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Re: More thoughts on polarization, divergence, time-stamps in CBF

  I for one wish to continue the polarisation issue discussion.  The
resulting tokens will be of value both for the core and for mmCIF, making
them a very natural fit to the imgCIF discussion group, which deals with
tokens that will be needed for synchrotron-based experiments.  I do not
believe that the polarisation discussion needs to hold up the review of
the rest of the CBF/imgCIF dictionary.  If/when we have a sound
polarisation category, it can be folded in to the appropriate dictionaries
once the necessary approvals have been achieved.

  Besides, the entire point of a review is to find out what we need to add
to the dictionary to maximize its utility.

  Now to substance.  On first rereading of Harry's remarks and David's,
the major issue seems to be reference axis systems.  The new AXIS category
in the CBF/imgCIF dictionary is, as David notes, grounded in a
source-goniometer-axis axis system, but exists precisely to allow for the
definition of other useful axis systems.  Note that axis definitions
may be nested, creating complex dependencies which reflect the ways in 
which hardware is built.  This creates a burden for the experiment
designer to relate, say, raster axes, to the source axis and
the pricipal goniometer axis, but it is hard to imagine a beam-line for
which that information is neither available nor derivable.  If we missed
something in the AXIS category necessary to support realistic measurements
of polarisation, let's augment the AXIS category.  I think we should
even be able to support definitions of polarisation which reference
"horizontal" and "vertical" axis, or even such concepts as beam-tangent
axes and synchrotron beam normal axes. 

  My apologies for my persistent use of "polarisation", rather than
"polarization".  Would some native English-English speaker care to add
some colour to the discussion and analyse the roots of the word.  

  Regards,
    Herbert

   
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****                BERNSTEIN + SONS
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**** *            Herbert J. Bernstein
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=====================================================

On Fri, 13 Oct 2000, Harry Powell wrote:

> On Fri, 13 Oct 2000, I. David Brown wrote:
> 
> > 
> > 
> > 	There is a version of imgCIF/CBF (0.7.0) that has almost completed
> > its review by the Comcifs Dictionary Review Committee and is on the point
> > of being forwarded for official Comcifs approval.  The problems of
> > reporting polarization are not trivial and and it would be a mistake to
> > try to slip a poorly thought out set of items into version 0.7.0 before it
> > is sent off for approval. I would recommend that we get version 0.7.0 on
> > the books and treat the addition of polarization and collimation as
> > something to be added once the topic has received the kind of in depth
> > consideration it deserves.  Examples of the kind of problems that need to
> > be considered are given below.
> 
> I'm bringing this (and other items which I will post when I have time) up
> now because Herbert asked me to. 
> 
> In the short term it doesn't matter unduly if items such as polarization
> aren't included in a usable fashion in the definitions, but from my point
> of view as someone who is writing integration software to read CBFs, it
> makes good sense to include these at the earliest possible date. I'd like
> to save my users the trouble of writing down these numbers on their
> synchrotron trips...
> 
> BTW, I've been working with 0.6.2. Finding a more recent version is not
> easy!
> 
> Harry 
> -- 
> Dr Harry Powell, MRC Laboratory of Molecular Biology, MRC Centre, Hills
> Road, Cambridge, CB2 2QH
> 
> 
>

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