Braunschweig University of Technology

About: Braunschweig University of Technology is a education organization based out in Braunschweig, Germany. It is known for research contribution in the topics: Population & Computer science. The organization has 13268 authors who have published 26707 publications receiving 611590 citations.

Polarity and Its Influence on Growth Mechanism during MOVPE Growth of GaN Sub-micrometer Rods

Abstract: The influence of polarity during the MOVPE growth of GaN based sub-micrometer (sub-μm) rods has mostly been neglected up to now. In this paper we demonstrate that the surface polarity plays a crucial role for the morphology of the GaN sub-μm rods. Based on the differences between N-polar and Ga-polar surfaces, a model is suggested to explain the influence of various parameters on the morphology of GaN sub-μm rods for the first time. For Ga-polar GaN, the {10−11} r-planes, similar to N-polar (000−1) c-planes, are terminated by nitrogen atoms. These N-terminated surfaces can be passivated by hydrogen, which leads to a stable surface with low growth rates and therefore tends to keep a pyramidal shape with stable r-planes. For N-polar GaN, {10−1−1} r-planes can be modified by H2 etching, leading to the formation of more stable {1−100} m-planes, hence supporting the formation of sub-μm rods with vertical sidewalls.

The Physics of Protoplanetesimal Dust Agglomerates. IV. Toward a Dynamical Collision Model

Abstract: Recent years have shown many advances in our knowledge of the collisional evolution of protoplanetary dust. Based on a variety of dust-collision experiments in the laboratory, our view of the growth of dust aggregates in protoplanetary disks is now supported by a deeper understanding of the physics involved in the interaction between dust agglomerates. However, the parameter space, which determines the collisional outcome, is huge and sometimes inaccessible to laboratory experiments. Very large or fluffy dust aggregates and extremely low collision velocities are beyond the boundary of today's laboratories. It is therefore desirable to augment our empirical knowledge of dust-collision physics with a numerical method to treat arbitrary aggregate sizes, porosities, and collision velocities. In this paper, we implement experimentally determined material parameters of highly porous dust aggregates into a smooth particle hydrodynamics (SPH) code, in particular an omnidirectional compressive-strength and a tensile-strength relation. We also give a prescription of calibrating the SPH code with compression and low-velocity impact experiments. In the process of calibration, we developed a dynamic compressive-strength relation and estimated a relation for the shear strength. Finally, we defined and performed a series of benchmark tests and found the agreement between experimental results and numerical simulations to be very satisfactory. SPH codes have been used in the past to study collisions at rather high velocities. At the end of this work, we show examples of future applications in the low-velocity regime of collisional evolution.

Strategic Management of Spare Parts in Closed-Loop Supply Chains--A System Dynamics Approach

Abstract: We developed tools for information management and spare-parts management in closed-loop supply chains. Our Internet-based information and communication platform provides data relevant to recycling based on Agfa-Gevaert's concept of a "recycling passport." We defined what data is relevant based on the product-recovery strategy. Using system dynamics, we modeled an integrated production and recovery system for supplying spare parts to evaluate possible strategies for meeting spare-parts demand for electronic equipment in the end-of-life service period. We will implement these instruments and methods in a pilot study within our partner companies, Agfa-Gevaert AG and Electrocycling GmbH. Decision makers at Agfa-Gevaert will then be able to determine whether and how recovering components could reduce costs in spare-parts management in the end-of-life service period.