Acta Crystallographica Section A

Foundations of Crystallography

Volume 52, Part 6 (November 1996)

Cover illustration: Indicatrix of the inverse of Young's modulus for ADP, a tetragonal crystal. Courtesy of A. Authier, Laboratoire de Minéralogie-Cristallographie, Université Pierre et Marie Curie, Paris, France.

• research papers
• short communications
• international union of crystallography

research papers

Acta Cryst. (1996). A52, 787-796    [doi:10.1107/S0108767396005934]

Combination Rule of Values at Triple Junctions in Cubic Polycrystals

K. Miyazawa, Y. Iwasaki, K. Ito and Y. Ishida

Synopsis: A combination rule of values at triple junctions in cubic polycrystals is given and several models of grain-boundary networks composed of specially selected coincidence boundaries are shown.

Acta Cryst. (1996). A52, 797-811    [doi:10.1107/S0108767396005648]

A Bayesian Approach to Laue Diffraction Analysis and its Potential for Time-Resolved Protein Crystallography

G. P. Bourenkov, A. N. Popov and H. D. Bartunik

Synopsis: A statistical method of deconvoluting energetic and spatial overlaps in Laue diffraction patterns is described. A test application demonstrates that the new approach solves the problem of the `low-resolution hole' in protein crystallography and yields density maps of high quality.

Acta Cryst. (1996). A52, 812-829    [doi:10.1107/S0108767396006320]

Diffraction by Polycrystalline Fibers with Correlated Disorder

W. J. Stroud and R. P. Millane

Synopsis: Theory and algorithms for calculating fiber diffraction patterns from polycrystalline fibers of helical molecules that contain correlated lattice disorder are presented. Calculated patterns illustrate the effects of correlated disorder, and comparison of calculated and measured diffraction patterns reveals the presence of correlated disorder in a polynucleotide fiber.

Acta Cryst. (1996). A52, 830-838    [doi:10.1107/S0108767396005971]

On the Definition and Classification of Bravais Lattices

M. Pitteri and G. Zanzotto

Synopsis: Bravais's original criterion for the classification of the three- dimensional lattices gives only 11 distinct lattice types, as opposed to the classical 14 types obtained from the conjugacy classes of arithmetic holohedries in GL(3,Z).

Acta Cryst. (1996). A52, 839-849    [doi:10.1107/S0108767396006654]

The Cauchy-Born Hypothesis, Nonlinear Elasticity and Mechanical Twinning in Crystals

G. Zanzotto

Synopsis: The natural hypothesis by Cauchy and Born that bridges the molecular descriptions of crystalline configurations and the continuum theories for crystal mechanics is mostly not valid for mechanical twinning deformations. This implies that nonlinear elasticity theory can be used to model the behavior of crystalline substances only in very special cases that are nonetheless of great experimental relevance.

Acta Cryst. (1996). A52, 850-878    [doi:10.1107/S0108767396006605]

Geometrical Aspects of the Diffraction Space of Serpentine Rolled Microstructures: their Study by means of Electron Diffraction and Microscopy

S. Amelinckx, B. Devouard and A. Baronnet

Synopsis: The geometry of the diffraction space of cylindrically and conically wound fibres is discussed. Chiral and achiral tubules consisting either of concentric cylinders or of a scroll are considered. In particular, the complicated electron diffraction patterns and high-resolution images due to single conical and scroll fibres can satisfactorily be interpreted on the basis of the proposed model.

Acta Cryst. (1996). A52, 879-889    [doi:10.1107/S0108767396007519]

Algebraic Description of Coordination Sequences and Exact TopologicalDensities for Zeolites

R. W. Grosse-Kunstleve, G. O. Brunner and N. J. A. Sloane

Synopsis: Coordination sequences (CS) have been calculated for all approved zeolite topologies, all dense SiO₂ polymorphs and 16 selected non-tetrahedral structures and the algebraic structure of these CS's has been analyzed.

Acta Cryst. (1996). A52, 890-897    [doi:10.1107/S0108767396007398]

Profile-Fitting Treatment of Single-Crystal Diffraction Data

A. Pavese and G. Artioli

Synopsis: A profile-fitting-based method to analyse single-crystal diffraction profiles is presented. This technique allows reflections to be recovered from common troubles (for instance scan truncation, multiple diffraction) in order to extract reliable integrated intensities to use for investigating fine structural properties such as electron-density and atomic displacement parameter analysis. A couple of applications are reported.

Acta Cryst. (1996). A52, 898-908    [doi:10.1107/S0108767396007581]

Elastic Scattering of Partially Coherent Beams of Fast Electrons in a Perfect Crystal

N. I. Borgardt

Synopsis: The diffraction of electron beams in a crystal under partially coherent illumination is described with the use of the mutual coherency function and Bloch-wave formalism.

Acta Cryst. (1996). A52, 909-922    [doi:10.1107/S0108767396008057]

Approximate Methods in Dynamical RHEED Calculations

L.-M. Peng, S. L. Dudarev and M. J. Whelan

Synopsis: Approximate methods for RHEED calculations have been examined. It is found that these methods speed up the calculations typically more than 15 times.

Acta Cryst. (1996). A52, 923-936    [doi:10.1107/S0108767396008379]

Low-Order Structure-Factor Amplitude and Sign Determination of an Unknown Structure Al_mFe by Quantitative Convergent-Beam Electron Diffraction

Y. F. Cheng, W. Nüchter, J. Mayer, A. Weickenmeier and J. Gjønnes

Synopsis: The quantitative convergent-beam electron diffraction technique has been applied, for the first time, to an unknown structure crystal, Al_mFe, to determine its accurate structure-factor amplitudes and phases for the purpose of determining its structure by electron diffraction techniques.

Acta Cryst. (1996). A52, 937-946    [doi:10.1107/S0108767396008744]

Direct Methods in Protein Electron Crystallography: the Ab Initio Structure Determination of Two Membrane Protein Structures in Projection using Maximum Entropy and Likelihood

C. J. Gilmore, W. V. Nicholson and D. L. Dorset

Synopsis: The maximum-entropy method is used to solve the structure of two membrane proteins ab initio using only projection data at 6 Å resolution.

Acta Cryst. (1996). A52, 947-954    [doi:10.1107/S0108767396009798]

Direct Methods for Incommensurately Modulated Structures. On the Applicability of Normalized Structure Factors

R. de Gelder, R. Israël, E. J. W. Lam, P. T. Beurskens, S. van Smaalen, Z.-Q. Fu and H.-F. Fan

Synopsis: It is shown that the probability distribution associated with the structure invariant E(-H)E(H')E(H-H'), where H and H' are reciprocal vectors of main and/or satellite reflections, has approximately the same functional form as the Cochran distribution but triplet phase relations are relatively less reliable when satellites are involved.

short communications

Acta Cryst. (1996). A52, 955-956    [doi:10.1107/S0108767396010392]

Vector algebra and crystallography

J. Sivardière

Synopsis: The properties of a crystal unit cell and its reciprocal cell are rederived in a concise way by means of an elementary formula in vector algebra.

Acta Cryst. (1996). A52, 957    [doi:10.1107/S0108767396011634]

Analysis of disorder in biopolymer fibers. Erratum

W. J. Stroud and R. P. Millane

Synopsis: Erratum to Acta Cryst. (1995), A51, 790-800.

international union of crystallography

Acta Cryst. (1996). A52, 958-999    [doi:10.1107/S0108767396099916]

Report of the Executive Committee for 1995

Acta Cryst. (1996). A52, 1000-1001    [doi:10.1107/S0108767396099904]

Prices of IUCr journals

Acta Cryst. (1996). A52, 1003-1006

Subject index to volume A52 (1996)

Acta Cryst. (1996). A52, 1007-1010

Author index to volume A52 (1996)

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