@article{9867, abstract = {{We report the piezoelectric properties of CuO-doped hydrothermal (K,Na)NbO3 ceramics that can be applied as hard-type lead-free piezoelectric ceramics. To date, we have succeeded in synthesizing high-quality KNbO3 and NaNbO3 powders by the hydrothermal method, which is based on an ionic reaction at high temperature (around 210 $\,^{\circ}$C) and pressure. Increasing both the piezoelectric constant d and the mechanical quality factor (Qm) is important for resonance-type piezoelectric devices, such as ultrasonic motors and transformers. CuO doping into hydrothermal (K,Na)NbO3 ceramics was examined to realize hard-type lead-free piezoelectric ceramics. By doping with 1.2 mol \% CuO, Qm was increased and the dielectric loss (tan δ) was decreased to 0.5\%. The grain size was also influenced by the amount of CuO doping, which indicates that Qm is related to the density. To achieve a higher Qm value, the grain size is required to be less than 5 µm; however, excessive CuO doping leads to anomalous grain growth. Optimal piezoelectric properties were obtained for 1.2 mol \% CuO-doped (K,Na)NbO3; k31 = 0.32, d31 = -44 pC/N, Qm (radial) = 959, and tan δ= 0.5\%. These characteristics showed that CuO doping with hydrothermal powders is effective for obtaining hard-type ceramics, and the mechanical quality factor is more than ten times higher than that of nondoped hydrothermal (K,Na)NbO3 ceramics. Therefore, compared with the conventional solid-state method, we could succeed in obtaining hard-type ceramics by a simple and short process.}}, author = {{Yokouchi, Yuriko and Maeda, Takafumi and Bornmann, Peter and Hemsel, Tobias and Morita, Takeshi}}, journal = {{Japanese Journal of Applied Physics}}, number = {{7S}}, title = {{{Piezoelectric Properties of CuO-Doped (K,Na)NbO3 Lead-Free Ceramics Synthesized with Hydrothermal Powders}}}, doi = {{10.7567/JJAP.52.07HB03}}, volume = {{52}}, year = {{2013}}, } @misc{503, author = {{Blix, Andreas}}, publisher = {{Universität Paderborn}}, title = {{{Optimale und adaptive binäre Bäume in Netzwerken}}}, year = {{2013}}, } @inbook{5031, author = {{Becker, Jörg and Bernhold, Torben and Beverungen, Daniel and Kaling, Nina and Knackstedt, Ralf and Vanessa, Lellek and Peter Rauer, Hans}}, booktitle = {{Dienstleistungsmodellierung 2012: Product-Service Systems und Produktivität}}, editor = {{Thomas, Oliver and Nüttgens, Markus}}, pages = {{208----226}}, title = {{{Softwaregestützte Konstruktion von Produktivitätsmodellen im Facility Management}}}, doi = {{10.1007/978-3-658-00863-5}}, year = {{2013}}, } @inproceedings{507, abstract = {{We study two-party communication in the context of directed dynamic networks that are controlled by an adaptive adversary. This adversary is able to change all edges as long as the networks stay strongly-connected in each round. In this work, we establish a relation between counting the total number of nodes in the network and the problem of exchanging tokens between two communication partners which communicate through a dynamic network. We show that the communication problem for a constant fraction of n tokens in a dynamic network with n nodes is at most as hard as counting the number of nodes in a dynamic network with at most 4n+3 nodes. For the proof, we construct a family of directed dynamic networks and apply a lower bound from two-party communication complexity.}}, author = {{Abshoff, Sebastian and Benter, Markus and Malatyali, Manuel and Meyer auf der Heide, Friedhelm}}, booktitle = {{Proceedings of the 17th International Conference on Principles of Distributed Systems (OPODIS)}}, pages = {{11--22}}, title = {{{On Two-Party Communication Through Dynamic Networks}}}, doi = {{10.1007/978-3-319-03850-6_2}}, year = {{2013}}, } @misc{510, author = {{Jayesh Parekh, Chintan}}, publisher = {{Universität Paderborn}}, title = {{{Meta-data based Search in Structured Peer-to-Peer Networks}}}, year = {{2013}}, } @inproceedings{513, abstract = {{This paper initiates the study of self-adjusting networks (or distributed data structures) whose topologies dynamically adapt to a communication pattern $\sigma$. We present a fully decentralized self-adjusting solution called SplayNet. A SplayNet is a distributed generalization of the classic splay tree concept. It ensures short paths (which can be found using local-greedy routing) between communication partners while minimizing topological rearrangements. We derive an upper bound for the amortized communication cost of a SplayNet based on empirical entropies of $\sigma$, and show that SplayNets have several interesting convergence properties. For instance, SplayNets features a provable online optimality under special requests scenarios. We also investigate the optimal static network and prove different lower bounds for the average communication cost based on graph cuts and on the empirical entropy of the communication pattern $\sigma$. From these lower bounds it follows, e.g., that SplayNets are optimal in scenarios where the requests follow a product distribution as well. Finally, this paper shows that in contrast to the Minimum Linear Arrangement problem which is generally NP-hard, the optimal static tree network can be computed in polynomial time for any guest graph, despite the exponentially large graph family. We complement our formal analysis with a small simulation study on a Facebook graph.}}, author = {{Avin, Chen and Häupler, Bernhard and Lotker, Zvi and Scheideler, Christian and Schmid, Stefan}}, booktitle = {{Proceedings of the 27th IEEE International Parallel and Distributed Processing Symposium (IPDPS)}}, pages = {{395--406}}, title = {{{Locally Self-Adjusting Tree Networks}}}, doi = {{10.1109/IPDPS.2013.40}}, year = {{2013}}, } @phdthesis{514, abstract = {{Diese Arbeit besch{\"a}ftigt sich mit dem Facility Location Problem. Dies ist ein Optimierungsproblem, bei dem festgelegt werden muss an welchen Positionen Ressourcen zur Verf{\"u}gung gestellt werden, so dass diese von Nutzern gut erreicht werden k{\"o}nnen. Es sollen dabei Kosten minimiert werden, die zum einen durch Bereitstellung von Ressourcen und zum anderen durch Verbindungskosten zwischen Nutzern und Ressourcen entstehen. Die Schwierigkeit des Problems liegt darin, dass man einerseits m{\"o}glichst wenige Ressourcen zur Verf{\"u}gung stellen m{\"o}chte, andererseits daf{\"u}r sorgen muss, dass sich Nutzer nicht all zu weit weg von Ressourcen befinden. Dies w{\"u}rde n{\"a}mlich hohe Verbindungskosten nach sich ziehen. Das Facility Location Problem wurde bereits sehr intensiv in vielen unterschiedlichen Varianten untersucht. In dieser Arbeit werden drei Varianten des Problems modelliert und neue Algorithmen f{\"u}r sie entwickelt und bez{\"u}glich ihres Approximationsfaktors und ihrer Laufzeit analysiert. Jede dieser drei untersuchten Varianten hat einen besonderen Schwerpunkt. Bei der ersten Varianten handelt es sich um ein Online Problem, da hier die Eingabe nicht von Anfang an bekannt ist, sondern Schritt f{\"u}r Schritt enth{\"u}llt wird. Die Schwierigkeit hierbei besteht darin unwiderrufliche Entscheidungen treffen zu m{\"u}ssen ohne dabei die Zukunft zu kennen und trotzdem eine zu jeder Zeit gute L{\"o}sung angeben zu k{\"o}nnen. Der Schwerpunkt der zweiten Variante liegt auf Lokalit{\"a}t, die z.B. in Sensornetzwerken von großer Bedeutung ist. Hier soll eine L{\"o}sung verteilt und nur mit Hilfe von lokalen Information berechnet werden. Schließlich besch{\"a}ftigt sich die dritte Variante mit einer verteilten Berechnung, bei welcher nur eine stark beschr{\"a}nkte Datenmenge verschickt werden darf und dabei trotzdem ein sehr guter Approximationsfaktor erreicht werden muss. Die bei der Analyse der Approximationsfaktoren bzw. der Kompetitivit{\"a}t verwendeten Techniken basieren zum großen Teil auf Absch{\"a}tzung der primalen L{\"o}sung mit Hilfe einer L{\"o}sung des zugeh{\"o}rigen dualen Problems. F{\"u}r die Modellierung von Lokalit{\"a}t wird das weitverbreitete LOCAL Modell verwendet. In diesem Modell werden f{\"u}r die Algorithmen subpolynomielle obere Laufzeitschranken gezeigt.}}, author = {{Pietrzyk, Peter}}, publisher = {{Universität Paderborn}}, title = {{{Local and Online Algorithms for Facility Location}}}, year = {{2013}}, } @misc{522, author = {{Feldotto, Matthias}}, publisher = {{Universität Paderborn}}, title = {{{HSkip+: A Self-Stabilizing Overlay Network for Nodes with Heterogeneous Bandwidths}}}, year = {{2013}}, } @unpublished{524, abstract = {{We study the complexity theory for the local distributed setting introduced by Korman, Peleg and Fraigniaud. They have defined three complexity classes LD (Local Decision), NLD (Nondeterministic Local Decision) and NLD^#n. The class LD consists of all languages which can be decided with a constant number of communication rounds. The class NLD consists of all languages which can be verified by a nondeterministic algorithm with a constant number of communication rounds. In order to define the nondeterministic classes, they have transferred the notation of nondeterminism into the distributed setting by the use of certificates and verifiers. The class NLD^#n consists of all languages which can be verified by a nondeterministic algorithm where each node has access to an oracle for the number of nodes. They have shown the hierarchy LD subset NLD subset NLD^#n. Our main contributions are strict hierarchies within the classes defined by Korman, Peleg and Fraigniaud. We define additional complexity classes: the class LD(t) consists of all languages which can be decided with at most t communication rounds. The class NLD-O(f) consists of all languages which can be verified by a local verifier such that the size of the certificates that are needed to verify the language are bounded by a function from O(f). Our main results are refined strict hierarchies within these nondeterministic classes.}}, author = {{Meyer auf der Heide, Friedhelm and Swirkot, Kamil}}, publisher = {{arXiv}}, title = {{{Hierarchies in Local Distributed Decision}}}, year = {{2013}}, } @misc{526, author = {{Mäcker, Alexander}}, publisher = {{Universität Paderborn}}, title = {{{Greedy Network Creation With Heavy And Light Edges}}}, year = {{2013}}, } @misc{537, author = {{Heindorf, Stefan}}, publisher = {{Universität Paderborn}}, title = {{{Dispersion of Multi-Robot Teams}}}, year = {{2013}}, } @inproceedings{541, abstract = {{Existing solutions for gossip-based aggregation in peer-to-peer networks use epochs to calculate a global estimation from an initial static set of local values. Once the estimation converges system-wide, a new epoch is started with fresh initial values. Long epochs result in precise estimations based on old measurements and short epochs result in imprecise aggregated estimations. In contrast to this approach, we present in this paper a continuous, epoch-less approach which considers fresh local values in every round of the gossip-based aggregation. By using an approach for dynamic information aging, inaccurate values and values from left peers fade from the aggregation memory. Evaluation shows that the presented approach for continuous information aggregation in peer-to-peer systems monitors the system performance precisely, adapts to changes and is lightweight to operate.}}, author = {{Graffi, Kalman and Rapp, Vitaly}}, booktitle = {{Proceedings of the International Conference on Computer Communications and Networks (ICCCN'13)}}, pages = {{1--7}}, title = {{{Continuous Gossip-based Aggregation through Dynamic Information Aging}}}, doi = {{10.1109/ICCCN.2013.6614118}}, year = {{2013}}, } @inproceedings{544, abstract = {{Comparative evaluations of peer-to-peer protocols through simulations are a viable approach to judge the performance and costs of the individual protocols in large-scale networks. In order to support this work, we enhanced the peer-to-peer systems simulator PeerfactSim.KOM with a fine-grained analyzer concept, with exhaustive automated measurements and gnuplot generators as well as a coordination control to evaluate a set of experiment setups in parallel. Thus, by configuring all experiments and protocols only once and starting the simulator, all desired measurements are performed, analyzed, evaluated and combined, resulting in a holistic environment for the comparative evaluation of peer-to-peer systems.}}, author = {{Feldotto, Matthias and Graffi, Kalman}}, booktitle = {{Proceedings of the International Conference on High Performance Computing and Simulation (HPCS'13)}}, pages = {{99--106}}, title = {{{Comparative Evaluation of Peer-to-Peer Systems Using PeerfactSim.KOM}}}, doi = {{10.1109/HPCSim.2013.6641399}}, year = {{2013}}, } @misc{545, author = {{Blumentritt, Fritz}}, publisher = {{Universität Paderborn}}, title = {{{Cliquenbildung in verteilten Systemen}}}, year = {{2013}}, } @inproceedings{546, abstract = {{Self-stabilization is the property of a system to transfer itself regardless of the initial state into a legitimate state. Chord as a simple, decentralized and scalable distributed hash table is an ideal showcase to introduce self-stabilization for p2p overlays. In this paper, we present Re-Chord, a self-stabilizing version of Chord. We show, that the stabilization process is functional, but prone to strong churn. For that, we present Ca-Re-Chord, a churn resistant version of Re-Chord, that allows the creation of a useful DHT in any kind of graph regardless of the initial state. Simulation results attest the churn resistance and good performance of Ca-Re-Chord.}}, author = {{Graffi, Kalman and Benter, Markus and Divband, Mohammad and Kniesburges, Sebastian and Koutsopoulos, Andreas}}, booktitle = {{Proceedings of the Conference on Networked Systems (NetSys)}}, pages = {{27--34}}, title = {{{Ca-Re-Chord: A Churn Resistant Self-stabilizing Chord Overlay Network}}}, doi = {{10.1109/NetSys.2013.11}}, year = {{2013}}, } @inproceedings{548, abstract = {{Peer-to-peer systems scale to millions of nodes and provide routing and storage functions with best effort quality. In order to provide a guaranteed quality of the overlay functions, even under strong dynamics in the network with regard to peer capacities, online participation and usage patterns, we propose to calibrate the peer-to-peer overlay and to autonomously learn which qualities can be reached. For that, we simulate the peer-to-peer overlay systematically under a wide range of parameter configurations and use neural networks to learn the effects of the configurations on the quality metrics. Thus, by choosing a specific quality setting by the overlay operator, the network can tune itself to the learned parameter configurations that lead to the desired quality. Evaluation shows that the presented self-calibration succeeds in learning the configuration-quality interdependencies and that peer-to-peer systems can learn and adapt their behavior according to desired quality goals.}}, author = {{Graffi, Kalman and Klerx, Timo}}, booktitle = {{Proceedings of the International Conference on Peer-to-Peer Computing (P2P'13)}}, pages = {{1--5}}, title = {{{Bootstrapping Skynet: Calibration and Autonomic Self-Control of Structured Peer-to-Peer Networks}}}, doi = {{10.1109/P2P.2013.6688720}}, year = {{2013}}, } @misc{555, author = {{Setzer, Alexander}}, publisher = {{Universität Paderborn}}, title = {{{Approximation Algorithms for the Linear Arrangement of Special Classes of Graphs}}}, year = {{2013}}, } @proceedings{558, editor = {{Flocchini, Paola and Gao, Jie and Kranakis, Evangelos and Meyer auf der Heide, Friedhelm}}, location = {{Sophia Antipolis, France}}, publisher = {{Springer}}, title = {{{Algorithms for Sensor Systems - 9th International Symposium on Algorithms and Experiments for Sensor Systems, Wireless Networks and Distributed Robotics}}}, doi = {{10.1007/978-3-642-45346-5}}, volume = {{8243}}, year = {{2013}}, } @inproceedings{559, abstract = {{Distributed hash tables are very versatile to use, as distributed storage is a desirable feature for various applications. Typical structured overlays like Chord, Pastry or Kademlia consider only homogeneous nodes with equal capacities, which does not resemble reality. In a practical use case, nodes might get overloaded by storing popular data. In this paper, we present a general approach to enable capacity awareness and load-balancing capability of homogeneous structured overlays. We introduce a hierarchical second structured overlay aside, which allows efficient capacity-based access on the nodes in the system as hosting mirrors. Simulation results show that the structured overlay is able to store various contents, such as of a social network, with only a negligible number of overloaded peers. Content, even if very popular, is hosted by easily findable capable peers. Thus, long-existing and well-evaluated overlays like Chord or Pastry can be used to create attractive DHT-based applications.}}, author = {{Wette, Philip and Graffi, Kalman}}, booktitle = {{Proceedings of the Conference on Networked Systems (NetSys)}}, pages = {{35--42}}, title = {{{Adding Capacity-Aware Storage Indirection to Homogeneous Distributed Hash Tables}}}, doi = {{10.1109/NetSys.2013.9}}, year = {{2013}}, } @inproceedings{562, abstract = {{In Distributed Cloud Computing, applications are deployed across many data centres at topologically diverse locations to improved network-related quality of service (QoS). As we focus on interactive applications, we minimize the latency between users and an application by allocating Cloud resources nearby the customers. Allocating resources at all locations will result in the best latency but also in the highest expenses. So we need to find an optimal subset of locations which reduces the latency but also the expenses – the facility location problem (FLP). In addition, we consider resource capacity restrictions, as a resource can only serve a limited amount of users. An FLP can be globally solved. Additionally, we propose a local, distributed heuristic. This heuristic is running within the network and does not depend on a global component. No distributed, local approximations for the capacitated FLP have been proposed so far due to the complexity of the problem. We compared the heuristic with an optimal solution obtained from a mixed integer program for different network topologies. We investigated the influence of different parameters like overall resource utilization or different latency weights.}}, author = {{Keller, Matthias and Pawlik, Stefan and Pietrzyk, Peter and Karl, Holger}}, booktitle = {{Proceedings of the 6th International Conference on Utility and Cloud Computing (UCC) workshop on Distributed cloud computing}}, pages = {{429--434}}, title = {{{A Local Heuristic for Latency-Optimized Distributed Cloud Deployment}}}, doi = {{10.1109/UCC.2013.85}}, year = {{2013}}, }