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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Multi-objective optimization in graphical models

Rollón, Emma 03 November 2008 (has links)
Many real-life optimization problems are combinatorial, i.e. they concern a choice of the best solution from a finite but exponentially large set of alternatives. Besides, the solution quality of many of these problems can often be evaluated from several points of view (a.k.a. criteria). In that case, each criterion may be described by a different objective function. Some important and well-known multicriteria scenarios are: · In investment optimization one wants to minimize risk and maximize benefits. · In travel scheduling one wants to minimize time and cost. · In circuit design one wants to minimize circuit area, energy consumption and maximize speed. · In knapsack problems one wants to minimize load weight and/or volume and maximize its economical value. The previous examples illustrate that, in many cases, these multiple criteria are incommensurate (i.e., it is difficult or impossible to combine them into a single criterion) and conflicting (i.e., solutions that are good with respect one criterion are likely to be bad with respect to another). Taking into account simultaneously the different criteria is not trivial and several notions of optimality have been proposed. Independently of the chosen notion of optimality, computing optimal solutions represents an important current research challenge. Graphical models are a knowledge representation tool widely used in the Artificial Intelligence field. They seem to be specially suitable for combinatorial problems. Roughly, graphical models are graphs in which nodes represent variables and the (lack of) arcs represent conditional independence assumptions. In addition to the graph structure, it is necessary to specify its micro-structure which tells how particular combinations of instantiations of interdependent variables interact. The graphical model framework provides a unifying way to model a broad spectrum of systems and a collection of general algorithms to efficiently solve them. In this Thesis we integrate multi-objective optimization problems into the graphical model paradigm and study how algorithmic techniques developed in the graphical model context can be extended to multi-objective optimization problems. As we show, multiobjective optimization problems can be formalized as a particular case of graphical models using the semiring-based framework. It is, to the best of our knowledge, the first time that graphical models in general, and semiring-based problems in particular are used to model an optimization problem in which the objective function is partially ordered. Moreover, we show that most of the solving techniques for mono-objective optimization problems can be naturally extended to the multi-objective context. The result of our work is the mathematical formalization of multi-objective optimization problems and the development of a set of multiobjective solving algorithms that have been proved to be efficient in a number of benchmarks. / Muchos problemas reales de optimización son combinatorios, es decir, requieren de la elección de la mejor solución (o solución óptima) dentro de un conjunto finito pero exponencialmente grande de alternativas. Además, la mejor solución de muchos de estos problemas es, a menudo, evaluada desde varios puntos de vista (también llamados criterios). Es este caso, cada criterio puede ser descrito por una función objetivo. Algunos escenarios multi-objetivo importantes y bien conocidos son los siguientes: · En optimización de inversiones se pretende minimizar los riesgos y maximizar los beneficios. · En la programación de viajes se quiere reducir el tiempo de viaje y los costes. · En el diseño de circuitos se quiere reducir al mínimo la zona ocupada del circuito, el consumo de energía y maximizar la velocidad. · En los problemas de la mochila se quiere minimizar el peso de la carga y/o el volumen y maximizar su valor económico. Los ejemplos anteriores muestran que, en muchos casos, estos criterios son inconmensurables (es decir, es difícil o imposible combinar todos ellos en un único criterio) y están en conflicto (es decir, soluciones que son buenas con respecto a un criterio es probable que sean malas con respecto a otra). Tener en cuenta de forma simultánea todos estos criterios no es trivial y para ello se han propuesto diferentes nociones de optimalidad. Independientemente del concepto de optimalidad elegido, el cómputo de soluciones óptimas representa un importante desafío para la investigación actual. Los modelos gráficos son una herramienta para la represetanción del conocimiento ampliamente utilizados en el campo de la Inteligencia Artificial que parecen especialmente indicados en problemas combinatorios. A grandes rasgos, los modelos gráficos son grafos en los que los nodos representan variables y la (falta de) arcos representa la interdepencia entre variables. Además de la estructura gráfica, es necesario especificar su (micro-estructura) que indica cómo interactúan instanciaciones concretas de variables interdependientes. Los modelos gráficos proporcionan un marco capaz de unificar el modelado de un espectro amplio de sistemas y un conjunto de algoritmos generales capaces de resolverlos eficientemente. En esta tesis integramos problemas de optimización multi-objetivo en el contexto de los modelos gráficos y estudiamos cómo diversas técnicas algorítmicas desarrolladas dentro del marco de los modelos gráficos se pueden extender a problemas de optimización multi-objetivo. Como mostramos, este tipo de problemas se pueden formalizar como un caso particular de modelo gráfico usando el paradigma basado en semi-anillos (SCSP). Desde nuestro conocimiento, ésta es la primera vez que los modelos gráficos en general, y el paradigma basado en semi-anillos en particular, se usan para modelar un problema de optimización cuya función objetivo está parcialmente ordenada. Además, mostramos que la mayoría de técnicas para resolver problemas monoobjetivo se pueden extender de forma natural al contexto multi-objetivo. El resultado de nuestro trabajo es la formalización matemática de problemas de optimización multi-objetivo y el desarrollo de un conjunto de algoritmos capaces de resolver este tipo de problemas. Además, demostramos que estos algoritmos son eficientes en un conjunto determinado de benchmarks.

From the i* diversity to a common interoperability framework

Cares Gallardo, Carlos 20 September 2012 (has links)
Since the i* framework emerged in the requirements engineering community in the mid-90s, different research groups have proposed variations to the modelling language proposed in the i* framework (¿the i* language¿). There are basically two reasons behind this fact: ¿ The definition of the i* language is loose in some parts, and some groups have opted by different solutions or proposed slight changes to the original definition. ¿ Some groups have used the i* framework with very different purposes, thus different concepts have become necessary, many of them have added their own modelling constructs. As a consequence, several i* variations at different maturity levels have been produced. The adaptability of i* to different needs is part of its own nature, therefore these variations are not to be considered pernicious, on the contrary, flexibility may be considered one of the framework¿s key success features. In this context, the objective of this thesis is to tackle the i* Interoperability Problem: to propose a framework to understand the variations of the i* modelling language and, considering this framework, to generate a proposal to support the interoperability and integration of these variations. To do so, the PhD thesis has identified and solved up to ten research questions related to the following categories: 1) The i* variants have been identified and characterized. Metamodels have been used to align these variants and identify an appropriate kernel. A critical look on the ¿why¿ this happened has been conducted from several perspectives. 2) An interoperability framework in terms of metamodel alignment has been formulated. This interoperability framework has come from the adaptation of a solution to metamodel evolution and model co-adaptation formulated in the domain of model-driven engineering. 3) An XML-based interoperability format implementing the framework, iStarML, has been deployed. 4) The solution has been validated in terms of community acceptance by means of an empirical study, and from a practical point of view by the interconnection of different existing tools. The set of related publications shows the research path, starting from the identification and characterization of the interoperability problem, pass trhought a theoretical explanation that sustaints a technical proposal, and ends illustrating inteoperation cases and its community acceptation.

An Online writer recognition system based on in-air and on-surface trajectories

Sesa Nogueras, Enric 20 September 2012 (has links)
The main motivation of this dissertation is the exploration of the field of online text-dependent writer recognition, in order to provide evidence of the usefulness of short sequences of text to perform identification and verification, which are the two tasks involved in recognition. From this motivation stem its main goals and contributions: an exploration performed from a practical perspective, thus requiring the development of a recognition system, and the gathering of evidence concerning the discriminative power of in-air trajectories (the trajectories described while not exerting any pressure on the writing surface, when the hand moves in the air while transitioning from one stroke to the next), i.e. their ability to discriminate among writers. In-air and on-surface trajectories have been analyzed from the perspective of information theory and the results yielded by this analysis show that, except for pressure, they contain virtually equal amounts of information and are notably non-redundant. This suggests that in-air trajectories may have a considerable discriminative power and that they may help improve the overall recognition performance when combined with on-surface trajectories. An innovative writer recognition system that fulfils the abovementioned practical goal has been devised. It follows an allographic approach, that is, it does not take into account the global characteristics of the text but focuses on character and character-fragment shapes. Strokes are considered the structural units of handwriting and any piece of text is regarded as two separate sequences, one of pen-up and one of pen-down strokes. The system relies on a pair of catalogues of strokes, built in an unsupervised manner by means of self-organizing maps, which allow mapping sequences of strokes into sequences of integers. The latter sequences, much simpler than the original ones, can be effectively compared by means of dynamic time warping, which takes advantage of the neighbouring properties exhibited by self-organizing maps. Measures obtained from each sequence can be combined in a later step. The recognition system has been experimentally tested using 16 uppercase words from the BiosecurID database, which contains 4 executions of each word donated by 400 writers. The experimental results obtained clearly sustain the claim that online words have a notable recognition potential and show the suitability of the allographic approach to perform writer recognition in the online text-dependent context. Regarding identification, the system compares positively to other word-based identification schemas. As for verification, the accuracy levels attained do not lie much below the accuracies reported for today¿s state-of-the-art signature verification methods. Furthermore, the results obtained from in-air trajectories have substantiated what the information analysis had already suggested: their considerable recognition power and their notable non-redundancy with respect to on-surface trajectories. Finally, a new method to generate synthetic samples of online words from real ones has been proposed. This method is based on the recognition system previously described, takes advantage of its main characteristics and can be seamlessly integrated into it. Synthetic samples are used to enlarge the enrolment sets, which has the effect of substantially improving the recognition accuracy of the system. / La principal motivació d’aquesta dissertació és la investigació en el camp del reconeixement d’escriptors en la modalitat online depenent del text, amb intenció de proporcionar evidències que avalin la utilitat de les seqüències curtes per a la identificació i la verificació, que són les dues tasques compreses en el reconeixement. D’aquesta motivació se’n deriven els seus objectius més rellevants: una exploració feta des d’una perspectiva pràctica que requereix, doncs, el desenvolupament d’un sistema de reconeixement; i la recerca d’evidència relacionada amb la potència discriminant de les trajectòries en l’aire (aquelles que són executades sense que l’estri d’escriptura exerceixi pressió sobre la superfície, en les transicions entre traços), això és, la seva capacitat per a reconèixer escriptors. Les trajectòries en l’aire i sobre la superfície han estat analitzades des de la perspectiva de la teoria de la informació. Els resultats obtinguts d’aquesta anàlisi mostren que, llevat de la pressió, ambdós tipus de trajectòries contenen quantitats d’informació pràcticament idèntiques, amb un nivell notable de no redundància. Això suggereix que les trajectòries en l’aire potser posseeixen una potència discriminant considerable i que la capacitat global de reconeixement pot millorar si es combinen amb les trajectòries sobre la superfície. S’ha desenvolupat un sistema de reconeixement innovador que representa l’assoliment de l’objectiu pràctic. Aquest sistema està basat en una aproximació al•logràfica, això és, no té en compte les característiques globals del text sinó que està focalitzat en les formes dels caràcters i dels seus fragments. Els traços són considerats la unitat estructural bàsica de l’escriptura i qualsevol fragment de text és entès com un parell de seqüències separades, una de traços en superfície i una de traços elevats. El sistema treballa en base a un parell de catàlegs de traços, construïts de manera no supervisada amb l’ajut de mapes autoorganitzats, que li permeten transformar les seqüències de traços en seqüències de números enters. Aquestes darreres seqüències, molt més simples que no pas les originals, poden ser comparades, de manera efectiva, mitjançant el dynamic time warping (alineament temporal dinàmic) el qual treu profit de les propietats de veïnatge característiques dels mapes autoorganitzats. Les mesures que s’obtenen de cada seqüència poden ser combinades en un pas posterior. El sistema de reconeixement ha estat provat experimentalment fent ús de les 16 paraules en majúscules de la base de dades BiosecurID, la qual en conté 4 realitzacions de cadascuna donades per 400 persones. Els resultats experimentals que s’han obtingut recolzen clarament l’afirmació que les paraules online presenten una potència discriminant notable i avalen l’adequació de l’aproximació al•logràfica per a dur a terme reconeixement d’escriptors en el context online depenent del text. Quant a la identificació, el sistema es compara favorablement amb altres mètodes basats en paraules. I, pel que fa a la verificació, els nivells de precisió obtinguts no es troben gaire lluny dels nivells assolits pels mètodes de verificació de signatura representatius de l’estat de l’art actual. És més, els resultats que s’obtenen de les trajectòries en l’aire han corroborat allò que havia estat suggerit per l’anàlisi de la informació: la seva considerable potència discriminant i la seva substancial manca de redundància respecte de les trajectòries sobre la superfície. Finalment, s’ha proposat un nou sistema de generació de mostres sintètiques de paraules online. Aquest mètode està basat en el sistema de reconeixement abans descrit, n’aprofita les característiques principals i s’hi pot integrar amb facilitat. Les mostres sintètiques s’utilitzen per engrandir els conjunts d’inscripció (enrolment sets), la qual cosa té com a efecte una millora substancial de la precisió del sistema.

Design of secure mobile payment protocols for restricted connectivity scenarios

Téllez Isaac, Jesús Augusto 12 September 2012 (has links)
The emergence of mobile and wireless networks made posible the extensión of electronic commerce to a new area of research: mobile commerce called m-commerce, which includes mobile payment), that refers to any e-commerce transaction made from a mobile device using wireless networks. Most of the mobile payment systems found in the literatura are based on the full connectivity scenario where all the entities are directly connected one to another but do not support business models with direct communication restrictions between the entities of the system is not a impediment to perform comercial transactions. It is for this reason that mobile payment systems that consider those situations where direct communications between entities of the system is not posible (temporarily or permanently) basically due to the impossibility of one of the entities connected to the Internet are required. In order to solve the current shortage in the scientific world of previous research works that address the problema of on-line payment from mobile devices in connectivity restricted scenarios, in this thesis we propose a set of secure payment protocols (that use both symmetric and non-traditional asymmetric cryptography), which have low computational power requirements, are fit for scenarios with communications restrictions (where at least two of the entities of the system cannot exchange information in a direct way and must do it through another entity) and offer the same security capabilities as those protocols designed for full connectivity scenarios. The proposed protocols are applicable to other types of networks, such as vehicular ad hoc network (VANETs), where services exist which require on-line payment and scenarios with communication restrictions.On the other hand, the implementation (in a multiplatform programming language) of the designed protocols shows that their performance is suitable for devices with limited computational power.

EmDeplo morphogenesis

Cocho Bermejo, Ana 26 October 2012 (has links)
These thesis will argue about the importance of Dynamic Parametric Architecture versus Static Parametric Architecture. Describing the architectonical and the algorithmic context within which the Emergency Deployable System emerged, it will be discussed the importance of adaptability as the missing concept of parametric architecture. Developing the concept of Human Oriented Parametric architecture, it will be discussed the need of implementing time as the lost parameter in current design techniques. Using the media-tic building, of the Spanish architect Enrique Ruiz Geli, as an example of a current design that tries to implement new technologies and parametric ideas in its design process, it will be explained the idea of the need of the building of working with the environment, not defending against it as the basis for a good adaptability. Geli¿s design is currently using 104 Arduino chips for an individual control and performance of the 104 ETFE pillows of the building façade. Through the creation of a virtual stimulus-reaction model of the system façade versus a model in which machine learning have been implemented for a better environmental performance, the efficacy on insulation of both models will be compared. Morphogenetic processes idea will be discussed through also the principle of an adaptable membrane, as the thought solution for future architecture design processes improvement. A model implementing a unique Arduino on the façade, will control the performance of the façade patterns, through, an Artificial Neural Network that will decide the kind of scenario the building is in, activating a Genetic Algorithm that will optimize insulation performance of the ETFE pillows. The final virtual model will be able to obtained the goal proposed, for this thesis, a homogeneous temperature in all the spaces of the building of 22ºC. The maximum thermal optimization obtained, nevertheless, appears if the opening of the pillows is free within and interval of 0 and 1 m thickness. The constrains of the opening of the ETFE pillows to three positions, will be demonstrated more effective than a just stimulus-reaction behaviour, but also, much less effective that an unconstrained façade system. The EmDeplo System will work with a Global behaviour, pattern performance of the façade, but also with a local behaviour for each pillow, giving the option of individual sun shading control. Machine learning implementation will give the façade the possibility to learn from the efficacy of its decisions through time, eliminating the need of an on-off behaviour for defending against the environment. Instead it will work with it, adapting to it, and evolving with its variabilities. / Esta tesis debatira la importancia de la Arquitectura Parametrica Dinamica versus la Arquitectura Parametrica Estatica.Describiento el actual escenario arquitectonico y algoritmico dentro del cual el "Emergency Deployable System" emergio,sera debatida la importancia de la adaptabilidad como el concepto perdido actualmente el la arquitectura parametrica. Desarrollando el concepto de "Human Oriented Parametric Architecture", sera discutida la necesidad de implementar el tiempo como el parametro perdido en los actuales procedimientos de diseño. Empleando el edificio Media-Tic, del arquitecto español Enrique Ruiz Geli, como un ejemplo de un diseño actual que intenta implementar nuevas tecnologias e ideas parametricas en su proceso de diseño,sera explicada la idea de la necesidad del edificio de trabajar con el entorno, no de defenderse contra el, como base para una buena adaptabilidad. El diseño de Geli usa 104 chipsArduino para un control y comportamiento individual de los 104 cojines de ETFe en su fachada. A traves de la creacion de un sistema virtual estimulo-reaccion de la fachada versus un modelo virtual en el cual el aprendizaje de maquinas ha sido implementado para un mejor comportamiento ambiental, la eficacia de ambos modelos sera compararda. La idea de los procesos Morfogeneticos sera discutida a traves del pricipio de una mebrana adaptable, como la solucion propuesta para la mejora futura del proceso de diseño arquitectonico. Un modelo implementando un unico Arduino en la fachada, controlara el comportamiento de los patrones de la fachada a traves de una Red Neuronal Artificial que decidira el tipo de escenario de entorno en que el edificio se encuentra, activando un Algoritmo Genetico que optimizara el aislamiento termico de os cojines ETFE. La maqueta virtual final sera capaz de llegar a la meta propuesta para esta tesis doctoral, una temperatura homogenea en todos los espacios del edificio de 22ºC. La maxima optimizacion termica obtenida, sin embargo, aparece si la posibilidad de apertura de los cojines ETFE es libre en un intervalo entre o y 1m de espesor. La reduccion de las posibilidades de apertura de los cojines a tres posiciones unicamente, sera demostrada como una posibilidad mejoor que el comportamiento estimulo-reaccion, sin embargo, mucho menos efectivo que una posibilidad de apertura de rango libre. El sistema EmDeplo funcionara con un comportamiento global, la variabilidad del patron de la fachada, pero tambien con un comportamiento local, el de cada cojin ETFE, dando la opcion de un control de sombra-sol individual. El aprendizaje de maquinas implementado dara a la fachada la posibilidad de aprender de la eficacia de sus decisiones a lo largo del tiempo, eliminando la necisidad de un comportamiento on-off para defenderse del entorno. En lugar de esta defensa, trabajara con el, adaptamdose a el, y evolucionando con su variabilidad.

Contributions to electromechanical systems diagnosis by means data fusion techniques

Delgado Prieto, Miguel 26 October 2012 (has links)
Electromechanical drives have traditionally found their field of application in the industrial sector. However, the use of such systems is spreading to other sectors within the field of transport, such as the automotive sector, or to the aircraft sector with the development of the concept of More Electric Aircraft (MEA). One of the major improvements of the MEA concept is related to the actuators of the primary flight controls, where so far only have been considered electrohydraulic actuators, although the current trend is to replace them with electromechanical actuators (EMA). Widespread use, in the future, of EMA in transport systems, is only possible with research and vances in algorithms for detection and diagnosis of faults that may occur both, in the electrical or mechanical parts, in order to ensure the reliability of the drive and the safety of users. During the last years, the study of electro-techanical systems and the fault diagnosis under varying conditions of torque and speed has been mandatory. Although these requirements have been studied deeply by different authors, most of the works are focused on single fault detection. Therefore, there is a lack of diagnosis methods able to detect different kinds of faults in an electro-mechanical actuator. There are very few studies related with diagnosis schemes capable of identifying various faults under different operating conditions, and even less analyzing deeply all the diagnosis chain to face the challenge from all possible perspectives. In this research work, it is proposed the nvestigation towards integral health monitoring schemes for electro-mechanical systems based on pattern recognition. In order to identify various faults under different operating conditions, the health monitoring scheme is developed from a data fusion point of view. The processing of great deals of information enhances the pattern recognition capabilities but, in turn, requires the mplementation of advanced techniques and methodologies. Therefore, first, it is proposed in this research work a review of the whole diagnosis chain, including the different stages (feature calculation, features reduction and classification), the methodologies and techniques. The review finishes by presenting the proposed strategies to take a step further in each diagnosis stage, proposing methodologies to be investigated which would allow a significant advance towards the integral diagnosis systems. In this sense, investigation towards a novel feature calculation methodology able to deal with non-stationary conditions is presented. Next, the feature reduction stage is covered by the proposal of collaborative methodologies by different techniques to improve the significance of the reduced feature set. Also, a more concrete approach is developed by non-lineal techniques, which are not commonly used. Finally, different classification structures are analyzed and novel classification architecture is proposed to be applied in multi-fault diagnosis problems. Experimental analyses are presented resulting from the application of the proposed strategies to different electro-mechanical arrangements. The obtained results achieve high performance levels, and the proposed methodologies can be adapted to the necessary diagnostic requirements. It should be noticed that the proposed contributions increase the information obtained from the system to a better understanding of its behavior and this, has a direct effect over the reliability of the system operation. / Els accionaments electromecànics han tingut tradicionalment el seu camp d'aplicació en el sector industrial. No obstant això l'ús d'aquest tipus de sistemes s'està estenent cap a altres sectors dins l'àmbit dels transports, com el sector de l'automòbil, o el sector de l'aeronàutica, amb el desenvolupament del concepte de l'Avió Més Elèctric (MEA). Una de les millores més importants del concepte MEA està relacionada amb els actuadors dels controls primaris de vol, on fins ara només s'han considerat actuadors electrohidràulics, encara que la tendència actual és reemplaçar-los per actuadors electromecànics (EMA). L'ús generalitzat, en el futur, d'accionaments EMA en sistemes de transport, passa per la investigació i els avenços en els algorismes de detecció i diagnòstic de fallides que es puguin produir, tant en la part elèctrica com en la mecànica, per tal de garantir la fiabilitat de l'accionament i la seguretat dels usuaris. Durant els últims anys, l'estudi de sistemes electromecànics i el diagnòstic de fallides en diverses condicions de parell i de règim de funcionament, han estat estudiats profundament per diferents autors, encara que la majoria dels treballs es centren en la detecció d'una única fallida. Per tant, hi ha una manca de mètodes de diagnòstic capaços de detectar diferents tipus de defectes en un actuador electromecànic. Hi ha molt pocs estudis relacionats amb els sistemes de diagnòstic, capaços d'identificar diverses fallides sota diferents condicions d'operació, i molt menys analitzar profundament tota la cadena de diagnòstic per afrontar el problema des de totes les perspectives possibles. En aquesta tesi, es proposa la investigació sobre tècniques per a la monitorització de condició de sistemes electromecànics, basada en el reconeixement de patrons. Per tal d'identificar diferents fallides sota diferents condicions d'operació, les tècniques propostes s'elaboren sota el prisma de la fusió de dades. El tractament de grans quantitats d'informació, millora els resultats dels algoritmes de reconeixement de patrons, però al seu torn, requereixen de l'aplicació de tècniques i metodologies avançades. Per tant, inicialment es realitza una revisió de la cadena de diagnòstic complerta, incloent les metodologies i tècniques per a les diferents etapes (càlcul d'indicadors, reducció de dimensionalitat i classificació). La revisió finalitza amb la presentació de les estratègies proposades com aportació en cada etapa de diagnòstic. Els resultats obtinguts permeten avenços significatius cap als sistemes de diagnòstic integrals. En aquest sentit, es presenta la investigació sobre metodologies de càlcul d'indicadors en condicions no estacionàries. A continuació, en l'etapa de reducció de dimensionalitat, es proposen metodologies col•laboratives aplicant diferents tècniques que permeten millorar la discriminació de classes, concretament es proposa un enfocament basant-se en tècniques no lineals, que no s'usen habitualment. Finalment, s'analitzen les diferents estructures de classificació i es proposa una arquitectura nova de classificació per ser aplicada en problemes de diagnòstic de múltiples fallides. Es presenten resultats experimentals de les diferents metodologies propostes, per a diferents configuracions electromecàniques. Els resultats obtinguts mostren un alt nivell de rendiment, i les metodologies proposades es poden adaptar als requisits de diagnòstic necessàries en diferents aplicacions. Es conclou que la informació resultant permet una millor comprensió del comportament del sistema sota test, i això té un efecte directe sobre la seva fiabilitat d'operació. / Los accionamientos electromecánicos han tenido tradicionalmente su campo de aplicación en el sector industrial. Sin embargo el uso de este tipo de sistemas se está extendiendo hacia otros sectores dentro del ámbito de los transportes, como el sector del automóvil, o el sector de la aeronáutica con el desarrollo del concepto del Avión Más Eléctrico (MEA). Una de las mejoras más importantes del concepto MEA está relacionada con los actuadores de los controles primarios de vuelo, donde hasta el momento sólo se han considerado actuadores electrohidráulicos, aunque la tendencia actual es remplazarlos por actuadores electromecánicos (EMA). El uso generalizado, en el futuro, de accionamientos EMA en sistemas de transporte, pasa por la investigación y los avances en los algoritmos de detección y diagnóstico de fallos que se puedan producir, tanto en la parte eléctrica como en la mecánica, con el fin de garantizar la fiabilidad del accionamiento y la seguridad de los usuarios. Durante los últimos años, el estudio de sistemas electromecánicos y el diagnóstico de fallos en diversas condiciones de par y de régimen de funcionamiento, han sido estudiados profundamente por diferentes autores, aunque la mayoría de los trabajos se centran en la detección de un único fallo. Por lo tanto, existe una falta de métodos de diagnóstico capaces de detectar diferentes tipos de defectos en un actuador electro-mecánico. Hay muy pocos estudios relacionados con los sistemas de diagnóstico, capaces de identificar diversos fallos bajo diferentes condiciones de operación, y mucho menos analizar profundamente toda la cadena de diagnóstico para afrontar el problema desde todas las perspectivas posibles. En esta tesis, se propone la investigación sobre técnicas para la monitorización de condición de sistemas electromecánicos, basados en el reconocimiento de patrones. Con el fin de identificar diferentes fallos bajo diferentes condiciones de operación, las técnicas propuestas se elaboran bajo el prisma de la fusión de datos. El tratamiento de grandes cantidades de información, mejora los resultados de los algoritmos de reconocimiento de patrones, pero a su vez, requieren de la aplicación de técnicas y metodologías avanzadas. Por lo tanto, inicialmente se realiza una revisión de la cadena de diagnóstico completa, incluyendo las metodologías y técnicas para las diferentes etapas (cálculo de indicadores, reducción de dimensionalidad y clasificación). La revisión finaliza con la presentación de las estrategias propuestas como aportación en cada etapa de diagnóstico. Los resultados obtenidos permiten avances significativos hacia los sistemas de diagnóstico integrales. En este sentido, se presenta la investigación sobre metodologías de cálculo de indicadores en condiciones no estacionarias. A continuación, en la etapa de reducción de dimensionalidad, se proponen metodologías colaborativas aplicando diferentes técnicas que permiten mejorar la discriminación de clases; concretamente se propone un enfoque basándose en técnicas no lineales, que no se usan habitualmente. Finalmente, se analizan las diferentes estructuras de clasificación y se propone una arquitectura novedosa de clasificación para ser aplicada en problemas de diagnóstico de múltiples fallos. Se presentan resultados experimentales de las diferentes metodologías propuestas, para diferentes configuraciones electro-mecánicas. Los resultados obtenidos muestran un alto nivel de rendimiento, y las metodologías propuestas se pueden adaptar a los requisitos de diagnóstico necesarias en diferentes aplicaciones. Se concluye que la información resultante permite una mejor comprensión del comportamiento del sistema bajo test, y esto tiene un efecto directo sobre su fiabilidad de operación.

Characterization, design and re-optimization on multi-layer optical networks

Ruiz Ramírez, Marc 21 December 2012 (has links)
L'augment de volum de tràfic IP provocat per l'increment de serveis multimèdia com HDTV o vídeo conferència planteja nous reptes als operadors de xarxa per tal de proveir transmissió de dades eficient. Tot i que les xarxes mallades amb multiplexació per divisió de longitud d'ona (DWDM) suporten connexions òptiques de gran velocitat, aquestes xarxes manquen de flexibilitat per suportar tràfic d’inferior granularitat, fet que provoca un pobre ús d'ample de banda. Per fer front al transport d'aquest tràfic heterogeni, les xarxes multicapa representen la millor solució. Les xarxes òptiques multicapa permeten optimitzar la capacitat mitjançant l'empaquetament de connexions de baixa velocitat dins de connexions òptiques de gran velocitat. Durant aquesta operació, es crea i modifica constantment una topologia virtual dinàmica gràcies al pla de control responsable d’aquestes operacions. Donada aquesta dinamicitat, un ús sub-òptim de recursos pot existir a la xarxa en un moment donat. En aquest context, una re-optimizació periòdica dels recursos utilitzats pot ser aplicada, millorant així l'ús de recursos. Aquesta tesi està dedicada a la caracterització, planificació, i re-optimització de xarxes òptiques multicapa de nova generació des d’un punt de vista unificat incloent optimització als nivells de capa física, capa òptica, capa virtual i pla de control. Concretament s'han desenvolupat models estadístics i de programació matemàtica i meta-heurístiques. Aquest objectiu principal s'ha assolit mitjançant cinc objectius concrets cobrint diversos temes oberts de recerca. En primer lloc, proposem una metodologia estadística per millorar el càlcul del factor Q en problemes d'assignació de ruta i longitud d'ona considerant interaccions físiques (IA-RWA). Amb aquest objectiu, proposem dos models estadístics per computar l'efecte XPM (el coll d'ampolla en termes de computació i complexitat) per problemes IA-RWA, demostrant la precisió d’ambdós models en el càlcul del factor Q en escenaris reals de tràfic. En segon lloc i fixant-nos a la capa òptica, presentem un nou particionament del conjunt de longituds d'ona que permet maximitzar, respecte el cas habitual, la quantitat de tràfic extra proveït en entorns de protecció compartida. Concretament, definim diversos models estadístics per estimar la quantitat de tràfic donat un grau de servei objectiu, i diferents models de planificació de xarxa amb l'objectiu de maximitzar els ingressos previstos i el valor actual net de la xarxa. Després de resoldre aquests problemes per xarxes reals, concloem que la nostra proposta maximitza ambdós objectius. En tercer lloc, afrontem el disseny de xarxes multicapa robustes davant de fallida simple a la capa IP/MPLS i als enllaços de fibra. Per resoldre aquest problema eficientment, proposem un enfocament basat en sobre-dimensionar l'equipament de la capa IP/MPLS i recuperar la connectivitat i el comparem amb la solució convencional basada en duplicar la capa IP/MPLS. Després de comparar solucions mitjançant models ILP i heurístiques, concloem que la nostra solució permet obtenir un estalvi significatiu en termes de costos de desplegament. Com a quart objectiu, introduïm un mecanisme adaptatiu per reduir l'ús de ports opto-electrònics (O/E) en xarxes multicapa sota escenaris de tràfic dinàmic. Una formulació ILP i diverses heurístiques són desenvolupades per resoldre aquest problema, que permet reduir significativament l’ús de ports O/E en temps molt curts. Finalment, adrecem el problema de disseny resilient del pla de control GMPLS. Després de proposar un nou model analític per quantificar la resiliència en topologies mallades de pla de control, usem aquest model per proposar un problema de disseny de pla de control. Proposem un procediment iteratiu lineal i una heurística i els usem per resoldre instàncies reals, arribant a la conclusió que es pot reduir significativament la quantitat d'enllaços del pla de control sense afectar la qualitat de servei a la xarxa. / The explosion of IP traffic due to the increase of IP-based multimedia services such as HDTV or video conferencing poses new challenges to network operators to provide a cost-effective data transmission. Although Dense Wavelength Division Multiplexing (DWDM) meshed transport networks support high-speed optical connections, these networks lack the flexibility to support sub-wavelength traffic leading to poor bandwidth usage. To cope with the transport of that huge and heterogeneous amount of traffic, multilayer networks represent the most accepted architectural solution. Multilayer optical networks allow optimizing network capacity by means of packing several low-speed traffic streams into higher-speed optical connections (lightpaths). During this operation, a dynamic virtual topology is created and modified the whole time thanks to a control plane responsible for the establishment, maintenance, and release of connections. Because of this dynamicity, a suboptimal allocation of resources may exist at any time. In this context, a periodically resource reallocation could be deployed in the network, thus improving network resource utilization. This thesis is devoted to the characterization, planning, and re-optimization of next-generation multilayer networks from an integral perspective including physical layer, optical layer, virtual layer, and control plane optimization. To this aim, statistical models, mathematical programming models and meta-heuristics are developed. More specifically, this main objective has been attained by developing five goals covering different open issues. First, we provide a statistical methodology to improve the computation of the Q-factor for impairment-aware routing and wavelength assignment problems (IA-RWA). To this aim we propose two statistical models to compute the Cross-Phase Modulation variance (which represents the bottleneck in terms of computation time and complexity) in off-line and on-line IA-RWA problems, proving the accuracy of both models when computing Q-factor values in real traffic scenarios. Second and moving to the optical layer, we present a new wavelength partitioning scheme that allows maximizing the amount of extra traffic provided in shared path protected environments compared with current solutions. Specifically, we define several statistical models to estimate the traffic intensity given a target grade of service, and different network planning problems for maximizing the expected revenues and net present value. After solving these problems for real networks, we conclude that our proposed scheme maximizes both revenues and NPV. Third, we tackle the design of survivable multilayer networks against single failures at the IP/MPLS layer and WSON links. To efficiently solve this problem, we propose a new approach based on over-dimensioning IP/MPLS devices and lightpath connectivity and recovery and we compare it against the conventional solution based on duplicating backbone IP/MPLS nodes. After evaluating both approaches by means of ILP models and heuristic algorithms, we conclude that our proposed approach leads to significant CAPEX savings. Fourth, we introduce an adaptive mechanism to reduce the usage of opto-electronic (O/E) ports of IP/MPLS-over-WSON multilayer networks in dynamic scenarios. A ILP formulation and several heuristics are developed to solve this problem, which allows significantly reducing the usage of O/E ports in very short running times. Finally, we address the design of resilient control plane topologies in GMPLS-enabled transport networks. After proposing a novel analytical model to quantify the resilience in mesh control plane topologies, we use this model to propose a problem to design the control plane topology. An iterative model and a heuristic are proposed and used to solve real instances, concluding that a significant reduction in the number of control plane links can be performed without affecting the quality of service of the network.

GMPLS-based provisioning of ethernet connections over WSON with quality of service

Bukva, Anica 10 December 2012 (has links)
The rapid growth of the data traffic, caused by the ever-growing number of Internet users and the services requiring huge bandwidth (e.g., videoconferences, IPTV, etc.) show that the existing transport network infrastructure is not optimal in terms of cost, flexibility and scalability. In this context, an appealing solution relies on deploying a multi-layer network (MLN) constituted by a dual layer infrastructure combining the benefits provided by flexible Connection Oriented (CO) - Ethernet and the huge transmission capacity provided by Wavelength Switched Optical Networks (WSON), controlled by a Generalized Multi-Protocol Label Switching (GMPLS) unified control plane. An important concept in such a MLN is the Forwarding Adjacency (FA). The aim of FAs is to exploit the grooming decisions where existent lower-layer Label Switched Paths (LSPs) (i.e., FA LSPs) with sufficient unreserved bandwidth are intelligently reused when accommodating and serving new upper-layer LSPs. By doing so, the established lower-layer LSPs form a Virtual Network Topology (VNT) for the provisioning of CO-Ethernet services. One of the main challenges in a MLN is how to accommodate dynamically requested higher-layer connections in the created VNT to optimally utilize the large capacity offered by a WSON. In this regard, we focus on the problem of path computation and LSP provisioning in a CO-Ethernet over WSON network, under the framework of GMPLS unified control plane. Firstly, we propose the usage of a FA TE link timer, which postpones the release of created FA TE link when there are no more upperlayer connections over such a link, rather than releasing it immediately. By doing so, we do reduce the signaling overhead due to consecutive triggering of FA TE links between the same pair of nodes. As a second contribution, we compare three approaches for dynamic VNT reconfiguration: semi-dynamic, virtual and dynamic, using our proposed online path computation algorithm. We show that with the dynamic approach the lowest connection blocking probability is obtained but at the expense of the increased setup delay. Finally, we have proposed a dynamic path computation algorithm that chooses the route depending on the current state of the network resources, favoring the usage/re-use of virtual and active FA TE links over establishing new optical LSPs occupying unused wavelength channels. The proposed algorithm provides better usage of the network resources, keeping the connection blocking probability low, comparing with selected algorithms proposed in the literature. Next, we focus on schemes and mechanisms for dedicated path protection in a CO-Ethernet over WSON network. In that sense, after classifying recovery mechanisms for MLN found in the literature, we compare both link- and Shared Risk Link Group (SRLG) - disjoint schemes. These schemes aim at computing a link- and SRLG-disjoint backup path with respect to the computed working paths, respectively. It is shown that, although the SRLG-disjoint scheme provides higher survivability comparing with the link-disjoint scheme, the connection blocking probability is still significantly higher. As a second contribution regarding dedicated path protection, we present a protection scheme which tries to accommodate a requested connection over the least congested TE links (i.e., higher unused bandwidth), while establishing both, working and backup paths. The aim of this contribution is to provide an efficient usage of the network resources and to minimize the number of connections affected by a link failure. Finally, we propose a Suurballe algorithm-based scheme that aims at decreasing the connection blocking probability due to working path SRLG-joint links that are removed during the backup path computation. The exhaustive performance evaluations of the above contributions are conducted through simulations under the assumption of dynamic traffic pattern and using well-known reference network topologies.

Distributed detection of anomalous internet sessions

García-Cervigon Gutiérrez, Manuel 02 November 2012 (has links)
Financial service providers are moving many services online reducing their costs and facilitating customers¿ interaction. Unfortunately criminals have quickly found several ways to avoid most security measures applied to browsers and banking sites. The use of highly dangerous malware has become the most significant threat and traditional signature-detection methods are nowadays easily circumvented due to the amount of new samples and the use of sophisticated evasion techniques. Antivirus vendors and malware experts are pushed to seek for new methodologies to improve the identification and understanding of malicious applications behavior and their targets. Financial institutions are now playing an important role by deploying their own detection tools against malware that specifically affect their customers. However, most detection approaches tend to base on sequence of bytes in order to create new signatures. This thesis approach is based on new sources of information: the web logs generated from each banking session, the normal browser execution and customers mobile phone behavior. The thesis can be divided in four parts: The first part involves the introduction of the thesis along with the presentation of the problems and the methodology used to perform the experimentation. The second part describes our contributions to the research, which are based in two areas: *Server side: Weblogs analysis. We first focus on the real time detection of anomalies through the analysis of web logs and the challenges introduced due to the amount of information generated daily. We propose different techniques to detect multiple threats by deploying per user and global models in a graph based environment that will allow increase performance of a set of highly related data. *Customer side: Browser analysis. We deal with the detection of malicious behaviors from the other side of a banking session: the browser. Malware samples must interact with the browser in order to retrieve or add information. Such relation interferes with the normal behavior of the browser. We propose to develop models capable of detecting unusual patterns of function calls in order to detect if a given sample is targeting an specific financial entity. In the third part, we propose to adapt our approaches to mobile phones and Critical Infrastructures environments. The latest online banking attack techniques circumvent protection schemes such password verification systems send via SMS. Man in the Mobile attacks are capable of compromising mobile devices and gaining access to SMS traffic. Once the Transaction Authentication Number is obtained, criminals are free to make fraudulent transfers. We propose to model the behavior of the applications related messaging services to automatically detect suspicious actions. Real time detection of unwanted SMS forwarding can improve the effectiveness of second channel authentication and build on detection techniques applied to browsers and Web servers. Finally, we describe possible adaptations of our techniques to another area outside the scope of online banking: critical infrastructures, an environment with similar features since the applications involved can also be profiled. Just as financial entities, critical infrastructures are experiencing an increase in the number of cyber attacks, but the sophistication of the malware samples utilized forces to new detection approaches. The aim of the last proposal is to demonstrate the validity of out approach in different scenarios. Conclusions. Finally, we conclude with a summary of our findings and the directions for future work.

Desarrollo de un workflow genérico para el modelado de problemas de barrido paramétrico en sistemas distribuidos

Reyes Ávila, Sebastian 23 November 2012 (has links)
This work presents the development and experimental validation of a generic workflow model applicable to any parameter sweep problem: the Parameter Sweep Scientific Workflow (PSWF) model. As part of it, a model for the monitoring and management of scientific workflows on distributed systems is developed. This model, Star Superscalar Status (SsTAT), is applicable to the StarSs programming model family. PSWF and SsTAT can be used by the scientific community as a reference for solving problems using the parameter sweep strategy. As an integral part of the work, the treatment of the parameter sweep problem is formalized. This is achieved by developing a general solution based on the PSNSS (Parameter Sweep Nested Summation Symbol) algorithm, using both the original sequential and a concurrent approach. Both versions are implemented and validated, showing its applicability to all automatable PSWF lifecycle phases. Load testing shows that large-scale parameter sweep problems can efficiently be addressed with the proposed approach. In addition, the SsTAT monitoring and management generic model is instantiated for a Grid environment. Thus, an operational implementation of SsTAT based on GRIDSs, GSTAT (GRID Superscalar Status), is developed. A series of tests performed on an actual heterogeneous Grid of computers shows that GSTAT can appropriately develop their functionality even in an environment so demanding as that. As a practical case, the model proposed here is applied to determining the molecular potential energy hypersurfaces. For this purpose, a specific instance of the workflow, called PSHYP (Parameter Sweep Hypersurfaces), is created. / En este trabajo se presenta el desarrollo y validación experimental de un modelo de workflow genérico, aplicable a cualquier problema de barrido de parámetros, denominado Parameter Sweep Scientific Workflow (PSWF). Asimismo, se diseña y prueba un modelo de monitorización y gestión de workflows científicos, en sistemas distribuidos, designado como SsTAT (Star Superscalar Status) que es aplicable a la familia de modelos de programación Star Superscalar (StarSs). Los modelos PSWF y SsTAT pueden ser utilizados por la comunidad científica como referencia a la hora de resolver problemas mediante la estrategia de barrido de parámetros. Como parte integral del trabajo se formaliza el tratamiento del problema del barrido de parámetros, desarrollándose una solución general concretada en el algoritmo PSNSS (Parameter Sweep Nested Summation Symbol) en su versión secuencial y concurrente. Ambas versiones se implementan y validan, mostrándose su aplicabilidad a todas las fases automatizables del ciclo de vida PSWF. Mediante la realización de varias pruebas de carga se comprueba que el tratamiento de problemas de barrido de parámetros de gran envergadura puede abordarse eficientemente con la aproximación propuesta. A su vez, el modelo genérico de monitorización y gestión SsTAT se particulariza para un entorno Grid, generándose una implementación operativa del mismo, basada en GRIDSs, denominada GSTAT (GRID Superscalar Status). La realización de una serie de pruebas sobre un Grid real de computadores heterogéneo muestra que GSTAT desarrolla apropiadamente sus funciones incluso en un entorno tan exigente como este. Como caso práctico, se aplica el modelo aquí propuesto a la obtención de la hipersuperficie de energía potencial molecular generando a tal efecto un workflow específico denominado PSHYP (Parameter Sweep Hypersurfaces)

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