[Ifeffit] RE : RE : problem with Athena's E0 !

Arezki, Bahia Bahia.Arezki at uni-siegen.de
Wed Jul 1 11:18:17 CDT 2009


I think I was misunderstood, I have nothing against the capabilities of Athena, which I have chosen to use for my xanes processing/analysis and I am happy about that.  In fact I only  referred to  the explanation in the Athena user's guide by telling that my case could be one of those few situations mentioned in the guide where one has to re-consider to the default value  [ the human attention :-)   ](see the text bellow) .

"....There are a few situations where the default algorithm will fail. Very noisy data can result in a spurious identification of «e0». Materials which have two inflections in the edge, such as zero-valent zirconium, might have the wrong inflection chosen. Materials with huge edge peaks, such as K2CrO4 , will have a point in the leading edge of the peak chosen rather than a point in the main edge......"

I know that Athena is simply a software and the user is responsible for its use.. As a  user, I only needed your help and wanted to know if my data processing was correct. I need to be sure about that in order to do a correct analysis/ interpretation of my results.

Once again, sorry for this misunderstanding (I realize just now that I did not chose the right objet name for my e-mail ) and thanks a lot for your help,


De : ifeffit-bounces at millenia.cars.aps.anl.gov [ifeffit-bounces at millenia.cars.aps.anl.gov] de la part de Bruce Ravel [bravel at bnl.gov]
Date d'envoi : mercredi 1 juillet 2009 16:42
À : XAFS Analysis using Ifeffit
Objet : Re: [Ifeffit] RE :  problem with Athena's E0 !

On Wednesday 01 July 2009 10:08:25 am Arezki, Bahia wrote:
> It seems that  ATHENA gives a  spurious value for  E0 (1728 eV for S36
> xanes)   due to a shoulder in the rising part of the white line which is
> quite intense at  RT (s11) and decreases during the cooling of the sample.
> So, for s36 xanes at 10 K, ATHENA is simply taking the highest maximum in
> the 1st derivative which is this time higher in energy than the first one .

I have to object to this characterization.  Athena has not done
anything "spurious".  In fact, in your case, it seems to have behaved
exactly as documented.

As Jeremy said, it is the responsibility of *you, the user* to
correctly process your data.  Athena is merely a computer program --
it can offer nothing more than default values and some simple
algorithms.  Sadly, science is not so simple that it can be done
without the attention of a human.



 Bruce Ravel  ------------------------------------ bravel at bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

 My homepage:    http://xafs.org/BruceRavel
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/

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