# Re: New fast-track definitionproposal: _diffrn_radiation_wavelength_nominal

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 Dear James, Thanks for your email copied below.  I think it is my responsibility as chair of the core dictionary maintenance group to circulate this to my group, so you need not be concerned about it.  I agree that Nick's proposal is a much more elegant one than the original, and I will put it out to my group for their comment.  Six weeks will take us into the New Year, but since the the COMCIFS list has already had a chance to comment, I assume that if the core DMG had no objections we could adopt the new item into the dictionary. Best wishes David James Hester wrote: I think Nick makes a fair point here: the same result could be achieved by instead defining an additional enumerated dataitem.  I have fleshed out an example below.  If this is acceptable to the rest of the committee, I will forward it back to the core CIF DWG for their consideration as an alternative to the original proposal. I think an enumerated dataitem is appropriate, as that will be machine-readable.   New definition =========== data_diffrn_radiation_wavelength_determination   _name                      '_diffrn_radiation_wavelength_determination'   _category                    diffrn_radiation_wavelength   _type                        char   _list                        both   _list_reference            '_diffrn_radiation_wavelength_id'  loop_    _enumeration    _enumeration_detail   'fundamental'            'Wavelength that is a fundamental property of matter e.g. MoK\alpha'   'estimated'                'Estimated from secondary information e.g. monochromator angle or time of flight'   'refined'                  'Based on refinement of a standard material'   _definition ;              The method of determination of incident wavelength. Further information may be provided in _diffrn_radiation_special_details ;    On Mon, Nov 9, 2009 at 8:22 PM, Nick Spadaccini wrote: > Here is the problem I have with this approach. It seems to me that you are > suggesting there are two wavelength values, both of which are relevant to > the data set and both of which have to be recorded. > > But what I think you have written is that there is only one wavelength, but > you are trying to record something about its properties. I can appreciate > the need for a data item that indicates something about the properties, but > don't appreciate the need for a new wavelength data item. > > Perhaps something like > > _diffrn_radiation_wavelength > > and > > _diffrn_radiation_wavelength_determination > > The latter being free text or preferably an enumerated type that indicates > the various possibilities. And one could re-use > > _diffrn_radiation_special_details > > to provide all additional information. > > I would be very wary of VARIANTS as discussed by Herb in a follow up > discussion. Adding variations to existing definitions is going to be a great > source of error from users. At its basis is a desire to employ CIF in a way > it was not originally intended to be used. CIF is essentially an archival > format, for the submission of the final model/data/results etc. Herb is > suggesting its use as a lab manual to record every assumption, through > process, error etc during the experiment and refinement. Vary admirable, but > not what CIF is about, and probably such a CIF would not be of great use > outside of the home lab. > > The new DDLm etc supports many powerful features for one to make local > changes to dictionaries, and while I have no problem with Herb's approach to > meet local needs (apart from the fact I would do it differently), I would be > concerned if it was part of the official archive. The import feature of DDLm > allows one to make changes at many levels of refinement to the dictionary - > preferably for local use. The official IUCr submission dictionary (for > archive purposes) will have different requirements. > > > On 3/11/09 10:52 AM, "James Hester" wrote: > >> Dear COMCIFS members: the following fast track proposal for a minor >> change to the coreCIF dictionary has been approved by the core >> Dictionary Maintenance Group after a 6-week comment period.  As per >> the recently approved fast track process, it is now open for comments >> from COMCIFS for a further 6 week period. >> >> James. >> ------------------------------------------------------------------------------ >> ---------------- >> >> 2009-08-23 proposed by James Hester. >> 2009-10-16 approved by the core Dictionary Maintenance Group under a fast >>           track approval process. >> >> Explanation >> =========== >> The wavelength used for a measurement defines the >>  length scales used in the crystallographic unit cell, so it is >>  important that the quality of the number used for wavelength is >>  understood.  When the bulk of experiments came from lab X-ray sources, >>  the wavelength value was an accurate and precise quantity that could >>  be relied on.  In contrast, synchrotron and neutron sources have >>  comparatively poorly-defined wavelengths, subject to systematic errors >>  (for example, changes in the monochromator d-spacing due to >>  temperature effects, and angular offset errors).  Many facilities do >>  not attempt to characterise the accuracy of such derived wavelength >>  values. Instead users may (or may not) refine against a standard >>  compound in order to recover an accurate wavelength value. I therefore >>  propose a separate tag for those wavelength values that are nominal, >>  that is, derived from positioning of optical elements rather than >>  proper standards.  This removes ambiguity in determining whether or >>  not a wavelength has been obtained from refinement against a standard, >>  or is simply a nominal value based on beamline optics. >> >> >> A new DDL1 item >> >>  data_diffrn_radiation_wavelength_nominal >>     _name                      '_diffrn_radiation_wavelength_nominal' >>     _category                    diffrn_radiation_wavelength >>     _type                        numb >>     _list                        both >>     _list_reference            '_diffrn_radiation_wavelength_id' >>      _enumeration_range           0.0: >>     _units                       A >>     _units_detail              'angstroms' >>     _definition >> ;              The incident radiation wavelength in Angstroms >>               calculated from secondary information, >>               for example monochromator angle or time of flight. >>               If the wavelength has been determined >>               using some type of standard, >>               _diffrn_radiation_wavelength should be used >> ; >> >> A change in definition of an existing item.  The current >> definition reads 'The radiation wavelength in angstroms'. >> >> >>  data_diffrn_radiation_wavelength >>     _name                      '_diffrn_radiation_wavelength' >>     _category                    diffrn_radiation_wavelength >>     _type                        numb >>     _list                        both >>     _list_reference            '_diffrn_radiation_wavelength_id' >>     _enumeration_range           0.0: >>     _units                       A >>     _units_detail              'angstroms' >>     _definition >> ;              The radiation wavelength in angstroms as >>               determined from measurements using standards, >>               for example an X-ray emission line, >>               or when a refinement based on a standard >>               material has been carried out. >>               The details of such a refinement should be >>               recorded in the _diffrn_radiation_special_details >>               item. >>  ; > > cheers > > Nick > > -------------------------------- > Associate Professor N. Spadaccini, PhD > School of Computer Science & Software Engineering > > The University of Western Australia    t: +61 (0)8 6488 3452 > 35 Stirling Highway                    f: +61 (0)8 6488 1089 > CRAWLEY, Perth,  WA  6009 AUSTRALIA   w3: www.csse.uwa.edu.au/~nick > MBDP  M002 > > CRICOS Provider Code: 00126G > > e: Nick.Spadaccini@uwa.edu.au > > > > > _______________________________________________ > comcifs mailing list > comcifs@iucr.org > http://scripts.iucr.org/mailman/listinfo/comcifs > -- T +61 (02) 9717 9907 F +61 (02) 9717 3145 M +61 (04) 0249 4148  _______________________________________________ comcifs mailing list comcifs@iucr.org http://scripts.iucr.org/mailman/listinfo/comcifs 
begin:vcard
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org:McMaster University;Brockhouse Institute for Materials Research
email;internet:idbrown@mcmaster.ca
title:Professor Emeritus
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