417 research outputs found

    A multigrid perspective on the parallel full approximation scheme in space and time

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    For the numerical solution of time-dependent partial differential equations, time-parallel methods have recently shown to provide a promising way to extend prevailing strong-scaling limits of numerical codes. One of the most complex methods in this field is the "Parallel Full Approximation Scheme in Space and Time" (PFASST). PFASST already shows promising results for many use cases and many more is work in progress. However, a solid and reliable mathematical foundation is still missing. We show that under certain assumptions the PFASST algorithm can be conveniently and rigorously described as a multigrid-in-time method. Following this equivalence, first steps towards a comprehensive analysis of PFASST using block-wise local Fourier analysis are taken. The theoretical results are applied to examples of diffusive and advective type

    Laudatio: Alphabetisierung als Aufgabenfeld der Medienpädagogik

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    Laudatio zur Verleihung des Promotionspreises der Sektion Medienpädagogik in der Deutschen Gesellschaft für Erziehungswissenschaft am 21.9.2017 in Magdeburg. Koppel, Ilka. 2017. Entwicklung einer Online-Diagnostik für die Alphabetisierung. Eine Design-Based Research-Studie. Wiesbaden: Springer Fachmedien Wiesbaden. https://doi.org/10.1007/978-3-658-15769-2

    All-electrical measurement of spin injection in a magnetic pp-nn junction diode

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    Magnetic pp-nn junction diodes are fabricated to investigate spin-polarized electron transport. The injection of spin-polarized electrons in a semiconductor is achieved by driving a current from a ferromagnetic injector (Fe), into a bulk semiconductor (nn-GaAs) via schottky contact. For detection, a diluted magnetic semiconductor (pp-GaMnAs) layer is used. Clear magnetoresistance was observed only when a high forward bias was applied across the pp-nn junction.Comment: 4 pages, 4 figure

    The Skill Structure of the Export Wage Premium: Evidence from German Manufacturing

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    We find a significant export wage premium for higher-skilled workers and a significant export wage discount for lower-skilled workers, using a matched employer-employee data set for German manufacturing firms. Estimates suggest that up to one third of the overall skill premia is associated with exporting. These results imply that increasing trade contributes to widening wage inequality by skill level in manufacturing. But an increase in exports also diminishes wage discrimination due to gender or nationality. In this way, trade contributes to narrowing wage gaps and mitigates wage inequality in German manufacturing

    Low rank surrogates for polymorphic fields with application to fuzzy-stochastic partial differential equations

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    We consider a general form of fuzzy-stochastic PDEs depending on the interaction of probabilistic and non-probabilistic ("possibilistic") influences. Such a combined modelling of aleatoric and epistemic uncertainties for instance can be applied beneficially in an engineering context for real-world applications, where probabilistic modelling and expert knowledge has to be accounted for. We examine existence and well-definedness of polymorphic PDEs in appropriate function spaces. The fuzzy-stochastic dependence is described in a high-dimensional parameter space, thus easily leading to an exponential complexity in practical computations. To aleviate this severe obstacle in practise, a compressed low-rank approximation of the problem formulation and the solution is derived. This is based on the Hierarchical Tucker format which is constructed with solution samples by a non-intrusive tensor reconstruction algorithm. The performance of the proposed model order reduction approach is demonstrated with two examples. One of these is the ubiquitous groundwater flow model with Karhunen-Loeve coefficient field which is generalized by a fuzzy correlation length

    The Contribution of Trade to Wage Inequality: The Role of Skill, Gender, and Nationality

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    International trade has been cited as a source of widening wage inequality in industrial nations. Consistent with this claim, we find a significant export wage premium for high-skilled workers in German manufacturing and an export wage discount for lower skilled workers, using matched employer-employee data. Estimates suggest that the export wage premium to high-skilled workers represents up to one third of their overall skill premium. But, while an increase in exports increases wage inequality along the dimension of skill, it diminishes the wage inequality associated with both gender and nationality. In this way, trade contributes to narrowing wage gaps and mitigating wage inequality in German manufacturing.
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