Tesis Doctorales

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Archivo Abierto Institucional de la Universidad Carlos III de Madrid: Tesis Doctorales

Esta colección contiene tesis leídas en la Universidad Carlos III, cuyos autores han autorizado su depósito en E-Archivo. A partir de 2012 se depositan todas las tesis leídas en la Universidad Carlos III de Madrid, conforme a lo dispuesto en el Real Decreto 99/2011, de 28 de enero por el que se regulan las enseñanzas oficiales de doctorado (art. 14.5), y al Reglamento de la Escuela de Doctorado de la Universidad Carlos III de Madrid, de 7 de febrero de 2013 (art. 26.5, art. 31.1 y art. 32.2).

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Role of porous microstructure on dynamic shear localization and ductile failure
(2024-01) Ambikadevi Rajasekharan Nair, Vishnu; Rodríguez-Martínez, José A.; UC3M. Departamento de Mecánica de Medios Continuos y Teoría de Estructuras; European Commission; Rordríguez-Martínez, José A.
This doctoral thesis aims to provide a comprehensive analysis of the role of porous microstructure on dynamic shear localization and ductile failure. For this purpose, a computational approach was developed that includes large-scale 3D finite element models incorporated with actual porous microstructures that are derived from different additively manufactured materials. This is the distinctive feature of the numerical simulations conducted in this study, in which a large population of voids that are statistically representative of the actual porosity in 3D-printed metals has been included. Additional microstructures varying the void volume fraction, the mean and standard deviation of the size distribution of voids were generated, enabling a systematic parametric analysis of the microstructural features. Finite element simulations of multiple shear bands formation in radially collapsing thick-walled cylinders and shear band formation in thin-tubes subjected to dynamic torsion were performed to investigate the effect of spatial and size distribution of voids on dynamic shear localization. The numerical results demonstrate that microstructural porosity promotes dynamic shear localization, determining preferential sites for the nucleation of the shear bands, accelerating their development, and tailoring their direction of propagation. Specifically, collapsing thick-walled cylinder calculations bring out that, for a given void volume fraction more shear bands are nucleated as the number of voids increases, while the shear bands are triggered earlier and develop faster as the size of the pores increases. Moreover, the numerical results for porous thin-tubes subjected to dynamic torsion quantitatively show that the size of the largest pore is a main microstructural feature controlling the specimen ductility. Furthermore, this numerical methodology was extended to perform unit-cell calculations to investigate the void growth in porous ductile materials under monotonic loading conditions by prescribing constant triaxiality and Lode parameter throughout the loading. The simulations were carried out with random spatial distributions of pores and with void clusters. The calculations with random spatial distribution of voids revealed that the interaction between neighboring pores dictates the volume evolution of individual voids, especially at higher macroscopic triaxiality. The calculations with clusters demonstrated that pores clustering promotes localization/coalescence due to increased interaction between the voids, resulting in an increased growth rate of voids in clusters with large number of pores. Moreover, the results for the evolution of the distribution of plastic strains in the unit-cell have provided some quantitative indications of the role of porous microstructure on the development of heterogeneous plastic strain fields which promote macroscopic strain softening.
No sólo los “temas de interés humano”: El compromiso literario en las novelas de Belén Gopegui
(2024-06) Zhang, Shenshen; Pérez-Rasilla Bayo, Eduardo; UC3M. Departamento de Humanidades: Filosofía, Lenguaje y Literatura; Pérez-Rasilla Bayo, Eduardo
La diplomacia pública interna como ejercicio de comunicación institucional. Análisis de situación para una estrategia en el caso español
(2024-05) Doncel Martín, Israel; Elías Pérez, Carlos José; UC3M. Departamento de Comunicación
La presente tesis doctoral realiza una investigación en torno al concepto de diplomacia pública interna, analizándolo dentro del campo de la comunicación institucional, y justificando -a través de casos de estudio, entrevistas en profundidad y revisión bibliográfica- su ejercicio desde este ámbito, algo que no siempre ocurre en la actualidad. Basándose en las fuentes señaladas aporta además dos definiciones propias de los conceptos de diplomacia pública y diplomacia pública interna. Incluye también un estudio cuantitativo que pretende ser un punto de partida en el diseño de una estrategia comunicativa de diplomacia pública interna para España. Este estudio se centra en la percepción que los españoles tienen de los posicionamientos internacionales del país que gozan de un mayor consenso entre los diferentes gobiernos de la historia de la democracia, tales como la colaboración con países aliados o la participación en organismos supranacionales como la Unión Europea o la Organización de Naciones Unidas. Además, analiza cómo los perfiles de consumo informativo de los encuestados afectan o condicionan sus respuestas. De este modo, gracias al estudio, se pueden identificar los mensajes más relevantes sobre los que esta comunicación para la diplomacia pública interna española debería realizar más esfuerzo. La investigación se ocupa también del análisis de la principal herramienta de diplomacia pública interna de España: la Red de Casas, un conjunto de instituciones dependiente del Ministerio de Asuntos Exteriores, en consocio con administraciones autonómicas, dedicadas a acercar diferentes culturas e identidades a la sociedad española. Profundiza así en su papel comunicativo, sus posibilidades como medio para lograr los objetivos marcados por el estudio anterior y su relevancia dentro de la sociedad civil española. Por último, se realiza un estudio de las posibilidades que una estrategia de comunicación institucional para la diplomacia pública interna puede ofrecer en la lucha contra las fake news y los discursos de odio. Así como un análisis sobre cómo este tipo de estrategias contribuyen a una mejora de la cohesión social y la convivencia de un país, justificándose su realización no solo desde el sector público, sino también desde las empresas –a través de su Responsabilidad Social Corporativa- y desde la propia sociedad civil, a través de sus movimientos organizativos.
Aristocracia y representación del Estado Moderno. Una historia social de la diplomacia a partir de los embajadores españoles en Francia en el reinado de Felipe IV (1621-1665)
(2024-06) Bueno Blanco, Álvaro; García Hernán, David; UC3M. Departamento de Humanidades: Historia, Geografía y Arte
Probabilistic domain decomposition algorithms for the numerical solution of large-scale elliptic boundary value problems
(2024-03) Morón Vidal, Jorge; Bernal Martínez, Francisco Manuel; UC3M. Departamento de Matemáticas; Bernal Martínez, Francisco Manuel
1.5. Organization and overview. This thesis is organized as follows. In chapter 2, I give a brief overview of the mathematical approaches and algorithms that have been used or considered during the formulation, analysis and implementation of the different approaches to PDDSparse. The chapter runs through the methods to tackle the probabilistic representation of BVPs numerically (sections 2.1). Then, it goes on to the idea of implementing substructuring techniques in PDDSparse (section 2.2) and gets deeper into the GMRES method and preconditioning techniques to solve the PDDSparse linear system (section 2.3). A brief overview of pseudospectral methods (section 2.4) is given before finally discussing some aspects of implementing the algorithms in supercomputing facilities (section 2.5). Then, the four articles of the compendium of publications are included: • In the first paper (chapter 3), a thorough formulation of PDDSparse is given for the case of a domain discretized into a mesh of square non-overlapping subdomains. The analysis of PDDSparse error motivates a three-stage algorithm to estimate such error and optimize the computational resources invested in its execution. This first approach to PDDSparse is illustrated with the results of numerical experiments conducted in Galileo100 which show the scalability and overall performance of the algorithm. • The second paper (chapter 4) revolves around the G matrix characterization. It contains a proof of the invertibility of G and a bound on its condition number that relates the algebraic properties of PDDSparse linear system with quantities derived from its stochastic formulation. The analysis carried out in this paper motivates the formulation of a preconditioner to improve the convergence of Krylov subspace methods. All this material is supported by a set of numerical experiments conducted in LUMI-C. • In the third paper (chapter 5), PDDSparse is used as the linear solver for two iterative schemes aimed at solving elliptic BVPs with positive reaction coefficients and semilinear BVPs, which are problems whose probabilistic representations can not be obtained via the Feynman-Kac formula. Those iterative algorithms are presented in this work alongside some proof of concept results attained in the supercomputer Marconi100. • In the last article of the compendium (chapter 6), PDDSparse is reformulated to solve a BVP by discretizing the domain with a mesh of overlapping circles instead of non-overlapping squares. This new approach avoids the Monte Carlo computations for many linear system coefficients. In this work, the parallel performance of the RAS preconditioner on solving the PDDSparse linear system with GMRES is also tested. Numerical results carried out in the supercomputer Fugaku are reported, supporting the validity of this approach to PDDSparse.
Multi-scale experimental characterisation and modelling of the thermo-electro-mechanical behaviour of 3D printed conductive thermoplastics
(2024-05) Crespo Miguel, Javier; Arias Hernández, Ángel; García González, Daniel; Martínez Tarifa, Juan Manuel; UC3M. Departamento de Mecánica de Medios Continuos y Teoría de Estructuras; Arias Hernández, Ángel
The conceptualisation of structural components in the current industry is experiencing an unprecedented change of paradigm. New materials are emerging to provide other functionalities while preserving certain structural functions. An exciting example is the field of conductive polymer composites (CPCs), that is providing applications where electrical current flows through mechanical components. The conductive properties of these materials derive from the interaction at the microscale of the conductive particles embedded in the polymeric matrix. The formation of paths by the conductive fillers allows the flow of a sufficiently high current, making these materials ideal candidates for conductive components. Nonetheless, the current flow is accompanied by an intrinsic heating due to the increase in kinetic energy derived from the electron movement, known as Joule heating. This thermo-electrical interplay introduces another important consideration, i.e., the thermo-mechanical response, specially with polymeric matrices that highly depend on temperature. Likewise, the mechanical response impacts the electrical properties via deformation-induced modulation of conductive paths. Hence, the mechanical, thermal and electrical responses are highly interlinked, requiring a multi-physical analysis for a correct implementation of CPCs in conductive components. Besides these complexities, additive manufacturing technologies have been employed to fabricate conductive components with intricate geometries. In this manner, the geometry limitations associated to traditional manufacturing techniques can be overcome. Yet, mesostructural defects originated during printing affect the material response at the functional level. In the case of pieces manufactured via Fused Filament Fabrication (FFF), the mesostructural porosity caused by the imperfect bonding between adjacent filaments leads to an orthotropic response at the macroscale. Given the nature of these materials, a comprehensive characterisation cannot be tackled only from a macroscopic or functional point of view. In this regard, the problem should be addressed following different approaches, attending to the different scales (i.e., micro, meso and macroscale) as well as to the different physical interplays (i.e., thermal, electrical and mechanical responses). This thesis aims to evaluate and determine the thermo-electro-mechanical interplays that appear in thermoplastic-based CPCs at the micro scale, analysing their modulation during FFF printing and the performance impact at the functional level. To reduce the lack of knowledge regarding the thermoelectro-mechanical behaviour of FFF CPCs, new numerical and experimental approaches have been developed. These methods account in both cases for the different scales and physics involved in the problem. From the experimental point of view, an extensive and comprehensive campaign has been performed isolating the interplays by pairs of physics at two scales. This multi-scale and multi-physical experimental campaign evidenced how the nature of the thermoplastic matrix, from both mechanical and thermal perspectives, alters the conductive response. This behaviour is also affected by the addition of conductive filler to the matrix, that modifies the thermal and mechanical behaviour of the composite, even in the absence of electrical current. From a numerical perspective, Finite Element Method (FEM) based frameworks have been conceptualised at the three scales of the problem. The microscopic framework was based on homogenisation approaches, accounting for the relations between conductive particles, olymeric matrix and microvoids present in 3D printing conductive filaments. At the mesoscale, the geometrical and material features derived from the printing process are studied. Finally, upscaling to a functional level, an orthotropic thermo-electro-mechanical model has been conceptualised accounting for the variation in properties due to printing orientation. Gathering all this development and comprehension involving the thermo-electro-mechanical response of 3D printing conductive thermoplastics, this thesis can contribute to both academic and industrial fields. The experimental methodologies presented allow for manufacturers to evaluate their products in a multi-functional fashion. Likewise, the proposed numerical frameworks can help to optimise the product design at different stages. First, the design of conductive filaments modifying the phase constituent ratios or properties is possible, controlling is such a manner the feedstock material. Then, the macroscopic response of a print can be obtained in terms of the desired printing parameters that affect on the mesostructure. Finally, the component geometry can be optimised accounting for the macroscopic boundary conditions of specific problems.
Preparación por hilado por soplado y caracterización de materiales nanocompuestos de matríz bi-componente con potenciales aplicaciones médicas
(2024-03) Lorente Fernández, Miguel Ángel; González Benito, Francisco Javier; UC3M. Departamento de Ciencia e Ingeniería de Materiales e Ingeniería Química; González Benito, Francisco Javier
A lo largo de este trabajo se aborda la importancia de los biomateriales en la medicina moderna, destacando la necesidad de evolucionar en el desarrollo de nuevos materiales para aplicaciones biomédicas, principalmente, con el objetivo de lograr biomateriales inteligentes como los BioMEMs. En ese sentido, los nuevos materiales no solo tienen que presentar una buena biocompatibilidad, sino que, además, deben permitir el control y monitorización de la actividad celular en respuesta a estímulos específicos, como temperatura, pH, luz, etc. Estos avances están estrechamente vinculados a la evolución de la nanotecnología, que permite la creación de nuevos materiales y/o sistemas con funciones cada vez más complejas. En particular, esta tesis doctoral está enfocada al desarrollo de nuevos biomateriales constituidos por fibras poliméricas sub-micrométricas, enfocados a aplicaciones en biomedicina como sistemas de transporte y liberación controlada de fármacos o agentes activos. Inicialmente se va a realizar una evolución histórica de los biomateriales desde la antigüedad en la que se mencionan los tipos de materiales empleados en cada etapa, entre los que se encuentran materiales naturales, como colágeno, elastina y quitina, y materiales sintéticos, como polímeros, cerámicas y aleaciones metálicas. En la actualidad, gracias a los avances en nanotecnología, se están explorando biomateriales compuestos por nanopartículas multifuncionales y nanoestructuras, para su aplicación en diversas áreas, como: la ingeniería de tejidos, para el desarrollo de scaffolds, que son estructuras 3D que imitan el tejido biológico y que favorecen la regeneración de áreas dañadas; y la farmacología, para la fabricación de nuevos sistemas de transporte y liberación de fármacos u otros agentes activos. Seguidamente, se van a mencionar distintos métodos de producción de fibras poliméricas detallando el propio proceso de producción de cada método y comentado las ventajas y desventajas de cada uno de ellos. Además, se comparan las características de los materiales desarrollados mediante cada técnica de procesamiento, que a su vez van a determinar las posibles aplicaciones de los materiales finales. A pesar de las distintas posibilidades existentes, en esta tesis se ha centrado la atención en la técnica de hilado por soplado o solution blow spinning (SBS), debido a su simplicidad en cuanto a condiciones de procesamiento, al igual que porque permite la fabricación de fibras con un tamaño sub-micrométrico. Adicionalmente, se van a exponer las características y propiedades generales de los polímeros seleccionados para producir las materiales: el poli(óxido) de etileno (PEO) y la poli-ɛ-caprolactona (PCL). Entre las características destacables, mencionar que, además de ser biocompatibles, ambos polímeros son biodegradables, es decir, pueden ser eliminados de forma natural del cuerpo sin necesidad de tener que ser retirados o extirpados. El hecho de que los polímeros seleccionados presenten estas características hace posible su aplicación en el campo de la biomedicina, particularmente, como estructuras para la regeneración de tejidos (scaffolds) y para el desarrollo de sistemas de transporte y liberación controlada de fármacos y/o agentes activos. Una vez seleccionados tanto los polímeros como la propia técnica de procesado, se van a llevar a cabo diferentes estudios. En un primer estudio, se van a determinar los valores óptimos de los distintos parámetros de procesamiento de la técnica de SBS para poder fabricar materiales fibrilares compuestos por PEO. Una vez fabricados, los materiales obtenidos se van a caracterizar en detalle, estructural y morfológicamente, al igual que se van a analizar sus propiedades térmicas y mecánicas. Finalmente, también va a estudiar el comportamiento de estos materiales en relación a su posible aplicación en sistemas de liberación de fármacos; se analizará el proceso de disolución de los materiales fabricados en presencia de agua, proceso que puede asociarse a la degradación del material. En un segundo estudio, se va a realizar una comparativa entre distintos conjuntos de materiales fabricados mediante SBS formados por PEO, PCL y una mezcla de ambos polímeros. Además, dentro de cada conjunto de materiales se fabricarán muestras aplicando diferentes velocidades de rotación del colector con el fin de forzar la orientación de las fibras dentro de los materiales. El objetivo de este estudio está enfocado en analizar las posibles variaciones, principalmente morfológicas, que puedan aparecer entre los distintos materiales. Estas diferencias en la morfología van a condicionar las propiedades mecánicas de los materiales, al igual que van a influir en el proceso de disolución de los mismos. Finalmente, se va a llevar a cabo la fabricación por medio de SBS de materiales fibrilares constituidos por fibras coaxiales, con un núcleo de PCL y una corteza de PEO. Para lograr producir este tipo de fibras, es necesario cambiar la configuración del equipo de SBS, particularmente, la boquilla empleada; además de optimizar nuevamente los valores de los parámetros asociados al procesado. Una vez ajustados los parámetros, se producirán distintos materiales que se recogerán a diferentes velocidades de rotación del colector, con el fin de conseguir una orientación preferencial de las fibras constituyentes. Los materiales resultantes se van a caracterizar, tanto estructural como morfológicamente, para estudiar posibles cambios en la estructura de los polímeros, al igual que posibles variaciones en la morfología. Además, se van a estudiar las propiedades térmicas y mecánicas de los materiales, con el fin de analizar si existe algún tipo de influencia o dependencia de la estructura y/o morfología.
PLA-PCL textile reinforced composites for connective tissues applications
(2024-01) Pereira Lobato Costa, Carolina; Campos Gómez, Mónica; González, Carlos Daniel; Llorca, Javier; UC3M. Departamento de Ciencia e Ingeniería de Materiales e Ingeniería Química; European Commission; Campos Gómez, Mónica
Tissue engineering presents a promising frontier in addressing injuries and degenerative conditions within the human body. This doctoral thesis focuses on developing biodegradable textile polymer composite materials, specifically woven from commingling yarns, to gain insights into their long-term performance for connective tissue engineering applications. This interdisciplinary project aims to advance the creation of robust materials for connective tissues, utilizing hybrid PLA/PCL and PLA/PLA commingled yarns to manufacture woven materials and composites. The unique combination of different grades of PLA and PCL characteristics in hybrid yarns enables the production of fabrics and composites with high strength and ductility. The mechanical, thermal, and biological performance of these materials is analyzed in the thesis, exploring the advantages of commingled hybrid yarns. Different degradation rates of PLA and PCL allow for tailoring this property. Materials undergo degradation in phosphate-buffered saline solution for up to 160 days at 37◦C and accelerated degradation at 50◦C. Observations reveal different degradation patterns of the materials. The PLAPCL woven textile shows minimal changes in thermal and mechanical properties after 80 days at 37◦C, with slight degradation observed after 160 days, which is attributed to chain scission in PLA fibres. This trend is also observed in the PLA-PCL composite materials. Conversely, PLA-PLA weaves experience a notable decrease in elastic modulus after 40 days. Upon immersion at 50°C, the PLA-PCL weave undergoes a rapid strength reduction after 40 days, primarily due to PLA hydrolysis, and significant degradation after 160 days, attributed to PCL chain scission. The PLA-PLA composite experiences the fastest deterioration, rendering it impossible to test samples after 40 days of degradation. The study concludes that all materials exhibit potential for connective tissue implants, assuming a six-month average regeneration time. Despite indirect tests did not ensured optimal biocompatibility, direct tests indicated a good cell/material interaction, with the PLA-PLA composite showcasing superior performance. These findings underscore the potential of hybrid commingled yarns in manufacturing textile scaffolds and composites with tailored mechanical properties and good ductility for connective tissue engineering applications.
Generación de Microondas mediante Técnicas basadas en Fotónica Integrada para Cargas de Pago Satelitales Flexibles
(2024-03) Zarzuelo García, Alberto; Carpintero del Barrio, Guillermo; Martín Jiménez, Fernando; Delgado Mendinueta, José Manuel; UC3M. Departamento de Tecnología Electrónica; Carpintero del Barrio, Guillermo
ESta Tesis doctoral realiza un estudio entre las distintas técnicas de generación de frecuencia en rango de microondas y milimétricas basadas en técnicas fotónicas, para encontrar la que más se adecue al campo de las Comunicaciones Satélite. Más específicamente, para cargas de pago útiles de alto rendimiento. La Tesis focaliza principalmente en sistemas que sean capaces de ser integrados en chip como parámetro clave. Se presentarán algunas de las estructuras basadas en láseres de semiconductor integrados más novedosas de la última década, con las que se pretende la generación de radiofrecuencia en las bandas Ka(25 GHz), Q(32 GHz) y V(50 GHz), como bandas de interés. Estás estructuras de láseres tienen como punto fuerte la capacidad de sintonización. Pueden cubrir todo el rango de microondas y milimétricas, manteniendo un tamaño, peso y consumo reducidos. Este factor supone una gran ventaja con respecto a los sistemas de radiofrecuencia convencionales. El mayor inconveniente es la estabilidad de la señal generada. La tesis propone un estudio de tres técnicas de generación basadas en láseres monomodo, láseres pulsados y láseres de cavidad extendida. Los láseres monomodo se han planteado desde el punto de vista de la utilización de distintas plataformas de integración, como el fosfuro de indio monolítico y el fosfuro de indio con polímero híbrido. Como figuras de mérito, utilizando láseres de semiconductor fabricados en fosfuro de indio monolítico se ha reportado una estabilidad de portadora eléctrica a 21 GHz de 300 MHz en 5 minutos de medida. Utilizando láseres de semiconductor en la plataforma híbrida de fosfuro de indio con polímero con una estabilidad de portadora eléctrica a 23 GHz de 120 MHz en 5 minutos de medida. Se ha planteado el uso de láseres pulsados para aumentar la estabilidad de la señal generada. Se ha utilizado una estructura láser conocida como láser de mode-locking. Mediante este dispositivo se ha reportado estabilidad de señal generada a 33 GHz de 2 MHz en 5 minutos de medida. Y por último, utilizando láseres integrados de cavidad extendida fabricados en una plataforma híbrida de fosfuro de indio con nitruro de silicio se ha reportado la estabilidad de señal generada a 25 GHz menor de 30 MHz en 10 horas de medida, siendo la opción que más se ajusta de las tres estudiadas. En esta tesis, se analiza también la técnica de generación basada en modulación externa como alternativa a la generación de frecuencia puramente con láseres. Se ha analizado desde el punto de vista integrado donde se ha demostrado la generación de señal desde DC hasta 16 GHz en un chip fabricado en la plataforma integrada de fosfuro de indio. Para compensar las limitaciones en frecuencia de la plataforma de integración se ha planteado la implementación utilizando componentes discretos donde se ha demostrado la generación de señal desde DC hasta 100 GHz utilizando esta técnica. Finalmente, se presenta el proyecto THORMUX. Proyecto financiado por la Agencia Espacial Europea (ESA) que fue concebido a raíz de los resultados obtenidos durante el desarrollo de esta tesis. Su principal objetivo es la implementación de un multiplexor/ demultiplexor fotónico capaz de trabajar en las bandas Ka, Q y V. Se presentarán algunos de los resultados preliminares obtenidos durante las primeras fases del proyecto y las líneas futuras a seguir.
Análisis de la influencia de los estilos de liderazgo directivo como impulsores de la Responsabilidad Social Corporativa
(2024-02) García Martín, Rafael; Durán Heras, Alfonso; UC3M. Departamento de Ingeniería Mecánica; Durán Heras, Alfonso
This thesis carries out a comparative analysis of the factors that affect Corporate Social Responsibility (CSR) and sustainable development in the European multinational Airbus and in the Indian company Tata Advanced Systems Ltd. (TASL), belonging to the multinational Tata Group, studying both its current state and where it should be in the future according to the vision of the participating leaders of both organizations. Two in-depth case studies have been carried out in the respective companies following the same methodology and in the same time frame, carrying out studies of the theoretical framework of the scientific literature and using structured interviews as tools complemented with a survey and statistical methods of a descriptive and non-parametric analytics. The research covers two specific areas that have not been sufficiently developed in the scientific literature, first the determination of the drivers and barriers of CSR in the aerospace and defense sector, and subsequently, within the drivers, in particular the area of managerial leadership styles, in order to identify which are, within three styles selected as representative and widely used in the industry, the transactional, the transformational and the service, the most influential and advisable for the future regarding the CSR and general benefits in both companies. This thesis sheds light on an industry lacking sufficient studies about CSR drivers and barriers, delivering results both on the current state and on the reorientation for a desirable future (as the study variables are observed and assessed according to the criteria, knowledge and experience of the participants). The findings contribute to complete the knowledge of the factors that drive and hinder CSR and the leadership styles influence on the economic, social, and environmental results of the aerospace and defense industries. Analyzing the obtained results in both firms, we conclude that the findings give qualified and limited sustenance for the at present predominant position among CSR researchers, in relation to both the superior importance of internal versus external determinants, as well as the determined by morality, e.g. the values of top management, versus those driven by economic benefits. The barriers to CSR in both companies are mainly found in structural limitations such as the lack of knowledge about CSR, the lack of time, the available economic budget and the insufficient number of specialized personnel for the development of CSR activities. The conclusions on the influence of leadership styles indicate that, although the three of them are observed and considered effective in both firms, servant and transformational styes give the best outcomes for CSR, sustainability, and the general benefits of the studied companies, with a positive contribution also from transactional leadership although on a smaller scale. In terms of the advisable future, according to the suggestions of the participants, the most appropriate style in both companies is the service style followed by the transformational, and to a lesser extent the transactional. The recommendations consider that it would be a gradual transition process where the hybrid model, with the three styles, is evolving, maintaining the three styles, but with more increasing emphasis towards the service and transformational styles. The data propose that the present situation of CSR may be characterized as contingent, transitional, and convergent. The most notable feature is convergence about the existence of a similarity in the possible future evolution of CSR and leadership models in this sector, even between companies from disparate countries, aligned in key aspects such as the increasing importance of the business values and culture and the change in the role of CSR from regulatory compliance obligations to a source of competitive advantage. This thesis is relevant because it provides conclusive data on the current situation and the advisable future path on the identified most determining factors of CSR and the influence of the studied leadership model on business results, which can be beneficial to researchers, directors, managers, executives and regulators to understand the nature of the CSR phenomenon to incentivize drivers, eliminate or mitigate barriers and create more effective leadership models to improve corporate management of CSR and the positive impacts of the organization at economic, social and environmental levels.
Periodismo de datos, transparencia y colaboración: un análisis comparativo del discurso periodístico en España, Estados Unidos y Argentina
(2024-06) Cortés del Álamo, Helena María; Luengo Cruz, María; UC3M. Departamento de Comunicación
En 2010, tres organizaciones periodísticas colaboraron con Wikileaks en una de las filtraciones internacionales de datos masivos más paradigmática de la era digital: los papeles de Afganistán. Desde entonces, el concepto de un nuevo periodismo de datos e investigación (“investigative data journalism”) se ha ido consolidando en las redacciones a nivel global. Este trabajo doctoral estudia, comparativamente, la evolución del discurso periodístico en torno al periodismo de datos y su aplicación a la investigación periodística en relación con conceptos básicos para su desarrollo, tales como la transparencia y la colaboración. El estudio se sirve, por un lado, del análisis de contenido cualitativo de publicaciones sobre los papeles de Afganistán, Panamá y Pandora, emitidos por diferentes tipos de organizaciones periodísticas –cabeceras tradicionales, nativos digitales y entidades sin ánimo de lucro– en España (El País, El Confidencial y Civio), Estados Unidos (New York Times, The Huffington Post y ProPublica) y Argentina (La Nación, Infobae y FOPEA) (N=1349). Mediante el análisis discursivo de la producción periodística sobre estos tres casos significativos del periodismo de datos e investigación, este trabajo pretende capturar la posible transformación del relato y la reflexión periodística sobre estas prácticas. La selección de casos ofrece un marco temporal que abarca desde 2010, año en el que se produjo la revelación de los diarios de guerra de Afganistán, pasando por 2016, momento de la publicación de los papeles de Panamá, hasta llegar a 2021, cuando tuvo lugar una de las últimas revelaciones masivas del periodismo de datos e investigación, los papeles de Pandora. Por otro lado, el trabajo completa la producción discursiva en torno a hitos del periodismo de datos e investigación con la observación y exploración de las opiniones de profesionales que trabajaron en equipos de datos de las redacciones mencionadas en los años en los que los casos de Afganistán, Panamá y Pandora vieron la luz, y expertos de esta disciplina en los tres países analizados. Estas opiniones resultaron de un total de 33 entrevistas en profundidad realizadas entre 2022 y 2023 para esta tesis. En síntesis, los resultados corroboran que la evolución del periodismo de investigación y datos ha pasado por una etapa de adopción en 2010, consolidación en 2016 y normalización en 2021. Para el futuro, emerge como concepto clave la cooperación, que permitirá producir reportajes de calidad con menos recursos.
Construyendo salud a través de los medios de comunicación: un análisis en prensa, radio y televisión sobre los determinantes sociales de la salud en España
(2024-06) Ugarte Iturrizaga, Aitor; Catalán Matamoros, Daniel Jesús; UC3M. Departamento de Comunicación
Esta tesis, tras proponer una novedosa definición de Comunicación y Salud, argumenta que existe una fundamentación teórica y lógica para sostener que los medios de comunicación deben ser entendidos como determinantes sociales de la salud (SDoH) y, como contribución original, aporta un modelo que incorpora los medios de comunicación entre los factores no sanitarios que tienen influencia en el bienestar y en las desigualdades en salud. En la parte empírica, se plantea como objetivo conocer qué concepción de salud predomina en la prensa, radio y televisión generalista española, asumiendo que en absoluto es indiferente que los medios de mayor audiencia adopten un framing de salud u otro. Para realizar este análisis se define que un contenido mediático puede tratar la salud desde 3 grandes encuadres: 1) concepción biomédica basada en la enfermedad y el sistema sanitario, 2) concepción preventiva basada en los estilos de vida y hábitos individuales y 3) concepción metasanitaria basada en los determinantes de la salud. Cuantitativamente, del análisis de contenidos se desprende que los medios de comunicación generalistas españoles continúan tratando la salud tras la pandemia desde una concepción mayoritariamente biomédica: las informaciones que en 2023 plantean esta perspectiva sanitaria (57%) triplican a las que representan aspectos metasanitarios relacionados con los determinantes de la salud (17%) y cuadruplican a las que se refieren a los estilos de vida preventivos (14%). La comparación de los resultados respecto a la etapa prepandémica muestra que los medios no han variado la concepción desde la que abordan la salud. Cualitativamente, se constata que los periodistas especializados en salud de estos medios son conscientes de la menor presencia de los determinantes de la salud en sus publicaciones, pero no así de la cada vez menor aparición de informaciones sobre estilos de vida. Dado el gran predominio del encuadre biomédico en las informaciones, se concluye que los medios de comunicación generalistas en España siguen propagando entre sus audiencias una concepción muy mayoritariamente sanitaria de salud, lo cual significa un gran condicionamiento para que 1) se perpetúe socialmente la errónea identificación de la sanidad y la salud como sinónimos y 2) se dificulte la expansión de otros encuadres mediáticos, más enfocados en actitudes preventivas y en la influencia de los factores sociales, económicos, políticos y ambientales sobre el hecho de que una población esté sana o enferma.
Development of meshfree RBF modeling method applied to helical piles
(2024-03) Simonenko, Stanislav; UC3M. Departamento de Mecánica de Medios Continuos y Teoría de Estructuras
Screw piles (also known as helical piling) are a common foundation technique that consists of screwing metal tubes into the ground with one or more welded round helices. These elements are increasingly employed in the industry due to their environmental neutrality and low cost compared to other foundation techniques. Helical piles have many advantages compared to other foundation types, including cost-effectiveness, removability and reusability, less noise and vibration during installation, and ease of installation. However, their study requires high experimental costs. This doctoral thesis focuses on the development of a mathematical tool that allows the calculation of piles according to the characteristics of the soil, the subjected loads, the number of helices, and their arrangement. This tool must be viable and focused on an industrial environment, i.e., easy to use. For its development, the Radial Basic Functions (RBF) method without mesh has been used, which allows to develop the calculation in less time than other approaches, such as the Finite Element Method. The research is carried out using an experimental and numerical methodology. First, a software based on RBF is developed and validated with simple cases of beams subjected to simple loads. Then, the feasibility of the developed software in heat transfer, elastodynamic, and articulated structures applications is studied. Finally, an experimental and numerical study is carried out under real conditions of heicoidal piles carried out in sandy soil in the city of Queven (Brittany, France). Experimental tests have been carried out with helical piles with different number of helices and distance between them, subjected to compression loads and lateral loads. The developed software correctly predicted the mechanical behavior of the pile driven into the ground. Once validated, the numerical tool is used to optimize the piles in Queven soil conditions, concluding that a pile with 3 helices is sufficient to comply with current European regulations, achieving a satisfactory balance between maximum load capacity and reduced production costs.
Energy-efficient digital and hybrid precoding algorithms for interference-limited cellular networks
(2024-01-23) Urquiza Villalonga, David Alejandro; Fernández-Getino García, María Julia; UC3M. Departamento de Teoría de la Señal y Comunicaciones; Fernández-Getino García, María Julia
The fifth-generation (5G) of cellular communications demands high values of data rates, energy efficiency (EE), reliability, and multi-connectivity. In this context, ultra-dense networks (UDNs) are envisioned as a promising solution to meet the requirements of 5G and beyond 5G (B5G) communications. UDNs are characterized by the deployment of a large number of small-cells (SCs) in the coverage area of the traditional macrocell. Each SC is composed of a low-power small base station (SBS) that provides short-range communication to the user equipment (UE). Network densification increases the spectral efficiency (SE), EE, spectrum allocation, and coverage. However, their performance is limited by the increase of inter-user interference caused by near SBSs that share the same time and frequency resources. Several emerging technologies have been proposed to enable the development of UDNs. The use of multiple-input multiple-output (MIMO) systems combined with precoding techniques has been proposed to increase the SE and EE. Interference alignment (IA) arises as a precoding strategy to manage interference while increasing the achievable degrees of freedom (DoF). However, the IA algorithms available in the literature have several limitations. In this thesis, novel digital and hybrid IA algorithms have been proposed to solve the main open problems of the existing solutions and hence to further improve the performance of UDNs. First, a two-tier network deployment is studied. Based on the cognitive radio (CR) paradigm, it is assumed that the SBS applies spectrum sensing techniques to detect spectrum holes in the frequency bands of the macrocell. The unoccupied bands are used by the SBS to transmit information to its corresponding UE. The more challenging aspect of the proposed model is the assumption that the SBS is equipped with an energy harvesting (EH) device that collects energy from the environment. Unlike previous strategies that are based on a constant sensing power value, novel power allocation policies are proposed in this thesis to maximize detection performance under energy constraints. Assuming that energy consumption only depends on the test statistic to detect the presence of signals, a closed-form expression is derived to relate energy consumption with the number of processed samples and the technology-dependent parameters of the processing unit. Since the obtained closed-form equation is concave with respect to the processing power, dynamic power allocation policies are proposed to maximize the probability of detection in offline and online scenarios based on convex optimization theory, dynamic programming (DP), and heuristic solutions with lower complexity (Constant Power and Greedy policies). The performance of proposed policies is validated by simulations for common detection techniques such as matched filter (MF), quadrature matched filter (QMF), and energy detector (ED). The proposed CR-EH policies enable the continuous operation of energy self-sufficient communications nodes guaranteeing also a high level of SE. Next chapters are addressed to the interference cancellation on a dense deployment of SCs. Clustered-IA has been widely studied to manage the interference in these dense scenarios. Nonetheless, the setups considered in previous works relied on oversimplified channel models and/or enforced single-stream transmission. In this thesis, a novel cluster design based on sizerestricted 𝑘-means algorithm is proposed to divide the SCs into different clusters considering both path loss and shadowing effects. Therefore, a more realistic solution than those available in the current literature is provided. Unlike previous works, this clustering method can also cater to spatial multiplexing scenarios. Also, several design parameters such as the number of transmit antennas, multiplexed data streams, and deployed SBSs are analyzed in order to identify trade-offs between performance and complexity. The relationship between density of network elements per area unit and performance is also investigated. Moreover, it is shown that the SE degradation due to the inter-cluster interference in UDNs points to the need of designing an interference management algorithm that accounts for both, intra-cluster and inter-cluster interference. Reported IA techniques neglect the nonlinear distortion (NLD) induced by power amplifiers (PAs). Thus, their performance is severely degraded in highly power-efficient transmissions operating close to the saturation point. Distortion-aware precoding techniques have been studied to reduce NLD in single base station scenarios either single-user or multi-user. Nevertheless, its extension to UDNs with multiple SBSs and UEs is not straightforward. In this thesis, a novel IA algorithm, named NLD-IA, is proposed to alternatively design the precoding and combining vectors to cancel both interference and nonlinearities, so that signal-to-interference-plus-noise ratio (SINR) is maximized in UDNs. Precoding vectors are obtained via a non-convex optimization problem that models the NLD correlation. An analytical solution based on the Newton method over the complex field is developed to solve this problem with low computational complexity. Simulation results show that the proposed NLD-IA significantly reduces interference and NLD. Thus, it significantly outperforms previous IA algorithms for a wide range of signal-to-noise ratio (SNR), network densification, and saturation level. Another problem of network densification is that spectral resources are being saturated. An attractive solution is to extend the communication services to the millimeter-wave (mmWave) frequencies that provide a huge available spectrum to support broadband applications. Nevertheless, the implementation of fully digital (FD) precoding strategies becomes prohibitive in massive MIMO (mMIMO) systems working at mmWave due to their hardware complexity. Therefore, hybrid digital-analog beamforming (HB) is considered to reduce the number of radio frequency (RF) chains. When the analog stage is implemented with low-resolution phase shifters (PSs), the SE is severely affected. In this thesis, a novel HB method to achieve a near-optimal FD performance for mMIMO systems with the minimum required number of RF chains is developed. The reduction of RF chains arises as a key procedure to obtain an EE design. The proposed HB scheme is based on a quantization-aware matrix composition (QMC) to systematically compensate for the residual quantization errors. Furthermore, a quantization strategy, called sum Euclidean quantization (SEQ), is introduced to improve the accuracy of the analog stage. Numerical results reveal that, unlike previously reported HB methods, a nearoptimal SE can be achieved with our proposal while minimizing the number of RF chains and thus, the hardware cost and power consumption. On the other hand, although IA algorithms have been widely studied following an FD approach, there are only a few works on HB-IA. Therefore, a new HB-IA is also proposed in this thesis for UDNs based on an iterative partial construction (IPC) procedure with the novelty of awareness of PSs quantization. The IPC algorithm relies on algebraic properties to iteratively compute the analog and digital matrices, via a partial submatrix composition, such that the Euclidean distance to the FD-IA solution is reduced. An additional digital block, based on an IA algorithm, is also applied to cancel the residual interference. Numerical results reveal that the proposed HB IPC-IA significantly outperforms reported works achieving a near FD-IA performance. Since MIMO precoding is a key enabling technology for 5G/B5G cellular networks, the 3rd Generation Partnership Project (3GPP) has standardized precoding techniques for single-user and multi-user MIMO systems to achieve a balanced trade-off between performance, complexity, and signal overhead. The implementation of these precoding strategies is covered in this thesis providing a comprehensive guide. The performance of the 5G New Radio (NR) precoder is compared with theoretical precoding techniques such as singular value decomposition (SVD) and block-diagonalization (BD) to quantify the margin of improvement of the standardized methods. Several configurations of antenna arrays, number of antenna ports, and parallel data streams are considered for simulations. Moreover, the effect of channel estimation errors on the system performance is analyzed. For a realistic framework, the SE values are obtained for a practical deployment based on a clustered delay line (CDL) channel model. These results provide valuable insights for system designers about the implementation and performance of the 5G-NR precoding matrices. Finally, a practical implementation of IA algorithms on a hardware platform using universal software radio peripherals (USRPs) is addressed. A synchronization stage, based on the Schmidl and Cox method, is implemented. In contrast to previous works, a hardware testbed, able to model heterogeneous SINR networks, is proposed. The role of both closed and open loop for channel estimation is evaluated. Then, the impact of channel state information (CSI) updating on the SE and bit error rate (BER) is also analyzed. All the results are based on real measurements providing a clear understanding of the benefits and limitations of IA techniques in interference-limited cellular networks.
FLIPEC: A free-boundary equilibrium solver in the context of Ideal MHD for toroidally axisymmetric plasmas in the presence of flows
(2024-02) Fernández-Torija Daza, Gonzalo; Sánchez Fernández, Luis Raul; Reynolds Barredo, José Miguel; UC3M. Departamento de Física; Sánchez Fernández, Luis Raul
Since the 1950s, science has been striving to extract energy in a controlled and usable manner from the same source that powers the Sun: the nuclear fusion of light nuclei. The immense gravity produced by the Sun’s mass creates pressure in its outer layers, heating and confining its predominantly hydrogen core for an extended period. Subjected to these high temperatures, hydrogen nuclei, composed of a single proton and its only electron, dissociate into the state of matter known as plasma. In this state, and under certain conditions, positively charged nuclei can collide, forming a different nucleus. Despite the relatively simple premise, the idea promised quasi-unlimited energy at a low cost for humanity. Unfortunately, the conditions within the Sun are impossible to replicate on Earth, as we lack the Sun’s gravitational energy to confine and heat the plasma; such a mechanism can only be achieved within stars. On our planet, we need to resort to smaller-scale methods to achieve nuclear fusion. One proposed method, known as "magnetic confinement fusion," involves using powerful magnetic fields to enclose plasma, which is a fluid composed of charged particles that react to these fields. This strategy faces several challenges that hinder the development of a commercial reactor capable of producing energy consistently and efficiently for the grid. The need to confine a plasma for an extended period, around ten times hotter than the solar interior is one of the most defiant. However, maintaining such a plasma at these temperatures for long enough to build a fusion plant is still a distant goal. Currently, the leading experimental reactors in fusion research are the stellarator and the tokamak. Both designs are based on toroidal geometries to confine plasma, but their magnetic field configurations impart different properties to their operation. While the stellarator possesses essentially three-dimensional configurations, tokamaks’ magnetic fields exhibit toroidal symmetry, simplifying some aspects while introducing other disadvantages. Notably, tokamaks require induced current in the plasma to maintain equilibrium. This work is specifically focused on tokamak equilibrium within the context of toroidally axisymmetric geometry. Balancing forces within the plasma is crucial for confining particles within the reactors. Due to the complexity of the equations describing plasma behavior in detail, finding equilibrium solutions for a reactor can become an overwhelming challenge, both analytically and computationally. One solution involves simplifications leading to a field known as Magneto-hydrodynamics (MHD), specifically Ideal MHD in this study, assuming zero resistivity in the plasma. Despite achieving a considerable simplification of the starting equations, finding equilibrium solutions in Ideal MHD remains a considerable challenge, especially for certain magnetic field configurations. Numerous 3D equilibrium codes, such as VMEC or SIESTA, are widely used by the scientific community to find solutions not only for tokamaks but also for the intricate geometries of stellarator magnetic fields. Fortunately, this work deals with a toroidal symmetry context, allowing for further simplification of mathematics and computation times. This reduction leads to an elegant second-order differential equation: the Grad-Shafranov equation. Its solution depends on a single variable, typically represented by the symbol ψ, providing a measure of the poloidal magnetic flux required to maintain a plasma in equilibrium with a certain pressure distribution ppψq under a toroidal field indirectly given by a profile Fpψq. This relative simplicity opens the door to new possibilities, including obtaining analytical solutions for certain cases and significantly reducing computational costs for numerical solutions. Both three-dimensional codes and those solving the Grad-Shafranov equation share a common characteristic: they deliberately disregard the presence of macroscopic flows. That is, the term describing velocity in MHD equations is considered negligible. However, toroidal and poloidal flows are present in most operating tokamaks. Addressing the Grad-Shafranov equation by including the velocity term is not particularly challenging; however, its final expression does entail a significant increase in the complexity of the equation. Flow profiles increase from two to five, becoming less intuitive, and the differential operator risks changing its nature if poloidal flows are significant. Moreover, there are no longer analytical solutions except for simple toroidal flow cases. Consequently, only a few codes can compute equilibria in the presence of general flows, including FLOW, CLIO, or FINNESSE. Thus, this work undertakes the task of developing a code from scratch that offers different characteristics than existing ones, contributing a unique tool for the fusion community to analyze flow effects differently than previously done. The effort was carried out in two phases. Firstly, an iterative code capable of running under free boundary conditions was built and validated. Subsequently, the focus shifted to providing the code with the necessary tools and capabilities to make it a useful resource for the community. Both phases are covered in two articles, one already published, and the other in the process of publication as of the writing of this document. Among FLIPEC’s main properties are: • An Eulerian mesh implemented initially in toroidal coordinates, where the computational domain adhered to a circle. The smaller radius was treated numerically with secondorder finite differences, while a pseudo-spectral method was used for poloidal dependencies. • An computational boundary update scheme was adapted for the code to enable the calculation of free-boundary equilibriums. This strategy had already been successfully implemented in SIESTA, a 3D static equilibrium code [1, 2]. • To enable the code to adapt to any toroidally symmetric fusion device, generalized coordinates were implemented. This is essential because point currents running through coils create a singularity in the generated magnetic field values, and a circle only suited a very limited number of tokamaks. • Calculations under free boundaries trigger a vertical instability causing plasma to move vertically. An effective scheme was introduced to correct this displacement in each iteration. • In tests, it was observed that, in cases with strong toroidal rotation near the magnetic axis, the total plasma current tended to decrease over iterations. Since the current remains fixed during reactor operation, an algorithm was added to obtain equilibriums by fixing the plasma current. This strategy may perhaps be replicated in the future for other parameters. All these features were tested with two reference configurations associated with two experimental reactors with notably different characteristics: ITER, an ambitious large tokamak under construction, and NSTX, a smaller spherical tokamak with a low aspect ratio.
Transición de la educación superior a formación híbrida: retos y enfoques metodológicos
(2024-02) Reina Sánchez, Karen; Durán Heras, Alfonso; UC3M. Departamento de Ingeniería Mecánica; Durán Heras, Alfonso
En la actualidad, las Instituciones de Educación Superior (IES) se enfrentan a una profunda reflexión sobre su papel en la sociedad del futuro. La pandemia puso de relieve las carencias del modelo de enseñanza tradicional y resaltó el potencial de modelos más flexibles, que combinan la docencia virtual y la presencial. Asimismo, las necesidades y expectativas de los estudiantes actuales apuntan hacia una mayor flexibilización y digitalización de la enseñanza superior. Los avances tecnológicos más recientes, especialmente en Inteligencia Artificial Generativa, advierten que no será posible retrasar por mucho tiempo la transformación digital de la educación. En el corto plazo, las IES deben emprender una metamorfosis digital para preservar su lugar en la sociedad. Los avances en esa dirección abarcan inversiones en tecnologías e infraestructura, pero muestran progresos menos significativos en cuanto a la transformación de las metodologías y las prácticas pedagógicas que se distancien de las tradicionales. En la última década, las IES con modelos de educación presenciales han realizado algunas incursiones en formatos de aprendizaje en línea, como la implementación de foros de discusión o de cursos en línea masivos abiertos o cerrados, para complementar la docencia presencia. Sin embargo, no fue hasta la irrupción de la pandemia, con el cambio mandatorio a la virtualidad, que las IES se enfrentaron de forma masiva a una transformación radical en sus métodos de enseñanza. La literatura científica posterior a 2020 refleja esa disrupción provocada por la pandemia en el modelo educativo de las IES, evidenciada en un crecimiento en las publicaciones sobre experiencias en docencia en línea síncrona e híbrida. Este auge en la producción científica y la relativa novedad de este campo de investigación, resaltan la necesidad de una revisión exhaustiva de la literatura que pueda arrojar luz sobre cuestiones fundamentales, tales como, identificar los principios que rigen una docencia efectiva en entornos virtuales síncronos e híbridos, comprender los retos inherentes a estas modalidades de impartición y evaluar el estado actual de las experiencias que se han publicado al respecto. Dar respuesta a estas cuestiones es crucial para orientar la transición hacia modelos de formación más digitales y flexibles en el ámbito de la Educación Superior (ES). Por otra parte, la influencia de la situación de excepcionalidad en las experiencias de docencia en línea síncrona e híbrida subraya la necesidad de examinar los enfoques aplicados en ese periodo y evaluar su aplicabilidad en circunstancias normales, así como de encontrar nuevos enfoques que contribuyan a garantizar una docencia digital de calidad en el futuro. Dada la generación de datos en los entornos de aprendizaje digital y la importancia de integrarlos en la toma de decisiones de docentes y directivos de las IES, se impone también el estudio de alternativas para su procesamiento y explotación como parte fundamental de la transición. Teniendo en cuenta todo lo anterior, se establece como objetivo general de esta tesis investigar enfoques metodológicos y de explotación de datos educativos para contribuir a la transición en educación superior a una formación híbrida eficaz. Para alcanzar este objetivo se plantea la revisión de la literatura más reciente sobre docencia en línea síncrona e híbrida en ES, la evaluación sistemática de enfoques metodológicos en entornos reales de aprendizaje y la caracterización, exploración y análisis de los datos que se generan en dichos entornos. La investigación se divide en tres fases. Una primera Fase de estudio teórico, que comprende los dos primeros objetivos de esta tesis, una Fase de estudio empírico que engloba, tanto la exploración de enfoques metodológicos como el análisis de los datos y una Fase de resultados y conclusiones. Para su presentación, este documento se estructuró en 10 capítulos, incluyendo un capítulo de introducción y uno de conclusiones. Entre los resultados más significativos de esta tesis se encuentra la conceptualización y caracterización de la docencia eficaz, profundizando en los principios que deben guiar la instrucción reglada para alcanzar la eficacia en los nuevos entornos de aprendizaje. Además, se aportan un conjunto de enfoques metodológicos sobre organización y gestión de la docencia, el fomento de la participación y la entrega de contenidos en entornos en línea síncronos, y la descripción de los resultados obtenidos durante la evaluación sistemática de dichos enfoques en dos asignaturas de la disciplina de Ingeniería de Organización. También se proporcionan detalles de la evaluación de enfoques que combinan el uso de actividades presenciales y en línea con sistemas ERP, la reutilización de recursos educativos y modificaciones en el sistema de evaluación, para mejorar las experiencias de aprendizaje de los estudiantes en un entorno presencial enriquecido con la tecnología. Como parte del estudio empírico se definen una serie de variables e indicadores asociados a las analíticas de aprendizaje en entornos en línea síncronos e híbridos, que permiten obtener información sobre los enfoques aplicados. Por último, se proponen un conjunto de análisis, que tienen por objetivo transformar los datos generados en las plataformas de aprendizaje en valor para las IES. Para facilitar la instrumentación tanto de los enfoques metodológicos como de los análisis de datos, en la tesis se proporcionan detalles de todo el proceso seguido, iteración tras iteración de Investigación-Acción y, además, se ha creado un repositorio con los procedimientos en Python generados en el marco de esta investigación para que puedan ser utilizados por otros investigadores, en línea con las demandas actuales de la ciencia abierta.
Self-adaptive hp finite element method with iterative mesh truncation technique accelerated with ACA
(2023-09) Barrio Garrido, Rosa María; García Castillo, Luis Emilio; Salazar Palma, Magdalena; UC3M. Departamento de Teoría de la Señal y Comunicaciones; García Castillo, Luis Emilio
Among the most prominent computer-aided techniques employed in Computational Electromagnetics (CEM) for the numerical resolution of the Maxwell’s equations, is the powerful and flexible Finite Element Method, or FEM. This methodology stands out among other general-purpose numerical techniques due to its versatile nature, which opens the possibility of the generation of “adapted” meshes. The most powerful type of adaptivity is the so called hp-adaptivity in which the h refinements (modification of element size) and the prefinements (variation of the polynomial order p) are performed simultaneously, providing exponential rates of convergence, even in the presence of singularities. Thus, very accurate solutions are yielded even in the presence of singularities or, equivalently, approximate solutions within engineering accuracy can be obtained by using a minimum number of unknowns. When these type of combined h and p optimal refinements for the the adaption of the mesh to the solution is made automatically, it is referred to as automatic hp-adaptivity or self-adaptive hp-finite elements. This makes hp self-adaptivity the paradigm of the future in the field of electromagnetic simulators and solvers. However, the mathematical and numerical complexity behind such techniques has until very recently relegated them to a purely academic role that is currently in the development phase. But most of the commercial simulation tools have had an academic beginning as numerical in-house software developed by research groups. In this regard, the research group headed by Professor Demkowicz (Texas University) has developed a novel, fully self-adaptive hp-FEM electromagnetic solver for two- and three-dimensional complex geometries. In fact, this simulator is unique in its field, as it is the only tool developed to date with fully automatic adaptivity in h and p simultaneously applied specifically to electromagnetic problem solving. However the hp code is not originally adapted to the solution of open region problems, as FEM’s original formulation allows the analysis of finite geometries only. One of the main contributions of the work group to which the author of the present Ph. D dissertation belongs, is an optimal truncation technique for the use and extension of the original FEM formulation to open region problems. This technique is referred herein as FE-IIEE (Finite Element - Iterative Integral Equation Evaluation). Thus, working together with Prof. Demkowicz, the advisor of the present doctoral thesis and his group have successfully integrated this iterative FE-IIEE methodology into the self-adaptive hp-FEM software, obtaining a competitive hp tool for the analysis of two-dimensional electromagnetic open problems at the time this doctoral thesis was developed. Nonetheless, FE-IIEE imposes an extra computational effort to evaluate the convolutional integral appearing on the fictitious boundary where the FE-IIEE algorithm is applied to enclose the infinite layout. And this is the framework for the research developed in this doctoral thesis. Taking advantage of the knowledge of these collaborative research groups and taking as a starting point this powerful hp-FE-IIEE auto adaptivity solver in 2D, the main goal of this Ph. D dissertation is the implementation of an accelerated technique to avoid the mentioned computational bottleneck of the self-adaptive hp-FE-IIEE software. The first objective of this research is the appropriate choice of the fast integration technique to be implemented in the hp code. In order to make this choice, two known methodologies of different nature have been pre-selected with a priori proven advantages: FMM and ACA. Both acceleration methods have been herein implemented in a 2D FEM version truncated by means of FE-IIEE, and their performance has been studied with respect to several aspects. Due to the high accuracy imposed by hp and the double error control carried out by two different error control parameters (one for the self-adaptivity and one for the FE-IIEE iterations, placed in a double nested loop), the response of the fast integration technique to the required accuracy (by its own error control parameter), is crucial. In addition, its robustness, as well as its behavior in meshes with different h sizes and different polynomial orders, including higher p-order meshes, must be taken into account. Finally, their ease of implementation and the generality offered by each of the methods tested have been also addressed. In light of the results, it has been proven that the kernel-independent and robust ACA is the preferred algorithm for its implementation in the hp-FE-IIEE software. The second and main objective is the implementation of the method of choice in the hp-FE-IIEE code for its acceleration, studying its viability and results obtained in terms of potential loss of accuracy and computational complexity gains. A novel formulation for ACA has been implemented for its adaptation to the boundary condition used in the Integral Equation evaluation. The implementation has been validated and its performance in terms of computational savings (CPU time consumption and memory savings) has been studied. It will be shown in this doctoral dissertation that in this context ACA exhibits a robust behavior, yields good accuracy and compression levels up to 90%, and provides a good fair control of the approximation, which is a crucial advantage for hp adaptivity. Theoretical and empirical results of performance (computational complexity or CPU time) comparing the accelerated and non-accelerated versions of the method are presented. Several canonical scenarios are addressed to resemble the behavior of ACA with h, p and hp adaptive strategies, and higher order methods in general. The main conclusions yielded by this research are easily extrapolated to geometries in three dimensions, as well as to higher order contexts.
Analysis of the wave-plasma interaction in electrodeless plasma thrusters
(2024-03) Jiménez Jiménez, Pedro José; Merino Martínez, Mario; Ahedo Galilea, Eduardo Antonio; UC3M. Departamento de Ingeniería Aeroespacial; European Commission; Comunidad de Madrid; Ministerio de Ciencia, Innovación y Universidades (España); Merino Martínez, Mario
La tesis presentada contribuye a la comprensión y el modelado numérico de propulsores de plasma sin electrodos (EPTs). Con un enfoque dual que combina herramientas prácticas de diseño y modelos de investigación fundamental, este trabajo ofrece un conjunto de herramientas versátil y completo para avanzar el estado del arte en física de plasmas de baja temperatura aplicada a propulsión eléctrica. El núcleo de la investigación lo constituyen los avances en el estudio de EPTs y tecnologías para su modelado y simulación. Estos se enfocadan principalmente en la interacción de ondas electromagnéticas y su relación con fenómenos de transporte en el plasma. El estudio comienza con un análisis detallado del modelo de plasma frío, aplicado a problemas de propagación de ondas en propulsores de plasma de clase Helicón (HPT). Cabe destacar la introducción de PWHISTLER, una herramienta de simulación de ondas que emplea el método de elementos finitos (FE). Este modelo destaca por su mayor velocidad, precisión y capacidad para simular geometrías complejas, mejorando significativamente el estudio de fenómenos electromagnéticos en plasmas magnetizados. Una serie de análisis utilizando tanto un modelo de diferencias finitas (FD) como PWHISTLER demuestran su efectividad en la caracterización de la propagación y absorción de ondas en HPTs, siendo una observación clave la absorción de potencia concentrada en la superficie de resonancia electrónica-ciclotrónica (ECR). La integración de PWHISTLER con el código de simulación para el transporte de plasma HYPHEN facilita un estudio exhaustivo de una nueva topología de campo magnético con cúspide en HPT. Las simulaciones, verificadas con datos experimentales, ofrecen conclusiones sobre las pérdidas de rendimiento y la eficiencia de empuje, destacando el papel de las corrientes de plasma a pared, la temperatura de electrones y la influencia de la topología magnética. Finalmente se presenta una nueva formulación de un algoritmo implícito de partículas en celda (PIC), diseñado específicamente para toberas magnéticas. El método PIC implícito mejora la eficiencia computacional frente a métodos bien establecidos, y constituye un avance sustancial en la simulación y optimización de toberas magnéticas para EPTs.
La protección de datos personales en el Sistema Internacional, Europeo e Interamericano. Con especial análisis de su recepción en México
(2023-11) Tovar Partida, Gilberto; Fernández Liesa, Carlos Ramón; UC3M. Instituto de Derechos Humanos Gregorio Peces-Barba
Hybrid and Bayesian modelling of passenger occupancy at Beijing metro
(2024-01) He, Sun; Cabras, Stefano; UC3M. Departamento de Estadística; Cabras, Stefano
The thesis defended here is that modeling passenger flows with acceptable properties can be done with the models exposed in the above chapters. This thesis explored statistical methods for modeling passenger flows in Beijing’s Metro. The focus was on Bayesian methods and their application to dynamic systems, particularly urban metros. The Bayesian paradigm, including prior probability, likelihood, and posterior probability, was emphasized. Computational challenges were addressed using Integrated Nested Laplace Approximations (INLA), suitable for large-dimensional parameters in complex models. The work started from the socio-economic and engineering contexts of Beijing’s rapid urbanization. The Beijing Metro, serving millions daily, faces challenges due to unpredictable ridership patterns influenced by various factors. Predictive analytics are therefore crucial for operational efficiency, expansion planning, and passenger experience enhancement. Bayesian analysis was used for its adaptability and learning capability from new data. INLA was employed for efficient Bayesian inference, particularly in complex spatial and spatio-temporal models relevant to the study. The framework proved effective for regression models, dynamic linear models, and spatial applications. Data from ticketing systems, turnstiles, smart card check-ins, and mobile apps provided essential input for analysis. This data was crucial for our research as it is for managing peak traffic, scheduling trains, ensuring passenger safety, and supporting strategic decision-making. The thesis demonstrated the effectiveness of Bayesian models in predicting passenger flow in urban metro systems. Future work could focus on enhancing the computational efficiency of these models and exploring their application in other dynamic urban systems. Further research could also delve into the integration of additional data sources and the development of more advanced predictive models. Although the primary focus is on the Beijing Metro, this research draws data from the 1st of September to the 31st of October in 2020 to ensure a comprehensive understanding. It is worth noting that while the Bayesian model developed might offer theoretical applications for other metro systems, its design, calibration, and validation remain rooted in Beijing’s context. Aspects like intermodal transportation or predictions for bus networks fall outside of this study’s purview. To our knowledge, at the moment the daily passenger model has also been fitted to data from the metro network in other cities with a performance similar to the one shown here.

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