[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Reply to: [list | sender only]
Re: polarization
- To: imgcif-l@bnl.gov
- Subject: Re: polarization
- From: "Herbert J. Bernstein" <yaya@bernstein-plus-sons.com>
- Date: Mon, 11 Sep 2000 10:55:57 -0400 (EDT)
- In-Reply-To: <Pine.BSI.4.10.10009110852050.29254-100000@web.msc.com>
Perhaps we could define a few new tokens. Would somebody be kind enough to suggest names with rough definitions? In order to ground the discussion, attached are the two current definitions from the core dictionary as they are carried in the mmCIF dictionary. These tags allow for definition of polarization referenced to the diffraction plane and the ratio between two orthogonal polarization components. If we are going to reference to gravity or to the normal to the plane of the synchrotron or some other appropriate reference direction, we should define an explicit tag. Perhaps we also need to consider measures of polarization other than a ratio. -- Herbert save__diffrn_radiation.polarisn_norm _item_description.description ; The angle in degrees, as viewed from the specimen, between the perpendicular component of the polarisation and the diffraction plane. See _diffrn_radiation_polarisn_ratio. ; _item.name '_diffrn_radiation.polarisn_norm' _item.category_id diffrn_radiation _item.mandatory_code no _item_aliases.alias_name '_diffrn_radiation_polarisn_norm' _item_aliases.dictionary cif_core.dic _item_aliases.version 2.0.1 loop_ _item_range.maximum _item_range.minimum . 0.0 0.0 0.0 _item_type.code float _item_units.code degrees save_ save__diffrn_radiation.polarisn_ratio _item_description.description ; Polarisation ratio of the diffraction beam incident on the crystal. It is the ratio of the perpendicularly polarised to the parallel polarised component of the radiation. The perpendicular component forms an angle of _diffrn_radiation.polarisn_norm to the normal to the diffraction plane of the sample (i.e. the plane containing the incident and reflected beams). ; _item.name '_diffrn_radiation.polarisn_ratio' _item.category_id diffrn_radiation _item.mandatory_code no _item_aliases.alias_name '_diffrn_radiation_polarisn_ratio' _item_aliases.dictionary cif_core.dic _item_aliases.version 2.0.1 loop_ _item_range.maximum _item_range.minimum . 0.0 0.0 0.0 _item_type.code float save_ ===================================================== **** BERNSTEIN + SONS * * INFORMATION SYSTEMS CONSULTANTS **** P.O. BOX 177, BELLPORT, NY 11713-0177 * * *** **** * Herbert J. Bernstein * *** yaya@bernstein-plus-sons.com *** * * *** 1-631-286-1339 FAX: 1-631-286-1999 ===================================================== On Mon, 11 Sep 2000, Jim Pflugrath wrote: > I use the polarization that Wolfgang Kabsch defined in his 1988 paper. > It consists of the degree of polarization and a vector which defines > a normal to the plane of polarization. So core CIF almost has it with > this vector implicit. The vector is defined is terms of the lab > coordinate system (remember the MSC system?). > > Jim > > > One thing I haven't seen in the imgCIF/CBF dictionary is a suitable data > > item for the beam polarization - the core CIF item seems to be based on a > > four-circle diffractometer equipped with a point detector, as the > > polarization is referenced to "the normal to the diffraction plane of the > > sample (i.e. the plane containing the incident and reflected beams)." > > (from http://www.iucr.org/iucr-top/cif/home.html#dics, section on > > _diffrn_radiation_polarisn_ratio). > > > > Would it be more sensible in the case of area detectors to have a > > definition based on "gravity" (or something more rigorous?). > > Yes, see above. > >
Reply to: [list | sender only]
- Follow-Ups:
- Re: polarization (Harry Powell)
- References:
- Re: polarization (Jim Pflugrath)
- Prev by Date: Re: polarization
- Next by Date: Re: polarization
- Prev by thread: Re: polarization
- Next by thread: Re: polarization
- Index(es):