University of Stuttgart, Institute of Parallel and Distributed High-Performance Systems (IPVR), Breitwiesenstr. 20-22, D-70565 Stuttgart, Germany;University of Stuttgart, Institute of Parallel and Distributed High-Performance Systems (IPVR), Breitwiesenstr. 20-22, D-70565 Stuttgart, Germany;University of Stuttgart, Institute of Parallel and Distributed High-Performance Systems (IPVR), Breitwiesenstr. 20-22, D-70565 Stuttgart, Germany