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

Leading SU(3)-breaking corrections to the baryon magnetic moments in Chiral Perturbation Theory

We calculate the baryon magnetic moments using covariant Chiral Perturbation Theory ($\chi$PT) within the Extended-on-mass-shell (EOMS) renormalization scheme. By fitting the two available low-energy constants (LECs), we improve the Coleman-Glashow description of the data when we include the leading SU(3) breaking effects coming from the lowest-order loops. This success is in dramatic contrast with previous attempts at the same order using Heavy Baryon (HB) $\chi$PT and covariant Infrared (IR) $\chi$PT. We also analyze the source of this improvement with particular attention on the comparison between the covariant results.Comment: 4 pages, 2 figures, accepted for publication in PR

Mutual optical injection in coupled DBR laser pairs

We report an experimental study of nonlinear effects, characteristic of mutual optical coupling, in an ultra-short coupling regime observed in a distributed Bragg reflector laser pair fabricated on the same chip. Optical feedback is amplified via a double pass through a common onchip optical amplifier, which introduces further nonlinear phenomena. Optical coupling has been introduced via back reflection from a cleaveended fibre. The coupling may be varied in strength by varying the distance of the fibre from the output of the chip, without significantly affecting the coupling time. © 2008 Optical. Society of America

[OI] disk emission in the Taurus star forming region

The structure of protoplanetary disks is thought to be linked to the temperature and chemistry of their dust and gas. Whether the disk is flat or flaring depends on the amount of radiation that it absorbs at a given radius, and on the efficiency with which this is converted into thermal energy. The understanding of these heating and cooling processes is crucial to provide a reliable disk structure for the interpretation of dust continuum emission and gas line fluxes. Especially in the upper layers of the disk, where gas and dust are thermally decoupled, the infrared line emission is strictly related to the gas heating/cooling processes. We aim to study the thermal properties of the disk in the oxygen line emission region, and to investigate the relative importance of X-ray (1-120 Angstrom) and far-UV radiation (FUV, 912-2070 Angstrom) for the heating balance there. We use [OI] 63 micron line fluxes observed in a sample of protoplanetary disks of the Taurus/Auriga star forming region and compare it to the model predictions presented in our previous work. The data were obtained with the PACS instrument on board the Herschel Space Observatory as part of the Herschel Open Time Key Program GASPS (GAS in Protoplanetary diskS), published in Howard et al. (2013). Our theoretical grid of disk models can reproduce the [OI] absolute fluxes and predict a correlation between [OI] and the sum Lx+Lfuv. The data show no correlation between the [OI] line flux and the X-ray luminosity, the FUV luminosity or their sum. The data show that the FUV or X-ray radiation has no notable impact on the region where the [OI] line is formed. This is in contrast with what is predicted from our models. Possible explanations are that the disks in Taurus are less flaring than the hydrostatic models predict, and/or that other disk structure aspects that were left unchanged in our models are important. ..abridged..Comment: 9 pages, accepted for publication in A&

Synchronization in a ring of pulsating oscillators with bidirectional couplings

We study the dynamical behavior of an ensemble of oscillators interacting through short range bidirectional pulses. The geometry is 1D with periodic boundary conditions. Our interest is twofold. To explore the conditions required to reach fully synchronization and to invewstigate the time needed to get such state. We present both theoretical and numerical results.Comment: Revtex, 4 pages, 2 figures. To appear in Int. J. Bifurc. and Chao

Acute Myocardial Infarction in the Puerperium

Os autores descrevem um caso clínico de paciente de 42 anos, com enfarte agudo do miocárdio (EAM) ao 3º dia de puerpério, tendo efectuado angioplastia directa. A propósito deste caso fez-se uma revisão das principais alterações fisiológicas cardiovasculares e da hemostase na gravidez, habitualmente bem toleradas pelas gestantes, mas que em mulheres com factores de risco ou com doença cardíaca prévia aumentam a probabilidade de eventos cardiovasculares. O volume sanguíneo e o débito cardíaco aumentam em média 50% durante a gestação, a concentração de hemoglobina diminui e a menor resistência vascular periférica condiciona uma queda da pressão arterial na primeira metade da gravidez. No pós parto imediato verifica-se um incremento na pressão de enchimento ventricular, volume sistólico e débito cardíaco e é no período peri-parto que o risco cardiovascular se encontra mais elevado. A incidência de EAM na gravidez e puerpério é baixa, no entanto a tendência é de aumento, tendo em conta o número crescente de gestações nos extremos da idade reprodutiva