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ISSN: 2053-2733

January 2019 issue

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Cover illustration: The combined use of Bragg reflections and diffuse scatter for structure determination is demonstrated by Morgan et al. [Acta Cryst. (2019), A75, 25-40], who show that continuous diffraction due to random displacements of protein molecules from each crystal lattice site provides the information needed to determine the structure without prior knowledge. The cover image shows how the uniqueness of the solution can be illustrated by considering the autocorrelation functions of a pair of ducks.

scientific commentaries


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The new lower bounds for the regularity radius for `regular systems' (orbits of a single point under a crystallographic group) in arbitrary dimension given by Baburin et al. [Acta Cryst. (2018) A74, 616–629] are discussed.

advances

aperiodic 2018


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This work examines the long-wavelength scaling properties of self-similar substitution tilings, placing them in their hyperuniformity classes. Quasiperiodic, non-PV (Pisot–Vijayaraghavan number) and limit-periodic examples are analyzed. Novel behavior is demonstrated for certain limit-periodic cases.

research papers


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A new approach is presented for ultrafast calculation of atomistic diffuse-scattering patterns. It is shown that the fast Fourier transform can be used to perform such calculations rapidly, and a fast method based on sampling theory can be used to reduce high-frequency noise in the calculations.

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This article reports on the combined use of Bragg reflections and diffuse scatter for structure determination in crystallography.

foundations

aperiodic 2018


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Local potential differences between the 36 and 32.4.3.4 vertex configurations are identified within a two-dimensional dodecagonal fullerene monolayer. In a local area of the 8/3 approximant, rotational switching fullerenes on 36 vertex sites are revealed by scanning tunneling microscopy.

research papers


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A new aspherical scattering factor formalism was implemented in SHELXL. It relies on Gaussian functions and can optionally complement the independent atom model to take into account the deformation of electron-density distribution due to chemical bonding and lone pairs. The automated atom-type assignment was derived from the invariom formalism.

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This article describes the modeling of energy-dispersive X-ray diffraction for high-symmetry crystal orientation. The work gives exact equations for determining the orientation. The results are discussed in terms of basic crystallography, formula applications without limitations, software for exact solutions and equipment.

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It is shown how to reconstruct the stacking sequence from the pairwise correlation functions between layers in close-packed structures using a simulated annealing procedure. The robustness of the procedure is tested with synthetic data, followed by an experimental example.

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Experimental and computational reduction of dynamical electron scattering allows for visualizing of individual hydrogen atoms.

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This article presents a method to determine planar edge-to-edge k-isocoronal tilings – tilings whose vertex coronae form k orbits or k transitivity classes under the action of the symmetry group.

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This work addresses the structure–property relationship of an interesting organic–inorganic material. The structural investigation is coupled with Hirshfeld surface analysis to examine the nonlinear optical properties.

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The unit-cell reduction described by Selling and used by Delone (Delaunay) is explained in a simple form.

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This article presents a simple method for finding formulas for coordination sequences, based on coloring the underlying graph according to certain rules. It is illustrated by applying it to several uniform tilings and their duals.

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The symmetry of the capsomers forming a viral shell determines the polyhedron underlying the shell structure. If the capsid is self-assembled from dimers, this is the rhombic triacontahedron with 30 equivalent rhombic faces.

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Direct methods techniques are revisited and new mathematical approaches are described.

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A new method of extracting the individual shapes of overlapping powder peaks with Lorentzian (or other long-range) tails is presented. This allows computation of microstructure directly in Fourier space, without the infamous `hook' problem at low frequency.

international union of crystallography




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