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The project for the work of a new bridge over Pisuerga river is described in this article. Considering how peculiar the topography of the place is, the idea of a truss-bridge is suggested, planning its construction thinking of the bearings that have to support the bridge and its constructive system, intending first its durability. Se describe el proyecto de obra del nuevo puente sobre el río Pisuerga. Teniendo en cuenta lo peculiar de la topografía del lugar, se sugiere la idea de puente atirantado, planteándose su construcción en el tipo de apoyos que ha de presentar dicho puente y su sistema constructivo, considerando, de manera especial, su durabilidad.

Novel composite algorithms for efficient off-lattice simulations of dense polymer phases are implemented and evaluated in the case of polyethylene in the united and explicit atom approximations. The simulation algorithms are based on combinations of traditional methods with recently developed Monte Carlo moves. The classical Metropolis Monte Carlo (MMC) and Reptation techniques are supplemented with the Continuum-Configuration Bias (CCB) and the Concerted-Rotation (CONROT) methods. Several extensions of the CONROT method, involving the simultaneous coordinated displacement of four to seven chain backbone sites, are developed and tested in this paper. CONROT-based methods enhance the performance of the algorithm at the level of local segmental motions, whereas the CCB component is important for the convergence of global properties, such as the relaxation of end-to-end distance vectors. The present composite algorithms are able to reproduce quite efficiently equilibrium thermodynamic properties, such as the density and the radial distribution function in the liquid state. However, they fail to generate completely equilibrated melts of long chains (polyethylene with 70 carbon atoms) at the molecular level. In spite of this shortcoming, we believe that these methods constitute the most promising currently available tools for the off-lattice simulation of realistic models of polymer melts and glasses. A satisfactory treatment of relatively long polyethylene chains (with up to 40 carbon atoms in the backbone, according to our estimates) is possible at experimental melt densities, both in the NVT and NPT ensembles. 116 282 318 Cited By :6

The concept of multiscale modeling embodies the idea that a comprehensive description of a material will require an understanding over multiple time and length scales. A multiscale model requires that descriptions at all levels be consistent with each other, which can be particularly demanding for advanced materials and complex fluids. For crystalline materials, emerging modeling approaches have married smalland intermediate-scale descriptions in a highly effective manner, but challenges remain at long time and length scales. For soft materials, such as polymers or liquid crystals, modeling techniques have adopted a more or less systematic coarse-graining approach, in which atomic and molecular details are gradually blurred as one seeks to describe longer length scales. This approach presents its own brand of challenges. And, in spite of rapid advances, entire classes of materials, including amorphous glasses, foams, and gels, have resisted attempts to describe their structure and dynamics over long and relevant length and time scales. This issue of MRS Bulletin covers some areas of materials modeling in which enormous advances have been made, but which continue to raise intriguing questions and formidable challenges.