Diffusion Definition and 399 Threads

I've done some research, and I've looked at the derivation of the diffusion equation, but I don't want to reproduce even a more simple version of it. I'd like something that can I do almost exclusively myself. The point of this is not to plot some graphs, and extract some line of best fit or...

In a forward-biased PN junction, the potential barrier decreases, allowing more majority carriers from one side to diffuse to the other side where they are minority carriers. After they cross the potential barrier, they form a diffusion current, the drift current of minority carriers is...

Hi, Could any kine soul please explain this to me: I know that diffusion is movement of impurities (dopants) into the semiconductor especially happening during heat cycles in fabrication process. but what is the dopant redistribution? Is it movement of impurities toward the surface? Thanks in...

Background: I'm currently doing a research project on diffusion. I've been thinking about how soluble gases can dissolve at higher concentrations in a colder liquid than a hot liquid. Question: If there are two connected containers, one with hot water and the other with cold water, and the cold...

Homework Statement In essence, I'm trying to make a model of how the heat from a point source diffuses through air. It should be a function of both distance and time (I'm assuming either a 1/r^2 or an exponential dependence on distance). Homework Equations I found this equation...

Hello. I know what is diffusion... chemical process when molecules from a material move from an area of high concentration to an area of low concentration... Typical example is ink in water. However, how it works? Molecules of water collide with molecules of ink? How it is happens from the...

Hello, I am having to find the rotational diffusion of a magnetic particle inside of water. I already have a diffusion coefficient but I do not know how to take into account the restoring force that the particle will feel from the magnetic field. The info that I know is: B-Field Strength...

When thinking of a spherical shaped particle moving about under Brownian motion, one describes its motion by Diffusion. The units being \frac{m^2}{s} I can understand this physically as a distance it will travel from a certain point in space averaged over x-y and z direction. Now rotational...

Q1what is ion implantation in wafer fabrication ? Ion implantation is process by which ion of material accelerated in electric field and impacted into silicon wafer Q2what is diffusion in wafer fabrication ?

Homework Statement A uniform rod of length l has an initial (at time t = 0) temperature distribution given by u(x, 0) = sin(\frac{πx}{l}), 0 \leq x \leq l. The temperature u(x, t) satisfies the classical one-dimensional diffusion equation, ut = kuxx The ends of the rod are...

I am confused about shared contacted diffusion in CMOS layout. Is it possible to use shared contacted diffusion for two nMOS transistors with different widths? BTW, two nMOS and pMOS transistors are never shared contacted diffusion, right?

Homework Statement Part (a): Under what circumstances do these equations work? Part (b): Find Temperature as a function of x, in steady state. Part (c): Show heat loss is proportional to r^1.5 Part (d):Assume A = 0, show solution works, and find γ.Homework Equations The Attempt at a Solution...

Consider a long semiconductor bar is doped uniformly with donor atoms so that the concentration is given by n = ND and is independent of position. Radiation falls upon the end of the bar at x=0, this light generates electron-hole pairs at x=0. light keeps on falling. Explanation...

I am looking at an object that diffuses randomly inside a circular plane. What is the easiest way to find the expectation value for how long would it take on average to reach the wall if it was initially placed at a random position? If it is easier: what if the initial position were the...

Hello, I have a certain diffusion problem I am trying to solve. Admittedly, I'm further behind on my math than I'd like, and have trouble setting it up properly, and no luck finding an exact analogue in the literature. I would like to solve for the time-dependent concentration profile...

Hello, Frustration in receiving timely responses from my teaching assistant has lead me to this website. Currently have a homework assignment on multiple group diffusion theory and one of the assigned questions is, Determine the thermal flux due to an isotropic point source, So fast...

I have a general question about the solution to the Diffusion equation using the explicit finite difference method. Now, it is known the solution is stable when D*dt/dx^2 is less than 0.5, based on the choice of time and space steps. However, how does the choice of the time and space steps...

I'm trying to implement a numerical code for the diffusion equation with moving boundaries. I have no problems with the numerical implementation, but with the transformation of coordinates. In spherical coordinates, the diffusion equation is \frac{\partial c}{\partial t} = D...

I have two cylindrical tubes connected at a 90 degree junction. One tube has a constant flow of a laminar fluid going through it and the fluid is saturated by a soluble particulate with a known concentration. The other tube has a much smaller radius, initially has no particles and is closed at...

This is killing me; not sure if I'm over-complicating or under-complicating it. I’m trying to understand if there is any difference between acoustic scattering and diffusion, and how that differs from attenuation. When particles collide, a small amount of heat is created, since the collision...

Hey everybody, first post here. Having some trouble with a biophysics questions. So, the question is basically this: You have a certain number of ants, you place them in the center of a large smooth table and after 1 minute a snapshot is taken and the number of ants in 5cm concentric circles is...

"Consider a solution of the diffusion equation ##u_{t} = u_{xx}## in {0 ≤ x ≤ L, 0 ≤ t ≤ ∞}. a) Let M(T) = the maximum of u(t,x) in the closed rectangle {0 ≤ x ≤ L, 0 ≤ t ≤ T}. Does M(T) increase or decrease as a function of T? b) Let m(T) = the minimum of u(t,x) in the closed rectangle {0 ≤ x ≤...

Hi everyone! Homework Statement We're given a three dimensional cone with perimeters d0 at the top and d1 at the bottom and a substance that diffuses through the cone with diffusion constant D from top to bottom. The concentration of the substance is held constant at the top plane of the...

Which process occur faster in semiconductors? drift or diffusion

Hi I'd appreciate any help on identifying the type of PDE the following equation is... *This is NOT homework, it is part of research and thus the lack my explanation of what this represents and boundary conditions. I have a numerical simulation of the solution but I'm looking to have a math...

Hi guys, This is my first post here, this place looks like a great resource. Well, jumping straight in, I have a couple of questions on diffusion. At work, I did a couple of experiments with Ion Exchange Resins. Not getting the results we wanted, my boss asked me to do an analysis of...

Hi, I want to ask if diffusion current can exist in the case: Assuming that small circles are electrons.

Can you help me explain this part from my book? In equilibrium, the pn junction has no external connections, i.e., the terminals are open and no voltage is applied across the device. If so, I wonder why there is drift current in the equation above. In equilibrium, the total current is zero...

Homework Statement Solve for the flux distribution using the 1D neutron diffusion equation in a finite sphere for a uniformly distributed source emitting S0 neutrons/cc-sec. My problem right now is that I can't figure out the boundary conditions for this problem. We usually work with...

Homework Statement Find the diameter of one atom of argon given that Dp = 2 where D is diffusion and p is pressure. The Attempt at a Solution molar mass of argon is 40g/mol using that for one atom can find mass in kgs. but that's its! im not given V, T or p. can put V in terms...

Ok so I wish to try solve a problem at work I will try explain as best I can . Problem Definition; Filling of a bundle of cylinders 17 x 50litre ( 850 000 k/m^3). 30 % Co2 in the cyindrical vessal followed by input of Nitrogen 70% to a final pressure of 200 bar Due to production...

You can put a diffuser in front of a visual light source (i.e. lightbulb) that will scatter light in all directions. In effect, the diffuser acts as an analog lightsource by making light go in all directions (some of the enegry will be absorbed). LCD screens use diffusers to spread out their...

Hello everyone, I have a question that is bothering me a bit. I would be happy if you could give an idea or tell me a specific point to look at. Lets say that we have an arbitrary function that obeys diffusion equation: f = f(η), here η is the scaling parameter for pde which equals to...

Homework Statement 1. Estimate the concentration of oxygen in the Earth's atmosphere (in molecules / m^3), at room temperature and at sea-level, assuming the fact that oxygen comprises 21 percent of the Earth's atmosphere by volume. 2. If you were to place a perfect oxygen sensor of...

Hi, I have read a lot about Diffusion Equation and solving neutron flux problems in different mediums, planes and groups, but I can't grasp this topic. In other words, I don't know why they mention: 1. Infinite/finite medium 2. Homogeneous/non-Homogenous medium 3. One/two or multi-group...

Homework Statement I'm having some difficulty deriving the equation for a concentration of CO2 as a function of length and time. Ultimately I end up with an equation that includes the summation of two error function terms that appear to have incorrect signs. Given: A cylinder of...

I am a graduate student in physics. Can someone recommend a book that explores transport phenomena or diffusion from a physical sciences (instead of engineering) point of view? I would like that because I'm not dealing with industrial equipment and don't want to spend chapters wading through...

diffusion coefficient meaning is the coefficient of particles diffuse when different in concentration. How about diffusion coefficient of a particle? the trajectory where a particle diffuse?

Hi there, This could be absolute nonsense but I just got thinking about this. Say you had a certain metal into which a quantity of hydrogen had diffused, and then you placed it in communication with another hydrogen-free metal (say, titanium), would it be possible that the hydrogen would move...

On an undergrad engineering level of talk, is there any difference between conduction and diffusion ways of heat transfer? Conduction occurs because of the vibrational freedom of atoms. And diffusion is, I think, because of diffusing of atoms?

does anyone know how dirac diffusion looks like, i.e. The solution of dirac equation with no potential and initial condition for 1 spinor component psi(x,t0) being delta(x-x0) ? Are the solution gaussian like the schroedinger case ? Thanks.

Homework Statement Calculate the time needed for a perfectly spherical balloon with rahis R to reduce its volume to R/2 due to diffusion by applying Fick's law of diffusion. Assuming the young modulus of balloon is E and the gas filled is nitrogen. diffusion constant of nitrogen is D. Please...

How to calculate the time needed for a perfectly spherical balloon with radius R to become R/2 due to diffusion of the gas inside, which is assumed to be nitrogen, by using Fick's Law of diffusion. Let the Young's Modulus be E. Fick's First law: J=-D∂C/∂x the change in pressure...

Homework Statement Find the mean speed of the molecules escaping through a hole of area \sigma. The vessel has volume V and the molecules mass m.Homework Equations dN_w^e = \frac {dA}{4V} w \frac{dN_w}{dw} dw w is the speed. dN_w = \frac {4N}{\sqrt \pi c^3} w^2 \exp {\frac {-w^2}{c^2} }dw...

I was working on my cloud chamber today, and I ran into two problems: A) It's not working :) To be more specific, I used compressed air to get the bottom extremely cold. The structure itself is a small plastic throw away cup, with a sponge with 91% alcohol stuck to the top. The bottom (the open...

Hi all, I'm working on a heat transfer problem with a gas stream in a tiny tube. At my dimensions and flow rates, the flow still has a parabolic velocity profile. The mean radial velocity of the gas is zero, and I've treated the radial aspect of the heat transfer as strictly diffusion...

I'm looking for the analytical solution for the 1D convection diffusion equation with a constant heat flux. Boundary conditions: The domain I'm looking at is x from 0 meters to 1 meter. The temperature at x=0 is T=0 degrees Celsius. At x=1, T=100 C. I'm given the equation...

Please I need help to understand how diffusion current can occur in a circuit that contains an N-type or P-type semiconductor without being connected to an electric souce such as a battery.And how can both drift and diffusion current occur when the circuit is connected to a battery?

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) Result of Situation A (tested approximately) xxx|xxx The explanation of this is that the...

BOUNDARY CONDITION PROBLEM I have came up with matrix for numerical solution for a problem where chemical is introduced to channel domain, concentration equation: δc/δt=D*((δ^2c)/(δx^2))-kc assuming boundary conditions for c(x,t) as : c(0,t)=1, c(a,t)=0. Where a is channel's length...