Efficacy of a magnetic shield against a Vlasov-Poisson plasma

The aim of the paper is to test on a simple model how impenetrable may be a magnetic shield. We study the time evolution of a single species positive plasma, confined in the half-space $x_1>0$. The confinement is the result of a balance between a magnetic field and an external field, both singular at $x_1=0$; the magnetic field forbids the entrance of plasma particles in the region $x_1 \leq 0$, whereas the external field attracts the plasma particles towards $x_1=0$. The plasma has finite total charge and velocities distributed with a Maxwell-Boltzmann law.Comment: arXiv admin note: text overlap with arXiv:1602.04164, arXiv:1706.0873

The Vlasov-Poisson equation in R3\mathbb{R}^3 with infinite charge and velocities

We consider the Vlasov-Poisson equation in $\mathbb{R}^3$ with initial data which are not $L^1$ in space and have unbounded support in the velocities. Assuming for the density a slight decay in space and a strong decay in velocities, we prove existence and uniqueness of the solution, thus generalizing the analogous result given in [5] for data compactly supported in the velocities

On the magnetic shield for a Vlasov-Poisson plasma

We study the screening of a bounded body $\Gamma$ against the effect of a wind of charged particles, by means of a shield produced by a magnetic field which becomes infinite on the border of $\Gamma$. The charged wind is modeled by a Vlasov-Poisson plasma, the bounded body by a torus, and the external magnetic field is taken close to the border of $\Gamma$. We study two models: a plasma composed by different species with positive or negative charges, and finite total mass of each species, and another made of many species of the same sign, each having infinite mass. We investigate the time evolution of both systems, showing in particular that the plasma particles cannot reach the body. Finally we discuss possible extensions to more general initial data. We show also that when the magnetic lines are straight lines, (that imposes an unbounded body), the previous results can be improved

Low temperature impact of composite hull wall with floating rigid body

An experimental activity conducted in order to assess the impact behavior, at room and low temperature, of laminates used in the shipbuilding industry, was reported. The conditions which reproduce the impact of a hull at low temperature with a solid body suspended in the water was reproduced. A test equipment was designed and realized to reproduce the real material behaviour in water to obtain a load distribution on the entire surface of the specimen. The results were obtained impacting the laminates placed between the cilyndrical steel impactor and the bag containing water. A falling weight machine equipped with an instrumented steel impactor and a thermal chamber was adopted for the experimental tests. Laminates made by vinyl ester matrix and carbon fibres were considered during the tests, and the results in terms of impact behaviour in hostile environments were compared to what obtained at room temperature. The data obtained under a distributed load were also compared with the results of impacts at concentrated loads

Media Literacy in Brazil: Experiences and Models in Non-formal Education

Este artículo analiza el estado actual de la alfabetización mediática existente en Brasil desde la perspectiva de la educación no formal. Cuantifica la situación mediante una muestra de proyectos (N=240) y de organizaciones (N=107) que desarrollan actividades conforme a las tres principales dimensiones de la educación mediática reconocidas internacionalmente (acceso/uso, comprensión crítica, y producción de contenidos mediáticos), y que están orientadas a diferentes comunidades de ciudadanos de acuerdo a diversos niveles de segmentación (edad, lugar, situación social, grupos sociales, y campos profesionales de aplicación). El análisis realizado muestra la preponderancia de actividades de producción de contenidos audiovisuales (65,4%) y de ampliación de derechos y capacidades comunicativas de ciertas comunidades de personas generalmente excluidas de los medios de comunicación tradicionales (45,8%). Además, la mayoría de las organizaciones trabajan con propuestas con un potencial medio y alto de empoderamiento (77,6%). Asimismo, y basándose en la literatura y el diagnóstico realizado, se propone un modelo con el que estudiar los proyectos de educación mediática desarrollados en el ámbito de la educación no formal. De este modo, la investigación presenta una primera imagen de la alfabetización mediática de carácter no formal existente en un país que, por sus dimensiones y grandes diferencias sociales, tiene que saber aprovechar las complementariedades que la educación no formal ofrece a la educación formal y al currículum educativo, respecto a desarrollar educación mediática y empoderar a la ciudadaníaThis article analyses the status of media literacy in Brazil from the perspective of non-formal education. It quantifies the situation through a sample of projects (N=240) and organizations (N=107) that develop media literacy activities according to the internationally recognized three dimensions of media education (access/use, critical understanding, and media content production). These projects are aimed at different communities of citizens according to various levels of segmentation (age, location, social status, social groups, and professional fields). The analysis shows the preponderance of activities geared to the production of audiovisual content (65.4%) and to expanding the rights and communicative capabilities of certain communities, generally excluded from the traditional mass media (45.8%). Moreover, the majority of institutions have projects with a medium and high potential of empowerment (77.6%). Based on the literature review and the analysis conducted, the research presents a model that can be used for studying media education projects in the field of non-formal education. Thus, this article offers an initial look at non-formal media literacy in a country that, due to its size and large social differences, should take advantage of the complementarities that non-formal education provides to formal education and its curriculum, regarding the development of media education and empowerment of citizen