute beginner to experienced. Ilikefood (talk) 01:37, 1 July 2008 (UTC)

SImple pendulum

1.If a simple pendulum with a period of 1 second is set in motion on the moon, determine the new period of this pendulum.

2. will a simple pendulum swing continuosly in air? explain why. suggest the condition required for a pendulum to swing continuoslyMinjiun (talk) 14:21, 29 June 2008 (UTC)Lmj

For #1, see the article on pendulum; see also the article on the moon for value of lunar gravitational acceleration. For #2, see the articles on drag and damping.

(After edit conflict) 1. Not enough information - doesn't say where the pendulum has a period of 1 second. But let's assume that is on the surface of the Earth. Somewhere in your texbook there is an expression for the period of a simple pendulum in terms of its length and the local acceleration due to gravity (or g) - if you can't find it in your textbook, take a look at our pendulum article. Now, keep everything constant apart from g. Reduce g to 1/6th of its value on Earth (that is approximately correct for the surface of the Moon). What is the change in the period of the pendulum ?

2. Another badly phrased question - the motion of any pendulum is always continuous. But let's assume it means continually or perpetually, not continuously. Think about energy and friction. Gandalf61 (talk) 14:43, 29 June 2008 (UTC)

You are assuming the question is badly phrased. It is likely verbatim to what the questioner's teacher said in class, drew a diagram of on the board, and explained would be in the homework - all while the questioner was busy texting his friends about much it sucks to repeat physics class in summer school. -- kainaw™ 00:27, 30 June 2008 (UTC)

There are places on the planet where the regular school year is still in session! —Preceding unsigned comment added by 62.145.19.66 (talk) 08:46, June 30, 2008 (UTC)

mars

can life exist on mars? —Preceding unsigned comment added by 117.97.3.66 (talk) 14:28, 29 June 2008 (UTC)

yes. Scray (talk) 14:50, 29 June 2008 (UTC)

See the article Life on Mars and Planetary habitability. Jdrewitt (talk) 14:56, 29 June 2008 (UTC)

Please clarify what you mean by "life", "exist", "on", and "can". And because I'm feeling mean, "mars". (Translation: Could a human being, without any form of life support, survive for any meaningful length of time on Mars? No. Is it possible that just below the surface of Mars there is a habitat in which single-celled creatures similar to those found on Earth could possibly survive? Definitely. In between? Maybe.) Confusing Manifestation(Say hi!) 22:59, 29 June 2008 (UTC)

But is there Life on Mars?--Shniken1 (talk) 16:42, 30 June 2008 (UTC)

Amount of energy on earth remains constant.

Is it true the amount of energy on earth is the same today as when the earth was formed? If so who is credited with the theory that the energy amount is the same only changed to a different form? I believe I remember in my study of Physics years ago that it was taught that if two boxcars were pushed together one was moving the other still that the energy of the moving one was transfer to the other and some energy went into heat and sound as the still boxcar would never begin moving as fast as the moving car.

My question is WHO —Preceding unsigned comment added by 24.19.226.142 (talk) 14:31, 29 June 2008 (UTC)

The general idea you're looking for is the conservation of energy, with the conservation of momentum relating a little closer to the boxcar example. However, it is not true that the amount of energy on Earth is unchanging, because the Earth is not a closed system. Solar energy radiates in (at a changing rate) and heat energy radiates away (at a changing rate). An ice age, for instance, is a period where the Earth has less energy (though I've no idea what that difference would be in percentage terms -- likely very very small if you start talking about "the whole earth").

As for "who", no one man can be credited with fully formulating an explanation of the conservation of energy. The history section of that article should be illuminating. — Lomn 14:40, 29 June 2008 (UTC)

Several energy factors are changing and I doubt it can simply be assumed that the total Earth energy is less during an ice age. Earth picks up more mass from the Solar system (meteors and such) than it looses. If the equivalent energy per mass–energy equivalence is included then it may be important. More heat energy radiates away than Solar energy radiates in. This once caused wrong estimates of the maximum age of the Earth because heat energy from radioactivity in the Earth was not discovered and included in the calculations. PrimeHunter (talk) 15:55, 29 June 2008 (UTC)

Excluding meteors (an excellent point, by the way), I think the ice age idea holds up pretty well. Air and surface temperatures decrease, and everything else holds. Insignificant in a grand e=mc² mass-of-the-earth example, but a good practical one. — Lomn 13:01, 30 June 2008 (UTC)

Oh no, not another "second law of thermodynamics" mangler. Imagine Reason (talk) 22:34, 29 June 2008 (UTC)

The first law of thermodynamics, you mean?. --Bowlhover (talk) 00:11, 30 June 2008 (UTC)

No, but I've seen that one too. Imagine Reason (talk)

Imagine Reason, have you investigated the articles breeder reactor and fast breeder reactor yet? --arkuat (talk) 08:38, 30 June 2008 (UTC)

No. Why? Imagine Reason (talk) 01:17, 1 July 2008 (UTC)

Because they produce fissile material from fertile material; that is, they produce more usable nuclear fuel than they consume. However, they're only liberating potential energy stored in the nuclei of (otherwise unusable as fuel) U-238 atoms. So they don't violate conservation of energy, but can easily be mistaken by a novice for doing so. --arkuat (talk) 04:49, 1 July 2008 (UTC)

Space left by crude oil

What is filled to the huge space left by the crude oil and gas? —Preceding unsigned comment added by 62.231.233.151 (talk) 14:55, 29 June 2008 (UTC)

Oil doesn't sit in voids in the earth, it is usually in porous rocks. So when oil is extracted, the rocks remain. Following extraction of the oil, the pores in the rocks will either be filled with natural or atmospheric gases or the oil may be replaced by water, which is either used to force the oil out or naturally seeps into the rock from the natural water table. Jdrewitt (talk) 15:04, 29 June 2008 (UTC)

In some cases, the pore spaces contract when you remove the fluids they have been storing. In effect, the land in the regions settles, but in general the amount of such settling is not very noticable for practical volumes of oil/gas. Dragons flight (talk) 00:55, 30 June 2008 (UTC)

wow 125.21.243.66 (talk) 06:43, 30 June 2008 (UTC)

So, geologists take note, if you pump oil or natural gas out of a land area, you may expect that land area's water table to contract naturally as a result. Or am I reading the replies wrong? --arkuat (talk) 08:28, 30 June 2008 (UTC)

That is possible, yes. But sometimes the way they get the oil out is by pumping water into the ground, the pressure of which pushes the oil up and out. I doubt that this method has an impact on the water table. Plasticup ^T/C 12:44, 30 June 2008 (UTC)

Very good point. Thanks --arkuat (talk) 04:53, 1 July 2008 (UTC)

Insect

There is an insect at my home in Kentucky. It looks like a cross between a bee and a humming bird or butterfly. Can you tell me what it is? And if it will sting me? 98.19.3.125 (talk) 20:41, 29 June 2008 (UTC)

A Hemaris sp. hummingbird moth would be my first guess. It is a moth, it is perfectly harmless. --Dr Dima (talk) 20:56, 29 June 2008 (UTC)

You may also want to look at Carpenter bee. It doesn't match the description you gave as closely, but it can sting if you try to catch it; so you may see if that's not it. --Dr Dima (talk) 21:00, 29 June 2008 (UTC)

Check out the Sphingidae article for more extremely hummingbirdy bugs in the same family as Dr. Dima's suggestion. These bugs are not to be trusted! Look at this Gaudy Sphinx Caterpillar: [5]. --76.182.119.241 (talk) 23:29, 29 June 2008 (UTC)

Wiki knows everything. Yay! 125.21.243.66 (talk) 06:42, 30 June 2008 (UTC)

June 30

Complexity and Self-organization in Thermodynamics

Consider computer simulations of dissipative (open) thermodynamical systems. Some examples include Cellular Automata grids, fluid motion, and autocatalytic sets. Have replicating "units" ever been observed emerging within such simulations, even in very simple ones? What about the so-called, effective dissipaters of gradients? paros (talk) 04:24, 30 June 2008 (UTC)

Take a look at Conway's Game of Life if you haven't already done so. --Dr Dima (talk) 08:17, 30 June 2008 (UTC)

If you only need a system of cellular automata with self-replicating entities, John von Neumann discovered one more than 50 years ago. Icek (talk) 09:46, 30 June 2008 (UTC)

artifact

While looking in a plowed field I found a round 1 inch ball made of stone. Could this be a native american artifact and if so what was its purposeCuriouspatty (talk) 01:02, 30 June 2008 (UTC)

Could you post a picture? --Shaggorama (talk) 01:04, 30 June 2008 (UTC)

Sounds like a Tom bowler. Graeme Bartlett (talk) 05:11, 30 June 2008 (UTC)

I am still very curious but I have to admit to being a computer novice and I don't know how to post a picture. I do know how to take the picture and put it on my computer. What would be the next step without giving my e-mail address? The ball is on tour through the family right now so it may take a couple of days.Curiouspatty (talk) 00:53, 1 July 2008 (UTC)

Do you have a digital camera? Fribbler (talk) 01:07, 1 July 2008 (UTC)

Once you have the file on your computer you can upload it with the "upload file" link on the left hand side of the screen. Graeme Bartlett (talk) 01:52, 1 July 2008 (UTC)

Why are the planets in that order?

Why Mars after Earth (and the moon!)? Venus after Mercury?, Andremeda galaxy after our own solar system?, etc. You get the picture. Is there a particular reason, such as this group of rocks formed over there, that group of rocks gathered yonder why things in space are laid out the way they are? 5 dollars rides on this bet.THE WORLD'S MOST CURIOUS MAN (talk) 01:28, 30 June 2008 (UTC)

Hi. Have you read Formation and evolution of the solar system? Also, the Andromeda Galaxy after ours is because we live in our own galaxy. Also, is there any reason why they seemingly shouldn't be in that order? Earth, for example, wouldn't support much life were it as close to the sun as Venus or as far as Mars. One theory states that the planets are in that order partly because the rocks were heavier and settled closer to the sun, but this isn't usually true in other solar systems. Venus is hotter than Mercury because it has a heavy Carbon dioxide atmosphere. Hope this helps. Thanks. ~AH1^(TCU) 01:37, 30 June 2008 (UTC)

Because we live in the best of all possible worlds. --Shaggorama (talk) 02:12, 30 June 2008 (UTC)

Or because this is the world we live in. — Lomn 13:03, 30 June 2008 (UTC)

When the solar system was forming two big rock smashed together. Their combined gravity pulled in more rock. Eventually the was a planet. So in answer to your question: Completely random (Unless you believe in God) 4.159.183.112 (talk) 02:37, 30 June 2008 (UTC)

Venus can be so bright because it's close enough to the Sun, but not so close as the Mercury so it's still often visible on the sky. It's quite obvious that the planet at that position has to be named after the godess of beuty. —Preceding unsigned comment added by B jonas (talk • contribs) 13:37, June 30, 2008 (UTC)

I don't quite follow your logic, why should the 2nd planet obviously be named Venus simply because of its position (as opposed to it's magnitude and majestic qualities)? Unless you mean that the position of the planet gives it those qualities, although I would say it is more to do with the thick cover of cloud. Additionally, Mercury is certainly visible from Earth, see Observation, although its proximity to the sun does limit how often the planet is visible from earth. Jdrewitt (talk) 14:49, 30 June 2008 (UTC)

Because calling them by other names makes you look silly--unless you live in another country. Then perhaps you won't. Imagine Reason (talk) 01:19, 1 July 2008 (UTC)

An "immortal" plant

I am looking for a plant that has a Wikipedia entry:

• I don't remember any of its names.
• It was probably originated from Africa or Asia.
• It also lives in Europe. (?)
• It can withstand prolonged dryness.
• In dry season, it becomes a brown ball.
• If you water it, it comes to life in about 3 hours.
• It can withstand multiple dry/wet cycles.
• Some people sell them by mail under a product name similar to "immortal plant".
• It is possibly a species of fern. (?)
• It may live up to 50 years.
• The Wikipedia entry has a lousy picture (dried).

What is the plant? -- Toytoy (talk) 02:11, 30 June 2008 (UTC)

Sounds like Selaginella lepidophylla, except that it's a North American plant. --Allen (talk) 04:01, 30 June 2008 (UTC)

I was talking about Rose of Jericho. Thank you! -- Toytoy (talk) 04:07, 30 June 2008 (UTC)

So you were right Allen. The Wikipicture looks fine,that's exactly how it looks when it is dry. another picture in its hydrated form might help. Richard Avery (talk) 07:52, 30 June 2008 (UTC)

It's also sold as a "dinosaur plant." Mac Davis (talk) 14:16, 30 June 2008 (UTC)

If you want to look at some truly immortal plants, check out Sequoia, Methuselah (tree), and this swedish Norway Spruce. --Shaggorama (talk) 16:18, 30 June 2008 (UTC)

But is that Spruce an individual stem that's that old, or is that the age of the genet? --Allen (talk) 17:56, 30 June 2008 (UTC)

Take a look at List of oldest trees. Apparently the 9550yr figure for this Spruce is just the age of the clone. And since there are much older clones in the world (quaking aspen), I'd say there's a bit of unwarranted hype surrounding this Norway Spruce. --Allen (talk) 18:00, 30 June 2008 (UTC)

Identify this kelp?

What is it??

I took a picture of this while visiting tidepools at the Oregon coast, but for the life of me I cannot figure out what it is. I can't find any species of kelp that have so many small, ruffly leaves, which seem to grow out of long, thin strap. Nor can I find anything with air bladders that shape and size. It's not very long, just a few feet. Any ideas? --Masamage ♫ 05:03, 30 June 2008 (UTC)

After some more hunting, I think it's Egregia menziesii. Here are some other pictures for comparison. Seems like a good match to me? --Masamage ♫ 06:09, 30 June 2008 (UTC)

Volume percent

What's the usual abbreviation for volume percent in English? %vol or vol% or something else? Our article doesn't say. (I'm more interested in the use in general chemistry, not necessarily in alcohol content of drinks.) 62.145.19.66 (talk) 08:03, 30 June 2008 (UTC)

For chemistry, I use more explicit "% v/v" or "% w/v" (g/100 mL) to clarify if the solute was measured in volume or mass. A bare "volume percent" value is only unambiguous in meaning--regardless of how it's written--if it's unambiguous what kind of measurements one is using:) DMacks (talk) 08:10, 30 June 2008 (UTC)

I'm translating a document out of German. I think the context will be clear enough to the reader; the original uses "Vol%", but German allows both "Vol%" and "%Vol" as abbreviations. I'm pretty sure only one of the two is usual in English, I just can't remember which. 62.145.19.66 (talk) 08:17, 30 June 2008 (UTC)

The ACS Style Guide remains fairly silent on this subject. DMacks is correct as far as the ambiguity, but if you are just translating, there may not be a preferred way for the ambiguous case. I would typically prefer something such as "25% by volume," but that might be just a personal preference. (Note: The style guide does list "vol %" in its list of abbreviations, but I don't know if that can be used as a unit or not). --Bennybp (talk) 18:14, 30 June 2008 (UTC)

I've usually seen and used vol% in the UK, in the context of chemistry and engineering. 86.141.89.124 (talk) 19:29, 30 June 2008 (UTC)

I went ahead and used vol%. Thanks for your help! 62.145.19.66 (talk) 06:05, 1 July 2008 (UTC)

Primates on the Moon

Excuse me, but I watched all the Neil Armstrong stuff on teevee when I was a child. Can someone please explain to me why primates aren't living and working on the Moon right now to help out all the primates and other species on Earth? I was brought up to believe that this would have happened by now, and I'm rather puzzled that it hasn't. Someone please explain this to me. --arkuat (talk) 08:48, 30 June 2008 (UTC)

Establishing a colony for people or animals on the Moon would be incredibly expensive and I don't see how it would help us on Earth. Itsmejudith (talk) 09:50, 30 June 2008 (UTC)

Oh, it would. We just have to send the right ones, e.g. this primate there.John Z (talk) 10:09, 30 June 2008 (UTC)

We have an article on colonization of the Moon but it's probably still far away. Some people have been too optimistic about costs, benefits and willingness. PrimeHunter (talk) 10:18, 30 June 2008 (UTC)

Okay, that makes sense, but why do some people think it is more important to have primates on Mars before we establish primates on the Moon? I guess that's the part that I really don't understand yet. --arkuat (talk) 11:04, 30 June 2008 (UTC)

In case the Earth gets shattered by an asteroid, which might take the moon with it. -- adaptron (talk) 20:07, 3 July 2008 (UTC)

Humans haven't been on Mars yet and many people want to go to new places. Mars is considered scientifically more interesting than the Moon, especially when looking for extraterrestrial life. In the really long run (and very hypothetical), Mars seems better suited for terraforming. PrimeHunter (talk) 11:59, 30 June 2008 (UTC)

Orbital dynamics can have odd effects: it takes less fuel (but more time) to reach Mars than it takes to reach the Moon. --Carnildo (talk) 21:55, 30 June 2008 (UTC)

I think that once America won the Space Race, the political point had been proven and there was insufficient imagination among our political leaders to understand why a sustained human presence on the moon would be useful for the long-term progress of our species. (Of course, this was before many folks realized how close we were to actually destroying the conditions on our planet that sustain life, leading to projects such as the Svalbard Global Seed Vault; nowadays, having a back-up planet or even moon might be viewed as handy.)

Atlant (talk) 13:55, 30 June 2008 (UTC)

Although Earth may be in worsening shape, it is still a much better environment for human life than any other planet or satellite in the solar system. Itsmejudith (talk) 14:56, 30 June 2008 (UTC)

Thanks to all of you for your many interesting responses, especially to PrimeHunter for posting the relevant link and to Carmildo for the interesting point, new to me, about fuel consumption. I will confess that I am interested in solar power satellites, which will probably require raw materials support from workers established on the Moon if they are to become economically feasible. --arkuat (talk) 05:01, 1 July 2008 (UTC)

I don't know whether it really requires less fuel to reach Mars than the Moon if the optimal path is used in both cases, but here are some links: Orbital mechanics, Interplanetary Transport Network, Low energy transfers. PrimeHunter (talk) 13:17, 1 July 2008 (UTC)

CERN

How long (current estimate) before the LHC starts doing crazy stuff? Black Carrot (talk) 11:28, 30 June 2008 (UTC)

Large Hadron Collider says "The first beams are due for injection in August 2008, with the first collisions planned to take place about two months later.". The source [6] is The New York Times 9 days ago. PrimeHunter (talk) 11:53, 30 June 2008 (UTC)

Well, I think we're all hoping that the LHC doesn't start doing crazy stuff. But yes, it begins operation soon. Exciting times, no?

Atlant (talk) 13:48, 30 June 2008 (UTC)

protein energy malnutrition

current stastics of kwashiorkar and marasmas occurence in india????? —Preceding unsigned comment added by 59.92.9.106 (talk) 11:29, 30 June 2008 (UTC)

This (from 1997) suggests both would be below 1 per cent, based on trends. --WikiJedits (talk) 18:18, 30 June 2008 (UTC)

Leap second

1. When will the next leap second be? 2. Why was 1972 given two leap seconds just because it was the year the leap second was invented? 208.76.245.162 (talk) 12:42, 30 June 2008 (UTC)

From the article :
Historically, leap seconds have been inserted about every 18 months. However, because the Earth's rotation rate is unpredictable in the long term, it is not possible to predict the need for them more than six months in advance.

And from INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE (IERS)
NO positive leap second will be introduced at the end of June 2008.

Essentially, there isn't one currently scheduled. However, if the 18 months figure it true, we're overdue since the last one was December 2005, 18 months later would have been June 2007. APL (talk) 13:01, 30 June 2008 (UTC)

The 18 months figure is approximate, and based on past trends which have apparently changed. We really don't know when the next leap second will be needed; we just have to keep monitoring the rotation of the Earth and noticing each time it slows down a little or speeds up a little.

As for your question 2, I'm not sure, but it may have just been a side-effect of a decision to set UTC, at that time, to a particular offset from Ephemeris Time or TAI during the years shortly before the introduction of leap seconds. The Ephemeris Time article may have more info. --arkuat (talk) 04:41, 1 July 2008 (UTC)

Endorphin half-life

How long does it take until we eliminate endorphin from our body? Mr.K. (talk) 12:51, 30 June 2008 (UTC)

Have a look-see here. Fribbler (talk) 13:05, 30 June 2008 (UTC)

Relevance of "Space, Time, and Gravity" by Robert Wald

I'm about to read Robert Wald's "Space, Time, and Gravity: The Theory of the Big Bang and Black Holes," second edition (1992). Should I? I'm wondering if there is anything significant in there refuted by recent discoveries. I might also ask the same question about the Feynman lectures. Cannongrandee (talk) 13:52, 30 June 2008 (UTC)

A lot has happened since 1992, but the basics are still (mostly) the same. Incidentally, I found Stephen Hawking's A Brief History of Time to be a great read.Plasticup ^T/C 14:03, 30 June 2008 (UTC)

I can tell you that the Feynman lectures are very unlikely to be refuted anytime soon. See our article, but basically it was intended for first year undergraduates. Consequently, much of the material in there was very well studied by that point. On a side note, they're an excellent text to learn from, good choice. EagleFalconn (talk) 18:41, 30 June 2008 (UTC)

(Relative) Quantification of Human Genetic Diversity

Someone on the innertubulars asked something along the lines of "Is it true [what I heard from someone in a philosophy discussion channel] that human genetic diversity is tiny, among the least diverse of all animals?". I was, of course, struck by an instant bout of premium-strength dubiosity regarding the source and reliability of the information. However, a brief attempt to remedy with a timely injection of actual scientific results was sadly unforthcoming. To which end, I wonder if anyone knows of any studies that have been conducted into the absolute or relative degree of genetic diversity in humans, or how best to go about finding such a study should one exist. It's possible, I'm aware, that the technology has only recently descended to the level of affordability to undertake such investigations, and as such relevant information may not yet be available, though I'd like to think that such a matter would have aroused scientific interest already. Appreciative regards 153.1.253.80 (talk) 15:26, 30 June 2008 (UTC)

I recall reading that humans came very close to going extinct relatively recently and that we are all descended from a very small group of survivors, so there is less genetic diversity than other, related species, such as chimps (see Population bottleneck). This article states that the "genetic diversity [of chimpanzees and bonobos] is much larger than that of our species", despite their much smaller numbers. This article concurs. Clarityfiend (talk) 16:47, 30 June 2008 (UTC)

I've read that as early as Darwin it was realized that diversity in Africa is greater than in any other place in the world, and that was the reason for Darwin's widely ridiculed out-of-Africa theory. Imagine Reason (talk) 11:34, 1 July 2008 (UTC)

Nemesis

I was just reading Nemesis (star) and the article says that "due to orbiting the Sun it would have a very low proper motion and would escape detection by proper motion surveys". Surely at 1–1½ light years away it would have a large proper motion compared with other stars. Am I missing something?--Shantavira|^{feed me} 17:48, 30 June 2008 (UTC)

In a bound orbit, the relative velocity of the two objects goes down as the orbit size increases. Hence, if Nemesis orbits the sun at such a great distance then relative to the sun it must be moving quite slowly. Much slower, in fact, than most of the stars we observe in the sky. Dragons flight (talk) 17:54, 30 June 2008 (UTC)

(ec) The trick is that both the Sun and Nemesis would be moving about a common center of gravity (the barycenter of the system), so the only contribution to proper motion would be from their very low orbital velocity about the barycenter of the system. If we assume that Nemesis has the mass of the Sun and orbits 1 light year out, we're looking at an orbital period of roughly two billion years (if I've plugged in numbers correctly...) which cooks down to a proper motion of something like 0.6 milli-arcseconds per year: very, very small. Of course, that doesn't say anything about improper motions. The parallax shift of such a near companion would be quite large, and would indeed stick out like a sore thumb if noticed. TenOfAllTrades(talk) 18:04, 30 June 2008 (UTC)

I think you're out by 5 orders of magnitude on the orbital period! At least, one of us is, and my 20 million figure matches the 26 million figure mentioned in the article as the average time between extinction events. --Tango (talk) 18:07, 30 June 2008 (UTC)

(ec) Nemesis is predicted to have an orbital period somewhere in the 20 million years range. 360 degrees, divided by 20 million years gives a proper motion of about 0.06 arcseconds per year. The star with the largest proper motion, Barnard's Star, has a proper motion of 10.3 arcseconds per year, so you can see that Nemesis wouldn't have a very large proper motion. --Tango (talk) 18:07, 30 June 2008 (UTC)

It would be exceedingly easy to spot it using a paralax technique. Plasticup ^T/C 18:37, 30 June 2008 (UTC)

Yes, but we still don't have an all-sky survey of paralax extending down to red dwarfs. Nemesis (star)#Looking for Nemesis lists a couple planned projects that would either find or exclude Nemesis (as a red dwarf) by comprehensively measuring paralax through out the local region of space. Dragons flight (talk) 21:36, 30 June 2008 (UTC)

Yes, the theory says it could be a Red Dwarf, but in its hypothesized orbit it would have an apparent magnitude between 9 and 12. We are talking about an object brighter than Pluto. Amateur astronomers would be able to see it with their own telescopes. A 12 inch aperture would be more than sufficient. An object that big with such a massive parallax shift would have been spotted decades ago. Plasticup ^T/C 12:14, 1 July 2008 (UTC)

Many thanks everyone. I was confusing proper motion with parallax shift.--Shantavira|^{feed me} 07:51, 1 July 2008 (UTC)

Another quick question about my parrot

It's nothing of any consequence but I've always wondered about this. Whenever I stroke/scratch my Hyacinth Macaw's head in a certain place, it makes her open her beak wide and stretch her neck, like she's yawning. It's always the same spot that triggers it off, just behind her beak on both sides. Any idea what causes this? It doesn't seem to actually bother her in any way. --84.66.131.165 (talk) 19:44, 30 June 2008 (UTC)

• It's a feeding reflex. Momma touches, beak opens, momma injects food. --jpgordon^∇∆∇∆ 19:52, 30 June 2008 (UTC)
  • Does that really still work for a bird that's 20-something years old? --84.66.131.165 (talk) 20:38, 30 June 2008 (UTC)
    • If you put your fingers to the back of your throat, you'll soon learn that reflexes can last a lifetime! (I don't actually recommend doing that, throwing up isn't nice, but the point stands) — CycloneNimrod ^talk?_contribs? 20:43, 30 June 2008 (UTC)

• • Thinking about it, my budgies do that sometimes after scratching their cheek areas with their claws or rubbing their faces against the aviary mesh. I always figured that it was just some sort of expression of relief from an itch. Same thing, you think? --Kurt Shaped Box (talk) 02:10, 1 July 2008 (UTC)

Frozen heart

In the film Rat Race a heart is shown is a cooler box on transit to a patient waiting for it to be installed. The driver says "it's been locked in that cooler box for seven hours". Can this really be true? The heart was not beating and was just shown in a plastic bag on top of ice. Would it really work if it was put into someone? Plemis monter (talk) 20:19, 30 June 2008 (UTC)

The article Heart transplantation suggests a max of 4-6 hours on ice. Friday (talk) 20:22, 30 June 2008 (UTC)

Of course, this isn't referenced. Wisdom89 _{(T / ^C)} 20:26, 30 June 2008 (UTC)

I don't know if "seven hours" is accurate or not, but even though there's always a great deal of hurry to get the patient into surgery after an organ becomes available, it's certainly true that they can be kept on ice for several hours before they're actually put into the recipient's body. This article, for example, tells us that a kidney was "put aboard an AirNet jet less than an hour after it was picked up from a Miami hospital. After a 2,700-mile flight, it arrived in San Diego the next morning for transplant into the patient." That's going to spend several hours in transport, no matter how you slice it. Of course, maybe kidneys travel better than hearts, I don't know, but seven hours doesn't sound that crazy to me. -- Captain Disdain (talk) 21:19, 30 June 2008 (UTC)

My understanding is that while 4-6 hours is the gold standard, hearts can and do remain viable for longer periods. This abstract describes a successful transplant with an ischemic time (the heart was without circulating, oxygenated blood) of 13 hours, including 12 hours on ice. There are various experimental procedures for extending the cold shelf life of donor hearts out to 24 hours or more (see [7] for example). Regarding Captain Disdain's comment above, it is indeed correct that different organs tolerate cold ischemia to different degrees. TenOfAllTrades(talk) 21:24, 30 June 2008 (UTC)

What is the limiting factor? It would be nice if organs could be stored much longer (i.e. years). That way we wouldn't have to waste organs if a donor becomes available but there is no immediately matching recipient. I assume it has been tried with animals, but what goes wrong? Obviously sperm and other more limited cell cultures can be preserved in liquid nitrogen for long times. Dragons flight (talk) 21:43, 30 June 2008 (UTC)

I have to catch a train, so I'll just cover freezing for now. Have you seen what happens to the texture of a chicken breast when you freeze and then thaw it? Just like chicken breast, the heart is muscle tissue, and freezing it without causing harm is very challenging. Leaving out the biology for a moment, there are two purely mechanical difficulties in freezing living cells and tissues. First, when water freezes, it expands slightly, while it contracts as it thaws. If you've ever had a can of soda explode in your freezer, or watched an ice cube crack when you drop it into warmer liquid, you can see why plain old expansion and contraction over a full-sized organ has the potential for harm. The second mechanical issue arises on a smaller scale—water, when it freezes, has a nasty habit of forming crystals. These crystals are very pretty when they make snowflakes, but their pointy little ends are deadly to delicate cell membranes.

In cell cultures, we can often get around these problems fairly easily. By adding a glassifying agent like DMSO or glycerol to our freezing medium, we can prevent or restrict the formation of ice crystals. (As the cells are chilled, the formation of large, ordered crystals is discouraged; the frozen state is more like a glass.) Expansion is a bit less of a problem for single cells; you don't have the accumulation of stress over large distances, and individual cells can stretch a bit. As well, some water actually comes out of cells during freezing. (Solidification of water happens outside the cell first, drawing liquid out.) Timing is important during the freezing process—freeze too quickly and the cells end up with too much water (ice) inside and are stressed; freeze too slowly and the cells start to find the glassifying agents toxic. Different cell types prefer different freezing regimens: different glassifying agents and different cooling rates.

Now, try and freeze a whole organ. You've got a combination of different cell types that each prefer different freezing conditions. You have a thick lump of material, so you can't chill it uniformly throughout. As the blood vessels freeze, it's difficult to get water in and out of the entire organ. You can see why freezing a heart is a nontrivial challenge. TenOfAllTrades(talk) 22:02, 30 June 2008 (UTC)

An important point that no one seems ot have made explicitly although everyone's hinting at it is that there is a big difference between "on ice" and "frozen." Laying an organ on top of ice but not in direct contact with the ice will keep it cold but it won't freeze. --Shaggorama (talk) 16:53, 1 July 2008 (UTC)

July 1

Adultration

how to cure adultration in products purchased from the market? —Preceding unsigned comment added by Jasleen302 (talk • contribs) 12:00, 28 June 2008 (UTC)

Best to avoid buying them in the first place. Check your product carefully before you buy, and insist on a pure product. Buying this sort of stuff will just encourage more adulteration. What products are you having trouble with. Graeme Bartlett (talk) 01:57, 1 July 2008 (UTC)

By having an effective network of inspectors, checking for adulteration, and with the power to take action when it is found? (if I have understood the question correctly?)87.102.86.73 (talk) 09:58, 1 July 2008 (UTC)

This has been a problem for a long time, and it ebbs and flows with waves of government regulation and deregulation. The classical (fictionalized) work on this is Upton Sinclair's muckraking novel The Jungle.

Atlant (talk) 16:57, 1 July 2008 (UTC)

Unmanned Aircraft

I was watching a documentary, Regulus - The First Nuclear Missile Submarines, after WW2, in that it states how they managed to make the missile from remote go up and down, right and left, and eventually land. More information: [8]. Anyways if can control a missile from remote, why has there been no unmanned aircraft yet? Like a remote control one? I mean with the GPS and satellite technology it is possible. Is the United States Forces holding back on something they have in secret? --69.156.94.136 (talk) 01:17, 1 July 2008 (UTC)

There are unmanned aircraft. They don't even need to be remote controlled, they can be controlled by computer AI. Unmanned combat aircraft are probably the future of air warfare. Bombers and attack aircraft will be first. Followed by fighter aircraft.ScienceApe (talk) 01:29, 1 July 2008 (UTC)

It's not a secret, and it's not being held back. The MQ-1 Predator is a remotely-controlled unmanned aerial vehicle that fills a variety of roles, including precision bombing. It has been flying armed missions since at least 2001. TenOfAllTrades(talk) 02:24, 1 July 2008 (UTC)

Coming soon to an administration near you: Ender's Game.

Atlant (talk) 16:55, 1 July 2008 (UTC)

Modern commercial airliners with an autopilot are virtually unmanned aircraft, see this section Autopilot#Modern autopilots, and potentially only need a pilot for taxiing. Human pilots are almost a back up system to the aircraft autopilot and to provide a sense of security to the passengers. Tobyc75 (talk) 17:59, 2 July 2008 (UTC)

Freezing Cheese: Good or Bad

I wanted some input on freezing cheese. I'm taking a five hour flight and want to take a two pound block of cheese with me. I know that many people say, cheese shouldn't be refrigerated because it inhibits the life, and flavor inside the cheese, But hey I'm an American. And I know that freezing turns the moisture inside items into sharp shards, basically perforating what ever your freezing from the inside. But is freezing cheese GOOD or BAD? —Preceding unsigned comment added by Semi-smart (talk • contribs) 03:34, 1 July 2008 (UTC)

Freezing cheese is mostly successful, hard or soft, but not ricotta, so anything close and without moisture traps inside. Julia Rossi (talk) 07:07, 1 July 2008 (UTC)

Freezing cheddar is no good, it destroys the texture and it all goes crumbly. Parmesan powder freezes OK though. For a short flight like this, just pre cool it in the fridge, and then wrap it in something insulated like bubble wrap to keep it cool. Graeme Bartlett (talk) 07:13, 1 July 2008 (UTC)

But freezing cheddar is fine if you're going to use it in cooking, since the texture won't matter [9]. My Googling suggests that this is true of a lot of cheeses... in applications where texture doesn't matter, freezing is usually fine. --Allen (talk) 07:18, 1 July 2008 (UTC)

I have successfully frozen Stilton style blue cheese, flavour and texture were unaffected after 3 months. Richard Avery (talk) 07:25, 1 July 2008 (UTC)

I agree with Graeme Bartlett that the best way to deal with this would be to just cool it and keep it cool by insulating it. A simple way to do this would be to buy a small cooler -- I've seen ones that are about the size of a small handbag -- and sticking a couple of ice packs in with the cheese. (The "ice pack" article appears to deal only with the medical ice packs, but what I mean is the thing that is also called a "freezer block" or "ice brick", a rigid plastic brick filled with water that you can freeze and then use to keep things cool, the mainstay of coolers all over the world. (Can it be that we really don't have an article for them, or am I just completely blanking on the terminology here?)) Depending on where you are and how paranoid they are about you using your cheese to destroy the plane in midair, taking that with you as carry-on might be problematic, but you could just stick it in your bag and check it.

That said, a cheaper and more low-tech approach would be simply wrapping the refrigerated cheese tightly in newspaper. It makes a pretty good insulator, and you could always stick in an ice pack with the cheese to make sure it stays cool, if you're worried about that, but the newspaper by itself will probably do the trick, if the cheese is cool to begin with. You can probably get some extra mileage out of the newspaper by sticking it in the fridge with the cheese so it's also cool. As long as the newspaper is dry (water conducts heat very well), it'll work just fine. -- Captain Disdain (talk) 11:02, 1 July 2008 (UTC)

Why don't you test it out? Try freezing a bit and seeing whether it survives. I would be interested in hearing your results. Plasticup ^T/C 13:01, 1 July 2008 (UTC)~

I say screw it. The flight is only 5 hours pal, leaving cheese out of the fridge for that long probably won't be that bad for it. Moreover, if it's 2 pounds of cheese it should hold a temperature for a while. I'm all for captain disdain's strategy of insulating the cheese. But for the record, remember that if you're flight is international they're probably going to take the cheese at customs. --Shaggorama (talk) 16:46, 1 July 2008 (UTC)

When we returned from France, we brought back a variety of cheeses, probably mostly of the semi-dry styles. They were wrapped well in butcher paper at the cheese shop and we then closed the cheese shop's plastic bag as well as we could and chucked them in the middle of the clothes in our luggage. Between the insulation of the clothing and the likely cold baggage hold of the plane, they survived the ten-ish hour trip just fine. And even though the cheeses were from (gasp!) France, we declared them at American customs and were still allowed back into the country, cheeses and and all. (The preceding does not constitute legal advice; it just recounts Wikipedian's one anecdote.)

Atlant (talk) 16:53, 1 July 2008 (UTC)

This might help clarify matters. [10] But be sure to print out a copy to hold under their noses in case someone makes a fuss. OR: I've encountered customs officials anywhere from waving people through to trying to declare that permitted goods were not so. (Chocolate could cause all sorts of delays in NY for a couple of years while back, but that seems to have dissipated. I assume some overzealous supervisor got retired.) As for transporting the cheese, if you have the spare luggage capacity you might freeze a couple of those soft Ice packs you can buy at drugstores or pharmacies or the like. If you are squeezing for space and weight a wet T-shirt or towel might do the trick to prevent your cheese from suffering in case your luggage ends up baking in the summer sun for a couple of hours instead of going directly from the cool terminal to the cold cargo hold. NB: make sure to unpack immediately once you're home and air out the luggage to prevent moisture damage. Bubble wrap suggested above would additionally prevent your cheese from turning into cheese crumble, thanks to baggage handling. Remember you won't be able to take it as carry-on [11]. 80.171.254.148 (talk) 01:33, 3 July 2008 (UTC)

The recommendation for hard cheese is probably good for customs reasons as well; you want to avoid bringing back anything like Abbaye de Citeaux, Chevrotin and Chabichou du Poitou, "the forbidden cheeses", which have a moisture content that makes U.S. Customs uncomfortable. (What is specifically banned is raw milk cheese aged less than 60 days, or aged more than 60 days but having a moisture content of more than 67% water). This is sad for Americans, because, in the words of the Amateur Gourmet, the "high moisture content gives a creamy, luxurious texture and the raw milk lends it complexity and depth." You will have to enjoy these abroad.... - Nunh-huh 02:59, 3 July 2008 (UTC)

QAM query

Hello to all Please if some one can guide me about data rates of different catagerizes of QAM that is the data rate of 8-QAM, 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM

thanks —Preceding unsigned comment added by Arsalan 80 (talk • contribs) 04:29, 1 July 2008 (UTC)

The different rates will depend on what bandwidth in general you want. For particular applications such as digital television or ADSL the appropriate standard will specify the rates to select from. With 8-QAM you will get 3 bits per symbol, 16-QAM will give you 4 bits per symbol, and so on till 256-QAM with 8 bits per symbol. Graeme Bartlett (talk) 06:18, 1 July 2008 (UTC)

statistics

what the the distinction between simulation,models,and experiments? —Preceding unsigned comment added by 72.75.74.106 (talk) 11:46, 1 July 2008 (UTC)

Experiments are tests on real-world things that yield real-world data. Simulations are more like thought-experiments. They are involve creating a model to imitate the real thing. Plasticup ^T/C 11:58, 1 July 2008 (UTC)

In my experience, a model is something that is fed into a simulation to give it the information needed to simulate, so to speak. Said in another way, the model is the abstraction and the simulator takes that abstraction and performs calculations on it to produce an expected result. The Monte Carlo method is a good example of this. The model is the input and the simulation is the action taken on it and the final result. In common parlance, they are often used interchangeably. An experiment is a totally different thing. It is an empirical study of something. Rather than having a known model, a series of observations are taken and analysed. In some cases, a model fit can be used to test a hypothesis. It is important to note that the experiment is totally based on observation. Simulation and modelling can be used to create a hypothesis, but experimentation is usually necessary to reject or not reject a hypothesis. Gjmulhol (talk) 12:06, 1 July 2008 (UTC)

A model can be more than just an idea. In biology, a model could be a live mouse, used to "simulate" a human for a particular purpose. Someguy1221 (talk) 03:22, 3 July 2008 (UTC)

Help with electronics

redirected from Wikipedia:Reference desk/Computing#Help with electronics

I have just begun building a guitar pedal, but no have no electronics expereience, but a good deal of knowledge (theoretical knowledge) of the subject.

I have become stuck where the schematic tells me to connect to ground.

I am soldering to a sheet of stripboard, and it has a thin copper track running down both sides of the board, but with no holes in them; Is this where i should connect grounded connections to? And do i connect all grounded connections to the one place, or should i cut the track so as to separate them from one another?

Any help would be much appreciated.

Thank you!! —Preceding unsigned comment added by 212.46.129.226 (talk) 09:33, 1 July 2008 (UTC)

If this is a standalone pedal (not powered by a wall outlet), it is very possible that you do not have ground inside the footpedal at all. In that case, I would assume that you are using a 1/4" plug from the guitar/amp and assume that the shielding of that connector is ground. So, attach there. If, instead, you are powering this from a wall outlet, ensure you are using a grounded plug (three prongs in the U.S.). Then, you will have ground where the power is soldered onto the board. Because this is an audio device, be wary of ground loops. If you ground your pedal and plug it into one outlet, then plug the guitar/amp into another outlet, it is possible that they do not share the same ground. You can easily get a hum or buzz on the speakers. So, inside the pedal, ensure you connect the ground from your power input to the ground on the shield of the cable from the guitar/amp. Then, you will joining the possible difference in grounds and eliminating the buzz. -- kainaw™ 12:54, 1 July 2008 (UTC)

Additional Help with Electronics

Thanks to kainaw for answering my previous question about grounding, but i still have some queries.

When you say to connect to the ground from the guitar jack, do you mean the input or the output jack?

And does it matter whether i connect all the grounded connections directly to the ground terminal of the jack, or if i connect them all (Including the ground from the jack) to the copper track at the side of the stripboard?

Thanks again for your help —Preceding unsigned comment added by 212.46.129.226 (talk) 13:41, 1 July 2008 (UTC)

"Ground" is often used in an imprecise way. The two most common usages are as "Ground"/"Earth" (yes I know this has reused "Ground") for the purpose of one or more of safety and screening/shielding and as 0V. Eventually Ground/Earthwants to get connected to a physical Ground - eg a copper rod stuck into the planet's soil. For this to work well as a safety connection, it wants to be well connected "in all directions". For it to work well as screening, you don't want current to flow through it, so only one connection to each bit of ground should be made, ideally in a star configuration but at worst as a tree configuration branching out from the trunk where the copper rod is. The other common usage informally means 0V. This has come about since often the 0V terminal of a PSU gets connected to ground to "stop it floating". This often creates loops and current flows in screening circuitry. With your pedals etc, you want all the 0V connected to each other once (no loops). A starter would be to see if, without your circuit in place the screen of the Inlet jack was connected somehow to the screen of the Outlet jack. If not, connect your ground signal to BOTH outers, otherwise choose one - the most convenient. There is an element of art rather than science about getting ground/0V/earth/screening right. -- SGBailey (talk) 13:52, 1 July 2008 (UTC)

To expand on SGBailey's point, "ground" in the context in which you're asking means "the reference voltage" (which we conventionally then call "0 volts"). All other signals in the circuit are measured "in reference" to this point, "the ground". For your guitar effects pedal, both the input and output jacks each have an outer terminal which should be connected to "the ground" (reference voltage) in your circuit.

Odds are that your guitar effects pedal should be designed to operate solely from battery power. Otherwise, any connection to mains/line power, even through a power supply/wall wart, is likely to cause a ground loop and that can induce your guitar amplifier to produce noise, hum, and other nasty stuff.

Atlant (talk) 16:42, 1 July 2008 (UTC)

A good book you might want to look into is "Do-It-Yourself Projects fo Guitarists" by Craig Anderton. I used to know a great website too, but I can't find it right now. --Shaggorama (talk) 16:09, 4 July 2008 (UTC)

Figure of the Earth image

I can't find this anywhere. I would like to know if there is an image which shows the figure of the earth without the water on it. I.e. only the rock part of the earth. Does such an image exist?  — Adriaan (T★C) 13:44, 1 July 2008 (UTC)

Bathymetry, [12]? -- Coneslayer (talk) 13:46, 1 July 2008 (UTC)

No, not what I'm looking for. I was wondering if there was a pic in true colour of the earth, just with the water edited out. Something like an artist's impression of what the earth would look like if all the water suddenly disappeared. Like a 3D pic of an object supposed to be the earth - but without water.  — Adriaan (T★C) 15:52, 1 July 2008 (UTC)

How about Mars? --Shaggorama (talk) 16:40, 1 July 2008 (UTC)

There's a 2D texture here. You could create a 3D image out of it quite easily with Xplanet. — Matt Eason ^{(Talk • Contribs)} 20:03, 1 July 2008 (UTC)

Space program benefits

In reading about the ancillary benefits of NASA's space program in articles like this and this, it strikes me that most the advances that are mentioned aren't dependent on the space travel part of the equation. Rather, they were inspired or triggered by space travel, but could just as easily have been developed for the same cost for a land-based application. For example, water filtration was (according to the NASA site above) developed in part for the Apollo program, but it's not as though it couldn't have been developed for non-space applications. Are there practical benefits to the space program, readily apparent to regular folks, that could only come with space travel? jeffjon (talk) 14:28, 1 July 2008 (UTC)

Define 'regularly apparent to regular folk'. There are thousands of experiments in space, many of which will have furthered our understanding of the world and how things react in given situations. Do you just want a list of products that use techniques based on the space program? Or do wooly benefits such as "improving the knowledge of mankind" and "continuing the exploration of the universe"? Personally I find that when people start to try to qualify the value of Nasa based on products/technological developments overlook the strongest argument for the space-program - that there's a universe out there that holds limitless possibilities and the more we go out there and the further we venture the more interesting things we will find. Of course this is from an exploratory enthusiast who supports the cause, certainly there are plenty of worthy groups vying for already scarce government funding. 194.221.133.226 (talk) 15:02, 1 July 2008 (UTC)

I'm with you; I think exploration for sake of pure discovery is motivation enough. My wife isn't convinced, so I was trying to come up with a more tangible benefit that she receives for that almost 1% of every dollar she pays in taxes, whether it's a product, a health benefit, a scientific advance with other implications, etc. jeffjon (talk) 15:10, 1 July 2008 (UTC)

IMHO the scientific benefits are good enough. But to counter the "they totally could've been developed anyway" argument, I guess the question is why. Why would any of that be built? Why would the US build a water filter when we've got good tapwater? Necessity is the mother of invention. We need a way to recycle water in space. It also happens to work really well on Earth? We should sell that to the third world and people who are superstitious about tap water! As the first source you cite mentions, if you look at a lot of the products, most of them are saying "NASA was doing this obscure scientific thing and it totally improved this product by leaps and bounds!" Thats pretty damn impressive, and I consider it a good testament to the power of a good R&D budget. EagleFalconn (talk) 15:24, 1 July 2008 (UTC)

I wouldn't expect R&D for space to be any more likely than anything else to have things that help in unexpected ways. If NASA didn't invent water filtration, maybe it wouldn't have occurred to anyone, but, by the same token, maybe there's something that hasn't occurred to us because we weren't spending that money on R&D for something of more obvious practical significance. Doing R&D for something practical has the added advantage of helping in expected ways. For those of you who think NASA does pull its weight, how much of your money do you donate to it? You don't think it's only worth it if it's money the government takes from you forcefully, do you? I'm currently saving up for college, but when I'm done with that, I plan on donating to a microcredit group, like Unitus. I think they have more practical significance than NASA. — DanielLC 15:49, 1 July 2008 (UTC)

Satellites enable my contributions to Wikipedia. There's your human benefit right there. ;-) Plasticup ^T/C 17:11, 1 July 2008 (UTC)

That's a bit of a red herring, isn't it? I don't make voluntary cash donations to my local water treatment plant or the city subway system, but I still think it's worthwhile for those projects to receive funding. If you want to talk about research, in the United States good solid research is carried out or funded by government agencies from the Department of Energy to the Department of Veterans Affairs; I don't make donations to those organizations either. TenOfAllTrades(talk) 17:26, 1 July 2008 (UTC)

Global Positioning System saves a lot of time and needless erring around. LINEAR is another point. And then, for people like me, it's simply interesting and sometimes even exciting to look at real pictures from space. And when I saw Neil Armstrong live on TV stepping on the moon that is something to remember. 77.3.134.249 (talk) 20:27, 1 July 2008 (UTC)

Though I am certainly no expert, I have read in the past that zero gravity experiments have been done on cultures of bacteria. These have shown unique characteristics. I also remember evidence of a super-bug, but I don't remember where that is from. Gravity is vital to life, it is important that we know how plants and animals react in such an environment. From a materials perspective (I am a materials scientist), some crystals and structures can only be formed in a zero-g environment. If extra-planetary colonization ever takes place, it would be good to know how to take advantage of these new, potentially revolutionary structures. Gjmulhol (talk) 11:55, 2 July 2008 (UTC)

Note that just because spinoff products are formed does not necessarily mean that NASA is a good way to get them. If you give me a billion dollars I'm sure I could get you some tangible benefit for it—but would that be a better approach to said products than, say, letting them develop on the free market? That is—the return on R&D in terms of secondary benefits is going to be pretty small, most likely, and not very efficient.

In my opinion a better argument focuses on the BIG, non-spinoff benefits. GPS. Satellite communications. Military advances in rocketry. Advances in computing, robotics, materials science, etc. Water filtration? Not impressive. You could easily have gotten something like that without NASA. But GPS? Probably not. (And while "knowledge for its own sake" works great for people who would post on a board like this, it's not that convincing for the common man. Very little of that knowledge for its own sake has any payoff, and there's a lot of different types of "knowledge for its own sake" that one could be funding, much of it for a lot cheaper than space budgets.) --98.217.8.46 (talk) 18:37, 3 July 2008 (UTC)

physics

Question: When we throw a ball on the wall in a particular direction, then why does the ball comes back to us in some other direction ?'' —Preceding unsigned comment added by 61.2.190.79 (talk) 16:33, 1 July 2008 (UTC)

Start with Reflection (physics), but the most basic principle is that "the angle of incidence equals the angle of reflection". And remember, gravity is constantly working on the path of the ball.

Atlant (talk) 16:37, 1 July 2008 (UTC)

More specifically, for a ball: Deflection (physics). This article could do with expansion though ....Jdrewitt (talk) 16:53, 1 July 2008 (UTC)

More simply: It would take more energy to send the ball back in the direction it came from. Mac Davis (talk) 16:57, 1 July 2008 (UTC)

Well, yes and no; it would just take a corner cube, but gravity is still affecting the track of the ball (which is probably what you were referring to in the need for "more energy").

Atlant (talk) 19:48, 1 July 2008 (UTC)

Also, it is very difficult to throw a ball with zero spin. If you are familiar at all with the sport of tennis you will know that depending on the surface the ball is striking, the spin can change the direction dramatically. This is particularly evident if you use a hard rubber ball on a rough surface (e.g., a lacrosse ball on asphalt). The spin will alternate and dampen until the ball rolls flat. Thus, you see a low, long bounce followed by a short, high bounce, and on and on until the ball flies with negligible spin or it simply starts rolling. Gjmulhol (talk) 11:52, 2 July 2008 (UTC)

Endorphin as drug

Why not simply inject endorphin instead of some artificial substance if the purpose is to feel right? —Preceding unsigned comment added by Mr.K. (talk • contribs) 18:42, 1 July 2008 (UTC)

And where would you obtain the natural endorphins? You can't just buy it. And if you synthesized it, it would then be an artificial rather than "natural" substance. The closest analogue is morphine, which is routinely injected during childbirth and other painful periods. ~Amatulić (talk) 18:53, 1 July 2008 (UTC)

I'm under the impression that one would have to inject the endorphin(s) directly into the brain, which sounds rather messy. --Several Times (talk) 20:13, 1 July 2008 (UTC)

This is a common question with relation to most centrally acting drugs (serotonin vs SSRIs, norepinephrine vs salbutamol, etc). The most common problem with endogenous substances is that they won't cross the blood-brain barrier, other problems are listed in the pharmacokinetics article (absorption, distribution, metabolism and excretion). --82.21.25.219 (talk) 08:21, 2 July 2008 (UTC)

Also note that administering natural endorphins long-term would likely cause the same problems as other such drugs. A tolerance would develop, requiring more and more to get the same effect. And addiction would occur, so people would feel sick if the endorphin supplement was ever stopped. StuRat (talk) 15:42, 2 July 2008 (UTC)

Insulators for copper wiring

I'm wondering if there is any way to accuratly measure the resistivity of a substance...is there a way to get a quantitative value for resistivity in substances that could potentially be used to insulate basic copper wiring? 24.34.168.154 (talk) 18:43, 1 July 2008 (UTC)Fiziks

Using a Megger? Fribbler (talk) 18:46, 1 July 2008 (UTC)

A megger is a good answer if you're interested in the performance of the insulator at relatively high voltages (~1KV), but at lower voltages, one would use a nanoammeter, a voltage source, and some careful experiment design including guarding. Keithley Instruments is a typical vendor of nanoammeters. And here's a good article from EDN about proper techniques: [13].

Atlant (talk) 19:43, 1 July 2008 (UTC)

July 2

Infantry vs. tank

[This is really eight related questions, some of which may share answers.] Consider either (a) one or (b) eight soldiers armed with normal-caliber machine guns and an arbitrary amount of any kind(s) (armor piercing rounds?) of ammunition for them. They are free to walk the top of a tall concrete wall that is, say, 75m on a side. Trapped inside the wall on open ground is either (a) one unarmed enemy tank or (b) one enemy and one friendly tank, armed only with their main cannons. All tanks are modern main battle tanks; the unarmed tank may be considered to be repairing supposedly-minor damage to its anti-personnel weapons in (vain) hopes that it may return fire, and the armed tanks fire only at each other. How may the infantry in each of the four situations disable or destroy the enemy tank (a) in the least time or (b) using the least ammunition?

The purpose of the first bifurcation is to increase the infantry's effectiveness in the situation where there is a friendly tank, as well as to allow them to surround the enemy. The purpose of the second is to distinguish between an enemy that is fighting (albeit not against the infantry) and one that is doing nothing but trying to evade/weather fire. The purpose of the third is obvious, but in the case where there is a friendly tank present the "least ammunition" option should be taken to require some material contribution to the battle. I would also be interested in hearing about the mechanism by which (a large amount of) machine gun fire damages the high-grade armor against which it is not frequently used. Thanks for the myriad answers. --Tardis (talk) 01:11, 2 July 2008 (UTC)

Good luck. Modern tank armor (e.g. Chobham armor) is really, really tough. I'm no expert, but I doubt that anything fired from a machine gun would have a chance of doing any real damage. You're probably better off having these guys break out their shovels and cover the trapped tank with dirt. Clarityfiend (talk) 06:49, 2 July 2008 (UTC)

They could try and open the hatch and shoot the people inside. Trying to damage the armour would be in vain, I imagine. --Tango (talk) 14:04, 2 July 2008 (UTC)

Yeah- small arms fire against modern armor would be useless, no matter what ammo you're using. You'd need to get the hatch open somehow. Trap the tanks somehow, and wait for the people inside to get hungry? I don't know. Friday (talk) 14:39, 2 July 2008 (UTC)

75m square? What sort of ground? Discharge five 40 tonne road tankers of diesel into the area (so 3cm deep without bothering to do the maths) and ignite it? The thermal conduction of armour is pretty high and baking the people in it cannot be too hard. --BozMo talk 14:55, 2 July 2008 (UTC)

Best you could with small arms would be to try to blind and deafen them by destroying the optics and antennas. --—— Gadget850 (Ed) ^talk - 14:58, 2 July 2008 (UTC)

Even with an arbitrary amount (and duration; give the tanks infinite fuel if needed) of sustained fire? Surely something would happen to the armor, even if it shattered or reflected the bullets, and it wouldn't get stronger… --Tardis (talk) 15:02, 2 July 2008 (UTC)

I suppose if you had a billion rounds of machine-gun bullets, you could eventually wear a hole in the armor, but that's just getting a bit silly, the occupants of the tank would starve to death first. There may be a few weak spots, though, like the exhaust port, which might be more vulnerable to small arms fire. StuRat (talk) 15:38, 2 July 2008 (UTC)

I suppose water dripping on the tank would eventually wear through the armor, too. Friday (talk) 17:28, 2 July 2008 (UTC)

Removable armor plates are common. If the tank is disabled and just sitting there, you could rush up and start removing armor. Eventually, the guys inside will try to come out to stop you and it will be man vs. man instead of man vs. tank. -- kainaw™ 17:33, 2 July 2008 (UTC)

(EC)

What about MacGyver solutions? Take the gunpowder out, make a kind of bomb, could at least blow the tracks off.

Could destroy the main gun in a similar way. With no movement or firepower you could burn the people out...--Shniken1 (talk) 17:37, 2 July 2008 (UTC)

I don't know if the Barrett M82 would be useless against the tracks of a tank. It have caliber .50 and the latter are the Achilles' heel of the tank. Just give it a try on a tank that you don't need anymore. Mr.K. (talk) 09:54, 3 July 2008 (UTC)

The infantry could lay siege to the tank until the crew starve or surrender. Daniel (‽) 19:39, 3 July 2008 (UTC)

Evolution - Woman as Well?

Today I was speaking to a Jehovah's Witness that came by my door. We got into talking about everyone's favorite topic, evolution. He brought up an objection to the theory that I had not heard before. I don't remember exactly what it was, but it was along the lines of "even if a man evolved into a human, what are the chances that a woman evolved too, at the same place, and the same time?". I'm sure there is an easy rebuttal to this, but I was wondering if this objection has a name and how I can rebut it in layman's terms. (In a somewhat related query, does anyone know where one can find very old (circa 1894) copies of the Watchtower magazine?) Thanks! Abeg92contribs 03:56, 2 July 2008 (UTC)

Let me see if I understand the argument first. The idea is that if a male evolves from Species A to Species B, then there has to be a female that goes from Species A to Species B as well, otherwise there would be no-one to breed with? I can see what's wrong with the argument, but I'm finding it hard to put into words, except to point out that (a) evolution isn't sudden jumps, it's a gradual process (at least gradual in the sense that new species don't suddenly crop up in a single generation), (b) speciation occurs when an entire hereditary line becomes so genetically different to another that they cannot reliably interbreed, so it's actually the combination of a man and a woman who are, by necessity, genetically different, passing a particular combination of those different genes onto their offspring that leads to the creation of a new species. I'd try to explain it in terms of the historical development of language, but presumably the Witnesses believe that all happened when God struck down the Tower of Babel. I will leave the understandable explanation to someone with more experience in the subject matter. Confusing Manifestation(Say hi!) 04:56, 2 July 2008 (UTC)

Put another way, your Jehovah's Witness friend is mistaken in thinking that the process of speciation is something that occurs in an individual. Populations become species, individuals do not. - Nunh-huh 05:06, 2 July 2008 (UTC)

In addition to speciation, the population genetics article may also be helpful. --arkuat (talk) 05:35, 2 July 2008 (UTC)

The entire mechanism of reproduction involves males and females sharing their genomes again and again. The amount of genome that differentiates males and females is tiny. Your friend seems to think that males and females are terribly genetically different. They aren't. And again, all members of the species are products of their mating. So the genome isn't going to get out of sync between the two of them. --98.217.8.46 (talk) 13:53, 2 July 2008 (UTC)

If you want a more technical answer, consider how traits are distributed upon reproduction. Say I have a hypothetical gene for red hair. (Hair is a bit more complicated than one Mendelian trait but for our example it is concrete.) It sits somewhere on one of my chromosomes. I mate with a woman who had a gene for brown hair. It sits on one of her chromosomes. Inside the sperm, egg, etc., half of my genes are randomly thrown together with half of her genes. It's entirely possible that all of our male or female children could have my gene expressed, or half with her gene expressed. The resulting children are a mix-and-match of our two gene pools. It isn't that the "female gene pool" is separate from the "male gene pool" and has to "evolve" at the same time. They'll evolve together, as long as none of the evolutionary changes are great enough to make evolving with another human impossible. The gene pool of course allows for a certain amount of flexibility (if it didn't, even simple reproduction with genetically different members of the same species would be impossible). Beneficial mutations have a certain chance of being passed down to children of either sex. Males and females are, again, genetically (and developmentally, up to a certain point) almost identical—they are both humans, and it is the firing off of different hormones at different times that differentiate the two physically, mentally, etc. --98.217.8.46 (talk) 14:09, 2 July 2008 (UTC)

The number of chromosome is different in man and chimp, lets asume that the last comon ancestor had the same number than one of the two species. So sometime ago a chromosome split or paired with another to get to the different number. This happened in one single individuum not to the whole group.What I know from genetics this makes interbreeding very complicated what it is seen in donkey and horse. Has this problem of genetics been solved yet?---Stone (talk) 14:25, 2 July 2008 (UTC)

There are lots of theories as to how this can work. Needless to say, yes, it seems pretty clear that it can work. Even in individual humans you can do weird things like have too many chromosomes (e.g. XYY syndrome, trisomy 21). It is not usually positive in such cases though, but the point is, it can happen—it doesn't mean automatic death of the organism or inability to reproduce. --98.217.8.46 (talk) 15:24, 2 July 2008 (UTC)

I haven't seen a definite resolution of this "problem", but from genetic sequencing of the human and chimp genomes, it's pretty certain that the Human chromosome 2 is equivalent to a fusion of two chimp chromosomes, including residual portions of the centromere and telomeres that are no longer functional. My best guess is that at some point in the past, a fusion event happened in a human ancestor, creating chromosome 2. At this point, all breeding partners to this individual still had the two separate chromosomes, but as the fused chromosome still had all the regulatory apparatus of both chromosomes, the cells were still able to line up and divide normally (although perhaps at reduced efficiency). Eventually for some reason (potentially unrelated to the chromosomal fusion) the fused chromosome came to be dominant (This can happen very rapidly - see founder effect). At that point the secondary centromere/etc. was superfluous, and could be lost through mutations, leaving us with a single chromosome. (See [14] for a related discussion - no endorcement implied, just the first decent result I got in searching) -- 128.104.112.147 (talk) 19:54, 2 July 2008 (UTC)

There seems to be a false assumption that males and females evolve completely independently of one another. This is untrue. For the most part, only the X and Y chromosomes evolve independently, in humans. I can try to make this into a reasonable objection to evolution:

"Since, in humans, the X chromosome determines (or at least triggers) female characteristics and the Y chromosome male characteristics, the two must evolve in parallel so that any change in females matches a corresponding change in males. For example, the tendency in females towards nurturing, homemaking, and gathering required a corresponding change in males toward hunting, to ensure that all the child-rearing and food provision needs of the group were met, utilizing a division of labor."

I suppose this is true, but, in cases where both sexes developed noncomplimentary traits, like everyone going hunting and leaving the children unattended, those traits would not be likely to be passed down. StuRat (talk) 15:30, 2 July 2008 (UTC)

What is the process of decompossition of the human body?

Do you need further information for that question? —Preceding unsigned comment added by Ros1701 (talk • contribs) 04:43, 2 July 2008 (UTC)

Have you read Decomposition#Human decomposition? Gwinva (talk) 05:04, 2 July 2008 (UTC)

Cavity in a Unifomly charged solid sphere..

consider a uniformly charged sphere with a cavity inside. the electric field inside the cavity is non zero and uniform... but if we draw a gaussian surface inside the cavity, the charge enclosed will be zero. so field zero on the surface... why the contradiction???? —Preceding unsigned comment added by 117.201.49.226 (talk) 07:46, 2 July 2008 (UTC)

The electric field is zero inside. I think you are confusing electric field and electrostatic potential. The latter is uniform inside and may or may not be zero, as you're free to define a point where it's zero. Icek (talk) 08:50, 2 July 2008 (UTC)

Maybe they were thinking of Shell_theory#Thick_shells - inside the 'solid' of this shell..

Shell_theory esp. Shell_theory#Inside_a_Shell may help here with the maths..

Shell theory explains the field (works for any inverse square relation ship) both inside and outside hollow spheres..

Note at the centre of the cavity the field is zero. I've no idea what you mean by "but if we draw a gaussian surface inside the cavity..." if you wan't the field then shell theory has a mathematical method of how to get it.

CLARIFY:Did you actually mean a solid sphere, or thick walled sphere with a hollow cavity inside or something else?87.102.86.73 (talk) 12:03, 2 July 2008 (UTC)

One answer "... inside the cavity, the charge enclosed will be zero. so field zero on the surface.." - the surface is not inside the cavity - it's on the boundary - which is different..87.102.86.73 (talk) 15:10, 2 July 2008 (UTC)

I hate to quibble, but nothing in the initial question stated that either: A) the cavity is spherical or B) the cavity is centered. Hence it could be inappropriate to jump straight to shell theory. Dragons flight (talk) 23:44, 2 July 2008 (UTC)

quote "consider a uniformly charged sphere..." - it's easily to miss..87.102.86.73 (talk) 12:05, 3 July 2008 (UTC)

That says nothing about the shape of the cavity within the sphere. Dragons flight (talk) 16:04, 3 July 2008 (UTC)

Actually, even if the field is neither centered nor spherical, it will still have zero electric field within, although yes, shell theory wouldn't apply. Someguy1221 (talk) 23:57, 2 July 2008 (UTC)

That's not true of a uniformly charged (in a volume sense) insolator. You are correct if you assume the sphere is a conductor, which also is not stated. Dragons flight (talk) 00:04, 3 July 2008 (UTC)

Can I get fully solved IIT-JEE question papers in Physics (mechanics only) of past 10-20 years?

I want to know whether I can get fully solved Physics question papers of past 10-20 years of the IIT-JEE examination from you. If you do this small favor for me,I'll be very very thankful to you.Please send them (if possible) as an attachment to your response mai

--Prateekgreat (talk) 10:22, 2 July 2008 (UTC)prateekgreat

What defines a yeast?

I posted this at Talk:Yeast but thought I should place it here too.

What defines a yeast? Do yeasts have some intrinsic trait that qualifies a particular species as being a "yeast" rather than just generically being a "fungus"? What is special about all (or most) of the species of yeast that qualifies them as yeasts? --Alecmconroy (talk) 15:07, 2 July 2008 (UTC)

According to yeast, yeast is unicellular. Otherwise, fungi are usually multicellular. I think that's probably the main distinction. — CycloneNimrod ^talk?_contribs? 16:08, 2 July 2008 (UTC)

How fast does the "wind" go when we blow on something?

Just blew on a crwling bug (likely an ant) to get it off my book outside, and it made me wonder - how fast does that "gust" blow that we creat when we blow?

I'm thikning, just from experimenting, maybe 50 MPH or so at first, but then of course air resistance will slow it down a lot. Plus, the amoung of saliva probably affects things. Holding my hand about a foot away from me (like when blowing out candles on a birthday cake) it still feels gusty, but not too much; maybe 20 MPH or so?209.244.30.221 (talk) 17:35, 2 July 2008 (UTC)

Sneeze gives some speed estimates. I would expect a sneeze is about the upper limit for how fast we can blow. So, somewhere less than the speed of a sneeze, which is itself the subject of widely varying estimates. Friday (talk) 17:43, 2 July 2008 (UTC)

Tree identification

My parents had a tree in their back yard, which was about, if I recall, about 3-5 metres tall, and had purple waxy leaves. It shed them in the winter, and was able to survive winter temperatures of -50 degrees celsius. I think it may have lived for about 15 years, and produced wrinkled, cherry like fruit. —Preceding unsigned comment added by Sliver Slave (talk • contribs) 20:25, 2 July 2008 (UTC)

First guess, purple leaf plum? Seems to survive in the cold, not sure about -50C though. --Wirbelwindヴィルヴェルヴィント (talk) 21:45, 2 July 2008 (UTC)

Crude oil estimates

Where/how do they come up with estimates for how long our fuel is going to last us? I mean how can they know how much there is when its all underground? --212.120.246.239 (talk) 22:06, 2 July 2008 (UTC)

Directly, geologists can use techniques like seismic mapping to figure out how large an oil pocket is. Indirectly, they can measure how fast oil is being pumped from the ground -- once the rate slows down, about half the available oil has been pumped out. Interesting articles to read are Hydrocarbon exploration, Exploration geophysics, and Hubbert curve --Carnildo (talk) 22:40, 2 July 2008 (UTC)

And, of course, how long oil lasts also depends on our rate of consumption. If we conserve energy and switch to alternative energy sources, oil should last longer. StuRat (talk) 03:54, 3 July 2008 (UTC)

They also have to account for the oil we haven't discovered yet, which can be estimated based on how commonly we find it, and they have to pick an arbitrary point where oil becomes too expensive to extract, and thus not counting things like tar sands. They also have to pick a point for not having enough fuel, as their will always be some left, but the speed at which we extract it will approach zero. — DanielLC 15:51, 3 July 2008 (UTC)

The traditional point of "too expensive to extract" is when the energy return on energy investment drops below 1: it takes more energy to extract the oil than can be gained by burning the oil. --Carnildo (talk) 21:46, 3 July 2008 (UTC)

Tar sands are counted as crude oil reserves, that's how Canada leapt at a stroke to become the nation with second-highest crude reserves. And in the case of the tar sands, the resource is at the surface, so it's relatively easy to estimate just how much is there. Franamax (talk) 01:04, 4 July 2008 (UTC)

Drafting

When driving on the interstate highways, if one wants to "draft" behind a fast moving eighteen wheeler, how close does he have to follow? WSC —Preceding unsigned comment added by 75.85.203.191 (talk) 22:29, 2 July 2008 (UTC)

Mythbusters did an episode on this. The benefit depends on how close you are: at a safe following distance, you get about a 5%-10% increase in fuel economy; if you're following at ten feet, your fuel economy doubles. --Carnildo (talk) 22:43, 2 July 2008 (UTC)

A word of caution: A truck driver once told me he really worries when someone drafts behind him. For one thing, you're driving in his blind spot when you're close enough to draft, and furthermore, truck tires sometimes throw their treads (you can see truck tire treads occasionally lying on the shoulders of freeways). These tire treads are heavy steel-belted rubber things that can fly right through your windshield. =Axlq 23:07, 2 July 2008 (UTC)

I keep hearing "If you can't see my mirrors, I can't see you", warnings about following too closely. I would expect that the truck driver would be more concerned about what's in front of him and to either side, since that is what controls his ability to maneuver. The obvious danger of drafting or tailgating is that the trucker slams his breaks on (presumably for good reason) and you don't, but that danger exists whether the trucker can see you or not.

A related question I've always wondered about: Has anyone ever studied the effect of drafting of the truck? I would think that the car would either (1) cause an increased low pressure behind the truck, thus causing additional drag and effectively stealing the trucks energy, or (2) the car would act as a tapered tail to the truck, thus decreasing the drag in the truck. -- Tcncv (talk) 23:33, 2 July 2008 (UTC)

A word of caution: with the Mythbusters episode in question, even the farthest distance tested was too close to constitute a safe highway-speed following distance.

As for the question of what drafting does to the truck's fuel economy -- interesting. You can't get something for nothing, but I don't know if car+truck would closely approximate a closed system for those purposes or not. — Lomn 00:11, 3 July 2008 (UTC)

The truck is already losing energy through air resistance - the car may well just be using that energy, so the truck doesn't lose any more. --Tango (talk) 00:15, 3 July 2008 (UTC)

At 55 mph, they got an 11% reduction in fuel usage at 100 ft and 39% reduction at 10 ft (Mythbusters' wiki). Whether or not you personally consider 100 ft to be safe may be something of a matter of opinion. It's not that uncommon on highways where I live to see cars following big rigs within that distance (which is about 6 car lengths). A big rig isn't capable of stopping on a dime, so even if he did slam on the brakes (which let's be honest isn't that common on freeways), you'd have the benefit of his slower stopping time to react and stop or dodge. Back when I was growing up 100 ft was actually the recommended distance at 60 mph, but I understand that people now recommend 150 ft. So you be the judge of whether the small reduction at 100 ft is worth the (in my opinion) small risk. Dragons flight (talk) 00:26, 3 July 2008 (UTC)

Given the huge mass the 18-wheeler carries, is it possible that even if you include reaction time that you would be able to brake safely in a normal vehicle?--droptone (talk) 12:14, 3 July 2008 (UTC)

By this reasoning a bicycle would out-brake a car, which is clearly not the case. Heavier vehicles have more powerful brakes, plus more wheels = more brakes to dissipate energy. Gandalf61 (talk) 16:17, 3 July 2008 (UTC)

Empirical evidence says otherwise. I haven't compared my 15-0 stopping distance to that of a bicycle, but I have compared 60-0 stopping distances with a semi (I was passing it when a car ahead of both of us lost control), and my car stopped well before the semi did. --Carnildo (talk) 21:54, 3 July 2008 (UTC)

The limiting factor in braking a bicycle is not the brakes. It's the tires, geometry, and weight distribution. The question is not whether you can slow down the wheels, but whether you can keep control of the bike when you do. Optimal braking is supposed to be around 70-30 or 75-25, weighting the front brake more, because the front tire presses into the pavement during braking and is therefore less prone to skidding. But hit the front brake too hard and you go over the handlebars. --Trovatore (talk) 22:15, 3 July 2008 (UTC)

Oh, that said--I think the drafting thing is seriously a bad idea. At highway speeds you should not cruise closer than 3 seconds behind the vehicle ahead of you. At 60 mph that's 264 feet. Of course you will have to get closer than that at times; you just shouldn't stay there. And if you don't stay there, you're not going to get much benefit in fuel economy. --Trovatore (talk) 22:47, 3 July 2008 (UTC)

Biting fly

Hi. What species of biting fly lives in southern Ontario, has a mildly painful bite, thrives near midday in June-July, and leaves a barely noticeable reddish bump about 1mm wide? I'm not asking for a diagnosis, just a vague species identification. The article doesn't seem to help, as it wasn't a mosquito, Tetse flies live in Africa, horse and deer flies are yellowish in colour, and black flies should be far more painful? I think it was grey-black in colour, had rufous-brown eyes, and was less than 1cm long. Its bite was that of a mild sting. It might sound like a blackfly, but aren't their bites more severe and larger? Thanks. ~AH1^(TCU) 22:35, 2 July 2008 (UTC)

Around the Great Lakes, I've been bitten by many basic black biting flies. It is a mild sting - no worse than a mosquito bite. I've been bitten by deer flies also - it is severe. One caused my whole ear to swell up. So, I see no reason for it to be anything more than a basic biting fly. -- kainaw™ 01:03, 3 July 2008 (UTC)

Why are Galaxies disc shaped?

Just curious why some galaxies are disc shaped and not 3D collections of stars (like how I imagine Nebulae are). --70.167.58.6 (talk) 23:30, 2 July 2008 (UTC)

Rotation - and nebulae are gas, not stars. Rmhermen (talk) 00:03, 3 July 2008 (UTC)

He wasn't saying nebulae were composed of stars actually. He was just referring to the shape. ScienceApe (talk) 18:50, 3 July 2008 (UTC)

Nebulae often contain stars as the condensing of the gas is what causes the formation of stars. Its why we can usually see them, the gas is illuminated by the stars in there. EagleFalconn (talk) 00:14, 3 July 2008 (UTC)

Galaxy formation and evolution and spiral galaxy are probably good places to start. As Rmhermen says, it's all to do with the rotation - when you rotate something, it generally flattens out. Just watch someone showing off while making pizza - rather than roll out the dough, they spin it round and it flattens out nicely. The reason for the difference in shape between spiral galaxies and nebulae, I would guess, is the speed of rotation (possibly, relative to their overall mass - it might be angular momentum that's actually important) and the length of time they've existed. It's going to vary from galaxy to galaxy and from nebula to nebula, though. Plenty of galaxies aren't disc shaped (see elliptical galaxy and irregular galaxy), and there may well be some disc shaped nebulae (I honestly don't know!). I hope that helps a little. --Tango (talk) 00:13, 3 July 2008 (UTC)

July 3

House water pressure from flow rate?

Can I determine the pressure of my water lines just from the flow rate and the physical dimensions of the tubing? Thanks.

I measured 2.1 GPM through a 1/2" copper tube.

--jcmaco (talk) 01:35, 3 July 2008 (UTC)

You may be able to get an approximation (e.g. water will flow through a hole at a rate determined by pressure based on its pressure coefficient) but in the case of water lines, you don't have any way to account for friction or restrictions upstream. When the water isn't flowing, your water pressure is independent of restrictions or friction that would affect the flow.

I recently measured my pressure after installing a reverse osmosis water filter in my kitchen. The manufacturer provided a table showing how much water would be drainable out of the storage tank for various water pressures. I drained 1.8 gallons out of a 4 gallon tank (meaning that my water pressure was sufficient to push 1.8 gallons into the tank), which equated to a fairly low pressure of 40 psi. =Axlq 05:43, 3 July 2008 (UTC)

Tell diffrence

If man and woman are berried in same grave how can u tell the diffrence after 1000 years/ —Preceding unsigned comment added by 79.76.174.168 (talk) 01:51, 3 July 2008 (UTC)

Human skeleton#Sex-based differences. PrimeHunter (talk) 02:02, 3 July 2008 (UTC)

I'd expect the boys to be blue-berried. :-) StuRat (talk) 03:38, 3 July 2008 (UTC)

Skin color of ancient Egyptians

So I've come across the debate of whether ancient Egyptians were black, white or something in-between. It seems that neither side has conclusive proof. My question is whether there are any accounts by travelers about the skin color of the country they had visited? If there are, then why is the debate still going on? —Preceding unsigned comment added by 24.7.54.224 (talk) 02:50, 3 July 2008 (UTC)

Mostly "white", or what essentially is the ethnic group we now call Arabs, I believe. Ancient Egypt consisted of Lower Egypt, in the North, and Upper Egypt, in the South, which were later united. South of that was Nubia and the kingdom of Kush, which, I believe were populated, then, as now, by "blacks". Since there was some interchange of populations, I'd expect some "blacks" to have been in ancient Egypt, especially Upper Egypt, as well. StuRat (talk) 03:27, 3 July 2008 (UTC)

As for evidence, there were many surviving color paintings in Egyptian tombs, so there's no need to resort to 2nd or third-hand accounts. Here's one that shows a nice racial blend: [15]. Forgive me if I break into a round of Ebony and Ivory while viewing it. :-) StuRat (talk) 03:31, 3 July 2008 (UTC)

Some people get confused about this because Cleopatra was white, but she had only four great-grandparents and all of them were of European descent. In general, you'd expect the skin shade of ancient Egyptian people to be about the same as that of peoples from around the world at the same latitudes, which would probably count as "somewhere in-between" on OP's proposed scale. --arkuat (talk) 03:44, 3 July 2008 (UTC)

It boggles my mind how anyone can have only four great-grandparents. Having eight should be more typical, no? Thank you for your replies, StuRat and Arkuat, but if what you said is correct, I don't understand why the debate still goes on. —Preceding unsigned comment added by 24.7.54.224 (talk) 05:02, 3 July 2008 (UTC)

Why the debate still goes on is perhaps a question better taken to the Humanities desk, but I think it has to do with the intellectual history of the African diaspora. Personally, I feel that it is important to recognize that people from all over Africa contributed to ancient Egyptian civilization, mostly for the simple reason that this is true.

As for having only four great-grandparents, that comes easy if your family culture encourages first-cousin marriage, or aunts marrying nephews, or uncles marrying nieces, or, as was expected of Egyptian royal families off and on since time immemorial, sisters marrying brothers. --arkuat (talk) 05:39, 3 July 2008 (UTC)

See pedigree collapse. Rmhermen (talk) 13:54, 3 July 2008 (UTC)

Pedigree of Don Carlos, illustrating pedigree collapse: grandparents (4) in yellow, great-grandparents (4) in blue

You may also be interested in Serious inbreeding among European Royals, which features several with four great-grandparents. - Nunh-huh 03:08, 4 July 2008 (UTC)

Good thing they didn't have Christmas then, talk about getting ripped off for presents! Franamax (talk) 19:55, 3 July 2008 (UTC)

We have an article on this debate: Race of ancient Egyptians. Rmhermen (talk) 13:54, 3 July 2008 (UTC)

"How" is quite simple: her grandparents on her father's side were siblings, and her grandfather on her mother's side was the brother of her paternal grandparents. The family tree at Cleopatra#Ancestry shows a remarkable degree of inbreeding. --Carnildo (talk) 22:02, 3 July 2008 (UTC)

The current majority in Egypt are arabs I believe, but they weren't the original inhabitants of Egypt when talking about ancient Egypt. I believe the copts are survivors of the original inhabitants of ancient Egypt. ScienceApe (talk) 17:26, 3 July 2008 (UTC)

hypoglycemia vs hypertriglycerides

what is the relationship of sugar to triglycerides? is it normal to have hypoglycemia with high triglycerides? —Preceding unsigned comment added by Docbenjie (talk • contribs) 05:54, 3 July 2008 (UTC)

Well, firstly hypoglycaemia is not normal. Secondly, hypoglycaemia (lack of glucose) is not affected by the level of triglycerides (which are fats). It's true that fat can be used as an energy source when glucose has been used up but that does not affect hypoglycaemia itself. That's just my knowledge though, if this affects you medically you should see a doctor. — CycloneNimrod ^talk?_contribs? 11:53, 3 July 2008 (UTC)

Hyperglycaemia (high sugar), seen in poor diabetic control, is associated with higher triglyceride levels. Not sure direct link, rather via common factor of hyperinsulinaemia (raised insulin levels in those who are insulin resistant due to obesity)... for a quick synopsis, see the PubMed abstract of: Reaven GM, Javorski WC, Reaven E (1975). "Diabetic hypertriglyceridemia". Am. J. Med. Sci. 269 (3): 382–9. PMID 168773.{{cite journal}}: CS1 maint: multiple names: authors list (link)David Ruben ^Talk 13:28, 3 July 2008 (UTC)

Cyclone: Hypoglycemia is not normal, but it's also not really abnormal, if that makes sense. Your body is constantly operating to maintain homeostasis, but sometimes one parameter or other shifts too much and your blood sugar drops. It's abnormal the same way dehydration is abnormal: it's an abnormal state of the body that can occur transiently to otherwise healthy people. Sometimes folks who exercise to hard without carb loading or people who eat an especailly carb heavy meal end up experiencing attacks of hypoglycemia. See Hypoglycemia#Causes and Reactive hypoglycemia --Shaggorama (talk) 07:13, 4 July 2008 (UTC)

Why don't spaceships turn into blackholes

According to Einstein, as a spaceship goes faster and faster towards the speed of light, the mass of the spaceship gets larger and larger while the lenght of the spaceship gets shorter and shorter.

So why don't spaceships turn into blackholes? 122.107.135.140 (talk) 12:17, 3 July 2008 (UTC)

Interesting question... I've never thought about it. I think it's just a matter of perspective, though - the spaceship gets denser from the point of view of a "stationary" observer, but it's density remains constant from its own point of view, and that's the reference frame you need to work in to tell if it's going to collapse into a black hole. --Tango (talk) 12:23, 3 July 2008 (UTC)

The question assumes you could accelerate the spaceship to a meaningful fraction of the spead of light, but as its mass increases, so does the force needed to accelerate further. Using the Lorentz transformation a ship at 99% the spead of light has a Mass 7 times that before and a length one seventh. Tango is correct that onboard every seems as normal, but to an outside observer indeed the density (M/V) would seem to be 7 / (1/7) = 49 times as great, which for any reasonable size ship is not going to have any real gravitational effect. 99.99% of c gets us to outside observer measured denisty x5000 and 99.9999%c to 500,000 density; so still not even in our thought experiments getting anywhere close to a density that might cause us problems. Schwarzschild radius indicates one would need to compress the Earth's 6,371km radius into just 9mm radius to become a black hole; that's a compression of over 700million !

See also Gravitational singularity#Curvature, about our assumptions about measurments of weight and distance need to be rethought.

Finally see Micro black hole#Creation of micro black holes for the effort to smash just a few atoms together (accelerator of 1000 light years) so I think we're safe from any fast spaceship ! David Ruben ^Talk 13:19, 3 July 2008 (UTC)

There is no physical limit on how close to the speed of light you can get. It may not be physically possible even under the most extreme assumptions to do it, but we can still discuss what would happen (as you can probably tell, I'm a mathematician, not a physicist!). So, if I got in a spaceship and travelled past the Earth at such an enormous that I observed the Earth's mass and dimensions to be such that it ought to collapse into a black hole, what would I see? The Earth obviously doesn't actually collapse, from the point of view of someone on Earth, but what would I see? I've been thinking about this, and I just don't know. --Tango (talk) 13:40, 4 July 2008 (UTC)

The rest mass doesn't change. Only the relative mass changes. The matter that makes up the ship doesn't increase, nor does it become more dense. In order for a black hole to form, you need to mash a large mass into a very dense form. Like collapsing Mount Everest into something smaller than a human cell. ScienceApe (talk) 17:20, 3 July 2008 (UTC)

Also, the situation described sounds an awful lot like a situation where you'd need quantum gravity. -RunningOnBrains 22:59, 3 July 2008 (UTC)

Our article on mass in general relativity answers this question. It says "Can an object move so fast that it turns into a black hole? No. An object that is not a black hole in its rest frame will not be a black hole in any other frame ...". There is also a link to this page in the Usenet Physics FAQ. Gandalf61 (talk) 14:55, 4 July 2008 (UTC)

Thanks Gandalf61 for pointing to that answer. I also not the later Q&A re heated atoms possibly having more mass because thay have kinetic energy when heated. David Ruben ^Talk 20:53, 4 July 2008 (UTC)

Wheat allergies

Hi. I'm curious about wheat allergies as someone I know has one. Could it be that such a person would have a worse reaction from eating a "whole wheat" product (say pasta) than a regular one? --Dweller (talk) 13:42, 3 July 2008 (UTC)

Wikipedia cannot, does not, and will not provide medical advice. That said, you may want to read our Wheat allergy article, a more medical website, or consult a physician. Plasticup ^T/C 13:57, 3 July 2008 (UTC)

I'm not looking for medical advice, nor do I need to consult a physician as there's nothing wrong with me. I'm just curious. But thanks for the articles - I'll read them. --Dweller (talk) 14:24, 3 July 2008 (UTC)

The first of those articles does mention whole wheat, but the reference comes in an incomprehensible paragraph. The second article does not mention whole wheat. --Dweller (talk) 14:29, 3 July 2008 (UTC)

Everything I look at merely lists foods to be avoided, with refined wheat and whole-wheat considered to be the same. It could be that the difference in allergic reaction, if any, is not significant enough to be mentioned. Fribbler (talk) 14:37, 3 July 2008 (UTC)

Thanks. --Dweller (talk) 14:47, 3 July 2008 (UTC)

Based on reading the wheat allergy article, it looks to me like, because there are many allergenic components in wheat, you get all of those components with whole wheat and less of them with processed wheat. The processing may remove some of the minor allergens (but seems to preserve the main one, gluten). A hypersensitive person could conceivably have a worse reaction if more allergens are present. ~Amatulić (talk) 17:43, 3 July 2008 (UTC)

botanical name

What is the botanical name of the tree that is supposed to go to sleep when the sun sets and rise up again with the sun? Its leaves droop down in the night and freshen up in the morning.

Shyam59.92.72.54 (talk) 14:47, 3 July 2008 (UTC)shyam

With heliotropism, flowers and leaves track the sun as it moves through the sky. At night they either default back to facing east or just some random orientation. -- MacAddct  1984 ^{(talk • contribs)} 16:31, 3 July 2008 (UTC)

There are several types of trees that do this. Albizia julibrissin is the one that came to mind first.--Eriastrum (talk) 23:19, 3 July 2008 (UTC)

I like the ones you touch and they fold, like Mimosa pudica. Then there's one with a folding name: Prayer plant. But they're not trees. Julia Rossi (talk) 09:56, 4 July 2008 (UTC)

Species with long luteal phase

I am interested in which species have a long luteal phase of the estrus cycle. So far I only know that dogs and elephants fall in that category. Any other species? Thanks in advance. Arisa. —Preceding unsigned comment added by 131.211.166.194 (talk) 15:05, 3 July 2008 (UTC)

After googling a bit, I gotta admit this information is difficult to find. I did confirm that elephants have the longest cycle. I thought maybe other large mammals like whales may also qualify, but I couldn't confirm that. ~Amatulić (talk) 21:59, 3 July 2008 (UTC)

Material acting like Maxwell's demon?

Hi all,

Is there anything theoretically impossible about a material, say some kind of not-yet-invented cloth made out of nanotubes, which only lets fast-moving molecules through? How about a material which only lets molecules through in one direction? I can't see anything wrong with the idea except that it may never be invented. But wouldn't such a material essentially act as Maxwell's demon and break the Second Law of Thermodynamics (allowing us to create order out of disorder)?

All the arguments against the demon seem to involve the energy that he must exert separating the molecules, or the energy that he adds observing them, or the lack of infinite memory to know where they all are (I've never really understood that one). This material, however, wouldn't need to "know" which molecules are fast any more than a coffee filter "knows" that water can pass through and larger particles can't. And likewise, like a filter, it wouldn't need to do any work to let the fast molecules through.

So is there anything theoretically wrong with this idea?

Thanks! Sam 16:51, 3 July 2008 (UTC)

I don't really see anything theoretically wrong, per se, with a membrane that would only allow things moving quickly to pass through. As I think about it more, theres plenty of those in existence...pretty much everything fits the criteria. Its just a matter of how you define fast. The penetration of cosmic rays through buildings and such is a good example. Unidirectional motion is also possible, but usually in cases like veins where you've got some kind of pressure being exerted and valves used to control flow.

A common error made when people look at the Second Law of Thermodynamics is they forget the caveat to that rule. You cannot create order out of disorder without adding energy. There is energy in the membrane. If it stops slow moving particles, then it is doing some kind of work from some energy source (mechanical, chemical or otherwise) to stop them. If we were to use a piece of paper as the membrane, its still doing that same work on a fast moving particle, but the fast moving particle has so much energy that it keeps going anyway and breaks the bonds or whatever. This seems a little convoluted, but I hope it helps. Lemme know if I should try again...EagleFalconn (talk) 17:14, 3 July 2008 (UTC)

This is an interesting question. Although I am certainly not the scientist that Maxwell was, nor do I claim to be anything close, I will give it a try. First, this is a thought experiment for a reason. We have several ideal parts of this system: the box, the particles, the wall, the evil-looking green demon, and an ideal separation from the rest of the universe. It is hard to imagine anything close to this level of ideality in a real world system. With that said, the second law of thermodynamics is built to work for ideal systems, too.

One comparison you draw is the difference between a coffee filter and a fast-molecule filter. This is a broken simile I think. A coffee filter distinguishes water from grounds based on size. Energy is a totally different beast. One of the facets of the uncertainty principle is that momentum and position cannot be measured simultaneously. This is because in the act of measuring, the particle is perturbed, changing the other property. In the same way, if a barrier were created such that only particles of a certain energy could pass through, it would strip the particles of that energy as it passed through the barrier, eliminating any gain in entropy. I say this carefully though, because if the particles being discussed were electrons, by using a tunnel barrier you could take advantage of the quantum tunnelling effect and allow particles of certain energy to pass through without such a loss in energy. The risk here is that tunnelling is itself a probabilistic process. ANY electron could conceivably tunnel without losing energy. Higher energy ones just have a larger probability of making the leap so to speak.

What all of these theories lack, however, is an impetus for separation. In your coffee filter example, water and beans are on the same side of the filter and gravity pushes the water through. Now imagine trying to operate the same system in a zero-g environment. That wouldn't really work. Sure all the grounds would stay on one side, but the water would be everywhere. In the same way, unless some gradient were created to move the particles in the right direction, equilibrium would still exist. If you started with all particles on one side and allowed them to move to the other via any of the previously mentioned methods without field, the particles could just as easily move back again, given a high energy. What you are talking about is some sort of thermodynamic diode or valve that requires no potential.

My last comment is this: great thinking. Diodes exist, spin valves exist, many things for separating particles of different properties exist. All need energy. Minimizing that energy is key. It is possible that Maxwell's demon may never exist, but something close to it (operating on the energy of room temperature, for example) would not violate the second law, and may well be very useful. Gjmulhol (talk) 17:18, 3 July 2008 (UTC)

Thanks for the two comments. In response to the argument about the "impetus for separation," I'm not sure that this is needed. (1) If we have a zero-g box with coffee and water on one side of a coffee filter, eventually there will be a mix on one side and pure water on the other, so some separation has occurred (even if not all the way), and (2) If it is a one-way filter (like I mentioned above), eventually each water molecule will have randomly gone to the other side and not been able to get back, thus completing the separation.

I think you're both probably right about the fact that it may be impossible to separate fast- and slow-moving molecules without slowing down the fast-moving ones -- making them rip through the filter, for instance. (I don't think, however, that a barrier has to do work on a slow-moving molecule to make it bounce off -- the molecule's energy would be maintained).

Does the energy that it seems that a molecule loses as it goes through the barrier have to be so much that the fast molecules that pass through it a turned into "slow" molecules? By which I mean, would it be theoretically possible for a barrier to stop all molecules with V < x, and when fast molecules (V > x) break through, their speed is still greater than x? If so, we're still creating a potential difference between the two sides of our box that could be used to generate work, right?

Thanks, Sam 17:45, 3 July 2008 (UTC)

Well, I think we need to distinguish between molecules and electrons here. I am not an expert in physical chemistry. I do have some training in solid state physics. When an electron impinges on a surface, it can do one of 3 things:

• bounce back
• tunnel through
• go over

By go over, I mean have enough energy that it is able to go through the barrier. If the barrier is an energetic one, which I think is what we are talking about here, it will sacrifice the energy used to overcome that barrier and fall to the lowest state available. If you were to erect a barrier of a specific height x (to use you example from before), then the only reason that the particle can pass is that it has enough energy to give. It is like buying a ticket, if you don't have the money, you don't get in. If you do have the money, you get it, but you leave the money.

I still stick with my p-n junction argument that I posted a few minutes ago farther down. I think that is the closest thing of a separating barrier. A solar cell is based on the exact principle described here, but you need that pesky addition of sun to provide some nominal amount of energy to cause current flow.

I honestly have no idea whether there is some corollary to molecular movement as I have described electron movement. Gjmulhol (talk) 23:28, 3 July 2008 (UTC)

Slightly different question, brought to mind from the comments above: Is a one-way filter alone theoretically plausible? If so, would this be a great way to produce usable energy out of un-ordered states? Say I strap a one-way filter to one side of a box, so that air can only go in. The pressure in the box can only increase. If I punch a hole in the other side and add a turbine, my one-way filter will create a stream of air, which could be used to generate electricity, right? Any theoretical objections to that one? Thanks again! — Sam 17:51, 3 July 2008 (UTC)

Well, other than being a perpetual motion machine... (The act of ordering states from unordered states requires energy. Pure and simple. Any instance when you find yourself suddenly getting lots of energy out without putting any energy in is a sure sign that something has gone wrong in your calculations.) --98.217.8.46 (talk) 18:26, 3 July 2008 (UTC)

The input energy in his example is from the random movement of particles in the air. I don't see any immediate flaws. Oh, and I like to think of your theoretical material as fish trap. Plasticup ^T/C 19:26, 3 July 2008 (UTC)

Probably the best example of something that seems to violate the second law is an optical isolator. But even a hypothetical perfect optical isolator doesn't do it, not that I really understand the explanation [16] Someguy1221 (talk) 19:37, 3 July 2008 (UTC)

One example of something similar is a solar cell. Although it does absorb energy, based on the p-n junction's built in potential, electrons flow one way and holes the other. This creates a current. It is a one-way system. Even when no light is on it, there is some small generated 'dark' current from heat effects. Like I said though, it is not a closed system and does require some sort of energy. Gjmulhol (talk) 23:16, 3 July 2008 (UTC)

(ec)Scale matters for this question. Newer research points out that the Second Law of Thermodynamics does not apply to nanoscale systems.[17] I read a few weeks ago that one of the most promising future ideas in nanotech is harnesing Brownian motion to power molecular machinery.-RunningOnBrains 23:18, 3 July 2008 (UTC)

I would be very interested to see the full text of that article. Much of the BBC coverage seems simplistic for a such bold claims. Do you have the DOI, author name, or date of the article? I know from personal experience that forces at the nanoscale level are much different than at even the micro level. For example, capillary action and surface tension are the dominant forces in any system with nanoscale features. I would guess (and remember I haven't yet read the article, so I don't know the details) that the Second Law of Thermodynamics is not being violated. There must be energy coming from somewhere (the shaking of the canister? heat from the room? potential energy of the charge on the bead? again, I don't even know what they measured). Do the researchers make such claims of violating the second law explicitly? If so, this paper really should have been in Nature or Science rather than PRL ;).

Much Brownian motion comes from heat. Motion cannot exist without energy. By harvesting the energy from Brownian motion, we will simply be absorbing heat. This could be done from phonons or diffusion current. Gjmulhol (talk) 23:36, 3 July 2008 (UTC)

Shooting down the barrel of a tank

Kinda inspired by a previous question. Lets say you have a high caliber machine gun, and you shoot down the barrel of the main gun of a tank with full automatic fire. What would happen? Would the cannon be damaged? Could it still fire as if nothing happened? Would the bullets cause a "clog" eventually? ScienceApe (talk) 17:16, 3 July 2008 (UTC)

That depends on a couple of things: (a) your aim, and (b) the cannon bore size. You could probably fairly easily shoot a 50-caliber machine gun down the barrel of a 155mm howitzer cannon, without the bullets touching the cannon barrel.

Even if the bullets did touch the side of the barrel, they impact at a grazing angle and will likely not cause any more damage than a cannon projectile being shot through it.

If a cannon barrel is clogged, you wouldn't want to fire the cannon, or you risk rupturing the barrel. ~Amatulić (talk) 17:30, 3 July 2008 (UTC)

Well basically what I'm asking is if you took a 50 cal and fired down the barrel of the cannon of a tank. Would it damage it, and/or would it clog it? ScienceApe (talk) 18:48, 3 July 2008 (UTC)

If there was a shell loaded, you might be able to detonate the shell (cover your face if you're looking down the barrel). Otherwise, the bullets would strike the breech - likely they wouldn't damage it all that much, unless you hit the firing mechanism, but you could stick enough lead onto the breech to make it unusable to seat the shell. And yes, if you keep firing an infinite number of bullets, eventually you'll clog the barrel with hot lead. Franamax (talk) 19:39, 3 July 2008 (UTC)

Ah... I assumed your original question was about firing a gun through a tank barrel from the inside of the tank. You're asking about firing a gun into the muzzle? That could damage the breech if the cannon isn't loaded, not only in the way Franamax describes, but also in that some cannons use a laser to detonate the propellant, and you could damage the laser window. If the gun is loaded, you might hit the fuzing mechanism of the round, or even clog the barrel, which would get cleared out when the cannon is fired, possible with damage to the barrel. However, I doubt you would do serious damage to the barrel by firing into it due to the grazing angle the bullets make with the inner wall of the barrel. ~Amatulić (talk) 21:53, 3 July 2008 (UTC)

If you simply roll a rock down the barrel or pack some mud in it and induce the tank crew to fire through the barrel, that should cause the gun to explode , possibly killing the crew. This recommendation is from a friend who says this was a tactic used against German tanks in WW2 when it was infantry against armor with no antitank weapons. A tank without infantry support is not all that secure against infantry attack. Edison (talk) 14:11, 4 July 2008 (UTC)

Strange skull

Hi guys, I was wondering if somebody could identify the animal this skull belongs (belonged :p) to:
It was found on the beach somewhere in northern Crete. It is around 5-6 cm in length.
http://img20.imageshack.us/img20/2782/scull1ad2.jpg
http://img20.imageshack.us/img20/4995/scull2gc4.jpg
http://img503.imageshack.us/img503/6638/scull3ft8.jpg
Thanx a lot!
PervyPirate (talk) 17:25, 3 July 2008 (UTC)

At first I thought it might be some sort of bird, but it looks like there are teeth in the front. A big rat, maybe? It doesn't look like what I'd expect for a fish. Great pictures, though. If someone can identify it, and Wikipedia has an article on it, please put that picture in the article. ~Amatulić (talk) 17:35, 3 July 2008 (UTC)

Was I the only person who saw those and immediately thought 'dragon'? :) At a guess, I'd say some sort of predatory eel... --Kurt Shaped Box (talk) 17:46, 3 July 2008 (UTC)

That was my first guess as well, since moray eels are quite common in that part of Greece, but a quick google image search proved me wrong... PervyPirate (talk) 17:54, 3 July 2008 (UTC)

Are you sure it's a skull? It looks to me like a pelvic bone. Compare the third image above with this of a seagulls pelvis: [18]. Fribbler (talk) 17:57, 3 July 2008 (UTC)

Wow! I would never have guessed! Thank you Fribbler (and everybody else)! However, since it's not a skull after all, I doubt the pics will be of any use in an article. PervyPirate (talk) 18:06, 3 July 2008 (UTC)

Why not? Bird anatomy in the skeletal section, or pelvis (currently an overly human-centric article) could benefit from one of those nice, clear pics! Fribbler (talk) 18:11, 3 July 2008 (UTC)

Fair enough. I will ask permission from the friend who made the pictures, upload them properly, and update the talk pages of the articles you mentioned. PervyPirate (talk) 22:12, 3 July 2008 (UTC)

Pelvis? Whoa. How utterly unexpected. Shades of three blind men and an elephant? ;) --Kurt Shaped Box (talk) 18:37, 3 July 2008 (UTC)

Great pictures by the way, you've got some skill, like that as a desktop background...(got any more?)87.102.86.73 (talk) 19:49, 3 July 2008 (UTC)

To be honest, these are not really my pics. But I'll pass the good words to the friend who made them. Cheers! PervyPirate (talk) 22:12, 3 July 2008 (UTC)

basic difference between stroke and depression?

Okay, first, let me assure you I'm not looking for a diagnosis. Rather, I have a question more about the basic differences in these two.

It seems in depression, some of the basic themes apply as to those in strokes. A person may have difficulty speaking, moving, etc.; becuase strokes apparently don't have to affect only one side of the body. And, that in severe enough depression, close to a nervous breakdown, such things can, in fact, stop, just like in a stroke.

Is it common for people to mistake the two? Or, to miss a stroke in a person who has severe depression? Becasue, if the person can't bring themselves to move, and suddenly can't move, how do you know the difference?

Also, has anyone ever tried stroke recovery methods for combatting depression? My guess is it wouldn't work, but a lot of those symptoms are seeming the same right now.

I'm sure things that confuse the common person (like myself) are very clear to someone who has spent 4 years in medical school, another 4 in residency :-)209.244.187.155 (talk) 18:25, 3 July 2008 (UTC)

They are totally different. Tennis elbow and amputation might both leave you with a sore arm, but they are not related in any way. A stroke is a physical disease and depression is a psychological one. Plasticup ^T/C 18:47, 3 July 2008 (UTC)

Depression does not cause paralysis! Jdrewitt (talk) 19:50, 3 July 2008 (UTC)

Perhaps you're confusing depression with a total nervous breakdown? They can prevent the body from functioning, but only because the central nervous system is so ovreloaded. It's not a clinical term per se, but a pshycological condition, in general, is a function of chemical imbalance, I believe, not like a stroke, where it is somply a blood clot blocking something. Also, during a nervous breakdown, cells don't die. (I'm putting it in very simple terms, but seening as you could be confused between physical and psychological conditions themselves, so I felt that might be helpful.)

I'm not sure that stroke therapy could help with a nervous breakdown, becasue the object of stroke therapy is to teach the brain to function again. (Again, making it very simple.) My guess is that it could help to some small degree, if the person views him or herself incapable of simple tasks (for instance, they had stopped speaking), and they need to be encouraged to do them...but that would only be part of the treatment.

I know this kind of goes off the OT, but...I'm struggling to understand the nature of the question, and I felt I had to try *something*. Somebody or his brother (talk) 01:08, 4 July 2008 (UTC)

One general way to think of it is that a stroke is neurological -- lack of oxygen to the brain -- whereas depression is psychological (very broad generalization that I realize treats chemical imbalances too lightly). As they are so different in nature, the treatment of one doesn't really apply to the other. One important difference between the two is that a stroke (also reffered to as a brain attack) is an emergency condition. If chronic depression is left untreated, over time the person may lose control of their lives and potentially kill themselves. If a stroke is left untreated for a matter of hours, the individual may suffer permanent nerve damage and die within days. --Shaggorama (talk) 06:59, 4 July 2008 (UTC)

There are several reasons why these two conditions should not be confused by a competent medical professional. Firstly the onset of the two conditions will be different. In the case of a stroke caused by a thrombus (as opposed to a cerebral bleed) there will be a fairly quick onset, varying from instantaneous to tens of minutes. Immobility caused by depression is likely to take weeks or months to develop, a gradual process that should be apparent to the person's family or friends. The presentation of the two conditions are quite different. Following a stroke the person will have variable paralysis and impairment of conciousness depending on the severity of the thrombus. There will be specific neurological signs present in a person who has suffered a stroke that will be absent in a person who has impaired movements caused by deep depression. In a person with incapacitating depression all their concious mental and physical bodily processes are inhibited but in a person who has suffered a stroke there will be some variability in the movements of the body, and their thought processes (those still working) will react at normal speed. The main difference will however show itself in the onset of the condition. It is very unlikely that 'stroke therapy' will assist someone suffering from a deep depression - or vice versa. Richard Avery (talk) 07:07, 4 July 2008 (UTC)

Gnat ID

I'm trying to identify a Gnat that has a black abdomen which is clearly separated from the thorax (although this could be an illusion produced by a black intrail or its contents and a clear thorax) like that of an ant and extremely large red eyes and relatively short wings which is about a mm long.

The remarkable thing about this Gnat is its ability to hover and to precisely adjust its location to maintain a distance of about 3 to 6 inches from any object which comes close and to relocate itself to its original position when the object moves away in sync with the objects motion.

What species might this Gnat be? -- adaptron (talk) 19:57, 3 July 2008 (UTC)

Could be a fruitfly. Take a look at this [19].--Eriastrum (talk) 23:14, 3 July 2008 (UTC)

Yes, very close for the eyes, thorax also is orange but only a transparent tint. The legs are also clear. Wings, however, are much shorter. The hovering behavior is so controlled and precise its scary - as if being operated remotely in real time by a much bigger brain. :-) -- adaptron (talk) 23:31, 3 July 2008 (UTC)

...as a matter of fact here it is... Drosophila melanogaster. -- adaptron (talk) 23:33, 3 July 2008 (UTC)

Trivalve moluscs

Do these actually exist? It's just that I seem to remember reading something about them years and years ago somewhere... --Kurt Shaped Box (talk) 00:30, 4 July 2008 (UTC)

I see trivalves mentioned fairly often in fantasy fiction and science fiction. There's also this story about Constantine Samuel Rafinesque concerning a discovery of a trivalve mollusk, which was a joke played on him by John James Audubon. There's also a page from Google books about the incident. ~Amatulić (talk) 00:52, 4 July 2008 (UTC)

Is tungsten ferromagnetic?

I checked the article, and all it said was no data... ScienceApe (talk) 06:12, 4 July 2008 (UTC)

I am pretty sure the answer is no. Graeme Bartlett (talk) 06:48, 4 July 2008 (UTC)

No, it isn't. Though some tungsten-containing compounds are. 131.111.228.15 (talk) 07:44, 4 July 2008 (UTC)

Well I know they use tungsten projectiles in railguns, so if it isn't ferrous, then how do they propel it? ScienceApe (talk) 16:32, 4 July 2008 (UTC)

The projectile (and rails) of a railgun only need to be good conductors; no ferromagnetism required. Algebraist 16:40, 4 July 2008 (UTC)

where do herring gulls and black back gulls sleep at night?

Does anyone know what sort of places they usually sleep in? They seem to all leave the town and the local landfill area at night and all go off in the same direction. I'd like to be able to drive out and see them sleeping one night. —Preceding unsigned comment added by 84.67.233.220 (talk) 07:29, 4 July 2008 (UTC)

I believe Gulls are naturally cliff dwellers, I imagine they would roost on cliff faces if they're near the sea. For urban gulls, buildings would present a similiar landscape. —Preceding unsigned comment added by 62.25.96.244 (talk) 09:42, 4 July 2008 (UTC)

Just to note that I am not a Gull and am not called Cliff. --Dweller (talk) 15:05, 4 July 2008 (UTC)

Battery-powered microphone amplifier

Can someone suggest a battery-powered circuit for amplifying the output of an electret mike to drive a headphone (the type commonly used for portable media players)? The circuit should draw very little power, require no more than 2 AA batteries, and be buildable using easy-to-find parts. —Preceding unsigned comment added by 71.175.20.73 (talk) 11:45, 4 July 2008 (UTC)

You might look at [20], they are a huge producer of ICs and sell all kinds of audio amps. You would probably be best to purchase from [21]. Depending on your requirements, this could be a good starting point for selecting them [22]. You should know the impedance of your headphones. The data sheets of all these audio amplifiers should have sample schematics of simple circuits that you can start from. Depending on your input, you might need a preamp. It is also important to note that if it is a condenser mic, you will need to bias the microphone as well. Gjmulhol (talk) 12:13, 4 July 2008 (UTC)

On a side note, be careful about grounding. Audio signals are very sensitive to bouncing ground planes. Gjmulhol (talk) 12:17, 4 July 2008 (UTC)

"Grounding" is important, as is shielding of microphone leads, to prevent hum from influence of the powerline frequency electricity, but certainly no earth-ground connection would be needed. Edison (talk) 14:04, 4 July 2008 (UTC)

Termite control in Scarborough, Ontario, Canada

Dear Wikipedians:

Does anyone know some termite control shops that are located in Scarborough, Ontario, Canada?

Thanks.

74.12.39.232 (talk) 15:31, 4 July 2008 (UTC)

• PCO Pest Control used to sponser my T-Ball team, but a phonebook or a google are better bets. WilyD 15:34, 4 July 2008 (UTC)

Hi. Have you tried yellowpages.ca? Thanks. ~AH1^(TCU) 15:41, 4 July 2008 (UTC)

Overlapping tidal radii

Hi. On an issue of SkyNews magazine, I read that stars can have large zones where an object will orbit it, 1.5 - 15 light-years in radius. It said that the Sun's zone, called the tidal radius, is 3.5 light-years. It also said that they can overlap. This made me wonder.

The nearest star system, Alpha Centauri/Rigil Kentarus/Toliman, is 4.3 light-years away from us. If the sun's tidal radius is 3.5 light-years, I'd expect Alpha Centauri's radius to be a bit larger as it has higher total mass, say 4.0 light-years. This leaves 3.2 light-years of overlapping tidal space at the horizontal plane diametre. Well, is it plausable that AlphaCen has an oort cloud of comets, just like the sun?

I would like to know (and this is not homework, and I don't know if I'm able to calculate this):

• The volume of overlapping space, in cubic light-years;
• The number of Oort cloud comets estimated to be orbiting the Sun in that space;
• The approximate percent of the Sun's tidal sphere surface that is within the overlapping zone;

Or, is the tidal zone not a sphere, but an elliptoid, just like the Heliophere? Oh no!!! Is the spherical model a good approximation? Or is it possible to calculate the same parameters for an elliptoidical model? Would we know in which direction the tidal elliptoid extends farthest and its shape, if it is indeed an elliptoid? Why is the Heliosphere elliptoidical, does its direction change over time, what direction does it point in, does it have any effects on comets just entering the Heliosphere, and could its shape be caused by Nemisis?

Consider the known non-returning comets, with eccentricities of ≥1. Do we know any which have the open end of the parabola(/hyperbola?) pointing towards the AlphaCen direction? Might they be from/going towards the AlphaCen system? Might some be coming back? Are there any other star systems which have tidal radii overlapping ours? Three or more overlapping together? Could this explain some Oort cloud collisions that send the comets plunging towards the sun?

How will AlphaCen's negative radial velocity change this zone over time? What about Gliese...(something, forgot its number, in Ophiuchus) and Barnard's Star as they approach our Sun? Is there an article concerning the subject of orbital tidal radii (and I'm not referring to the Roche limit, which "orbital radius" redirects to)? Might this explain some extinctions?

Using current extimates, about how many comets are sent towards our sun due to the overlapping tidal zone from AlphaCen per each specified specific period of time (eg. per year, per century, per millenium, and how many actually arrive)? Or is it not possible to answer some of these questions due to limited knowledge data? Thanks. ~AH1^(TCU) 16:17, 4 July 2008 (UTC)

I've never heard of "tidal radius" before, and our article on it redirects to Roche limit, which has nothing to do with what you're talking about. The closest term to what you describe that I've heard is Hill sphere, but that's for one object orbiting another, rather than two separate stars. So, I'm not really sure what a tidal radius is meant to be (I can't see what your description has to do with tidal forces, for a start!). The maximum distance at which you can have a stable orbit around a star is going to depend on the other stars around it, and there won't be any overlap (they might go right up to eachother, though, I'm not sure if there would be a region of instability inbetween or not). It's certainly not going to be a sphere. An orbit around the sun in a plane perpendicular to the direction of Alpha Centauri could be larger than the distance to Alpha Centauri, I suppose, but one in the same plane as Alpha Centauri would be unstable if it got too close to the star. --Tango (talk) 16:47, 4 July 2008 (UTC)

convert -

A hole guage of 10-32 -> diameter(inches) —Preceding unsigned comment added by 75.60.90.55 (talk) 19:50, 4 July 2008 (UTC)

I'm assuming that 10-32 is refering to a screw size. Take a look at [23] for dimensional information. -- Tcncv (talk) 20:02, 4 July 2008 (UTC)

Or here: Unified Thread Standard. --Heron (talk) 21:02, 4 July 2008 (UTC)

Simple mechanics.

Let's say there's a stick lying on the ground and I kick it. Well depending on where I hit it and at what angle, the stick will gain some linear momentum and some angular momentum. If I always kick it staight on (i.e. perpendicular to the stick), then only the position matters. So my question is, how can I determine how much angular and linear momentum the stick will possess as a function of the kick's position? Now I gave this question a shot, and my guess is that because the stick has a bit of thickness, the angle between the force and the radius of rotation changes depending on rotation, and that product of the sin of the angle and the force would give the angular acceleration and so on. Is this right? A second and somewhat related question, why does the stick always spin around the center?

Bounce

Why does a ball bounce when it hits the floor?