Members have had the opportunity to meet once a year: Beijing (1993), Les Diablerets (1994) and Balatonfüred (1995). In addition, there has been frequent communication among the members by electronic mail, which has established efficient and almost instantaneous working relations. The Commission maintains a World-Wide Web (WWW) server relating the activities in the field of aperiodic crystals ( http://emmy.smith.edu/aperiodic). Future meetings, conferences and information on this topic are listed on the server.
The Commission prepared and submitted a checklist for the description of incommensurate modulated crystal (IC) structures. This document specifies the relevant parameters and information that should be included in a database or publication for their complete characterization. It should also assist journal editors and referees in their activities. This document has been approved by the Executive Committee. The Commission on Journals suggested some modifications which were included in the final version, which is expected to appear in Acta Crystallographica [Acta Cryst. (1997), A53, 95-100].
CIF Dictionary for modulated structures
Following the checklist for the description of incommensurate modulated structures, the CIF Dictionary for modulated structures has been approved by COMCIFS (the IUCr CIF Management Committee). Work has been started for the extension of the CIF Dictionary to include incommensurate structures. The creation of a database containing the information on the IC structures published to date is under discussion. In addition to the structure descriptors fulfilling the checklist, additional items concerning composite crystals have been considered. The Commission is further pursuing its work on this matter.
Much of the effort of the Commission was dedicated to organizing the conference Aperiodic '94, held 18-22 September 1994 in Les Diablerets (Switzerland). According to its terms of reference, the Commission is to actively promote the organization of this series of conferences on a triennial basis. All the members of the Commission acted as the Programme Committee and thus contributed to the success of the conference by selecting a very high level of invited speakers and by a careful choice of abstracts. The Programme Committee took great care to ensure the interdisciplinary character of the conference by maintaining a balance between quasicrystal, incommensurate and composite crystal, and polytype specialists. A full report of the conference has been published elsewhere (IUCr Newsletter, 1995, Vol. 3, and also our WWW server). The conference organizers took full advantage of the possibilities offered by the WWW, using it to make the abstracts available first to the Programme Committee and then to interested scientists. All the conference information, including the programme, was available on the Internet well in advance of the conference. This was the first meeting sponsored by the IUCr to operate within the framework of the WWW and the experience gathered will be useful to future meeting organizers. The Commission also participated actively in the preparation of the Aperiodic '94 conference proceedings by carefully selecting the contributions. The volume was published by World Scientific (Singapore) in 1995 and was delivered to the participants nine months after the meeting.
The Commission was very active in coordinating meetings in the field of aperiodic crystals and participating actively in Programme Committees: the International School on Quasicrystals (Balatonfüred, Hungary, May 1995); the 5th International Conference on Quasicrystals (Avignon, France, May 1995); ECM-16 (Lund, Sweden, August 1995); the NATO Advanced Study Institute on the Mathematics of Long Range Aperiodic Order (Waterloo, Canada, August 1995); the IUCr Congress (Seattle, USA, August 1996); ECM-17 (Lisbon, Portugal, August 1997).
The Commission supported many organizers in their efforts to obtain financial help from the IUCr.
18 May 1996 G. C. Chapuis, Chairman
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