Sums of free membrane eigenvalues

LetD be a simply connected domain in the plane which is the image of the unit disk under a normalized conformal mapping, and let μ₁=0<μ₂≤μ₃ be the free membrane eigenvalues. We prove that for anyn≥2,

Synthese und dynamisches verhalten von einigen pentamethylcyclopentadienylsilanen und -germanen

By reaction of pentamethylcyclopentadienyllithium (pcpLi) with the corresponding chloro-silanes and -germanes, the h¹-pcp-silanes and -germanes I–IX are synthesized. Nucleophilic substitution reactions at the pcp-chlorogermane VII lead to the h¹-pcp-germanes X–XIII. The activation parameters for the sigmatropic rearrangements in these compounds have been evaluated from the ¹H DNMR data. They show little influence of the remaining ligands at silicon or germanium on the speed of these dynamic processes.     

UV-A breakage sensitivity of human chromosomes as measured by COMET-FISH depends on gene density and not on the chromosome size

COMET-FISH, a single cell-based combination of COMET-assay (also known as single cell gel electrophoresis (SCGE)) with fluorescence in situ hybridization (FISH) allows region specific studies on DNA stability and damage. COMET-FISH can be used to investigate UV-A-induced DNA damage of selected whole chromosomes. In the present work, a modified COMET-FISH protocol with whole chromosome painting probes was used to study whether UV-A-induced DNA damage is distributed randomly over the whole genome or occurs at preferred sites. The study was performed with 12 different chromosome painting probes (for chromosomes 1, 2, 3, 8, 9, 11, 14, 18, 19, 21, X and Y). The results on human lymphocytes irradiated with 500 kJ/m2 at a wavelength of 365 nm indicate that the induced number of chromatin strand breaks does not correlate with the chromosome size. They therefore are distributed in a non-random manner. For example, fragments of the gene-rich chromosome chromosome 1 were found in the comet tail in only 3% of the examined cells, and thus chromosome 1 is rather stable, whereas fragmentation of the gene-poor chromosome 8 was observed in 25% of all comets. On the basis of all 12 chromosomes analyzed, an inverse correlation between the density of active genes and the sensitivity toward UV-A radiation is found.     

Near-infrared light-fiber spectroscopic reaction monitoring of the synthesis of diphenylurethane

The extension from the mid-infrared (MIR) to the near-infrared (NIR) region alongside the introduction of light-fiber optics has had a significant impact on vibrational spectroscopy for chemical quality- and process-control. In the present contribution the application of NIR light-fiber spectroscopy to the remote monitoring of the synthesis of diphenylurethane shall demonstrate the potential of this analytical technique.     

Further Characterization of UVB Radiation Effects on Langerhans Cells: Altered Expression of the Costimulatory Molecules B7-1 and B7-2

We have reported previously that low-dose UVB radiation (UVBR, 50-200 J/m²) perturbs the antigen-presenting cell (APC) function of murine Langerhans cells (LC) by interfering with yet undefined costimulatory signals. In this study, we investigated (1) the effects of UVBR on the expression of the costimulatory molecules B7-1 and B7-2 on murine LC, (2) the functional consequences of defective B7-1 and B7-2 signalling on primary and secondary T-cell responses induced by LC and (3) the mechanism by which UVBR interferes with B7-1 and B7-2 expression. Ultraviolet-B radiation dose-dependently inhibited the culture-induced upregulation of B7-1 and B7-2 on LC from both UVB-susceptible (UVB_s, C57BL/6) and UVB-resistant (UVB_R, Balb/c) mice and abrogated their capacity to stimulate proliferation of naive alloreactive T cells and of the KLH (keyhole limpet hemocyanin)-specific T helper (Th)1 clone HDK-1. The UVBR-induced suppression of B7-1 and B7-2 on LC and their perturbed APC function were related, because exogenous triggering of the B7/CD28 pathway with a stimulatory monoclonal antibody (mAb) for CD28 to UVB-irradiated LC partially restored T-cell proliferation. Such reconstitution was not observed when the mAb was added to killed LC, indicating that the UVBR-induced suppression of APC function was not due to lethal effects on LC. Conditioned supernatants from UVB-irradiated epidermal cells did not inhibit the functional upregulation of B7-1 and B7-2, suggesting that UVBR inhibits B7-1 and B7-2 upregulation by acting directly on LC and not by altering LC costimulatory function via release of soluble immunosuppressive factors. In conclusion, UVBR distorts the functional expression of B7-1 and B7-2 on LC from both UVBs and UVBR mice, thereby contributing to the failure of UVB-irradiated LC to stimulate resting alloreactive T cells or KLH-specific Thl cells.     

Homogenitätsuntersuchungen und Bestimmung der molaren Konzentration x an CdxHg1–xTe mit Hilfe der Elektronenstrahlmikrosonde

The semiconductor Cd_xHg_1–xTe serves as a starting material for the production of infrared detectors with a high detectivity and a small time constant. Cd_xHg_1–xTe single crystals are necessary to manufacture detectors efficiently. The single crystals should not contain segregations and have to include a homogeneous molar concentration x. An electron microprobe X-ray analyzer meets all requirements expected from the measuring method for checking the homogeneity of Cd_xHg_1–xTe crystals. — Results of qualitative and quantitative studies in the microscopical and macroscopical range are presented. Typical defects of the crystals were detected by using the qualitative electron microprobe X-ray analysis. The quantitative analysis was carried out with standard samples. The method for determination of the molar concentration x of the standard samples is described.