CH> data_diffrn_standards_decay_%_lt CH> I like the concept HF--> Personally I hate it. If it is difficult to use, it makes another HF--> good reason to ditch it. I see no difficulty in just reporting a value HF--> of zero with its standard uncertainty. HF--> Is a negative decay an increase in intensity of the standards? CH Comment >> The concept I like is being able to avoid claiming 0% decay. I agree that it could be difficult to use. I also agree that a std uncertainty would accomplish this without a new term I have often wondered about what it meant when I had a decay of -3(1)%, perhaps we should be defining a new entry that would "replace" the current term How about data_diffrn_standards_variation But I don't really like that either because no standards are measured in the typical area detector experiment How about data_diffrn_stability_variation_% But I don't really like that either BECAUSE I am wondering how I get this information in the area detector experiment. Typically data are corrected with some scaling program ( SCALEPACK, SADABS, MULABS, SORTAV .... ) Do any of these programs have the ability to separate out "decay" from other corrections? If not, then what are we accomplishing by asking scientists to provide a number that they do not have ready access to. One could argue that the programs should be rewritten to provide the info. This may happen, but the probabilities are not high. With respect to symmetry you are right (as usual). I was leaving my crystallographers hat on while interpreting the English. It is much better to not use c glide in the definition as that immediately makes me think crystallographically and then glide (or perhaps more accurately glide plane) does imply reflection and translation. -----Original Message----- From: Howard Flack [mailto:Howard.Flack@cryst.unige.ch] Sent: Tuesday, 15 July, 2003 11:07 AM To: Multiple recipients of list Subject: Re: Comments on CIF core changes for 2.3 CH> data_atom_site_refinement_flags_adp Curt's comments make good sense to me. I also very much enjoyed going to dinner with him in a Chinese restaurant in Los Angeles. CH> What is partial occupancy constraint? Curt: If you look carefully in the revised version that Brian has circulated, the word 'partial' only occurs just once, in the item 'data_atom_site_refinement_flags' which the _definition says "It is retained in this dictionary only to provide compatibility with legacy CIFs". Amongst the corrections Brian implemented on my bequest, was the removal of the word 'partial' because I could not understand what it meant either. CH> data_diffrn_standards_decay_%_lt CH> I like the concept Personally I hate it. If it is difficult to use, it makes another good reason to ditch it. I see no difficulty in just reporting a value of zero with its standard uncertainty. Is a negative decay an increase in intensity of the standards? CH> Doesn't c-glide define reflection and if so isn't reflection redundant? > _example_detail > 'x,1/2-y,1/2+z' 'c glide reflection through the plane (x,1/4,z)' Using the wording of ITA page 5 for the defining the symmetry operation, in full this should be _example_detail 'x,1/2-y,1/2+z' 'glide reflection through the plane (x,1/4,z), with glide vector 1/2 c' The somewhat cumbersome wording is in part forced by the necessity of distinguishing between a symmetry operation and the related symmetry element. So the symmetry operation is 'glide reflection' with the related symmetry element being a 'glide plane'. In my way of understanding English, there is no sense of 'reflection through a plane' associated with 'glide'. > I must admit that until I read (or misread) Howard's comments I would have > made C2/m look like the simpler example. The old definition of _symmetry_equiv_pos_as_xyz says > Symmetry equivalent position in the 'xyz' representation. Except > for the space group P1, this data will be repeated in a loop. > The format of the data item is as per International Tables for > Crystallography, Vol. A. (1987). All equivalent positions should > be entered, including those for lattice centring and a centre of > symmetry, if present. which makes me think that the simpler version is not the good one. However, .... > The suggested extended examples could help resolve ambiguities. Perhaps the > extended example could also include a non standard setting. That all sounds like very good advice and makes very good sense. I always look at the examples first and read the definitions afterwards. > but I do not know how to set it up to give something > that looks like this. I have the same problem. In principle I know how to do it, in practice I always get it wrong! H.
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