issue contents

ISSN: 2053-2733

July 2017 issue

Highlighted illustration

Cover illustration: Tomographic rendering of barium sulfate clusters ingested by a macrophage cell. Multiple projections of the cell were recorded by X-ray holography while sitting in a hydrated environment, and phased by advanced near-field phase-retrieval methods [Krenkel et al. (2017). Acta Cryst. A73, 282-292].

scientific commentaries

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The new holo-TIE approach to cellular imaging described by Krenkel et al. [Acta Cryst. (2017), A73, 282–292] is discussed.


research papers

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Phase-contrast X-ray imaging of biological cells in two and three dimensions can be carried out with a low dose, based on free propagation and a setting of optimized wavefronts in cone-beam geometry. In order to reach the required contrast level, images have to be recorded in the holographic regime. The main result of this work is holographic recordings of a quality that is fully amenable to quantitative phase retrieval, beyond previous approximations. Different approaches to sample preparations, data recording and phase retrieval are compared.

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A novel, high-resolution X-ray diffraction (XRD) technique that provides completely non-destructive, high-quality XRD analyses of unprepared samples is demonstrated. The method shows great potential in the characterization of cultural heritage artefacts.

short communications

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In this study, a first-prototype multi-determinant X-ray constrained wavefunction approach is proposed. The new X-ray constrained wavefunction is written as a linear combination of pre-determined single Slater determinants constructed with extremely localized molecular orbitals. By exploiting experimental structure factors, the novel method enables one to extract resonance structure weights for molecules having a multi-reference character.


research papers

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It is shown how small-angle scattering (SAS) data can be reduced to a set of invariant parameters used to reliably estimate structural moments beyond the radius of gyration, thereby rigorously expanding the actual set of model-free quantities one can extract from experimental SAS data. The pair distance distribution function is also entirely described by this invariant set and the Dmax parameter can be measured.

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The forms of the tensors describing thermoelectric transport properties in magnetically ordered crystals are given for the 122 space-time point groups up to second order in an applied magnetic field.

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Computational mechanics is used to solve the Ising next-nearest-neighbour model in the context of close-packed polytype analysis. The stacking arrangement is seen as an information processing system generating symbols. A general method for solving the stochastic matrix of the random Gibbs field is described and applied. The ∊-machine of the process is built which allows one to describe the system statistically. The occurrence of higher-order polytypes at the borders of the phase diagram is discussed.

book reviews

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