Diagnostics of classical and dusty plasmas w ith collecting and emissive langmuir probes = Diagnosis de plasmas clásicos y granulares mediante sondas colectoras y emisoras de Langmuir

Las sondas eléctricas se emplean habitualmente en la diagnosis de plasmas. La presente tesis aborda la operación de las sondas colectoras y emisoras de Langmuir en plasmas fríos de baja densidad. El estudio se ha centrado en la determinación del potencial de plasma, Vsp, mediante el potencial flotante de una sonda emisora. Esta técnica consiste en la medida del potencial de la sonda correspondiente a la condición de corriente neta igual a cero, el cual se denomina potencial flotante, VF. Este potencial se desplaza hacia el potencial del plasma según aumenta la emisión termoiónica de la sonda, hasta que se satura cerca de Vsp. Los experimentos llevados a cabo en la pluma de plasma de un motor iónico y en un plasma de descarga de glow muestran que la corriente de electrones termoiónicos es mayor que la corriente de electrones recogidos para una sonda polarizada por debajo del potencial del plasma, resultado inconsistente con la teoría tradicionalmente aceptada. Para investigar estos resultados se ha introducido el parámetro R, definido como el cociente entre la corriente de electrones emitidos y recogidos por la sonda. Este parámetro, que está relacionado con la diferencia de potencial VF - Vsp, también es útil para la descripción de los modos de operación de la sonda emisora (débil, fuerte y más allá del fuerte). Los resultados experimentales evidencian que, al contrario de lo que indica la teoría, R es mayor que la unidad. Esta discrepancia se puede solucionar introduciendo una población efectiva de electrones. Con dicha población, el nuevo modelo para la corriente total de la sonda reproduce los datos experimentales. El origen de este grupo electrónico es todavía una cuestión abierta, pero podría estar originada por una nueva estructura de potencial cerca de la sonda cuando ésta trabaja en el régimen de emisión fuerte. Para explicar dicha estructura de potencial, se propone un modelo unidimensional compuesto por un mínimo de potencial cerca de la superficie de la sonda. El análisis numérico indica que este pozo de potencial aparece para muy altas temperaturas de la sonda, reduciendo la cantidad de electrones emitidos que alcanzan el plasma y evitando así cualquier posible perturbación de éste. Los aspectos experimentales involucrados en el método del potencial flotante también se han estudiado, incluyendo cuestiones como las diferentes técnicas de obtención del VF, el cociente señal-ruido, el acoplamiento de la señal de los equipos utilizados para la obtención de las curvas I-V o la evidencia experimental de los diferentes modos de operación de la sonda. Estas evidencias empíricas se encuentran en todos los aspectos de operación de la sonda: la recolección de electrones, el potencial flotante, la precisión en las curvas I-V y la emisión electrónica. Ésta última también se estudia en la tesis, debido a que un fenómeno de super emisión tiene lugar en el régimen de emisión fuerte. En este modo de operación, las medidas experimentales indican que las corrientes termoiónicas de electrones son mayores que aquéllas predichas por la ecuación de Richardson-Dushman clásica. Por último, la diagnosis de plasmas usando sondas eléctrica bajo presencia de granos de polvo (plasmas granulares) en plasmas fríos de baja densidad también se ha estudiado, mediante la aplicación numérica de la técnica del potencial flotante de la sonda emisora en un plasma no convencional. Los resultados apuntan a que el potencial flotante de una sonda emisora se vería afectado por altas densidades de polvo o grandes partículas. ABSTRACT Electric probes are widely employed for plasma diagnostics. This dissertation concerns the operation of collecting and emissive Langmuir probes in low density cold plasmas. The study is focused on the determination of the plasma potential, Vsp, by means of the floating potential of emissive probes. This technique consists of the measurement of the probe potential, corresponding to the zero net probe current, which is the so-called floating potential, VF . This potential displaces towards the plasma potential as the thermionic electron emission increases, until it saturates near Vsp. Experiments carried out in the plasma plume of an ion thruster and in a glow discharge plasma show the thermionic electron current of the emissive Langmuir probe is higher than the collected electron current, for a probe with a bias potential below Vsp, which is inconsistent with the traditional accepted theory. To investigate these results, a parameter R is introduced as the ratio between the emitted and the collected electron current. This parameter, which is related to the difference VF - Vsp, is also useful for the description of the operation modes of the emissive Langmuir probe (weak, strong and beyond strong). The experimental results give an inconsistency of R > 1, which is solved by a modification of the theory for emissive probes, with the introduction of an effective electron population. With this new electron group, the new model for the total probe current agrees with the experimental data. The origin of this electron group remains an open question, but it might be originated by a new potential structure near the emissive probe when it operates in the strong emission regime. A simple one-dimension model composed by a minimum of potential near the probe surface is discussed for strongly emitting emissive probes. The results indicate that this complex potential structure appears for very high probe temperatures and the potential well might reduce the emitted electrons population reaching the plasma bulk. The experimental issues involved in the floating potential method are also studied, as the different obtaining techniques of VF, the signal-to-noise ratio, the signal coupling of the I-V curve measurement system or the experimental evidence of the probe operation modes. These empirical proofs concern all the probe operation aspects: the electron collection, the floating potential, the I-V curve accuracy as well as the electron emission. This last issue is also investigated in this dissertation, because a super emission takes place in the strong emission regime. In this operation mode, the experimental results indicate that the thermionic electron currents might be higher than those predicted by the classical Richardson-Dushman equation. Finally, plasma diagnosis using electric probes in the presence of dust grains (dusty plasmas) in low density cold plasmas is also addressed. The application of the floating potential technique of the emissive probe in a non-conventional complex plasma is numerically investigated, whose results point out the floating potential of the emissive probe might be shifted for high dust density or large dust particles.

Desarrollo de un sistema de reconocimiento facial

El objetivo principal alrededor del cual se desenvuelve este proyecto es el desarrollo de un sistema de reconocimiento facial. Entre sus objetivos específicos se encuentran: realizar una primera aproximación sobre las técnicas de reconocimiento facial existentes en la actualidad, elegir una aplicación donde pueda ser útil el reconocimiento facial, diseñar y desarrollar un programa en MATLAB que lleve a cabo la función de reconocimiento facial, y evaluar el funcionamiento del sistema desarrollado. Este documento se encuentra dividido en cuatro partes: INTRODUCCIÓN, MARCO TEÓRICO, IMPLEMENTACIÓN, y RESULTADOS, CONCLUSIONES Y LÍNEAS FUTURAS. En la primera parte, se hace una introducción relativa a la actualidad del reconocimiento facial y se comenta brevemente sobre las técnicas existentes para desarrollar un sistema biométrico de este tipo. En ella se justifican también aquellas técnicas que acabaron formando parte de la implementación. En la segunda parte, el marco teórico, se explica la estructura general que tiene un sistema de reconocimiento biométrico, así como sus modos de funcionamiento, y las tasas de error utilizadas para evaluar y comparar su rendimiento. Así mismo, se lleva a cabo una descripción más profunda sobre los conceptos y métodos utilizados para efectuar la detección y reconocimiento facial en la tercera parte del proyecto. La tercera parte abarca una descripción detallada de la solución propuesta. En ella se explica el diseño, características y aplicación de la implementación; que trata de un programa elaborado en MATLAB con interfaz gráfica, y que utiliza cuatro sistemas de reconocimiento facial, basados cada uno en diferentes técnicas: Análisis por componentes principales, análisis lineal discriminante, wavelets de Gabor, y emparejamiento de grafos elásticos. El programa ofrece además la capacidad de crear y editar una propia base de datos con etiquetas, dándole aplicación directa sobre el tema que se trata. Se proponen además una serie de características con el objetivo de ampliar y mejorar las funcionalidades del programa diseñado. Dentro de dichas características destaca la propuesta de un modo de verificación híbrido aplicable a cualquier rama de la biometría y un programa de evaluación capaz de medir, graficar, y comparar las configuraciones de cada uno de los sistemas de reconocimiento implementados. Otra característica destacable es la herramienta programada para la creación de grafos personalizados y generación de modelos, aplicable a reconocimiento de objetos en general. En la cuarta y última parte, se presentan al principio los resultados obtenidos. En ellos se contemplan y analizan las comparaciones entre las distintas configuraciones de los sistemas de reconocimiento implementados para diferentes bases de datos (una de ellas formada con imágenes con condiciones de adquisición no controladas). También se miden las tasas de error del modo de verificación híbrido propuesto. Finalmente, se extraen conclusiones, y se proponen líneas futuras de investigación. ABSTRACT The main goal of this project is to develop a facial recognition system. To meet this end, it was necessary to accomplish a series of specific objectives, which were: researching on the existing face recognition technics nowadays, choosing an application where face recognition might be useful, design and develop a face recognition system using MATLAB, and measure the performance of the implemented system. This document is divided into four parts: INTRODUCTION, THEORTICAL FRAMEWORK, IMPLEMENTATION, and RESULTS, CONCLUSSIONS AND FUTURE RESEARCH STUDIES. In the first part, an introduction is made in relation to facial recognition nowadays, and the techniques used to develop a biometric system of this kind. Furthermore, the techniques chosen to be part of the implementation are justified. In the second part, the general structure and the two basic modes of a biometric system are explained. The error rates used to evaluate and compare the performance of a biometric system are explained as well. Moreover, a description of the concepts and methods used to detect and recognize faces in the third part is made. The design, characteristics, and applications of the systems put into practice are explained in the third part. The implementation consists in developing a program with graphical user interface made in MATLAB. This program uses four face recognition systems, each of them based on a different technique: Principal Component Analysis (PCA), Fisher’s Linear Discriminant (FLD), Gabor wavelets, and Elastic Graph Matching (EGM). In addition, with this implementation it is possible to create and edit one´s tagged database, giving it a direct application. Also, a group of characteristics are proposed to enhance the functionalities of the program designed. Among these characteristics, three of them should be emphasized in this summary: A proposal of an hybrid verification mode of a biometric system; and an evaluation program capable of measuring, plotting curves, and comparing different configurations of each implemented recognition system; and a tool programmed to create personalized graphs and models (tagged graph associated to an image of a person), which can be used generally in object recognition. In the fourth and last part of the project, the results of the comparisons between different configurations of the systems implemented are shown for three databases (One of them created with pictures taken under non-controlled environments). The error rates of the proposed hybrid verification mode are measured as well. Finally, conclusions are extracted and future research studies are proposed.

Evaluación del uso y de productividad del agua de la Comunidad de Regantes “Río Adaja”

El agua de riego en España se ha reducido del 80 % al 70% tras la rehabilitación de los sistemas tradicionales de riego y el incremento de riegos a presión. La política española ha favorecido la creación de nuevos regadíos con fines sociales, para asentar a la población rural en zonas con disponibilidad de recursos hídricos. Este contexto es aplicable a la Comunidad de Regantes “Rio Adaja” (CCRR), que comenzó a funcionar en 2010 por lo que se la ha elegido para evaluar el uso y productividad del agua y manejo del riego en CCRR modernizadas de la cuenca del Duero. El estudio del manejo del riego se realizó con evaluaciones de campo, el primer año de funcionamiento, en una muestra de sistemas de riego (pivotes centrales, ramales de avance frontal, cobertura total) representativa de los sistemas predominantes en la CCRR. Además, se analizó la carta de riego propuesta por el fabricante de los pivotes centrales, considerando una distribución de caudal continua a lo largo del ramal, y se propuso una nueva carta con emisores de riego que mejoraban la uniformidad de aplicación del agua. El uso del agua en la CCRR se evaluó considerando tanto los indicadores de eficiencia del riego: suministro relativo de riego (anual relative irrigation supply, ARIS), suministro relativo del agua (anual relativewater supply, ARWS), suministro relativo de precipitación (rainfall relative supply, RRS) como los de productividad: productividad del agua (water productivity, WP) productividad del agua de riego (irrigation water productivity, IWP) y productividad de la evapotranspiración (evapotranspiration water productivity, ETWP). Primero, se determinaron: las necesidades hídricas de los cultivos para mantener un contenido de humedad óptimo en su zona radical, el coeficiente dual del cultivo, el agua disponible total (ADP) y agua fácilmente aprovechable (AFA). Después, se estimaron las necesidades hídricas de los cultivos considerando tres años tipo: húmedo, normal y seco correspondientes a la probabilidad de disponibilidad de la precipitación del 20, 50 y 80%, respectivamente. Así mismo, se realizó una encuesta a los regantes de la CCRR para conocer la dosis de riego y rendimiento anual de los cultivos principales durante sus tres años de funcionamiento: 2010-2011, 2011-2012 y 2012-2013.Finalmente, se simuló el efecto del riego y su manejo en la producción de los cultivos y en la productividad del agua. Además, el modelo de simulación AQUACROP (Geerts et al., 2010) se ha utilizado para estudiar la mejora del uso del agua de los cultivos de la CCRR. Dado que este modelo requiere de calibración específica para cada cultivo y cada zona y dado que, de todos los cultivos de la CCRR, sólo el girasol cumplía el requisito, este cultivo fue elegido para estudiar si la estrategia de riego deficitario mejoraría el uso del agua. Los resultados obtenidos indican que el 90% de los sistemas de riego evaluados distribuye el agua con una uniformidad adecuada (CUC≥75%). La simulación de la distribución del agua con las cartas de riego propuestas por el fabricante en pivotes centrales resultó en coeficientes CUC< 75% y sus valores mejoraban al eliminar el aspersor distal. La uniformidad del riego mejoraría si se trabajase con la carta de riego propuesta y que se compone por emisores de riego seleccionados en este estudio. En la mayoría de los cultivos, se aplicó riegos deficitarios (ARIS < 1 en los dos primeros años de funcionamiento de la CCRR y riegos excedentarios (ARIS > 1) el tercer año siendo significativas las diferencias observadas. El manejo del riego fue bueno (0,9 ≤ ARWS ≤1,2) en la mayoría de los cultivos. Así mismo, los indicadores de productividad del agua (WP e IWP (€.m-3)) varió entre cultivos y años estudiados y, destacan los valores observados en: cebolla, patata, zanahoria y cebada. En general, la productividad del agua en los riegos deficitarios fue mayor observándose además, que los índices de productividad mayores correspondieron al año con precipitación mayor aunque, las diferencias entre sus valores medios no fueron significativas en las tres campañas de riego estudiadas. Los resultados apuntan a que la metodología del balance hídrico y las herramientas presentadas en este trabajo (uniformidad de distribución de agua, indicadores de eficiencia del uso de agua y de su productividad) son adecuadas para estudiar el manejo del agua en CCRR. En concreto, la uniformidad en la aplicación del agua de la CCRR mejoraría seleccionando emisores de riego que proporcionen una mayor uniformidad de distribución del agua, lo que conllevaría a cambiar el diámetro de la boquilla de los emisores y/o eliminar el aspersor distal. Así mismo, puede ser de interés adoptar estrategias de riego deficitario para incrementar la productividad en el uso del agua, y las rentas de los regantes, para lo cual se propone utilizar un patrón de cultivos de referencia. Finalmente, el riego deficitario puede ser una estrategia para mejorar la eficiencia y productividad en el uso del agua de la CCRR siempre que lleve asociado un manejo del riego adecuado que resulta, relativamente, más fácil cuando se dispone de sistemas de riego con una uniformidad de aplicación alta. Sin embargo su aplicación no sería aconsejable en los cultivos de remolacha azucarera, regado con sistemas de riego con un coeficiente de uniformidad de Christiansen CUC < 75%, y maíz, regado con sistemas de riego con un coeficiente de uniformidad de Christiansen CUC < 65%. ABSTRACT The irrigation scheme modernization and the increase of sprinkler irrigation area have reduced the irrigation water use from 80 to 70%. The national irrigation policy favored the creation of new irrigation schemes with the purpose to settle the rural population in areas with availability in water resources. Within this context, the irrigation district “Río Adaja” (CCRR) started in 2010 so, it has been chosen as a case study to evaluate the water use and the irrigation management in a modernized CCRR. Several field evaluations were carried out during the first operation year, in a sample of irrigation systems (center pivot, moving lateral and solid set) selected among all the systems in the CCRR. Likewise, the manufacturer irrigation chart for the center pivot systems has been considered and the pressure and discharge distribution along the pivot have been estimated, assuming a continuous flow along the pipe. Then; the sprinkler nozzles were selected order to increase the uniformity on water application. The water use in the CCRR has been assessed by considering the water use efficiency indicators: annual relative irrigation supply (ARIS), annual relative water supply (ARWS), relative rainfall supply (RRS) and also the productivity indicators: water productivity (WP), irrigation water productivity (IWP) and evapotranspiration water productivity (ETWP). On the one hand, it has been determined the crop water requirement (to maintain the optimal soil water content in the rooting zone), the dual crop coefficient, the total available water and the readily available water. The crop water requirement was estimated by considering the typical wet, normal and dry years which correspond to the probability of effective precipitation exceedance of 20, 50 and 80%, respectively. On the other hand, the irrigation depth and crop yield by irrigation campaign have been considered for the main crops in the area. This information was obtained from a farmer’s survey in 2010-2011, 2011-2012 and 2012-2013. For sunflower, the irrigation effect and its management on the crop yield and water productivity have been simulated. Also a deficit irrigation strategy, which improves the water resources, has been determined by means of AQUACROP (FAO). The results showed that 90% of the evaluated irrigation systems have adequate irrigation water application uniformity (CUC ≥ 75%). The CUC values in center pivots, which were calculated using the manufacturer irrigation chart, are below < 75% . However, these values would increase with the change of emitter nozzle to the proposed nozzles selection. The results on water use showed a deficit irrigation management (ARIS < 1), in most of crops during the first two operation years, and an excess in irrigation for the third year (ARIS > 1) although non-significant difference was observed. In most cases, the management of irrigation is adequate (0,9≤ ARWS≤ 1,2) although there are differences among crops. Likewise, the productivity indicators (WP and IWP (€.m-3)) varied among crops and with irrigation events. The highest values corresponded to onion, potato, carrot and barley. The values for deficit irrigation were the highest and the productivity indicators increased the year with the highest effective precipitation. Nevertheless, the differences between the average values of these indicators by irrigation campaign were non-significant. This study highlights that the soil water balance methodology and other tools used in the methodology are adequate to study the use and productivity of water in the irrigation district. In fact, the water use in this CCRR can be improved if the irrigation systems were designed with higher water distribution uniformity what would require the change of sprinkler nozzles and/or eliminate the end gun. Likewise, it is advisable to set up deficit irrigation strategies to increase the water productivity taking into account certain limits on water application uniformities. In this respect, a reference cropping pattern has been proposed and the limits for water uniformity have been calculated for several crops.

Design and optimization of optical, fiber based PSK demodulators for high-bit-rate optical networks

El objetivo principal de esta tesis ha sido el diseño y la optimización de receptores implementados con fibra óptica, para ser usados en redes ópticas de alta velocidad que empleen formatos de modulación de fase. En los últimos años, los formatos de modulación de fase (Phase Shift keying, PSK) han captado gran atención debido a la mejora de sus prestaciones respecto a los formatos de modulación convencionales. Principalmente, presentan una mejora de la eficiencia espectral y una mayor tolerancia a la degradación de la señal causada por la dispersión cromática, la dispersión por modo de polarización y los efectos no-lineales en la fibra óptica. En este trabajo, se analizan en detalle los formatos PSK, incluyendo sus variantes de modulación de fase diferencial (Differential Phase Shift Keying, DPSK), en cuadratura (Differential Quadrature Phase Shift Keying, DQPSK) y multiplexación en polarización (Polarization Multiplexing Differential Quadrature Phase Shift Keying, PM-DQPSK), con la finalidad de diseñar y optimizar los receptores que permita su demodulación. Para ello, se han analizado y desarrollado nuevas estructuras que ofrecen una mejora en las prestaciones del receptor y una reducción de coste comparadas con las actualmente disponibles. Para la demodulación de señales DPSK, en esta tesis, se proponen dos nuevos receptores basados en un interferómetro en línea Mach-Zehnder (MZI) implementado con tecnología todo-fibra. El principio de funcionamiento de los MZI todo-fibra propuestos se asienta en la interferencia modal que se produce en una fibra multimodo (MMF) cuando se situada entre dos monomodo (SMF). Este tipo de configuración (monomodo-multimodo-monomodo, SMS) presenta un buen ratio de extinción interferente si la potencia acoplada en la fibra multimodo se reparte, principal y equitativamente, entre dos modos dominantes. Con este objetivo, se han estudiado y demostrado tanto teórica como experimentalmente dos nuevas estructuras SMS que mejoran el ratio de extinción. Una de las propuestas se basa en emplear una fibra multimodo de índice gradual cuyo perfil del índice de refracción presenta un hundimiento en su zona central. La otra consiste en una estructura SMS con las fibras desalineadas y donde la fibra multimodo es una fibra de índice gradual convencional. Para las dos estructuras, mediante el análisis teórico desarrollado, se ha demostrado que el 80 – 90% de la potencia de entrada se acopla a los dos modos dominantes de la fibra multimodo y se consigue una diferencia inferior al 10% entre ellos. También se ha demostrado experimentalmente que se puede obtener un ratio de extinción de al menos 12 dB. Con el objeto de demostrar la capacidad de estas estructuras para ser empleadas como demoduladores de señales DPSK, se han realizado numerosas simulaciones de un sistema de transmisión óptico completo y se ha analizado la calidad del receptor bajo diferentes perspectivas, tales como la sensibilidad, la tolerancia a un filtrado óptico severo o la tolerancia a las dispersiones cromática y por modo de polarización. En todos los casos se ha concluido que los receptores propuestos presentan rendimientos comparables a los obtenidos con receptores convencionales. En esta tesis, también se presenta un diseño alternativo para la implementación de un receptor DQPSK, basado en el uso de una fibra mantenedora de la polarización (PMF). A través del análisi teórico y del desarrollo de simulaciones numéricas, se ha demostrado que el receptor DQPSK propuesto presenta prestaciones similares a los convencionales. Para complementar el trabajo realizado sobre el receptor DQPSK basado en PMF, se ha extendido el estudio de su principio de demodulación con el objeto de demodular señales PM-DQPSK, obteniendo como resultado la propuesta de una nueva estructura de demodulación. El receptor PM-DQPSK propuesto se basa en la estructura conjunta de una única línea de retardo junto con un rotador de polarización. Se ha analizado la calidad de los receptores DQPSK y PM-DQPSK bajo diferentes perspectivas, tales como la sensibilidad, la tolerancia a un filtrado óptico severo, la tolerancia a las dispersiones cromática y por modo de polarización o su comportamiento bajo condiciones no-ideales. En comparación con los receptores convencionales, nuestra propuesta exhibe prestaciones similares y además permite un diseño más simple que redunda en un coste potencialmente menor. En las redes de comunicaciones ópticas actuales se utiliza la tecnología de multimplexación en longitud de onda (WDM) que obliga al uso de filtros ópticos con bandas de paso lo más estrechas posibles y a emplear una serie de dispositivos que incorporan filtros en su arquitectura, tales como los multiplexores, demultiplexores, ROADMs, conmutadores y OXCs. Todos estos dispositivos conectados entre sí son equivalentes a una cadena de filtros cuyo ancho de banda se va haciendo cada vez más estrecho, llegando a distorsionar la forma de onda de las señales. Por esto, además de analizar el impacto del filtrado óptico en las señales de 40 Gbps DQPSK y 100 Gbps PM-DQPSK, este trabajo de tesis se completa estudiando qué tipo de filtro óptico minimiza las degradaciones causadas en la señal y analizando el número máximo de filtros concatenados que permiten mantener la calidad requerida al sistema. Se han estudiado y simulado cuatro tipos de filtros ópticos;Butterworth, Bessel, FBG y F-P. ABSTRACT The objective of this thesis is the design and optimization of optical fiber-based phase shift keying (PSK) demodulators for high-bit-rate optical networks. PSK modulation formats have attracted significant attention in recent years, because of the better performance with respect to conventional modulation formats. Principally, PSK signals can improve spectrum efficiency and tolerate more signal degradation caused by chromatic dispersion, polarization mode dispersion and nonlinearities in the fiber. In this work, many PSK formats were analyzed in detail, including the variants of differential phase modulation (Differential Phase Shift Keying, DPSK), in quadrature (Differential Quadrature Phase Shift Keying, DQPSK) and polarization multiplexing (Polarization Multiplexing Differential Quadrature Phase Shift Keying, PM-DQPSK), in order to design and optimize receivers enabling demodulations. Therefore, novel structures, which offer good receiver performances and a reduction in cost compared to the current structures, have been analyzed and developed. Two novel receivers based on an all-fiber in-line Mach-Zehnder interferometer (MZI) were proposed for DPSK signal demodulation in this thesis. The operating principle of the all-fiber MZI is based on the modal interference that occurs in a multimode fiber (MMF) when it is located between two single-mode fibers (SMFs). This type of configuration (Single-mode-multimode-single-mode, SMS) can provide a good extinction ratio if the incoming power from the SMF could be coupled equally into two dominant modes excited in the MMF. In order to improve the interference extinction ratio, two novel SMS structures have been studied and demonstrated, theoretically and experimentally. One of the two proposed MZIs is based on a graded-index multimode fiber (MMF) with a central dip in the index profile, located between two single-mode fibers (SMFs). The other one is based on a conventional graded-index MMF mismatch spliced between two SMFs. Theoretical analysis has shown that, in these two schemes, 80 – 90% of the incoming power can be coupled into the two dominant modes exited in the MMF, and the power difference between them is only ~10%. Experimental results show that interference extinction ratio of 12 dB could be obtained. In order to demonstrate the capacity of these two structures for use as DPSK signal demodulators, numerical simulations in a completed optical transmission system have been carried out, and the receiver quality has been analyzed under different perspectives, such as sensitivity, tolerance to severe optical filtering or tolerance to chromatic and polarization mode dispersion. In all cases, from the simulation results we can conclude that the two proposed receivers can provide performances comparable to conventional ones. In this thesis, an alternative design for the implementation of a DQPSK receiver, which is based on a polarization maintaining fiber (PMF), was also presented. To complement the work made for the PMF-based DQPSK receiver, the study of the demodulation principle has been extended to demodulate PM-DQPSK signals, resulting in the proposal of a novel demodulation structure. The proposed PM-DQPSK receiver is based on only one delay line and a polarization rotator. The quality of the proposed DQPSK and PM-DQPSK receivers under different perspectives, such as sensitivity, tolerance to severe optical filtering, tolerance to chromatic dispersion and polarization mode dispersion, or behavior under non-ideal conditions. Compared with the conventional receivers, our proposals exhibit similar performances but allow a simpler design which can potentially reduce the cost. The wavelength division multiplexing (WDM) technology used in current optical communications networks requires the use of optical filters with a passband as narrow as possible, and the use of a series of devices that incorporate filters in their architecture, such as multiplexers, demultiplexers, switches, reconfigurable add-drop multiplexers (ROADMs) and optical cross-connects (OXCs). All these devices connected together are equivalent to a chain of filters whose bandwidth becomes increasingly narrow, resulting in distortion to the waveform of the signals. Therefore, in addition to analyzing the impact of optical filtering on signal of 40 Gbps DQPSK and 100 Gbps PM-DQPSK, we study which kind of optical filter minimizes the signal degradation and analyze the maximum number of concatenated filters for maintaining the required quality of the system. Four types of optical filters, including Butterworth, Bessel, FBG and FP, have studied and simulated.

Herramienta de interacción persona-ordenador para la operación de vehículos aéreos no tripulados

En la presente memoria se describe el trabajo de diseño de una herramienta de interacción persona-ordenador (HMI) para la operación y supervisión de vehículos aéreos no tripulados (UAV). En primer lugar se hace una introducción a los tipos de UAVs y aplicaciones más comunes, describiendo sus características técnicas y los componentes que integra en el sistema. Mediante la revisión y análisis de los diferentes niveles de autonomía y las diferentes soluciones de presentación existentes en el mercado, se identifican los modos de operación y componentes principales de la interfaz. A continuación se describe el diseño final del software de la interfaz y el proceso de desarrollo de la misma, para ello se hace un análisis previo del software robótico sobre el que opera el sistema abordo del UAV y se establecen los enlaces de comunicación entre cada uno de los componentes y los requisitos de integración con el sistema. Finalmente, se muestran las pruebas que se han realizado para validar la construcción de la herramienta. This report outlines the design and construction of a human-machine interface (HMI), designed to facilitate the supervision and operation with unmanned aerial vehicles (UAV). First, it is described an introduction to UAVs classification and application fields, reviewing the hardware features and software integration components. In order to define the basic components and operation modes in the general design, a brief review of the different presentation solutions and autonomous levels is described. As a result, it is presented the final software design, the components details and the system integration requirements. Finally, it is also concluded with some of the tests that have been conducted to validate the design and construction of the human-machine interface

Evidence for non-conservative current-induced forces in the breaking of Au and Pt atomic chains

This experimental work aims at probing current-induced forces at the atomic scale. Specifically it addresses predictions in recent work regarding the appearance of run-away modes as a result of a combined effect of the non-conservative wind force and a ‘Berry force’. The systems we consider here are atomic chains of Au and Pt atoms, for which we investigate the distribution of break down voltage values. We observe two distinct modes of breaking for Au atomic chains. The breaking at high voltage appears to behave as expected for regular break down by thermal excitation due to Joule heating. However, there is a low-voltage breaking mode that has characteristics expected for the mechanism of current-induced forces. Although a full comparison would require more detailed information on the individual atomic configurations, the systems we consider are very similar to those considered in recent model calculations and the comparison between experiment and theory is very encouraging for the interpretation we propose.

Benchmarking numerical models of brittle thrust wedges

We report quantitative results from three brittle thrust wedge experiments, comparing numerical results directly with each other and with corresponding analogue results. We first test whether the participating codes reproduce predictions from analytical critical taper theory. Eleven codes pass the stable wedge test, showing negligible internal deformation and maintaining the initial surface slope upon horizontal translation over a frictional interface. Eight codes participated in the unstable wedge test that examines the evolution of a wedge by thrust formation from a subcritical state to the critical taper geometry. The critical taper is recovered, but the models show two deformation modes characterised by either mainly forward dipping thrusts or a series of thrust pop-ups. We speculate that the two modes are caused by differences in effective basal boundary friction related to different algorithms for modelling boundary friction. The third experiment examines stacking of forward thrusts that are translated upward along a backward thrust. The results of the seven codes that run this experiment show variability in deformation style, number of thrusts, thrust dip angles and surface slope. Overall, our experiments show that numerical models run with different numerical techniques can successfully simulate laboratory brittle thrust wedge models at the cm-scale. In more detail, however, we find that it is challenging to reproduce sandbox-type setups numerically, because of frictional boundary conditions and velocity discontinuities. We recommend that future numerical-analogue comparisons use simple boundary conditions and that the numerical Earth Science community defines a plasticity test to resolve the variability in model shear zones.

Sedimentological investigations and age model on sediment core PS2561-2

Benthic d13C values (F. wuellerstorfi), kaolinite/chlorite ratios and sortable silt median grain sizes in sediments of a core from the abyssal Agulhas Basin record the varying impact of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) during the last 200 ka. The data indicate that NADW influence decreased during glacials and increased during interglacials, in concert with the global climatic changes of the late Quaternary. In contrast, AABW displays a much more complex behaviour. Two independent modes of deep-water formation contributed to the AABW production in the Weddell Sea: 1) brine rejection during sea ice formation in polynyas and in the sea ice zone (Polynya Mode) and 2) super-cooling of Ice Shelf Water (ISW) beneath the Antarctic ice shelves (Ice Shelf Mode). Varying contributions of the two modes lead to a high millennial-scale variability of AABW production and export to the Agulhas Basin. Highest rates of AABW production occur during early glacials when increased sea ice formation and an active ISW production formed substantial amounts of deep water. Once full glacial conditions were reached and the Antarctic ice sheet grounded on the shelf, ISW production shut down and only brine rejection generated moderate amounts of deep water. AABW production rates dropped to an absolute minimum during Terminations I and II and the Marine Isotope Transition (MIS) 4/3 transition. Reduced sea ice formation concurrent with an enhanced fresh water influx from melting ice lowered the density of the surface water in the Weddell Sea, thus further reducing deep water formation via brine rejection, while the ISW formation was not yet operating again. During interglacials and the moderate interglacial MIS 3 both brine formation and ISW production were operating, contributing various amounts to AABW formation in the Weddell Sea.

A novel method for the production of aluminium nitride

A method has been developed to produce thick (> 400 mu m) AlN surface layers oil aluminium plates at 540 degrees C, under nitrogen at atmospheric pressure. A critical element of the process is the use of Mg powder placed in close proximity to the Al plate surface. The Mg reduces/disrupts the natural, protective oxide film on the Al surface. The nitride layers form through two distinct modes, one growing outward from the Al plate surface and the other growing into the Al. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Beach face and berm morphodynamics fronting a coastal lagoon

This study documents two different modes of berm development: (I) vertical growth at spring tides or following significant beach cut due to substantial swash overtopping, and (2) horizontal progradation at neap tides through the formation of a proto-berm located lower and further seaward of the principal berm. Concurrent high-frequency measurements of bed elevation and the associated wave runup distribution reveal the details of each of these berm growth modes. In mode I sediment is eroded from the inner surf and lower swash zone where swash interactions are prevalent. The net transport of this sediment is landward only, resulting in accretion onto the upper beach face and over the berm crest. The final outcome is a steepening of the beach face gradient, a change in the profile shape towards concave and rapid vertical and horizontal growth of the berm. In mode 2 sediment is eroded from the lower two-thirds of the active swash zone during the rising tide and is transported both landward and seaward. On the falling tide sediment is eroded from the inner surf and transported landward to backfill the zone eroded on the rising tide. The net result is relatively slow steepening of the beach face, a change of the profile shape towards convex, and horizontal progradation through the formation of a neap berm. The primary factor determining which mode of berm growth occurs is the presence or absence of swash overtopping at the time of sediment accumulation on the beach face. This depends on the current phase of the spring-neap tide cycle, the wave runup height (and indirectly offshore wave conditions) and the height of the pre-existing berm. A conceptual model for berm morphodynamics is presented, based on sediment transport shape functions measured during the two modes of berm growth. (c) 2006 Elsevier B.V. All rights reserved.

Multi-function controllers for a hydraulic pump

This project has been undertaken for Hamworthy Hydraulics Limited. Its objective was to design and develop a controller package for a variable displacement, hydraulic pump for use mainly on mobile earth moving machinery. A survey was undertaken of control options used in practice and from this a design specification was formulated, the successful implementation of which would give Hamworthy an advantage over its competitors. Two different modes for the controller were envisaged. One consisted of using conventional hydro-mechanics and the other was based upon a microprocessor. To meet short term customer prototype requirements the first section of work was the realisation of the hydro-mechanical system. Mathematical models were made to evaluate controller stability and hence aid their design. The final package met the requirements of the specification and a single version could operate all sizes of variable displacement pumps in the Hamworthy range. The choice of controller options and combinations totalled twenty-four. The hydro-mechanical controller was complex and it was realised that a micro-processor system would allow all options to be implemented with just one design of hardware, thus greatly simplifying production. The final section of this project was to determine whether such a design was feasible. This entailed finding cheap, reliable transducers, using mathematical models to predict electro-hydraulic interface stability, testing such interfaces and finally incorporating a micro-processor in an interactive control loop. The study revealed that such a system was technically possible but it would cost 60% more than its hydro-mechanical counterpart. It was therefore concluded that, in the short term, for the markets considered, the hydro-mechanical design was the better solution. Regarding the micro-processor system the final conclusion was that, because the relative costs of the two systems are decreasing, the electro-hydraulic controller will gradually become more attractive and therefore Hamworthy should continue with its development.

In-fibre twist sensor based on a fibre Bragg grating with 81º tilted structure

We report a strong polarization dependent coupling behavior of fiber Bragg gratings with excessively tilted structures up to 81 . This unique property has been utilized to implement a novel twist sensor, showing high torsion sensitivity. The twist induced light coupling interchange between the two birefringence modes makes it possible to interrogate such a sensor using low-cost intensity demodulation technique.

Intracavity dynamics in high-power mode-locked fiber lasers

A theoretical model is developed which characterizes the intracavity pulse evolutions in high-power fiber lasers. It is shown that experimentally observed dynamics of the key pulse parameters can be described by a reduced model of ordinary differential equations. Critical in driving the intracavity dynamics is the amplitude and phase modulations generated by the discrete elements in the laser. The theory gives a simple geometrical description of the intracavity dynamics and possible operation modes of the laser cavity. Furthermore, it provides a simple and efficient method for optimizing the performance of complex multiparametric laser systems.

Pattern competition in homogeneously heated fluid layers

Simulations examining pattern competition have been performed on a horizontal homogeneously heated layer that is bounded by an isothermal plane above an adiabatic plane. Several different circulation patterns arose as the heating regime applied to the horizontal layer was modified. The sequence of the patterns formed as the Grashof number was increased had the following order: laminar layer, rolls, squares, hexagons and pentagons, and then two square modes of differing orientations. Fourier analysis was used to determine how the key modes interact with each pattern.

Spiral attractor created by vector solitons

Mode-locked lasers emitting a train of femtosecond pulses called dissipative solitons are an enabling technology for metrology, high-resolution spectroscopy, fibre optic communications, nano-optics and many other fields of science and applications. Recently, the vector nature of dissipative solitons has been exploited to demonstrate mode locked lasing with both locked and rapidly evolving states of polarisation. Here, for an erbium-doped fibre laser mode locked with carbon nanotubes, we demonstrate the first experimental and theoretical evidence of a new class of slowly evolving vector solitons characterized by a double-scroll chaotic polarisation attractor substantially different from Lorenz, Rössler and Ikeda strange attractors. The underlying physics comprises a long time scale coherent coupling of two polarisation modes. The observed phenomena, apart from the fundamental interest, provide a base for advances in secure communications, trapping and manipulation of atoms and nanoparticles, control of magnetisation in data storage devices and many other areas. © 2014 CIOMP. All rights reserved.