Parallelized tree–code for clusters of personal computers

We present a tree-code for integrating the equations of the motion of collisionless systems, which has been fully parallelized and adapted to run in several PC-based processors simultaneously, using the well-known PVM message passing library software. SPH algorithms, not yet included, may be easily incorporated to the code. The code is written in ANSI C; it can be freely downloaded from a public ftp site. Simulations of collisions of galaxies are presented, with which the performance of the code is tested.Fil: Viturro, Hector Ruben. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Carpintero, Daniel Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica la Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin

Orbit classification in the meridional plane of a disk galaxy model with a spherical nucleus

We investigate the regular or chaotic nature of star orbits moving in the meridional plane of an axially symmetric galactic model with a disk and a spherical nucleus. We study the influence of some important parameters of the dynamical system, such as the mass and the scale length of the nucleus, the angular momentum or the energy, by computing in each case the percentage of chaotic orbits, as well as the percentages of orbits of the main regular resonant families. Some heuristic arguments to explain and justify the numerically derived outcomes are also given. Furthermore, we present a new method to find the threshold between chaos and regularity for both Lyapunov Characteristic Numbers and SALI, by using them simultaneously.Comment: Published in Celestial Mechanics & Dynamical Astronomy (CMDA) journa

On the trapping of stars by a newborn stellar supercluster

Numerical experiments conducted by Fellhauer et al. (MNRAS, 372, 338, 2006) suggest that a supercluster may capture up to about 40 per cent of its mass from the galaxy where it belongs. Nevertheless, in those experiments the cluster was created making appear its mass out of nothing, rather than from mass already present in the galaxy. Here we use a thought experiment, plus a few simple computations, to show that the difference between the dynamical effects of these two scenarios (i.e., mass creation vs. mass concentration) is actually very important. We also present the results of new numerical experiments, simulating the formation of the cluster through mass concentration, that show that trapping depends critically on the process of cluster formation and that the amounts of gained mass are substantially smaller than those obtained from mass creation.Comment: 6 pages, 3 figures. Submitted to MNRA

Drogas y familia: leyendo juntos a Jordi Sierra i Fabra. Selección de lecturas para la prevención del consumo de drogas con familias

En aquest treball es proposen uns recursos de lectura per treballar des de l’educació social la prevenció del consum de drogues amb famílies. S’ha realitzat una guia de selecció de lectures de l’autor Jordi Sierra i Fabra, amb l’objectiu de proporcionar als adolescents i als seus pares un material de suport, que sigui motivador per a ambdós i que pugui generar l’anàlisi i la discussió sobre els comportaments i les conseqüències del consum de drogues. Les lectures són la base per fomentar el treball conjunt i buscar la trobada entre pares i fills. La proposta de treball està orientada pels objectius proposats en el Pla d’Acció contra les Drogues, 2013-2016, de conscienciació social sobre els riscos associats al consum de drogues i l’augment de les capacitats i habilitats personals, com a factor de protecció davant del consum.This paper proposes a set of reading resources for working from Social Education with families on the prevention of drug use. A guide list of texts by Jordi Sierra i Fabra has been prepared in order to provide adolescents and their parents with motivating support material that should help generate analysis and discussion of behaviours and consequences of drug use. The readings provide the basis for fostering joint work and positive contact between parents and children. The work proposal accords with the objectives outlined in the Action Plan on Drugs, 2013-2016, for social awareness of the risks associated with drug use and of enhancing personal skills and capabilities as a protective factor against consumption.En este trabajo se proponen unos recursos de lectura para trabajar desde la educación social la prevención del consumo de drogas con familias. Se ha realizado una guía de selección de lecturas del autor Jordi Sierra i Fabra, con el objetivo de proporcionar a los adolescentes y a sus padres un material de apoyo, que sea motivador para ambos y que pueda generar el análisis y la discusión sobre los comportamientos y las consecuencias del consumo de drogas. Las lecturas son la base para fomentar el trabajo conjunto y buscar el encuentro entre padres e hijos. La propuesta de trabajo está orientada por los objetivos propuestos en el Plan de Acción contra las Drogas, 2013-2016, de concienciación social sobre los riesgos asociados al consumo de drogas y el aumento de las capacidades y habilidades personales, como factor de protección frente al consumo

A new method to find the potential center of N-body systems

We present a new and fast method to nd the potential center of an N-body distribution. The method uses an iterative algorithm which exploits the fact that the gradient of the potential is null at its center: it uses a smoothing radius to avoid getting trapped in secondary minima. We have tested this method on several random realizations of King models (in which the numerical computation of this center is rather dicult, due to the constant density within their cores), and com- pared its performance and accuracy against a more straightforward, but computer intensive method, based on cartesian meshes of increasing spatial resolution. In all cases, both methods converged to the same center, within the mesh resolution, but the new method is two orders of magnitude faster. We have also tested the method with one astronomical problem: the evolu- tion of a 105 particle King model orbiting around a xed potential that represents our Galaxy. We used a spherical harmonics expansion N-body code, in which the potential center determination is crucial for the correct force computation. We compared this simulation with another one in which a method previously used to determine the expansion center is employed (White 1983). Our routine gives better results in energy conservation and mass loss.Fil: Aguilar, L. A.. Universidad Nacional Autonoma de Mexico. Instituto de Astronomia; MéxicoFil: Cruz, F.. Universidad Nacional Autonoma de Mexico. Instituto de Astronomia; MéxicoFil: Carpintero, Daniel Diego. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin

LP-VIcode: a program to compute a suite of variational chaos indicators

An important point in analysing the dynamics of a given stellar or planetary system is the reliable identification of the chaotic or regular behaviour of its orbits. We introduce here the program LP-VIcode, a fully operational code which efficiently computes a suite of ten variational chaos indicators for dynamical systems in any number of dimensions. The user may choose to simultaneously compute any number of chaos indicators among the following: the Lyapunov Exponents, the Mean Exponential Growth factor of Nearby Orbits, the Slope Estimation of the largest Lyapunov Characteristic Exponent, the Smaller ALignment Index, the Generalized ALignment Index, the Fast Lyapunov Indicator, the Othogonal Fast Lyapunov Indicator, the dynamical Spectra of Stretching Numbers, the Spectral Distance, and the Relative Lyapunov Indicator. They are combined in an efficient way, allowing the sharing of differential equations whenever this is possible, and the individual stopping of their computation when any of them saturates.Comment: 26 pages, 9 black-and-white figures. Accepted for publication in Astronomy and Computing (Elsevier

Una nueva especie de Cyrtotylus (Heteroptera: Miridae: Orthotylinae) de la Guayana Francesa

Se describe a la nueva especie Cyrtotylus henryi (Orthotylinae, Orthotylini) en base a una hembra de la Guayana Francesa. Se dan justificaciones para esta acción. El género CyrtotylusBergroth, 1922 es mencionado por primera vez para la Guayana Francesa.Cyrtotylus henryi (Orthotylinae, Orthotylini) is described as a new species on the base of a female from French Guyana. Justifications are offered for this action. The genus Cyrtotylus Bergroth, 1922 is mentioned for the first time from French Guyana.Fil: Carpintero, Diego Leonardo. Fundación de Historia Natural Félix de Azara; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; ArgentinaFil: Chérot, Frédéric. Service Public de Wallonie; Bélgic