issue contents

ISSN: 2053-2733

March 2008 issue

Highlighted illustration

Cover illustration: An octagonal mosaic from the Kasbah de Telouet, High Atlas, Morocco, based on a modified quasilattice. The underlying quasilattice can best be seen in the blue-and-black portions of the pattern where the `standing' lozenges define bars of unit width and the diagonally positioned lozenges define bars with a width equal to [square root]2. Four orientations of the bar scheme, 45° apart, and phason shifts (alternation of bars in the sequence) are present. Picture taken by Emil Makovicky during the 24th European Crystallographic Meeting 2007.

research papers

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An object can be reconstructed from its diffraction pattern incoherently averaged with respect to a discrete group of symmetries under conditions on the shape of the object and the order of the group.

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The (n,d)-dimensional superspace crystallography is extended to include n-dimensional crystallographic point groups and not only those isomorphic to finite subgroups of the orthogonal group O(d), with d the physical dimension.

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The maximum-entropy method for solving zeolite structures from electron diffraction data is supplemented with potential-density histograms.

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The maximum-entropy method for solving structures from electron diffraction data is modified to use potential density-building functions and used successfully to solve eight zeolite and related structures.

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The capabilities and limitations are demonstrated and discussed of a common-line method of assembling a three-dimensional oversampled diffraction data volume suitable for structure solution from diffraction patterns of randomly oriented protein molecules obtained with a fourth-generation X-ray source. The method requires a detected photon count of 10 per pulse/pixel, about three orders of magnitude greater than anticipated for a 500 kDa protein.

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Ferromagnetic, ferroelectric and ferroelastic classifications of multiferroic crystals are extended to include ferrotoroidic crystals.

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A method for the determination of the anomalous scattering factor very near an absorption edge is proposed based on the fact that phase change of the real part of the atomic scattering factor is large and affects the peak position of the rocking curve. As an example, the anomalous scattering factor of Ge is determined with accuracy better than 1%.

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Algorithms for calculating minimally resolution biased electron-density maps are described.

short communications

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Bragg-case Pendellösung involves wavefields belonging to the same branch of the dispersion surface if the dispersion surface is considered in an infinite medium but wavefields belonging to different branches if the actual dispersion surface is considered in the semi-infinite medium where they are generated by the incident wave.

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Images generated using the phases from structure A and the amplitudes from structure B look recognizably like A. This paper quantifies that similarity by calculating statistics such as the correlation coefficient between the true and phase-swapped structures.

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The maximal subgroups of index ≤4 of the one-, two- and three-dimensional magnetic space groups and the two- and three-dimensional magnetic subperiodic groups are tabulated.

book reviews

Acta Cryst. (2008). A64, 348
doi: 10.1107/S0108767308002419

international union of crystallography

Acta Cryst. (2008). A64, 352
doi: 10.1107/S0108767308002572

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