Propiedades electrónicas del grafeno sobre un sustrato piezoeléctrico

Tesis de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 20/09/2018In the present work, we investigate theoretically the electronic propierties of a graphene layer on a piezoelectric substrate. Specifically, we study the efect of the surface acoustic vibration modes on the graphene electrons.This work is divided in six chapters plus several appendices whose goal is to render the material as self-contained as possible. The rest chapter introduces a basic survey of the main actors in this work. Graphene is a two-dimensional material that has received increasin gworldwide attention since its isolation by Novoselov and Geim in 2004. It is formed by a honeycomb lattice of carbon atoms. Graphite, the most common form of pure carbon, can be viewed as made of weekly coupled graphene layers. The single-atom thickness of graphene, combined with its unique electronic properties stemming from the effectively massless behavior of electrons, converts this material into a special object of high fundamentaland applied interest...En el presente trabajo investigamos teoricamente las propiedades electrónicas de una capa de grafeno sobre un sustrato piezoelectrico. Concretamente, estudiamos el efecto de los modos de vibracion acusticos de superficie sobre los electrones del grafeno. Este trabajo esta dividido en seis captulos y varios apendices, siendo el objetivo de estos ultimos el que el material sea lo mas autocontenido posible. El primer capítulo introduce una vision general de los actores principales en este trabajo. El grafeno es un material de dos dimensiones que ha atraído una atencion creciente internacionalmente desde su aislamiento por Novoselov y Geim en 2004. Esta formado por una red de átomos de carbono en forma de panal. El grafito, la forma mas común de carbono puro, puede ser visto como si estuviera hecho por laminas de grafeno debilmente acopladas. El grosor atomico del grafeno, combinado con sus propiedades electrónicas únicas originadas por el comportamiento de sus electrones como si no tuvieran masa, convierte a este material en un objeto excepcional de elevado interés fundamental y aplicado...Depto. de Física de MaterialesFac. de Ciencias FísicasTRUEunpu

Confidence-Based Learning in Investment Analysis

The aim of this study is to determine the effectiveness of using multiple choice tests in subjects related to the administration and business management. To this end we used a multiple-choice test with specific questions to verify the extent of knowledge gained and the confidence and trust in the answers. The tests were performed in a group of 200 students at the bachelor's degree in Business Administration and Management. The analysis made have been implemented in one subject of the scope of investment analysis and measured the level of knowledge gained and the degree of trust and security in the responses at two different times of the course. The measurements have been taken into account different levels of difficulty in the questions asked and the time spent by students to complete the test. The results confirm that students are generally able to obtain more knowledge along the way and get increases in the degree of trust and confidence in the answers. It is confirmed as the difficulty level of the questions set a priori by the heads of the subjects are related to levels of security and confidence in the answers. It is estimated that the improvement in the skills learned is viewed favourably by businesses and are especially important for job placement of students

Robustness of airline alliance route networks

The aim of this study is to analyze the robustness of the three major airline alliances’ (i.e., Star Alliance, oneworld and SkyTeam) route networks. Firstly, the normalization of a multi-scale measure of vulnerability is proposed in order to perform the analysis in networks with different sizes, i.e., number of nodes. An alternative node selection criterion is also proposed in order to study robustness and vulnerability of such complex networks, based on network efficiency. And lastly, a new procedure – the inverted adaptive strategy – is presented to sort the nodes in order to anticipate network breakdown. Finally, the robustness of the three alliance networks are analyzed with (1) a normalized multi-scale measure of vulnerability, (2) an adaptive strategy based on four different criteria and (3) an inverted adaptive strategy based on the efficiency criterion. The results show that Star Alliance has the most resilient route network, followed by SkyTeam and then oneworld. It was also shown that the inverted adaptive strategy based on the efficiency criterion – inverted efficiency – shows a great success in quickly breaking networks similar to that found with betweenness criterion but with even better results.Peer ReviewedPostprint (author’s final draft

An unconditional maximum likelihood test for a unit root

We investigate a test for unit roots in autoregressive time series based on maximization of the unconditional likelihood. This is the likelihood function appropriate for stationary time series. While this function is the true likelihood only under the stationary alternative, it can nevertheless be maximized for any data including data from a unit root process. It thus gives a way to test for unit roots, provided percentill~s can be calculated. For models with estimated means, the power of the new test is better than that of some currently popular tests

La caracterización de la práctica docente de cuatro profesores sobresalientes en el área de matemáticas para ingenierías a nivel universitario

En el área de matemáticas para ingeniería generalmente se imparten las materias de cálculo diferencial e integral, cálculo multivariable, ecuaciones diferenciales, entre otros. Aunque Moreno (2005) se refiere específicamente al cálculo, la enseñanza de los principios de estas asignaturas resulta problemática ya que frecuentemente se logran competencias algorítmicas y algebraicas pero se queda lejos de una verdadera comprensión de los conceptos y métodos de pensamiento de esta parte de las matemáticas. De esta forma se presenta un círculo vicioso en donde “... para obtener niveles aceptables de éxito se evalúa aquello que los estudiantes pueden hacer mejor, convirtiendo lo evaluado en lo esencial para los estudiantes” (Artigue, 1995 citado en Moreno, 2005, p.82). Otro riesgo que se presenta en esta situación es que se propicia que los contenidos matemáticos queden desvinculados de la problemática que se abordan en la ingeniería. Zúñiga (2007) señala “Esto tiene consecuencias negativas cuando los que aprenden son estudiantes que en el ejercicio de su profesión requieren de conocimientos y habilidades que les permitan resolver problemas de verdad”. Ante este panorama se considera conveniente investigar el proceso de enseñanza-aprendizaje con miras a generar conocimiento de esta situación, y a partir de esta comprensión, apoyar en la búsqueda de caminos para que las matemáticas que se imparten a nivel universitario se vayan convirtiendo en un espacio rico en alternativas para la formación de los futuros ingenieros. Del proceso de enseñanza-aprendizaje esta investigación se enfoca estudiar la práctica docente. Específicamente la de los profesores sobresalientes, tomando como marco de referencia la relación pedagógica propuesta por Fierro, Fortoul y Rosas (1999)

Power Factor Corrector Design applied to an 85-kHz Wireless Charger

Wireless charging technology extends the battery autonomy by allowing more flexible and practical ways of recharging it even when the electric vehicle is on move. The frequency conversion, which is required to generate a kHz-ranged magnetic field, also leads to considerable harmonics. As a result, the power factor and the corresponding efficiency decrement. This paper proposes a Power Factor Corrector which overcomes this drawback. The most relevant feature of the designed Power Factor Corrector is that it does not need any electrical signal from the secondary side to adjust its operation properly. The simulation results show the ability of the proposed scheme to increment the system efficiency for different State-Of-Charge in the Battery.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech