issue contents

ISSN: 2053-2733

July 2004 issue

Highlighted illustration

Cover illustration: Diffuse scattering about the 002 reflection of an AlAs/GaAs superlattice grown on an oriented GaAs substrate. The in-plane and out-of plane components of the momentum transfer vector are oriented horizontally and vertically, respectively. The observed features are explained on the basis of the distorted-wave Born approximation. See Chernov et al. [Acta Cryst. (2003), A59, 551-559].

research papers

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X-ray diffraction in continuously deformed crystals is reconsidered on the basis of the analogy between X-rays in crystals and two-level systems in quantum mechanics. The different forms of Takagi's equations are shown to be different ways to represent the same propagation equation. An exact solution of Takagi's equations in the case of a constant strain gradient is given and approximation methods are also considered.

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SPEDEN is a computer program that reconstructs the electron density of single particles from their X-ray diffraction patterns using an adaptation of the holographic method in crystallography. It is designed to deal successfully with sparse, irregular, incomplete and noisy data.

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A new method employing Sayre's equations and a genetic algorithm to solve the phase problem is developed for centrosymmetric structures. Compared to simulated annealing, a genetic algorithm is more efficient.

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Vector radiations, as particular examples of eutactic transformations, are defined and studied.

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A methodology for estimation of statistical uncertainties for parameters fit to pair distribution functions is developed.

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In U4O9, the hkl reflections obey the extinction rules for atoms occupying special 12-fold [12(b) of space group I\bar43d] sites. An explanation is given for this effect, which can be generalized to any space group.

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The structure of β-U4O9 has been refined from single-crystal neutron data in the space group I\bar43d taking into account the findings described in the previous paper.

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The structures of two crystals have been solved using a new iterative phasing method developed from the `charge-flipping' method.

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X-ray standing waves (XSW) were analysed within the dynamical theory for a thin epilayer and the substrate under the epilayer with application to a Zn1−xCoxO epilayer on ZnO(00.\bar 1)–O substrate.

short communications

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Data distribution plot for three-dimensional structure analysis of two-dimensional crystals.

book reviews

Acta Cryst. (2004). A60, 355
doi: 10.1107/S0108767304014412

books received

Acta Cryst. (2004). A60, 355
doi: 10.1107/S0108767304015065
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