Dissertationen zum Thema „Comets Dynamics“

The Solar System presents a complex dynamical structure and is not isolated from the Galaxy. In particular the comet reservoir of our planetary system, the Oort cloud, is extremely sensitive to the the galactic environment due to its peripheral collocation inside the Solar System. In this framework, the growing evidences about a possible migration of the Sun open new research scenarios relative to the effects that such kind of migration might induce on the cometary motion. Following several previous studied, we identified the spiral arm structure as the main perturbation that is able to produce an efficient solar migration through the disk. Widening the classical model for the spiral arms, provided by Lin& Shu to a 3D formalism, we verified the compatibility between the presence of the spiral perturbation and a significant solar motion for an inner Galactic position to the current one, in agreement with the constrains in position, velocity and metallicity due to the present conditions of our star. The main perturbers of the Oort cloud, the close stellar passages and the tidal field of the Galaxy, might be both affected by the variation of Galactic environment that the solar migration entails. Despite that, in order to isolate the effects to the two different perturbators, we decided to focus our attention only on the Galactic tide. The perturbation due to the spiral structure was included in the study on the cometary motion, introducing the solar migration and adding the direct presence of the non-axisymmetric component in the Galactic potential of the tidal field. The results show a significant influence of the spiral arm in particular on cometary objects belonged to the outer shell of the Oort cloud, for which provides an injection rate three times bigger than the integration performed without the spiral arms. The introduction of the spiral perturbation seems to bolster the planar component of the tide, indeed it produces the most significant variation of the perihelion distance for moderate inclination orbits with respect to the plane. The peak for the cometary injections has been registered between 6 and 7 kpc. If this evidence will be confirmed by more realistic cometary sample, it might involve a redefinition of the habitability edges in the Galaxy (GHZ). In particular regions not precluded to the formation of life, may compromise the development of the life with a high cometary impact risk
Il Sistema Solare è una struttura con una dinamica complessa e non isolata da quella galattica. In particolare la riserva cometaria del nostro sistema planetario, la nube di Oort, a causa della sua periferica collocazione all’interno del Sistema Solare, risulta estremamente sensibile all'ambiente galattico circostante. In questo contesto, le crescenti evidenze di una possibile migrazione del Sole, aprono un nuovo scenario di indagine relativo ai cambiamenti che tale migrazione potrebbe indurre sul moto cometario. Seguendo un filone di ricerca già tracciato, abbiamo identificato nella struttura a spirale la principale perturbazione in grado di produrre un efficace effetto migratorio per il Sole. Ampliando il classico modello di Lin & Shu con una modellizzazione 3D per i bracci a spirale considerati in regime transiente, siamo stati in grado di verificare la compatibilità tra tale perturbazione e un moto solare attraverso il disco, in accordo con i vincoli di posizione, velocità e metallicità imposti dalla attuale condizione della nostra stella. Malgrado i maggiori perturbatori della nube di Oort, i passaggi stellari ravvicinati e il campo mareale della Galassia, siano entrambi potenzialmente sensibili alla variazione di ambiente galattico che una migrazione solare comporta, abbiamo concentrato il nostro studio unicamente sulla marea galattica. La perturbazione dovuta alla spirale, è stata incorporata nello studio dei moti cometari, sia attraverso l’introduzione della migrazione solare, che come effetto diretto sulle comete grazie alla presenza della componente non assisimmetrica nel campo mareale. I risultati mostrano un’influenza significativa della spirale, in particolar modo sulla popolazione cometaria del guscio più esterno della nube, per la quale si sono registrati tassi di immissione cometaria 3 volte maggiori rispetto al caso senza tale perturbazione. La spirale sembra rinforzare l’azione della componente piana della marea, producendo infatti le maggiori variazioni sui perieli cometari in corrispondenza di orbite con inclinazioni moderate rispetto al piano galattico. Si è inoltre rilevato che il picco di immissione cometaria si trova in corrispondenza di distanze galattiche per il Sole comprese tra 6 e 7 kpc. Se tale evidenza fosse confermata anche da campioni cometari più realistici, potrebbe comportare un vincolo ulteriore alla definizione della zona di abitabilità galattica (GHZ). In particolare, regioni del disco non attualmente precluse alla formazione della vita, potrebbero risultare inadatte allo sviluppo della stessa per un rischio di impatto cometario troppo elevato

Les comètes sont une population de petits corps du Système Solaire souvent décrits comme les objets les plus primitifs de notre Système Solaire, détenant des informations précieuses sur sa formation et son évolution. Formées tôt, au même temps que les planètes géantes, dans les parties externes du disque protoplanétaire et dispersées vers l'extérieur peu après leur formation pour être stockées dans des réservoirs lointains et froids, elles sont considérées comme ayant largement conservé leurs propriétés et composition primordiales. Cependant, le niveau de leur nature primitive a commencé à être revu, car un nombre croissant d'observables et d'études théoriques suggèrent la possibilité d'altérations thermiques avant leur retour dans les parties internes du Système Solaire où elles sont généralement étudiées et observées. Dans ce contexte, ce travail vise à examiner le niveau de cette nature primitive pour les différentes familles cométaires de notre Système Solaire. Dans ce but, nous avons développé un modèle d'évolution thermique dédié, conçu pour un couplage efficace aux simulations N-corps qui suivent l'évolution orbitale à long terme des planétésimaux, provenant des parties externes du disque protoplanétaire et évoluant vers des orbites dans la région planétaire, après un séjour prolongé dans les réservoirs extérieurs du système solaire. Nos résultats révèlent la possibilité d'altérations thermiques, affectant principalement le contenu condensé primordial d'hyper-volatiles et dans un second lieu le contenu primordial modérément volatile et la glace d'eau amorphe, au cours des premières phases de la vie des comètes. Une étude comparative indique que les comètes à longue période devraient être la population la moins altérée. Une activité intense, mais sporadique, est également enregistrée dans la région des planètes géantes, alors que les comètes reviennent dans le Système Solaire interne, compatible avec les observables actuelles concernant la population de Centaures. Ces résultats indiquent que l'évolution thermique des noyaux cométaires est inextricablement liée à leur évolution orbitale. Ils indiquent également que l'activité cométaire observée dans les parties internes du Système Solaire provient très probablement de couches déjà altérées, soulignant la nécessité de prendre en compte l'histoire dynamique des comètes lors de l'interprétation des observations actuelles
Comets are a population of small Solar System bodies, often described as the most primitive population in our Solar System, holding valuable information on its formation and evolution. Formed early, at the same time as the giant planets, in the outer parts of the protoplanetary disk and scattered outwards shortly after their formation towards distant and cold reservoirs, they are considered to have preserved their primordial composition and properties to a great extent. However, the level of this primitive nature has started to be reevaluated recently, as a growing body of observational evidence and an important number of theoretical studies are suggesting the possibility of thermally-induced alterations before their return to the inner parts of the Solar System, where they are usually studied and observed. In this context, our work aims to examine the level of the primitive nature of different cometary families in our Solar System. To do so, we developed a dedicated thermal evolution model, designed for an efficient coupling to N-body simulations, tracking the long-term orbital evolution of planetesimals, originating in the outer parts of the protoplanetary disk and evolving into planetary-crossing orbits after a prolonged stay in outer Solar System reservoirs. Our results reveal the possibility of thermal processing, affecting mainly the primordial condensed hyper-volatile content and on a lesser extent the primordial moderately-volatile and amorphous water ice content, during the early phases of a comet's lifetime. A comparative study is indicating that long-period comets are expected to be the least altered population. Intense, yet sporadic, activity is also recorded in the planetary region, as comets return in the inner Solar System, compatible with the current observables on the Centaur population. These results indicate that the thermal evolution of cometary nuclei is inextricably related to their orbital evolution. They are also indicating that the cometary activity observed in the inner parts of the Solar System is very likely triggered from thermally processed subsurface layers, highlighting the necessity of considering the past evolutionary history of comets when interpreting the current observations in a broader context

The Kuiper belt is a population of small bodies located outside Neptune's orbit. The observed Kuiper belt objects (KBOs) can be divided into several subclasses based on their dynamical structure. I construct models for these subclasses and use numerical integrations to investigate their long-term evolution. I use these models to quantify the connection between the Kuiper belt and the Centaurs (objects whose orbits cross the orbits of the giant planets) and the short-period comets in the inner solar system. I discuss how these connections could be used to determine the physical properties of KBOs and what future observations could conclusively link the comets and Centaurs to specific Kuiper belt subclasses.

The Kuiper belt's structure is determined by a combination of long-term evolution and its formation history. The large eccentricities and inclinations of some KBOs and the prevalence of KBOs in mean motion resonances with Neptune are evidence that much of the Kuiper belt's structure originated during the solar system's epoch of giant planet migration; planet migration can sculpt the Kuiper belt's scattered disk, capture objects into mean motion resonances, and dynamically excite KBOs. Different models for planet migration predict different formation locations for the subclasses of the Kuiper belt, which might result in different size distributions and compositions between the subclasses; the high-inclination portion of the classical Kuiper belt is hypothesized to have formed closer to the Sun than the low-inclination classical Kuiper belt. I use my model of the classical Kuiper belt to show that these two populations remain largely dynamically separate over long timescales, so primordial physical differences could be maintained until the present day.

The current Kuiper belt is much less massive than the total mass required to form its largest members. It must have undergone a mass depletion event, which is likely related to planet migration. The Haumea collisional family dates from the end of this process. I apply long-term evolution to family formation models and determine how they can be observationally tested. Understanding the Haumea family's formation could shed light on the nature of the mass depletion event.

Cometary nuclei may be our best available probes of the physical and chemical nature of the presolar nebula. However, in situ sampling of cometary nuclei to determine their composition is generally not feasible. Instead, remote spectroscopic observations of cometary comae are used to infer cometary composition. This approach relies on one's ability to model accurately the density distributions of gas and dust in the comae and a complex network of photochemical and molecular processes. Previously, a variety of theoretical models had been developed and, unfortunately, they are applicable only to a portion of the coma or to specific problems. In the first part of this thesis we introduce a preliminary version of a gas model built upon the concepts of dilute gas theory. This model is valid over the whole coma and it incorporates all previous models as its special cases, thus providing a new theoretical foundation for future cometary studies. In the second part of the thesis we discuss a spectral outflow model. This model is a special case of the dilute gas model and is tailored specifically to retrieve kinematic properties of cometary comae from velocity-resolved spectral line profiles. We review the formation of cometary spectral line profiles and we develop an analytic expression that maps three dimensional number density distributions into synthetic spectral line profiles. After discussing simplifications and Monte Carlo computational procedures, we apply the spectral outflow model to interpret infrared observations of H₂O in comets Halley and Wilson.

The paper describes the background and concepts behind a master’s thesis platform known as COMET (Constrained Optimization of Multiple-dimensions for Efficient Trajectories) created for mission designers to determine and evaluate suitable interplanetary trajectories. This includes an examination of the improvements to the global optimization algorithm, Differential Evolution, through a cascading search space pruning method and decomposition of optimization parameters. Results are compared to those produced by the European Space Agency’s Advanced Concept Team’s Multiple Gravity Assist Program. It was found that while discrepancies in the calculation of ΔV’s for flyby maneuvers exist between the two programs, COMET showed a noticeable improvement in its ability to avoid premature convergence and find highly isolated solutions.

El primer capítol d’aquesta Tesis porta per Títol “Trade Patterns, Income Differences and Gains From Trade” i ha estat elaborada conjuntament amb el meu col·lega Wyatt J. Brooks. Quantificar els guanys provinents de comerç internacional és una àrea de recerca que ha estat estudiada usant una gran varietat de models de comerç. Al mateix temps, s’ha mostrat com les no-homoteticitats són molt útils per explicar patrons de comerç observats en dades molt desagregades. Posem ambdues literatures juntes per preguntar com les no-homoteticitats afecten les prediccions de guanys de comerç. A tal fi, desenvolupem un model de comerç amb N països amb els mateixos volums de comerç internacional, població, PIB per càpita i desigualtat dins de cada país que a les dades. Incloem les no-homoteticitats per tal que el comerç entre països rics i països pobres sigui igual al que observem a les dades. Amb aquest model, podem comparar els resultats en benestar obtinguts amb els que impliquen Arkolakis, Costinot, and Rodriguez-Clare (2012) – que dóna una fórmula senzilla de guanys comercials per part d’un gran nombre de models homotètics (també la versió d’aquest model quan les preferències són homotètiques). El principal resultat és que els models homotètics esbiaixen a la baixa els guanys comercials en països amb poca població i baixa productivitat, i a l’alça el dels països molt poblats i molt productius. El model homotètic esbiaixa a l’alça els guanys comercials dels EE.UU. i de Japó en 14% i 22%, mentre que ho fa a la baixa per Espanya i Itàlia en un 24% i un 14%. El segon capitol d’aquesta Tesis porta per títol “Measured Productivity and International Trade: An Unresolved Puzzle”. Utilitzar models de dinàmica d’empreses correctes quan s’analitza l’impacte del comerç és clau a fi d’entendre completament quins són els efectes a la part productiva de l’economia quan aquesta es dedica a comerciar més. Hi ha diversos models de comerç que intenten entendre la relació entre comerç i dinàmica d’empreses, però un d’ells és sens dubte el més utilitzat per economistes de comerç: el de Melitz (2003). Aquest model explica algunes característiques de les dades. En particular, vol explicar per què les empreses més productives exporten. És de comú parer entre els economistes que aquest model explica bé les característiques de productivitat de les empreses. En aquest capítol ens preguntem: ho és? Concretament, mostrem que si hom mesura la productivitat als resultats del model tal i com es fa a les dades, ens trobem amb resultats sorprenents sobre quines són les empreses més productives: poden ser les que no exporten. El tercer capítol de la Tesis es titula “Distortions, Productivity, and Idiosyncratic Shocks” i és escrita conjuntament amb el meu professor José María Da Rocha. Considerem distorsions en un model on les plantes tenen xocs idiosincràtics a la productivitat que evolucionen amb una moció Browniana. Introduir els xocs en el model implica que les plantes tenen beneficis no constants i com a resultat el marge de sortida es torna exogen, i les plantes han de decidir en cada període si es queden o no produint. Utilitzem l’equació de Kolmogorov per tal de caracteritzar l’equilibri estacionari. La contribució de l’estudi consisteix en mostrar que si un model es calibra/s’estima sense xocs idiosincràtics, les plantes tenen productivitat constant en el temps i la rati de sortida és exògena a fi d’obtenir els moments generats pel model amb xocs i sortida endògena, les distorsions en PTF són esbiaixades a l’alça.
The first chapter of this Thesis is entitled Trade Patterns, Income Differences and Gains From Trade and is coauthored with my colleague Wyatt J. Brooks. Quantifying the gains from international trade is an area of research that has been widely studied using a variety of trade models. At the same time, it has been shown that nonhomotheticities are useful for matching the systematic patterns of trade present in disaggregated trade data. We bring these two literatures together to ask how nonhomotheticities affect our predictions for gains from trade. To do so, we develop a N-country trade model that exactly matches bilateral trade, population, GDP per capita and within country income inequality for many countries. We include nonhomotheticities to match patterns of trade between rich and poor countries that we observe in highly disaggregated trade data. We then make use of the results from Arkolakis, Costinot, and Rodriguez-Clare (2012), which gives a simple formula for gains from trade in a large class of homothetic models, including a version of our model with the nonhomotheticity removed. Our main finding is that homothetic models underestimate gains from trade in countries with small populations and low productivities, and overestimate gains in countries with large populations and high productivities. The homothetic model overestimates the gains from being open to trade in the U.S. and Japan by 14% and 22%, and underestimates them in Spain and Italy by 24% and 14%. The second chapter of this Thesis is entitled Measured Productivity and International Trade: An Unresolved Puzzle. Using correct models of firm dynamics when analyzing the impact of trade is key in order to fully understand what are the effects to the supply side of the economy when it engages into trade. There are several models of trade that try to understand the role of trade and firm dynamics, but there is one that is most used by trade economists: the Melitz model (2003). This model explains several features of the data. In particular, it aims to explain why more productive firms export. It is a common agreement among economists that the model is well suited in order to explain these patterns. In this chapter we ask: is it? In particular, we show that measuring productivity in the model's outcome as it is done in the data may lead to some surprising results regarding what more productive firms do: they may be the non-exporters. The third chapter of this Thesis is entitled Distortions, Productivity, and Idiosyncratic Shocks and is coauthored with my professor José María Da Rocha. We consider policy distortions in a model where plants face idiosyncratic productivity shocks that evolve following a Brownian motion. Introducing idiosyncratic shocks into the model implies that plants have non-constant operating profits and as a result there is an endogenous exit margin and incumbent plants must decide in each period whether or not to remain in the industry. By using the forward Kolmogorov equation, we analytically characterize the Stationary Equilibrium. Our main contribution is to show that if a model is being calibrated/estimated without idiosyncratic shocks, where plants face constant productivity over time and the exit rate is exogenous to fit data generated from a model with shocks and endogenous entry, TFP distortions will be overestimated.

The Context Change Potential (CCP) model of presupposition, due primarily to Kartunnen and Heim, is formally elaborated and modified within a propositional dynamic logic, a first-order dynamic logic, and within a three sorted type theory. It is shown that the definitions of connectives and quantifiers can be motivated independently of the phenomenon of presupposition by consideration of the semantics of anaphora and epistemic modality (cf. the work of Groenendijk & Stokhof and Veltman), and that these independently motivated definitions provide a solution to the projection problem for presupposition. It is argued that with regard to the interaction between presupposition and quantification the solution is empirically superior to those in competing accounts. The treatment of epistemic modality is also shown to be superior to existing dynamic accounts, combining solutions to traditional model identity problems with an adequate treatment of presuppositions in quantified contexts. A compositional semantics which integrates dynamic treatments of quantification, anaphora, modality and presupposition is then specified for a fragment of English. Finally, a formal modal of global accommodation (cf. Lewis, Heim, van der Sandt) is defined, this model differing from previous accounts in being non-structural. This means that the accommodated material cannot be deduced from formal properties of the utterance alone, but is essentially dependent on world-knowledge and common sense reasoning. Thus the model provides an essentially pragmatic account in the style of Stalnaker. It is shown that the formal model provides both a general solution to the problem of the in-formativeness of presuppositions, and a specific solution to a problem within the CCP model, namely its tendency to yield innapropriately weak conditionalised presuppositions. It argued that a pragmatic model can provide superior predictions to any purely semantic theory of presupposition, and to any theory based on a purely structural account of accommodation or cancellation (cf. Gazdar).

Le travail realise durant cette these a consiste en le developpement, la realisation et les tests de deux instruments destines a l'etude des environnements neutres et ionises planetaires et cometaires. Le premier instrument, idm (ion dynamics monitor), est un spectrometre a plasma thermique et suprathermique (< 200 ev) developpe initialement lors de la phase de consolidation du projet cometaire europeen rosetta. Une version amelioree a ensuite ete adaptee pour l'etude de l'ionosphere et de la couche limite de mars dans le cadre du projet dynamo. Les deux versions du spectrometre ont ete testees en laboratoire et les resultats, en tres bon accord avec la simulation, ont montre le respect des specifications necessaires a la mesure. Le second instrument est destine a la mesure des parametres dynamiques d'une atmosphere neutre. Une etude detaillee des techniques de mesures actuelles de la dynamique d'un gaz neutre est tout d'abord presentee et montre l'interet de l'utilisation d'un concept instrumental reposant sur des jauges de densite a impact electronique et des chambres d'equilibre. L'instrument cops (comet pressure sensor), premiere realisation de ce concept, sera embarque a bord de la sonde rosetta et permettra l'evaluation de la vitesse d'expansion et de la densite du gaz cometaire. Le developpement de l'instrument a necessite la mise au point de techniques de modelisation de l'interaction d'un gaz et d'un solide en regime moleculaire et a conduit a la realisation de tests sous faisceau moleculaire. Les resultats montrent que les principaux objectifs sont atteints. Une seconde application de ce concept instrumental destinee a l'etude de la haute atmosphere martienne est aussi presentee.

This thesis investigates the concept of leadership in four comedies of Aristophanes. In the first chapter (Lysistrata) I focus on the relationship of the female leadership with religious rituals and medical pathology, and I show that the power of women lies in their important biological role and their ability to conceive and (re)produce life in the context of marriage. In chapter two (Knights) I examine the operation of leadership through the alimentary and sacrificial codes of the play. I argue that the Sausage-seller gradually manifests himself as the sacrificial cook Agorakritos who sacrifices Demos. In this way he puts an end to the politics of savage, raw consumption as they were employed by Paphlagon (and, occasionally, by Demos himself), and saves the day by inaugurating a new era of political practice. In chapter three (Birds) I focus on the political competition between the former leader of the Birds, Tereus, and the newcomer Peisetairos. I argue that Peisetairos captivates his audience through the abuse of rhetoric and sophistry, and gradually adopts more brutal ways, by perverting the ritual of hospitality, committing cannibalism, and becoming sexually aggressive. In this respect, Peisetairos is assimilated to the tragic Tereus of the Sophoclean tragedy, but finally emerges as a more successful version of both the comic and the tragic Tereus. In the fourth and last chapter (Ecclesiazusae) I discuss the women’s disruption and overturn of the normal social order by focusing on the practice of cross-dressing and on love-magic rituals: the exchange of costume between the two sexes, as well as the control of magic practices by the women over men, empower women and, by contrast, disempower and ridicule men, who are finally reduced to a state of impotence, infertility and almost death.

Deploying mobile robots in social environments requires novel navigation algorithms which are capable of providing valid solutions in such challenging scenarios. The main objective of the present dissertation is to develop new robot navigation approaches able to solve in an intelligent way the navigation problem in urban settings while considering at the same time the interactions with pedestrians, similar to what people easily do with little attention. Before studying in depth navigation algorithms, this thesis focuses on prediction algorithms to provide a more detailed model of the scene. Understanding human motion in outdoor and indoor scenarios is an appealing requirement to characterize correctly urban settings. Urban environments consist essentially of static obstacles and people, which are treated as dynamic and highly uncertain obstacles. Accordingly, it is mandatory to calculate people's intentions in order to successfully build a human prediction model that generates the corresponding human trajectories and considers their interactions with the environment, such as other pedestrians, static obstacles or even robots. It is of great interest that service robots can navigate successfully in typical urban environments, which are dynamic and constrained. In addition, people's behavior should not be conditioned by the presence and the maneuvering of robots. To this end, the robot navigation should seek to minimize its impact on the environment, in our case, on people. This thesis proposes new robot navigation methods that contemplate the social interactions taking place in the scene. In order to procure more intelligence to the navigation algorithm, we propose to integrate seamlessly the human motion prediction information into a new robot planning approach. Real experimentation is essential for the validation of the navigation algorithms. As there are real people involved, we must validate the results in real settings since simulation environments have limitations. In this thesis, we have implemented all the prediction and navigation algorithms in our robotic platform and we have provided plenty of evaluations and testings of our algorithms in real settings.
Ubicar robots móviles en entornos sociales requiere novedosos algoritmos de navegación que sean capaces de aportar soluciones válidas en éstos exigentes escenarios. El prinicipal objetivo de la presente disertación es el de desarrollar nuevas soluciones para la navegación de robots que sean capaces de resolver, de una manera más inteligente, los problemas de navegación en emplazamientos urbanos, a la vez que se consideran las interacciones con los transeúntes de manera similar a lo que la gente hace fácilmente prestando poca atención. Antes de estudiar en profundidad los algoritmos de navegación, esta tesis se centra en los algoritmos de predicción para proporcionar un modelo más detallado de la escena. Entender el movimiento humando en entornos exteriores e interiores es un requerimiento deseable para caracterizar correctamente emplazamientos urbanos. Los entornos urbanos están consistituídos por muchos objetos dinámicos y altamente impredecibles, la gente. Por lo tanto, es obligatorio calcular las intenciones de la gente para constriur de manera exitosa un modelo de predicción humano que genere las correspondientes trayectorias humanas y considere sus interacciones con el entorno, como otros peatones, obstáculos estáticos o incluso robots. Es de gran interés que los robots de servicios puedan navegar correctamente en entornos típicamente urbanos, que son dinámicos y acotados, además de que el comportamiento de las personas no debería estar condicionado por la presencia y las maniobras de los robots. Con este fin, la navegación de robots debe buscar minimizar su impacto al entorno, en nuestro caso, a la gente. Esta tesis propone nuevos métodos para la navegación de robots que contemplen las interacciones sociales que suceden en la escena. Para proporcionar una navegación más inteligente, proponemos integrar de manera suave el algoritmo de predicción del movimiento humano con un nuevo enfoque de planificación de trayectorias. La experimentación real es esencial para la validación de los algoritmos de navegación. Ya que hay personas reales implicadas, debemos validar los resultados en emplazamientos reales porque el entorno de simulación tiene limitaciones. En esta tesis hemos implementado todos los algoritmos de predicción y de navegación en la plataforma robótica y hemos proporcionado multitud de evaluaciones y pruebas de nuestros algoritmos en entornos reales.

La era actual de computación a gran escala se caracteriza por el uso de aplicaciones paralelas ejecutadas en miles de cores. Sin embargo, el rendimiento obtenido al ejecutar estas aplicaciones no siempre es el esperado. La sintonización dinámica es una potente técnica que puede ser usada para reducir la diferencia entre el rendimiento real y el esperado en aplicaciones paralelas. Actualmente, la mayoría de las aproximaciones que ofrecen sintonización dinámica siguen una estructura centralizada, donde un único módulo de análisis, responsable de controlar toda la aplicación paralela, puede convertirse en un cuello de botella en entornos a gran escala. La principal contribución de esta tesis es la creación de un modelo novedoso que permite la sintonización dinámica descentralizada de aplicaciones paralelas a gran escala. Dicho modelo se apoya en dos conceptos principales: la descomposición de la aplicación y un mecanismo de abstracción. Mediante la descomposición, la aplicación paralela es dividida en subconjuntos disjuntos de tareas, los cuales son analizados y sintonizados separadamente. Mientras que el mecanismo de abstracción permite que estos subconjuntos sean vistos como una única aplicación virtual y, de esta manera, se puedan conseguir mejoras de rendimiento globales. Este modelo se diseña como una red jerárquica de sintonización formada por módulos de análisis distribuidos. La topología de la red de sintonización se puede configurar para acomodarse al tamaño de la aplicación paralela y la complejidad de la estrategia de sintonización empleada. De esta adaptabilidad surge la escalabilidad del modelo. Para aprovechar la adaptabilidad de la topología, en este trabajo se propone un método que calcula topologías de redes de sintonización compuestas por el mínimo número de módulos de análisis necesarios para proporcionar sintonización dinámica de forma efectiva. El modelo propuesto ha sido implementado como una herramienta para sintonización dinámica a gran escala llamada ELASTIC. Esta herramienta presenta una arquitectura basada en plugins y permite aplicar distintas técnicas de análisis y sintonización. Empleando ELASTIC, se ha llevado a cabo una evaluación experimental sobre una aplicación sintética y una aplicación real. Los resultados muestran que el modelo propuesto, implementado en ELASTIC, es capaz de escalar para cumplir los requerimientos de sintonizar dinámicamente miles de procesos y, además, mejorar el rendimiento de esas aplicaciones.
The current large-scale computing era is characterised by parallel applications running on many thousands of cores. However, the performance obtained when executing these applications is not always what it is expected. Dynamic tuning is a powerful technique which can be used to reduce the gap between real and expected performance of parallel applications. Currently, the majority of the approaches that offer dynamic tuning follow a centralised scheme, where a single analysis module, responsible for controlling the entire parallel application, can become a bottleneck in large-scale contexts. The main contribution of this thesis is a novel model that enables decentralised dynamic tuning of large-scale parallel applications. Application decomposition and an abstraction mechanism are the two key concepts which support this model. The decomposition allows a parallel application to be divided into disjoint subsets of tasks which are analysed and tuned separately. Meanwhile, the abstraction mechanism permits these subsets to be viewed as a single virtual application so that global performance improvements can be achieved. A hierarchical tuning network of distributed analysis modules fits the design of this model. The topology of this tuning network can be configured to accommodate the size of the parallel application and the complexity of the tuning strategy being employed. It is from this adaptability that the model's scalability arises. To fully exploit this adaptable topology, in this work a method is proposed which calculates tuning network topologies composed of the minimum number of analysis modules required to provide effective dynamic tuning. The proposed model has been implemented in the form of ELASTIC, an environment for large-scale dynamic tuning. ELASTIC presents a plugin architecture, which allows different performance analysis and tuning strategies to be applied. Using ELASTIC, experimental evaluation has been carried out on a synthetic and a real parallel application. The results show that the proposed model, embodied in ELASTIC, is able to not only scale to meet the demands of dynamic tuning over thousands of processes, but is also able to effectively improve the performance of these applications.

This thesis is focused on the study of dynamics and control of a multi-tethered satellite formation, where a multi-tethered formation is made up with several satellites (agents) connected by means of cables (tethers). The goal of the first part of the study is to evaluate the effect of tether mass on multi-tethered clusters. Due to the complexity of the formations analyzed, the stability of the formation is assessed through a numerical simulation. The behavior is evaluated in the ideal case of circular orbits, but also in non-ideal cases such as that of elliptical reference orbit or perturbed motion. For circular reference orbits, the dynamics of tethered satellite formation is studied, showing that tether mass affects formation dynamics for closed configurations featuring external tethers. This leads to significant instability effects affecting the position of deputies with respect to the parent body neglected by a more elementary modeling approach. When combined effect of orbit eccentricity and tether mass on tethered formations is analyzed, the most noticeable effect due to eccentricity is the increase in the variation of the local spin rate of the cluster between perigee and apogee passes of the reference elliptical orbit. This effect has consequences over the elongation of tethers, shape of tether oscillations and angular separation between adjacent tethers especially for open formations. When taking into account the J2 effect on massive tethered satellite formations, in the Earth¿facing scenario, the trajectory of the parent body presents oscillations of increasing amplitude in the direction perpendicular to the orbital plane. The second part of the study is focused on deriving a control law for position and attitude control of an Earth-facing double pyramid multi-tethered cluster. The control problem is decomposed in two levels: A first level to perform position and attitude coarse control of the formation as a whole, and a second level to achieve accurate position and control of each agent of the cluster. For the purpose of attitude control, and taking advantage again of the similarities between a tethered cluster and a rigid body, the virtual structure approach is chosen as the most suitable option. The formulation shown in this thesis augments the general virtual structure equations valid for a static formation by adding the kinematics of a spinning formation, since the original formulation is valid only to achieve a static final state. The controller is designed to modify the spin rate and the moment of inertia of the formation through a reeling mechanism, and therefore to be able to control the Likins-Pringle tilting angle of the cluster. For the derivation of the accurate positioning control law, the study initially discusses different alternatives based on the state of the art of the robotics control literature. After evaluating other alternatives, two control laws are chosen for this application: One based on a PID controller and one based on the sliding mode control technique. For the sliding mode based control, a proof of semi-global exponential stability is provided. Results of a representative simulation assess the viability of the control approach proposed leading to a submillimetric positioning accuracy.
La tesi es centra en l'estudi de la dinàmica i control de formacions de satèl·lits connectats per tethers. Aquestes formacions estan compostes per diversos satèl·lits (agents) connectats per cables (tethers). L'objectiu de la primera part de l'estudi, és l'avaluació de l'efecte de la massa a clústers connectats per múltiples tethers. Degut a la complexitat de les formacions analitzades, l'estabilitat de la formació s'analitza a través de simulacions. S'estudia el comportament pel cas ideal d'orbites circulars, així com en casos no ideals tals com orbites de referència el·liptiques, o moviment sota l'efecte de pertorbacions. La tesi analitza la dinàmica de les formacions per òrbites circulars, mostrant que l'efecte de la massa dels tethers afecta la dinàmica de formacions de geometria tancada (on el perímetre extern esta definit per tethers) amb un satèl·lit central. Aquest efecte dóna lloc a una clara inestabilitat que afecta la posició dels agents respecte a l'objecte central. Aquest efecte no és apreciable en models simplificats on s'ignora l'efecte de la massa al model. Quan es combina una òrbita de referència el·liptica amb un model que incorpora la massa dels tethers, l'efecte més notori és la variació de la velocitat de rotació local del clúster entre el pas per l'apogeu i perigeu de l'òrbita de referència. Aquest efecte té conseqüències sobre l'elongació dels tethers, la forma de les oscil·lacions, i la separació entre tethers adjacents (especialment en el cas de formacions obertes). Quan es té en compte l'efecte de la pertorbació J2, en el cas de formacions orientades envers la Terra, la trajectòria de l'objecte central presenta oscil·lacions d'amplitud creixent en la direcció perpendicular al pla orbital. La segona part de l'estudi es centra en la definició d'una llei de control per regular la posició i orientació d'un clúster amb geometria de doble piràmide orientat envers la Terra. El problema de control es descompon en dos nivells. Un primer nivell per un control primari de posició i orientació del cluster, i un segon nivell per un control de posició precís per a cada agent del cluster. Per tal d'aconseguir el primer nivell de control, i aprofitant les similituds entre un cluster connectat per tethers i un sòlid rígid, s'utilitza la tècnica d'estructura virtual. La formulació utilitzada en aquest estudi amplia el model general d'estructura virtual utilitzat per formacions estàtiques, tot afegint les equacions necessàries per a una formació que gira sobre un eix propi. El controlador esta dissenyat per permetre el canvi de la velocitat de gir i el moment d'inèrcia de la formació a través d'un sistema que permet modificar la longitud dels tethers. D'aquesta forma es permet controlar l'angle d'inclinació de Likins-Pringle del clúster. Per a la definició del control de precisió, l'estudi avalua inicialment diferents alternatives basades en l'estat de l'art de sistemes de control aplicats a robòtica. Després de descartar altres alternatives, es proposen dues lleis de control : Una primera basada en un controlador PID, i una basada en control lliscant. Per l'opció de control lliscant es presenta una demostració d'estabilitat exponencial semiglobal. Els resultats de simulacions confirmen la viabilitat de la solució de control que permet posicionament amb precisió submil·limetrica

State-of-the-art biophysical techniques featuring high temporal and spatial resolution have allowed for the first time the direct visualization of individual transmembrane proteins on the cell membrane. These techniques have revealed that a large amount of molecular components of the cell membrane do not organize in a random manner but they rather grouped together forming so-called clusters at the nanoscale. Moreover, the lateral behavior of these clusters shows a great dependence on the compartmentalization of the cell membrane by, e.g., the actin cytoskeleton at multiple temporal and spatial scales. Since these lateral and temporal organizations have been shown to be crucial for the regulation of the biological activity by these transmembrane proteins, the understanding of the spatiotemporal behavior of membrane receptors, and of proteins in general, is a necessary step towards understanding the biology of the cell. Protein nanoclustering and membrane compartmentalization have been shown to play a crucial role on leukocytes, particularly on the surface of antigen presenting cells. Hence, the direct visualization of membrane proteins on the cell membrane of antigen presenting proteins represents a crucial step in understanding how an immune response can be controlled by leukocytes at the molecular level. In Chapter 1, the immune system, the membrane receptor DC-SIGN and the antigen presenting protein CD1d are briefly introduced. Moreover, recent advances in superresolution microscopy and single particle tracking techniques which allow the study of membrane proteins at the nanoscale are discussed. Finally, an updated review of protein nanoclustering on the cell membrane shows examples of the importance of protein nanoclustering in regulating biological function in the immune system. Chapter 2 presents the quantitative methodology for analyzing STED nanoscopy images and multi-color single particle tracking data used throughout this thesis. Chapter 2 also describes the single-molecule fluorescence sensitive microscopes implemented in this thesis for multi-color single particle tracking experiments and the corresponding data analysis. At the end of Chapter 2, cartography maps combining high temporal with micron-scale spatial information on the basis of single-molecule detection are presented. The following chapters in this thesis describe the major results obtained on two important receptors of the immune system. In Chapter 3, we address the role of the neck region of DC-SIGN in fine-tuning the nanoclustering degree of DC-SIGN on the cell membrane. Moreover, Chapter 3 also links the nanoclustering capability of DC-SIGN with its virus binding capability. The meso-scale organization of DC-SIGN and its dependence on a glycan-based connectivity is addressed on Chapter 4. This glycosylation network enhances the interaction between DC-SIGN and clathrin beyond stochastic random encountering. In Chapter 5, we showed that DC-SIGN shows subdiffusive behavior and weak ergodicity breaking (wEB) that cannot be described using the continuous time random walk (CTRW) model. Instead, our data are more consistent with a model in which the plasma membrane is composed of "patches" that change in space in time. In Chapter 6, we demonstrate that the antigen presenting protein CD1d organizes in nanoclusters on the cell membrane of antigen presenting cells whose size and density are tightly controlled by the actin cytoskeleton. Moreover, we also showed that this cytoskeletal control of the CD1d nanoclustering predominantly occurs on the pool of CD1d that has undergone lysosomal recycling, including under inflammatory conditions. Finally, in Chapter 7 we summarize the main results of this thesis and highlight future experiments that will expand the knowledge obtained so far regarding the role of plasma membrane organization and biological regulation.
Gracias a su alta resolución temporal y espacial, las técnicas biofísicas de última generación han permitido la observación directa de proteínas de transmembrana de forma individual en la membrana celular. Estas técnicas han mostrado que la organización de una gran parte de las proteínas de transmembrana no es aleatoria sino que éstas están agrupadas en la membrana celular formando nano-agregados, o "clusters". En el caso concreto del sistema inmune, se ha demostrado que el agrupamiento de proteínas y los compartimentos de la membrana celular juegan un papel determinante en las células presentadoras de antígenos a la hora de controlar la iniciación de una respuesta inmune. Por tanto, la visualización directa de proteínas de membrana en células presentadoras de antígenos a la escala nanométrica representa un paso crucial en el entendimiento del sistema inmune y en un futuro desarrollo de terapias basadas en el sistema inmune humano. En el primer capítulo de esta tesis, se presentará al lector una breve introducción del sistema inmune y una descripción general de las dos proteínas que se han estudiado extensivamente en esta tesis: el receptor reconocedor de patógenos DC-SIGN y la proteína presentadora de antígenos glicolipídicos CD1d. Se discutirán además los últimos avances en técnicas de microscopía de fluorescencia con alta resolución temporal y espacial que permiten el estudio de proteínas a la escala nanométrica. Finalmente, el primer capítulo concluye con una revisión de los últimos avances en la caracterización de la organización lateral de proteínas de membrana mostrando cómo dicha organización determina la función biológica de estas proteínas. En el capítulo 2, se presentan los distintos tipos de metodología utilizados en esta tesis para cuantificar imágenes de microscopía de super-resolución STED así como para analizar datos provenientes del seguimiento de partículas individuales usando varios colores. Al final del capítulo 2 se presenta una nueva metodología desarrollada en esta tesis que permite el estudio lateral de proteínas de membrana con una alta resolución temporal y una escala espacial de orden de micras y a la que hemos denominado mapas cartográficos. Los siguientes capítulos de esta tesis se enfocan en el estudio de dos importantes proteínas involucradas en el sistema inmune. En el capítulo 3 se describe como la parte central de la estructura del receptor captador de patógenos DC-SIGN determina su grado de nano-agrupamiento sobre la membrana celular. A su vez, este agrupamiento tiene una incidencia clave en la capacidad de DC-SIGN en unirse a partículas virales. La organización de DC-SIGN a la escala mesoscópica y la dependencia de dicha organización de una conectividad en la membrana celular basada en la glicosilación de proteínas es descrita en el capítulo 4. En el capítulo 5 descubrimos que DC-SIGN tiene un comportamiento que no solo es sub-difusivo en la membrana celular sino que también conlleva a la ruptura de ergodicidad por parte de este receptor. Esta rotura de ergodicidad no puede ser descrita por el modelo "continous time random walk" (CTRW) sino por un modelo nuevo donde la difusión de la partícula cambia constantemente en el espacio y en el tiempo. En el capítulo 6 de esta tesis describimos como la molécula CD1d forma nano-agrupamientos en la membrana celular cuyo tamaño y densidad son controlados por el citoesqueleto de actina. Además, observamos que dicho control mayoritariamente sucede cuando CD1d ha sido reciclado a través de compartimentos lisosomales, incluyendo procesos inflamatorios. Finalmente, en el capítulo 7 se discuten las conclusiones generales de esta tesis y se sugieren experimentos a futuro de manera de incrementar, en base a los resultados obtenidos en esta tesis, nuestro conocimiento de la membrana celular y el papel que la organización espacial y temporal juega en el control del sistema inmune.

El crecimiento de la potencia de procesamiento de los sistemas de computación paralelos requiere redes de interconexión de mayor nivel de complejidad y un mayor rendimiento, por lo que consumen más energía. Mayor cantidad de energía consumida conduce a muchos problemas relacionados con los costos, la infraestructura y la estabilidad del sistema de refrigeración. Los enlaces de la red contribuyen en una proporción sustancial al consumo total de energía de dichas redes. Varias propuestas se han ido acercando a una mejor administración de la energía de los enlaces. En esta tesis, aprovechamos ciertas características integradas en la tecnología actual de los enlaces para ajustar dinámicamente la velocidad de los mismos en función del tráfico. De esta manera, la red de interconexión consume menos energía cuando el tráfico es ligero. También proponemos una política de enrutamiento que tiene en cuenta la velocidad del enlace que favorece las conexiones de alta velocidad en el proceso de enrutamiento de paquetes para aumentar el rendimiento de la red cuando se despliega el mecanismo de ahorro de energía. Los resultados de la evaluación muestran que las redes que usan el mecanismo de ahorro de energía aquí propuesto, reducen el consumo de energía a expensas de un aumento en el promedio de latencia de paquetes. Sin embargo, con la propuesta de política de enrutamiento que tiene en cuenta la velocidad del enlace, nuestro mecanismo incurre en un menor aumento en el promedio de la latencia de paquetes mientras se logra un ahorro de energía similar, en comparación con otros enfoques convencionales de la literatura.
The growing processing power of parallel computing systems requires interconnection networks a higher level of complexity and higher performance, thus they consume more energy. A larger amount of energy consumed leads to many problems related to cost, cooling infrastructure and system stability. Link components contribute a substantial proportion of the total energy consumption of the networks. Several proposals have been approaching a better link power management. In this thesis, we leverage built-in features of current link technology to dynamically adjust the link speed as a function of traffic. By doing this, the interconnection network consumes less energy when traffic is light. We also propose a link speed aware routing policy that favors high-speed links in the process of routing packets to boost the performance of the network when the energy saving mechanism is deployed. The evaluation results show that the networks deploying our energy saving mechanism reduce the amount of energy consumption with the expense of an increase in the average packet latency. However, with the link speed aware routing policy proposal, our mechanism incurs a less increase in the average packet latency while achieving similar energy saving, compared with other conventional approaches in literature.

Els darrers anys, els models de negoci han experimentat un impuls notable en la recerca acadèmica. Com a resposta a les demandes recents de la literatura en matèria de direcció estratègica, aquesta tesi amplia l’estudi dels models de negoci mitjançant l’anàlisi d‘una dimensió que rarament s‘estudia a la literatura: la transformació del model de negoci i les seves dinàmiques internes. Malgrat el paper destacat dels models de negoci en la recerca recent, se sap poc sobre com es transformen els models de negoci en el temps i com s’adapten a ecosistemes canviants. A través de tres assaigs, aquesta tesi explora la transformació dels models de negoci centrant-se en la dinàmica de la innovació dels models de negoci i la transformació d’aquests models amb la internacionalització. Avançant en les conclusions empíriques dels tres assaigs i les idees integradores que impulsen l’agenda de la recerca sobre els models de negoci, proposo un nou model conceptual i presento la transformació del model de negoci com un constructe multidimensional, que es basa en les eleccions estratègiques de l’empresa. Aquestes eleccions, a seu torn, es reflecteixen en les limitacions que determinen l’espai d‘oportunitat de l‘empresa focal, que s‘ha de realitzar amb l‘objectiu d‘incrementar la creació de valor de l‘empresa focal i el seu potencial de captació de valor. Aquesta tesi té com a fonaments la recerca en direcció estratègica i la teoria de l’organització, i també es basa en la teoria institucional i la internacionalització, cosa que contribueix als debats actuals en els camps de l’estratègia, la innovació i la direcció internacional. Alhora que se centra en el desenvolupament de la teoria i adopta un enfocament semiconstructivista, la tesi utilitza diversos mètodes de recerca, com l’anàlisi teòrica, la grounded theory, i recorre a diversos casos per desenvolupar i demostrar diverses proposicions, i també el concepte de transformació dels models de negoci en la literatura. La tesi conclou proposant potencials vies per al desenvolupament d’investigacions futures.
En los últimos años, los modelos de negocio han cobrado sustancial impulso en la investigación académica. Como respuesta a las recientes peticiones de la literatura en dirección estratégica, esta tesis extiende el estudio de modelos de negocio mediante la exploración de una dimensión raramente considerada en la literatura: la transformación del modelo de negocio y sus dinámicas subyacentes. A pesar del papel destacado de los modelos de negocio en la investigación reciente, poco se sabe acerca de cómo los modelos de negocio se transforman en el tiempo y cómo se adaptan a ecosistemas cambiantes. A través de tres ensayos, esta tesis explora la transformación de modelos de negocio enfocándose en la dinámica de la innovación de los modelos de negocio y la transformación de los modelos de negocio en la internacionalización. Avanzando en los hallazgos empíricos de los tres ensayos y las ideas integradoras que impulsan la agenda de investigación modelo de negocio, propongo un nuevo modelo conceptual y presento la transformación del modelo de negocio como un constructo multidimensional, que reside en las elecciones estratégicas de la empresa. Estos, a su vez, se reflejan por las restricciones que determinan espacio de oportunidades de la empresa focal, que ha de ser realizado con el objetivo de aumentar la creación y captura de valor potencial de la misma. Esta tesis tiene como pilares la investigación en dirección estratégica así como la teoría de organización, basándose en la teoría institucional y la internacionalización, lo que contribuye a los debates actuales dentro de los campos de estrategia, innovación y dirección internacional. Mientras se mantiene el foco en el desarrollo de la teoría, en un enfoque semi-constructivista, la tesis emplea diversos métodos de investigación, como el análisis teórico, grounded theory, y varios estudios de caso para desarrollar y testear diversas proposiciones, así como establecer el concepto de transformación de modelos de negocio en literatura. La tesis concluye con potenciales vías para el desarrollo de futuras investigaciones.
In recent years, business models have gained substantial momentum in academic research. As a response to recent calls in strategic management literature for novel research, this dissertation extends the study of business models by exploring a dimension rarely considered in literature: business model transformation and its underlying dynamics. Despite the prominent role of business models in recent research, little is known about how business models transform over time and adapt to evolving ecosystems. In three essays, I address this gap by exploring the notion of business model transformation enabled through its dynamics of business model innovation and business model growth through internationalization. Advancing on the empirical findings from the three essays and the integrative insights that move the business model research agenda forward, I propose a conceptual model and introduce business model transformation as a multi-dimensional construct, which resides in the focal firm’s strategic choices. These choices, in turn, are reflected by the constraints that determine the focal firm’s opportunity space, which is to be realized with the objective to increase the focal firm’s value creation and value capture potential. I theoretically build on strategic management research as well as on organization, institutional and internationalization theory as the three pillars of this thesis, contributing to the current debates within the strategy, innovation and international management fields. While maintaining the focus on theory development, in a semi-constructivist approach, I employ diverse research methods, such as theoretical analysis, grounded theory, and multiple case studies to develop and test various propositions, as well as establish the concept of business model transformation in literature. The thesis concludes with fruitful avenues for future research.

The limited dynamic range of digital images can be extended by composing different exposures of the same scene to produce HDR images. This thesis is composed of an overview of the state of the art techniques and three methods to tackle the image alignment and deghosting problems in the HDR imaging domain. The first method detects the areas affected by motion, registers the dynamic objects over a reference image, and combines low-dynamic range values to recover HDR values in the whole image. The second approach builds multiscopic HDR images from LDR multi-exposure images. It is based on a patch match algorithm which was adapted and improved to take advantage of epipolar geometry constraints of stereo images. The last method proposes to replace under/over exposed pixels in the reference image by using valid HDR values from other images in the multi-exposure LDR image sequence.
El limitado rango dinámico de las imágenes digitales puede ampliarse mezclando varias imágenes adquiridas con diferentes valores de exposición. Esta tesis incluye un detallado resumen del estado del arte y tres métodos diferentes para alinear las imágenes y corregir el efecto ’ghosting’ en imágenes HDR. El primer método está centrado en detectar las áreas afectadas por el movimiento y registrar los objetos dinámicos sobre una imagen de referencia de modo que se logre recuperar información a lo largo de toda la imagen. Nuestra segunda propuesta es un método para obtener imágenes HDR multiscópicas a partir de diferentes exposiciones LDR. Está basado en un algoritmo de ’patch match’ que ha sido adaptado para aprovechar las ventajas de las restricciones de la geometría epipolar de imágenes estéreo. Por último proponemos reemplazar los píxeles saturados en la imagen de referencia usando valores correctos de otras imágenes de la secuencia.

Els models matemàtics quantitatius són simplificacions de la realitat i per tant el comportament obtingut per simulació d'aquests models difereix dels reals. L'ús de models quantitatius complexes no és una solució perquè en la majoria dels casos hi ha alguna incertesa en el sistema real que no pot ser representada amb aquests models. Una forma de representar aquesta incertesa és mitjançant models qualitatius o semiqualitatius. Un model d'aquest tipus de fet representa un conjunt de models. La simulació del comportament de models quantitatius genera una trajectòria en el temps per a cada variable de sortida. Aquest no pot ser el resultat de la simulació d'un conjunt de models. Una forma de representar el comportament en aquest cas és mitjançant envolupants. L'envolupant exacta és complete, és a dir, inclou tots els possibles comportaments del model, i
correcta, és a dir, tots els punts dins de l'envolupant pertanyen a la sortida de, com a mínim, una instància del model. La generació d'una envolupant així normalment és una tasca molt dura que es pot abordar, per exemple, mitjançant algorismes d'optimització global o comprovació de consistència. Per aquesta raó, en molts casos s'obtenen aproximacions a l'envolupant exacta. Una aproximació completa però no correcta a l'envolupant exacta és una envolupant sobredimensionada, mentre que una envolupant correcta però no completa és subdimensionada. Aquestes propietats s'han estudiat per diferents simuladors per a sistemes incerts.

Water delivery systems usually work in continuous way based on some prescribed flow conditions and user's needs . However there are situations in which abrupt changes in the operating conditions must be carried on. Typical examples are the alternative closing of a canal system during the non-demand periods to save water for other purposes as energy production, and the closure of a canal due the danger of water pollution in the supplier river. Closure of a canal means setting zero flow conditions by closing the gates along the canal, while maintaining specific water levels under the maximum allowed value. The closure operation requires a progressive and well planned set of actions to avoid overtopping and cracking in the canal lining, which can involve both economic and environmental issues. The opening operation involves restarting the canal to its normal operating condition from zero flow condition. This thesis is devoted to develop a supervised decentralized predictive control strategy for solving the problems related to the closure and opening operations of canal systems. The evaluation is fulfilled by means of numerical simulation on two cases of study in a variety of operating scenarios. The strategy is also experimentally validated through real-time implementation in a laboratory canal available in the Technical University of Catalonia (canal PAC-UPC). The control strategy has been developed in a two-level architecture: (i) a set of individual decentralized downstream water level predictive controllers, which are formulated via an optimal control problem under dynamic constraints and implemented by upstream local gates; and (ii) a supervising level to achieve the compromise of fast execution with smooth gate trajectories and water level regulation, even in the presence of disturbances. The simulation and real-time implementation scenarios have demonstrated that the proposed strategy is convenient for closure and opening of irrigation canals. Problems presented when the canal closure operations are not managed properly, such as overtopping, have been avoided in all the scenarios.
Los canales de riego usualmente trabajan en forma continua bajo unas condiciones de flujo prescritas y acorde a las necesidades de agua de los usuarios. Sin embargo hay situaciones en las cuales se presentan cambios abruptos en las condiciones de operación. Un típico ejemplo es la alternativa de cierre durante los periodos de inactividad de los regantes. Dicho cierre tiene por objeto el ahorro de agua para otros propósitos, como puede ser la producción de energía. Otro ejemplo es la necesidad de cierre de un canal ante la presencia de un vertido de contaminantes aguas arriba en la fuente abastecedora de agua. El cierre de un canal requiere cerrar de forma progresiva y suave las compuertas de todo el canal, evitando desbordamientos y manteniendo unos calados de seguridad en los diferentes tramos del canal hasta llegar a una condición de caudal cero. La violación de los calados máximos puede producir inundaciones y pérdidas de agua innecesarias. La reducción de los niveles de agua por debajo de los calados mínimos permitidos puede causar daños en la estructura física del canal. Esta tesis se centra en el desarrollo de una estrategia de control predictivo descentralizado supervisado para gestionar de forma automática las operaciones de cierre y apertura de canales de riego. La evaluación de la estrategia se lleva a cabo mediante la simulación numérica en dos casos de estudio. Dicha evaluación se completa mediante experimentos en tiempo real realizados en un canal de laboratorio existente en la Universitat Politècnica de Catalunya (canal PAC-UPC). La estrategia de control se ha desarrollado con una arquitectura de dos niveles: (i) un conjunto de controladores individuales descentralizados para el control de niveles de aguas abajo, cuya formulación se plantea como un problema de control óptimo con restricciones dinámicas; y (ii) un nivel de supervisión encargado de alcanzar el compromiso de una ejecución rápida del proceso de cierre (o apertura) con movimientos suaves de compuerta y de una regulación de los niveles de agua dentro de los márgenes de consigna, incluso en presencia de perturbaciones. Tanto los escenarios de simulación como los de implementación en tiempo real, han demostrado que la estrategia propuesta en esta tesis es satisfactoria para operaciones de cierre y apertura de canales de riego. En efecto, la estrategia de control ha sido capaz de evitar problemas, como por ejemplo el desbordamiento, que se presentan cuando la operación de cierre de un canal no se realiza adecuadamente.

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FAPEAM - Fundação de Amparo à Pesquisa do Estado do Amazonas
Many machine learning applications have to deal with classification problems in dynamic environments. This type of environment may be affected by concept drift, which may reduce the accuracy of classification systems significantly. In this context, methods using ensemble of classifiers are interesting due to the fact that ensembles of classifiers allow the design of strategies for drift detection and reaction more accurate and robust to changes. A classification system based on ensemble of classifiers may be divided into three main phases: classifier generation; single classifier or subset of classifier selection; and classifier fusion. The selection phase may be performed as a dynamic process. In this case, for each unknown sample, the individual classifier or classifier ensemble most likely to be correct is chosen to assign a label to the sample. In this work, it is proposed a method for concept drift detection and reaction based on dynamic classifier ensemble selection. The proposed method choses the expert classifier ensemble according to diversity and accuracy values. Focusing on evaluating the impact of dynamic ensemble selection guided by diversity and accuracy in terms of concept drift detection and reaction, four series of experiments were carried in this work using both synthetic and real datasets. In addition, since the proposed method is broken down into four phases: pool of ensemble classifiers generation; dynamic ensemble selection; drift detection; and drift reaction, different versions of the proposed method were investigated by varying the parameters of each phase. The results show that, in general, all these different versions attain very similar accuracy values. Besides, when compared to two baselines: (1) DDM - single classifier-based; and (2) Leveraging Bagging - classifier ensemble-based, our method outperforms both baselines since it achieved higher accuracy, lower detection delay and false detection rates, and it did not present missing detection. However, both baselines present lower time complexity. Therefore, this work shows that dynamic classifier ensemble selection guided by diversity and accuracy helps to improve detection precision and the general accuracy of classification systems employed in problems with concept drift.
Muitas aplicações de aprendizado de máquina estão relacionadas com problemas de classificação em ambientes dinâmicos. Mudança de conceito figura nesse tipo de ambiente e pode prejudicar muito a acurácia de sistemas de classificação. Nesse contexto, a utilização de comitês de classificadores é interessante porque possibilita a implementação de processos de detecção e de reação à mudança mais acurados e robustos. Sistemas de classificação que utilizam comitês podem possuir três grandes fases: geração; seleção; e integração de classificadores. A etapa de seleção pode ser feita de forma dinâmica, isto é, para cada instância desconhecida, o classificador ou comitê de classificadores com maior probabilidade de acerto é escolhido para atribuir uma classe à essa instância. Neste trabalho, é proposto um método para detecção e reação à mudança de conceito que utiliza seleção dinâmica de comitês de classificadores. O método proposto escolhe o comitê especialista com base nos valores de diversidade e de acurácia de cada comitê candidato. A fim de avaliar o impacto do uso de seleção dinâmica guiada por diversidade e acurácia nas tarefas de detecção e reação a mudança de conceito, foram realizadas quatro séries de experimentos com bases sintéticas e reais. Além disso, como o método proposto é dividido em quatro fases: geração da população de comitês; seleção dinâmica do comitê especialista; detecção de mudanças; e reação à mudança, diferentes versões desse método foram investigadas em função da definição de parâmetros de cada fase. Os resultados dos experimentos mostraram que, de maneira geral, as versões estudadas são bem equivalentes em termos de acurácia média final. Adicionalmente, quando comparado a dois baselines: (1) DDM - que utiliza um único classificador; e (2) Leveraging Bagging - que utiliza um comitê de classificadores, o método proposto alcançou melhores taxas de acurácia, menores taxas de atraso de detecção, não deixou de detectar as mudanças conhecidas nas bases e produziu reduzidas taxas de falsa detecção, apesar de apresentar maior complexidade computacional. Portanto, o trabalho mostra que o uso de seleção dinâmica guiada por diversidade e acurácia melhora a precisão de detecção, bem como a acurácia geral de sistemas de classificação utilizados em problemas que apresentam mudança de conceitos.

Observations provided from RPC-ICA in combination with the data from RPC-MAG and ROSINA-COPS show that many aspects of the time variability of the detected ions is correlated with the magnetic field or -- to a smaller extent -- with neutral atmosphere density. We also show that not all changes in the cometary ion data reflect the nature of the plasma dynamics, but are a consequence of the instrumental limitations. The main outcome of the article in Appendix 1 is that the cometary ions can be divided into two populations with distinct characteristics. One population we termed the convecting population, is accelerated to higher energies through the interaction with the solar wind. The other population we termed the expanding population is moving radially away from the nucleus in the terminator plane. Both populations exhibit a significant anti-sunward component.In addition we present in this thesis a case with observations day-side of the terminator plane. There we show how the expanding population has a sunward component, consistent with initial radial expansion of the ions from the nucleus which gradually turn into an anti-sunward flow which is then observed in the terminator plane.

The Oort Cloud (OC) is a roughly spherical cloud of comets surrounding the solar system, stretching from well beyond the orbit of Neptune, half way to the nearest star. This body of comets is interesting because it contains a record of the gravitational perturbations suffered by the solar system over its lifetime. Here, we investigate the effects of a particular class of perturbing objects - enormous complexes of molecular gas called giant molecular clouds (GMCs). Recent evidence has shown that the classical picture of Oort Cloud formation is inadequate to describe certain properties of the OC. To re-investigate the dynamical evolution of the Oort Cloud, we simulate the Sun's emergence from its natal molecular cloud, and its subsequent encounters with GMCs. While the role of giant molecular clouds in OC formation has been explored before, they have been implemented in a general way, not explicitly taking into account the 3D structure of the cloud. In this research, we draw on an extensive body of evidence which suggests that GMCs are not uniform, diffuse objects, but are instead organized into high density clumps, connected by a very diffuse inter-clump medium. Recent research has shown that GMCs are likely to be fractal in nature, and so we have modeled them as fractal distributions with dimension 1.6. We then perform N-body simulations of the passage of the Sun and its Oort Cloud through such a molecular cloud. We find that the fractal structure of the GMC is, in fact, an important parameter in the magnitude of the cometary energy change. The significant energy changes occur as a result of interactions with the GMC substructure, not simply as a result of its overall density distribution. We find that interactions with GMCs can be quite destructive to the OC, but can also serve to move comets from tightly bound orbits to less tightly bound orbits, thus partially replacing those lost to stripping. Simulations of the Sun's relatively slow exit from its birth GMC paint a picture of a potentially very destructive era, in which a large portion of the OC's evolution may have occured.
Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-09-21 13:05:17.527

博士
國立中央大學
天文研究所
104
I developed a systematic method to analyze the snapshot images from sky survey projects such as the Pan-STARRS 1 (PS1) and Palomar Transient Factory (PTF) on all the numbered Jupiter Family Comets (JFCs). There are three objectives for my image processing pipeline to handling the five years survey data: to find out images that contains target of interest; to identify the signature of coma activity; and to measure the level of outgassing activity. Given that cometary activities are generally triggered by the sublimation of water ice, I introduce the water ice snowline at 3 au as an indicator for the comet classification. All comets analyzed in this work are classified into four groups based on its behaviors: regular active comets with coma activities within the snowline only, abnormal active comets with coma activities detected beyond the snowline, low active comets that are always inactive and appear as point-like sources, and undetectable comets. I also use the Mercury integrator to study dynamic features of JFCs by numerical methods. Combining the observational and numerical results, a connection between active behaviors and dynamics has been established: due to the limited amount of volatiles in the cometary nuclei, dynamic age roughly reflects the appearance of cometary activity. A detail discussion is given in this thesis for possible explanations of various cometary activities.

Radio-frequency microelectromechanical systems (RF MEMS) are widely used for contact actuators and capacitive switches. These devices typically consist of a metallic membrane which is activated by a time-periodic electrostatic force and makes periodic contact with a contact pad. The increase in switch capacitance at contact causes the RF signal to be deflected and the switch thus closes. Membrane motion is damped by the surrounding gas, typically air or nitrogen. As the switch opens and closes, the flow transitions between the continuum and rarefied regimes. Furthermore, creep is a critical physical mechanism responsible for the failure in these devices, especially those operating at high RF power. Simultaneous and accurate modeling of all these different physics is required to understand the dynamical membrane response in these devices and to estimate device lifetime and to improve MEMS reliability. It is advantageous to model fluid and structural mechanics and electrostatics within a single comprehensive numerical framework to facilitate coupling between them. In this work, we develop a single unified finite volume method based numerical framework to study this multi-physics problem in RF MEMS. Our objective required us to develop structural solvers, fluid flow solvers, and electrostatic solvers using the finite volume method, and efficient mechanisms to couple these different solvers. A particular focus is the development of flow solvers which work efficiently across continuum and rarefied regimes. A number of novel contributions have been made in this process. Structural solvers based on a fully implicit finite volume method have been developed for the first time. Furthermore, strongly implicit fluid flow solvers have also been developed that are valid for both continuum and rarefied flow regimes and which show an order of magnitude speed-up over conventional algorithms on serial platforms. On parallel platforms, the solution techniques developed in this thesis are shown to be significantly more scalable than existing algorithms. The numerical methods developed are used to compute the static and dynamic response of MEMS. Our results indicate that our numerical framework can become a computationally efficient tool to model the dynamics of RF MEMS switches under electrostatic actuation and gas damping.
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