Wikipedia:Reference desk/Archives/Science/2008 June 27

= 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)  it will find it ++Lar: t/c 04:46, 27 June 2008 (UTC)
 * Awww...

Repost - Black holes and Hawking radiation


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. &mdash; 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 — 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. --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)