Wikipedia:Reference desk/Archives/Science/2006 December 13

= December 13 =

de Broglie / Compton wavelengths
What would happen if, in order to gain as high a resolution as possible of a particle, the probing photons' wavelengths were decreased until it was of similar order of size of the particle's de Broglie wavelength? Would the circumstances be different if its Compton wavelength was considered instead? —The preceding unsigned comment was added by Icthyos (talk • contribs).


 * I presume you mean "measure a particle's position to as high a resolution as possible", and I linked your articles. This makes the Compton wavelength more relevant, as it does not depend on the subject particle's momentum; as the article says, if you use photons of sufficient energy to match the particle's Compton wavelength, the photon has energy equal to that of the subject and is therefore (in a sense) equivalent to it.  The measurement of the particle is thus confounded by the fact that your measurement is as much artifact as it is observation.  For the de Broglie wavelength, you are matching the subject's momentum rather than its energy; I believe the important point there would be that the uncertainty in the measurement due to the wavelength of the photon would be equal to the inherent uncertainty of the particle's position and thus no further improvements in resolution would be possible.  I believe also that the Compton wavelength is always the smaller of the two (if we consider the particle's relativistic mass in defining it, which I believe is appropriate).  Does that help?  --Tardis 18:26, 13 December 2006 (UTC)


 * Thanks, that does. I'm more interested in pushing the limits of the uncertainty principle though - as I understand it, space is quantized, and am trying to understand if this can be shown from Heisenberg's - ie, does dx have a minimum, as dp increases, and how can this be estimated from a thought experiment? I've tried a variety of methods, but am unsure of what estimates to use for certain values. (I'm guessing an accurate guess would yield the Planck length? Icthyos 18:54, 13 December 2006 (UTC)


 * The uncertainty principle should not be taken too literally - it does not really say that "space is quantized". It's really a relationship that comes out of pairs of conjugate variables, and can be beautifully illustrated with Fourier transforms and time-frequency uncertainty - but this is a digression. What you might be interested in, are say, coherent states of light, particularily squeezed coherent states. Very active area of reasearch - exploring the sort of ideas I think you're curious about. --HappyCamper 05:19, 14 December 2006 (UTC)

Serotonin/Melatonin in nightshift workers
--NiteRN 17:02, 13 December 2006 (UTC)I have been working part-time nights (5 on 9 off) for ? 10yrs. I have been having problems lately with anxiety effects - palpitations, choking sensation, PAC's. These have reduced dramatically with Effexor 75mg/day but I would like to get off it. Symptoms rebound drastically. How long do they last? Would taking some 5-htp help? I also have chronic GI issues - Could that cause problems with serotonin? Thanks--NiteRN 17:02, 13 December 2006 (UTC)


 * We cannot provide medical advice here - I suggest you contact a medical professional. For more information on some of the topics you mention, you might want to read our articles on Circadian rhythm and serotonin. Hipocrite - &laquo; Talk &raquo; 17:09, 13 December 2006 (UTC)


 * NiteRN, I do not think you should despair. You have the right to ask for help in obtaining appropriate information and Wikipedia has much more approriate information for you. Venlafaxine is specifically discussed in the article on SSRI Discontinuation syndrome. The article notes the prolonged withdrawal regime which may be necessary to avoid distressing symptoms of withdrawal ("discontinuation syndrome" = pharmaceutical spin for "withdrawal"), and describes the symptoms. Regimes for reducing discomfort on withdrawal include a very gradual reduction in dose (over 6 to 12 weeks), and changing to a SSRI with a long half life, e.g. fluoxetine. However, you say that you are experiencing a return of your original symptoms, which suggests that the cause for the original problem has not disappeared. So may be wise to consult a health professional, and try to work out some approach to resolving whatever is causing the symptoms, as opposed to simply suppressing symptoms. This may well include addressing your work situation. I cannot find any evidence that 5-HT makes a difference to the anxiety state or the medication withdrawal. Your question about the gut and 5-HT is addressed at IBS (5-HT), while the association with your more general problems is noted at IBS - Stress. Night time and shift work is a stressor, but it cannot be considered "the only" explanation for your difficulties, else all shift workers should have the same. Therefore one would not expect the use of melatonin to be of benefit, but your doctor may think that it could be part of a more comprehensive solution to your difficulties. --Seejyb 22:40, 13 December 2006 (UTC)

Another option may be light therapy. StuRat 05:20, 14 December 2006 (UTC)
 * Or, for that matter, try and get on an earlier shift. It'll do wonders for your social life, which may help with the anxiety issues. Cernen Xanthine Katrena 12:57, 14 December 2006 (UTC)

Helium to lift 5kg
What would the aprox. minimal diametre of a spherical helium balloon have to be in order to slowly lift 5kg off the ground? It doesn't have to be very precise. Thank you Keria 17:29, 13 December 2006 (UTC)
 * The density of Helium is 0.1786 kg/m3, the density of air is 1.2 kg/m3: therefor x cubic metres of Helium will be ~1.02 kg lighter than air.. and so will have a lifting capacity of ~1kg. So I guess just more than 5 cubic meters should do it.83.100.254.21 17:46, 13 December 2006 (UTC)

That's r=cube root of 1,1936... ? How do I solve that? Secondary school is 10 years away. Keria 18:24, 13 December 2006 (UTC)


 * Since you join secondary school at the age off 11, your dam sophisticated 1 year old.


 * $$V = \frac{4}{3}\pi r^3$$


 * $$\sqrt[3]{\frac{3V}{4 \pi}} = r$$


 * $$r = 1.06078442m\,$$


 * Ok? Philc  TECI 19:36, 13 December 2006 (UTC)


 * er...I meant college 10 years ago. Thank you very much. Keria 19:53, 13 December 2006 (UTC)


 * Air pushes up against 1 m^3 of helium with a force of 1.0214 kg. Since 1 m^3 of helium can lift 1.0214 kg, a 1 kg load will require 0.97904 m^3 of helium to lift (1/1.0214).  Therefore, a 5 kg load will require 4.8952 m^3 of helium to lift.  That's equivilent to a sphere with r=1.05332 m.  If we assume the mass of the balloon is 46 g, then the radius becomes 1.057 m.  --Bowlhover 21:17, 13 December 2006 (UTC)


 * As a matter of curiosity, why'd you pick 46 g for the estimated mass of the balloon? Does this come from some real-life balloon? I'd've guessed that a 2 m diameter balloon would be a in the hundreds of grams. --Anonymous, December 13, 23:30 (UTC).

Parallel Line Assay
I work frequently with pharacopoeial compendia (USP, EP) and I'm having a problem with a calculation method they describe. For assays in which the response curve of different concentrations of a standard is compared to a similar curve generated for a sample of unknown potency, the compendia specify fitting regression lines to the curve and calculating a potency for the unknown sample using a "Parallel line assay". Now, I've done similar things before where a potency calculation is based simply on a comparison between the slopes of the two regression lines, but I can find no reference on how to do this calculation. I get lots of links wanting to sell me software, but none explaining how it's done. Does anyone here have experience with this calculation? Since the main use of this seems to be limited to bioassays, I thought this may be a more appropriate venue for the questions as opposed to the Math desk. --Mabris 17:55, 13 December 2006 (UTC)

Lack of Antigens
Is it possible for a microorganism to have no antigens on it's surface and if it is, are there any around like that today? Also, would the immune system be able to combat the microorganism if is has no antigens (i.e. the white blood cells cannot make antibodys to fit nothing)? Thanks Herbynator 22:24, 13 December 2006 (UTC)


 * An antigen is any fragment of a molecule sufficiently different from self-molecules to be recognized by an antibody. It is very difficult to imagine anything living that would not have a hundred potentially antigenic bulges, curves, and irregularities. Certainly no examples in the natural world. alteripse 01:13, 14 December 2006 (UTC)


 * Rather than have no surface antigens, some microbes switch antigens. Take a look at An immune evasion mechanism for spirochetal persistence in Lyme borreliosis and this. --JWSchmidt 05:29, 14 December 2006 (UTC)

Banyan trees and adventitious roots
Any botany sleuths on this board?

I'm looking for the name of particular species of banyan tree where the adventitious roots become unusually robust and complex. During my childhood in Florida there was one in my town that had grown its trunks into a three pronged tunnel large enough for a kid to walk through (which we did gleefully). Although Florida has large numbers of introduced species, this particular tree was probably well over 100 years old so I guess it was native. Wikipedia's article doesn't tell me more than I already know. Durova Charg e! 23:35, 13 December 2006 (UTC)


 * I often use this guys website for the curious plant stuff. And sure enough he has your tree there too. Is the one you're thinking of Ficus bengalensis?  it is probably the biggest one and in Florida too.  David D. (Talk) 00:16, 14 December 2006 (UTC)
 * Thanks for the link. Durova Charg e!  02:08, 14 December 2006 (UTC)