Einfluss des Zirkonium-Gehalts auf die Leitfähigkeitseigenschaften dotierter Cerdioxid-Zirkondioxidsysteme

Sauerstoffionenleitende Systeme sind aufgrund ihrer unterschiedlichen Anwendungsgebiete von besonderem Interesse in der anorganischen Festkörperchemie. Systeme mit vorwiegender Sauerstoffionenleitfähigkeit und geringer Elektronenleitfähigkeit, beispielsweise Gd-dotiertes Cerdioxid oder Y-stabilisiertes Zirkondioxid, werden als Elektrolytmaterialien in Brennstoffzellen oder Sensoren eingesetzt. Im Bereich der Elektrodenmaterialien ist zusätzlich eine hohe elektronische Leitfähigkeit erwünscht. In der Katalyse spielen Cerdioxid/Zirkondioxidsysteme wegen der hohen Sauerstoffspeicherfähigkeit eine große Rolle. In dieser Arbeit wurden die Leitfähigkeitseigenschaften Gd- und Y-dotierter Cerdioxid-Zirkondioxid-Mischsystemen in Abhängigkeit vom Cer/Zirkonium-Verhältnis untersucht. Bei gleichen Anteilen an Ce und Zr wurde ein Minimum der Sauerstoffionenleitfähigkeit und ein Maximum der Elektronenleitfähigkeit gefunden. Dies lässt auf die Ausbildung geordneter Strukturen im Kristall schließen

Improved Bounds for Online Multi-Path Routing in Faulty Mesh Networks

We consider the problem of route discovery in a mesh network with faulty nodes. The number and the positions of the faulty nodes are unknown. It is known that a flooding strategy like expanding ring search can route a message linear in the minimum number of steps d while it causes a traffic (i.e. the total number of messages) of O(d²). For optimizing traffic a single-path strategy is optimal producing traffic O(d + p), where p is the number of nodes that are adjacent to faulty nodes. In TR-RSFB-05-077 "Online Multi-Path Routing in a Maze" we presented a deterministic multi-path online routing algorithm that delivers a message within O(d) steps causing traffic O((d + p) log³ d). Here, we show an improvement of the traffic bound to O((d + p) log² d). This algorithm is asymptotically as fast as flooding and nearly traffic-optimal up to a polylogarithmic factor

Fourth annual report to the European Parliament on Commission monitoring of the application of Community law - 1986. OJ C 338, 16 December 1987. COM (87) 250 final, 24 August 1987

We investigate distributed algorithms for mobile ad hoc networks for moving radio stations with adjustable transmission power in a worst case scenario. We consider two models to find a reasonable restriction on the worst-case mobility. In the pedestrian model we assume a maximum speed v_max of the radio stations, while in the vehicular model we assume a maximum acceleration a_max of the points. Our goal is to maintain..

von

This work would not have been possible without the understanding of my friends, the encouragement of my parents and the support of all the colleagues with whom I worked together. I have to thank them all and I am especially indebted to the following people. I would like to sincerely thank my advisor Friedhelm Meyer auf der Heide for giving me the opportunity to choose the direction of my research, for his optimism and his encouragement. I am also grateful to my co-advisor Christian Schindelhauer for the good cooperation in research and teaching, for having patience with me in numerous discussions and for his invaluable help. I also thank Inés Bebea González for burning the midnight oil when working on our research project and the good cooperation despite the thousand miles between Paderborn and Madrid. ¡Muchas gracias! Special thanks to Silke Geisen and Peter Birkner who didn’t shrink away from reading parts of this work in a preliminary state. Their comments helped a lot in improving its readability. Paderborn, July 2006 Stefan Rühru

Online Multi-Path Routing in a Maze

We consider the problem of routing a message in a mesh network with faulty nodes. The number and positions of faulty nodes is unknown. It is known that a flooding strategy like expanding ring search can route a message linear in the minimum number of steps h while it causes a traffic (i.e

ABSTRACT Worst Case Mobility in Ad Hoc Networks

We investigate distributed algorithms for mobile ad hoc networks for moving radio stations with adjustable transmission power in a worst case scenario. We consider two models to find a reasonable restriction on the worst-case mobility. In the pedestrian model we assume a maximum speed vmax of the radio stations, while in the vehicular model we assume a maximum acceleration amax of the points. Our goal is to maintain persistent routes with nice communication network properties like hop-distance, energy-consumption, congestion and number of interferences. A route is persistent, if we can guarantee that all edges of this route can be uphold for a given time span ∆, which is a parameter denoting the minimum time the mobile network needs to adopt changes, i.e. update routing tables, change directory entries, etc. This ∆ can be used as the length of an update interval for a proactive routing scheme. We extend some known notions such as transmission range, interferences, spanner, power spanner and congestion to both mobility models and introduce a new parameter called crowdedness that states a lower bound on the number of radio interferences. Then we prove that a mobile spanner hosts a path system that polylogarithmically approximates the optimal congestion. We present distributed algorithms based on a grid clustering technique and a high-dimensional representation of the dynamical start situation which construct mobile spanners with low congestion, low interference number, low energy-consumption, and low degree. We measure the optimality of the output of our algorithm by comparing it with the optimal choice of persistent routes under the same circumstances with respect to pedestrian or vehicular worst-case movements. Finally, we present solutions for dynamic position information management under our mobility models. ∗ Institute of Computer Science, {schindel, talu