[Ifeffit] Re: Ifeffit Digest, Vol 22, Issue 1

[Bruce Ravel]

On Wednesday 01 December 2004 03:41 pm, Grant Bunker wrote:
> Hi, Bruce - Ge crystals certainly are a must. Shouldn't forget that people
> use Si monochromator crystals at different temps also. Instead of making
> a list of d spacings for each reflection, I would just keep values of the
> lattice constants at a few reference temps and interpolate the lattice
> constant a for the temp of interest, then any of the d spacings can be
> calculated as d[hkl]=a/Sqrt[h^2+k^2+l^2] (if memory serves me correctly)
> Same for Ge and Diamond since they are the same structure. That way it's
> just a handful of numbers, no big deal.
>
> Matt's point as to whether it really should be athena's job to read in all
> file formats is a good one. Mostly you want to make it easy for a
> new format to be added by the end user. A scripting language would
> suffice although perl might be difficult for most people to deal with.
> Perhaps the equation parser used in ifeffit could be deployed as end-user
> configurable preprocessor for massaging beamline data into the right
> form. If those were saveable as templates for different types of data it
> would be convenient.

Hi Grant,

Thanks for the comments.

I am indeed computing d-spacings from lattice constants.  The notion
of interpolating from a table for different temperatures is a good
solution.

I have actually been suprised at how small of a deal it has been to
handle different data file formats.  It turns out that almost
everyone's beamline spits out data that ifeffit and athena's column
selection dialog can handle just fine.  There are a few exceptions,
but not many.  In any case, I find that encoder readings fit into
Athena's column selection dialog well enough that it's worth
supporting. 

I agree that it's a fool's game trying to stay on top of every single
goofy format that too-clever-by-half DAQ software programmers have
come up with.  Much better than that would be to suggest standards for
an exafs data file format.  At this late date, we have a pretty good
grasp of the technology involved in exafs measurements and so we know
what needs to be in the file.  If someone -- say the International
XAFS Society -- were to publish a standard, it would provide guidance
that would benefit the programmers of DAQ software, of analysis
software, and of any tools to link the two.

B



-- 
 Bruce Ravel  ----------------------------------- ravel at phys.washington.edu
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 NRL Synchrotron Radiation Consortium (NRL-SRC)
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 National Synchrotron Light Source
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 My homepage:    http://feff.phys.washington.edu/~ravel 
 EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/