Diffusion Definition and 476 Threads

Hi, I've decided to make my own meter for measuring laser power to around 10% accuracy if possible. Optical power meters are way too expensive for me though. One building block I've decided to use is a phototransistor, because I've found one which has very good linear response - when measuring...

Homework Statement A cylindrical wire of thermal conductivity k, radius a and resistivity p uniformly carries a current I. The temperature of its surface is fixed at T0 using water cooling. Show that the temperature T(r) inside the wire at radius r is given by T(r) = T0 + p(I^2)(a^2 -...

Homework Statement diffusion thru a semipermeable membrane. Homework Equations section 1 of the lab LAB - dialysis tubing containing distilled water and the beaker containing glucose and starch .. put it in water. Leave it over night and jot the changes, it goes through osmosis but...

a theoretical qstn.. the diffusion constant D, represents the avg. rate of unit displacement by a fluid particle. should D increase or decrease in time? and should D increase or decrease if length (lets say length of the capillary through with its travelling) increases? - m

Does anyone know of any good Diffusion (ie. Fick's laws, interstitial jumps, etc) online resources? Thanks!

Homework Statement Considering the periodic boundary conditions (given below) I am supposed to find the solution T(x,t) with the initial condition T(x,0)=\delta(x) Also I am limited to use method of images so I can't use separation of variables unfortunately. Homework Equations The boundary...

Hello everyone, a wave propagates at a speed (group of phase speed), less than the speed of light, no matter what type of wave we are dealing with (electromagnetic, mechanical,...). Why is infinite velocity characteristic of a diffusion process? What does that mean? For something to...

Hi, I am not sure if this is the right place to post a COMSOL question. If not I apologise, could you point me to the right place. I have a 3D geometry in COMSOL shape like a "T" where I want to model flow using navier stokes and a chemical diffusion using convection and diffusion. Both...

VERY URGENT: Please help with Diffusion Question and Membrane Protein question Proteins associated with the plasma membrane can be classified as either integral membrane proteins or peripheral membrane proteins. For the following types of proteins, please specify whether they would be integral...

I'm wondering if anyone is aware of any computational/theoretical work on solving the problem of describing the motion of a biological macromolecule in a cellular microdomain? This would have to mean setting up and solving a stochastic partial differential equation with boundary conditions...

i know that idea would seem a bit weird but, let us suppose we have a surface or volume in d- dimension, here d can be any real number (fractional dimension) the question is that we do not know what value 'd' is \frac{\partial \phi}{\partial t} = D\,\Delta \phi D is a diffusion...

Homework Statement For a steel alloy below, it has been determined that a carburizing heat treatment of 15 hr duration will raise the carbon concentration to 0.35% at a point 2.0 mm from the surface. Estimate the time necessary to achieve the same concentration at a point 6.0 mm position for...

isotropic equation, so k, ρ, and c are constant, where k is thermal conductivity, c is specific heat, and ρ is the density of the body. the equation boils down to \left( \frac{c\rho}{k}\right) \left(\frac{\partial u}{\partial t}\right) - \left(\frac{\partial^{2} u}{\partial...

Please provide me Diffusion coefficients of following ions in water at different temparatures (25 deg celcius, 75, 125, 300 etc) 1. Fe2+ 2. H2O 3. Fe(OH)+ 4. Fe(OH)2(aq) 5. H+ 6. OH- 7. CO3-2 8. H2CO3 9. HCO3- 10. Na+ 11. Cl-...

Hi. I've thought for some time about a problem that I'm not able to solve (to my own surprise). We have closed container, say a relatively high cylinder, placed vertically. In it are two gases of different density enclosed. Obviously the lighter one will 'fleet' and stay on top of the...

Homework Statement Since the problem involved formulas I have posted it as an attachment. Please check the attachment first. (I have not scanned this problem, just wrote it in word and posted it) The Attempt at a Solution My approach on this problem is to start with separation of variables...

I do not understand the difference between diffusion and migration is case of anion/cations. Thank you!

Hello everybody, I don't know if this is the right place to post this question. Sorry for that. I have the following system: small particles (I don't know exactly the composition) in a batch stilled tank reactor in which i add some hydrochloric acid. How I evaluate the concentration of...

which gas would diffuse the quickest? the slowest? A. methane B. oxygen C. nitrogen D. C2H6 (need to show work to verify!)

I have trying solving this PDE for some random boundary values, and were wondering if someone could verify my calculations? \[ \begin{array}{l} T_t = DT_{xx} \\ T\left( {0,t} \right) = 0,T(\pi ,t) = 0,T(x,0) = \frac{1}{4}\left( {\left( {x - \frac{\pi }{2}} \right)^2 + \frac{{\pi ^2...

Hey all, I'm wondering if someone can help me understand how to apply the boundary conditions to the diffusion equation in one dimension. Diffusion equation is: \frac{\partial u}{\partial t}=D*\frac{(\partial)^{2}u}{\partial x^{2}} The initial condition is: u(x,0)=0 And the boundary...

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 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...

If something like oxygen were to be released into a room, it would diffuse much faster than something like a heavy smoke. Has someone ever measured the rate of diffusion of different gases and particles? A quick Google search turned up nothing. I'd like to know the distribution of how many...

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?

Homework Statement We have a tube filled with water where there is a plug of substance at one closed end. Diffusion constant of this substance is known and its concentration at t=0 is given as: Co(x)= 10mg/ml if x<= 100mm Co(x)= 0mg/ml if x> 100mm Distribution of particles from the plug...

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...

Homework Statement I'm wondering if there is an explicit traveling wave solution to a simple epidemiology diffusion model. This model is a basic representation of rabies spread among organisms. Rabies causes its victims to become delirious; hence the diffusion there. Here x is the...

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'm having some trouble understanding semipermeable diffusion questions. Does anyone know of a good book or web source with examples? Also, if anyone could help me out on these... What is the equilibrium situation? Left side has90 mM KCL and right side has 20 mM KCl. Membrane in...