Local Buckling of Composite Laminated Cylindrical Shells with Oblique Edges under External Pressure: Asymptotic and Finite Element Simulations

The problem of local buckling ofa thin composite laminated cylindrical shell under external pressure is studied. Each layer of the shell is assumed to be isotropic. The special case of the shell being non-circular and/or having no plane edges is considered here. Presupposing that buckling takes place in the neighborhood of some so-called “weakest” generator, the asymptotic Tovstik’s method is appliedfinding the critical pressure and the elgenmodes. As an example, buckling of a three-layered circular thin cylinder with a sloped edge is investigated. Besides the asymptotic approach the finite element simulation is applied to facilitate the estimation of the range to which the results obtained can be applied

Positronium chemistry studied by AMOC measurements using a relativistic positron beam

Beam-based Age-Momentum Correlation (β+γΔE AMOC) measurements using an MeV positron beam have become a powerful tool to study chemical reactions of positronium by time-domain observations of the different positron states tagged by the Doppler-broadening (ΔE) characteristics of the 511 keV annihilation radiation. As an example, the investigation of the spin-conversion reaction in the system HTEMPO/methanol is reported. The experimental data for small HTEMPO concentrations can be fitted quite well to a rate-equation model containing the conversion rate as the only adjustable parameter. This model can presumably be applied not only to spin conversion but also to other chemical reactions and to inhibition of positronium. Possible effects of oxidation, complex formation, and inhibition are discussed by way of examples

Numerical and experimental investigation of dielectric recovery in super-critical nitrogen

A supercritical (SC) nitrogen (N2) switch is designed and tested. The dielectric strength and recovery rate of the SC switch are investigated by experiments. In order to theoretically study the discharge and recovery process of the SC N2 switch under high repetition rate operation, a numerical model is developed. For SC N2 with initial parameters of p = 80.9 bar and T = 300 K, the simulation results show that within several nanoseconds after the streamer bridges the switch gap, the spark is fully developed and this time depends on the applied electric field between electrodes. During the whole discharge process, the maximum temperature in the channel is about 20 000 K. About 10μs after the spark excitation of 200 ns duration, the temperature on the axis decays to Taxis 1500 K, mainly contributed by the gas expansion and heat transfer mechanisms. After 100μs, the dielectric strength of the gap recovers to above half of the cold breakdown voltage due to the temperature decay in the channel. Both experimental and numerical investigations indicate that supercritical fluid is a good insulating medium that has a proved high breakdown voltage and fast recovery speed

Relation between composition and vacant oxygen sites in the mixed ionicelectronic conductors La5.4W1 yMyO12 delta M Mo, Re; 0 lt; y lt; 0.2 and their mother compound La6 xWO12 delta 0.4 lt; x lt; 0.8

A detailed analysis of specimen composition, water uptake and their interrelationship in the systems La6 xWO12 amp; 948; 0.4 amp; 8804; x amp; 8804;0.8 and La6 xW1 yMyO12 amp; 948; 0 amp; 8804;y amp; 8804;0.2; M Mo, Re is presented. The three specimen series were investigated in dry and wet D2O conditions. A systematic trend in mass loss and onset temperature variation was observed in La6 xWO12 amp; 948; 0.4 amp; 8804;x amp; 8804;0.8 . Even very small amounts lt; 1 wt of secondary phases were found to notably modify the specimen s water uptake and onset temperature of mass loss. The theoretical model for vacancy concentration available was used to calculate the vacant oxygen sites starting from mass loss values determined by thermogravimetry. A discrepancy between the calculated and observed concentration of vacant oxygen sites is observed for all three systems. The effect of substitution of W by Re or Mo on the vacancy amount is explained taking into account diffraction measurements and information on the oxidation state of the substituting elements Mo and R

Direct observation of Levy flight of holes in bulk n-InP

We study the photoluminescence spectra excited at an edge side of n-InP slabs and observed from the broadside. In a moderately doped sample the intensity drops off as a power-law function of the distance from the excitation - up to several millimeters - with no change in the spectral shape.The hole distribution is described by a stationary Levy-flight process over more than two orders of magnitude in both the distance and hole concentration. For heavily-doped samples, the power law is truncated by free-carrier absorption. Our experiments are near-perfectly described by the Biberman-Holstein transport equation with parameters found from independent optical experiments.Comment: 4 pages, 3 figure

Monoclonal antibodies against human astrocytomas and their reactivity pattern

The establishment of hybridomas after fusion of X63-Ag8.653 mouse myeloma cells and splenocytes from mice hyperimmunized against human astrocytomas is presented. The animals were primed with 5 × 106 chemically modified uncultured or cultured glioma cells. Six weeks after the last immunization step an intrasplenal booster injection was administrated and 3 days later the spleen cells were prepared for fusion experiments. According to the specificity analysis of the generated antibodies 7 hybridoma products (MUC 7-22, MUC 8-22, MUC 10-22, MUC 11-22, MUC 14-22, MUC 15-22 and MUC 2-63) react with gliomas, neuroblastomas and melanomas as well as with embryonic and fetal cells but do not recognize non-neurogenic tumors. The selected monoclonal antibodies (McAbs) of IgG1 and IgG2a isotypes are not extensively characterized but these antibodies have been demonstrated to be reactive with a panel of glioma cell lines with varying patterns of antigen distribution. Using the McAbs described above and a series of cryosections of glioma biopsies and paraffin sections of the same material as well as glioma cultures established from these, variable antigenic profiles among glioma cell populations could be demonstrated. From these results it is evident that there is not only a distinct degree of antigenic heterogeneity among and within brain tumors, but also that the pattern of antigenic expression can change continuously. Some of the glioma associated antigens recognized by the selected antibodies persist after fixation with methanol/acetone and Karnovsky's fixative and probably are oncoembryonic/oncofetal antigen(s). The data suggest that the use of McAbs recognizing tumor associated oncofetal antigens in immunohistochemistry facilitates objective typing of intracranial malignancies and precise analysis of fine needle brain/tumor biopsies in a sensitive and reproducible manner

The global wave front set of tempered oscillatory integrals with inhomogeneous phase functions

We study certain families of oscillatory integrals $I_\varphi(a)$, parametrised by phase functions $\varphi$ and amplitude functions $a$ globally defined on $\mathbb{R}^d$, which give rise to tempered distributions, avoiding the standard homogeneity requirement on the phase function. The singularities of $I_\varphi(a)$ are described both from the point of view of the lack of smoothness as well as with respect to the decay at infinity. In particular, the latter will depend on a version of the set of stationary points of $\varphi$, including elements lying at the boundary of the radial compactification of $\mathbb{R}^d$. As applications, we consider some properties of the two-point function of a free, massive, scalar relativistic field and of classes of global Fourier integral operators on $\mathbb{R}^d$, with the latter defined in terms of kernels of the form $I_\varphi(a)$.Comment: 30 pages, 2 figures, mistakes and typos correctio

Ein implantierbares Telemetriesystem zur Impedanzspektroskopie

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Die kontinuierliche Überwachung des intrakorporalen Zustandes von Geweben beispielsweise zur Erkennung ischämischer Vorgänge nach gefäßchirurgischen Eingriffen oder im Rahmen der Rejektionsdiagnostik läßt sich durch bisher vorhandene Meßsysteme nur bedingt erreichen. Speziell die direkte Erfassung sensitiver Gewebeparameter über einen längeren Zeitraum ohne Belastung für den Patienten stellt in diesem Zusammenhang ein Problem dar. In der nachfolgenden Arbeit wird das Konzept eines implantierbaren Telemetriesystems vorgestellt, das die Bewertung des Gewebezustandes über die Messung der frequenzabhängigen Bioimpedanz ermöglicht. Besondere Beachtung wird der Auslegung und Umsetzung der einzelnen Systemkomponenten sowie der Vorstellung erster in vitro Messungen zur Evaluierung des Meßsystems geschenkt