# Recent content by Old Guy

1. ### Best textbook or video or device for understanding QM

I absolutely found Dirac to have the best explanation of Dirac notation (Go figure!)
2. ### Too late for a 16 year old to pursue a career in Physics?

Let me just add: IT'S NEVER TOO LATE TO PURSUE YOUR PASSION I got a chemical engineering degree in 1978, and had a very satisfying career. In 2006, I decided I wanted to understand quantum mechanics, so I went back to school. I got a Schaum's outline for calculus (because I hadn't done calculus...
3. ### Dimensions of intensity

Homework Statement I know that intensity is power per unit area. When I do a dimensional analysis, it reduces down to mass per cubic time. Is there any physical significance to that? Homework Equations I=P/A The Attempt at a Solution
4. ### Leas squares curve fit problem

If your problem is that you have vectors x and y that contain your data, and you want to find A, B, C and D for the equation shown as a fit to that data, try the curve fitting toolbox. Run cftool, select x and y as your data set, then under fit select custom equation and you can enter the...
5. ### MATLAB Indicate mean with a bar in Matlab

Thanks for your help, but I could not get this to work because I am trying to change a .fig file in the property editor. I tried generating the code, and then making the modification there, but I was unable to save as .fig after that. Any suggestions?
6. ### MATLAB Indicate mean with a bar in Matlab

I want to put the following as an axis label on a plot, but I cannot figure out how to get the bar on top in Matlab \bar \xi Thanks.
7. ### Why is diffusion coefficient = 1/2?

Of course, now I get it! Thank you.
8. ### Why is diffusion coefficient = 1/2?

Thank you, but can you expand on your answer a bit? Not sure I understand what you mean in your second sentence.
9. ### Why is diffusion coefficient = 1/2?

Homework Statement I'm working with a 0ne-dimensional random walk and looking at Fick's second law, below. All I've read seems to take D = 1/2 as a given for ordinary diffusion, but where does this come from? Is there a way to derive it? Homework Equations \frac{\partial } {{\partial...
10. ### Function works on Windows but not Linux

Thanks to you both. Ultimately it was a path issue, although I thought I had checked that thoroughly before I posted.
11. ### Function works on Windows but not Linux

I downloaded largestcomponent.m today and it runs fine on my PC (Win 7 Enterprise SP 1) but when I try it on my Linux machine (Ubuntu 10.04 LTS) I get this message: ??? Undefined function or method 'largestcomponent' for input arguments of type 'double'. Even if I put the function file in...
12. ### MATLAB Matlab Legend Problem

I am trying to make a plot of four pairs of time series. The plot appears fine; I have two lines in each color as I want. The problem, in this case, is that the first two legend items both have red lines, and the second two both have black lines. I want each legend entry to match the color of...
13. ### Ordinary Diffusion and integration by parts

Thank you for your help, diazona. I still haven't completely wrapped my mind around probability densities yet. Nonetheless, with your suggestion (and some mathematical sleight of hand) I was able to satisfy myself that p(x,t) in the form of 2/x made the terms vanish as needed. A function that...
14. ### Ordinary Diffusion and integration by parts

I understand, of course, about the boundary terms. It seems to work out if I assume that p(0,t)=1 (ie, the particle(s) all start at the origin) and that p(\infty,t)=0 (there is nothing at the infinite boundary). This still leaves me multiplying zero times infinity, and isn't that considered to...
15. ### Ordinary Diffusion and integration by parts

Homework Statement For ordinary 1D diffusion show that the mean value of the square of the position is equal to 2Dt Homework Equations \left\langle {x^2 \left( t \right)} \right\rangle \equiv \int\limits_0^\infty {x^2 p\left( {x,t} \right)dx} \frac{\partial }{{\partial t}}p\left(...