issue contents

ISSN: 2053-2733

July 2009 issue

Highlighted illustration

Cover illustration: Electron-density isosurface of silicon coloured with electrostatic potential (red for lowest and blue for highest), together with a convergent-beam electron-diffraction (CBED) pattern of silicon. The red regions between neighbouring atoms indicate that the electrostatic potential is lowered due to the excess (bonding) electrons. The electrostatic potential and electron density were determined using a CBED structure-refinement method [Ogata et al. (2008), Acta Cryst. A64, 587-597]. The figure was drawn using VESTA [Momma & Izumi (2008), J. Appl. Cryst. 41, 653-658].

research papers

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The origin of X-ray interference fringes observed in the beams diffracted from a lateral surface of a thin plane-parallel Ge crystal is shown to be the interference between the beams in the Bragg–Laue and the Bragg–Bragg–Laue cases.

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Several mathematical results pertaining to the representation of texture information in the axis–angle parameterization by the hyperspherical harmonic expansion are provided. In particular, an addition formula for the basis functions of this expansion and an alternative form of the matrix by which a rotation of the sample affects the basis functions are presented.

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Piezoelectric lithium sulfate monohydrate, Li2SO4·H2O, was analyzed with respect to the relationship between the static structural properties of the crystal and its response to an external electric field. The distortions of the cation–anion bond lengths in the LiO4, LiO3(H2O) and SO4 tetrahedra were evaluated and were found to reflect the electron-density-related properties of the Li—O and S—O bonds.

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The possibility of using a tetrahedron instead of a cell (i.e. a parallelepiped) as a representative body of a lattice is examined. Necessary and sufficient conditions for its uniqueness are found for lattices having a shortest basis with a · b ≥ 0, a · c ≥ 0, b · c ≥ 0.

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The joint probability distribution function method is combined with MAD techniques to solve the phase problem from powder data.

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Discussion of the consequences of different treatments of H atoms in experimental charge-density studies of model complexes of DMAN leads to the best model for H atoms in experimental charge-density refinement.

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An algorithm for reconstructing macromolecular envelopes from solvent contrast variation data is described and illustrated by simulations.

short communications

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The use of Student's t-distribution in a probability plot is discussed.

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Previous results on intensity statistics of Friedel opposites, for general and special reflections, are concisely re-examined and confirmed by purely statistical methods. A complete classification of the reflections, based on the above, is presented.

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Three new types of interpenetrating homogeneous sphere packings with symmetries Ccce and Fddd are described.
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