[Ifeffit] two measurements of the same compound in different beam-lines

María Elena Montero Cabrera elena.montero at cimav.edu.mx
Fri Aug 13 15:18:52 CDT 2010


Hi Scott,
Thanks a lot, Scott!
I didn't know about epsilon!
Take care
  Maria Elena

2010/8/13 Scott Calvin <SCalvin at slc.edu>

> Hi Maria,
>
> You have several choices. First, note that the merge function in Athena
> allows you to select options of weight by chi-noise, or weight by
> importance. If you weight by chi-noise, noisier data will be counted less.
> If you have some other way of estimating the quality of the data sets, you
> can enter different numbers in the "importance" field and then weight by
> importance.
>
> If working on two different beamlines, you might consider merging chi(k)
> data, rather than norm(E), as the backgrounds may be different. And mu(E)
> probably makes no sense at all.
>
> Another option is to obtain separate chi(k)'s, but then fit both spectra
> simultaneously in Artemis. The Artemis/Ifeffit default behavior in that case
> will be to use high-R noise for weighting, but you can override that by
> assigning an epsilon to each data set if you choose. This method has several
> advantages: it lets you see if one data set is fitting differently from the
> other; it lets you choose different k-ranges if noise begins dominating one
> data set at a lower value of k; it lets you use different values of S02 if
> there are pinhole, harmonic, or self-absorption effects; and it lets you use
> different values of delE0 if the data sets are hard to align properly.
>
> --Scott Calvin
> Sarah Lawrence College
>
>
>
> On Aug 12, 2010, at 8:44 PM, María Elena Montero Cabrera wrote:
>
>  Hi all!
>> I have performed two independent XAFS measurements of Cr K-edge of the
>> same Fe-Cr sample at two different beam-lines at SSRL. I have obtained the
>> Fe-K edge data only once. The quality of data are different in each
>> measurement. However, I cannot average spectra from different Cr-K
>> measurements, and I don't know if I could take somehow advantage from having
>> almost twice the information for the Cr- K adge, or I have to use only the
>> better quality data and discard the other. What do you advice? If I can use
>> both measurements, how can I do the fitting in Artemis?
>> Thank you very much and all take care
>>
>> --
>> María Elena
>>
>> Dra. María Elena Montero Cabrera
>> Departamento de Medio Ambiente y Energía
>> Centro de Investigación en Materiales Avanzados (CIMAV)
>> Miguel de Cervantes 120, Compl. Ind. Chihuahua
>> Chihuahua CP 31109, Chih. México
>> Tel (614) 4391123
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>> Ifeffit mailing list
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>>
>
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-- 
María Elena

Dra. María Elena Montero Cabrera
Departamento de Medio Ambiente y Energía
Centro de Investigación en Materiales Avanzados (CIMAV)
Miguel de Cervantes 120, Compl. Ind. Chihuahua
Chihuahua CP 31109, Chih. México
Tel (614) 4391123
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