Science desk
< January 31	<< Jan \| February \| Mar >>	February 2 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

February 1

pubmed error

Why can't I find this title in pubmed? "GSTP1 CpG island hypermethylation as a molecular biomarker for prostate cancer" ----Seans Potato Business 01:01, 1 February 2008 (UTC)[reply]

I found it. [1] Someguy1221 (talk) 01:16, 1 February 2008 (UTC)[reply]

What search string did you use? Why doesn't the title work? I tried the title, the title without the first few words, the main author and date... ----Seans Potato Business 07:52, 1 February 2008 (UTC)[reply]

I just copy-pasted the title into google scholar and voila, the pubmet hit was number three. Someguy1221 (talk) 10:11, 1 February 2008 (UTC)[reply]

Okay, I'll remember that for next time (but I still think that pubmed have a problem (not the first time that I've encountered it, either; I've contacted them before and was fobbed off with some rubbish). ----Seans Potato Business 12:14, 1 February 2008 (UTC)[reply]

I was intrigued by this...GSTP1 CpG island hypermethylation as a molecular biomarker for prostate cancer gives this search string:

Translations: 
CpG island ("cpg islands"[TIAB] NOT Medline[SB]) OR "cpg islands"[MeSH Terms] OR CpG island[Text Word] 
as a as a[Author] 
biomarker ("biological markers"[TIAB] NOT Medline[SB]) OR "biological markers"[MeSH Terms] OR biomarker[Text Word] 
prostate cancer ("prostatic neoplasms"[TIAB] NOT Medline[SB]) OR "prostatic neoplasms"[MeSH Terms] OR prostate cancer[Text Word]

For whatever reason, PubMed was taking "as a" and doing an author search! If you just do a search for GSTP1 CpG island hypermethylation molecular biomarker for prostate cancer (note the missing "as a") the article pops right up. Weird. — Scientizzle 00:17, 6 February 2008 (UTC)[reply]

impulse of photon

I want to know about impulse of photon on reflection from a surface.please provide with a formula. —Preceding unsigned comment added by 59.95.77.49 (talk) 06:25, 1 February 2008 (UTC)[reply]

Well I not 100% sure but...firstly you have to keep in mind that when you're dealing with photons it's not quite the same as in regular newtonian physics...after all a photon has no rest mass and doesn't 'reflect' off a surface. That aside, and assuming you mean it 'reflects' back in the opposite direction from which it came, and knowing that impulse is the change in momentum, and that the momentum of a photon is h/λ, I guess the impulse would be I = 2h/λ, where h is plancks constant and λ is the wavelength. I'm sure someone will kindly correct me if I'm wrong... Trimethylxanthine (talk) 06:47, 1 February 2008 (UTC)[reply]

Quite right. While quantum wave-particles don't interact according to Newton's laws, the various conservation rules still apply. So the important facts of simple reflection is that a photon went in with h/λ momentum, and left with -h/λ momentum. Therefore, the remainder of the system experienced a change in momentum of 2h/λ, even without knowing what really took place. Someguy1221 (talk) 10:14, 1 February 2008 (UTC)[reply]

Don't forget the angle - making it 2h sin(a)/λ where a is the angle to the reflective plane.. (is that still right?)87.102.12.64 (talk) 15:00, 1 February 2008 (UTC)[reply]

Yes; I just prefer to operate in as few dimensions as necessary ;-) Someguy1221 (talk) 15:50, 1 February 2008 (UTC)[reply]

Burning Sensation in the chest when exerting oneself

Medical question removed. It may very well be that your condition is simply due to over-exertion, but we goofs on the refdesk are not able or allowed to make that call. See your doctor. If you really think that will be a problem, see if you can talk to a nurse or pharmacist or someone at a drop-in clinic. Semi-anonymous encyclopedia geeks are not a good source of medical help! Matt Deres (talk) 19:32, 1 February 2008 (UTC)[reply]

chloroplasts

With present technologies is it possible to keep a chloroplast working (making photosynthesis) outside of a cell, in vitro? sorry if my english is not correct thank you 87.2.65.209 (talk) 17:33, 1 February 2008 (UTC)[reply]

As far as I know, yes. Since photosynthesis depends on the transport of electrons through ATP producing carrier protiens (and the electron transport chain which is controlled by light), chloroplasts can be placed in an acidic solution so diffusion will transport H

^{+}

ions into the chloroplast. Then, when the chloroplast is placed into a basic solution, a concentration gradient will be created between the basic solution and the high concentration of H

^{+}

ions in the cell. This will cause the electrons to diffuse through the ATP producing carrier proteins, thus producing ATP. Zrs 12 (talk) 20:01, 1 February 2008 (UTC)[reply]

But can the chloroplast survive outside the cell to begin with? − Twas Now ( talk • contribs • e-mail ) 01:21, 2 February 2008 (UTC)[reply]

I'm not sure. However, I suppose they could. See [this link] (answer number 3) and make what you will of it. It seems to me though, this link means they could and just don't. Zrs 12 (talk) 01:49, 2 February 2008 (UTC)[reply]

Yes. The endosymbiotic theory. But can we remove them and keep them alive indefinitely? It would be extremely difficult, I think, to match the environment of a cell in vitro. − Twas Now ( talk • contribs • e-mail ) 02:21, 2 February 2008 (UTC)[reply]

I just found another link which seems to claim it wouldn't be possible.[1] In which it says about half way down the page, "Mitochondria and chloroplasts have lost so many genes that they can't live separate from their "host cell"; but they are essentially degenerate procaryotes." However, being in vitro in an ideal environment would provide them with nutrients and other things which the cell would normally provide. So, apparently, depending on which genes have been lost, they may or may not be able to be kept "alive" in vitro. Zrs 12 (talk) 02:43, 2 February 2008 (UTC)[reply]

Chloroplasts cannot live indefinitely, which is why they are called semi autonomous organelles. They can live long enough to be useful. Some sea slugs harvest them from algae and store them in specialised pouches for their own benefit. This is known by the term Kleptoplasty. David D. (Talk) 03:07, 2 February 2008 (UTC)[reply]