issue contents

Journal logoJOURNAL OF
ISSN: 1600-5767

June 2001 issue

Highlighted illustration

Cover illustration: Diffuse scattering around a 200 Bragg peak from a Cu-Ti single crystal (the intensities are in ln scale, the plane is (001), with the [100] direction horizontal, and the Bragg peak is masked by the blue beam stop). Courtesy of O. Lyon, C. Servant & J. P. Simon [J. Appl. Cryst. (2000), 33, 928-937].

research papers

J. Appl. Cryst. (2001). 34, 229-238
doi: 10.1107/S0021889801000462
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The first X-ray study of the metastable states of a spin-crossover compound is presented, including spin transition without volume change.

J. Appl. Cryst. (2001). 34, 239-251
doi: 10.1107/S0021889801001832
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String Fit is a novel molecular-structure-oriented neutron and X-ray reflectivity analysis method.

J. Appl. Cryst. (2001). 34, 252-257
doi: 10.1107/S002188980100228X
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A procedure for computing the resolution function for a time-of-flight diffractometer with curved slits chopper, using the matrix computation technique, is presented.

J. Appl. Cryst. (2001). 34, 258-262
doi: 10.1107/S0021889801002254
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Thermal neutron transmission measurements have been made as a function of wavelength on a pyrolytic graphite monochromator crystal that has been set to diffract a horizontal beam at different take-off angles. With respect to multi-instrument beamline design, the data show that it is best for a monochromator with the greatest (horizontal) take-off angle to be placed upstream, while monochromators with decreasing take-off angles should be placed progressively further downstream.

J. Appl. Cryst. (2001). 34, 263-270
doi: 10.1107/S0021889801002497
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This paper describes a method for the calculation of a stress-free lattice parameter from the analysis of diffraction data, utilizing the elastic anisotropy of a stressed material. The technique is demonstrated using data from a uniaxial load test.

J. Appl. Cryst. (2001). 34, 271-279
doi: 10.1107/S0021889801002898
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A refinement strategy based on a bivariate analysis with a stepwise truncation of low-order reflection data and a rejection of outliers (LOT analysis), which had successfully been applied to X-ray single-crystal data, is applied to Rietveld refinements. Model calculations and refinements show an improvement in the determination of the site occupancy factors when the LOT strategy is used.

J. Appl. Cryst. (2001). 34, 280-288
doi: 10.1107/S0021889801003077
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Some improvements are proposed for the statistical analysis of orientation data within individual grains, in particular by allowing for crystallographic symmetries. A method based on quaternions is then presented to characterize orientation spreads including anisotropic effects.

J. Appl. Cryst. (2001). 34, 289-297
doi: 10.1107/S0021889801003260
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The Bragg edges appearing in time-of-flight neutron transmission experiments of polycrystalline materials are used to define lattice parameters precisely. The technique is specially suited for very fast characterization of bulk samples as well as for mapping spatial changes in the lattice parameter and hence the strain in engineering samples.

J. Appl. Cryst. (2001). 34, 298-310
doi: 10.1107/S0021889801003715
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Two different methods of diffraction peak profile analysis are suggested for the determination of microstructural parameters in terms of crystallite size distribution and dislocation structure. The first is based on modified Williamson–Hall and Warren–Averbach procedures; the second is a whole-profile fitting by using the Fourier coefficients of ab initio size and strain profiles.

J. Appl. Cryst. (2001). 34, 311-317
doi: 10.1107/S0021889801004046
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The new diffractometer is devoted to the detection of phase transitions, to the determination of thermal expansion curves and to the study of kinetic chemical reactions in situ. The apparatus has been tested by measuring the cell parameter of the standard material cubic Na2Ca3Al2F14 in the 90–600 K range, and by measuring the thermal expansion of the cell parameter of cubic AgI in the 303–553 K range, revealing a first-order phase transition.

J. Appl. Cryst. (2001). 34, 318-324
doi: 10.1107/S0021889801004332
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A novel method for the estimation of the background in a powder diffraction pattern has been developed using a robust Bayesian analysis. The underlying probability theory is discussed in terms of going beyond the Gaussian approximation normally associated with counting statistics and least-squares analysis, and various examples are presented that illustrate the general applicability of the approach.

J. Appl. Cryst. (2001). 34, 325-329
doi: 10.1107/S0021889801004745
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The fit of a set of simulated noisy EXAFS (extended X-ray absorption fine structure) spectra can be used to sample the frequency distribution of structural parameters and provide their statistical estimators (mean, dispersion, correlations).

J. Appl. Cryst. (2001). 34, 330-335
doi: 10.1107/S002188980100468X
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A systematic study of the application of collimating and slightly focusing polycapillary optics to the X-ray crystallographic structure determination of egg-white lysozyme using two different sources, a standard rotating anode source and a low-power table-top microfocusing source, is presented.

J. Appl. Cryst. (2001). 34, 336-342
doi: 10.1107/S0021889801004691
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The complicated inverse scattering problem of reconstructing depth-dependent lattice parameters from high-resolution X-ray diffraction spectra is analysed by using neural networks. Attention is paid to the practically important case of structural modifications in the near-surface layers of ion-implanted single crystals.

J. Appl. Cryst. (2001). 34, 343-357
doi: 10.1107/S0021889801005106
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Neutron imaging with bent crystals is considered in the linear approximation of neutron optics. A matrix formalism analogous to that of conventional lens optics is developed.

J. Appl. Cryst. (2001). 34, 358-364
doi: 10.1107/S0021889801005064
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The possibility of extending the Rietveld method to incorporate textured polycrystalline materials is demonstrated with a zircaloy sample. By assigning the pole densities obtained by separate texture analysis to the preferred orientation factors in the mathematical model of the Rietveld method, good profile refinement results are achieved with the neutron diffraction patterns.

cryocrystallography papers

J. Appl. Cryst. (2001). 34, 365-370
doi: 10.1107/S0021889801003697
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The feasibility of growing isolated protein crystals inside X-ray capillaries from gelled solutions of proteins has been demonstrated experimentally. Using these same X-ray capillaries, X-ray diffraction data were collected at both room temperature and 100 K.

teaching and education

J. Appl. Cryst. (2001). 34, 371-374
doi: 10.1107/S0021889801003624
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New academic courses for teaching protein crystallography to biology and chemistry students have been developed. They include model-building exercises using adapted general-purpose kits and application of Web tools for practical classes and for conducting educational/examination quizzes.

short communications

J. Appl. Cryst. (2001). 34, 375-380
doi: 10.1107/S0021889801003053
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A citation analysis of papers published by the CCDC for the period 1981–1998 shows rapidly increasing citation frequencies over time, over journals and over geographical regions. The ten most highly cited papers, comprising database descriptions, geometrical tabulations and basic research papers, together received an average of 1058 citations per annum over the period 1995–1998.

J. Appl. Cryst. (2001). 34, 381-385
doi: 10.1107/S0021889801004009
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An X-ray powder diffraction profile analysis of ball-milled ceramic vanadium pentoxide samples reveals the development of nanostructure with significant plastic strain and its confinement.

J. Appl. Cryst. (2001). 34, 386-387
doi: 10.1107/S0021889801003685
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An algorithm for the optimization of data collection is described. The algorithm ensures optimum quality of measurements at the set survey rate and operates efficiently and simply by the flexible distribution of time between first and second measurements of a reflection.

J. Appl. Cryst. (2001). 34, 388-391
doi: 10.1107/S0021889801004666
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A simple innovation of the conventional vapor-diffusion method, involving the introduction of a capillary barrier (for hanging drop) or a punched film barrier (for sitting drop), has been set up. Crystallization experiments showed that this modified vapor-controlling-diffusion method is very effective for producing large protein crystals.

computer programs

J. Appl. Cryst. (2001). 34, 392-397
doi: 10.1107/S0021889801002904
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The program Quanto is described; it is devoted to quantitative phase analysis of polycrystalline samples by means of the Rietveld method.

J. Appl. Cryst. (2001). 34, 398-404
doi: 10.1107/S0021889801003302
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A new version of the computer program JANA is introduced that allows Rietveld refinements of periodic and aperiodic crystal structures. Applications to (CO)xC60 and the incommensurately modulated structure of NbTe4 are presented.

computer program abstracts

J. Appl. Cryst. (2001). 34, 405
doi: 10.1107/S0021889801002928
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The program TWIN3.0 is intended to test single-crystal data sets for the possible existence of twinning by merohedry.

addenda and errata

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