TY - GEN A1 - Hellwig, Udo A1 - Nikolaus, Hartwig T1 - CFD-Simulation zur Untersuchung des Strömungsverhaltens in Strukturrohren T2 - Wissenschaftliche Beiträge 2004 N2 - Die CFD (Computational Fluid Dynamics)-Simulation hat mittlerweile in alle technischen Bereiche Einzug gehalten, in denen die Vorhersage strömungstechnischer Ereignisse relevant ist. Nach wie vor ist allerdings eine Validierung von Rechenergebnissen mit Messdaten unerlässlich, um zu vertrauenswürdigen Simulationsergebnissen zu kommen. Dies ist u. a. darauf zurückzuführen, dass die am Markt verfügbare CFD-Software darauf ausgerichtet ist, ein möglichst breites Anwendungsspektrum zu bedienen. Die implementierten Berechnungsmodelle müssen im Rahmen der Modellierung durch die Wahl geeigneter Randbedingungen an den zu untersuchenden Anwendungsfall angepasst werden. Y1 - 2004 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-3991 SN - 0949-8214 VL - 9 SP - 26 EP - 33 ER - TY - JOUR A1 - Wolf, Bodo A1 - Richter, Asta T1 - The concept of differential hardness in depth sensing indentation JF - New Journal of Physics N2 - Since in-depth sensing indentation load–depth data of the entire loading–unloading cycle are available, more information than a single hardness value and an elastic modulus can be extracted from the experimental data. The conventional hardness H (h) = F (h)/Ac(h) and the differential hardness Hd(h)=dF/dAc are calculated as continuous functions of depth h and compared to each other in this paper (F: load, Ac: contact area). It turns out that Hd describes the momentary material resistance to deformation, whereas H integrates over deformation states from first tip–sample contact to current penetration h. This difference is particularly important for materials not homogeneous in depth (e.g. layer systems), and for situations where time-dependent external factors influence the momentary deformation resistance. Photoplasticity is considered as an example for the latter. Y1 - 2003 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-5657 SN - 1367-2630 VL - 5 IS - 15 SP - 15.1 EP - 15.17 ER - TY - JOUR A1 - Grytsenko, Kostyantyn A1 - Lozovski, Valeri A1 - Strilchuk, Galyna A1 - Schrader, Sigurd T1 - Evaluation of the Mechanism of the Gold Cluster Growth during Heating of the Composite Gold-Polytetrafluoroethylene Thin Film JF - Nanomaterials N2 - Nanocomposite films consisting of gold inclusions in the polytetrafluoroethylene (PTFE) matrix were obtained by thermal vacuum deposition. Annealing of the obtained films with different temperatures was used to measure varying of film morphologies. The dependence of optical properties of the films on their morphology was studied. It was established that absorption and profile of the nanocomposite film obtained by thermal vacuum deposition can be changed with annealing owing to the fact that different annealing temperatures lead to different average particle sizes. A method to calculate the optical properties of nanocomposite thin films with inclusions of different sizes was proposed. Thus, comparison of experimental optical spectra with the spectra obtained during the simulation enables estimating average sizes of inclusions. The calculations give the possibility of understanding morphological changes in the structures. KW - nanocomposite KW - gold KW - polytetrafluoroethylene KW - optical spectroscopy KW - microscopy KW - thin film Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-6387 SN - 2079-4991 VL - 2 IS - 4 SP - 366 EP - 378 ER - TY - JOUR A1 - Enders, Peter T1 - Historical Prospective: Boltzmann’s versus Planck’s State Counting—Why Boltzmann Did Not Arrive at Planck’s Distribution Law JF - Journal of Thermodynamics N2 - Why does Planck (1900), referring to Boltzmann’s 1877 probabilistic treatment, obtain his quantum distribution function while Boltzmann did not? To answer this question, both treatments are compared on the basis of Boltzmann’s 1868 three-level scheme (configuration—occupation—occupancy). Some calculations by Planck (1900, 1901, and 1913) and Einstein (1907) are also sketched. For obtaining a quantum distribution, it is crucial to stick with a discrete energy spectrum and to make the limit transitions to infinity at the right place. For correct state counting, the concept of interchangeability of particles is superior to that of indistinguishability. Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-6281 SN - 1687-9252 VL - 2016 ER - TY - GEN A1 - Harendt, Andreas A1 - Beyer, Harald A1 - Rolle, Siegfried T1 - Die näherungsweise Lösung der elektrostatischen Aufgabe mit der Finite – Element – Methode zur Modellierung behinderter elektrischer Entladungen T2 - Wissenschaftliche Beiträge 2002 N2 - Es wird erläutert, warum man mit der Finite-Element-Methode (FEM) das elektrostatische Problem mit Grenzflächen und darauf befindlichen Flächenladungen prinzipiell nicht lösen kann. Es werden dann Verfahren entwickelt, dies näherungsweise zu tun. Anschließend wird eine Methode entwickelt, die es gestattet, aus den so erhaltenen Lösungen näherungsweise konsistent auf die Ausgangsgleichungen zurückzurechnen und so den Driftterm der Kontinuitätsgleichung für die hydrodynamische Modellierung einer Gasentladung zu ermitteln. Y1 - 2002 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-6852 SN - 0949-8214 VL - 7 SP - 15 EP - 24 ER - TY - GEN A1 - Marx, Mathias T1 - Untersuchung von bipolaren Vakuumbögen auf Erste-Wand-Materialien N2 - Die vorliegende Arbeit untersucht bipolare Vakuumbögen auf Erste-Wand-Materialien von Fusionsreaktoren. Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus-1687 ER - TY - GEN A1 - Tolkiehn, Günter-Ulrich T1 - Untersuchung der Lumineszenz von festem Xenon mit Hilfe von Emissions- und Anregungsspektroskopie im Temperaturbereich von 5K bis 75K T1 - Investigation of the luminescence of solid Xenon by menas of emission- and excitation-spectroscopy in the temperature range from 5K to 75K N2 - Verschiedene Eigenschaften der Emissions- und Anregungsspektren von festem Xenon wurden im Detail untersucht. Wesentliche Aspekte konnten gut mit Hilfe der Vorstellung der Diffusionsbewegung des freien n=1-Exzitons und dessen strahlungsloser Rekombination an Restgasatomen auf der Probenoberfläche erklärt werden. Eine wesentliche Änderung des Emissionsspektrums bei höheren Temperaturen konnte dokumentiert, jedoch mit Hilfe der bekannten Modelle nicht erklärt werden. N2 - Different features of the emission- and excitation-spectra of solid Xenon were invertigated in detail. Substantial aspects could be explained well by the concept of diffusion of the free n=1-exciton and its radiationless recombination at rest gas atoms on the sample surface. A substantial change of the emission spectrum at higher temperature was documented, but could not explained within the known models. KW - Exziton KW - Xenon KW - Lumineszenz KW - Synchrotronstrahlung KW - Hamburg / Deutsches Elektronen-Synchrotron KW - Monochromator KW - Vakuum-UV-Spektroskopie KW - Anregung KW - self-trapped exciton KW - excitation spectrum Y1 - 1976 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus-1745 ER - TY - JOUR A1 - Shams, S. Fatemeh A1 - Schmitz, Detlef A1 - Smekhova, Alevtina A1 - Ghazanfari, Mohammad Reza A1 - Giesen, Margret A1 - Weschke, Eugen A1 - Chen, Kai A1 - Luo, Chen A1 - Radu, Florin A1 - Schmitz-Antoniak, Carolin T1 - Element-specific contributions to improved magnetic heating of theranostic CoFe2O4 nanoparticles decorated with Pd JF - Scientific Reports N2 - Decoration with Pd clusters increases the magnetic heating ability of cobalt ferrite (CFO) nanoparticles by a factor of two. The origin of this previous finding is unraveled by element-specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD) combined with atomic multiplet simulations and density functional theory (DFT) calculations. While the comparison of XAS spectra with atomic multiplet simulations show that the inversion degree is not affected by Pd decoration and, thus, can be excluded as a reason for the improved heating performance, XMCD reveals two interrelated responsible sources: significantly larger Fe and Co magnetic moments verify an increased total magnetization which enhances the magnetic heating ability. This is accompanied by a remarkable change in the field-dependent magnetization particularly for Co ions which exhibit an increased low-field susceptibility and a reduced spin canting behavior in higher magnetic fields. Using DFT calculations, these findings are explained by reduced superexchange between ions on octahedral lattice sites via oxygen in close vicinity of Pd, which reinforces the dominating antiparallel superexchange interaction between ions on octahedral and tetrahedral lattice sites and thus reduces spin canting. The influence of the delocalized nature of Pd 4d electrons on the neighboring ions is discussed and the conclusions are illustrated with spin density isosurfaces of the involved ions. The presented results pave the way to design nanohybrids with tailored electronic structure and magnetic properties. Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-14756 SN - 2045-2322 VL - 11 ER - TY - CHAP A1 - Metzler, Volker H. A1 - Vandenhouten, Ralf A1 - Krone, Jörg A1 - Grebe, Reinhard T1 - Unsupervised image segementation by stochastic reconstruction T2 - Proceedings of SPIE N2 - To segment complex and versatile image data from different modalities it is almost impossible to achieve satisfying results without the consideration of contextual information. In this approach, image segmentation is regarded as a high- dimensional optimization task, that can be solved by stochastical methods like evolutionary algorithms (EA). Initially, the iterative algorithm is provided with a set of good-quality sample segmentations. An efficient EA-based learning strategy generates a segmentation for a given target image from the provided samples. This two-level process consists of a global image-based optimization whose convergence is enhanced by locally operating pixel-based Boltzmann processes which restrict the search space to reasonable subsets. The stochastic reconstruction extracts the relevant information from the samples in order to adapt it onto the current segmentation problem, which results in a consistent labeling for the target image. The algorithm works unsupervised, because the range of possible labels and their contextual interpretation is provided implicitly by the sample segmentations. To prove the usefulness of the method experimental results based on both, reproducible phantom images and physiological NMR scans are presented. Moreover, an analysis of the basic segmentation and convergence properties is provided. Y1 - 1998 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-9329 SN - 1996-756X VL - 3338 ER -