University of Paderborn

About: University of Paderborn is a education organization based out in Paderborn, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Control reconfiguration & Software. The organization has 6684 authors who have published 16929 publications receiving 323154 citations.

Fast algorithms for Taylor shifts and certain difference equations

Abstract: Joachim von zur Gathen Jurgen Gerhard Fachbereich 17 Mathematik-Informatik Universitat-GH Paderborn D-33095 Paderborn, Germany {gathen, jngerhar}@uni-paderborn. de http://www.uni-paderborn .de/cs/gathen .html

Beyond the molecular movie: Dynamics of bands and bonds during a photoinduced phase transition

Abstract: Ultrafast nonequilibrium dynamics offer a route to study the microscopic interactions that govern macroscopic behavior. In particular, photoinduced phase transitions (PIPTs) in solids provide a test case for how forces, and the resulting atomic motion along a reaction coordinate, originate from a nonequilibrium population of excited electronic states. Using femtosecond photoemission, we obtain access to the transient electronic structure during an ultrafast PIPT in a model system: indium nanowires on a silicon(111) surface. We uncover a detailed reaction pathway, allowing a direct comparison with the dynamics predicted by ab initio simulations. This further reveals the crucial role played by localized photoholes in shaping the potential energy landscape and enables a combined momentum- and real-space description of PIPTs, including the ultrafast formation of chemical bonds.

Grain boundary characterization and energetics of superalloys

Abstract: In many engineering alloys, there exists a wide distribution of grain sizes; we investigate the role of grain boundaries as a strengthening mechanism in such a material. The coincidental site lattice (CSL) model is a powerful mathematical tool to characterize grain boundaries (GBs) and identify ‘special’ boundaries, which display beneficial mechanical behavior. We define the CSL and describe a detailed procedure to obtain this information from the grain orientation mapping via electron back scattering diffraction (EBSD). From this information, we show the evolution of the CSL for a nickel-based superalloy, Udimet 720 (U720), throughout various stages of processing (billet and forging) and experiments (tension, compression, and fatigue). A deeper level of understanding the GB's role in the mechanical behavior of the material is investigated through atomic simulations using molecular dynamics (MD) as the GB energy is determined for the most prevalent GBs within this material. The spatial map of the orientation and grain sizes measured from EBSD is linked to the GB energies calculated from MD. Based upon the large number of boundaries analyzed (29,035), there is a strong inverse correlation between GB energy and grain size for every specimen examined during the various processing and testing conditions.

Single-photon sources: Approaching the ideal through multiplexing.

Abstract: We review the rapid recent progress in single-photon sources based on multiplexing multiple probabilistic photon-creation events. Such multiplexing allows higher single-photon probabilities and lower contamination from higher-order photon states. We study the requirements for multiplexed sources and compare various approaches to multiplexing using different degrees of freedom.