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ISSN: 2053-2733

January 2002 issue

Highlighted illustration

Cover illustration: Electrostatic equilibrium of simultaneous Coulomb attraction and core repulsion for an ensemble {\cal F}=(X_1^-,X_2^-); the conjoint centroids, shown in yellow, characterize force-free positions of the fragment inside the unit cell. For comparison, the pure Coulomb equilibrium is shown in the background. See Mädler, Behrends & Knorr [Acta Cryst. (2001). A57, 20-23].

obituaries


research papers


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The orbital ordering effect of the Mn2+ ion on the structure factors of an LaMnO3 crystal have been calculated. Lower-order structure-factor measurement methods such as Bragg X-ray and the QCBED method are discusssed and compared.

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Kinematical intensity profiles are compared with dynamical, as well as extinction-corrected, intensity distributions. Primary-extinction correction factors are discussed.

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Thanks to a new interpretation of the direct-methods modulus sum function, its relation to other existing phase-refinement functions can be easily visualized. The behaviour of the modulus sum function has been optimized by analysing the effect of the two most important control parameters on a selection of test structures.

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Lattice parameters are determined from harmonic emission reflected from crystalline targets irradiated by short femtosecond laser pulses.

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A detailed analysis of multiple diffraction data collected by the stereoscopic multibeam imaging technique from a tetragonal lysozyme crystal is reported. The proposed procedures provide a practical way of reconstructing diffraction profiles for experimental phase determination for macromolecular crystals.

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A new optimization algorithm, the guided simulated annealing method, for use in X-ray crystallographic studies is presented.

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Topological properties of the geodesics of a net allow an algebraic calculation of the generating function for its coordination sequences.

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Analysis of X-ray integrated intensities measured as a function of crystal thickness revealed that the two correlation lengths in the theory are absolutely required to interpret the variations of the intensities. It is shown that X-ray diffraction is more sensitive to the two correlation lengths than γ-ray diffraction.

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Algorithms for the treatment of special positions in three-dimensional crystallographic space groups are presented.

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An analysis of the normal modes of vibration of a cubic perovskite that have condensed out to produce phases with tilted octahedra is presented. A Landau expansion of the excess free energy is presented involving the seven distinct modes found in the possible structures.

short communications


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The inclusion of low-resolution reflections and taking into account a bulk-solvent correction improves drastically the signal in molecular replacement searches for the molecular position.

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A theorem is introduced and applied to determine the latent symmetry of composite systems.

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A simple tiling of Euclidean space by infinite tiles with all hexagonal faces is described and related to a dense cylinder packing with symmetry Ia{\bar 3}d. Some related structures with the same symmetry are also described.

addenda and errata



international union of crystallography


book reviews



books received


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