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Journal logoJOURNAL OF
ISSN: 1600-5767

April 1998 issue

Highlighted illustration

Cover illustration: Powder diffraction pattern of LaB6 obtained using a 200 x 400 mm flat imaging plate mounted at an angle of 45 degrees with the incoming X-ray beam. Experimental conditions: lambda = 0.8884 angstroms, D0 = 104 mm, exposure time 60 s. Courtesy of Poul Norby.

research papers

J. Appl. Cryst. (1998). 31, 113-120
doi: 10.1107/S0021889897006560
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A method is presented that links the measured peak separations in X-ray rocking curves to the strain tensor of the epilayer. Different critical thicknesses for the relaxation in the [110] and [110] directions are determined for (Zn,Mn)Se on ZnSe buffer on GeAs substrate.

J. Appl. Cryst. (1998). 31, 121-127
doi: 10.1107/S0021889897006936
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The phonon contributions to the thermal expansion of solid crystals are studied. The Debye temperature and the values of the lattice parameters exptrapolated to 0 K are determined so that extra contributions (electronic or magnetic) are displayed.

J. Appl. Cryst. (1998). 31, 128-135
doi: 10.1107/S0021889897007802
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Methods and algorithms are described for the measurement and analysis of the response of crystals to irradiation by pulsed laser light. They are tested in a 40 K study of the 2.44 ms lifetime excited state of [RhBr2(pyridine-d5)]Br.

J. Appl. Cryst. (1998). 31, 136-148
doi: 10.1107/S002188989700825X
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Considering the forward problem of deriving and evaluating pole density functions from given crystallographic orientation density functions, it is shown that the corresponding inverse problem is mathematically ill posed. Very different orientation density functions, differing in both even and odd terms of their harmonic series expansion, result in very similar pole density functions.

J. Appl. Cryst. (1998). 31, 149-153
doi: 10.1107/S0021889897008789
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The problem of the retrieval of the particle size distribution of scatterers from small-angle scattering experiments with noisy data is addressed.

J. Appl. Cryst. (1998). 31, 154-162
doi: 10.1107/S0021889897008868
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Diffuse scattering has been recorded for the KTP analogue material TlSbOGeO4, and a preliminary interpretation made using Monte Carlo simulation. The diffuse scattering originates predominantly from the disorder of the thallium cations between alternative sites Tl and Tl', and the occupancy of these sites tends to alternate along the b crystal direction.

J. Appl. Cryst. (1998). 31, 163-168
doi: 10.1107/S002188989700900X
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When neutron diffraction is used, texture measurements are affected by extinction and anisotropy of grain size. A method of correction is proposed and tested.

J. Appl. Cryst. (1998). 31, 169-175
doi: 10.1107/S0021889897009084
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A graphite double monochromator has been built and tested. With a Weissenberg camera and an image plate, diffuse superstructure reflections and diffuse planes have been recorded.

J. Appl. Cryst. (1998). 31, 176-180
doi: 10.1107/S0021889897009795
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Models for the anisotropic broadening of the Bragg peaks caused by microstrain and crystallite size are derived for all Laue groups. The models are suitable for implementation in the Rietveld refinement programs.

J. Appl. Cryst. (1998). 31, 181-184
doi: 10.1107/S002188989700928X
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An oscillating reflective intensity was measured with the sample and detector at fixed specular angles during the thin-film growth. This oscillating intensity carries the information of thin-film thickness and roughness.

J. Appl. Cryst. (1998). 31, 185-197
doi: 10.1107/S0021889897009643
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This paper examines the dependence of experimental noise in an X-ray rocking curve and develops a procedure for the use of this noise characteristic as a weight function for the optimization and analysis of calculated fits of the rocking curve.

J. Appl. Cryst. (1998). 31, 198-203
doi: 10.1107/S0021889897009990
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The addition of an azimuthal detector rotation to a (2+2)-type diffractometer makes it fully equivalent to a z-axis type. The geometric correction factors for this (2+3)-type diffractometer, which are needed to obtain structure factors from measured integrated intensities, are derived.

J. Appl. Cryst. (1998). 31, 204-211
doi: 10.1107/S0021889897010005
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Some new properties of the least-angle rotation between two cubic crystals are derived. The extent to which a misorientation may alternatively be described by some low-index axis rotation is also examined.

J. Appl. Cryst. (1998). 31, 212-222
doi: 10.1107/S002188989701011X
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Transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) have been used to study hardening precipitation in a 6056 Al–Mg–Cu–Si alloy at peak ageing. TEM gives the precipitate morphology and structure while the SANS data analysis yields their distribution and mean size.

J. Appl. Cryst. (1998). 31, 223-234
doi: 10.1107/S0021889897011771
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The storage of cold neutrons in a longitudinally vibrating silicon crystal is demonstrated by time-resolved transmission experiments on a high-resolution backscattering spectrometer. The experimental results are compared with Monte Carlo simulations.

J. Appl. Cryst. (1998). 31, 235-240
doi: 10.1107/S0021889897014581
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Surface-induced scattering from Si(111) crystal has been studied and attributed to the network of cracks produced by cutting. This scattering can be significantly reduced by deep etching of the crystal.

J. Appl. Cryst. (1998). 31, 241-251
doi: 10.1107/S0021889897009096
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A new approach to the simulation of high-resolution X-ray diffraction spectra is developed using direct summation of scattered waves. The simulation procedure permits the introduction of short-range variations of structural and geometrical parameters of multilayered systems.

cryocrystallography papers

J. Appl. Cryst. (1998). 31, 252-257
doi: 10.1107/S0021889897009229
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Measurements of cooling rates were made for different cryoprotectants with different sample volumes and cooling agents. Approaches by which the increase in mosaic spread during flash cooling of macromolecular crystals might be minimized are discussed.

short communications

J. Appl. Cryst. (1998). 31, 258-261
doi: 10.1107/S0021889897011795
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Among the various diffraction geometries possible with the incident illumination specified, symmetric Bragg-case reflection has the valuable special property of invariant direction of reflected rays, independent of wavelength and the extinction distance of the reflection.

computer programs

J. Appl. Cryst. (1998). 31, 262-269
doi: 10.1107/S002188989700811X
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This report introduces a software package for quantitative texture analysis, applicable to all crystal symmetries. The 20 computer programs provide for processing of experimental data, calculation of the orientation distribution and anisotropic properties as well as various graphic representations.

J. Appl. Cryst. (1998). 31, 270-274
doi: 10.1107/S0021889897013253
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A new program for automatically determining heavy-atom derivative sites from SIR data and anomalous-scatterer sites from MAD-FA coefficients is described. The program is deployed with a set of interactive graphical tools for checking and editing the heavy-atom sites against difference Patterson and cross-difference Fourier maps.

J. Appl. Cryst. (1998). 31, 275-277
doi: 10.1107/S0021889897010558
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A direct-methods computer program to evaluate Hauptmann's three-phase triple-invariant estimates for single-wavelength anomalous dispersion data is described.

CIF applications

J. Appl. Cryst. (1998). 31, 278-281
doi: 10.1107/S0021889897007280
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CYCLOPS2 is a major revision of the program CYCLOPS, which is used, in conjunction with Crystallographic Information File (CIF) dictionaries, to validate names in an ASCII file.

J. Appl. Cryst. (1998). 31, 282-295
doi: 10.1107/S0021889897007309
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pdb2cif is a new version of an awk script originally written by P. E. Bourne in 1993 to translate from the 1992 Protein data Bank (PDB) format to the macromolecular Crystallographic Information File (mmCIF) definition. This new version of pdb2cif translates all current PDB formats.

laboratory notes

J. Appl. Cryst. (1998). 31, 296-298
doi: 10.1107/S0021889897009199
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A device that allows reorientation of a crystal at low temperature, without remounting or warming to ambient temperature, is described.

J. Appl. Cryst. (1998). 31, 299-301
doi: 10.1107/S002188989701056X
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A new furnace insert has been devised in which a sample can be studied using neutron scattering techniques in situ under several atmospheres of gas pressure and temperatures up to 1350 K.

fast communications

J. Appl. Cryst. (1998). 31, 302-304
doi: 10.1107/S0021889897018062
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The use of imaging plates as detectors in X-ray crystallography requires a correction for oblique incidence of the diffracted beam on the plate. The correction becomes important for wavelengths less than about 1 Å.

J. Appl. Cryst. (1998). 31, 305-307
doi: 10.1107/S0021889898002714
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Moving median filters have been employed to remove impulse noise from two-dimensional area-detector data. The median filters are compared to generalized moving mean filters.
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