André Drews

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Small grid-connected photovoltaic systems up to 5 kWp are often not monitored because advanced surveillance systems are not economical. Hence, some system failures which lead to partial energy losses stay unnoticed for a long time. Even a failure that results in a larger energy deficit can be difficult to detect by PV laymen due to the fluctuating energy(More)
S. Stettler, P. Toggweiler, E. Wiemken, W. Heidenreich, A.C. de Keizer, W.G.J.H.M. van Sark, S. Feige, M. Schneider, G. Heilscher, E. Lorenz, A. Drews, D. Heinemann 1Enecolo AG, Lindhofstr. 52, 8617 Mönchaltorf, Switzerland, T: +41 1 994 9001, F: +41 1 994 9005, E: Fraunhofer ISE, Heidenhofstr. 2, 79110 Freiburg, Germany, T.: +49 761 4588(More)
Time-resolved x-ray microscopy is used to image the influence of alternating high-density currents on the magnetization dynamics of ferromagnetic vortices. Spin-torque-induced vortex gyration is observed in micrometer-sized permalloy squares. The phases of the gyration in structures with different chirality are compared to an analytical model and(More)
We experimentally study the magnetization dynamics of pairs of micron-sized permalloy squares coupled via their stray fields. The trajectories of the vortex cores in the Landau-domain patterns of the squares are mapped in real space using time-resolved scanning transmission x-ray microscopy. After excitation of one of the vortex cores with a short(More)
The influence of the magnetostatic interaction on vortex dynamics in arrays of ferromagnetic disks is investigated by means of a broadband ferromagnetic-resonance setup. Transmission spectra reveal a strong dependence of the resonance frequency of vortex-core motion on the ratio between the center-to-center distance and the element size. For a decreasing(More)
Different numerical approaches for the stray-field calculation in the context of micromagnetic simulations are investigated. We compare finite difference based fast Fourier transform methods, tensor-grid methods and the finite-element method with shell transformation in terms of computational complexity, storage requirements and accuracy tested on several(More)
Topological singularities occur as antivortices in ferromagnetic thin-film microstructures. Antivortices behave as two-dimensional oscillators with a gyrotropic eigenmode which can be excited resonantly by spin currents and magnetic fields. We show that the two excitation types couple in an opposing sense of rotation in the case of resonant antivortex(More)
The interaction of a current-driven domain wall with an anisotropy boundary in nanowires with perpendicular magnetic anisotropy is investigated. A local reduction of the anisotropy constant is used to create an artificial boundary where the domain wall gets pinned. Micromagnetic simulations and analytical calculations, based on a one-dimensional model, are(More)
Systematische Untersuchungen bei 54 Doppelbeinamputierten lassen keine typischen Abweichungen der Herz- und Kreislaufsituation von der bei Gesunden entsprechenden Lebensalters nachweisen. Die Häufigkeit elektrokardiographischer Veränderungen, von Zeichen der Gefäßsklerose, des Bluthochdrucks und des Übergewichts weicht nicht von der bei gleichaltrigen(More)