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Herrmann M.,University of Oxford | Rademacher J.D.M.,National Research Center for Mathematics and Computer Science
Nonlinearity | Year: 2010

We consider FPU-type atomic chains with general convex potentials. The naive continuum limit in the hyperbolic space-time scaling is the p-system of mass and momentum conservation. We systematically compare Riemann solutions to the p-system with numerical solutions to discrete Riemann problems in FPU chains, and argue that the latter can be described by modified p-system Riemann solvers. We allow the flux to have a turning point, and observe a third type of elementary wave (conservative shocks) in the atomistic simulations. These waves are heteroclinic travelling waves and correspond to non-classical, undercompressive shocks of the p-system. We analyse such shocks for fluxes with one or more turning points. Depending on the convexity properties of the flux we propose FPU-Riemann solvers. Our numerical simulations confirm that Lax shocks are replaced by so-called dispersive shocks. For convex-concave flux we provide numerical evidence that convex FPU chains follow the p-system in generating conservative shocks that are supersonic. For concave-convex flux, however, the conservative shocks of the p-system are subsonic and do not appear in FPU-Riemann solutions. © 2010 IOP Publishing Ltd and London Mathematical Society. Source

Vitanyi P.M.B.,National Research Center for Mathematics and Computer Science | Vitanyi P.M.B.,University of Amsterdam
IEEE Transactions on Information Theory | Year: 2011

Information distance is a parameter-free similarity measure based on compression, used in pattern recognition, data mining, phylogeny, clustering and classification. The notion of information distance is extended from pairs to multiples (finite lists). We study maximal overlap, metricity, universality, minimal overlap, additivity and normalized information distance in multiples. We use the theoretical notion of Kolmogorov complexity which for practical purposes is approximated by the length of the compressed version of the file involved, using a real-world compression program. © 2011 IEEE. Source

Herrmann M.,University of Oxford | Rademacher J.D.M.,National Research Center for Mathematics and Computer Science
SIAM Journal on Mathematical Analysis | Year: 2010

We consider infinite Fermi-Pasta-Ulam-type atomic chains with general convex potentials and study the existence of monotone fronts that are heteroclinic travelling waves connecting constant asymptotic states. Iooss showed that small amplitude fronts bifurcate from convex-concave turning points of the force. In this paper, we prove that fronts exist for any asymptotic states that satisfy certain constraints. For potentials whose derivative has exactly one turning point, these constraints mean precisely that the front corresponds to an energy conserving supersonic shock of the "p-system, " which is the naive hyperbolic continuum limit of the chain. The proof is achieved via minimizing an action functional for the deviation from this discontinuous shock profile. We also discuss qualitative properties and the numerical computation of fronts. © 2010 Society for Industrial and Applied Mathematics. Source

Grond M.O.W.,TU Eindhoven | Luong N.H.,National Research Center for Mathematics and Computer Science | Morren J.,TU Eindhoven | Slootweg J.G.,TU Eindhoven
Proceedings of the Universities Power Engineering Conference | Year: 2012

Efficient operation and planning of power systems is important for a reliable and sustainable electricity supply. Therefore, optimization techniques have been applied to several optimization problems in power systems in order to achieve technical and economic efficiency. This paper presents an overview of existing optimization techniques and applications in power systems, with a special focus on multi-objective optimization in power system planning. Power system planning is by its nature a very complex multi-objective optimization problem involving perspectives of different stakeholders. Besides, a single stakeholder can also have various objectives that need to be optimized at the same time. This paper provides a review of the state-of-the-art in multi-objective evolutionary algorithms applied to power systems planning problems. © 2012 IEEE. Source

Robu V.,National Research Center for Mathematics and Computer Science | Noot H.,National Research Center for Mathematics and Computer Science | La Poutre H.,National Research Center for Mathematics and Computer Science | Van Schijndel W.-J.,VOS Logistics Organizing
Expert Systems with Applications | Year: 2011

This paper describes an agent-based platform for the allocation of loads in distributed transportation logistics, developed as a collaboration between CWI, Dutch National Center for Mathematics and Computer Science, Amsterdam and Vos Logistics Organizing, Nijmegen, The Netherlands. The platform follows a real business scenario proposed by Vos, and it involves a set of agents bidding for transportation loads to be distributed from a central depot in the Netherlands to different locations across Germany. The platform supports both human agents (i.e. transportation planners), who can bid through specialized planning and bidding interfaces, as well as automated, software agents. We exemplify how the proposed platform can be used to test both the bidding behaviour of human logistics planners, as well as the performance of automated auction bidding strategies, developed for such settings. The paper first introduces the business problem setting and then describes the architecture and main characteristics of our auction platform. We conclude with a preliminary discussion of our experience from a human bidding experiment, involving Vos planners competing for orders both against each other and against some (simple) automated strategies. © 2010 Elsevier Ltd. All rights reserved. Source

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