The IUCr Executive Committee approved in April 1991 the establishment of the Commission on an ad interim basis with the following membership: J. M. Pérez-Mato (Chairman), G. Chapuis, M. Farkas-Jahnke, M. L. Senechal and W. Steurer. This Commission substituted as a new start the earlier ad interim Commission on Modulated Structures, Polytypes and Quasicrystals. The Commission first elaborated its terms of reference, which were published in Acta Cryst. (1992), A48, 928.
During these years, the Commission has actively supported the organization of two meetings: an International Workshop on Methods of Structural Analysis of Modulated Structures and Quasicrystals (Lekeitio, Spain, 1991), which focused on structure determination of both incommensurate structures and quasicrystals, and an International Conference on Modulated Structures, Polytypes and Quasicrystals (MOSPOQ 91) which took place in Balatonszéplak, Hungary, also in 1991. In 1992, the 4th International Conference on Quasicrystals, celebrated in St Louis, USA, was also sponsored by the IUCr, under the recommendation of this Commission. For the Beijing Congress in August 1993, the Commission devised the programme of the session on Quasicrystals and Incommensurate Crystal Structures.
After consulting other experts, the Commission has elaborated a set of guidelines for the contents to be included in structural reports of incommensurately modulated structures. This checklist has been presented to the IUCr Executive Committee for its approval and publication in Acta Crystallographica. The list is a set of recommendations to be considered by journal editors and authors as a substitute for the usual checklist considered in the case of normal crystals. The elaboration of a similar list for incommensurate composite structures has been postponed until, within this subfield, some standards become commonly accepted.
At the ACA meeting in Pittsburgh in 1992, some members of the Commission ascertained the feeling of many people involved in the field that, at present, the adoption by the IUCr of a standard nomenclature for higher-dimensional space groups is premature. Sharing this opinion, the Commission sent a formal letter in this sense to the Sub-committee on the Nomenclature of N-Dimensional Crystallography of the IUCr Commission on Crystallographic Nomenclature.
Finally, according to its terms of reference, the Commission is organizing the next International Conference on Aperiodic Crystals for 18-22 September 1994, at Les Diablerets, close to Lausanne, Switzerland. Its first announcement has already been distributed. This type of conference will continue on a triennial basis and substitutes the former MOSPOQ meetings.
5 May 1993 J. M. PÉREZ-MATO, Chairman
See also 16th General Assembly decision to establish this commission.
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 IUCr Triennial Report: Commission on Aperiodic Crystals
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