Electronic transport in locally gated graphene nanoconstrictions

We have developed the combination of an etching and deposition technique that enables the fabrication of locally gated graphene nanostructures of arbitrary design. Employing this method, we have fabricated graphene nanoconstrictions with local tunable transmission and characterized their electronic properties. An order of magnitude enhanced gate efficiency is achieved adopting the local gate geometry with thin dielectric gate oxide. A complete turn off of the device is demonstrated as a function of the local gate voltage. Such strong suppression of device conductance was found to be due to both quantum confinement and Coulomb blockade effects in the constricted graphene nanostructures.Comment: 3 pages 3 figures; separated and expanded from arXiv:0705.3044v

The Medical Profession. A Construction of the Professional Ideology

Objectives: Describe the ideological components in the educational process of medical professionals and their practice

Electronic Transport in Dual-gated Bilayer Graphene at Large Displacement Fields

We study the electronic transport properties of dual-gated bilayer graphene devices. We focus on the regime of low temperatures and high electric displacement fields, where we observe a clear exponential dependence of the resistance as a function of displacement field and density, accompanied by a strong non-linear behavior in the transport characteristics. The effective transport gap is typically two orders of magnitude smaller than the optical band gaps reported by infrared spectroscopy studies. Detailed temperature dependence measurements shed light on the different transport mechanisms in different temperature regimes.Comment: 4 pages, 3 figure

Dinámica estocástica en física y biología

Tesis de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Estructura de la Materia, Física Térmica y Electrónica, leída el 26-10-2018Stochastic processes are present in virtually any field of science. Actually, in general deterministic processes are no more than an approximation of more complex stochastic processes in some regime of validity. In the present thesis, we will study some systems that appear in Physics and Biology where the presence of these stochastic processes plays a major role. First, we will study the Brownian ratchet systems, which are able to generate a directed motion simply by rectifying the thermal fluctuations to which Brownian particles are subjected. These Brownian ratchets began to be studied in the field of Statistical Physics as a Gedanken experiment that apparently broke the Second Law of Thermodynamics. Later they were applied to study the operation of some molecular motors. In this thesis we will study different types of Brownian ratchets, characterizing the average flux, the efficiency, and the quality of the transport of particles they produce..En prácticamente cualquier rama de la ciencia están presentes los procesos estocásticos. De hecho, en general los procesos deterministas no son más que una aproximación de procesos estocásticos más complejos en algún régimen de validez. En la presente tesis, estudiaremos algunos sistemas que aparecen en Física y Biología donde la presencia de dichos procesos es crucial.Primero, estudiaremos los conocidos como trinquetes brownianos, que son capaces de generar movimiento dirigido simplemente a través de la rectificación de las fluctuaciones térmicas a las que se ven sometidas las partículas Brownianas. Estos trinquetes Brownianos se empezaron a estudiar en el campo de la Física Estadística como un experimento mental que aparentemente rompía la Segunda Ley de la Termodinámica. Sin embargo, más adelante se ha visto que pueden ser aplicados para estudiar el funcionamiento de algunos motores moleculares. En esta tesis estudiaremos distintos tipos de trinquetes Brownianos, caracterizando el flujo medio, la eficiencia, y la calidad del transporte de partículas que producen...Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEunpu

Introducción

Aunque ha habido algunas excepciones –el neonacionalismo británico disconforme con la revisión de la culpabilidad alemana en el origen de la guerra–, lo cierto es que la tónica general de estas conmemoraciones ha sido el intentar escapar al mero ámbito nacional para llegar a uno primero europeo y, en realidad, global. Basta con darse cuenta de que los libros que han sido importantes en la mayor parte de los países y que más se han vendido han sido prácticamente los mismos, con el de Christopher Clark a la cabeza. Estimo que –pese a diferentes acentos en los debates, bien mostrados por los artículos del presente dossier– hoy día se puede hablar sin exagerar de una conmemoración verdaderamente global

Agujeros negros de Reissner-Nordstrom en teorías de electrodinámica modificada

Máster de Física Fundamental. Facultad de Ciencias Físicas. Curso 2013-2014.In the context of modified and gauge invariant Electrodynamics theories minimally coupled with gravitation we look for the U(1) Lagrangian densities supporting electric and magnetic monopoles which provide sta Nordström black-hole solutions. We achieve a sufficient condition for general Lagrangian densities supporting this kind of solutions, and we propose a simple model which can be interpreted as a small correction to the usual Electrodynamics theory, which is proven to be correct in the asymptotic limit r → ∞ . For these models we obtain their correspondent metrics, and then by employing the Euclidean Action approach we perform a thermodynam- ics analysis and study the existing phases depending on the sign of the heat capacity and the Helmholtz free energy. Thus, we obtain that modified Electrodynamics theories lead to ve different thermodynamics properties and, in some particular cases, to a new phase which does not appear in the usual theory.En el marco de las teorías de electrodinámica modificada, invariantes gauge y minimamente acopladas a la gravedad, buscamos las densidades lagrangianes con simetría U(1) que admiten monopolos eléctricos y magnéticos en soluciones de agujero negro de Reissner-Nordström estáticas, esféricamente simétricas y de curvatura constante. En este trabajo obtenemos una condición suficiente para que las densidades Lagrangianas posean este tipo de soluciones, y proponemos un modelo simple que puede ser interpretado como una pequeña corrección a la teoría electrodinámica usual, la cual sabemos que es correcta en el límite asintótico r → ∞ . Para dichos modelos obtenemos las correspondientes métricas, y empleando el método de la acción euclídea realizamos un análisis termodinámico y estudiamos las fases de estabilidad presentes, en función del signo de la capacidad calorífica y de la energía libre de Helmholtz. Así, obtenemos que las teorías de electrodinámica modificada conllevan propiedades termodinámicas muy diferentes para las soluciones y, en algunos casos particulares, una nueva fase de estabilidad que no aparece en la teoría usual.Depto. de Física TeóricaFac. de Ciencias FísicasTRUEunpu

NUMERICAL SIMULATION OF A UAV WING AND SEVERAL MODIFICATIONS TO IMPROVE RANGE AND ENDURANCE

This thesis presents numerical simulations aimed at improving the aerodynamic performance of an unmanned aerial vehicle (UAV) wing through minor modifications. On most aircraft, the bulk of the lift and a large portion of the drag are produced by the wing; therefore, optimization of the wing is likely to have the most significant impact on aircraft performance, including critical parameters like range and endurance. When minor changes are required, there are prominent options to explore for improving the wing's aerodynamic efficiency. Three different configurations were analyzed; wing extension, raked wingtip, and blended winglet, to find which affects in a more positive way the performance of the UAV wing. Taking advantage of the short processing time delivered for low-fidelity numerical tools like Flow5, the exploration of the main parameters for the three configurations were explored and optimized to reach the best lift to drag ratio (L/D). Finally, the optimized configurations were analyzed using Ansys-CFX software to capture the viscous effects and boundary layer behavior more accurately, which are known limitations of the low-fidelity tools. The study found that incorporating raked wingtips into the UAV wing design is the most effective way to improve the aircraft's range and endurance. This modification only slightly increases the wing bending moment and has practically no impact on the pitching moment.Approved for public release. Distribution is unlimited.Outstanding ThesisCapitan de Corbeta, Mexican Nav

Introducción

.