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Re: Core CIF - revision to accommodate Acta C Notes for Authors

  • To: Brian McMahon <bm@iucr.org>
  • Subject: Re: Core CIF - revision to accommodate Acta C Notes for Authors
  • From: "I. David Brown" <idbrown@mcmail.CIS.McMaster.CA>
  • Date: Tue, 18 Nov 1997 15:25:29 -0500 (EST)
  • In-Reply-To: <000000001@iucr.org>
	A quick look through the proposed core changes raises the
following queries and comments:

*_obs
	These items are all referenced to *_gt.  Since we have decided to
go for *_gt, why are we now introducing *_obs items for the first time? 
Surely it is bad enough to build in obsolescence without actually
introducing data names that are already obsolete before they are defined! 
(Does 'obs' stand for obsolete? :).  The same comment applies to
*_shift/esd_*. 

_refine_ls_wR_factor_gt
	We discussed the definitions of R factors some time ago and I
thought we had decided that there was only one possible definition of wR,
namely what here is called *_wR_factor_ref.  Any omitted reflections are
those in which w is set equal to zero, so, since w is presumably defined
for each reflection, *_wR_factor_gt is a nonsense and should not be
allowed into the dictionary (this would also exclude *_obs).  If it is
absolutely essential to include this definition for historical reasons, is
there anyway we can point out its mathematical absurdity and
inappropriateness for any valid crystallographic purpose? 

_refine_ls_shift/su_mean
	The related item I assume should be *_shift/esd_mean, not
*_shift/su_mean.

_reflns_number_Friedel
	The last line of the definition should read 'anomalous scattering'
not 'inelastic scattering'.

_reflns_threshold_expression
	Would it be better to say 'USUALLY based on multiples of' or
'based on FUNCTIONS of'?  I do not see any need to restrict the nature of
the function being defined in such a drastic way, even if it does cover
99% of current usage.

			David

*****************************************************
Dr.I.David Brown
Brockhouse Institute for Materials Research, 
McMaster University, Hamilton, Ontario, Canada
Tel: 1-(905)-525-9140 ext 24710
Fax: 1-(905)-521-2773
*****************************************************

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