Polytechnic University of Catalonia

About: Polytechnic University of Catalonia is a education organization based out in Barcelona, Spain. It is known for research contribution in the topics: Finite element method & Population. The organization has 16006 authors who have published 45325 publications receiving 949306 citations. The organization is also known as: UPC - BarcelonaTECH & Technical University of Catalonia.

Modeling the routing and spectrum allocation problem for flexgrid optical networks

Abstract: Flexgrid optical networks are attracting huge interest due to their higher spectrum efficiency and flexibility in comparison with traditional wavelength switched optical networks based on the wavelength division multiplexing technology. To properly analyze, design, plan, and operate flexible and elastic networks, efficient methods are required for the routing and spectrum allocation (RSA) problem. Specifically, the allocated spectral resources must be, in absence of spectrum converters, the same along the links in the route (the continuity constraint) and contiguous in the spectrum (the contiguity constraint). In light of the fact that the contiguity constraint adds huge complexity to the RSA problem, we introduce the concept of channels for the representation of contiguous spectral resources. In this paper, we show that the use of a pre-computed set of channels allows considerably reducing the problem complexity. In our study, we address an off-line RSA problem in which enough spectrum needs to be allocated for each demand of a given traffic matrix. To this end, we present novel integer lineal programming (ILP) formulations of RSA that are based on the assignment of channels. The evaluation results reveal that the proposed approach allows solving the RSA problem much more efficiently than previously proposed ILP-based methods and it can be applied even for realistic problem instances, contrary to previous ILP formulations.

Potential of mean force by constrained molecular dynamics: A sodium chloride ion-pair in water

Abstract: The constrained molecular dynamics simulation method has been used to obtain the mean force and the mean force potential between two particles in solution. The method has been tested for a Lennard-Jones liquid and applied to the study of a Na+-Cl− ion-pair in aqueous solution. A flexible SPC model for water has been assumed. The results have been interpreted in the light of the solvent structure around the ions for separations corresponding to the maxima and minima of the mean force potential. In contrast to earlier studies using rigid water models, the solvent separated ion pair configurations are more stable than the contact ion pair configurations.