To Dear authors: We have a Rbkg question about Rutile, and in order to demonstrate these questions more clearly, we make it up on attach .ppt file, and thanks for your great helping before. Pei ___________________________________________________________________ 付費才容量無上限？Yahoo!奇摩電子信箱2.0免費給你，信件永遠不必刪！ - 馬上體驗！
Pei, The following page will help: http://cars9.uchicago.edu/~ravel/software/doc/Athena/html/bkg/rbkg.html I think what you are seeing is just effects of removing data that contributes to the mu(E) spectrum. As for why the feature (low-R junk) increases as Rbkg is adjusted from 1.0 to 1.21 but disappears at 1.22, I'm not sure but my guess is that this is an artifact of removing some of the data that contributes to the feature, and by 1.22 you have removed enough that the feature disappears (hopefully someone will correct me if I'm wrong). I would be weary of using an Rbkg of 1.22 though (as I think you see why in the plots - Question 3). Cheers, Richard
To Dear authors: We have a Rbkg question about Rutile, and in order to demonstrate these questions more clearly, we make it up on attach .ppt file, and thanks for your great helping before.
Pei
___________________________________________________________________ ¥I¶O¤~®e¶qµL¤W¡HYahoo!©_¼¯¹q¤l«H½c2.0§K¶Oµ¹§A¡A«H¥ó¥Ã»·¤£¥²§R¡I - °¨¤WÅéÅç¡I_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
-- Richard Mayes Barnes Group 450/452 Buehler Hall Department of Chemistry University of Tennessee Knoxville, TN 37996
Hello Pei: On Sat, 15 Mar 2008, Richard Mayes wrote:
As for why the feature (low-R junk) increases as Rbkg is adjusted from 1.0 to 1.21 but disappears at 1.22, I'm not sure but my guess is that this is an artifact of removing some of the data that contributes to the feature, and by 1.22 you have removed enough that the feature disappears (hopefully someone will correct me if I'm wrong). I would be weary of using an Rbkg of 1.22 though (as I think you see why in the plots - Question 3).
I think that Rbkg=1.22 is generally a bit too high for comfort is your first shell distances are fairly short. In my opinion, you should set Rbkg below 1.0, in the regions where the low-R peak first disappears. Try changing Rbkg by 0.02 at a time while looking at the k^3 weighting. There is usally a point at which you see a significant reduction in the background peak and then not much more change for a while. The other thing you can do is to model the data with Rbkg=0.9 and 1.22 to see how the fit results compare. This might help you figure out the best way to handle these data. Cheers, Carlo -- Carlo U. Segre -- Professor of Physics Associate Dean for Special Projects, Graduate College Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://www.iit.edu/~segre segre@debian.org
Hi Pei, Another parameter that affects the curvature of the background is where you choose E0 and kmin for the spline. Sometimes if you choose a value that is far down the edge, like half the edge step height, then the background has to curve alot to get through the edge region of the spectrum. You can see if this is the case by making three copies of the data set in Athena and then choose rbkg values of 0.8 1.0 and 1.2 and compare the chi(K) spectra produced with a low k-weight value. The region of the spectra where all three chi(k) data are the same should be used in the Fourier transform as kmin. That should help reduce the dependence of the chi(k) spectra on the rbkg value. Another approach is to bring E0 up the edge so that the background doesn't have to curve so much, and then make the same comparison. Good luck, Shelly ________________________________ From: ifeffit-bounces@millenia.cars.aps.anl.gov on behalf of ?? ? Sent: Sat 3/15/2008 12:34 AM To: ifeffit@millenia.cars.aps.anl.gov Subject: [Ifeffit] Rutile Rbkq remove question. To Dear authors: We have a Rbkg question about Rutile, and in order to demonstrate these questions more clearly, we make it up on attach .ppt file, and thanks for your great helping before. Pei ___________________________________________________________________ ?????????Yahoo!??????2.0????,???????! - ???? http://tw.rd.yahoo.com/referurl/mail/mail20/tag_hot0103/*http://tw.mg0.mail.... !
participants (4)
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Carlo Segre -
Kelly, Shelly D. -
Richard Mayes -
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