Recent content by gdumont

Hi, I have the following problem : I generate GaAs (zinc blende structure) supercells, and then I want to replace some As atoms by N atoms. Let's say I have fcc conventional cell repeated twice in the x, y and z direction so that I have a total of 64 atoms, 32 of Ga and 32 of As. 8 atoms...

OK, but is the distribution function OK?

Hi, I have the following problem to solve: Consider a planet of radius R and mass M. The plante's atmosphere is an ideal gas of N particles of mass m at temperature T. Find the equilibrium distribution function of the gas accounting for the gas itself and the gravitationnal potential of...

Hi, I have the following function to evaluate in a power series: f(a)=\frac{\pi}{8d}\frac{1}{\left (\sinh \left ( \frac{\pi a}{2 d} \right) \right)^2} Maple computes then following f(a) = \frac{\pi}{8d} \left ( \frac{4 d^2}{\pi^2 a^2} - \frac{1}{3} + O(a^2) \right) When I ask Maple if this...

I realized that it was the \sinh x function and not the inverse function. And yes I used the geometric series to show the relation. Thanks anyways!

Hi, I'm trying to find a way to prove that \sum_{n=1}^{\infty} n e^{-n x} = \frac{1}{4}\sinh^{-2} \frac{x}{2} Any help greatly appreciated

Ok, here's what I tought: If the gas has density \rho than the number of molecules in a volume \sigma_{\textrm{tot}}dx is dN=\pi \rho a^2 dx. If collisions are ellastic, then \textbf{p}_s + \textbf{p}_i = \textbf{p}_s' + \textbf{p}_i' where the s and the i denote respectively the...

Quick reply Take this expression U=-\tau^2 \frac{\partial(F/ \tau)}{\partial \tau} use the product rule for derivatives. And you'll get back to the prior equation

You are right use the product rule f(x)=u(x)v(x) then f'(x) = u'(x)v(x) + v'(x)u(x) here u(x)=-6x and v(x)=(1-x^2)^2

Use energy conservation : At time t=0 Tarzan has zero kinetic energy (he is at rest). If Tarzan is, say, l meters above the ground, can you find an expression for his potential energy? Then you can relate l with the length of the vine using trig. Then at the bottom of the swing all energy...

Ok, I need to find the frictional force on sphere of radius a and mass M moving with velocity v in an ideal gas at temperature T. If I put myself in the sphere frame, then diffrential cross-section is \frac{d\sigma}{d\Omega} = \frac{a^2}{4} and the total cross-section is...

I don't really get why is that... any chance you can explain it to me Thanks

Any ideas?

I have this problem, it doesn't seem very complicated but I can't figure out how to do it. A gas obeys to the equation of state P(V-b) = Nk\zeta where k is the Boltzman's constant. The internal energy of the gas is a function of \zeta alone. Show that \zeta=T using a Carnot cycle. Any help...

I had a look at your solution and there is something I don't understand. At the end of the first page you wrote $ i \chi^\dagger \bar{\sigma}^\mu \sigma^\nu (\partial_\nu \partial_\mu \phi ) \sigma^2 \epsilon^\ast = i\epsilon^\dagger \sigma^2 \chi^\ast (\partial^\mu \partial_\mu \phi)$ This...