# Questions tagged [diffusion]

Diffusion is the net movement (spreading out) of molecules or atoms down a concentration gradient: from a region of high concentration to a region of low concentration.

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### What is the link between path integral source terms and the propagator?

Consider a diffusion process defined by $$\frac{\partial \phi}{\partial t} = D \frac{\partial ^2 \phi}{\partial x^2}$$ where $\phi$ is the probability density of a particle's position and $D$ is the ...
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### Green's function for moving solidification front

Consider a liquid solid interface $z =\zeta(x,t)$ moving at constant speed $v$, for a two dimensional problem. Due to solidification interface is changing it position. For simplicity heat ...
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### How to estimate loss of water from skin?

The question came to while hiking. We are often told that we must drink at least 8 glasses of water regularly to compensate water loss by evaporation from the skin. So how does one compute the rate ...
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### Chemical Potential of Interacting Particles

I'm interested in studying the diffusion of (classical) particles that have some interaction with each other. More specifically, let the potential energy of any two of particles separated by a ...
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### Critical mass (radius) of U235

I am calculating the critical mass (radius) of $U^{235}$ sphere. I want to calculate the mass for three different cases: 1. air/vacuum surrounds the sphere (diffusion coefficient is infinite) 2. ideal ...
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### diffusion of gases in both directions

I am a technical specialist that works on analytical equipment. Gas chromatographs use carrier gases like helium and hydrogen that flow through long, thin glass tubes coated on the inner surface with ...
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### Can a mechanical forced oscillation of a gas column significantly affect diffusion rates through the column?

High Frequency Ventilation (HFV) is a special type of mechanical ventilation used in critical intensive care units. Rather than moving gas volumes in bulk at conventional breath rates, HFV operates at ...
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### Diffusion and Drift currents in forward bias

Why do the current in diode in forward bias configuration called "Diffusion current" even if this current is a resultant of external voltage supply which create electric field in diode ,hence should ...
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### Numerical integration of the heat equation with variable thermal diffusivity using spectral discretization

I want to integrate this equation in time: $$\frac{\partial u(x,t)}{\partial t} = \frac{\partial}{\partial x} \kappa(x) \frac{\partial u(x,t)}{\partial x}$$ with initial condition u(x,0) = \frac{...
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### On the derivation of diffusion coefficient in thermodynamic terms

I'm trying to express the diffusion coefficient $D$, regarding particles suspended in a liquid, in terms of thermodynamic parameters. In this, some evident problems were encountered when trying to ...