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ISSN: 2053-2733

July 2015 issue

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Cover illustration: A new technique for the imaging of ferroelectric domains via resonant X-ray diffraction from a single Bragg reflection is described by Fabrizi et al. [Acta Cryst. (2015), A71, 361-367]. The domain contrast is achieved through the energy dependence of the resonant scattering around an atomic absorption edge.

advances

scientific commentaries


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A guide to the collection and processing of MicroED data invites X-ray crystallographers and electron microscopists to solve atomic structures from tiny protein crystals.

feature articles


research papers


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The identification and high-resolution mapping of the absolute crystallographic structure in multi-domain ferroelectric KTiOPO4 is achieved through a novel synchrotron X-ray diffraction method. On a single Bragg reflection, the intensity ratio in resonant diffraction below and above the Ti absorption K edge demonstrates a domain contrast up to a factor of ∼270, thus implementing a non-contact, non-destructive imaging technique with micrometre spatial resolution, applicable to samples of arbitrarily large dimensions.

foundations

research papers


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A detailed and comprehensive theoretical description of X-ray diffraction moiré fringes for a bicrystal specimen is given on the basis of a calculation by plane-wave dynamical diffraction theory, where the effect of the Pendellösung intensity oscillation on the moiré pattern is explained in detail.

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The number-theoretic concept of diaphony, as a measure of uniform distribution, is reviewed, highlighting its relation to crystallographic concepts like the largest interplanar spacing of a lattice, the structure-factor equation and the Patterson function.

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This paper describes a method for unbiased peak extraction from atomic pair distribution functions using the information-theoretic Akaike information criterion.

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A procedure for the approximation of viral capsids by icosahedral tilings is proposed and illustrated for a range of viruses from different families. The output tilings can be used as coarse-grained models of viral capsids, providing a basis for further mathematical modelling of their dynamic behaviour and assembly.

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A closed-form method is developed to calculate correlation functions of arbitrarily stacked close-packed structures.

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For investigation of the proton-disordered structure of clathrate hydrates, a new approach is presented which is based on topological crystallography.

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Iterative projection algorithms are used to determine the structures of two tetrameric proteins starting with only a low-resolution envelope and the position of the non-crystallographic axes.

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Temperature (20–300 K)- and energy-dependent phase shifts of resonant multiple-beam X-ray diffraction in germanium crystals, involving forbidden (002) and weak (222) reflections, are reported.

short communications


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Some properties of the anisotropic displacement tensor have been revised. Complete tables for site-symmetry restrictions covering all special positions as listed in International Tables for Crystallography, Vol. A, are provided.

book reviews


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