Substitution of electrolytic capacitors commonly used in solar inverters by film capacitors specifically designed for the application

68 páginasTrabajo fin de Máster supervisado por Jorge Aguilera Tejero. Se presenta una revisión de topologías de inversores solares, enfocándose en las tecnologías usadas para el diseño del banco DC-link de condensadores. Se presenta un nuevo diseño de condensador de cinta apropiado para el uso en inversores solares. Se repasan sus características y se comparan con las que ofrecen otras tecnologías de condensadores, principalmente, los electrolíticos// Capacitors are profusely used in photovoltaic systems as protecting elements for people and the equipment, also as filters and, more specifically, in the solar inverter in the so-called DC-Link position. The operation of the solar generators is certainly singular both in the environmental operating conditions but also in the electrical conditions that their subsystems must withstand during operation. On the one hand, they are usually subjected to strong variations and possible over-voltages. On the other hand, the high quality and reliability levels increasingly demanded by designers and final users of the equipments should be added to these special requirements

Indeterminacy and the onset of motion in a simple granular packing

We examine the relatively simple problem of a disk placed in a symmetric V-shaped channel, and subjected to gravity and a torque. We obtain analytic predictions of the contact forces and disk motion using two different models. In the first model, the disk is assumed to be perfectly rigid, leading to force indeterminacy. In the second model, the disk is assumed to interact with the walls of the channel via linear springs, leading to a unique solution for the contact forces. The results of these two models are compared. It is shown that there are two possible ways motion can occur—through the appearance of a null eigenvector of the stiffness matrix, or through an instability. When motion occurs through an instability, the first model cannot predict when the disk will rotate; it is necessary to know the undetermined forces in order to predict the motion of the disk. It is also shown how indeterminacy in the first model is linked to memory in the second. The analytical results are also compared with numerical simulations using two different methods, each related to one of the models

Brownian motion in a granular gas

The dynamics of a heavy particle in a gas of much lighter particles is studied via the Boltzmann-Lorentz equation with inelastic collisions among all particles. A formal expansion in the ratio of gas to tagged particle mass transforms the Boltzmann-Lorentz equation into a Fokker Planck equation. The predictions of the latter are tested here using direct Monte Carlo simulation of the Boltzmann-Lorentz equation. Excellent agreement is obtained for the approach to a homogeneous cooling state, the temperature of that state, approach to diffusion, and the dependence of the diffusion constant on dissipation parameters. Some results from molecular-dynamics simulations are also presented and shown to agree with the theoretical predictions.España, Dirección General de Investigación Científica y Técnica grant PB98-112

A robust support vector algorithm for nonparametric spectral analysis

A new approach to the nonparametric spectral estimation on the basis of the support vector method (SVM) framework is presented. A reweighted least squared error formulation avoids the computational limitations of quadratic programming. The application to a synthetic example and to a digital communication problem shows the robustness of the SVM spectral analysis algorithm.Publicad

Indeterminacy, Memory, and Motion in a Simple Granular Packing

We apply two theoretical and two numerical methods to the problem of a disk placed in a groove and subjected to gravity and a torque. Methods assuming rigid particles are indeterminate -- certain combinations of forces cannot be calculated, but only constrained by inequalities. In methods assuming deformable particles, these combinations of forces are determined by the history of the packing. Thus indeterminacy in rigid particles becomes memory in deformable ones. Furthermore, the torque needed to rotate the particle was calculated. Two different paths to motion were identified. In the first, contact forces change slowly, and the indeterminacy decreases continuously to zero, and vanishes precisely at the onset of motion, and the torque needed to rotate the disk is independent of method and packing history. In the second way, this torque depends on method and on the history of the packing, and the forces jump discontinuously at the onset of motion.Comment: 11 pages, 7 figures, submitted to Phys Rev

Phase response calibration of a distributed antenna array for satellite acquisition

A distributed antenna array system, named Spanish acronym for fast acquisition of satellites system (SARAS), has been designed as an acquisition aid to parabolic telemetry, tracking, and command antennas when tracking satellites in launch and early orbit phase or during critical maneuvers. The system relies on digital signal processing, based on the array changing phase response to incoming signals as a function of their direction of arrival. One critical aspect for proper performance of the system is to establish a reliable model of this phase response, termed the array manifold, prior to and during satellite acquisition, through novel calibration techniques that are the focus of this letter

Self-diffusion in freely evolving granular gases

A self-diffusionequation for a freely evolving gas of inelastic hard disks or spheres is derived starting from the Boltzmann–Lorentz equation, by means of a Chapman–Enskog expansion in the density gradient of the tagged particles. The self-diffusion coefficient depends on the restitution coefficient explicitly, and also implicitly through the temperature of the system. This latter introduces also a time dependence of the coefficient. As in the elastic case, the results are trivially extended to the Enskog equation. The theoretical predictions are compared with numerical solutions of the kinetic equation obtained by the direct simulation Monte Carlo method, and also with molecular dynamics simulations. An excellent agreement is found, providing mutual support to the different approaches.The Dirección General de Investigación Científica y Técnica (Spain) through Grant No. PB98-112

Hydrodynamic Maxwell demon in granular systems

Spontaneous symmetry breaking in a vibrated system confined into two connected compartments in the absence of external fields is reported. For a small number of particles, the grains are equipartitioned, but if it is increased beyond a critical value, the number of particles in each of the compartments becomes different in the steady state, and the number of particles in one of the compartments decreases monotonically tending to a given value. This phase transition is accurately described by the hydrodynamic equations for a granular gas. The relationship with previous phenomena of phase separation in vibrofluidized granular materials is discussed

Aplicació d’eines TIC a la millora de les competències clíniques en l’àmbit de l’òptica i l’optometria: “OPTOstream”

Actualment, l’estudiantat de la Facultat d’Òptica i Optometria de les assignatures clíniques (Grau i Màster) participen de forma activa en l’atenció de pacient reals, sota la supervisió del professorat. Els casos atesos durant les sessions pràctiques es plantegen i discuteixen en les sessions de seminari amb els docents i la resta del grup. Malgrat el valor docent d’aquesta metodologia, l’estudiant no tenia la possibilitat de comprovar la seva actuació durant l’atenció d’un cas real, a partir de les observacions del docent. Aquesta situació dificulta un aprofitament òptim de l’experiència d’aprenentatge per part de l’estudiant. La incorporació de solucions tècniques contrastades en l’àmbit de la formació, com és el cas de l’enregistrament i visionat posterior o en temps real de casos, permeten a l’estudiant participar més activament en el seu procés d’aprenentatge i contribueixen a fer més efectiva l’adquisició de determinats coneixements i competències bàsiques per al desenvolupament de la seva carrera professional i investigadora. El projecte “OPTOstream” ha permès desenvolupar una metodologia pròpia basada en l’elaboració i anàlisi posterior de casos enregistrats en vídeo o bé la projecció en temps real de les actuacions clíniques al nou auditori de la Facultat.Peer Reviewe