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Abstract: Dehydration of protein crystals is rarely used, despite being a post-crystallization method that is useful for the improvement of crystal diffraction properties, as it is difficult to reproduce and monitor. A novel device for hydration control of macromolecular crystals in a standard data-collection environment has been developed. The device delivers an air stream of precise relative humidity that can be used to alter the amount of water in macromolecular crystals. The device can be rapidly installed and is fully compatible with most standard synchrotron X-ray beamlines. Samples are mounted in cryoloops and the progress of dehydration can be monitored both optically and by the acquisition of diffraction images. Once the optimal hydration level has been obtained, cryocooling is easy to achieve by hand or by using a sample changer. The device has been thoroughly tested on several ESRF beamlines and is available to users.

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Abstract: This study investigated Zn adsorption to an extracellular polymeric substance (EPS)-producing bacterial strain, Bacillus licheniformis S-86. Batch metal adsorption experiments and spectroscopic (EXAFS) analysis were conducted using both native (EPS-covered) cells and EPS-free cells in order to assess the contribution made by EPS to metal adsorption by this strain. Thermodynamic modelling of the macroscopic adsorption data indicated that Zn complexation to both native and EPS-free cells was predominantly to carboxyl (pK(a) 5.3-5.4) and phosphate (pK(a) 7.4-7.5) functional groups, but with some adsorption to phosphodiester (pK(a) 3.3-3.4) groups also evident. EXAFS analysis shows Zn-carboxyl complexation, but possibly with a significant contribution from a second, phosphate functional group. Apparently, EPS removal does not affect the metal adsorption capacity at the metal: biomass ratios used here. As the concentration of carboxyl and phosphate functional groups is only slightly affected by EPS extraction, complexation to these functional groups explains why EPS removal does not reduce the amount of Zn adsorbed by the cells. It was also observed that EPS production induces aggregation of cells in suspension. This may reduce the cell surface area available for metal adsorption, thus counteracting any greater availability of metal-complexing ligands in the EPS layer compared to an EPS-free cell surface. Furthermore, the EPS layer appears to be the major source of dissolved organic carbon (DOC) released to solution during the metal adsorption experiments. This DOC may reduce metal binding to the cell surfaces by acting as a competing complexing ligand. These observations have implications for industrial application of biofilms and suggest that over-production of EPS in bio-reactors may reduce the metal removal efficiency of the biomass. (C) 2009 Elsevier Inc. All rights reserved.

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Abstract: This article addresses an important current development in medical and biological imaging: the possibility of imaging soft tissue at resolutions in the micron range using hard X-rays. Challenging environments, including the cochlea, require the imaging of soft tissue structure surrounded by bone. We demonstrate that cochlear soft tissue structures can be imaged with hard X-ray phase contrast. Furthermore, we show that only a thin slice of the tissue is required to introduce a large phase shift. It is likely that the phase contrast image of the soft tissue structures is sufficient to image the structures even if surrounded by bone. For the present set of experiments, structures with low-absorption contrast have been visualized using in-line phase contrast imaging and a grating interferometer. The experiments have been performed at the Advanced Photon Source at Argonne National Laboratories, a third generation source of synchrotron radiation. The source provides highly coherent X-ray radiation with high-photon flux (>1012 photons/s) at high-photon energies (5–70 keV). Radiographic and light microscopy images of the gerbil cochlear slice samples were compared. It has been determined that a 20-?m thick tissue slice induces a phase shift between 1/3? and 2/3?. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc.

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Abstract: Spin-polarized neutron-reflectivity measurements have been performed on superconducting Pb films. For fields applied in the plane of the film we are able to determine the magnetic field profile across the thickness of the film in the superconducting state. This allows the direct observation of distinct mesoscopic ground states in this geometry, from Meissner expulsion to a double row of vortices, which occur as a function of film thickness and external magnetic field. The data can be compared directly with solutions of the time-dependent Ginzburg-Landau equations, where we demonstrate good agreement between data and simulation. This provides a powerful demonstration of this widely applicable experimental technique to study mesoscopic ground states and a useful validation of this theoretical approach.

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Abstract: We used hard X-ray photoelectron spectroscopy (HAXPES) with 8 keV X-rays to investigate the Is emission of carbon. We recorded spectra extending from the peak of the C 1s electrons ("elastic" line) to electrons with Lip to 110 eV energy-loss. Using two samples side by side, we Could compare the inelastic mean free paths (IMFPs) of the electrons of almost 8 keV in diamond and graphite and find them to be practically identical despite about 50% difference in densities. Published extrapolations of their IMFP calculations at lower energies are in good agreement with this result. We show that information from the almost structureless region of overlapping multiple extrinsic energy-losses can be used to quantify the fraction of photoelectrons experiencing intrinsic energy-losses (those due to the sudden creation of the hole). We find that this fraction is 58% of the primary excited C 1s electrons for diamond and is practically the same for graphite. This is at first sight an unexpected result since hole-screening should differ in a semimetal from that in an insulator The observation can be accounted for by dynamic screening in contrast to static screening. (C) 2009 Elsevier B.V. All rights reserved.