10,861 research outputs found

    A New Look at the Higgs-Kibble Model

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    An elementary perturbative method of handling the Higgs-Kibble models and deriving their relevant properties, is described. It is based on Wightman field theory and avoids some of the mathematical weaknesses of the standard treatments.Comment: Based on a talk delivered at the `Ringberg Symposium' in honor of Wolfhart Zimmermann, February 200

    What is the Magnetic Moment of the Electron?

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    A direct definition of the intrinsic magnetic moment of the electron is given, which does not use infrared regularizations and interactions with external fields. The expression does not depend on the unavoidable ambiguities of the definition of a 1-electron state (exact form of its soft photon cloud). The method leads to the same analytic expression as the conventional approach, thus preserving the excellent agreement between theory and experiment.Comment: 24 pages, 4 figures, uses axodraw.st

    Plastic dislocation and incompatibility density as indicators for residual stresses

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    Residual stresses in forming simulations are typically investigated by analyzing the remaining stress state after removing all external loadings. However, the generation of the stress state during forming remains unknown. As a remedy, we use the plastic and elastic dislocation and incompatibility densities - derived from continuum mechanical and differential geometrical considerations - as indicators to track the generation of residual stresses through out a forming operation. Theoretical backgrounds for small and large strain plasticity are highlighted and practical aspects regarding implementation are provided. Two examples demonstrate the functionality of the approach, whereby the plastic incompatibility density in phenomenological, multiplicative large strain plasticity serves as indicator

    Interface of the polarizable continuum model of solvation with semi-empirical methods in the GAMESS program

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    An interface between semi-empirical methods and the polarized continuum model (PCM) of solvation successfully implemented into GAMESS following the approach by Chudinov et al (Chem. Phys. 1992, 160, 41). The interface includes energy gradients and is parallelized. For large molecules such as ubiquitin a reasonable speedup (up to a factor of six) is observed for up to 16 cores. The SCF convergence is greatly improved by PCM for proteins compared to the gas phase

    Remote infrared spectroscopy of the earth

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    The infrared reflexion-spectra of minerals and rocks are used for remote sensing of targets. The reflexion-spectra of silicate rocks vary quite significantly from mineral to mineral in the wave length region from 8 to 12 micrometers. The rock forming minerals like quartz, feldspar, mica and the clay minerals show very different spectral shapes and positions of their maximum of the spectral reflexion. The presence of a good atmospherical window in that spectral region makes the method of differential-reflexion measurement feasible, for remote sensing application. A tunable CO2-laser was used as transmitter for infrared radiation. Laboratory tests showed the feasibility of the method under different simulated environmental conditions. Because of the very narrow bandwidth of the laser-emission lines, reflexion-spectra with extremely high spectral resolution were obtained

    Homogenization of heterogeneous, fibre structured materials

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    This contribution presents a multi-scale homogenization method to model Ô¨Ābre structured materials. On the macroscopic level textiles are characterized by a large area-to-thickness ratio, such that a discretization with shell elements is numerically eÔ¨Écient. The material behavior is strongly inÔ¨āuenced by the heterogeneous micro structure. To capture the contact on the micro level, the RVE is explicitly modelled by means of a volumetric micro sample and a shell speciÔ¨Āc homogenization scheme is applied to transfer the microscopic response to the macro level. Theoretical aspects are discussed and a numerical example for contact behavior of a periodic knitted structure is give

    The origin of compression influences geometric instabilities in bilayers

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    Geometric instabilities in bilayered structures control the surface morphology in a wide range of biological and technical systems. Depending on the application, different mechanisms induce compressive stresses in the bilayer. However, the impact of the chosen origin of compression on the critical conditions, post-buckling evolution and higher-order pattern selection remains insufficiently understood. Here, we conduct a numerical study on a finite-element set-up and systematically vary well-known factors contributing to pattern selection under the four main origins of compression: film growth, substrate shrinkage and whole-domain compression with and without pre-stretch. We find that the origin of compression determines the substrate stretch state at the primary instability point and thus significantly affects the critical buckling conditions. Similarly, it leads to different post-buckling evolutions and secondary instability patterns when the load further increases. Our results emphasize that future phase diagrams of geometric instabilities should incorporate not only the film thickness but also the origin of compression. Thoroughly understanding the influence of the origin of compression on geometric instabilities is crucial to solving real-life problems such as the engineering of smart surfaces or the diagnosis of neuronal disorders, which typically involve temporally or spatially combined origins of compression

    Inverse form finding with h-adaptivity and an application to a notch stamping process

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    The aim is to determine the optimized semi-finished workpiece geometry to its given target geometry after a forming process. Hereby, a novel approach for inverse form finding, a type of a shape optimization, is applied to a notch stamping process. As a special feature, h-adaptive mesh refinement is considered within the iteratively performed forming simulation
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