Re: [Ifeffit] Ifeffit Digest, Vol 67, Issue 15

Matt, We do use a cam when doing QEXAFS. Along with time and detector values we record the Bragg angle of the Si(111) monochromator as a function of optical encoder readout. The encoder values are random numbers but linear with the Bragg angle. Under normal routine QEXAFS we have developed programs to convert the QEAXFS data and make it compatible with Athena analysis. That works fine. In this particular case I wanted to compare Ni EXAFS scan done in conventional way to the one I got in 100 ms. For this particular scan I could not use the programs that we developed (for data conversion to Athena compatible, for many reasons). I wanted to see how a time axis converted to energy, compares with conventional EXAFS at FFT stage. It was also to find out, as you mentioned, if two energy points will match, then will it compare to conventional EXAFS in this particular case?? Syed Khalid -----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov]On Behalf Of ifeffit-request@millenia.cars.aps.anl.gov Sent: Tuesday, September 09, 2008 1:00 PM To: ifeffit@millenia.cars.aps.anl.gov Subject: Ifeffit Digest, Vol 67, Issue 15 Send Ifeffit mailing list submissions to ifeffit@millenia.cars.aps.anl.gov To subscribe or unsubscribe via the World Wide Web, visit http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit or, via email, send a message with subject or body 'help' to ifeffit-request@millenia.cars.aps.anl.gov You can reach the person managing the list at ifeffit-owner@millenia.cars.aps.anl.gov When replying, please edit your Subject line so it is more specific than "Re: Contents of Ifeffit digest..." Today's Topics: 1. Re: Ifeffit Digest, Vol 67, Issue 12 (Matt Newville) ---------------------------------------------------------------------- Message: 1 Date: Tue, 9 Sep 2008 11:14:12 -0500 From: "Matt Newville" Subject: Re: [Ifeffit] Ifeffit Digest, Vol 67, Issue 12 To: "XAFS Analysis using Ifeffit" Message-ID: Content-Type: text/plain; charset=ISO-8859-1 Syed, Adam, I think the suggestion from Adam and one of the suggestions from Anatoly assume the energy linear in time. Is that the really case? For quick-scanning modes, many beamlines run the mono at a constant angular velocity, so that time maps linearly to angle, which then needs to be converted (non-linearly) to energy. Then again, some quick-scanning beamlines use a special cam drive, in which neither angle nor energy would be linear in time. Again, you need know these details in order to correctly assign energies to the data. None of it is particularly difficult, so there's no point in guessing, and stretching or massaging the energy scale until two energy points correct does not mean the rest are correct. You need to find out from the beamline how the data mapped onto energy and fix that. While you can probably use Ifeffit macros within Athena to do this correction, this is really a job for the beamline, not for Athena. Having an option in Athena that allowed the user to say "I don't know why my energy scale is bad, but can you please stretch the energies so that these two energies are what I'd like them to be" is a horrible idea. --Matt ------------------------------ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit End of Ifeffit Digest, Vol 67, Issue 15 ***************************************