Acta Crystallographica Section A

Foundations of Crystallography

Volume 53, Part 5 (September 1997)

Cover illustration: A structural model of the decagonal Al-Pd-Mn quasicrystal, which consists of clusters represented by decagons and ten pentagons surrounding each decagon. This is obtained from a periodic structure in five-dimensional space by taking a three-dimensional section. Courtesy of A. Yamamoto.

obituaries
research papers
short communications
international union of crystallography

obituaries

Acta Cryst. (1997). A53, 531-534 [doi:10.1107/S010876739700593X]

Boris Konstantinovich Vainshtein, 1921-1996

V. I. Simonov and L. A. Feigin

Acta Cryst. (1997). A53, 535-536 [doi:10.1107/S0108767397008738]

Edward Norman (Ted) Maslen, FAA, 1935-1997

S. R. Hall

research papers

Acta Cryst. (1997). A53, 537-545 [doi:10.1107/S0108767397006004]

Correction for Thermal Diffuse Scattering in Time-of-Flight NeutronDiffraction

N. C. Popa and B. T. M. Willis

Synopsis: A numerical algorithm is described for calculating the TDS correction to Bragg peaks that are observed in time-of-flight neutron diffraction studies on single crystals.

Acta Cryst. (1997). A53, 546-555 [doi:10.1107/S0108767397004224]

A Tensor Classification of Twinning in Crystals

V. K. Wadhawan

Synopsis: Four different types of twinning in crystals are recognized, based on a tensor distinction of their properties and on a new and rigorous definition of prototype symmetry.

Acta Cryst. (1997). A53, 556-563 [doi:10.1107/S0108767397004236]

Modelling Electrostatic Potential from Experimentally Determined Charge Densities. II. Total Potential

N. Bouhmaida, N.-E. Ghermani, C. Lecomte and A. Thalal

Synopsis: A new method for the determination of atomic moments fitted to theoretical or X-X experimental electrostatic potential is described. It is also shown that a reduced set of moments respecting local symmetry and chemical equivalence reproduces accurately V(r) and then can be used in force-field calculations.

Acta Cryst. (1997). A53, 564-575 [doi:10.1107/S0108767397004522]

Improved Estimation of Structure-Factor Difference Amplitudesfrom Poorly Accurate Data

T. Ursby and D. Bourgeois

Synopsis: A method is presented that improves the estimation of structure-factor difference amplitudes by using Bayesian statistics. The method is shown to give significant improvement for poor data and is straightforward to use.

Acta Cryst. (1997). A53, 576-589 [doi:10.1107/S0108767397005539]

Multislice Method for Large Beam Tilt with Application to HOLZ Effects in Triclinic and Monoclinic Crystals

J. H. Chen, D. Van Dyck and M. Op de Beeck

Synopsis: Three different multislice formulations for large beam tilt are compared and evaluated. The tested multislice formulations are then applied to calculate higher-order Laue-zone reflections in non-orthogonal crystals.

Acta Cryst. (1997). A53, 590-602 [doi:10.1107/S0108767397005989]

X-ray Scattering by Dislocations in Crystals. General Theory and Application to Screw Dislocations

L. E. Levine and R. Thomson

Synopsis: This paper presents a rigorous theoretical framework for understanding X-ray scattering from dislocations. This theory is then applied to the specific case of screw dislocations.

Acta Cryst. (1997). A53, 603-614 [doi:10.1107/S010876739601570X]

The Use of Structure Analysis Methods in Combination with Semi-empirical Quantum-Chemical Calculations for the Estimation of Quadratic Nonlinear Optical Coefficients of Organic Crystals

A. V. Yakimanski, U. Kolb, G. N. Matveeva, I. G. Voigt-Martin and A. V. Tenkovtsev

Synopsis: Electron crystallography was combined with quantum-mechanical calculations in order to estimate quadratic nonlinear optical coefficients of two-dimensional organic molecules.

Acta Cryst. (1997). A53, 615-631 [doi:10.1107/S0108767397006260]

De Nive Sexangula Stellata

A. Janner

Synopsis: The scaling symmetry observed in the morphology of snow crystals is analysed on the basis of the point group of a multimetrical space group of ice.

Acta Cryst. (1997). A53, 632-642 [doi:10.1107/S010876739700500X]

High-Order Supersatellite Reflections in Labradorite. A SynchrotronX-ray Diffraction Study

M. Kalning, V. Dorna, B. Burandt, W. Press, S. Kek and H. Boysen

Synopsis: High-resolution X-ray synchrotron radiation study of the supersatellites in the feldspar mineral labradorite. Data analysis shows a transverse displacement modulation with a large amplitude.

Acta Cryst. (1997). A53, 643-648 [doi:10.1107/S0108767397006429]

Evaluation of Reflection Intensities for the Components of Multiple Laue Diffraction Spots by the Maximum-Entropy Method

Y. Xie and Q. Hao

Synopsis: A maximum-entropy algorithm for deconvoluting intensities of multiple Laue diffraction spots is described. Test results have shown that this method is capable of producing high-quality data without the requirement of data redundancy.

Acta Cryst. (1997). A53, 649-662 [doi:10.1107/S0108767397006272]

Dynamical Diffraction in Periodic Multilayers

V. F. Sears

Synopsis: Extra reflectivity curves, calculated numerically for various periodic multilayers using the optical-matrix method, are used to test the dynamical theory of diffraction.

Acta Cryst. (1997). A53, 663-672 [doi:10.1107/S0108767397005990]

Anisotropic Thermal Vibrations and Dynamical Electron Diffraction by Crystals

L.-M. Peng

Synopsis: General expressions are derived for the elastic and absorptive atomic scattering amplitudes and for the general case of anisotropic thermal parameters.

Acta Cryst. (1997). A53, 673-675 [doi:10.1107/S0108767397007277]

Comparing Independently Determined Structures

S. C. Abrahams

Synopsis: The application of normal probability methods to a comparison of structural parameters recently derived from independent X-ray and neutron diffraction refinement identifies systematically underestimated uncertainties in addition to significantly differing atomic displacement parameters that previously had been overlooked.

Acta Cryst. (1997). A53, 676-688 [doi:10.1107/S0108767397004856]

Combined Standard Uncertainties for Interatomic Distance in One-Dimensionally Modulated Crystals

H. Leligny and D. Grebille

Synopsis: A method is proposed for the calculation of combined standard uncertainties for interatomic distances taking into account covariance terms involved by linear relations of symmetry constraints in one-dimensionally modulated crystals.

short communications

Acta Cryst. (1997). A53, 689-691 [doi:10.1107/S0108767397008234]

On the uniformity of crystallographic orbits

S. Krivovichev

Synopsis: The uniformity characteristics R of crystallographic orbits are studied by the geometrical analysis of the fundamental regions for the corresponding space groups.

international union of crystallography

Acta Cryst. (1997). A53, 692-748 [doi:10.1107/S0108767397099819]