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Spin waves in yttrium iron garnet (YIG) nano-structures attract increasing attention from the perspective of novel magnon-based data processing applications. For short wavelengths needed in small-scale devices, the group velocity is directly proportional to the spin-wave exchange stiffness constant λ ex . Using wave vector resolved Brillouin light scattering spectroscopy, we directly measure λ ex in Ga-substituted YIG thin films and show that it is about three times larger than for pure YIG. Consequently, the spin-wave group velocity overcomes the one in pure YIG for wavenumbers k > 4 rad/μm, and the ratio between the velocities reaches a constant value of around 3.4 for all k > 20 rad/μm. As revealed by vibrating-sample magnetometry and ferromagnetic resonance spectroscopy, Ga:YIG films with thicknesses down to 59 nm have a low Gilbert damping (α < 10 − 3 ), a decreased saturation magnetization μ 0 M S ≈ 20 mT, and a pronounced out-of-plane uniaxial anisotropy of about μ 0 H u 1 ≈ 95 mT, which leads to an out-of-plane easy axis. Thus, Ga:YIG opens access to fast and isotropic spin-wave transport for all wavelengths in nano-scale systems independently of dipolar effects. [ABSTRACT FROM AUTHOR]

The effect of sapphire-substrate thickness on the curvature and stress in thick hydride vapor phase epitaxial GaN films was studied by high-resolution x-ray diffraction at variable temperatures. The curvature was found to have the maximum value for comparable thicknesses of the film and the substrate, while the stress at the film surface decreases with increasing film thickness and increases with increasing substrate thickness, which is in very good agreement with the simulation results. The curvature at the growth temperature was found to be strongly influenced by the value of the intrinsic tensile strain, which is determined by the film/substrate thickness ratio. [ABSTRACT FROM AUTHOR]

The mosaicity of GaN layers grown by metalorganic vapor phase epitaxy, on (0001) sapphire and exhibiting different grain diameters is studied using high-resolution x-ray diffraction. The coherence lengths, the tilt, and the twist of the mosaic structure are determined utilizing data taken in different x-ray scattering geometries. The results of different models, which were applied, are then compared and discussed. The dislocation densities, obtained from the x-ray data, are compared with the results of plan-view transmission electron microscopy and atomic force microscopy. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Various bacterial species are known to produce metabolites of the 4-quinolone N-oxide class. These compounds have antibiotic activities, and are believed to target the respiration of competing microbes by interfering with menaquinone-binding sites in enzymes of the electron-transport chain. Interestingly, even minor structural changes in related N-oxides produced by the same organism can produce a dramatic difference in antibiotic activity, suggesting possible functional specialization. [ABSTRACT FROM AUTHOR]

Early occurrence of small-fibre neuropathy (SFN) is a common feature of Fabry disease (FD) - an X-linked storage disorder caused by reduced activity of the α-galactosidase A ( α-GAL). Although SFN may result from different disorders, the cause is often unclear. Therefore, we investigated the frequency of FD in patients with SFN of unknown aetiology. Patients with idiopathic SFN, established by sensory quantitative testing and/or skin biopsy, were examined for mutations in the α-GAL gene. Where mutations in the α-GAL gene were identified, levels of globotriaosylceramide (Gb) were measured in urine and blood and the α-GAL activity was evaluated. When new mutations were detected, a diagnostic work-up was performed as well as a Gb accumulation in the skin, lyso-Gb in blood and Gb_24 in urine were proved. Twenty-four of 29 eligible patients were enrolled in the study. Mutations in the α-GAL gene were observed in five patients. A typical mutation for FD (c.424T>C, [C142R]) was detected in one patient. In four patients, a complex intronic haplotype within the α-GAL gene (IVS0-10C>T [rs2071225], IVS4-16A>G [rs2071397], IVS6-22C>T [rs2071228]) was identified. The relevance of this haplotype in the pathogenesis of FD remains unclear until now. However, these patients showed increased concentrations of Gb and/or lyso-Gb, while no further manifestations for FD could be proved. Fabry disease should be considered in patients with SFN of unknown aetiology, and screening for FD should be included in the diagnostic guidelines for SFN. The significance of the intronic haplotype regarding SFN needs further evaluation. [ABSTRACT FROM AUTHOR]

The strain distribution in thick hydride vapor-phase epitaxial (HVPE)-GaN layers grown on metal-organic vapor-phase epitaxial GaN templates was studied by means of photoluminescence, x-ray mapping, and lattice parameter analysis. A variable temperature x-ray study of the film curvature was used for verification of the strain type. The relation between the strain inhomogeneity and the wafer bending in films residing on sapphire and freestanding on the thickness of the layer and the substrate is analyzed. Possibilities to improve the uniformity of the film characteristics and to reduce the bending of the HVPE-GaN films are discussed. [ABSTRACT FROM AUTHOR]

Elevated levels of glutamate, an endogenous excitatory amino acid, contribute to the development of neuronal injury in various cerebral diseases. Using a microdialysis approach, the response of extracellular levels of amino acids and metabolic parameters to glutamine synthetase inhibition by l-methionine sulfoximine was monitored simultaneously in the hippocampal formation and in the frontal cortex of the rabbit brain. In the hippocampal formation the decrease of glutamine levels during l-methionine sulfoximine treatment was more pronounced than in the frontal cortex, and was accompanied by a delayed decline of extracellular glutamate concentrations. Furthermore, l-methionine sulfoximine diminished the increase of lactate and pyruvate concentrations in the hippocampal formation, but not in the frontal cortex. Neither l-methionine sulfoximine treatment nor microdialysis probe insertion caused neuronal apoptosis, as measured by in situ tailing. An impaired function of hippocampal astrocyte glutamate uptake mechanisms or a higher functional capacity of the cortical glutamine synthetase may be possible explanations for the differences demonstrated. The present data are in accordance with regional differences in glutamine synthetase activation during bacterial meningitis and may explain, in part, the higher susceptibility of certain areas of the hippocampal formation (i.e., the dentate gyrus) to neuronal injury. [ABSTRACT FROM AUTHOR]

Addition of NHC→SiCl4 to the highly Lewis acidic bis(pentafluoroethyl)silane ((C2F5)2SiH2) afforded the salt [(NHC)2SiCl2H][(C2F5)2SiCl3] with pentacoordinate silicon in the cation and the anion. The anion represents the first example of a chlorosilicate structurally characterized in the solid state. In this reaction, the long sought pentacoordinate NHC-adduct of silicochloroform was identified as an intermediate and its crystal structure is presented. [ABSTRACT FROM AUTHOR]