This thesis aims at quantitatively characterizing the recent (last few decades) and future climate variability of marine climate in the Western Mediterranean Sea and the North Atlantic Ocean. Namely it focuses on sea level and wind-waves, as these are the variables with a larger potential impact on coastal ecosystems and infrastructures. We first use buoy and altimetry data to calibrate a 50-year wind-wave hindcast over the Western Mediterranean in order to obtain the best characterization of the wave climate over that region. The minimization of the differences with respect to observations through a non-linear transformation of the Empirical Orthogonal Functions of the modelled fields results in an improvement of the hindcast, according to a validation test carried out with independent observations. We then focus on the relationship between the large scale atmospheric forcing and our target variables. Namely we quantify and explore the cause-effect relations between the major modes of atmospheric variability over the North Atlantic and Europe, i.e. the North Atlantic Oscillation, the East Atlantic pattern, the East Atlantic Western Russian pattern and the Scandinavian pattern, and both the Mediterranean sea level and the North Atlantic wave climate. To do so, we use data from different sets of observations and numerical models, including tide gauges, wave buoys, altimetry, hydrography and numerical simulations. Our results point to the North Atlantic Oscillation as the mode with the largest impact on both, Mediterranean sea level (due to the local and remote influence on its atmospheric component) and the North Atlantic wave climate (due to its effect on both the wind-sea and swell components). Other climate indices have smaller but still meaningful contributions; e.g. the East Atlantic pattern plays a significant role in the wave climate variability through its impact on the swell component. Finally, we explore the performance of statistical models to project the future wave climate over the North Atlantic under global warming scenarios, including the large scale climate modes as predictors together with other variables such as atmospheric pressure and wind speed. Notably, we highlight that the use of wind speed as statistical predictor is essential to reproduce the dynamically projected long-term trends. / Esta tesis caracteriza cuantitativamente la variabilidad climática reciente (las últimas décadas) y futura del clima marino en el Mar Mediterráneo y en el Océano Atlántico Norte. Concretamente, se centra en el nivel del mar y en el oleaje, ya que éstas son las variables con un mayor impacto potencial en ecosistemas e infraestructuras costeras. En primer lugar, utilizamos datos de boyas y altimetría para calibrar un hindcast de oleaje de 50 años en el Mediterráneo Occidental, con el objetivo de obtener la mejor caracterización climática del oleaje sobre esta región. La minimización de las diferencias con respecto a las observaciones a través de una transformación no lineal de las Funciones Empíricas Ortogonales de los campos modelados se traduce en una mejora del hindcast, de acuerdo al test de validación llevado a cabo con observaciones independientes. Luego nos centramos en las relaciones entre el forzamiento atmosférico de gran escala y nuestras variables de interés. En concreto, cuantificamos y exploramos las relaciones causa-efecto entre los modos de variabilidad atmosférica más importantes del Atlántico Norte y Europa (la Oscilación del Atlántico Norte, el patrón del Atlántico Oriental, el patrón del Atlántico Oriental/Rusia Occidental y el patrón Escandinavo) y el nivel del mar del Mediterráneo y el oleaje del Atlántico Norte. Para ello, usamos datos de diferentes conjuntos de observaciones y modelos numéricos, incluyendo mareógrafos, boyas de oleaje, altimetría, hidrografía y simulaciones numéricas. Nuestros resultados señalan la Oscilación del Atlántico Norte como el modo de mayor impacto, tanto en el nivel del mar del Mediterráneo (debido a la influencia local y remota en su componente atmosférica) como en el oleaje del Atlántico Norte (debido a su efecto en las componentes de mar de viento y de mar de fondo). Otros índices climáticos tienen contribuciones más pequeñas pero todavía significativas; e.g. el patrón del Atlántico Oriental juega un papel importante en la variabilidad del oleaje a través de su impacto en la componente de mar de fondo. Finalmente, exploramos la capacidad de los modelos estadísticos de proyectar el clima futuro del oleaje sobre el Atlántico Norte bajo escenarios de calentamiento global, incluyendo los modos climáticos de gran escala como predictores junto con otras variables como la presión atmosférica y la velocidad del viento. En particular, destacamos que el uso de la velocidad del viento como predictor estadístico es esencial para reproducir las tendencias a largo plazo proyectadas de por los modelos dinámicos.

En termes de propulsió la rigidesa flexural i l'efecte terra en una placa rectangular en piteig pur han estat investigats. Velocimetria per imatges per partícules, mesures de forces i moments amb una cèl·lula de carga de 6 eixos, mesures de velocitat i adquisició d'imatges de la cinemàtica de la placa han estat realitzades per estudiar els patrons de flux i les forces hidrodinàmiques en plaques de diferent flexibilitat. La presència de la paret va millorar la velocitat de creuer fins a un 25% i l'empenta fins a un 45% per angles escombrats de 160 i 240 graus. El mecanisme físic sota aquest efecte és discutit estudiant els camps de vorticitat produïts per l'estela de l'aleta bioinspirada en un rajiforme. Les forces hidrodinàmiques linkejades a les tècniques de visualització, van permetre calcular eficiències i camps de vorticitat promitjats en fase. Aquestes dades van revelar com l'angle escombrat de la placa juga un paper fonamental en la distribució de moment en l'estela d'una placa rígida per incrementar la propulsió. En termes de rigidesa flexural, l'òptima flexibilitat va ser determinada amb una placa semi-flexible amb una eficiència d'un 69% amb un angle d'atac de 72 graus. / En términos de propulsión la rigidez flexural y el efecto suelo en una placa rectangular en puro picheo han sido investigados. Velocimetría de imágenes por partículas, medidas de fuerzas y momentos con una célula de carga de 6 ejes, medidas de velocidad y adquisiciones de imágenes de la cinemática de la placa han sido realizadas para estudiar los patrones de flujo y las fuerzas hidrodinámicas en placas con diferentes flexibilidad. La presencia de la pared mejoró la velocidad de crucero hasta en un 25% y el empuje hasta un 45% para ángulos barridos de 160 y 240 grados. El mecanismo físico bajo este efecto es discutido estudiando los campos de vorticidad producidos por la estela de la aleta bioinspirada en un rajiforme. Las fuerzas hidrodinámicas linkadas a las técnicas de visualización, permitieron calcular eficiencias y campos de vorticidad promediados en fase. Estos datos revelaron como el ángulo barrido de la placa juega un papel fundamental en la distribución de momento en la estela de un foil rígido para incrementar la propulsión. En términos de rigidez flexural la óptima flexibilidad fue determinada con la placa semi-flexible con una eficiencia de un 69% con un ángulo de ataque de 72 grados. / The roles of the chordwise flexural stiffness and ground effect in a rectangular plate undergoing in pure pitching motion have been investigated. Digital Particle image velocimetry (DPIV), load measurement with a 6-axes balance, measurements of the swimming speed and image acquisition of the kinematics of the foil have been done to study the flow patterns and hydrodynamics forces around the flapping flexible plates. The presence of the wall enhances the cruising velocity in some cases up to 25% and the thrust by a 45% , for swept angles of 160 and 240°. The physical mechanisms underlying of this effect are discussed by studying the vorticity dynamics in the wake of the foil. Experimental data of the hydrodynamic forces and moments allowed to obtain the efficiencies of the flapping propulsion. These load measurements were linked to the wakes of the flapping foils in order to reveal configurations with higher thrust. The momentum distribution in the wake of the foil has allowed the physical explanation for the cases with highest thrust production capacity. In terms of flexural stiffness, the optimum flexibility has been determined with the semi − flexible plate up to 69% of efficiency under a swept angle of 72 degrees for Re = O(10^4) tested in the investigation.

This thesis explores the analytical capabilities of low-loss electron energy loss spectroscopy (EELS), applied to disentangle the intimate configuration of advanced semiconductor heterostructures. Modern aberration corrected scanning transmission electron microscopy (STEM) allows extracting spectroscopic information from extremely constrained areas, down to atomic resolution. Because of this, EELS is becoming increasingly popular for the examination of novel semiconductor devices, as the characteristic size of their constituent structures shrinks. Energy-loss spectra contain a high amount of information, and since the electron beam undergoes well-known inelastic scattering processes, we can trace the features in these spectra down to elementary excitations in the atomic electronic configuration. In Chapter 1, the general theoretical framework for low-loss EELS is described. This formulation, the dielectric model of inelastic scattering, takes into account the electrodynamic properties of the fast electron beam and the quantum mechanical description of the materials. Low-loss EELS features are originated both from collective mode (plasmons) and single electron excitations (e.g. band gap), that contain relevant chemical and structural information. The nature of these excitations and the inelastic processes involved has to be taken into account in order to analyze experimental data or to perform simulations. The computational tools required to perform these tasks are presented in Chapter 2. Among them, calibration, deconvolution and Kramers-Kronig analysis (KKA) of the spectrum constitute the most relevant procedures, that ultimately help obtain the dielectric information in the form of a complex dielectric function (CDF). This information may be then compared to the one obtained by optical techniques or with the results from simulations. Additional techniques are explained, focusing first on multivariate analysis (MVA) algorithms that exploit the hyperspectral acquisition of EELS, i.e. spectrum imaging (SI) modes. Finally, an introduction to the density functional theory (DFT) simulations of the energy-loss spectrum is given. In Chapter 3, DFT simulations concerning (Al, Ga, In)N binary and ternary compounds are introduced. The prediction of properties observed in low-loss EELS of these semiconductor materials, such as the band gap energy, is improved in these calculations. Moreover, a super-cell approach allows to obtain the composition dependence of both band gap and plasmon energies from the theoretical dielectric response coefficients of ternary alloys. These results are exploited in the two following chapters, in which we experimentally probe structures based on group-III nitride binary and ternary compounds. In Chapter 4, two distributed Bragg reflector structures are examined (based upon AlN/GaN and InAlN/GaN multilayers, respectively) through different strategies for the characterization of composition from plasmon energy shift. Moreover; HAADF image simulation is used to corroborate he obtained results; plasmon width, band gap energy and other features are measured; and, KKA is performed to obtain the CDF of GaN. In Chapter 5, a multiple InGaN quantum well (QW) structure is examined. In these QWs (indium rich layers of a few nanometers in width), we carry out an analysis of the energy-loss spectrum taking into account delocalization and quantum confinement effects. We propose useful alternatives complementary to the study of plasmon energy, using KKA of the spectrum. Chapters 6 and 7 deal with the analysis of structures that present pure silicon-nanocrystals (Si-NCs) embedded in silicon-based dielectric matrices. Our aim is to study the properties of these nanoparticles individually, but the measured low-loss spectrum always contains mixed signatures from the embedding matrix as well. In this scenario, Chapter 6 proposes the most straightforward solution; using a model-based fit that contains two peaks. Using this strategy, the Si-NCs embedded in an Er-doped SiO2 layer are characterized. Another strategy, presented in Chapter 7, uses computer-vision tools and MVA algorithms in low-loss EELS-SIs to separate the signature spectra of the Si-NCs. The advantages and drawbacks of this technique are revealed through its application to three different matrices (SiO2, Si3N4 and SiC). Moreover, the application of KKA to the MVA results is demonstrated, which allows to extract CDFs for the Si-NCs and surrounding matrices. / Este trabajo explora las posibilidades analíticas que ofrece la técnica de espectroscopia electrónica de bajas pérdidas (low-loss EELS), capaces de revelar la configuración estructural de los más avanzados dispositivos semiconductores. El uso de modernos microscopios electrónicos de transmisión-barrido (STEM) nos permite obtener información espectroscópica a partir de volúmenes reducidos, hasta llegar a resolución atómica. Por ello, EELS es cada vez mas popular para la observación de los dispositivos semiconductores, a medida que los tamaños característicos de sus estructuras constituyentes se miniaturiza. Los espectros de pérdida de energía contienen mucha información: dado que el haz de electrones sufre unos bien conocidos procesos de dispersión inelástica, podemos trazar relaciones entre estos espectros y excitaciones elementales en la configuración atómica de los elementos y compuestos constituyentes de cada material. Se describe un marco teórico para el estudio del low-loss EELS: el modelo dieléctrico de dispersión inelástica, que toma en consideración las propiedades electrodinámicas del haz de electrones y la descripción mecano-cuántica de los materiales. Adicionalmente, se describen en detalle las herramientas utilizadas en el análisis de datos experimentales o la simulación teórica de espectros. Monitorizando las energías de band gap y plasmon en los datos experimentales de low-loss EELS se obtiene información directa sobre propiedades electrónicas de los materiales. Además, usando análisis Kramers-Kronig en los espectros se obtiene información dieléctrica que puede ser comparada con las simulaciones o con otras técnicas (ópticas). Se demuestra el uso de estas herramientas con una serie de estudios sobre estructuras basadas en nitruros del grupo-III. Por otro lado, el uso de algoritmos para el análisis multivariante permite separar las contribuciones individuales que se miden mezcladas en espectros de estructuras complicadas. Hemos utilizado estas avanzadas herramientas para el análisis de estructuras basadas en silicio que contienen nano-cristales embebidos en matrices dieléctricas.

During the last two decades, High-Performance Computing (HPC) has grown rapidly in performance by improving single-core processors at the cost of a similar growth in power consumption. The single-core processor improvement has led many scientists to exploit mainly the process level parallelism in their codes. However, the performance of HPC systems is becoming increasingly limited by power consumption and power density, which have become a primary concern for the design of new computer systems. As a result, new supercomputers are designed based on the power efficiency provided by new homogeneous and heterogeneous architectures. The growth in computational power has introduced a new approach to science, Computational Physics. Its impact on the study of nuclear fusion and plasma physics has been very significant. This is because the experiments are difficult and expensive to perform whereas computer simulations of plasma are an efficient way to progress. Particle-In-Cell (PIC) is one of the most used methods to simulate plasma. The improvement in the processing power has enabled an increase in the size and complexity of the PIC simulations. Most PIC codes have been designed with a strong emphasis on the physics and have traditionally included only process level parallelism. This approach has not taken advantage of multiprocessor platforms. Therefore, these codes exploit inefficiently the new computing platforms and, as a consequence, they are still limited to using simplified models. The aim of this thesis is to incorporate in a PIC code the latest technologies available in computer science in order to take advantage of the upcoming multiprocessor supercomputers. This will enable an improvement in the simulations, either by introducing more physics in the code or by incorporating more detail to the simulations. This thesis analyses a PIC code named EUTERPE on different computing platforms. EUTERPE is a production code used to simulate fusion plasma instabilities in fusion reactors. It has been implemented for traditional HPC clusters and it has been parallelized prior to this work using only Message Passing Interface (MPI). Our study of its scalability has reached up to tens of thousands of processors, which is several orders of magnitude higher than the scalability achieved when this thesis was initiated. This thesis also describes the strategies adopted for porting a PIC code to a multi-core architecture, such as introducing thread level parallelism, distributing the work among different computing devices, and developing a new thread-safe solver. These strategies have been evaluated by applying them to the EUTERPE code. With respect to heterogeneous architectures, it has been possible to port this kind of plasma physics codes by rewriting part of the code or by using a programming model called OmpSs. This programming model is specially designed to make this computing power easily available to scientists without requiring expert knowledge on computing. Last but not least, this thesis should not be seen as the end of a way, but rather as the beginning of a work to extend the physics simulated in fusion codes through exploiting available HPC resources. / Durant les darreres dues dècades, la Computació d'Alt Rendiment (HPC) ha crescut ràpidament en el rendiment mitjançant la millora dels processadors d'un sol nucli a costa d'un creixement similar en el consum d'energia. La millora en els processadors d'un sol nucli ha portat a molts científics a explotar tot el paral·lelisme a nivell de procés en els seus codis. No obstant això, el rendiment dels sistemes HPC està cada cop més limitat pel consum d'energia i la densitat de potència, que s'han convertit en una de les principals preocupacions en el disseny dels nous sistemes informàtics. Com a resultat, els nous supercomputadors estan dissenyats sobre la base de l'eficiència energètica proporcionada per les noves arquitectures homogènies i heterogènies. El creixement de la potència de càlcul ha introduït un nou enfocament a la ciència, la Física Computacional. El seu impacte en l'estudi de la fusió nuclear i la física del plasma ha estat molt significatiu. Això és perquè els experiments són difícils i costosos de realitzar mentre que les simulacions del plasma amb computadors són una manera eficaç de progressar. Particle-In-Cell (PIC) és un dels mètodes més utilitzats per simular el plasma. La millora en la potència de processament ha permès un augment en la grandària i la complexitat de les simulacions PIC. La majoria dels codis PIC s'han dissenyat amb un fort èmfasi en la física i tradicionalment han inclòs només paral·lelisme a nivell de procés. Aquest enfocament no ha aprofitat les plataformes multiprocessador. Per tant, aquests codis exploten ineficientment les noves plataformes de computació i, com a conseqüència, encara estan limitats a tractar amb models simplificats. L'objectiu d'aquesta tesi és incorporar en un codi PIC les últimes tecnologies disponibles en informàtica per tal d'aprofitar els propers supercomputadors multiprocessador. Això permetrà una millora en les simulacions, ja sigui mitjançant la introducció de més física en el codi o mitjançant la incorporació de més detall en les simulacions. Aquesta tesi analitza un codi PIC anomenat EUTERPE en diferents plataformes de computació. EUTERPE és un codi de producció utilitzat per simular les inestabilitats del plasma en els reactors de fusió. S'ha implementat per clústers HPC tradicionals i s'ha paral·lelitzat prèviament a aquest treball usant només la Interfície de Pas de Missatges (MPI). El nostre estudi de la seva escalabilitat ha arribat fins a desenes de milers de processadors, que és diversos ordres de magnitud més gran que l'escalabilitat que s'havia assolit quan es va iniciar aquesta tesi. Aquesta tesi també descriu les estratègies adoptades per portar un codi PIC a una arquitectura multi-nucli, com ara la introducció de paral·lelisme a nivell de thread, la distribució de la feina entre diferents dispositius de computació i el desenvolupament d'un nou solver thread-safe. Aquestes estratègies han estat avaluades amb la seva aplicació al codi EUTERPE. Pel que fa a les arquitectures heterogènies, ha estat possible portar aquest tipus de codis de la física del plasma reescrivint part del codi o mitjançant l'ús d'un model de programació anomenat OmpSs. Aquest model de programació està especialment dissenyat per posar aquesta potència de càlcul a l'abast dels científics sense necessitat de coneixements d'experts en computació. Finalment, però no menys important, aquesta tesi no ha de ser vista com el final d'un camí, sinó més aviat com l'inici d'un treball per estendre la física simulada en els codis de fusió nuclear mitjançant l'explotació dels recursos disponibles de HPC.

The concept of nanotechnology is attributed to Nobel prize winner Richard Feynman who gave a very famous, visionary in 1959 (published in 1960) during one of his lectures, saying: "the principles of physic, as far as I can see, do not speak against the possibility of maneuvering things atom by atom". At the time, Feynman’s words were received as pure science fiction". Today, we have instruments that allow precisely what Feynman had predicted: creating structures by moving atoms individually. In principle, the ultimate results of this research study leads to the synthesis of magnetic and porous carbon based nanoparticles as the material and tool for biomedical applications. Currently, we are in a battle with a dangerous and destructive diseases such as cancers, and nanotechnology is then presented as a tool that can help us win control. This work is to support medical and other applications of nanotechnology specifically aimed to prepare carbon based nanoparticles. Magnetic nanoparticles are being of great interest because of their unique properties especially in drug delivery, hyperthermia, magnetic resonance imaging and cell separation. In many clinical situations, medication doses are oversized as a result of impaired drug absorption or tissue unspecific delivery. The ultimate goal of magnetically controlled drug delivery and drug therapy is to selectively delivering drug molecules to the diseased site without a concurrent increase in its level in healthy tissues. Consequently, in this research study the objective is to develop an approach to control the synthesis of carbon encapsulated iron nanoparticles in the form of core@shell nanostructure. Accordingly, understanding and revealing the growth mechanism of carbon encapsulated iron nanoparticles is necessary by doing characterization. Furthermore, engineering of suitable carbon based nanoparticles for biomedical applications has been also considered. Common challenges for synthesis of carbon encapsulated iron nanoparticles are improving uniformity, enhancing coating protection and controlling particles compositions, shape and core/shell sizes. In addition, due to the lack of comprehensive understanding of the optimal parameters and formation mechanism most of the current fabrication process are empirical, which means a large number of experimental trials are required to optimize any given process. Since the last two decades, arc discharge technique leads to the discovery of two important carbon based materials, nanotubes and fullerenes. However, the formation of nanomaterials by thermal plasma still remains poorly understood and need further investigation. The focus in this study is on synthesis of carbon based nanoparticles by arc discharge method, particularly carbon encapsulated iron nanoparticles in the form of Core@Shell nanostructure. An arc discharge reactor that was patented by FEMAN group was used with slight modification. The growth processes were elucidated through many experiments and characterizations. Precise control over carbon encapsulated iron nanoparticles were addressed. In addition, a new carbon encapsulated multi iron nanoparticles is introduced. The results have been lead to new elements for understanding the growth mechanism of iron core and carbon shell nanostructure. In order to improve the synthesis process, a new modified arc discharge reactor was developed and implemented. Two new materials are prepared through a new facile synthetic method; carbon nanoparticles decorated by fullerenes and spherical porous carbon microparticles. Last but not least, in this research medical application requirements have been taken into account to prepare suitable nanoparticle. / El concepto de la nanotecnología se atribuye al ganador del premio Nobel Richard Feynman, científico visionario, quien dio una muy famosa conferencia en 1959 (publicada en 1960), en la que dijo: "los principios de la física, por lo que yo puedo ver, no están en contra de la posibilidad de maniobrar los objetos átomo por átomo "(Feynman, 1960). En ese momento, se recibieron las palabras de Feynman como pura ciencia ficción, sin embargo, a día de hoy, tenemos instrumentos que permiten precisamente lo que Feynman ya había predicho: La creación de estructuras de átomos en movimiento de forma individual. En principio, los resultados finales del presente trabajo de investigación conduce a la síntesis de nanoestructuras del tipo core@shell, consistentes en nanopartículas de hierro encapsulado en carbono, en nanopartículas de carbono decoradas con fullerenos y micropartículas de carbono porosas esféricas como material y herramienta para aplicaciones biomédicas. Actualmente, nos encontramos en un frente contra enfermedades peligrosas y destructivas como el cáncer, y la nanotecnología se presenta como una herramienta que nos puede ayudar a establecer un control de este tipo de dolencias. Este trabajo se enmarca en la Nanotecnología y tiene por objetivo el estudio y preparación de nanopartículas a base de carbono que puedan ser útiles para ciertas aplicaciones aplicaciones médicas o biomédicas y otras del ámbito de la nanotecnología más general.

The objective of this work was to study two different light management approaches to enhance the efficiency of thin film Si solar cells and these were the manipulation of the light path (light trapping) and changing the incoming photon energy (upconversion). In the first approach the light path was manipulated by creating either periodic or random textured interfaces. Periodic patterns were created at the front AZO by means of direct laser ablation. Amongst all the patterns assessed, the best result was achieved with a linear pattern of 10 lam of pitch and 360 nm of groove depth, that yielded to an Rs of 11 SI/sq and a haze of 12.7% at 600 nm. However structures in the sub-micrometer range cannot be created because the minimum period is limited by the laser spot. By means of the Aluminum Induced Texturing method (AIT) random textures were performed on glass substrates. In this method, a thin Al film is deposited onto a glass substrate and a redox reaction between the Al and the SiO2 of the glass is induced by high temperature annealing. The reaction products are wet-etched and the result is a uniform and rough glass surface. The process parameters were varied in order to control the resultant glass roughness and it was found that the most critical was the Al deposition method. By using evaporation smooth U-shaped craters morphology and roughness up to 90 nm were created, whereas the sputtered films resulted in rough and porous textures with roughness until 145 nm. AZO grown over the U-shape crater morphology led to a double texture with haze values above 10% at 600 nm, transparency above 84%, and Rs-7 SI/sq whereas AZO over very rough glass resulted in a cauliflower-like surface with haze values >32% at 600 nm, Rs around 9.5 SI/sq and transmittance of 74%. A-Si:H solar cells were deposited on different AIT textures and an improvement of the short circuit current, as well as a reduction of the device reflectivity was achieved in all cases in comparison to the cells deposited on smooth glass textures. The second approach was to create a transparent and conducting upconverter to be used on top of the rear reflector of a thin film Si solar cell. For that purpose, ZnO was doped with Er and Yb ions and was post-annealed under different treatments. The unique spectral properties of rare earth (RE) elements due to their electronic configuration occur as a result of their intra 4f-4f shell transitions. In the case of Er, its excitation takes places at 1500 nm and 980 nm and the upconverted photons are emitted within the Si absorption range. Moreover, codoping with Yb can enhance the Er visible emission because they cooperate together due to the matching of their energy levels for k=980 nm. As deposited ZnO doped with rare earths (RE) was found to be transparent and conducting but not luminescent. RE ions need to be surrounded by 6 oxygen in a distorted octahedron to be optically active and REs replacing zinc in the ZnO lattice do not present this symmetry; hence, a post deposition treatment is needed. When the films were post-annealed in air, visible upconversion (UC) was seen at 660 nm under 980 nm laser excitation, however, the films become almost insulating. When the films were annealed in vacuum, lower UC luminescence was achieved, and the resistivity increased 1 order of magnitude. By using CW laser radiation, the electrical properties were maintained and high UC was observed. UC came from clusters of RE06 as well as from RE203 inside or outside the matrix. When annealing in air, in vacuum or by laser radiation, oxygen from the atmosphere bound to the RE to form RE oxides and/or RE06 complexes but just laser annealing was able to preserve the conductivity while producing optically active centers. / L'objectiu d'aquesta tesi és la millora de l'eficiència de les cèl•lules solars de silici en capa prima mitjançant l'estudi de nous mètodes per a l'aprofitament de la llum solar al dispositiu. El primer mètode consisteix en texturar el substrat de vidre per dispersar la llum incident i així incrementar l'absorció en la capa activa. El mètode emprat es la texturització induïda per alumini (AIT); que es basa en una reacció de reducció no uniforme entre el vidre i una capa prima d'alumini gràcies a un tractament tèrmic. Posteriorment els productes de la reacció s'eliminen mitjançant una solució basada en àcid i el resultat és un vidre transparent i texturat. S'ha fet un estudi de la rugositat en funció dels paràmetres del procés i s'ha aconseguit obtenir rugositats controlades i uniformes en superfícies de fins a 10x 10 cm2. Diferents textures s'han provat en cèl.lules solars de silici amorf i s'ha demostrat l'eficàcia d'aquestes en la millora del corrent respecte a les mateixes cèl•lules dipositades sobre vidre pla. El segon mètode estudiat és el fenomen de l'up-conversion que consisteix en la conversió de fotons de baixa energia (E<Eg), que normalment són transmesos, en fotons d'alta energia (E>Eg) que podran ser absorbits en la zona activa; així doncs s'ha intentat fer una capa conductora, transparent i amb propietats d'up-conversion per utilitzar com a contacte per a cèl• lules solars. Per aquest propòsit s'han estudiat capes conductores i transparents d'òxid de zinc dopat amb erbi i iterbi dipositades per polvorització catòdica sobre vidre. Com que les terres rares han d'estar envoltades d'oxigen per actuar com a centres òptics actius, i en les capes de ZnO:Er:Yb no es dóna aquesta configuració, les capes s'han hagut de sotmetre a diferents tractaments tèrmics, com escalfament en aire, en buit o escalfament amb làser. Escalfant en aire o en buit s'aconsegueix obtenir up-conversion però la conductivitat disminueix notablement, en canvi, escalfant amb radiació làser es possible de mantenir les propietats elèctriques i a més, activar òpticament les terres rares.

The search for analytical tools suitable for wide-scale application of DNA analysis is an hot research topic, although thanks to well-established microarray based technology, analysis of DNA sequences and SNP detection can be worked out through a fairly laboratory routine. DNA analysis has nowadays become of increasing interest for several different purposes, mainly thanks to the successful employment of microarray technology, characterized by high sensitiveness and high-throughput analysis, which rapidly advanced genetics leading to devel- opment of many fields of application of DNA analysis, which keeps high the trend in alternative technologies, which could overcome inherent limitations of microarrays technology. In this regard, many efforts have been spent to study electrochemical/electrical based detection strategies by means of which it could be possible to accomplish sensitive analysis by using portable equipments, cheaper and more practical than optical ones, and with scalable-devices compatibles with standard microelectronic processing. Emerging nano-probes with increased chemical-physical properties are considered with growing interest in DNA biosensors as ideal candidates to enhance electrochemical/electrical based detection systems. Among these, nano-gaps adjusted to fit DNA, or in general analyte molecules sizes, are very promising because they can enable direct electrical detec- tion schemes, thus providing a straightforward electronic analogue of the successful DNA microarray standard. Electrical properties of DNA have been the principal focus of many experimental and theoretical research, since early experimental founding confirmed an old hypothesis, for its relevance in the biological function of DNA, being related both with damage and base repair, but also for the appealing potential for biosensor and, in general, in bioelectronic applications. Thanks to its peculiar interactions, it allows versatile manipulations of the structure, compared to other organic and synthetic polymers which have been considered for such purposes. Even though many questions still are open on electrical properties of DNA, it is generally accepted that DNA's conductivity is intimately linked with details of the sequences involved, its length and the overall environment in which molecule is found. The sensitivity to structure's alteration, as that induced by the presence of a mutation, confirmed by experimental and theoretical works allows to exploit DNA electrical properties for biosensor applications. Relying on this agreed description of DNA electrical properties features, the general aim of this thesis was to explore the possibility of developing a platform for the direct transduction of DNA hybridization event based on a nano-gap device and electrical signaling enabled by long range electron transport through DNA molecules. / La detección de hibridación de cadenas de ADN es un reto relevante científicamente y tecnológicamente, que puede aprovechar de las posibilidades proporcionadas por los alcances en los procesos de nano fabricación y caracterización, inspiradores de la idea de una medicina en el punto de atención. El propósito de este trabajo es de establecer un sistema de detección de hibridación de ADN, y polimorfismo de un solo nucleótido (SNP), basado en la medida eléctrica de la reasistencia de un nano-gap funcional izado con el ADN diana. El desarrollo y test del sistema se ha llevado a cabo fijando diferentes objetivos. Un estudio preliminar de la literatura relacionada con las propiedades eléctricas del ADN se ha conducido con la finalidad de establecer el marco de factibilidad del proyecto. De acuerdo con los resultados de este estudio ha sido posible idear el sistema y optimizar su eficacia respeto a las experiencias reportadas. Fijar una estrategia de fabricación de los dispositivos capaz de proveer nano-gaps aptos a la medida de conductividad muy baja, según una rutina de fácil implementación y con alta reproducibilidad de los resultados. Estos se han caracterizados mediante el utilizo de diferentes técnicas basadas primariamente en métodos de detección Óptica y Eléctrica/Electro-química. Obtener la bio-funcionalización selectiva de los electrodos en el nano-gap testando y caracterizando métodos diferentes. Probar el principio de funcionamiento del sistema a través de la medida de la conductividad en los nano-gap durante las diferentes etapas de funcionalización con los bio-receptores y el DNA target. Optimizar el sensor testando su selectividad respeto a la presencia de mutaciones, la sensibilidad a medir diferentes concentraciones del target, y finalmente la posibilidad de regeneración del dispositivo después desnaturalización del ADN hibridado

Air pollution is a major environmental and public health concern, especially in urban areas where both emission sources and population are concentrated. The pollution sources and the evolution of aerosols and gaseous pollutants once emitted into the atmosphere depend on geographical, climatological and meteorological conditions of the study area. In the Western Mediterranean Basin, the coastal city of Barcelona (Spain) is characterized by a warm dry climate, scarce precipitation and high urban density, as well as being geographically constrained by the coastal range thus hindering the dispersion of pollutants. Within this context, the intensive SAPUSS (Solving Aerosol Problems by Using Synergistic Strategies) campaign developed in October 2010 in Barcelona consisted on concurrent aerosol measurements at different sites in the city region, with the aim of studying the aerosol temporal variability and spatial distribution, progressively moving away from urban aerosol sources. Several sites were selected: Road Site (RS) and Urban Background (UB) were located on ground levels, whereas Torre Mapfre (TM) and Torre Collserola (TC), representative of the urban/suburban environment were located at certain height (150 m a.s.l. and 415 m a.s.I., respectively). Finally, the Regional Background site (RB) located 50 km from the city allowed for the study of the transport of urban emissions outside the city. Results from simultaneous measurements of aerosol size distributions at the RS, UB, TC and RB with a Scanning Mobility Particle Sizer (SMPS) were studied after performing a k-means cluster analysis on the combined data sets. This allowed the classification of all size distributions in 9 clusters: three clusters account for traffic conditions (30% of the time), three account for background pollution (54%) and three described specific special cases (16%). Traffic emissions heavily impact the closest sites, and some of these particles evaporate when the air mass move away from the traffic hot spots. The analysis of long term SMPS data sets in the high insolation urban environments of Barcelona, Madrid, Brisbane, Rome and Los Angeles also by k-means clustering analysis revealed traffic and nucleation events as the two most relevant sources of ultrafine particles (44-63% and 14-19% of the time, respectively). Moreover, nucleation particles accounted for 21% of total N, evidencing the importance of nucleation processes to ultrafine particles concentrations in high insolation urban areas. The urban nucleation events consist on particles bursts starting around midday and lasting 3-4 hours while growing to 20-40 nm, opposite to regional nucleation “banana shape” events which usually grow to larger sizes. Regarding the composition of the PM1 fraction (PM mass levels below 1 μm) at the RS and UB during SAPUSS, a source apportionment PMF analysis was carried out. The resulting 9 factors could be broadly grouped in the following categories: road traffic (23-36% of PM1 mass), industrial and shipping emissions (42%), secondary aerosols (29%) and biomass burning (1%). The joint analysis of organic and inorganic species was able to identify a high number of sources resulting in in a more complete and realistic study of the aerosol sources in Barcelona. The study of the PM10 fraction (PM mass levels below 10 μm) at the RS, UB, TM and TC during SAPUSS by means of a PMF source apportionment study enabled the assessment of the spatial variability in vertical and horizontal levels. The 8 resulting factors accounted for primary traffic emissions (Exhaust and wear and Road dust, 19- 38% of PM10 mass), primary inorganic aerosols (Mineral dust and Aged marine, 28- 39%), industry (Heavy oil and Industrial, 5-7%) and secondary aerosols (Sulphate and Nitrate,28-36%). The main factors influencing the different sources concentration at each site were: proximity to the emission source, air mass origin and meteorological parameters. The complete study of aerosol fractions affecting the urban area of Barcelona and similar urban environments (Madrid, Brisbane, Roma and Los Angeles), from ultrafine to coarse particles, enables the identification of the main sources affecting each size fraction in particular and aerosols in general. Owing to the results obtained and the different techniques applied, recommendations regarding air pollution studies and air quality measures have been proposed. / La contaminació atmosfèrica en ambients urbans és motiu de preocupació pel seu impacte en el medi ambient i en la salut de la població. Les fonts d'emissió d'aerosols atmosfèrics i la seva evolució a l'atmosfera depenen de factors geogràfics així com de les condicions climàtiques i meteorològiques de l'àrea d'estudi. A la conca Mediterrània Occidental, i a la ciutat de Barcelona en particular, el clima càlid, l'escassa precipitació, l'alta densitat de població i determinats factors geogràfics que poden dificultar la dispersió dels contaminants i influenciar molt marcadament els nivells i composició dels aerosols. En aquest context es va desenvolupar la campanya intensiva SAPUSS (Solving Aerosol Problems by Using Synergistic Strategies) a Barcelona a l'octubre de 2010, que consistia en mesures simultànies d'aerosols a diversos llocs de la ciutat, amb l'objectiu d'estudiar la variabilitat espacial i temporal dels aerosols. L'estudi dels nivells d'aerosols en funció de la mida de les partícules a 4 ciutats més amb un clima d'alta insolació similar al de Barcelona (Madrid, Brisbane, Roma i Los Angeles) ha permès avaluar les fonts que afecten a la variabilitat de partícules ultrafines en aquests ambients urbans. En particular s'han estudiat les característiques dels episodis de nucleació urbans (formació de noves partícules), així com la seva freqüència. També s'han caracteritzat les principals fonts d'aerosols de diàmetre inferior a 1µm i 10 iim (PM1 i PM10, respectivament) en diverses ambients urbans de Barcelona durant SAPUSS. Això ha permès estudiar la variabilitat a nivells horitzontal i vertical dins l'atmosfera urbana. L'estudi de les fonts que afecten els aerosols de l' àrea urbana de Barcelona i ambients similars en funció de la seua mida (des de les ultrafines fins a les grolleres) ha permès identificar les principals fonts que afecten a cada fracció en particular i als aerosols en general i per tant proposar mesures aplicables per a l'avaluació i millora de la qualitat de l'aire.

From the fundamental point of view, NPs formed by MFe2O4 with (M= Co, Fe) are ideal system models to study the new magnetic phenomena associated with the so-called particle-like behaviour, which emerges from the size reduction towards the nanometre scale and contrasts with the well-established magnetic properties of their bulk-counterparts. It is well known that most of the particle-like behaviour and in general the large variability of the magnetic properties observed in this kind of nanomaterials are related to structural features of the NPs rather than being originated from intrinsic finite-size or surface effects, at least for NPs bigger than a few nanometers. These structural features, such as crystallographic defects, polycrystalline nature of the NPs, lack of crystallinity at the particle surface, etc., have strong influence on their magnetic properties and can be modified at will through the synthesis method. Therefore, whenever this particle-like behaviour is unwanted for applications with highly demanding requirements, the choice of a suitable synthesis method is of key importance to obtain NPs of high-crystalline quality. On the contrary, particle-like behaviour controlled by the crystalline nature of the NPs could be useful to tailor their magnetic properties for specific applications. Among the common synthesis methods, high-temperature decomposition of metal-organic precursors results the best alternative due to the remarkable final properties of the obtained NPs, such as narrow size distribution, high crystallinity and relatively simple tuning of their size and shape. So this will be the chemical route chosen in this work to study the capabilities of this synthesis method to control the final properties of the NPs through their nanostructure. In addition, to get a deeper insight in the magnetic and structural properties of those materials and to shed light on relevant issues that are still under discussion (dynamic response, magnetic frustration or inter¬particle interactions) it could be useful to combine experimental techniques enabling the characterization of the system from macroscopic scales towards single-particle structures. Within this framework, we present this work that is divided into three main parts. First, it is studied the effect of the concentration of two common reactants, involved in the thermal decomposition method, on the final properties of magnetic NPs based on iron oxides aiming at optimizing the synthesis procedure and getting a good control of the structure of the final product. In the second part, those NPs obtained in the former way are applied to demonstrate the crucial role of the nanostructure on the physical properties of nanoparticulate systems; specially, the strong interplay existent between structure and both magnetic frustration and interparticle interactions. Finally, in the third part, MFM experiments with an external applied magnetic field have been performed to directly observe the reversal of the magnetization of isolated particles and the dynamic behaviour of small aggregates.

In this thesis we have made progress on the study of higher dimensional gravity by focusing on the properties of black holes and branes and their dynamics. We have developed two main projects: • provide several maps between different spacetimes • determine the hydrodynamical behavior of fluids dual to some classes of black holes This work improves the current understanding of GR in spacetimes with general dimension and gives hints for holography in spacetimes different from AdS. Here we give a brief summary of the work developed underling the main results achieved. In Chapter 2, we introduce the techniques applied for studying black brane hydrodynamics. In the long-wavelength regime, black hole dynamics can be related to fluid dynamics and one can develop effective theories which capture the hydrodynamical description of such black holes. We review two of these: the fluid/gravity correspondence and the blackfold approach. We have hence learnt that black holes behave as fluids under certain circumstances. One can therefore compute the effective stress energy tensor associated to the fluid, extract the corresponding dissipative transport coefficients and possibly perform a stability analysis. In Chapter 3, we have introduced the AdS/Ricci flat correspondence, which is a relation between a class of AdS spacetimes and Einstein solutions with zero cosmological constant. Remarkably, we have developed an extension of such correspondence to spacetimes with positive cosmological constant, including scalar matter. This AdS/dS correspondence may possibly give hints to improve our understanding of holography in dS space. We have also found a new Kerr/AdS solution with hyperbolic horizon from a known Kerr/dS one through the map. The hydrodynamics of fluids using the KK dimensional reduction was studied in Chapter 4. Choosing a generic relativistic fluid, performing a boost in N internal dimensions, compactifing them and reducing on an N dimensional torus we have obtained a charged fluid with N charges. Therefore, we have investigated the variation of the transport coefficients, the shear and bulk viscosity, of the original theory and we were also able to compute the thermal conductivity. The same analysis has been applied to a particular fluid: the fluid dual to a black p-brane. We were able to compute the shear viscosity, bulk viscosity and thermal conductivity matrix for a black p-brane with N charges in the compact directions. This method is particularly interesting since it allows studying the hydrodynamics of charged objects without performing a perturbative analysis but only applying dimensional reduction techniques. Using the AdS/Ricci flat correspondence we have checked that our mapped transport coefficients coincide with the ones obtained for a known charged AdS black branes. In Chapter 5 we have investigated the hydrodynamics properties of fundamentally charged (dilatonic) black branes and branes with Maxwell charge smeared over their worldvolume. We have determined the dissipative behavior of the effective fluids associated to those branes in terms of the transport coefficients of the effective stress energy tensor. Studying the response to small long-wavelength perturbations we have analyzed the dynamical stability of both classes of charged black branes. We have moreover modified the AdS/Ricci flat correspondence to include charged cases using a non-diagonal KK reduction. In this thesis we have shown how higher dimensional gravity is surprisingly rich of new phenomena and bizarre features. Playing with spacetime dimension is the key to probe GR. Hopefully, we will able to improve our comprehension of this mysterious and powerful theory. Holography is an extremely useful tool available for this aim. Mapping apparently unrelated theories living in different number of dimensions has revealed various successful predictions and results but above all opens new perspective for our perception and understanding of GR. / Esta tesis se centra principalmente en el estudio de la gravedad en dimensiones superiores con un enfoque en las relaciones entre diferentes tipos de espaciotiempo y el análisis y caracterización de agujeros negros. Para este último objetivo hemos desarrollado y adaptado teorías efectivas que nos permiten estudiar la dinámica de agujeros negros en ciertos regímenes. Hemos presentado dos de ellas: la "fluid/gravity correspondence" y el metodo de "blackfold". Se puede demostrar entonces que los agujero negros admiten una descripción hidrodinámica y se puede calcular el tensor energía-impulso asociado al fluido dual al agujero negro y extraer los coeficientes de transporte al primer orden en derivadas. Hemos utilizado estas técnicas para analizar propiedades hidrodinámicas de branas negras en el caso en que las branas llevan cargas de diferentes tipos. En particular, consideramos los casos en que la brana negra está acoplada a un potencial de (p+1)-forma, que llamamos brana con carga fundamental, y brana acoplada a un campo de Maxwell. También hemos investigado las propiedades de estabilidad de estos sistemas hidrodinámicos . Otra línea de investigación es el estudio de la hidrodinámica de fluidos utilizando la reducción dimensional de Kaluza Klein. Empezamos considerando un fluido genérico y luego hemos particularizado el cálculo al fluido dual a una p-brana negra. Hemos investigado como varían los coeficientes de transporte de la teoría inicial como la "shear and bulk viscosity" y además hemos conseguido calcular la matriz de conductividad térmica. Como último proyecto hemos desarrollo mapas entre espaciotiempos diferentes. En particular hemos extendido el "AdS/Ricci-flat correspondence" para espacios de Einstein con curvatura positiva y negativa. Una vez derivado el mapa, lo hemos aplicado a espacios de Sitter (dS) y AdS y a agujeros negros de Schwarzschild-dS/AdS. Además, hemos estudiado perturbaciones en la frontera de AdS, que a través del mapa nos dan sugerencias sobre una posible construcción de holografía en espacio de dS. De hecho, la frontera de un espacio asintóticamente AdS se mapea en una brana en el centro de dS y las perturbaciones cerca de la frontera tienen como fuente un tensor energía-impulso confinado en esta brana.