On Thursday 22 March 2007 17:18, Shantanu Behera wrote:
1. There is a k-weight button in the background removal column in Athena. How's that used and what's its significance?
The background removal algorithm involves a Fourier transform to R-space in an effort to optimize the low-frequency components by varying the parameters of the spline. The k-weight you are asking about is the k-weight used in that FT. Setting that k-weight to 2 or 3 can sometimes help with data that has very little or no signal at high k by penalizing the spline for not staying close to the data. A word of caution, though -- high k-weight values for the background removal can have surprising interactions with large values of the high-end spline clamp.
2. Assume that I have collected data up to 14k, and I see that the signal beyond 12k is very noisy. I want to use the data up to 12k and within that data range pick a F-filter window of 2-10k or 3-10k. How do I go about this? Can I do that with the spline range (in k or E) options in bkg removal (Athena) column?
You can restrict the range of the background removal then Fourier transform over the entire remaining range. Or you can remove the background over the entire data range and restrict the FT using the FT kmax parameter. In principle, those should be equivalent although the latter seems like a better and more flexible solution. In practice, real data sometimes works better with a restricted background removal range. The only way to know is to try both and see. Hopefully, Athena does a good job of allowing you to try looking at your data in several different ways quickly and efficiently. HTH, B -- Bruce Ravel ---------------------------------------------- bravel@anl.gov Molecular Environmental Science Group, Building 203, Room E-165 MRCAT, Sector 10, Advance Photon Source, Building 433, Room B007 Argonne National Laboratory phone and voice mail: (1) 630 252 5033 Argonne IL 60439, USA fax: (1) 630 252 9793 My homepage: http://cars9.uchicago.edu/~ravel EXAFS software: http://cars9.uchicago.edu/~ravel/software/