On the variational structure of breather solutions

In this paper we give a systematic and simple account that put in evidence that many breather solutions of integrable equations satisfy suitable variational elliptic equations, which also implies that the stability problem reduces in some sense to $(i)$ the study of the spectrum of explicit linear systems (\emph{spectral stability}), and $(ii)$ the understanding of how bad directions (if any) can be controlled using low regularity conservation laws. We exemplify this idea in the case of the modified Korteweg-de Vries (mKdV), Gardner, and sine-Gordon (SG) equations. Then we perform numerical simulations that confirm, at the level of the spectral problem, our previous rigorous results, where we showed that mKdV breathers are $H^2$ and $H^1$ stable, respectively. In a second step, we also discuss the Gardner and the Sine-Gordon cases, where the spectral study of a fourth-order linear matrix system is the key element to show stability. Using numerical methods, we confirm that all spectral assumptions leading to the $H^2\times H^1$ stability of SG breathers are numerically satisfied, even in the ultra-relativistic, singular regime. In a second part, we study the periodic mKdV case, where a periodic breather is known from the work of Kevrekidis et al. We rigorously show that these breathers satisfy a suitable elliptic equation, and we also show numerical spectral stability. However, we also identify the source of nonlinear instability in the case described in Kevrekidis et al. Finally, we present a new class of breather solution for mKdV, believed to exist from geometric considerations, and which is periodic in time and space, but has nonzero mean, unlike standard breathers.Comment: 55 pages; This paper is an improved version of our previous paper 1309.0625 and hence we replace i

La reforma procesal penal en Chile: Nuevos agentes, sus trayectorias y la reestructuración de un campo

En un contexto marcado por el fin de la dictadura, la transición democrática y a partir del estado del campo jurídico en Chile, el artículo analiza la trayectoria de los juristas que promovieron la reforma procesal penal y la estrategia que para este objetivo llevan a cabo. Estos agentes incorporan a representantes de los diversos intereses al interior del campo jurídico y, también como parte de esta estrategia, importan una expertise jurídica, brindándole de esta manera legitimidad política y técnica a sus propuestas. Esto, sumado al capital jurídico que adquieren en este proceso, permite que estos agentes puedan instalar su propuesta en la agendade reformas a la justicia durante la transición democrática. Finalmente, se observa cómo este capital y legitimidad, que son resultado de la interacción del nivel internacional y local, les permiten participar en la transformación y estructuración del emergente espacio regional de reformas de la justicia

Giant magnetoresistance in ultra-small Graphene based devices

By computing spin-polarized electronic transport across a finite zigzag graphene ribbon bridging two metallic graphene electrodes, we demonstrate, as a proof of principle, that devices featuring 100% magnetoresistance can be built entirely out of carbon. In the ground state a short zig-zag ribbon is an antiferromagnetic insulator which, when connecting two metallic electrodes, acts as a tunnel barrier that suppresses the conductance. Application of a magnetic field turns the ribbon ferromagnetic and conducting, increasing dramatically the current between electrodes. We predict large magnetoresistance in this system at liquid nitrogen temperature and 10 Tesla or at liquid helium temperature and 300 Gauss.Comment: 4 pages, 4 figure

Carbon dioxide hydrogenation by means of plasmonic resonance activation

En la presente tesis se ha realizado la transformación del dióxido de carbono con el objetivo de producir metanol. Para ello se ha propuesto un novedoso método que incluye la síntesis de un nuevo catalizador que puede absorber mayor cantidad de luz gracias a la resonancia superficial de plasmones, y que se ha integrado en aerogeles de sílice transparentes que actúan como soporte para la reacción. Se ha diseñado una planta experimental en la que el catalizador se impregna en microreactores de vidrio rodeados de luces LED que son la fuente de energía para la reacción. El sistema ha sido optimizado para lograr la máxima velocidad de conversión del dióxido de carbono posible.Departamento de Ingeniería Química y Tecnología del Medio AmbienteDoctorado en Investigación en Ingeniería Termodinámica de Fluido

Hydrogenated Graphene Nanoribbons for Spintronics

We show how hydrogenation of graphene nanoribbons at small concentrations can open new venues towards carbon-based spintronics applications regardless of any especific edge termination or passivation of the nanoribbons. Density functional theory calculations show that an adsorbed H atom induces a spin density on the surrounding $\pi$ orbitals whose symmetry and degree of localization depends on the distance to the edges of the nanoribbon. As expected for graphene-based systems, these induced magnetic moments interact ferromagnetically or antiferromagnetically depending on the relative adsorption graphene sublattice, but the magnitude of the interactions are found to strongly vary with the position of the H atoms relative to the edges. We also calculate, with the help of the Hubbard model, the transport properties of hydrogenated armchair semiconducting graphene nanoribbons in the diluted regime and show how the exchange coupling between H atoms can be exploited in the design of novel magnetoresistive devices

Diseño y construcción de sensores automatizados de gases de efecto invernadero en la baja troposfera

La determinación del contenido de monóxido de carbono (CO) y metano (CH4) en la baja troposfera tiene gran importancia en los estudios de cambio climático y polución del aire. Por este motivo, este trabajo se enfocó en el diseño, construcción y calibración de un instrumento que permita medir la concentración de CO y CH4, además de la temperatura y presión ambiental. El dispositivo diseñado cuenta con un circuito de acople para los sensores de CO, CH4, temperatura y presión, un microcontrolador, una pantalla LCD, un reloj y una microSD para el almacenamiento y transmisión de datos a través de un convertidor RS- 232 a USB. Los resultados indican que la señal de los detectores de CO y CH4 genera una respuesta de tipo exponencial proporcional con la concentración en el rango de 0 a 120 ppm, sin embargo, se estableció que la respuesta fue de tipo lineal para concentraciones bajas en el rango 0 a 15 ppm. La respuesta de los gases evaluados difiere para cada uno de los sensores, siendo el CH4 el que mostró la mejor sensibilidad en el rango de 0 a 2 ppm. // The determination of carbon monoxide (CO) and methane (CH4) in the lower troposphere is of great importance in studies of climate change and air pollution. This work is focused on the design, construction and calibration of an instrument to measure the concentration of CO and CH4, as well as the temperature and pressure of atmospheric air. The designed device also has a coupling circuit, a microcontroller, a LCD display, a clock and a MicroSD which enables the storage and transmission of data via a RS-232 to USB. The results indicate that the signal of the CO and CH4 detectors have an exponential response, which is proportional to the concentration in the range of 0 to 120 ppm, however, it was established that the response was linear for low concentrations in the range 0 to 15 ppm. The instrument sensitivity differs for both gases evaluated, being CH4 which showed the best sensitivity in the range of 0 to 2 ppm

El desarrollo de un programa de preservación ideal para documentos digitales

Se presenta una guía práctica de las etapas que llevan a cabo aquellos quienes se embarcan en el proceso de la preservación digital o que proyectan hacerlo. El objetivo del plan de preservación que aquí se describe es el de preservar la integridad de los objetos digitales para permitir a los usuarios su localización, visualización y en último término utilización de los mismos haciendo frente a constantes cambios tecnológicos. En este sentido, es una necesidad el preservar a lo largo del tiempo tanto el documento creado directamente en digital como aquel que ha sido reconvertido o digitalizado. El artículo analiza el elenco de opciones existentes en cuanto a la preservación digital se refiere determinando las habilidades requeridas por el profesional de la información para que éste sea capaz de preservar dichos objetos.This article intended to provide practical guidance to those undertaking digital preservation or considering doing so. The purpose of the following preservation planning is to preserve the integrity of digital objects and to retain the ability for users to retrieve, display, and otherwise use them in the face of constantly changing technology. There is therefore a need to preserve long term both born-digital and digital surrogate material. The report explores the range of options for digital preservation provides an analysis of the digital landscape, focusing on features that affect the integrity of digital information objects and which determine the ability of information professionals to preserve such objects over the long term

Coherent transport in graphene nanoconstrictions

We study the effect of a structural nanoconstriction on the coherent transport properties of otherwise ideal zig-zag-edged infinitely long graphene ribbons. The electronic structure is calculated with the standard one-orbital tight-binding model and the linear conductance is obtained using the Landauer formula. We find that, since the zero-bias current is carried in the bulk of the ribbon, this is very robust with respect to a variety of constriction geometries and edge defects. In contrast, the curve of zero-bias conductance versus gate voltage departs from the $(2n+1) e^2/h$ staircase of the ideal case as soon as a single atom is removed from the sample. We also find that wedge-shaped constrictions can present non-conducting states fully localized in the constriction close to the Fermi energy. The interest of these localized states in regards the formation of quantum dots in graphene is discussed.Comment: 9 pages, 9 figure

An Analysis Of Strategic Information Published By Large Spanish Hotel Chains.

At present when the market is increasingly demanding free-flowing information concerning corporate expectations, we often encounter criticism as to the absence of this type of information in annual reports. The relevance of this lack of information is based, among other reasons, on the fact that it is the only information that businesses make public. With this hypothesis as a point of departure, we have asked ourselves if this same situation is also produced in the Spanish hotel sector. Our interest in this business is due to the importance of the tourism sector in the Spanish economy. To contrast this hypothesis, we have carried out field work consisting of, firstly, a review of annual reports for the fiscal years 2000, 2001 and 2002 published by hotel chains representative of the sector and, secondly, an analysis of the information concerning the strategies published in these reports. This paper is part of a research stream that remains open and whose objective is the elaboration of a Balanced Scorecard prototype for the Spanish Hotel Sector.