Mapping fibre orientation in complex-shaped biological systems with micrometre resolution by scanning X-ray microdiffraction

A fully automated procedure to extract and to image local fibre orientation in biological tissues from scanning X-ray diffraction is presented. The preferred chitin fibre orientation in the flow sensing system of crickets is determined with high spatial resolution by applying synchrotron radiation based X-ray microbeam diffraction in conjunction with advanced sample sectioning using a UV micro-laser. The data analysis is based on an automated detection of azimuthal diffraction maxima after 2D convolution filtering (smoothing) of the 2D diffraction patterns. Under the assumption of crystallographic fibre symmetry around the morphological fibre axis, the evaluation method allows mapping the three-dimensional orientation of the fibre axes in space. The resulting two-dimensional maps of the local fibre orientations - together with the complex shape of the flow sensing system - may be useful for a better understanding of the mechanical optimization of such tissues.

Barley oxalate oxidase is a hexameric protein related to seed storage proteins: evidence from X-ray crystallography

The oxalate oxidase enzyme expressed in barley roots is a thermostable, protease-resistant enzyme that generates H2O2. It has great medical importance because of its use to assay plasma and urinary oxalate, and it has also been used to generate transgenic, pathogen-resistant crops. This protein has now been purified and three types of crystals grown. X-ray analysis shows that the symmetry present in these crystals is consistent with a hexameric arrangement of subunits, probably a trimer of dimers. This structure may be similar to that found in the related seed storage proteins.

Solving surface structures from normal incidence X-ray standing wave data

A program is provided to determine structural parameters of atoms in or adsorbed on surfaces by refinement of atomistic models towards experimentally determined data generated by the normal incidence X-ray standing wave (NIXSW) technique. The method employs a combination of Differential Evolution Genetic Algorithms and Steepest Descent Line Minimisations to provide a fast, reliable and user friendly tool for experimentalists to interpret complex multidimensional NIXSW data sets.

A potential lag between the open solar magnetic source flux and solar EUV and X-ray emissions as measured by the Earth's ionosphere during total solar eclipses

Measurements of the ionospheric E-region during total solar eclipses have been used to provide information about the evolution of the solar magnetic field and EUV and X-ray emissions from the solar corona and chromosphere. By measuring levels of ionisation during an eclipse and comparing these measurements with an estimate of the unperturbed ionisation levels (such as those made during a control day, where available) it is possible to estimate the percentage of ionising radiation being emitted by the solar corona and chromosphere. Previously unpublished data from the two eclipses presented here are particularly valuable as they provide information that supplements the data published to date. The eclipse of 23 October 1976 over Australia provides information in a data gap that would otherwise have spanned the years 1966 to 1991. The eclipse of 4 December 2002 over Southern Africa is important as it extends the published sequence of measurements. Comparing measurements from eclipses between 1932 and 2002 with the solar magnetic source flux reveals that changes in the solar EUV and X-ray flux lag the open source flux measurements by approximately 1.5 years. We suggest that this unexpected result comes about from changes to the relative size of the limb corona between eclipses, with the lag representing the time taken to populate the coronal field with plasma hot enough to emit the EUV and X-rays ionising our atmosphere.

Wide-angle X-ray scattering for swollen and glassy poly(2-hydroxyethyl methacrylate)

The wide angle X-ray scattering from glassy poly(2-hydroxyethyl methacrylate) (1) is presented together with that obtained from oriented and swollen samples. The scattering is compared with that previously reported for poly(methyl methacrylate) (PMMA) and the structure discussed in relation to this polymer. The chain conformation is similar to that of PMMA, although some measure of molecular interlocking appears to reduce the main interchain peak while correlated regions of inaccessible free volume between the substantial side groups are held responsible for the main peak at s = 1,25 Å−1.