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3
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1answer
70 views

Spin drift velocity?

I am currently reading this Phys Rev paper by H C Torrey. In this paper, he derives the Bloch equations with an additional diffusion term. He says that the current density is given by $$\mathbf ...
2
votes
1answer
14 views

Thermal healing of defects in crystals

Thermal treatment can heal point defects due to the diffusion of atoms towards empty points. In a solid crystal structure, atoms do not diffuse at room temperature (correct?) Energy of thermal ...
2
votes
1answer
65 views

Heat diffusion: evanescent waves?

It has been recently pointed out to me that the solution of the heat equation in a semi-infinite material with an oscillating boundary condition at the surface is not an evanescent wave. The argument ...
1
vote
1answer
17 views

How do I set up the tridiagonal matrix for a heat diffusion with layers of different thermal diffusivity?

I have Scala code that recreates the Crank-Nicolson solutions for the diffusion equations, and matches 'Excel for Scientists and Engineers' (Joe Billo, Wiley). However, I would like to be able to ...
0
votes
1answer
43 views

How does a minority carrier diffuse?

I have gone through a lot of questions but none of them ask how do the minority carriers approach the depletion layer in the first place. When a p-n junction is formed, negative space charge ...
7
votes
0answers
140 views

Diffusion of gases in the atmosphere

Suppose that the atmosphere is composed of 21% $O_2$ and 78% $Kr$ (instead of $N_2$). Since the density of $Kr$ is greater than the density of $O_2$, the lower atmosphere (where we live) should be ...
2
votes
0answers
62 views

Diffussivity of gases, molecular weight and Lewis number

I am trying to understand the following figure of laminar premixed flames: The Lewis number is defined as $Le = \frac{\alpha_{mix}}{D_{fuel}}$ where $\alpha_{mix}$ is the thermal diffusivity of ...
1
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0answers
45 views

Diffusion of particles

If $n(\vec{r},t)$ is the number of particles per unit volume and $V$ the volume, then $N = nV $is the number of particles in volume $V$ For a small volume, it should be $dN = d(nV) = Vdn + ndV$ But ...
1
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0answers
35 views

Validity of a steady state solution of reaction-diffusion equation

I am performing a simulation involving growth of bacteria. This is an agent-based simulation where the solutes (glucose, oxygen etc.) are represented as a concentration field discretised over space, ...
1
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0answers
23 views

Solid state diffusion as a function of shear stress

I am hoping to get some clarification on the impact of shear stress or shear strain on atomic diffusion in a metallic solid. More specifically, will the kinetics for the dissolution of secondary phase ...
1
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0answers
116 views

Leakage rate Calculation

I have to calculate leak rate for helium/air from an enclosure which is made of fabric. This is similar to helium balloons. There are small holes in the fabric. How should i proceed ?
1
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0answers
77 views

Concentration of Proteins

You release a billion protein molecules at position $x = 0$ in the middle of a narrow capillary test tube. The molecules’ diffusion constant is $10^{−6} \ cm^2 s^{−1}$. An electric field pulls ...
1
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0answers
172 views

Mechanical effects of convective flow in steady-state stagnant film diffusion

When analysing diffusion problems in the context of the simplified film model, two limiting cases are ussually introduced during the solution of the differential chemical species mass balance ...
0
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0answers
31 views

Temperature dependence for specific thermal diffusivity in the diffusion formula

I recently found this answer about the diffusion equation (nice one actually), but have one doubt about the temperature dependence of this formula. If the "packet" of energy (terminology suggested ...
0
votes
0answers
17 views

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 ...
0
votes
0answers
72 views

First passage time of diffusing particle with partially absorbing boundary

Given the solution to the spatiotemporal evolution of a single particle on a 1-D surface $P(x,t)$ a nice result (that I gleaned elsewhere on physics.SE) is that for a boundary at $x=0$ where ...
0
votes
0answers
31 views

Deriving diffusion coefficients from velocity field?

If I know the velocity, $\mathbf{v}(\mathbf{r},t)$, everywhere, is it possible to determine the diffusion coefficient, $D(\mathbf{r},t)$ everywhere as well? Would it be possible from using Fick's ...
0
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0answers
46 views

Interpretation of Einstein relation in kinetic theory

I am reviewing my (independent) study notes on diffusion and found the following comment preceding the derivation of the Einstein relation: Now, since the particles that deliver the stochastic ...
0
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0answers
31 views

Textbook on Diffusion and Diffusion NMR Spectroscopy

I am looking for textbooks ( Mathematical / Theoretical Physics ) that cover diffusion in general. Although it is not necessary that your recommendation covers it, I am also particularly interested ...
0
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0answers
77 views

Determining The Coefficient of Viscosity and Diffusivity in an Estuary?

I am curious and eager to discuss about the experience of determining viscosity and diffusivity coefficient for our coastal or estuary model. I myself, just start to use the range of: ...
0
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0answers
47 views

Diffusion coefficient of a crystal

I've been trying to work this out so I can give a hand waving argument for one of the effects I'm observing on the fly and I find myself going down a rabbit hole that seems way too complicated for ...
0
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0answers
33 views

Should particles in Smoothed Particle Hydrodynamics (SPH) always move during a simulation?

Or can they just be used as an interpolation points and use some other "transported property" which are just evolved and propagated from boundary conditions like for eg. heat conduction through a ...
0
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0answers
61 views

Ask for help: the Reaction-Diffusion related problem

In container there are two kinds of molecules A and B which are distributed uniformly. Initially the quantities of A and B are $N_A$ and $N_B$ respectively A and B are distributed uniform, i.e., in ...