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July 2008 issue
Cover illustration: Schematic of a scanning X-ray microprobe with a segmented transmission detector (see Hornberger, de Jonge, Feser, Holl, Holzner, Jacobsen, Legnini, Paterson, Rehak, Strüder and Vogt, pages 355-362). Three different segmentations are shown on the left. The difference signal between opposing segments measures beam deflections and therefore phase gradients in the specimen. The bottom figures illustrate the difference between absorption contrast (total transmitted intensity) and differential phase contrast (difference of opposing segments) for a cardiac myocyte imaged at 10 keV photon energy, and a diatom imaged at 1.79 keV.
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research papers
Spatial resolution measurements at Advanced Light Source beamline 1.4.4 are used to determine the wavelengths at which a cross-over from diffraction-limited to electron-beam-source-size-limited resolution occurs. Performance is then predicted for different synchrotrons, beamline optics and endstation microscopes.
An in situ synchrotron X-ray imaging technique for visualizing the water in a polymer electrolyte fuel cell has been developed. The technique is very effective and useful for studying water management in a polymer electrolyte fuel cell.
The radiation properties of two classes of insertion devices, a long-period wiggler and a short-period undulator, are calculated and compared, using different computer codes. Special care is found to be needed when modeling these properties.
An optimized crystal design for a low-background Bonse–Hart camera for small-angle X-ray scattering is presented. Details about achieving the best surface quality of the crystals are described giving also perspectives for further applications in X-ray optics.
Research on underground motion at the SSRF site with and without a heavy truck is reported.
A segmented transmission detector has been developed and installed at sector 2 instruments at the Advanced Photon Source for differential phase-contrast imaging in parallel with absorption and fluorescence measurements.
A three-dimensional structured scintillator capable of 1 µm resolution has been characterized with Monte Carlo simulations for 30–200 keV X-rays with a factor of 5–15 gain in efficiency over unstructured scintillators.
X-ray transmission mirrors, which function as high-pass energy filters, have been made out of silicon nitride and tested in synchrotron X-ray beams. The high-energy cut-off can be selected by adjusting the incidence angle of the transmission mirror.
Element-specific microtomographic analysis of the central nervous system of adult Drosophila melanogaster stained with gold and platinum probes has revealed the nerve tissue structure responsible for biological functions.
X-ray photon correlation spectroscopy was performed on a colloidal suspension of hard spheres under shear flow. This study describes a new experimental method that can be used to avoid X-ray-induced beam damage while measuring `internal' mesoscale dynamics in soft-matter or biological systems.
The SSRF R&D magnet girder assemblies are structure optimized. Vibration measurements have been performed to investigate the mechanical stability and influence of cooling water on magnet vibration.
Two semi-transparent X-ray beam-position monitors have been developed to study the submicroradian angular stability of the X-ray beam at a nanofocusing beamline.
The groove-function dependence of the wavefront aberration coefficients of gratings is reported.
X-ray kinoform lenses of the clessidra type, which are composed of many small triangular prisms, can be used under suitable conditions effectively as arrays of refractive micro-lenses. These arrays can provide relatively large apertures in long-focal-length focusing.
A vacuum-compatible portable chamber, optimized for working in a middle-pressure regime and adaptable to UHV conditions, is presented. Its compact design and its modularity are highlighted. These characteristics make it a very versatile piece of equipment, useful for in situ X-ray scattering studies of various systems under different conditions.
short communications
Radiation damage by heating of samples at high-flux synchrotron radiation circular dichroism spectroscopy beamlines can result in protein denaturation. This study compares the degree of damage that occurs at a number of beamlines worldwide in order to define the threshold beam flux density above which significant denaturation occurs.
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