Again, sorry for the very long wait to get a response to this question. On Monday, October 22, 2012 07:44:05 AM Bingjie Ouyang wrote:
Hi, I just joined the mailing list recommended by a friend, I hear this is a really good place to communicate and learn. So I'm here, actually I need help for some basic questions on Iffeffit software:
1, In Athena, how to make a fourier transform draft?
I don't understand this question. I don't know what a FT "draft" is.
2, In Artemis, since I was told that each shell in R-space can be fitted separatly, is it OK to fit each shell in the R-range respectively, and then join up the fitted curve and just ignore the not match part in other R-ranges? And can a shell be comprised of several different paths (like Fe-O and Fe-S)?
There is, currently, no way to exclude an interior region from a fit in Artemis (i.e. there is no way to fit from 1 to 2 and from 2.5 to 3.5, but to exclude the region from 2 to 2.5). I actually think that's a bad idea and doubt that I would ever implement such a thing. The reason I don't like this idea is that, in general, shells in the EXAFS signal are not completely isolated. Because of the limited data range and other reasons, the signals form the various shells have long tails and overlap considerably. That overlap is a very important part of the problem. Getting the small parts of the chi(R) spectrum right is just as important as getting the large parts right. Excluding an interior region could artificially remove this overlap from the evaluation of the fit. That would have a very serious impact on the statistical quality of the analysis. I also worry that an interior exclusion would be used in an attempt to minimize the impact of multiple scattering paths on the analysis. That, too, would be a statistics disaster. In short, you should embrace the correlations between the parts of the problem. HTH, B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://xafs.org/BruceRavel Software: https://github.com/bruceravel