Parallel accelerated cyclic reduction preconditioner for three-dimensional elliptic PDEs with variable coefficients

We present a robust and scalable preconditioner for the solution of large-scale linear systems that arise from the discretization of elliptic PDEs amenable to rank compression. The preconditioner is based on hierarchical low-rank approximations and the cyclic reduction method. The setup and application phases of the preconditioner achieve log-linear complexity in memory footprint and number of operations, and numerical experiments exhibit good weak and strong scalability at large processor counts in a distributed memory environment. Numerical experiments with linear systems that feature symmetry and nonsymmetry, definiteness and indefiniteness, constant and variable coefficients demonstrate the preconditioner applicability and robustness. Furthermore, it is possible to control the number of iterations via the accuracy threshold of the hierarchical matrix approximations and their arithmetic operations, and the tuning of the admissibility condition parameter. Together, these parameters allow for optimization of the memory requirements and performance of the preconditioner.Comment: 24 pages, Elsevier Journal of Computational and Applied Mathematics, Dec 201

A detour in the Road to Totalitarianism:: An extended review of the book “Causas y causantes del desastre económico en Venezuela. Un homenaje a Hugo J. Faría”

An extended review of the book “Causas y causantes del desastre económico en Venezuela. Un homenaje a Hugo J. Faría” (Causes and agents of the economic disaster in Venezuela. A tribute to Hugo J. Faría

Percepción sobre las competencias para escribir artículos científicos en investigadores de ciencias sociales y humanas

Considering that scientific writing presents complex challenges, we sought to determine the level of perception that social and human science researchers have about their competencies to write scientific articles, through a cross-sectional descriptive study in which 129 researchers of both sexes with various years of research experience participated. They self-assessed their writing using the Scale for Evaluating Scientific Articles in Social and Human Sciences by López-López, Tobón and Hernández-Juárez (2019), and an overall result of high level in writing competence was obtained, with a significant effect size; scoring highest in the Results and Reference List sections; while the lowest were in Style and Format and Appendices. When comparing writing competence with the variables gender, research experience or the number of books and articles published, no significant differences were found, despite the fact that in this study males presented a greater number of publications. However, the Methodology section, evaluated with the scale, research experience, as well as belonging to the male gender, were the predictor variables for the publication of articles. Finally, it is recommended that more support be given to female researchers and that more methodological training be provided to new researchers in the interest of promoting educational equity.  Considerando que la escritura científica presenta complejos desafíos, se buscó determinar el nivel de percepción que tienen los investigadores de ciencias sociales y humanas sobre sus competencias para escribir artículos científicos mediante un estudio descriptivo transversal en el que participaron 129 investigadores de ambos sexos con diversos años de experiencia investigadora. Autoevaluaron su escritura mediante la Escala para Evaluar Artículos Científicos en Ciencias Sociales y Humanas de López-López, Tobón y Hernández-Juárez (2019), y se obtuvo un resultado global de nivel alto en la competencia de redacción, con un significativo tamaño del efecto. Las secciones de Resultados y Lista de referencias obtuvieron las puntuaciones más altas, mientras que Estilo y formato y Apéndices fueron las más bajas. Al comparar la competencia en la redacción con las variables género, experiencia investigativa o la cantidad de libros y artículos publicados, no se encontraron diferencias significativas a pesar que en este estudio los varones presentaron mayor número de publicaciones. Sin embargo, la sección de Metodología, evaluado con la escala, la experiencia en investigación, así como pertenecer al género masculino, fueron las variables predictoras de la publicación de artículos. Finalmente, se recomienda apoyar más a las investigadoras y brindar mayor capacitación metodológica a los nuevos investigadores con el interés de fomentar la equidad educativa

From Giant H II regions and H II galaxies to globular clusters and compact dwarf ellipticals

Massive starforming regions like Giant HII Regions (GHIIR) and HII Galaxies (HIIG) are emission line systems ionized by compact young massive star clusters (YMC) with masses ranging from $10^4$M$_\odot$ to $10^8$M$_\odot$. We model the photometric and dynamical evolution over a Hubble time of the massive gravitationally bound systems that populate the tight relation between absolute blue magnitude and velocity dispersion ($M_{B}-\sigma$) of GHIIR and HIIG and compare the resulting relation with that one of old stellar systems: globular clusters, elliptical galaxies, bulges of spirals. After 12~Gyr of evolution their position on the $\sigma$ vs. M$_B$ plane coincides -- depending on the initial mass -- either with the globular clusters for systems with initial mass $M < 10^6$M$_\odot$ or with a continuation of the ellipticals, bulges of spirals and ultracompact dwarfs for YMC with $M >10^6$M$_\odot$. The slope change in the $M_{B}-\sigma$ and $M_B$-size relations at cluster masses around $10^6$M$_\odot$ is due to the larger impact of the dynamical evolution on the lower mass clusters. We interpret our result as an indication that the YMC that ionize GHIIR and HIIG can evolve to form globular clusters and ultra compact dwarf ellipticals in about 12 Gyr so that present day globular clusters and ultra compact dwarf ellipticals may have formed in conditions similar to those observed in today GHIIR and HIIG.Comment: 11 pages, 6 figures, accepted for publication in MNRA