Diffusion Definition and 399 Threads

hello everyone,:wink: is this definition correct? drift current is flow due to applied voltage across P-N junction & Diffusion is flow due to different concentration of hole & electron across P-N junction. warning: [i read this definition somewhere, hence not my own work] 1:-- the...

Hey, I want to solve a parabolic PDE with boundry conditions by using FINITE DIFFERENCE METHOD in fortran. (diffusion) See the attachment for the problem The problem is that there is a droplet on a leaf and it is diffusing in the leaf the boundry conditions are dc/dn= 0 at the upper...

Hey, I want to solve a parabolic PDE with boundry conditions by using FINITE DIFFERENCE METHOD in fortran. (diffusion) See the attachment for the problem The problem is that there is a droplet on a leaf and it is diffusing in the leaf the boundry conditions are dc/dn= 0 at the upper...

Homework Statement N particles diffuse in one dimension in the potential U(x)=ax2, with a > 0. For example, such a potential could be provided by a line-shaped optical tweezer trap. The particles have the diffusion constant D. Find the steady-state concentration, C0 (x). Homework...

Hello experts in diffusion, I am having some trouble understanding some concepts in calculating diffusion. First, I understand activity (or chemical potential) drives diffusion, but where does this come into play in the calculations? Is it in the activation energy (Q) in the Arrhenius...

Hallo everyone, I have a 1-D diffusion equation with decay as dA/dt = d2A/dx2-L*A with initial condition C(x,0)=C0=exp(-ax) and boundary condition= -Ddc/dx = I0 where L= decay constant A = certain concentration the concentration A is not in equilibrium. We can solve the above...

Hi, I am looking to model the diffusion of a particle through 2 layers using the finite difference method in matlab. I already successfully have modeled this in a mono-layer configuration, however I am looking to code it through two layers. I have two layers, one is 1 micron (1E-6) and the...

Hi everyone, I'd like to ask you a question. How to calculate the diffusion speed from a bulk of gas with density of n to vacuum? Thank you!

I've got a closed system that consists of a glass container (non gas permeable) filled with pure CO2 at atmospheric pressure, with an airlock that will let CO2 escape if the pressure inside the system becomes higher (barometric pressure changes, etc.), but will not let air back into the system...

hi all, i am a new member here. nice to meet you all. i remember seeing a derivation of diffusion equation from the equation of motion \dot{x}=\eta(t) where \eta(t) is white noise. i can't remember where i saw this... could anyone please help me on that? it should be something like...

When you square the probability amplitude and it shows there is 20% probability of it occurring, and you perform the experiment 100 times.. you would find exactly 20 times as dictated by the probability. In radioactive decays, individual alpha particle may tunnel at different times but when you...

I've been combing over websites and papers on this, but I can't get a handle on trying to explain or visualize the similarity between them. The wave equation "smears out" over time as does the diffusion equation?

I'm trying to model a reaction-diffusion system on MATLAB and am struggling. I'm starting off with 4 particles on a lattice with 15 sites for ease, will take it to a larger scale when I've got the simple version down. the idea is to get randomly walking particles to eventually meet each other...

I see that the diffusion coefficient (of diffusivity) D has units of something like cm^2 / s. I'm having trouble understanding what those units mean. For example, speed has such units because something travels a certain LENGTH in a certain TIME. Could someone explain this for me? Thank you.

We have been trying to fit experimental diffusion results to the diffusion equation using Matlab to evaluate the Diffusion coefficient. The equation we used: y=C*erfc(x/(2*sqrt(D*t))) Experimental values [x],[y] and t are given. C and D are to be evaluated from the curve fit. We used cftool of...

Hello I am trying to find an analytic expression for the probability that a particle will have passed a position x after a time t. It is a 1D random walk, the probability distribution after time t that a particle will end at position x is given by a gaussian, but I need to know how many...

This might be a stupid question, but it has me kind of confused. In diffusion, molecules will flow from high concentration to low concentration, and the explanation typically given is that in the laws of thermodynamics there is a net increase in entropy over time. But I am trying to think of...

thermal diffusion equation - URGENT Homework Statement Please see attached q Homework Equations The Attempt at a Solution Ok so thermal diffusion equation is DT/Dt = D del squared T apparently this is a steady state problem, so DT/dt = 0, how am i meant to know? any hints on...

Show that S2 = S(x,t)S(y,t) solves St = k (Sxx + Syy) well St = St(x,t)S(y,t) + S(x,t)St(y,t) Sxx = Sxx(x,t)S(y,t) Syy=Syy(y,t)S(x,t) but what do i do from there?

I have been googling as many terms possible, but still not successful in finding a list of diffusion coefficients of common minerals eg; Quartz, Beryl, Spinel, Corundum etc... I will highly appreciate your contributions.

So i have an organic chemical in a bio-film reactor being diffused into a bio-film and also being metabolized at constant rate R by bacteria. the concentration into the reactor Cin = 2mg/L with f-in at 20 m^3/hr the concentration in the reactor is C1 C3 is the concentration in the...

Hi: I am doing a research project in which I need to diffuse PFA(Paraformaldehyde) into agar gel. I want to know how to calculate the diffusion rate. The agar gel is 1%, and 2 mm thickness. How long approximately does it take for PFA to diffuse from the top to the bottom? Is there any...

How could i reduce the effect of diffusion of ions in an electrolysis cell. e.g AgNO3 Ag+ Stirring constanly would help? but that's not easily kept fair or constant. Could i replace this idea with rotating electrodes? Many Thanks, Adam

Homework Statement You use the solid diffusion source wafers PH-950 from St. Gobain (see data sheet on TSquare, Diffusion Chapter) to form phosphorous-doped resistors in a p-type wafer with a background doping concentration of 1015 cm-3. According to the data sheet, a 60-min predeposition at...

Homework Statement Solve u_{tt} - 4u_{xx} = 0, x \in \mathbb{R}, t > 0 u(x, 0) = e^{-x^2} , x \in \mathbb{R} Homework Equations General solution to the diffusion equation: u(x, t) = \frac{1}{\sqrt{4\pi kt}} \int\limits_{-\infty}^{\infty} e^\frac{{-(x - y)^2}}{4kt} \varphi(y) \, dyThe...

Dears I know that the neutron diffusion coefficient D= (The transport mean free path/3), but in some documents i read that:( D=The transport mean free path*v/3) where v=The neutron number. How is that?

I am trying to do simulations of a random walk, I get out a normal distribution in 1D how do I get the "diffusion length" from the gaussian fit?

Heres a short question, How does diffusion affects the rate of adsorption?. If the diffusivity of a fluid increases, will the rate of adsorption increase or decrease? Thanks in advance Cheers

Hi! Can anyone name me literature about the penetration depth of Oxygen in iron thin films? I am wondering how deep an iron film can be oxidized. Thanks for any suggestions about this topic :)

[EM] Scattering by a rod Hello everyone :) I'm interrested by the diffusion of an electromagnetic field by a rod with rectangular section i.e. a parallelepiped with one infinite dimension. Does anyone know if that's already been done ? If it is even possible analytically ? Thanks in...

Is the property of evaporation and spreading out of drop of ink in water is said to be example of diffusion in liquids or not? I think property of rapid intermixing of a substance to another is called diffusion so in liquids evaporation can be regarded as diffusion property.

Hello all, I am reading through Stephen Turns' An Introduction to Combustion. The third chapter is essentially a crash course on mass transport. In it, he talks about "the Stefan Problem" as it pertains to diffusion and Fick's Laws. I am understanding most of it, but I am realizing that I...

I have the following diffusion equation \frac{\partial^{2}c}{\partial r^{2}} + \frac{2}{r}\frac{\partial c}{\partial r} = \frac{1}{\alpha}\frac{\partial c}{\partial t} where \alpha is the diffusivity. The solution progresses in a finite domain where 0 < r < b, with initial...

Dear Everyone, I am working on a physics problem of exciton diffusion involved in organic optoelectronics. It is in the form of y''+a*y+b*y^2=0. Is there a general solution to this equation? Thanks! elfine

Hi Everyone, on page 238 of lamarsh, section 5.5, first paragraph, it says "flux must also be finite". What does it mean?

Homework Statement A the density of a gas \rho obeys the modified diffusion equation \frac{\partial \rho(x,t)}{\partial t}-D\frac{\partial^2 \rho(x,t)}{\partial x^2}=K\delta(x)\delta(t) A) Express \rho in terms of its 2D Fourier transform \widetilde{\rho}(p,\omega) and express the right...

I'm having a wording issue in a paper I'm writing. Specifically, I'm trying to decide between arguing something is "diffusion" vs. "dispersion". Can anyone point me to a reference that clearly demarcates between these? In specific, I'm referring to the diffusion/dispersion of an injected drug...

How shall diffusion of precursor atoms be treated if the core is in liquios state(as is MSR)[I mean regarding to its low volumetric density, shall we treat it as gas-liquid diffusion and is diffusion approximation or even transport theory valid for it anymore, what's the meaning of state space...

Homework Statement You have a solar cell with a constant electron density n, and known dimensions. I am looking for the change in density due to diffusion, so basically the diffusion current. All other relevant parameters are also known (temperature, D diffusion constant, etc.) To summarize...

Homework Statement Obtain the solution of the diffusion equation, u(t,x) a) satisfying the boundary conditions: u(t,0)=u1, u(t,l)=u2, u(0,x)=u1+(u2-u1)x/l+a.sin(n\pix/l); b) in the semi-plane x > 0, with u(t,0)=u0+a.sin(\omegat). Homework Equations Wish I knew... The...

I would like to calculate a diffusion of water vapor in stagnant air. Does anybody know if it is a case of equimolar or nonequimolar diffusion. How one could calculate a diffusion in my case? Which variables is diffusion coefficient dependant on?

hi all: i have some insects/particles that i placed in the center of an arena, and tracked their position after a set period of time. what i can get in MATLAB is a 2d scatter plot (several hundred x,y points). i have several different types of particles that show a larger or smaller degree...

Dear all, I'm trying to solve the diffusion PDE for my system, shown below: \frac{\partial C}{\partial t} = D (\frac{\partial^2 C}{\partial r^2} + \frac{1}{r} \frac{\partial C}{\partial r}) where C is the concentration, changing with time t and radius r. D is the diffusion...

Homework Statement One tool in analyzing proteins is gel diffusion. The technique is used to determine the size of the protein being analyzed. The following values are for diffusion through agarose gel. D (m2/s) Lysozyme 1.18E-10 BSA 3.90E-11 adolase 6.50E-11 Cu2+ 1.00E-10 glucose...

Hi, I'm looking for information on blood and neuron cells. Specifically I need to know how the membrane transport mechanism in blood and neuron cells work? I am aware of concepts such as active diffusion, facilitated diffusion, and simple diffusion. The task is to look at the membrane...

Something has been bothering me recently regarding a diffusion problem. Consider a source of particles in a box, diffusing outwards. Set the boundary conditions so that the density is zero at the edge of the box. We can solve this problem in "steady state" and we find essentially a parabolic...

Homework Statement http://img42.imageshack.us/img42/1082/clipboard01lx.jpg Homework Equations (see solution) The Attempt at a Solution I literary just spent 5 hours trying to apply those boundary conditions, trying exponentials, sines, cosines, hyperbolic function etc... I...

Homework Statement Solve the equation U{t}=kU{xx}+cU Hint:use an integrating factor Homework Equations The Attempt at a Solution

Homework Statement Hello, I have this project due for next Friday. I need help. Its on diffusion limited aggregation. A topic which is unfamiliar to me. I know exactly how to do the problem, but I don't know how to code it correctly. Basically I allow a seed particle to be in a location in a...

I am going to run an experiment where I have a laminar flow of water with a dye solvent. It is necessary that the velocity of the dye particles is mostly in the horisontal directions. Naturally particles will diffuse but my questions is how I can ascertain that this is kept below some...