Numerical solution of an eigenvalue problem for bounded plasma

This article is the result of a research on the propagation of electromagneticwaves in a plasma found confined in a cylindrical metal structure through an intenseaxial magnetic field. The eigenvalue problem resulting from this study is numericallysolved and frequencies of the first electromagnetic modes are obtained. Results ofthis work could be applied to characterize plasmas at the laboratory

Numerical solution of an eigenvalue problem for bounded plasma

This article is the result of a research on the propagation of electromagneticwaves in a plasma found confined in a cylindrical metal structure through an intenseaxial magnetic field. The eigenvalue problem resulting from this study is numericallysolved and frequencies of the first electromagnetic modes are obtained. Results ofthis work could be applied to characterize plasmas at the laboratory

The influence of thermal evolution in the magnetic protection of terrestrial planets

Magnetic protection of potentially habitable planets plays a central role in determining their actual habitability and/or the chances of detecting atmospheric biosignatures. Here we develop a thermal evolution model of potentially habitable Earth-like planets and super-Earths (SEs). Using up-to-date dynamo-scaling laws, we predict the properties of core dynamo magnetic fields and study the influence of thermal evolution on their properties. The level of magnetic protection of tidally locked and unlocked planets is estimated by combining simplified models of the planetary magnetosphere and a phenomenological description of the stellar wind. Thermal evolution introduces a strong dependence of magnetic protection on planetary mass and rotation rate. Tidally locked terrestrial planets with an Earth-like composition would have early dayside magnetopause distances between 1.5 and 4.0 Rp , larger than previously estimated. Unlocked planets with periods of rotation ~1 day are protected by magnetospheres extending between 3 and 8 Rp . Our results are robust in comparison with variations in planetary bulk composition and uncertainties in other critical model parameters. For illustration purposes, the thermal evolution and magnetic protection of the potentially habitable SEs GL 581d, GJ 667Cc, and HD 40307g were also studied. Assuming an Earth-like composition, we found that the dynamos of these planets are already extinct or close to being shut down. While GL 581d is the best protected, the protection of HD 40307g cannot be reliably estimated. GJ 667Cc, even under optimistic conditions, seems to be severely exposed to the stellar wind, and, under the conditions of our model, has probably suffered massive atmospheric losses

Implicaciones metodológicas e inconsistencias de la Tercera Comunicación Nacional sobre Cambio Climático de Colombia

Las Comunicaciones Nacionales sobre Cambio Climático (CNCC) son un mecanismo para que los países informen sus avances en mitigación y adaptación, y constituyen uno de los elementos de base para la política sobre cambio climático a escala nacional. Colombia ha emitido tres CNCC. La tercera plantea un escenario que considera las proyecciones de diversos modelos incluidos en la quinta fase del Proyecto de Comparación de Modelos Acoplados (Coupled Model Intercomparison Project, CMIP), el cual se estima como el promedio de las proyecciones correspondientes a las cuatro trayectorias de concentración representativa (Representative Concentration Pathways,RCP) presentadas en el quinto reporte de evaluación del Panel Intergubernamental sobre Cambio Climático. Cada una de estas RCP representa una trayectoria de concentración de gases de efecto invernadero (GEI) para un escenario particular de crecimiento poblacional, económico y tecnológico que conduce a una posible trayectoria de evolución del sistema climático. En este estudio se comparan las proyecciones presentadas en la Tercera CNCC con las obtenidas directamente de los modelos empleados. Nuestros resultados demuestran que al utilizarse un promedio de RCP se pierden escenarios alternos que podrían ser importantes a la hora de considerar posibles futuros diferentes y anulan la utilidad de plantear diversas trayectorias de emisiones de GEI. Más aun, una comparación entre la Segunda y la Tercera CNCC muestra proyecciones de precipitación opuestas para diferentes regiones del país, lo cual es de particular importancia, pues el escenario de cambio climático planteado en la Tercera CNCC sirve de referencia para la toma de decisiones en materia de cambio climático a nivel nacional

Global Spatial Risk Assessment of Sharks Under the Footprint of Fisheries

Effective ocean management and conservation of highly migratory species depends on resolving overlap between animal movements and distributions and fishing effort. Yet, this information is lacking at a global scale. Here we show, using a big-data approach combining satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively) and were also associated with significant increases in fishing effort. We conclude that pelagic sharks have limited spatial refuge from current levels of high-seas fishing effort. Results demonstrate an urgent need for conservation and management measures at high-seas shark hotspots and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real time, dynamic management

Asymptotic, non-linear solutions for ambipolar diffusion in one dimension

Artículo de publicación ISIWe study the effect of the non-linear process of ambipolar diffusion (joint transport of magnetic flux and charged particles relative to neutral particles) on the long-term behaviour of a non-uniform magnetic field in a one-dimensional geometry. Our main focus is the dissipation of magnetic energy inside neutron stars (particularly magnetars), but our results have a wider application, particularly to the interstellar medium and the loss of magnetic flux from collapsing molecular cloud cores. Our system is a weakly ionized plasma in which neutral and charged particles can be converted into each other through nuclear beta decays (or ionizationrecombination processes). In the ‘weak-coupling’ limit of infrequent inter-particle interactions, the evolution of the magnetic field is controlled by the beta decay rate and can be described by a non-linear partial integro-differential equation. In the opposite, ‘strong-coupling’ regime, the evolution is controlled by the inter-particle collisions and can be modelled through a non-linear diffusion equation.We show numerically that, in both regimes, ambipolar diffusion tends to spread out the magnetic flux, but, contrary to the normal Ohmic diffusion, it produces sharp magnetic-field gradients with associated current sheets around those regions where the magnetic field is weak.This work was financed by the Gemini-CONICYT Fund, project no 32070014; FONDECYT regular projects 1060644 and 1070854; the FONDAP Center for Astrophysics (15010003); Proyecto Basal PFB-06/2007 and the joint project ‘Estudio Computacional del decaimiento de campos magn´eticos en estrellas de neutrones’ between Universidad de Medell´ın (Summa Group), Pontificia Universidad Cat´olica de Chile and Universidad de Chile. The post-doctoral stay of JHH at Astrophysikalisches Institut Potsdam was possible due to the financial support of Deutscher Akademischer Austauschdienst (DAAD), Germany, and Comisi´on Nacional de Investigaci´on Cientifica y Tecnol´ogica (CONICYT), Chile, through the postdoctoral fellowship no A0772255-2007-07-DOCDAAD-25. We also thank the FONDECYT International Cooperation Project 7090020

Landau damping in cilyndrical inhomogeneous plasmas

We study the Landau damping for electromagnetic waves in a inhomogeneous cylindrical plasma in the presence of a strong axial magnetic field. For this task we use the kinetic theory for plasmas. This kind of phenomena can not be studied using only macroscopic fluid models. The results of our work can be relevant to identify the behavior of different electromagnetic normal modes propagating through the system, in particular, the energy of the damped modes can be transferred to the plasma particles through resonant interactions and according to the mode polarization can be used in modern particle accelerators based in plasmas. © Published under licence by IOP Publishing Ltd

Asymptotic, non-linear solutions for ambipolar diffusion in one dimension

We study the effect of the non-linear process of ambipolar diffusion (joint transport of magnetic flux and charged particles relative to neutral particles) on the long-term behaviour of a non-uniform magnetic field in a one-dimensional geometry. Our main focus is the dissipation of magnetic energy inside neutron stars (particularly magnetars), but our results have a wider application, particularly to the interstellar medium and the loss of magnetic flux from collapsing molecular cloud cores. Our system is a weakly ionized plasma in which neutral and charged particles can be converted into each other through nuclear beta decays (or ionization-recombination processes). In the ‘weak-coupling’ limit of infrequent inter-particle interactions, the evolution of the magnetic field is controlled by the beta decay rate and can be described by a non-linear partial integro-differential equation. In the opposite, ‘strong-coupling’ regime, the evolution is controlled by the inter-particle collisions and can be modelled through a non-linear diffusion equation. We show numerically that, in both regimes, ambipolar diffusion tends to spread out the magnetic flux, but, contrary to the normal Ohmic diffusion, it produces sharp magnetic-field gradients with associated current sheets around those regions where the magnetic field is weak

Una visión de las ciencias básicas. Modelación y formación aplicadas a casos reales

Una Visión de las Ciencias Básicas (Modelación y Formación aplicadas a casos reales) pretende ilustrar el impacto del modelado y la computación sobre la enseñanza, la investigación y la forma de analizar los fenómenos científicos. En esta obra se muestra como, a partir de estas herramientas, se pueden lograr soluciones a problemas en casos reales en las áreas de Sismología, Imágenes Médicas, Astrofísica, Tratamiento de aguas residuales y en Enseñanza de las Matemáticas. Este libro es producto de investigaciones realizadas por los grupos de Investigación del Departamento de Ciencias Básicas de la Universidad de Medellín: Educación Matemática (SUMMA), Modelación y Computación Científica, Materiales Nano Estructurados y Biomodelación y Ciencias de la Tierra y el Espacio. Los resultados, presentados en este libro, fueron socializados en las X Jornadas de Investigación de la Universidad de Medellín, realizadas en Septiembre de 2012