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: Computer science & Context (language use). The organization has 6684 authors who have published 16929 publications receiving 323154 citations.

Effect of disperse Ti3N4 particles on the martensitic transformations in titanium nickelide single crystals

Abstract: The effect of the size and volume fraction of Ti 3 N 4 particles in Ti-(50.3-51.5) at % Ni single crys- tals on their martensitic transformation temperatures and temperature hysteresis is studied. Aging at T = 673- 823 K leads to a nonmonotonic change in the martensitic transformation temperatures and temperature hyster- esis, which is related to a change in the Ni concentration in the matrix, the hardening of the high-temperature phase, a change in the elastic and surface energies generated upon the martensitic transformations, and the inter- nal stresses that appear because of the difference in the lattice parameters of the particles and the matrix. As a result of the high strength of the B 2 phase and the high elastic and surface energies that are generated upon the martensitic transformations due to the precipitation of particles of size d < 40 nm at an interparticle distance λ < 50 nm, the martensitic transformation temperatures decrease down to the suppression of the R - B 19' transi- tions upon cooling to 77 K. A thermodynamic description for the martensitic transformations in heterophase crystals is proposed, and an analogy between the martensitic transformations in heterophase Ti-Ni single crys- tals with nanoparticles of size d = 20-100 nm and those in single-phase Ti-Ni polycrystals with a grain size of 50-200 nm is found.

Increasing stability of crew and aircraft schedules

Abstract: Stability describes the grade of the ability of a plan to remain feasible and cost efficient under variations of the operating environment without major modifications to the plan. In airline traffic delays often lead to additional delays, because of interdependencies between different resources such as ai rcraft, crews and airport facilities. In this paper we focus on reactionary delays that result from crews changing aircraft. Based on a stochastic model for delay propagation we propose an indicator for stability of airline crew and aircraft schedules. This indicator is used to generate more robust aircraft and crew schedules. An integrated formulation for the aircraft and crew scheduling problem results in a non-linear stochastic recourse function. We decompose this formulation into separate linear problems connected by the objective function. The decomposed stochastic problem may be solved using a heuristic iterative approach based on column generation and dynamic programming for the recourse functions. In order to evaluate the robustness of the generated schedules and to compare with a deterministic approach for robust scheduling we use an also presented simulation model.

UML for electronic systems design: a comprehensive overview

Abstract: UML has been widely accepted by the software community for several years. As electronic systems design can no longer be seen as an isolated hardware design activity, UML becomes of significant interest as a unification language for systems description combining both HW and SW components. This article provides a comprehensive view of the UML applied to System-on-Chip (SoC) and hardware-related embedded systems design. The modeling concepts in the UML language are first introduced, including major diagrams for the representation of the behavior and the structure of systems. The principles behind application specific UML customizations (UML profiles) are summarized, and several examples relevant for SoC design are given, such as the SysML (System Modeling Language) and the SoC Profile. Thereafter, various approaches associating UML with existing HW/SW design languages are presented. Beyond language aspects, the article addresses the question of UML-based design flows, and shows how UML can be applied concretely to the development of electronic-based systems. The current situation about tool support constitutes the last focus of the article. In particular, we show how UML tools can be combined with well-known simulation environments, such as MATLAB.

Routing in Wireless Sensor Networks

Abstract: Wireless sensor networks are formed by small sensor nodes communicating over wireless links without using a fixed network infrastructure. Sensor nodes have a limited transmission range, and their processing and storage capabilities as well as their energy resources are also limited. Routing protocols for wireless sensor networks have to ensure reliable multi-hop communication under these conditions. We describe design challenges for routing protocols in sensor networks and illustrate the key techniques to achieve desired characteristics, such as energy efficiency and delivery guarantees. We give a survey of state-of-the-art routing techniques with a focus on geographic routing, a paradigm that enables a reactive message-efficient routing without prior route discovery or knowledge of the network topology. Different geographic routing strategies are described as well as beaconless routing techniques. We also show the physical layer impact on routing and outline further research directions.

Visualization of dynamic polaronic strain fields in hybrid lead halide perovskites.

Abstract: Excitation localization involving dynamic nanoscale distortions is a central aspect of photocatalysis1, quantum materials2 and molecular optoelectronics3. Experimental characterization of such distortions requires techniques sensitive to the formation of point-defect-like local structural rearrangements in real time. Here, we visualize excitation-induced strain fields in a prototypical member of the lead halide perovskites4 via femtosecond resolution diffuse X-ray scattering measurements. This enables momentum-resolved phonon spectroscopy of the locally distorted structure and reveals radially expanding nanometre-scale strain fields associated with the formation and relaxation of polarons in photoexcited perovskites. Quantitative estimates of the magnitude and shape of this polaronic distortion are obtained, providing direct insights into the dynamic structural distortions that occur in these materials5–9. Optical pump–probe reflection spectroscopy corroborates these results and shows how these large polaronic distortions transiently modify the carrier effective mass, providing a unified picture of the coupled structural and electronic dynamics that underlie the optoelectronic functionality of the hybrid perovskites. Diffuse X-ray scattering with femtosecond resolution shows the formation and relaxation of polaronic distortions in halide perovskites. These structural changes are also quantified and correlated to transient changes in carrier effective mass.