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  1. K

    Breit-Wigner formula

    I see. Thank you!
  2. K

    Breit-Wigner formula

    In Fermi's golden rule for the reaction rate, there is the DOS as a factor, and this is proportional to the number of spin states. I got it from Perkin's book "I. to High Energy Physics". I think I'll quote the questionable paragraph: "So far, we have not considered particle spin. The...
  3. K

    Breit-Wigner formula

    Hello The Breit-Wigner formula says that the cross section for a resonance is proportional to \frac{1}{(2S_a + 1)(2 S_b + 1)}, where Sa and Sb are the spins of the incident particles. What's the reason for this? I don't understand it because for a general cross section there appears just...
  4. K

    LaTeX Introducing LaTeX Math Typesetting

    Thank you! That's exactly what I've looked for.
  5. K

    LaTeX Introducing LaTeX Math Typesetting

    Hello everybody Sorry if this has been discussed already, I couldn't find anything like it: How can I create a statement like \hat{\xi}(g_0) \longrightarrow \infty \ (g_0 \rightarrow g_0^*), but with the second limit written smaller and below the first arrow? Thanks, Bruno
  6. K

    Calculating Theoretical Landé Factor for Dy_2O_3 and Er_2O_3

    Thank you. So, what I've written in 1) is correct, i.e. in this case l=11*3 and s=3/2 ? Is there an easy way to understand why Er3+ has this particular configuration and not 4f9-6s2? Regards Bruno
  7. K

    Calculating Theoretical Landé Factor for Dy_2O_3 and Er_2O_3

    Hello everyone I did an experiment about magnetic susceptibility of Dy_2O_3 and Er_2O_3. For data evaluation I have to calculate the theoretical Landé factor for the paramagnetic atoms in these salts which is defined as g_j=1+\frac{j(j+1)+s(s+1)-l(l+1)}{2j(j+1)} where l and s are the net...
  8. K

    Nobel Prize for Mathematics?

    Our math teacher told us it's because Mr. Nobel's wife once cheated on him with a mathematician. :biggrin: Therefore...well, you can figure out the rest. I don't know if you knew the story (I don't know if it's true either). Moral: Even the noblest man is just a man :wink:
  9. K

    Who is your favourite female singer?

    Ah, thank you marlon...Britney Spears minus Adobe Photo Shop :biggrin: Favourite female singer? Hm, out of the one or two I know in the first place :uhh:, I'd say: Björk
  10. K

    Islamic Contributions To Science

    Who has asked you?
  11. K

    News Hu Jintao replaces Jiang Zhemin

    :confused: :confused: :confused: How long the communists are in charge now? If they were able or even willing to solve these problems they would have had enough time to do it. totalitary society = gross human right abuses inefficient administration with now democratic control, a lot...
  12. K

    Boltzmann's version of 2nd Law -log relationship

    You want the Entropy to be a quantum that adds up when you're looking at more than one system: E. g. if you have two containers filled with gas, you want the relationship S(container A & container B) = S(container A) + S(container B). But if the system A has W_a states and the system B has...
  13. K

    Complex square roots

    Ah, it's all right, I've just figured out how that works. Good. Very good. The exams may come :biggrin:
  14. K

    Complex square roots

    Thank you, Hurkyl. I'm still not 100% clear... I understand now why to cut the interval out, but then: let's say we have the square root with sqrt(2)>0 on the complex plane without the negative real axis, and we have f(z)=6z^2-5z+1. If we want to take the square root of f, we have to take...
  15. K

    Complex square roots

    I've got a homework problem from my function theory course that I never fully understood. It's getting hot again since the exams are nearing...please help :smile: It goes simply like this: Compute the Integral \int_{\vert z \vert=1}\frac{dz} {\sqrt{6 z^2-5 z +1}} The square root is chosen...
  16. K

    Playing Piano: Mastering Für Elise and More

    For the beginner's/intermediate level I can recommend the collection "Classics to Moderns" by Denes Agay, Yorktown Music Press. It's available in 6 differently graded volumes, plus there is the extra series "More Classics to Moderns" which makes twelve books in total. As somehow suggested...
  17. K

    What will you be studying this semester?

    Geez...I haven't even begun my exams yet :biggrin: :cry: :cry:
  18. K

    I drink distilled water

    I think this is immoral. ...Nevermind :biggrin:
  19. K

    Why can't we ban adult sites?

    I doubt that anyone wanted to read this on PF. Do you think you're the only one who doesn't like this stuff? That's why you're allowed to avoid it. You may think of other people whatever you want, but don't expect other people to accept your moral values.
  20. K

    News Taking a Euro Trip

    Hahaha, uhh... :yuck: I hope thet's better now. At least Euro and USD should be accepted everywhere, but I can't guarantee you that the conductors have become any friendlier :rolleyes: About biking: I'm a hobby race bicyclist for three years now and I almost never had any problems with...
  21. K

    About how to prevent being struck by lightning

    :eek: Good to know But the best way to protect yourself is and will ever be: Don't blaspheme :devil: :wink:
  22. K

    News Taking a Euro Trip

    I live in Switzerland, but I guess Ivan Seeking can give you better tips than I :biggrin: :blush: I personnally live in Lucerne, quite a classical tourist's town (though not really in winter). If you know how to ski, go anywhere you like, Zermatt, Engelberg, Arosa, name it, we got it...
  23. K

    Why used left hand to hold the torch?

    I'd go with this explanation. I'm sure there's not much of Greek mythology behind this. The Olympic torch was introduced 1936 the Nazis.
  24. K

    About how to prevent being struck by lightning

    Yes, that sounds logical. I wondered about it because a few days ago I almost got into such an uncomfortable situation. I was climbing on a mountain top when I heared thunder from far away, and the "top" actually was a big rubble waste dump, no big rock or anything around. So, whatever I...
  25. K

    Can't explain to my friend properly

    The falling-elevator-thread is back again... :smile:
  26. K

    About how to prevent being struck by lightning

    They say if you're in a thunderstorm and you have no other place to go, you should search a hollow, crouch and hold your feet close together. The hollow thing and the crouching thing are easy to understand, but what's the reason for putting your feet together?
  27. K

    Do you know them?

    I can see Lenin, too! :biggrin:
  28. K

    Mother country vs father country

    But Patria comes from Pater which means father. So, in the latin languages as well as in German it's "father country" instead of "mother country". My explanation for this is: Traditionally it's your father from which you inherit things. You inherit his name, his fortune, maybe his profession...
  29. K

    Who is the greatest comedian?

    Since I've seen the movie "Man on the Moon" I must say I'm a fan of Andy Kaufman, though I don't know him very well. Actually I've only seen that half hour original material that came with the DVD, e.g. the "And the Bird Goes" song and some woman-wrestling scenes. But that was just soo cool...
  30. K

    Navier-stokes and 1 million dollars

    The "Million-Dollar-Problem" is purely mathematical and does not deal with physical reality at such a low scale. Of course there is no such thing as a non-smooth velocity field in a real liquid.
  31. K

    Exploring the Physics Behind Finger Tapping Violin Strings

    This way of playing has a name: Flageolett. Also used on other string instruments. It's not like I play the violin or something, I heard this expression in a physics lesson :rolleyes:
  32. K

    Heat equation in a sphere surface

    The only necessary boundary condition is indeed the initial temperature distribution. With that and the condition that no heat leaves or "enters" the thin surface the whole development in time is determined. I'm not sure if the angular periodicity can be called a boundary condition...its more...
  33. K

    Heat equation in a sphere surface

    I've figured out a way of solving it, I'm not sure if it works. Anyway here I go: The initial temperature distribution can be written as an infinite sum of spherical functions, T(\theta, \phi, t=0) = \sum_{l=0}^\infty \sum_{m=-l}^{+l}a_{l,m} Y_{l,m}(\theta, \phi) The heat equation for one...
  34. K

    Newton must respect the law of lever

    If the work done on the bodies have opposite sign, why do they both gain kinetic energy? Last time I checked, work was positive when force and displacement are pointing in the same direction.
  35. K

    The physics of the lever

    With a nice language feature! :biggrin: :wink:
  36. K

    Homework puzzle from 15 years ago never solved -

    I think the problem is indeed not soluble. It consists of five rooms (six if you count the outside too) and doors in between. As Zorodius said, if the line enters one room it has to leave it again. The only exceptions are the rooms where the line starts or ends. These two rooms have an odd...
  37. K

    What is the difference btw 2 loops?

    I'd say they don't have the same charge density but the same current density. So they produce the same magnetic field, but the "charged ring" situation implies also an electric field which has to be considered when you compute the force on another charged particle. About w and I: How much...
  38. K

    Temperature and spectral lines

    I think the definition is made up with the internal energy of the system which is rotational, vibrational energy of the particles and translational energy wrt the center of mass. To get the total energy one has to add P^2 / 2 M(total mass/momentum). Like this the definition is frame invariant.
  39. K

    Why doesn't gravity violate the 1st law of thermodynamic's?

    And what about the fact that the moon's rotation is in in the same direction as its orbit rotation? Or the fact that Uranus' rotation axis lies more or less in the plane of ecliptic? That makes no sense at all.
  40. K

    Hello, good-bye, and thank you.

    No big deal, it's just that "große(r) Gott" means "great god", and even in catholic southern Germany people may wonder about you if you tell them all the time how good god is... :) Grüssen=to greet Gross=great, big
  41. K

    Hello, good-bye, and thank you.

    Wow, you even managed to type the double-s, not even I know how to do this with my keyboard :rolleyes: But it's rather "Grüss' Gott" than the other, except you're some religious freak...:biggrin:
  42. K

    Favorite radioactive isotope?

    Go go Otto "Rehakles" Rehagel! :biggrin: :biggrin: Geez those semifinals were boooring...
  43. K

    EM waves from standing charge

    I haven't had any lectures on quantum ED yet, but as I understand it the particles that cause the force in the non-moving case are only virtual Photons, they "transport" momentum between the two electrons but do not affect any other particle, therefore cannot be detected. So they do not form a...
  44. K

    Electric field of two polar molecules

    Aren't Van der Waals force and dipole-dipole attraction two different things?
  45. K

    Favorite radioactive isotope?

    Ah I see :)
  46. K

    Favorite radioactive isotope?

    No I'm not. But my heart is, at least until wednesday. How tall I am? I am Three Times as high as a man, and I can strangle a bull with my bare hands, and I have no idea why you're asking this question :rolleyes: ...whateva :smile:
  47. K

    Favorite radioactive isotope?

    Lol, blaming the referee again (who did an excellent job)... Take it like a man, it was a foul. Would have liked to see England and Portugal in the semi final though...that is life.
  48. K

    Favorite radioactive isotope?

    Oh no! So then: Czech Republic because they just beat the Danish 3:0 (and because of their beer)
  49. K

    Favorite radioactive isotope?

    Favorite Radioactive Isotope: Plutonium, carefully steamed, with a nice glass of 1987 chateau Rothschild. Excellent. Favorite Mineral: Evian Favorite Eastern European Nation: Latvia, because they won the European song contest (...did they?) Favorite Presidential Cabinet Member: It's so hard...