Lift devices in the flight of Archaeopteryx

Archaeopteryx has played a central role in the debates on the origins of avian (and dinosaurian) flight, even though as a flier it probably represents a relatively late stage in the beginnings of fl ight. We report on aerodynamic tests using a life-sized model of Archaeopteryx performing in a low turbulence wind tunnel. Our results indicate that tail deflection significantly decreased take-off velocity and power consumption, and that the first manual digit could have functioned as the structural precursor of the alula. Such results demonstrate that Archaeopteryx had already evolved high-lift devices, which are functional analogues of those present in today's birds.

Estudio numérico y experimental del efecto de tamaño en modo mixto de los paneles de yeso laminado y lana de roca

Los paneles sándwich de yeso laminado y lana de roca presentan una abundante patología de fisuración debida a flechas excesivas de forjados. Existe, por tanto, la necesidad de avanzar en la simulación y predicción de comportamiento bajo solicitaciones de tracción y cortante de ese tipo de paneles, a pesar de que en las aplicaciones habituales no tienen responsabilidad estructural. El comportamiento de este material puede ser considerado cuasi-frágil, y en base a ello en este trabajo ha sido estudiado haciendo uso de modelos de fisura cohesiva, cuya aplicación a otros materiales cuasifrágiles, como el hormigón, ha aportado resultados muy satisfactorios. En esta comunicación se presenta el trabajo realizado para estudiar el efecto del tamaño del elemento de yeso laminado y lana de roca en su comportamiento mecánico-resistente. Para ello se diseñó una campaña de ensayos en modo mixto sobre probetas de diferente tamaño. Se han realizado ensayos de flexión en tres puntos en modo mixto de unas probetas entalladas, geométricamente similares y de diferente tamaño, obteniéndose las curvas carga-desplazamiento y cargaabertura de la boca de la entalla. Para simular numéricamente el comportamiento en fractura del panel en modo mixto se ha utilizado un modelo de elementos finitos con fisura embebida basado en la fisura cohesiva en el que se introducen como entrada los parámetros obtenidos a partir de la experimentación de trabajos anteriores, obteniéndose un buen ajuste. En función de estos resultados se analiza el efecto del tamaño en los paneles. Sandwich panels of laminated gypsum and rockwool have an abundant pathology of cracking due to excessive slabs deflection. Therefore, it is necessary to progress in the simulation and prediction of behaviour under tensile and shear load of such panels, although in typical applications have no structural responsability. The behaviour of this material may be considered quasi-brittle and, based on this idea, in this work has been studied using a cohesive crack model that has been applied to other quasi-brittle materials, such as concrete, and has provided very satisfactory results. This communication presents the work carried out to study the size effect of the specimen of plasterboard and rockwool in its mechanical and resistant behaviour. The authors designed an experimental campaign under mixed mode composed by testing specimens of different sizes. Assymetrical three-point bending tests have been performed on notched specimens, geometrically similar and of different size, to obtain load-displacement and load-crack moutn opening displacement curves. To numerically simulate the mixed-mode fracture behaviour of the panels we have used a finite element model with embedded crack, based on the cohesive crack model, using as input the experimental parameters obtained in previous work, obtaining a good adjustment. Based on these results we analyze the size effect of the panels

Estudio numérico y experimental del efecto de tamaño en modo mixto de los paneles de yeso laminado y lana de roca

Los paneles sándwich de yeso laminado y lana de roca presentan una abundante patología de fisuración debida a flechas excesivas de forjados. Existe, por tanto, la necesidad de avanzar en la simulación y predicción de comportamiento bajo solicitaciones de tracción y cortante de ese tipo de paneles, a pesar de que en las aplicaciones habituales no tienen responsabilidad estructural. El comportamiento de este material puede ser considerado cuasi-frágil, y en base a ello en este trabajo ha sido estudiado haciendo uso de modelos de fisura cohesiva, cuya aplicación a otros materiales cuasifrágiles, como el hormigón, ha aportado resultados muy satisfactorios. En esta comunicación se presenta el trabajo realizado para estudiar el efecto del tamaño del elemento de yeso laminado y lana de roca en su comportamiento mecánico-resistente. Para ello se diseñó una campaña de ensayos en modo mixto sobre probetas de diferente tamaño. Se han realizado ensayos de flexión en tres puntos en modo mixto de unas probetas entalladas, geométricamente similares y de diferente tamaño, obteniéndose las curvas carga-desplazamiento y cargaabertura de la boca de la entalla. Para simular numéricamente el comportamiento en fractura del panel en modo mixto se ha utilizado un modelo de elementos finitos con fisura embebida basado en la fisura cohesiva en el que se introducen como entrada los parámetros obtenidos a partir de la experimentación de trabajos anteriores, obteniéndose un buen ajuste. En función de estos resultados se analiza el efecto del tamaño en los paneles. Sandwich panels of laminated gypsum and rockwool have an abundant pathology of cracking due to excessive slabs deflection. Therefore, it is necessary to progress in the simulation and prediction of behaviour under tensile and shear load of such panels, although in typical applications have no structural responsability. The behaviour of this material may be considered quasi-brittle and, based on this idea, in this work has been studied using a cohesive crack model that has been applied to other quasi-brittle materials, such as concrete, and has provided very satisfactory results. This communication presents the work carried out to study the size effect of the specimen of plasterboard and rockwool in its mechanical and resistant behaviour. The authors designed an experimental campaign under mixed mode composed by testing specimens of different sizes. Assymetrical three-point bending tests have been performed on notched specimens, geometrically similar and of different size, to obtain load-displacement and load-crack moutn opening displacement curves. To numerically simulate the mixed-mode fracture behaviour of the panels we have used a finite element model with embedded crack, based on the cohesive crack model, using as input the experimental parameters obtained in previous work, obtaining a good adjustment. Based on these results we analyze the size effect of the panels.

On the design of spherical gradient index lenses

Classical spherical gradient index (GRIN) lenses (such as Maxwell Fish Eye lens, Eaton lens, Luneburg lens, etc.) design procedure using the Abel integral equation is reviewed and reorganized. Each lens is fully defined by a function called the angle of flight which describes the ray deflection through the lens. The radial refractive index distribution is obtained by applying a linear integral transformation to the angle of flight. The interest of this formulation is in the linearity of the integral transformation which allows us to derive new solutions from linear combinations of known lenses. Beside the review of the classical GRIN designs, we present a numerical method for GRIN lenses defined by the Abel integral equation with fixed limits, which is an ill-posed problem.

Contribución al estudio de sistemas de hipertermia óptica y su aplicación en muestras biológicas

Las nanopartículas de metales nobles (especialmente las de oro) tienen un gran potencial asociado al desarrollo de sistemas de terapia contra el cáncer debido principalmente a sus propiedades ópticas, ya que cuando son irradiadas con un haz de luz sintonizado en longitud de onda con su máximo de Resonancia de Plasmón Superficial, absorben de manera muy eficiente dicha luz y la disipan rápidamente al medio en forma de calor localizado. Esta característica por tanto, puede ser aprovechada para conseguir elevar la temperatura de células tumorales hasta sobrepasar umbrales a partir de los cuales se produciría la muerte celular. Partiendo de estos principios, esta tesis se centra en el desarrollo y la caracterización de una serie de prototipos de hipertermia óptica basados en la irradiación de nanopartículas de oro con un haz de luz adecuado, así como en la aplicación in vitro de la terapia sobre células cancerígenas. Además, el trabajo se orienta a identificar y comprender los procesos mecánicos y térmicos asociados a este tipo de hipertermia, y a desarrollar modelos que los describan, estudiando y planteando nuevas formas de irradiación, para, en última instancia, poder optimizar los procesos descritos y hacerlos más efectivos. Los resultados obtenidos indican que, el uso de nanopartículas de oro, y más concretamente de nanorods de oro, para llevar a cabo terapias de hipertermia óptica, permite desarrollar terapias muy efectivas para inducir muerte en células cancerígenas, especialmente en tumores superficiales, o como complemento quirúrgico en tumores internos. Sin embargo, los efectos de la toxicidad de las nanopartículas de oro, aún deben ser detalladamente estudiados, ya que este tipo de terapias sólo será viable si se consigue una completa biocompatibilidad. Por otro lado, el estudio exhaustivo de los procesos térmicos que tienen lugar durante la irradiación de las nanopartículas ha dado lugar a una serie de modelos que permiten determinar la efectividad fototérmica de las nanopartículas y además, visualizar la evolución de la temperatura tanto a escala nanométrica como a escala macrométrica, en función de los parámetros ópticos y térmicos del sistema. El planteamiento de nuevas formas de irradiación y el desarrollo de dispositivos orientados a estudiar los fenómenos mecánicos que tienen lugar durante la irradiación pulsada de baja frecuencia y baja potencia de nanopartículas de oro, ha dado lugar a la detección de ondas de presión asociadas a procesos de expansión termoelástica, abriendo la puerta al desarrollo de terapias de hipertermia que combinen la muerte celular producida por calentamiento con la muerte derivada de los fenómenos mecánicos descritos.VII Noble metal nanoparticles (especially gold ones), have a huge potential in the development of therapy systems against cancer mainly due to their optical properties, so that, when these particles are irradiated with a light that is syntonized in wavelength with their maximum of Surface Plasmon Resonance, they effectively absorb and dissipate the light to the surrounding medium as localized heat. We can take advantage of this characteristic for rising the temperature of cancer cells above the threshold at which cellular death would occur. From these principles, this thesis is oriented to the development and characterization of a series of optical hyperthermia prototypes based on the irradiation of gold nanoparticles using the suitable light, and on the in vitro application of this therapy over cancer cells, to understand the mechanical and thermal processes associated with this kind of hyperthermia, developing descriptive models, and to study and to approach new ways of irradiation in order to, ultimately, optimize the described processes and make them more effective. The obtained results show that, the use of gold nanoparticles, and more specifically, of gold nanorods, to carry out optical hyperthermia therapies, allows the development of very effective therapies in order to induce death in VIII cancer cells, especially in superficial tumors, or like surgical complement in more internal tumors. However, the toxicity effects of the gold nanoparticles still need to be studied more detail, because this kind of therapies will be feasible only if a complete biocompatibility is achieved. On the other hand, the exhaustive study of the thermal processes that take place during the irradiation of the nanoparticles resulted in a series of models that allow the determination of the photothermal efficiency of the nanoparticles and also the visualization of the temperature evolution, both at nanoscale and at macroscale, as a function of the optical and thermal parameters of the system. The proposal of new ways of irradiation and the development of devices oriented to study the mechanical effects that take place during the low frequency and low power pulsing irradiation of gold nanoparticles has led to the detection of pressure waves associated to thermoelastic expansion processes, opening the door to the development of hyperthermia therapies that combine the cellular death due to the heating with the death derived from the described mechanical phenomena.

Análisis de la influencia de los diferentes parámetros de diseño en la aparición de fatiga superficial en contactos mecánicos

La fatiga superficial es uno de los principales problemas en las transmisiones mecánicas y es uno de los focos de atención de las investigaciones de los últimos anos en Tribología. La disminución de viscosidad de los lubricantes para la mejora de la eficiencia, el aumento de las potencias a transmitir, el aumento de la vida de los componentes o la mejora de su fiabilidad han supuesto que los fenómenos de fatiga superficial hayan cobrado especial relevancia, especialmente los fenómenos de pitting y micropitting en cajas multiplicadoras/reductoras de grandes potencias de aplicación, por ejemplo, en el sector eólico. Como todo fenómeno de fatiga, el pitting y micropitting son debidos a la aplicación de cargas ciclicas. Su aparición depende de las presiones y tensiones cortantes en el contacto entre dos superficies que al encontrarse en rodadura y deslizamiento varian con el tiempo. La principal consecuencia de la fatiga superficial es la aparición de hoyuelos de diferente magnitud segun la escala del fenómeno (pitting o micropitting) en la superficie del material. La aparición de estos hoyuelos provoca la perdida de material, induce vibraciones y sobrecargas en el elemento que finalmente acaba fallando. Debido a la influencia de la presión y tensión cortante en el contacto, la aparición de fatiga depende fuertemente del lubricante que se encuentre entre las dos superficies y de las condiciones de funcionamiento en las cuales este trabajando. Cuando el contacto trabaja en condiciones de lubricacion mixta-elastohidrodinamica tiende a aparecer micropitting debido a las altas tensiones localizadas en las proximidades de las asperezas, mientras que si el régimen es de lubricación completa el tipo de fatiga superficial suele ser pitting debido a las tensiones mas suavizadas y menos concentradas. En esta Tesis Doctoral se han analizado todos estos factores de influencia que controlan el pitting y el micropitting prestando especial atención al efecto del lubricante. Para ello, se ha dado un enfoque conjunto a ambos fenómenos resolviendo las ecuaciones involucradas en el contacto elastohidrodinamico no-Newtoniano (la ecuación de Reynolds, la deformación elástica de los sólidos y la reologia del lubricante) para conocer la presión y la tensión cortante en el contacto. Conocidas estas, se resuelve el campo de tensiones en el interior del material y, finalmente, se aplican criterios de fatiga multiaxial (Crossland, Dang Van y Liu-Mahadevan) para conocer si el material falla o no falla. Con la metodología desarrollada se ha analizado el efecto sobre las tensiones y la aparición de la fatiga superficial del coeficiente viscosidad-presion, de la compresibilidad, del espesor especifico de película y de la fricción así como de la influencia de las propiedades a fatiga del material y de las condiciones de funcionamiento (radios de contacto, velocidad, deslizamiento, carga y temperatura). Para la validación de los resultados se han utilizado resultados teóricos y experimentales de otros autores junto con normas internacionales de amplia utilización en el mundo industrial, entre otras, para el diseño y calculo de engranajes. A parte del trabajo realizado por simulación y cálculo de los diferentes modelos desarrollados, se ha realizado un importante trabajo experimental que ha servido no solo para validar la herramienta desarrollada sino que además ha permitido incorporar al estudio factores no considerados en los modelos, como los aditivos del lubricante. Se han realizado ensayos de medida del coeficiente de fricción en una maquina de ensayo puntual con la que se ha validado el cálculo del coeficiente de fricción y se ha desarrollado un proceso de mejora del coeficiente de fricción mediante texturizado superficial en contactos puntuales elastohidrodinamicos mediante fotolitografia y ataque quimico. Junto con los ensayos de medida de fricción en contacto puntual se han realizado ensayos de fricción y fatiga superficial en contacto lineal mediante una maquina de discos que ha permitido evaluar la influencia de diferentes aditivos (modificadores de fricción, antidesgaste y extrema-presion) en la aparición de fatiga superficial (pitting y micropitting) y la fricción en el contacto. Abstract Surface fatigue is one of the most important problems of mechanical transmissions and therefore has been one of the main research topics on Tribology during the last years. On the one hand, industrial demand on fuel economy has led to reduce lubricant viscosity in order to improve efficiency. On the other hand, the requirements of power and life of machine elements are continuously increasing, together with the improvements in reliability. As a consequence, surface fatigue phenomena have become critical in machinery, in particular pitting and micropitting in high power gearboxes of every kind of machines, e.g., wind turbines or cranes. In line with every fatigue phenomena, pitting and micropitting are caused by cyclic loads. Their appearance depends on the evolution of pressures and shear stresses with time, throughout the contact between surfaces under rolling and sliding conditions. The main consequence of surface fatigue is the appearance of pits on the surface. The size of the pits is related to the scale of the fatigue: pitting or micropitting. These pits cause material loss, vibrations and overloads until the final failure is reached. Due to the great influence of the pressures and shear stresses in surface fatigue, the appearance of pits depends directly on the lubricant and the operating conditions. When the contact works under mixed regime (or under elastohydrodynamic but close to mixed regime) the main fatigue failure is micropitting because of the high pressures located near the asperities. In contrast, when the contact works under elastohydrodynamic fully flooded conditions the typical fatigue failure is pitting. In this Ph.D. Thesis, the main factors with influence on pitting and micropitting phenomena are analyzed, with special attention to the effect of the lubricant. For this purpose, pitting and micropitting are studied together by solving the equations involved in the non-Newtonian elastohydrodynamic contact. Thus, pressure and shear stress distributions are found by taking into account Reynolds equation, elastic deflection of the solids and lubricant rheology. Subsequently, the stress field inside the material can be calculated and different multiaxial fatigue criteria (Crossland, Dang Van and Liu- Mahadevan) can be applied to predict whether fatigue failure is reached. The influences of the main parameters on pressure and surface fatigue have been studied, taking into account the lubricant compressibility and its viscosity-pressure coefficient, the specific film thickness, the friction coefficient and the fatigue properties of the contacting materials, together with the operating conditions (contact radius, mean velocity, sliding velocity, load and temperature). Several theoretical and experimental studies of different authors have been used to validate all the results obtained, together with international standards used worldwide in gear design industry. Moreover, an experimental stage has been carried out in order to validate the calculation methods and introduce additional influences not included previously, e.g., lubricant additives. The experimentation includes different friction tests in point contacts performed with a tribological equipment in order to validate the results given by the calculations. Furthermore, the reduction and optimization of the friction coefficient is analyzed by means of textured surfaces, obtained combining photolithography and chemical etching techniques. Besides the friction tests with point contact, friction and surface fatigue tests have also been performed with line contact in a tribological test rig. This equipment is also used to study the influence of different types of additives (friction modifiers, anti-wear and extreme-pressure additives) on surface fatigue (pitting and micropitting).

Enhancing the thermomechanical behaviour of poly(phenylene sulphide) based composites via incorporation of covalently grafted carbon nanotubes

The thermal and thermomechanical properties of poly(phenylene sulphide) (PPS) based nanocomposites incorporating a polymer derivative covalently anchored onto single-walled carbon nanotubes (SWCNTs) were investigated. The grafted fillers acted as nucleating agents, increasing the crystallization temperature and degree of crystallinity of the matrix. They also enhanced its thermal stability, flame retardancy, glass transition (Tg) and heat deflection temperatures while reduced the coefficient of thermal expansion at temperatures below Tg. A strong rise in the thermal conductivity, Young?s modulus and tensile strength was found with increasing filler loading both in the glassy and rubbery states. All these outstanding improvements are ascribed to strong matrix-filler interfacial interactions combined with a compatibilization effect that results in very homogeneous SWCNT dispersion. The results herein offer useful insights towards the development of engineering thermoplastic/CNT nanocomposites for high-temperature applications.

Inorganic Nanoparticle-Modified Poly(Phenylene Sulphide)/ Carbon Fiber Laminates: Thermomechanical Behaviour

Carbon fiber (CF)-reinforced high-temperature thermoplastics such as poly(phenylene sulphide) (PPS) are widely used in structural composites for aerospace and automotive applications. The porosity of CF-reinforced polymers is a very important topic for practical applications since there is a direct correlation between void content and mechanical properties. In this study, inorganic fullerene-like tungsten disulphide (IF-WS2) lubricant nanoparticles were used to manufacture PPS/IF-WS2/CF laminates via melt-blending and hot-press processing, and the effect of IF-WS2 loading on the quality, thermal and mechanical behaviour of the hybrid composites was investigated. The addition of IF-WS2 improved fiber impregnation, resulting in lower degree of porosity and increased delamination resistance, compression and flexural properties; their reinforcement effect was greater at temperatures above the glass transition (Tg). IF-WS2 contents higher than 0.5 wt % increased Tg and the heat deflection temperature while reduced the coefficient of thermal expansion. The multiscale laminates exhibited higher ignition point and notably reduced peak heat release rate compared to PPS/CF. The coexistence of micro- and nano-scale fillers resulted in synergistic effects that enhanced the stiffness, strength, thermal conductivity and flame retardancy of the matrix. The results presented herein demonstrate that the IF-WS2 are very promising nanofillers to improve the thermomechanical properties of conventional thermoplastic/CF composites.

Mechanical and thermal behaviour of isotactic polypropylene reinforced with inorganic fullerene-like WS2 nanoparticles: Effect of filler loading and temperature

The thermal and mechanical behaviour of isotactic polypropylene (iPP) nanocomposites reinforced with different loadings of inorganic fullerene-like tungsten disulfide (IF-WS2) nanoparticles was investigated. The IF-WS2 noticeably enhanced the polymer stiffness and strength, ascribed to their uniform dispersion, the formation of a large nanoparticle?matrix interface combined with a nucleating effect on iPP crystallization. Their reinforcement effect was more pronounced at high temperatures. However, a drop in ductility and toughness was found at higher IF-WS2 concentrations. The tensile behaviour of the nanocomposites was extremely sensitive to the strain rate and temperature, and their yield strength was properly described by the Eyring s equation. The activation energy increased while the activation volume decreased with increasing nanoparticle loading, indicating a reduction in polymer chain motion. The nanoparticles improved the thermomechanical properties of iPP: raised the glass transition and heat deflection temperatures while decreased the coefficient of thermal expansion. The nanocomposites also displayed superior flame retardancy with longer ignition time and reduced peak heat release rate. Further, a gradual rise in thermal conductivity was found with increasing IF-WS2 loading both in the glassy and rubbery states. The results presented herein highlight the benefits and high potential of using IF-nanoparticles for enhancing the thermomechanical properties of thermoplastic polymers compared to other nanoscale fillers.

Finite element simulation of sandwich panels of laminated plaster and rockwool under mixed mode fracture

Sandwich panels of laminated gypsum and rock wool have shown large pathology of cracking due to excessive slabs deflection. Currently the most widespread use of this material is as vertical elements of division or partition, with no structural function, what justifies that there are no studies on the mechanism of fracture and mechanical properties related to it. Therefore, and in order to reduce the cracking problem, it is necessary to progress in the simulation and prediction of the behaviour under tensile and shear load of such panels, although in typical applications have no structural responsability.

Bifurcation diagrams for polymer blends with diffuse interfaces in confined and adaptive geometries

Dynamics of binary mixtures such as polymer blends, and fluids near the critical point, is described by the model-H, which couples momentum transport and diffusion of the components [1]. We present an extended version of the model-H that allows to study the combined effect of phase separation in a polymer blend and surface structuring of the film itself [2]. We apply it to analyze the stability of vertically stratified base states on extended films of polymer blends and show that convective transport leads to new mechanisms of instability as compared to the simpler diffusive case described by the Cahn- Hilliard model [3, 4]. We carry out this analysis for realistic parameters of polymer blends used in experimental setups such as PS/PVME. However, geometrically more complicated states involving lateral structuring, strong deflections of the free surface, oblique diffuse interfaces, checkerboard modes, or droplets of a component above of the other are possible at critical composition solving the Cahn Hilliard equation in the static limit for rectangular domains [5, 6] or with deformable free surfaces [6]. We extend these results for off-critical compositions, since balanced overall composition in experiments are unusual. In particular, we study steady nonlinear solutions of the Cahn-Hilliard equation for bidimensional layers with fixed geometry and deformable free surface. Furthermore we distinguished the cases with and without energetic bias at the free surface. We present bifurcation diagrams for off-critical films of polymer blends with free surfaces, showing their free energy, and the L2-norms of surface deflection and the concentration field, as a function of lateral domain size and mean composition. Simultaneously, we look at spatial dependent profiles of the height and concentration. To treat the problem of films with arbitrary surface deflections our calculations are based on minimizing the free energy functional at given composition and geometric constraints using a variational approach based on the Cahn-Hilliard equation. The problem is solved numerically using the finite element method (FEM).

Deflexiones transversales de radiación luminosa en estructuras prismáticas de cristal líquido

A novel structure , based on a wedge shaped configuration, is presented . This structure , previously used in one of his forms,for refraction index measurements is analysed in this paper. The results obtained give the possibility of his use in electro snd magneto-optical modulation and deflection.

High Fidelity Models for Near-Earth Object Dynamics

Motivado por los últimos hallazgos realizados gracias a los recientes avances tecnológicos y misiones espaciales, el estudio de los asteroides ha despertado el interés de la comunidad científica. Tal es así que las misiones a asteroides han proliferado en los últimos años (Hayabusa, Dawn, OSIRIX-REx, ARM, AIMS-DART, ...) incentivadas por su enorme interés científico. Los asteroides son constituyentes fundamentales en la evolución del Sistema Solar, son además grandes concentraciones de valiosos recursos naturales, y también pueden considerarse como objectivos estratégicos para la futura exploración espacial. Desde hace tiempo se viene especulando con la posibilidad de capturar objetos próximos a la Tierra (NEOs en su acrónimo anglosajón) y acercarlos a nuestro planeta, permitiendo así un acceso asequible a los mismos para estudiarlos in-situ, explotar sus recursos u otras finalidades. Por otro lado, las asteroides se consideran con frecuencia como posibles peligros de magnitud planetaria, ya que impactos de estos objetos con la Tierra suceden constantemente, y un asteroide suficientemente grande podría desencadenar eventos catastróficos. Pese a la gravedad de tales acontecimientos, lo cierto es que son ciertamente difíciles de predecir. De hecho, los ricos aspectos dinámicos de los asteroides, su modelado complejo y las incertidumbres observaciones hacen que predecir su posición futura con la precisión necesaria sea todo un reto. Este hecho se hace más relevante cuando los asteroides sufren encuentros próximos con la Tierra, y más aún cuando estos son recurrentes. En tales situaciones en las cuales fuera necesario tomar medidas para mitigar este tipo de riesgos, saber estimar con precisión sus trayectorias y probabilidades de colisión es de una importancia vital. Por ello, se necesitan herramientas avanzadas para modelar su dinámica y predecir sus órbitas con precisión, y son también necesarios nuevos conceptos tecnológicos para manipular sus órbitas llegado el caso. El objetivo de esta Tesis es proporcionar nuevos métodos, técnicas y soluciones para abordar estos retos. Las contribuciones de esta Tesis se engloban en dos áreas: una dedicada a la propagación numérica de asteroides, y otra a conceptos de deflexión y captura de asteroides. Por lo tanto, la primera parte de este documento presenta novedosos avances de apliación a la propagación dinámica de alta precisión de NEOs empleando métodos de regularización y perturbaciones, con especial énfasis en el método DROMO, mientras que la segunda parte expone ideas innovadoras para la captura de asteroides y comenta el uso del “ion beam shepherd” (IBS) como tecnología para deflectarlos. Abstract Driven by the latest discoveries enabled by recent technological advances and space missions, the study of asteroids has awakened the interest of the scientific community. In fact, asteroid missions have become very popular in the recent years (Hayabusa, Dawn, OSIRIX-REx, ARM, AIMS-DART, ...) motivated by their outstanding scientific interest. Asteroids are fundamental constituents in the evolution of the Solar System, can be seen as vast concentrations of valuable natural resources, and are also considered as strategic targets for the future of space exploration. For long it has been hypothesized with the possibility of capturing small near-Earth asteroids and delivering them to the vicinity of the Earth in order to allow an affordable access to them for in-situ science, resource utilization and other purposes. On the other side of the balance, asteroids are often seen as potential planetary hazards, since impacts with the Earth happen all the time, and eventually an asteroid large enough could trigger catastrophic events. In spite of the severity of such occurrences, they are also utterly hard to predict. In fact, the rich dynamical aspects of asteroids, their complex modeling and observational uncertainties make exceptionally challenging to predict their future position accurately enough. This becomes particularly relevant when asteroids exhibit close encounters with the Earth, and more so when these happen recurrently. In such situations, where mitigation measures may need to be taken, it is of paramount importance to be able to accurately estimate their trajectories and collision probabilities. As a consequence, advanced tools are needed to model their dynamics and accurately predict their orbits, as well as new technological concepts to manipulate their orbits if necessary. The goal of this Thesis is to provide new methods, techniques and solutions to address these challenges. The contributions of this Thesis fall into two areas: one devoted to the numerical propagation of asteroids, and another to asteroid deflection and capture concepts. Hence, the first part of the dissertation presents novel advances applicable to the high accuracy dynamical propagation of near-Earth asteroids using regularization and perturbations techniques, with a special emphasis in the DROMO method, whereas the second part exposes pioneering ideas for asteroid retrieval missions and discusses the use of an “ion beam shepherd” (IBS) for asteroid deflection purposes.

Refuerzo de vigas de hormigón armado mediante la aplicación de fuerzas exteriores introducidas por predeformación de perfiles metálicos

Una técnica de refuerzo de elementos flectados en general y, en particular, de vigas y forjados de hormigón armado, consiste en la disposición de perfiles metálicos por debajo de los elementos a reforzar y retacados a ellos. En muchos casos este refuerzo se diseña con un planteamiento pasivo, es decir, los perfiles no entran en carga hasta que no se incrementan las acciones sobre el elemento reforzado, o lo hacen sólo ligeramente y de forma cuantitativamente no controlada efectuando el retacado mediante cuñas metálicas. En el presente trabajo se estudia la alternativa del refuerzo de vigas de hormigón armado frente a momentos flectores con un planteamiento activo, introduciendo unas fuerzas (por ejemplo, mediante gatos o barras roscadas) entre el perfil y el elemento a reforzar, y retacando posteriormente el perfil a la viga en los puntos de introducción de las fuerzas, mediante cuñas metálicas, mortero, etc. La propuesta que formulamos en el presente trabajo de investigación para el control de las fuerzas introducidas consiste en la medida de las flechas que se producen en el perfil metálico al hacerlo reaccionar contra la viga. Esto permite el empleo de procedimientos sencillos para la predeformación del perfil que no dispongan de dispositivos de medida de la carga introducida, o bien controlar la veracidad de las medidas de las fuerzas que dan tales dispositivos. La gran fiabilidad que tiene el cálculo de flechas en jácenas metálicas hace que con este procedimiento se puedan conocer con gran precisión las fuerzas introducidas. Las medidas de las flechas se pueden llevar a cabo mediante los procedimientos de instrumentación habituales en pruebas de carga, con una precisión más que suficiente para conocer y controlar con fiabilidad el valor de las fuerzas que el perfil ejerce sobre la viga. Los perfiles necesarios para el refuerzo con esta técnica son netamente inferiores a los que se precisarían con el planteamiento pasivo antes indicado. En el trabajo de investigación se recoge un estudio sobre el número, posición y valor de las fuerzas de refuerzo a introducir, en función de la carga para la que se diseña el refuerzo y la capacidad resistente del elemento a reforzar, y se analizan los valores máximos que pueden tener dichas fuerzas, en función de la capacidad de la pieza frente a momentos de signo contrario a los debidos a las cargas gravitatorias. A continuación se analiza la interacción viga-perfil al incrementarse las cargas sobre la viga desde el instante de la ejecución del refuerzo, interacción que hace variar el valor de las fuerzas que el perfil ejerce sobre la viga. Esta variación permite contar con un incremento en las fuerzas de refuerzo si, con las cargas permanentes presentes al reforzar, no podemos introducirlas inicialmente con el valor necesario, o si se producen pérdidas en las propias fuerzas. Este es uno de los criterios a la hora de seleccionar las características del perfil. Por el contrario, dicha variación puede suponer que en algunos puntos a lo largo del vano se supere la capacidad a flexión frente a momentos de signo contrario a los debidos a las cargas gravitatorias, lo que también debe ser tenido en cuenta. Seguidamente se analizan diferentes aspectos que producen una variación en el valor de las fuerzas de refuerzo, como son las deformaciones diferidas del hormigón (fluencia y retracción), los gradientes de temperatura en la pieza, o la actuación de sobrecargas en los vanos adyacentes. Se concluye los efectos de estos fenómenos, que en ocasiones tienen gran influencia, pueden ser cuantificados por el proyectista, recogiéndose propuestas sencillas para su consideración en casos habituales. Posteriormente recogemos una propuesta de metodología de comprobación del refuerzo, en cuanto a cómo considerar la fisuración y evolución del módulo de deformación de la viga, la introducción de la seguridad, la influencia de las tolerancias de laminación en el perfil sobre el valor calculado de las flechas necesarias en el perfil para introducir las fuerzas iniciales proyectadas, o la situación accidental de fuego, entre otros aspectos. Por último, se exponen las conclusiones más relevantes de la investigación realizada, y se proponen futuras líneas de investigación. One technique for strengthening flexural members in general, and reinforced concrete beams and slabs in particular, entails caulking the underside of these members with steel shapes. This sort of strengthening is often designed from a passive approach; i.e., until the load is increased, the shapes are either not loaded or are only slightly loaded to some unquantified extent by caulking with steel shims. The present study explored the possibility of actively strengthening the capacity of reinforced concrete beams to resist bending moments by applying forces (with jacks or threaded bars, for instance) between the shape and the member to be strengthened. The shape is subsequently caulked under the beam at the points where the forces are applied with steel shims, mortar or similar. The proposal put forward in the present study to monitor the forces applied consists in measuring the deflection on the steel shape as it reacts against the beam. With this technique, the shape can be pre-strained using simple procedures that do not call for devices to measure the force applied, or the accurancy of the respective measurements can be verified. As deflection calculations in steel girders are extremely reliable, the forces applied with this procedure can be very precisely determined. Standard instrumental procedures for load testing can be used to measure deflection with more than sufficient precision to reliably determine and monitor the value of the forces exerted on the beam by the shape. Moreover, the shapes required to strengthen members with this technique are substantially smaller than the ones needed in the aforementioned passive approach. This study addressed the number, position and value of the strengthening forces to be applied in terms of the load for which strengthening was designed and the bearing capacity of the member to be strengthened. The maximum value of such forces was also analysed as a function of the capacity of the member to resist counter-gravity moments. An analysis was then conducted of beam-shape interaction when the load on the beam raises since the instant that strengthening is applied, interaction that alters the forces applied to the beam by the shape. This variation can provide an increment in the forces if we cannot introduce them initially with the value calculated as necessary because they were limited by the permanent loads existing when strengthening, or if losses occur in the forces themselves. This is one of the criteria for defining shape specifications. Conversely, such variation may cause the forces to exceed beam counter-gravity bending strength at some points in the span, a development that must also be taken into consideration. Other factors inducing variations in the strengthening force values were then analysed, including deferred concrete strain (creep and shrinkage), temperature gradients in the member and the live loads acting on adjacent spans. The inference drawn was that these developments, which may on occasion have a heavy impact, can be quantified by the design engineer, particularly in ordinary situations, for which simple procedures are proposed. Methodology is likewise proposed for verifying strength in terms of how to appraise beam's cracking and variations in modulus of deformation; safety concerns; the effect of shape lamination tolerance on the calculated deflection necessary for the shape to apply the design forces; and fire-induced situations, among others. Lastly, the most prominent conclusions are discussed and future lines of research are suggested.

An autostereoscopic device for mobile applications based on a liquid crystal microlens array and an OLED display

In recent years, many experimental and theoretical research groups worldwide have actively worked on demonstrating the use of liquid crystals (LCs) as adaptive lenses for image generation, waveform shaping, and non-mechanical focusing applications. In particular, important achievements have concerned the development of alternative solutions for 3D vision. This work focuses on the design and evaluation of the electro-optic response of a LC-based 2D/3D autostereoscopic display prototype. A strategy for achieving 2D/3D vision has been implemented with a cylindrical LC lens array placed in front of a display; this array acts as a lenticular sheet with a tunable focal length by electrically controlling the birefringence. The performance of the 2D/3D device was evaluated in terms of the angular luminance, image deflection, crosstalk, and 3D contrast within a simulated environment. These measurements were performed with characterization equipment for autostereoscopic 3D displays (angular resolution of 0.03 ).