Eine Green Card für EDV-Spezialisten? - Wird Deutschland ein Einwanderungsland?

--

Anomalous behavior of control pulses in presence of noise with singular autocorrelation

We report on the anomalous behavior of control pulses for spins under spin-spin relaxation and subject to classical noise with a singular autocorrelation function. This behavior is not detected for noise with analytic autocorrelation functions. The effect is manifest in the different scaling behavior of the deviation of a real pulse to the ideal, instantaneous one. While a standard pulse displays scaling $\propto \tau_\mathrm{p}^1$, a first-order refocusing pulse normally shows scaling $\propto \tau_\mathrm{p}^2$. But in presence of cusps in the noise autocorrelation the scaling $\propto \tau_\mathrm{p}^{3/2}$ occurs. Cusps in the autocorrelation are characteristic for fast fluctuations in the noise with a spectral density of Lorentzian shape. We prove that the anomalous exponent cannot be avoided; it represents a fundamental limit. On the one hand, this redefines the strategies one has to adopt to design refocusing pulses. On the other hand, the anomalous exponent, if found in experiment, provides important information on the noise properties.Comment: 11 pages, 8 figure

Change agency in (old) industrial regions : Shaping new futures

The aim of the dissertation is to develop a better understanding of the role of local agency in the transformation of old industrial regions. Theoretically the dissertation builds on concepts which are important in the debate on regional development in old industrial regions such as path dependency, negative lock-ins, the role of institutions, and new path development, while exploring and unpacking the role of agency. Old industrial regions are studied using a dynamic and process-oriented approach. Together with detailed, longitudinal case studies, it enhances our understanding of when, why and by whom agency is used in new path development. This challenges the assumption that old industrial regions are static, without any large variations, and that their fate is pre-determined. Empirically, the dissertation investigates agency expressions and regional development in three traditional Swedish industrial regions (Borås, Kiruna, and Olofström) which have suffered from decline and structural crisis. Different types of development and industries are under scrutiny, and the dissertation offers valuable methodological insights into the study of agency. Old industrial regions are structurally constrained and locked-in. Nevertheless, the dissertation finds that new path development is possible in heavily constrained regions. Furthermore, it finds that local actors use their agency in every part of industrial development, and use both local and non-local resources. The dissertation distinguishes between change agency and reproductive agency, which work in tandem. Change agency is important for developing new products, perceiving new futures, and bringing local actors together and, thus, is mainly used in initial stages of path development, whereas reproductive agency is used to stabilise later phases. Change agency can initiate institutional changes, which can pave the way for further change agency. Furthermore, the dissertation nuances our understanding of reproductive agency by showing that, reproductive behaviour can also be the result of a lack of perceived agency or the enforcement of a continued power asymmetry. When no agency is perceived, change agency becomes impossible

First principles simulation of resistivity recovery in irradiated beryllium

Future fusion devices like ITER or DEMO require closed fuel cycles. These vitally depend on neutron multiplying materials as part of a breeding blanket module like beryllium pebbles in the European Helium-Cooled Pebble-Bed. During operation the beryllium pebbles will accumulate point defects, tritium, and helium due to inevitable exposure to highly energetic neutron irradiation as emitted by the fusion plasma. A detailed knowledge of the characteristics of point defects is decisive for reliable simulations of microstructure evolution in irradiated beryllium. Such models are a prerequisite for predicting tritium inventory during operation as well as after the blanket ́s end of life since tritium retention and release is the paramount safety concern. A well-established experimental approach to assess the dynamics of relevant atomic defects consists in measuring electrical resistivity recovery (ERR) after irradiation during annealing. Within this approach, temperatures corresponding to electrical recovery steps are correlated with activation energies which are associated with different type of reactions between defects. In this work, results of our ongoing efforts to model and understand the ERR of beryllium are presented. To that end, we introduce a rate equation-based approach to model ERR spectra (see picture below) utilizing density functional theory results as input. Within this approach, electrical resistivity recovery models comprising the volume of spontaneous recombination of monovacancies and self-interstitial atoms in beryllium as well as various additional defects are considered. As a result, an intricate interplay between different defect dynamics is uncovered, suggesting a clear route for further research to obtain systematically improved electrical resistivity recovery models