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.

Fixed-parameter algorithms for (k, r)-center in planar graphs and map graphs

Abstract: The (k, r)-center problem asks whether an input graph G has ≤k vertices (called centers) such that every vertex of G is within distance ≤r from some center. In this article, we prove that the (k, r)-center problem, parameterized by k and R, is fixed-parameter tractable (FPT) on planar graphs, i.e., it admits an algorithm of complexity f(k, r)nO(1) where the function f is independent of n. In particular, we show that f(k,r) = 2O(r log r) √k, where the exponent of the exponential term grows sublinearly in the number of centers. Moreover, we prove that the same type of FPT algorithms can be designed for the more general class of map graphs introduced by Chen, Grigni, and Papadimitriou. Our results combine dynamic-programming algorithms for graphs of small branchwidth and a graph-theoretic result bounding this parameter in terms of k and r. Finally, a byproduct of our algorithm is the existence of a PTAS for the r-domination problem in both planar graphs and map graphs.Our approach builds on the seminal results of Robertson and Seymour on Graph Minors, and as a result is much more powerful than the previous machinery of Alber et al. for exponential speedup on planar graphs. To demonstrate the versatility of our results, we show how our algorithms can be extended to general parameters that are “large” on grids. In addition, our use of branchwidth instead of the usual treewidth allows us to obtain much faster algorithms, and requires more complicated dynamic programming than the standard leaf/introduce/forget/join structure of nice tree decompositions. Our results are also unique in that they apply to classes of graphs that are not minor-closed, namely, constant powers of planar graphs and map graphs.

Meso-structural study of concrete fracture using interface elements. I: numerical model and tensile behavior

Abstract: A recently developed FE-based mesostructural model for the mechanical behavior of heterogeneous quasi-brittle materials is used systematically to analyze concrete specimens in 2D. The numerical model is based on the use of zero-thickness interface elements equipped with a normal-shear traction-separation constitutive law representing non-linear fracture, which may be considered a mixed-mode generalization of Hillerborg’s “Fictitious Crack Model.” Specimens with 4 × 4 and 6 × 6 arrays of aggregates are discretized into finite elements. Interface elements are inserted along the main lines in the mesh, representing potential crack lines. The calculations presented in this paper consist of uniaxial tension loading, and the continuum elements themselves are assumed to behave as linear elastic. In this way, the influence of various aspects of the heterogeneous geometry and interface parameters on the overall specimen response has been investigated. These aspects are aggregate volume fraction, type of arrangement and geometry, interface layout, and values of the crack model parameters chosen for both the aggregate-aggregate and matrix-aggregate interfaces. The results show a good qualitative agreement with experimental observations and illustrate the capabilities of the model. In the companion second part of the paper, the model is used to represent other loading states such as uniaxial compression, Brazilian test, or biaxial loading.

A procedure for the solution of multicomponent reactive transport problems

Abstract: [1] Modeling transport of reactive solutes is a challenging problem, necessary for understanding the fate of pollutants and geochemical processes occurring in aquifers, rivers, estuaries, and oceans. Geochemical processesinvolving multiple reactive species are generally analyzed using advanced numerical codes. The resulting complexity has inhibited the development of analytical solutions for multicomponent heterogeneous reactions such as precipitation/dissolution. We present a procedure to solve groundwater reactive transport in the case of homogeneous and classical heterogeneous equilibrium reactions induced by mixing different waters. The methodology consists of four steps: (1) defining conservative components to decouple the solution of chemical equilibrium equations from species mass balances, (2) solving the transport equations for the conservative components, (3) performing speciation calculations to obtain concentrations of aqueous species, and (4) substituting the latter into the transport equations to evaluate reaction rates. We then obtain the space-time distribution of concentrations and reaction rates. The key result is that when the equilibrium constant does not vary in space or time, the reaction rate is proportional to the rate of mixing, * T u D Vu, where u is the vector of conservative components concentrations and D is the dispersion tensor. The methodology can be used to test numerical codes by setting benchmark problems but also to derive closed-form analytical solutions whenever steps 2 and 3 are simple, as illustrated by the application to a binary system. This application clearly elucidates that in a three-dimensional problem both chemical and transport parameters are equally important in controlling the process.

Penelope: The NBTI-Aware Processor

Abstract: Transistors consist of lower number of atoms with every technology generation Such atoms may be displaced due to the stress caused by high temperature, frequency and current, leading to failures NBTI (negative bias temperature instability) is one of the most important sources of failure affecting transistors NBTI degrades PMOS transistors whenever the voltage at the gate is negative (logic input "0") The main consequence is a reduction in the maximum operating frequency and an increase in the minimum supply voltage of storage structures to cope for the degradation Many PMOS transistors affected by NBTI can be found in both combinational and storage blocks since they observe a "0 " at their gates most of the time This paper proposes and evaluates the design of Penelope, an NBTI-aware processor We propose (i) generic strategies to mitigate degradation in both combinational and storage blocks, (ii) specific techniques to protect individual blocks by applying the global strategies, and (Hi) a metric to assess the benefits of reduced degradation and the overheads in performance and power