Homogenization methods and macro-strength of composites

A multi-phase periodic composite subjected to inhomogeneous shrinkage or temperature deformation and prescribed mechanical loads is considered. The asymptotic homogenisation is applied for calculation of homogenized macrostresses. A non-local approximate macro-strength condition, defined on homogenised stress-field, is derived from the micro-strength conditions and their convergence to the approximate macro-strength condition, as the structure period tends to zero, is proved

From metastable to stable modifications-in situ Laue diffraction investigation of diffusion processes during the phase transitions of (GeTe)(n)Sb2Te3 (6 < n < 15) crystals.

Temperature dependent phase transitions of compounds (GeTe)nSb2Te3 (n = 6, 12, 15) have been investigated by in situ microfocus Laue diffraction. Diffusion processes involving cation defect ordering at B300 8C lead to different nanostructures which are correlated to changes of the thermoelectric characteristics

A scanning probe-based pick-and-place procedure for assembly of integrated quantum optical hybrid devices

Integrated quantum optical hybrid devices consist of fundamental constituents such as single emitters and tailored photonic nanostructures. A reliable fabrication method requires the controlled deposition of active nanoparticles on arbitrary nanostructures with highest precision. Here, we describe an easily adaptable technique that employs picking and placing of nanoparticles with an atomic force microscope combined with a confocal setup. In this way, both the topography and the optical response can be monitored simultaneously before and after the assembly. The technique can be applied to arbitrary particles. Here, we focus on nanodiamonds containing single nitrogen vacancy centers, which are particularly interesting for quantum optical experiments on the single photon and single emitter level.Comment: The following article has been submitted to Review of Scientific Instruments. After it is published, it will be found at http://rsi.aip.org

Application of Many-Body Techniques to Canonically Quantized Yang-Mills-Theories

In der vorliegenden Arbeit untersuchen wir Yang-Mills-Theorien in der Weyleichung mit Hilfe des Schroedingerbildes, und untersuchen ob Methoden aus der Vielteilchenphysik auf Yang-Mills-Theorien uebertragen werden koennen. Im ersten Kapitel stellen wir die kanonische Quantisierung der Theorie, in der Arbeit benutzte Variationsprinzipien und einige in der Literatur verwandte Methoden zur Behandlung des Gaussgesetzes kurz vor. Das zweite Kapitel ist dem Projektor auf den physikalischen Unterraum der eichinvarianten Zustaende gewidmet. Wir beginnen mit zwei in der Literatur betrachteten Naeherungsverfahren fuer den Projektor. Dann wenden wir uns einer mean-field Behandlung mittels Gaussscher Wellenfunktionale zu. Wir betrachten, wie das Gaussgesetz stoerungstheoretisch durch Modifikationen des Gaussschen Wellenfunktionals erfuellt werden kann, und zeigen die Grenzen dieses Zugangs auf. Dann wechseln wir den Standpunkt und betrachten, wie man deformierte, d.h. eichvariante, Zustaende im Rahmen des Diracschen Variationsprinzips benutzen kann. Das fuehrt zum in der Kernphysik wohlbekannten cranking-Modell, bei dem die Ankopplung externer Ladungen auf Ein-Schleifen-Niveau jedoch falsch ist. Der letzte Zugang in diesem Kapitel ist die Kamlah-Entwicklung, die in Verbindung mit Stoerungstheorie die Erwartungen an ein projiziertes Energiefunktional erfuellt. Im dritten Kapitel betrachten wir die verallgemeinerte Random Phase Approximation (gRPA). Wir stellen sowohl die auf Diracs Variationsprinzip beruhende Formulierung als auch einen Operatorzugang dar und beweisen, dass unter bestimmten Umstaenden beide Zugaenge dasselbe Spektrum ergeben. Im Operatorzugang koennen Symmetrien der vollen Theorie leichter in die gRPA-Behandlung uebersetzt und Korrekturen zur Energie eines deformierten mean-field-Grundzustands angegeben werden. Wir berechnen diese Energiekorrekturen in Stoerungstheorie in fuehrender Ordnung, und vergleichen sie mit den Energiekorrekturen der Kamlahentwicklung.In this thesis, we study Yang-Mills theories in the Weyl gauge employing the Schroedinger picture, and investigate whether techniques from many-body physics can be transcribed to Yang-Mills theories. In the first chapter we give a succinct account of the canonical quantization of the theory, the variational principles used in this thesis and approaches followed in the literature to overcome the Gauss law constraint. The second chapter is devoted to the projector onto the physical subspace of gauge invariant states. First, we present two approximation schemes for the projector that have been applied in the literature. Then we turn to a mean-field treatment based on Gaussian wave functionals. We study how the Gauss law constraint can be implemented perturbatively by modifications of the Gaussian wave functional and show the limitations of this approach. Then we change the point of view and consider how one can use 'deformed' or gauge-noninvariant states in Dirac's variational principle. This leads to the cranking model well known from nuclear physics, where, however, the coupling of external charges is incorrect at a one-loop level. The last approach we consider in this chapter is the Kamlah expansion. When combined with perturbation theory, it reproduces nicely what is expected of the projected energy functional. In the third chapter we study the generalized Random Phase Approximation (gRPA). We present both the formulation based on Dirac's variational principle and an operator approach, and prove that under certain circumstances the two formulations give an identical spectrum. In the operator approach, the symmetries of the full theory are more easily translated to the gRPA treatment, and one can determine the corrections to the energy of a deformed mean-field ground state. We evaluate these corrections in leading order perturbation theory and compare them to the corrections of the Kamlah expansion

Kamlah Expansion and Gauge Theories

In Yang-Mills theories, variational calculations of the Rayleigh-Ritz type face the problem that on the one hand, calculability puts severe constraints on the space of test wave functionals; on the other hand, the test wave functionals have to be gauge invariant. The conflict between the two requirements can be resolved by introducing a projector. In this paper we present an approach to approximating the projector in a way known and successfully employed in nuclear physics: the Kamlah expansion. We discuss it both for electrodynamics and for Yang-Mills theories to leading order in a perturbative expansion, and demonstrate that the results are compatible with what one would expect from perturbation theory.Comment: 26 pages, REVTeX4, uses amsfonts and package longtabl

Comparison of Arterial Wall Models in Fluid-Structure Interaction Simulations

Monolithic fluid-structure interaction (FSI) of blood flow with arterial walls is considered, making use of sophisticated nonlinear wall models. These incorporate the effects of almost incompressibility as well as of the anisotropy caused by embedded collagen fibers. In the literature, relatively simple structural models such as Neo-Hooke are often considered for FSI with arterial walls. Such models lack, both, anisotropy and incompressibility. In this paper, numerical simulations of idealized heart beats in a curved benchmark geometry, using simple and sophisticated arterial wall models, are compared: we consider three different almost incompressible, anisotropic arterial wall models as a reference and, for comparison, a simple, isotropic Neo-Hooke model using four different parameter sets. The simulations show significant quantitative and qualitative differences in the stresses and displacements as well as the lumen cross sections. For the Neo-Hooke models, a significantly larger amplitude in the in- and outflow areas during the heart beat is observed, presumably due to the lack of fiber stiffening. For completeness, we also consider a linear elastic wall using 16 different parameter sets. However, using our benchmark setup, we were not successful in achieving good agreement with our nonlinear reference calculation

Die Zukunft des Bildungssystems: Lernen auf Abruf - eigenverantwortlich und lebenslänglich! Oder: die langfristige Entwicklung und politische Implementierung eines postindustriellen Bidlungsparadigma

The German educational system passes through a lasting conversion under the aegis of terms like "market", "competition", and "personal responsibility". As a result the rapport of corporate and individual responsibility will be reversed: education solely becomes a resource of individual competitiveness in deregulated markets. The article deciphers the conversion as an example for the long lasting strategy of neoliberal politics. Thereby a special focus lies on a certain kind of "sub-politics" carried out by advocacy think tanks, which are acting in the threshold of science, media and politics

Die Verwertung humaner Exkremente als Ressource: Potentiale, Praxisbeispiele und politische Regulierung

In einem Webinar, das im WiSe2020/21 im Rahmen der 5. Progressiven Einführungswochen, der 7. Ökosozialen Hochschultage und des Onlineseminars „Bioökonomie“ an der OVGU Magdeburg veranstaltet wurde, referierte Herr Enno Schröder zur Nutzung von humanen Exkrementen als Ressource für die Bioökonomie. Unter dem Titel „Ab wann ist Scheiße Dünger? Bioökonomie ganz praktisch“ stellte Herr Schröder die Aktivitäten des Sozialunternehmens „Goldeimer gGmbH“ sowie des Netzwerks für Nachhaltige Sanitärsysteme e.V. (netsan.org) dar. Dabei wurden mögliche Verfahren der Kompostierung von humanen Fäkalien, potentielle Risiken sowie die aktuellen gesetzlichen Regulierung im Detail dargestellt. Aus Sicht von Goldeimer erschwert letztere eine kommerzielle Nutzung von humanen Fäkalien als eine wertvolle Ressource für die Bioökonomie. Mit einer Kombination aus wissenschaftlicher Grundlagenforschung, Standardisierung und Qualitätsicherung bei der Kompostierung, Netzwerk-Arbeit und Lobbyarbeit versuchen die Goldeimer gGmbH und Partner des Netzwerkes die Bedingungen hierfür zu verbessern. Der Bericht zu diesem Seminar wurde von Oliver Keminer verfasst und durch einige Verweise (Fussnoten) und Anmerkungen ergänzt.In a webinar organized in WiSe2020/21 as part of the 5th Progressive Introductory Weeks, the 7th Eco-social University Days and the online seminar "Bioeconomy" at OVGU Magdeburg, Mr. Enno Schröder gave a presentation on the use of human excrement as a resource for the bioeconomy. Under the titel “When does human shit become fertilizer? Bioeconomy in practice”, Mr. Schröder presented the activities of the social enterprise "Goldeimer gGmbH" and the “Netzwerk für Nachhaltige Sanitärsysteme e.V. (netsan.org)". In the talk, possible methods of composting human faeces, potential risks as well as the current legal regulation were presented in detail. From Goldeimer\u27s perspective, the latter makes it difficult to commercially utilize human feces as a valuable resource for the bioeconomy. With a combination of basic scientific research, standardization and quality assurance in composting, networking and lobbying, Goldeimer gGmbH and partners of the network try to improve the conditions for this. The report on this seminar was written by Oliver Keminer and supplemented by some references (footnotes) and comments

Evaluation of nitrogen- and silicon-vacancy defect centres as single photon sources in quantum key distribution

We demonstrate a quantum key distribution (QKD) testbed for room temperature single photon sources based on defect centres in diamond. A BB84 protocol over a short free-space transmission line is implemented. The performance of nitrogen-vacancy (NV) as well as silicon-vacancy defect (SiV) centres is evaluated and an extrapolation for next-generation sources with enhanced efficiency is discussed.Comment: 14 pages, 5 figure