Hi Geoff, I don't think that I understand your definition of dk, so I am going to give you mine. A Fourier transform is a complex transformation that requires the data that is being transformed to be defined from -infinity to +infinity. Since our data does not cover this range, we pad the data set with zeros for most of the transformed data range. At the edges in between the actual data range and all the zeros there is a step function, as the data goes from zero to some non-zero number abruptly. A Fourier transform (FT) of a step function is a bunch of signals at all R-values called a FT ripple. This is not a good think to have in your FT. So we spread out the step function by applying a window. The length of the window is defined by dk. In general dk should not be zero. See this presentation for some more discussion of dk. http://www.mesg.anl.gov/Presentations/basics%20of%20exafs%20analysis%202 003.pdf HTH Shelly

-----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit- bounces@millenia.cars.aps.anl.gov] On Behalf Of Geoff Eldridge Sent: Monday, April 24, 2006 10:29 AM To: Ifeffit List Subject: [Ifeffit] dk setting in Athena

Hello everyone,

I've just started doing EXAFS in my research and I have found all your posts to be very helpful.

My question is about the dk setting in Athena. I know from earlier reading that dk affects where the window for the FT is set in k-space (i.e. a dk setting of one moves the window out further than the k-min and k-max settings). I believe the purpose of this is to prevent cutting the tops of peaks out of the FT window. If this is the case, would a dk setting of 0 then be appropriate provided no parts of peaks are clipped as shown in a k-space plot with the window shown?

Thanks,

Geoff _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit