Diffusion Definition and 399 Threads

This is in the beginning of a long set of problems, and I am lost. I don't get anything like this answer. Any guidance? I have a feeling its simple but haven't done much of these. Write down the diffusion equation for the neutron flux in a multiplying sphere of radius R containing a constant...

Hi! I am studying the diffusion of CO2, can anyone tell me the value (or/and any references) of the diffusion coefficient (and/or mean thermal speed and mean free path) of [SIZE="4"]CO2 in normal air? Many Many and a hundred many thanks! Raymond

Is neutron diffusion, traveling neutrons from the nucleus, to direction outside of the nucleus? In my textbook says that there is neutron diffusion, where there is not nuclear reaction. In that case are neutron bouncing off the nucleus?

in literatures, people are discussing about the phase diffusion of a bose einstein condensate what does it mean? the phase of the bec drifts on the unit circle randomly? does this concept come from quantum optics?

Ok, I have been given the steady state diffusion equation in 1d spherical polar coordinates as; D.1/(r^2).'partial'd/dr(r^2.'partial'dc/dr)=0 I know that the solution comes in the form c(r) = A+B/r where A and B are some constants. I just don't know how to get from here to there. I...

Homework Statement The solution to the diffusion equation in 1D may be written as follows: n'(x,t) = N/sqrt(4piDt) * exp(-x^2/4DT) where n'(x,t) is the concentration of the particles at position x at time t, N is the total number of particles and D is the diffusion coefficient. a)...

Homework Statement Calculate the flux of oxygen across a square centimeter membrane [2\mu, or 2x10 ^{-6}m thick if the concentration on the right hand side of the membrane is 4mL/L and on the left side is 2mL/L. Homework Equations fick's first law of diffusion Flux = dC/dx = D[C2-C1] where...

[SOLVED] Diffusion coefficient. Hi everybody I have a Nitrogen atom sitting at the octahedral site in fcc iron. I have calculated the minimum energy path (diffusion path) when moving the Nitrogen atom to the neighboring octahedral site. My question is: How can i calculate the diffusion...

[SOLVED] Non-Steady State Diffusion Homework Statement For a steel alloy below, it has been determined that a carburizing heat treatment of 10 hr duration will raise the carbon concentration to 0.45%. Estimate the time necessary to achieve the same concentration at a point 5.0 mm position for...

A sample of an unknown gas takes 434 s to diffuse through a porous plug at a given temperature. At the same temperature, N2(g) takes 175 s to diffuse through the same plug. What is the molar mass of the unknown gas? \frac {Rate_{A}}{Rate_{B}} = \sqrt {\frac {\mathcal{M}_{B}}{\mathcal{M}_{A}}}

while talking abt diffusion, we take it for granted that particles diffuse from a region of high concentration to a region of low concentration. is there a fundamental/first principle theory that explains this? how do the particles in the high concn. region see the concentration gradient and...

i did an experiment involving gas diffusion through a glass tube. HCl was on one side of the tube, while NH3 was on the other side. it took about 5 minutes for the gases to meet in the middle of the tube and form a precipitate. but the mean velociries of the HCL and NH3 gas molecules at...

Plasmolysis, diffusion, osmosis, imbibition My Reason: its the shrinkage of cell. The rest are process involved in the transport of water

entropy increases? entropy decreases ? no change in entropy? diffusion, evaporating, mixing, melting, separation i think diffusion - increase evaporation - increase mixing - increase melting - increase but what about separation :S? and if anyone thinks any others are...

Hi there, I'm looking for an algorithm which describes the numeric solution to solve the diffusion equation (1D or 2D). I've taken a look on some textbook such as Hamilton and Henry ones but I didn't find a simple solution. anybody knows about it? Where can I find what I'm looking for? Thanks.

Will Helium diffusion through stainless steel at 250 Deg C and approx 700 psi Delta P present any practical problem?

It's part of my homework to find an analytical solution to a slab reactor with a reflector. The setup of the core is two slabs of equal thickness (-a to 0 and another 0 to +a) but different values for the diffusion coefficent, macroscopic absorption cross sections, and \nu \Sigma_f. There is a...

Hello, the work I am doing now requires numerical solution of several reaction-diffusion equations such as the standard advection diffusion equation (ADE) or IE Fisher's equation. So far I have been using the only method I am familiar with, the simplest one I believe: to express the time...

Hi, I need to make a simple and cheap device that I can water droplet at a constant rate (from a bucket of water). The size of the droplet doesn't matter, it just needs to be dropping at a constant rate (at least for a day). So I was thinking, can I achieve that by putting half of a cloth...

Homework Statement Solve: \frac{\partial u}{\partial t} = k\frac{\partial^2 u}{\partial x^2}, 0<x<\pi, t>0 with initial condition u(x,0)=f(x)=\left\{\begin{array}{cc} 1,& 0\leq x< \pi/2 \\ 0, &\pi/2 \leq x < \pi \end{array}\right and with non-homogeneous boundary conditions...

The solution to the diffusion equation in 1D may be written as follows: n'(x,t) = N/sqrt(4piDt) * exp(-x^2/4DT) where n'(x,t) is the concentration of the particles at position x at time t, N is the total number of particles and D is the diffusion coefficient. Write down an expression for the...

Hello, I wonder why the process of diffusion takes place... Why should the molecules of gas for example, travel from a region of higher concentration to the region of lower concentration till an equilibrium is achieved? I'll be thankful for your guidance :)

Homework Statement I have solved the equation for the neutron density as a function of position and time. I need the boundary conditions to change my infinite number of solutions (the varying separation constant) into one value so that my answer for the critical radius does not contain a...

Homework Statement Doing a science project for school. I have a fish tank and a divider separating one colored liquid on one side and another colored liquid on the other. I need it air tight initially, but will later remove the divider to allow the liquids to mix, demonstrating diffusion...

Hi all, I am stuggling with this question ... http://img86.imageshack.us/img86/2662/picture6fb5.png so far i have only tried part (a), but since i can't see how to do that so far... :( ok so what to do... do we first look at an 'associated problem' ? ... something like...

Hi, I'd like to figure out the amount of heat lost in the kinematic action of putting your foot on the ground while walking. I'm not interested in the diffussion of body heat through the shoe or anything, just the heat energy released by the impact itself. I know this is obscure, and probably...

Hello every body I have previously post my question in this topic: Physics Help and Math Help - Physics Forums > Science Education > Homework & Coursework Questions > Other Sciences > Fick and Cottrell Law And after Goku suggestion I post my question here. So my problem deal with the...

Hi all, I'm abit confused about diffusion - I can't seem to understand how to translate the question at hand to equation (from there it is only math...). I have a box with a gas at concentration n0 in it, which is divided from the rest of the box where you have vacuum (for simplicity, the...

hi i have been trying to solve the diffusion equation using separation of variables. i know the answer should turn out something like the normal probability density function but its just turns into a mess when i try it. i am given the following information: \frac{\partial p}{\partial...

Basically the steady-state diffusion equation can be written in a form \nabla^2\phi\,+\,k^2\phi\,=\,S When S = 0, this is just the Helmholtz equation - http://mathworld.wolfram.com/HelmholtzDifferentialEquation.html See also -...

Hi. I want to know what's the difference between scatter and diffusion... I am trying to understand what happens to the electromagnetic wave when we are talking about scattering and about light diffusion.. I think that the result of scattering it to make the light to diffuse.. Is that right?

Hi, I'm not understanding an example in my book. Can someone please shed some light on it? > Derive the equation satisfied by the temperature u\left( {\mathop r\limits^ \to ,t} \right) at time t for a material of uniform conductivity k, specific heat capacity s and density \rho . Express the...

This phenomina I really don't undertsand. I know that a difference in 2 pressures will cause a force through P= F/A, but what I want to know is, what is type of force of it, what's going on, on the quantum level?

Can somebody give me for mind refreshment the differences between those process : diffraction diffusion effusion ?

i know that the molecules in the "freedom" form that have charges equal 0. but i wonder why the molecules still moving to create the diffusion and the effusion? some one please explain to me. thanks:!)

I have a question of the form, "how did they go from this step to that step?" I am following a paper from R. Kubo, called "The fluctuation-dissipation theorem". I suspect variable substitution and a simple assumption are used, but I don't know how. Here is the basic expression from which...

I have calculated the coefficient of diffusion of H2 into Air and He into Air as Hirschfelder do so based on Lennard Jones Potential in his book about "Molecular Theory of Gases and Liquids". My figures are: D_{H_2-Air}=7,78 \cdot 10^{-5} m^2/s D_{He-Air}=7,17 \cdot 10^{-5} m^2/s both...

http://arxiv.org/abs/astro-ph/0506364 Title: Neutron Diffusion and Nucleosynthesis in an Inhomogeneous Big Bang Model Authors: Juan F. Lara Comments: accepted for publication in Physical Review D This article presents an original code for Big Bang Nucleosynthesis in a baryon...

Describe the process of simulating a brownian motion with drift of 4 units and diffusion of 2 units. write a program in any application to imulate such a brownian motion. Anyone knows where should i start first if i use excel to do it. I don't know what equation to use.

I am doing research with a professor and he asked me to graph some solutions to a 1D diffusion equations of the following form: C_e \frac{\partial T_e}{\partial t}=\frac{\partial}{\partial z}\left( \kappa \frac{\partial T_e}{\partial z} \right) - g(T_e-T_i)+\alpha (1-R)If(t)\exp (-\alpha z)...

Hello all, I need to know the rate at which Helium will diffuse through a solid, specifically silicon. Assume I accelerate and implant a He+ ion into a bulk silicon substrate. How long will it take to diffuse out of the silicon? I know it will depend on the temp of Si and the depth of...

Hello, I've a fysical problem. A small container (about 10x10x15cm) has a source which releases hydrogen at a small rate. The container has an small oppening 30mm^2. The question is how fast does the hydrogen diffuse to the outside of the container. I've made simmulation (see...

what makes the particles move from a high concentration to a lower concentration?

HELP! A cylindrical metal wire of cross sectional area A = 1 mm2 and length, L = 1 cm, is composed of a material with electron density N = 1029/m3. As a result of scattering, it has a mean free time of ƒä torque = 3 ¡Ñ 10-12 sec. Describe the motion of electrons and the resulting current...

Hand-to-Hand Model for Tropomyosin Fast Diffusion. Semiconductor Mechanism for Diffusion of Tightly-Binding Proteins: http://actomyosin.narod.ru/h2h-model.htm Would you be so kind as to recommend me some expert who could be interested in view a possible semiconductor mechanism for...

The concept of diffusion is confusing me, as it seems to contradict gravity. x = particles of matter with a mass of 1 | = a barrier particle x can permeate Situation A: xxxxx|x (1)In my biology class, we're told, and do experiments to prove that, in this situation, the result will...

[SOLVED] self diffusion of water Hi, I was wondering if anyone could give me a hand- or point in the right direction about a question I have concerning the self diffusion coefficients of HDO vs H2O18. To calculate the effective diffusion coefficients of isotopes of water in groundwater most...

Hello, In a biological course in the university, I asked my professor Which force governs diffusion and He didn't know. Note that i don't mean Fick's first or second law, Einstein's law of diffusion, the Brownian Motion and not even the The Second Law of Thermodynamics, simply what "compels"...

[SOLVED] Which force governs diffusion? Hello, In a biological course in the university, I asked my professor which force governs diffusion and He didn't know. Note that i don't mean Fick's first or second law, Einstein's law of diffusion, the Brownian Motion and not even the The Second Law...