[Ifeffit] Too many points in pre-edge

[Barton, David (DG)]

Carlo and Matt:

> With these files, the location of the edge (and element 
> identification as well) using the first derivative 
> does not work. 
 
I also had a similar problem when we had a somewhat noisy pre-edge and edge data.  Often our analysis of the XANES requires high confidence in the edge energy to determine energy shifts and to accurately align our spectra using metal foil references.  Of course, I can always manually assign the edge position in Athena, but it would be nice if Ifeffit was a bit smarter about how it chooses Eo since it is critical for Athena operation when a reference standard is used to calibrate a sample spectra.  I would guess that there is some robust algorithm that one could implement which would more accurately determine either (1) the maximum in the first derivative or (2) the zero of the second derivative for data with any number of data points or noisy data.  I imagine that such an algorithm would include some sort of adjustable "smoothing" parameter to filter the signal from noise.

Dave
  _________________________________ 
  David Barton 
  The Dow Chemical Company 
  Catalysis R&D 
  1776 Building 
  Midland, MI 48674 USA 
  Ph: (989) 636-4753    Fax: (989) 638-9350 
  Email: dgbarton at dow.com 




  > -----Original Message-----
  > From: ifeffit-bounces at millenia.cars.aps.anl.gov 
  > [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On 
  > Behalf Of Carlo U. Segre
  > Sent: Thursday, December 02, 2004 9:44 AM
  > To: IFEFFIT Mailing List
  > Subject: [Ifeffit] Too many points in pre-edge
  > 
  > 
  > 
  > Matt:
  > 
  > I am running into a somewhat annoying problem with 
  > continuous scan data 
  > imports into athena where there are many datapoints before 
  > the edge (I 
  > think > 400 or so).  With these files, the location of the 
  > edge (and 
  > element identification as well) using the first derivative 
  > does not work. 
  > The edge is identified as being somewhere in the pre-edge.  
  > As I reduce 
  > the number of data points in the pre-edge, the edge 
  > identification moves 
  > closer to the true edge and then locks in correctly when 
  > the number of 
  > data points in the pre-edge is small enough (again, I think 
  > this is less 
  > than 400 points).
  > 
  > I can address this problem by running these data through a 
  > rebinning 
  > process in the pre-edge but I think that if it is possible 
  > to handle this 
  > in ifeffit, that would be a good idea.
  > 
  > On a second note, would you tell me whether you or Bruce is 
  > planning to 
  > maintain the ifeffit perl wrapper?  At this time, ifeffit 
  > 1.2.6a and horae 
  > 046 have different versions of the Ifeffit.pm script (1.3 and 1.301 
  > respectively).  I recently ran into a problem because I had 
  > the ifeffit 
  > version and horae 046.
  > 
  > 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
  > Carlo.Segre at iit.edu    http://www.iit.edu/~segre
  > _______________________________________________
  > Ifeffit mailing list
  > Ifeffit at millenia.cars.aps.anl.gov 
  >   > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
  >