Some applications of semi-discrete variational integrators to classical field theories

We develop a semi-discrete version of discrete variational mechanics with applications to numerical integration of classical field theories. The geometric preservation properties are studied.Comment: 14 page

An assessment of bottom current controlled sedimentation in Pacific Ocean abyssal environments

The effect of the circulation of polar-sourced dense waters on the deep seafloor is still largely unknown. This paper presents multibeam bathymetric evidence for the existence of present-day contourite drifts on the central Pacific ocean at depths ranging between 4000 and 5000 m, based on the identification of their diagnostic erosive (moats, linear moats, furrows and abyssal sinuous channels) and depositional (plastered, elongated separated and abyssal contourite-fan drifts) contourite morphological features. These contourite drifts display a patchy distribution, sculpted by the secondary flows of the Lower Circumpolar Water (LCPW) and the North Pacific Deep Waters (NPDW), as well as local dynamics of the flow in the form of internal waves and bottom currents modulated by tides, which are capable of accelerating the typically sluggish bottom currents and contribute to the erosion, transport and deposition of sediments. The formation of contourites is also predominantly controlled by the presence of large-scale tectonic and volcanic features (ridges, seamounts and deep elongated valleys), which affect the morphology and distribution of the basins and induce the acceleration of bottom currents. Overall, this study allows to re-assess the effects, distribution and significance of bottom-current controlled sedimentation in abyssal environments, where examples of contourite features are still rather scarce in part because of the technical challenges and their remote location, but also because the effect of bottom currents is not well known in the central oceanic basins and only capable of marginally affecting their sedimentological record

Imaginación y reacción en los Campamentos de refugiados saharauis : construcción de la cotidianeidad e identidad frente al otro extranjero (nasrani) en el contexto de la diáspora

Los Campamentos de refugiados son una parte dramática de la historia del pueblo saharaui con poca referencia bibliográfica. Esta situación ha impuesto una serie de límites ante los cuales la imaginación de la sociedad civil ha reaccionado y ha generado un espacio alternativo donde vivir. La revolución contra el colonialismo es además una lucha por cambiar el propio pasado y algunos hábitos culturales. Y desde el refugio y el exilio se han abierto nuevas alternativas que ha aprovechado la educación como pilar fundamental de la revolución. Desde ella se prepara a las nuevas generaciones para la libertad y a través de ella se recupera y enseña la identidad nacional saharaui. Este trabajo muestra la labor y las dificultades que rodean al mundo de la educación en el refugio y la importancia que tiene la memoria histórica.Saharawi refugee camps, with little references, are part of the recent tragic history. This situation has imposed a series of limits to which the imagination of civil society has reacted and has generated an alternative space in which to live. The revolution against colonialism was also a struggle to change the past and some cultural habits. And the refuge and the exile have opened new alternatives which have taken education as a fundamental pillar of the revolution. Since it prepares future generations for freedom and through it to recover and teach the Saharawi national identity. This paper shows the work and the difficulties surrounding the world of education at the shelter and the importance of historical memory

CEST and MEST: Tools for the simulation of radio frequency electric discharges in waveguides

This is the author’s version of a work that was accepted for publication in Simulation Modelling Practice and Theory. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Simulation Modelling Practice and Theory, 16, 9, (2008) http://dx.doi.org/10.1016/j.simpat.2008.08.002In this paper we present two software tools for the simulation of electron multiplication processes in radio frequency (RF) waveguides. The electric discharges are caused by the multiplication of a small initial number of electrons. These are accelerated by the RF field and produce new electrons either by collisions with the walls of the waveguide (ripping new electrons from them), or by ionization of the neutral atoms of a gas inside the device. MEST allows simulating the Multipactor effect, a discharge produced in vacuum and generated by the collision of the electrons with the walls. CEST simulates the discharge when in addition a neutral gas is present in the waveguide, at pressures lower than ground levels (often denominated Corona discharge). The main characteristic of both tools is that they implement individual-based, microscopic models, where every electron is individually represented and tracked. In the case of MEST, the simulation is discrete-event, as the trajectory of each electron can be computed analytically. In CEST we use a hybrid simulation approach. The trajectory of each electron is governed by the Langevin stochastic differential equations that take into account a deterministic RF electric force and the random interaction with the neutral atom background. In addition, wall and ionizing collisions are modelled as discrete events. The tools allow performing batches of simulations with different wall coating materials and gases, and have produced results in good agreement with experimental and theoretical data. The different output forms generated at run-time have proven to be very useful in order to analyze the different discharge processes. The tools are valuable for the selection of the most promising coating materials for the construction of the waveguide, as well as for the identification of safe operating parameters.Work sponsored by the ESA, TRP activity program 17025/03/NL/EC: Surface Treatment and Coating