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December 2011 issue
Cover illustration: Selected images of optical birefringence recorded during the heating of dodecasil-3C crystals. Courtesy of Lethbridge et al. [J. Appl. Cryst. (2010), 43, 168–175].
research papers
The standard ab initio VLD phasing algorithm has been improved; small to medium-size structures and proteins can be solved with greater efficiency.
A complete list of distinct twist boundaries and zones of tilt boundaries for low-Σ coincident site lattice misorientations is provided. For these misorientations, maps of twist and tilt boundary planes are drawn. The maps allow for ascribing twist or tilt boundaries to peaks on experimental boundary distributions, and indicate boundaries with two-dimensional periodicities.
The scattering pattern from micrometre-sized phase-shifting objects is calculated by using its Radon transform and Fraunhofer diffraction, and good agreement is found (in the case of a homogeneous sphere) for particle sizes up to 50 µm.
A method to identify the type and the Burgers vector of dislocations visualized via transmission electron microscopy is proposed. The basic principle of the method is to use previous knowledge of the crystal structure to calculate the possible dislocation line vectors in the transmission electron microscope screen coordinate system and compare them with the observed dislocation lines.
It is shown that an extremely inclined X-ray double-crystal monochromator can diffract a beam with the required wavelength and at the same time may reflect a great deal of unwanted radiation in a broad range of Bragg angles. The properties of such a device are discussed.
Grazing-incidence small-angle X-ray scattering on epitaxial magnetic alloy nanostructures is reported.
A new method for determination of the orientation matrix of Laue X-ray data is presented. The method is based on matching of the patterns of central reciprocal lattice rows projected on a unit sphere centered on the origin of the reciprocal lattice of the Laue data set with the corresponding pattern of a monochromatic data set on the same material.
The effect of initial cold-rolling reduction on the microtexture development of retained austenite in an aluminium-containing transformation-induced plasticity (TRIP) steel has been studied.
A study of the differential evolution global optimization algorithm applied to fitting X-ray reflectivity data is presented. The results are summarized as rules of thumb for tuning the optimization algorithm.
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Rietveld refinements have been performed on diffraction diagrams collected on nanomaterials under grazing incidence X-ray diffraction.
This article introduces an efficient method for X-ray diffraction data collection mapping on a given curved surface.
A method is introduced for surface structure refinement using both anomalous and normal diffraction data simultaneously.
The orientation relationship between austenite and 5M martensite in Ni–Mn–Ga alloys has been unambiguously determined by experimental measurements and crystallographic calculation without residual austenite.
The thermal expansion coefficient of a marble is directly related to the preferred crystallographic orientation of its constituent minerals (calcite and dolomite). The thermal properties also depend on the existence of impurities and the presence of dislocations in single calcite and dolomite crystals.
Small- and ultra-small-angle neutron scattering measurements show that the pore wall of porous TiO2 is not sharp but is rather diffuse.
Several sets of special directions (SDs) for cubic lattices are proposed, which could be utilized in both theoretical and experimental investigations. These sets allow for the construction in the whole Brillouin zone of some quantities known for a limited number of such SDs.
short communications
The use of quasi-mosaic crystals for the focusing of hard X-rays at high resolution in a Laue lens is proposed. Comparison with traditional mosaic crystals with the same size and energy passband shows that quasi-mosaic crystals increase the signal-to-noise ratio by about an order of magnitude; moreover, for quasi-mosaic crystals no mosaic defocusing occurs.
CIF applications
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iotbx.cif is a comprehensive toolbox for the development of applications that make use of the CIF format.
computer programs
DADIMODO is a program for refining atomic models of multidomain proteins or complexes against small-angle X-ray scattering data. Interdomain distance and orientational restraints, such as those derived from NMR measurements, can be included in the optimization process.
VESTA is a three-dimensional visualization system for crystallographic studies and electronic state calculations. It has been upgraded to the latest version, VESTA 3, which implements many new features.
SAAF is a tool for analyzing small-angle neutron scattering data using analytical model functions. One of its features is the ability to perform de-smearing on data sets with variable and convoluted instrument resolutions.
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ShelXle is a user-friendly graphical user interface for SHELXL. It combines an editor with syntax highlighting for SHELXL-associated files with an interactive graphical display for visualization of a three-dimensional structure.
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The program ANODE determines anomalous (or heavy-atom) densities by reversing the usual procedure for experimental phase determination. Instead of adding a phase shift to the heavy-atom phases to obtain a starting value for the native protein phase, this phase shift is subtracted from the native phase to obtain the heavy-atom substructure phase.
laboratory notes
A sample holder for rough characterization of protein powder by in-house X-ray powder diffraction has been designed. The holder is further adaptable to X-ray absorption spectroscopy measurements, enabling the combination of the two techniques.
A new modification of the zero-background holder is proposed for handling small bulk samples.
A new cuvette has been designed, possessing eight identical chambers, which enables fast acquisition of a data set in biological solution scattering experiments and extrapolation of the data set to infinite dilution within 20 min.
A compact pneumatic device is presented here, capable of simultaneously applying heat (up to ∼470 K) and stress (up to 500 N) to an evacuated fibre sample. Initial results shows slight but significant effects of stress and heating on the internal void structure of poly(p-phenylene terephthalamide) fibres.
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