Parallel structurally-symmetric sparse matrix-vector products on multi-core processors

We consider the problem of developing an efficient multi-threaded implementation of the matrix-vector multiplication algorithm for sparse matrices with structural symmetry. Matrices are stored using the compressed sparse row-column format (CSRC), designed for profiting from the symmetric non-zero pattern observed in global finite element matrices. Unlike classical compressed storage formats, performing the sparse matrix-vector product using the CSRC requires thread-safe access to the destination vector. To avoid race conditions, we have implemented two partitioning strategies. In the first one, each thread allocates an array for storing its contributions, which are later combined in an accumulation step. We analyze how to perform this accumulation in four different ways. The second strategy employs a coloring algorithm for grouping rows that can be concurrently processed by threads. Our results indicate that, although incurring an increase in the working set size, the former approach leads to the best performance improvements for most matrices.Comment: 17 pages, 17 figures, reviewed related work section, fixed typo

Sustainable management of miombo woodlands in the Northern part of Mozambique (Niassa National Reserve - NNR).

Poster presented at Commiting Science to Global Development. Lisbon (Portugal). 29-30 Sep 2009

Confining potential in a color dielectric medium with parallel domain walls

We study quark confinement in a system of two parallel domain walls interpolating different color dielectric media. We use the phenomenological approach in which the confinement of quarks appears considering the QCD vacuum as a color dielectric medium. We explore this phenomenon in QCD_2, where the confinement of the color flux between the domain walls manifests, in a scenario where two 0-branes (representing external quark and antiquark) are connected by a QCD string. We obtain solutions of the equations of motion via first-order differential equations. We find a new color confining potential that increases monotonically with the distance between the domain walls.Comment: RevTex4, 5 pages, 1 figure; version to appear in Int. J. Mod. Phys.

Mutual information in random Boolean models of regulatory networks

The amount of mutual information contained in time series of two elements gives a measure of how well their activities are coordinated. In a large, complex network of interacting elements, such as a genetic regulatory network within a cell, the average of the mutual information over all pairs is a global measure of how well the system can coordinate its internal dynamics. We study this average pairwise mutual information in random Boolean networks (RBNs) as a function of the distribution of Boolean rules implemented at each element, assuming that the links in the network are randomly placed. Efficient numerical methods for calculating show that as the number of network nodes N approaches infinity, the quantity N exhibits a discontinuity at parameter values corresponding to critical RBNs. For finite systems it peaks near the critical value, but slightly in the disordered regime for typical parameter variations. The source of high values of N is the indirect correlations between pairs of elements from different long chains with a common starting point. The contribution from pairs that are directly linked approaches zero for critical networks and peaks deep in the disordered regime.Comment: 11 pages, 6 figures; Minor revisions for clarity and figure format, one reference adde

Variação intra-anual dos teores foliares de carboidratos e atividade de invertases em videiras no Vale do rio São Francisco.

O pólo de agricultura irrigada do Vale do Rio São Francisco a presenta um crescente aumento na produção de uvas para vinificação. Entre os vinhos finos ali produzidos, destaca-se aquele obtido da cv. Petite Syrah, que se adaptou bem às condições climáticas da região. Pouco se conhece, no entanto, sobre o metabolismo de carboidratos das videiras nessa região. O objetivo deste trabalho foi avaliar os teores de açúcarese de amido, bem como a atividade de invertases, durante dois ciclos de produção consecutivos. O experimento foi realizado na Embrapa Semi-Árido e na Vitivinícola Santa Maria, localizadas, respectivamente, em Petrolina e em Lagoa Grande - PE. Semanalmente, de janeiro a dezembro de 2003, foram coletadas folhas para análise dos teores de açúcares redutores (AR), açúcares solúveis totais (AST) e amido,bem como ensaios de invertases ácida (IA) e neutra (IN). Os resultados indicam que os teores de AR, AST e amido aumentam durante a maturação dos frutos e que estes acompanham as variações da temperatura, radiação e insolação. O ciclo de produção do segundo semestre apresentou maiores teores de AR e AST e menores teores de amido que o ciclo do primeiro semestre. A atividade de IA foi maior que ade IN e estas também variaram de acordo com as condições climáticas. A fase de maturação de frutos apresentou maiores teores de açúcares e maior atividade de invertases nas folhas, indicando um alto metabolismo e transporte de açúcares durante essa fase.bitstream/CPATSA/33115/1/BPD70.pd