Recent content by thepolishman

The initial velocity distribution is mostly just assumed to be a known distribution function. The distribution function I specified was just given as an example. As for the viscous stress and pressure terms, I assumed them to be zero since the gas density is very low (<1E17 cm-3 initially, and...

Right, but doing that gives: ##F=-Mx+C## But since the initial condition is: ##u=Ax^{1/2}## There doesn't seem to be any way for me to match the initial condition and the function ##F## since one has an ##x## with an exponent of 1/2 and the other an exponent of 1.

I'm in the same boat, not great at PDEs. I also initially took the approach that ##g(x)## and ##f(t)## were simply constants, but then there was no way to match the result with the initial condition. I may just be approaching this problem incorrectly.

Hey all. I'm trying to understand the evolution of the velocity distribution function of a gas undergoing free expansion. I know that at t=0, the velocity distribution function is given by ##u(t=0, x)=Ax^{1/2}##, where ##A## is a known constant. From the momentum equation, I have: ##du/dt+u...

Thanks!

Hey all. Was wondering if anyone knew how I would go about determining the amount of reflectance that occurs when there is a gradual change in the refractive index. For example, if I have a material in air whose refractive index begins at e_r=1 (i.e. it matches the refractive index of the air)...

Basically, I'm wondering if there have been any attempts to calculate/model what the radius of the sun should be based on gravitational, thermal, and electromagnetic pressures. If there has, where can I find the calculation/model, and how closely does it match the actual radius of the sun...

Not really a solid, just a very dense electron gas. Using femtosecond laser ablation allows the material to reach several 10s of eVs with electron densities at or above the density of the solid. Since the pulse duration is on the order of ~100 fs, the material does not have sufficient time to...

Unfortunately, the temperatures that I'm interested are in the range of 10 eV or more (>~120,000 K), with the laser energy sufficient to cause material ablation and produce an expanding plasma plume. As a result, most low temperature approximations are no longer accurate. However, the...

Basically the thread title. For some background, I'm trying to model laser-material interactions, where I'm assuming that the laser is interacting with a free electron gas (copper). To model the interaction, I need to determine the properties of the electron gas, such as the heat capacity...

Hello all, I have been learning to use FDTD to model light interaction with various materials. I've successfully managed to model light interaction with semiconductors/insulators. However, I've been having trouble understanding how to incorporate metals into this model. The code becomes...

I wasn't sure where to post this question, so I posted it here. As the title suggests, I want to know how to calculate (at least roughly) the electric field induced by excitation and ionization of a material (such as a metal) using a high intensity laser. My final goal is to compare the...

Wow, I got some great answers to my questions. Thank you for all the replies. I'll definitely be using PF more often from now on.

Thanks. Adding to my question a bit, is there a reason (mathematical or physical) that the conduction band spreads out over the material whereas the valence band remains localized to a single atom (at least that's what I'm assuming)?

As my title states, I want to understand why electrons in the conduction band can move around so easily in the material. Is it due to the presence of many closely spaced (blurred out) energy levels which make it easy for the electrons to move around? Or are the electrons undergoing some kind...