792 research outputs found
Applications of resonant hard x-ray diffraction for characterization of structural modifications in crystals
Die Arbeit behandelt die vielseitigen Möglichkeiten im Bereich der Kristallstrukturanalyse mit Röntgenstrahlung, welche sich zusätzlich bei resonanter Anregung von Elektronenübergängen ergeben. Existierende resonante Methoden aus diesem Bereich werden im materialwissenschaftlichen Kontext neu dargelegt und ausgebaut. Zudem werden neue Methoden zur Strukturverfeinerung vorgestellt, welche darauf zielen, mithilfe resonanter Anregung kleine Abweichungen von der Idealstruktur oder aber Phasenumwandlungen zu beschreiben. Im Vordergrund steht dabei die hier erstmals ausgearbeitete Methode der Unterdrückung von Beugungsintensität durch Variation der atomaren Streufaktoren über gezieltes Einstellen der Röntgenenergie. Dies ist stark abhängig von internen Strukturparametern und ermöglichte so eine pikometergenaue Bestimmung von Atompositionen in einer neuen, polaren Oberflächenschicht des Strontiumtitanats. Weitere Anwendungen auf verschiedene Klassen kristalliner Materialien werden vorgestellt und basieren auf unterschiedlichen Aspekten resonanter Beugung wie zum Beispiel verbotenen Reflexen
Theory and Algorithms
The article surveys and extends variational formulations of the thermodynamic
free energy and discusses their information-theoretic content from the
perspective of mathematical statistics. We revisit the well-known Jarzynski
equality for nonequilibrium free energy sampling within the framework of
importance sampling and Girsanov change-of-measure transformations. The
implications of the different variational formulations for designing efficient
stochastic optimization and nonequilibrium simulation algorithms for computing
free energies are discussed and illustrated. View Full-Tex
Variational approach to rare event simulation using least-squares regression
We propose an adaptive importance sampling scheme for the simulation of rare
events when the underlying dynamics is given by a diffusion. The scheme is
based on a Gibbs variational principle that is used to determine the optimal
(i.e. zero-variance) change of measure and exploits the fact that the latter
can be rephrased as a stochastic optimal control problem. The control problem
can be solved by a stochastic approximation algorithm, using the Feynman-Kac
representation of the associated dynamic programming equations, and we discuss
numerical aspects for high-dimensional problems along with simple toy examples.Comment: 28 pages, 7 figure
The personality traits of self-made and inherited millionaires
Very wealthy people influence political and societal processes by wielding their economic power through foundations, lobbying groups, media campaigns, as investors and employers. Because personality shapes goals, attitudes, and behaviour, it is important to understand the personality traits that characterize the rich. We used representative survey data to construct two large samples, one from the general population and one consisting of individuals with at least 1 million euros in individual net wealth, to analyse what personality traits characterize the wealthy and why their traits differ from those of the general population. High wealth was associated with higher Risk tolerance, Emotional Stability, Openness, Extraversion, and Conscientiousness. This “rich” personality profile was more prominent among individuals who had accumulated wealth through their own efforts (“self-mades”) than among individuals who had been born into wealth (“inheritors”). Thus, our evidence is suggestive of a unique configuration of personality traits contributing to self-made millionaires’ economic success
Effect of treatments with 1,3-dimethylol-4,5-dihydroxy-ethyleneurea (DMDHEU) on the tensile properties of wood
The thin-veneer strip technique was applied to investigate the modifying effects of 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) on the tensile strength of wood. Pinewood veneers treated with solutions of DMDHEU alone and in combination with magnesium chloride (MgCl2) as a catalyst showed considerable strength losses of up to 50% in zero-span and up to 70% in finite-span testing modes. The higher strength losses in the latter case are due to hemicellulose degradation, which cannot be assessed in zero-span testing. Strength loss observed after treatment with DMDHEU and MgCl2 was approximately as high as the sum of the strength losses determined after individual treatments with MgCl2 or DMDHEU. Micrographs of veneers after finite-span testing revealed that catalysed DMDHEU treatment changed the predominant failure mode from interfibre fracture (in controls) to intrafibre fracture. The mechanism of strength loss resulting from treatment with DMDHEU is discusse
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