issue contents

ISSN: 2053-2733

September 2011 issue

Highlighted illustration

Cover illustration: Polar mode GM6 (left) and antiferrodistortive mode M3-1q (right) present in the monoclinic structure of SrAl2O4, together with a graph of maximal subgroups showing their isotropy subgroups. The amplitude of mode GM6 is much larger, and ab initio calculations confirm its soft character, while distortion M3-1q is a hard mode frozen as an induced secondary distortion [Perez-Mato et al. (2010). Acta Cryst. A66, 558-590]. The mode figures were drawn using FullProf Studio [Rodriguez-Carvajal (1993). Physica B, 192, 55-69].

research papers

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A space of 480 matrices with cyclic consecutive powers, determinant 1, elements from {0, ±1} and new geometric characterization is analyzed and offered as the conceptual and practical framework for dealing with the `arithmetic symmetry' of reduced lattices.

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A large variance in the `shake-and-bake' minimized target function Rh) can identify large subsets of phases whose mean phase error is considerably smaller than the average during unsuccessful phasing trials when the overall phase error occasionally dips below 75 or 80°. Efforts to exploit this observation to promote convergence to the solution, however, are generally not successful.

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Search spaces in the method of molecular replacement are shown to be coset spaces of the Lie group of rigid-body motions by the chiral space group of a crystal. The resulting `motion space' can be endowed with a quasigroup operation that has interesting properties which are explored here.

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The method of joint probability distribution functions has been applied to formulate a probabilistic analysis of the hybrid Fourier syntheses.

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An attempt to implement a robust regression procedure in a least-squares multipole crystal structure refinement is presented and discussed, together with some explanatory case studies.

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A direct experimental approach to the problem of anisotropic extinction is presented.

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The radial integrals, 〈jL〉, where L = 0, 2, 4, for several electronic configurations in the 5d electrons of transition metal atoms and ions are calculated. The resultant values are fitted to Gaussian analytical expressions with four exponential terms, and the coefficients of the expressions are tabulated.

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X-ray free-electron lasers are being used to determine the three-dimensional structure of objects from random snapshots. The two apparently very different Bayesian algorithms capable of performing this at ultra-low signal are fundamentally the same.

short communications

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An atomic resolution incoherent imaging mode in scanning transmission electron microscopy using detectors in real space, achieving a resolution comparable to conventional HAADF-STEM with good contrast, is presented. Simulations based on a newly proposed imaging mechanism shows excellent qualitative agreement with the experiments.
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