Ultrafast pulses allow observation of molecular dynamics with femtosecond time resolution through pump probe experiments. However, averaging over an ensemble of molecules tends to wash out phase sensitive information, necessary to probe quantum effects, due to the intrinsic inhomogeneity in molecular conformations, orientations and interactions that lead to unique potential energy landscapes for each molecule. It is therefore important to go beyond the ensemble average when looking at quantum dynamics of organic systems at room temperature, and resolve the behaviour of specific molecules on an individual basis. In this thesis, we show the creation, manipulation and observation of ultrafast coherent effects in single molecules at room temperature, and resolve a certain measure of environmental influence on the specific dynamics of each molecule. Moreover, we apply this insight to investigate a functional light harvesting biosystem, and lay the basis for a technique that has the time and space resolution required to observe these systems in vivo. In chapter 1, we introduce the concepts and techniques the research in this thesis is built on. In chapter 2, we treat the possibility of controlling ultrafast pulses at the high-NA diffraction limit, and come to conclusions about the procedure to follow there that hold for all pulse-shaping experiments. We show in proof of principle experiments that we can control the ultrafast characteristics of optical pulses in nanometric excitation volumes. In chapters 3 and 4 we report the creation, detection and control of ultrafast quantum dynamics in single organic molecules at room temperature. We show that manipulation of superposition states is possible in these systems within a coherence dephasing time of ~50 fs. This leads to the first observation of rabi-oscillations in room temperature single molecules, to ultrafast operation of an organic qubit, and to the creation of non-stationary superposition states (vibrational wavepackets). We probe the influence of the local environment on the composition and dynamics of these wavepackets and show we can optimize the state preparation protocol for each individual molecule in its own nanoenvironment, leading to high fidelity coherent control. In these chapters we lay out the proof of principle work of detecting the quantumdynamics of a complex system in interaction with its environment at room temperature. In chapter 5 we discuss application of these techniques to the investigation of long lived coherence in photosynthetic systems. We show that electronic coherence between different rings of the LH2 system persists to time scales of 100s of femtoseconds at room temperature. Moreover we show that the energy transfer pathways in LH2 adapt to environmentally induced changes in the molecule and that the nature of the transfer remains coherent for each pathway, providing strong evidence that coherent energy transfer is the optimum process for energy transfer in photosynthesis. Finally, in chapter 6 we take the technical development one step further and report on the creation of a framework based on plasmonic antennas that allows for control of the amplitude-phase characteristics in nanometric sized hotspot fields. We show for the first time that the ultrafast characteristics of plasmonic hotspots can directly be engineered through design of the plasmonic system and experimentally demonstrate two much-anticipated examples: a sub-diffraction resolution phase shaper and an ultrafast plasmonic switch for pump probe experiments. The results presented in this thesis form the first creation and observation of ultrafast coherent dynamics in individual molecular systems at room temperature. This is a necessary step to be able to do true quantum tomography in complex systems, resolve the influence of the environment on molecular dynamics, and investigate the physics that determines evolutionary optimization and functionality in biomolecules.

Physical and mathematical models are extremely useful to understand key processes in population and evolutionary dynamics. Such models allow the study of many diverse features in spatial systems such as front propagation, the evolution of the population number density, interactions between species (or individuals), the evolution of strategies, etc. This thesis is devoted to several physical models describing spatial systems. The first model focuses on the effects of the population structure in two-dimensional invasive fronts. An expression for the front speed is derived from the equations for structured populations. The second model is devoted to the study of Vesicular Stomatitis Virus infections. In this case, reaction-diffusion equations are used to describe the interactions between uninfected cells, infected cells and virus populations. In the last model, the Prisoner's Dilemma game is used to study the evolution of cooperation and defection strategies / Els models físics i matemàtics són de gran utilitat a l'hora d'entendre processos clau en la dinàmica poblacional i evolutiva. Aquests models permeten l'estudi de característiques molt diverses dels sistemes espacials, com són la propagació de fronts, l'evolució de la densitat de població, les interaccions entre espècies (o individus), l'evolució d'estratègies, etc. Aquesta tesi presenta diversos models físics que descriuen sistemes espacials. El primer model estudia els efectes de l'estructura de la població en fronts invasius bidimensionals. Una expressió per la velocitat del front és derivada de les equacions per a poblacions estructurades. El segon model es consagra a l’estudi d’infeccions del Vesicular Stomatitis Virus. En aquest cas, s’utilitzen equacions de reacció-difusió per descriure les interaccions entre les poblacions de cèl·lules no infectades, cèl·lules infectades i virus. A l’últim model, el joc del Dilema del Presoner s'utilitza per estudiar l'evolució d'estratègies de cooperació i deserció

The next generation of particle colliders will be characterized by linear lepton colliders, where the collisions between electrons and positrons will allow to study in great detail the new particle discovered at CERN in 2012 (presumably the Higgs boson). At present time, there are two alternative projects underway, namely the ILC (International Linear Collider) and CLIC (Compact LInear Collider). From the detector point of view, the physics aims at these particle colliders impose such extreme requirements, that there is no sensor technology available in the market that can fulfill all of them. As a result, several new detector systems are being developed in parallel with the accelerator. This thesis presents the development of a GAPD (Geiger-mode Avalanche PhotoDiode) pixel detector aimed mostly at particle tracking at future linear colliders. GAPDs offer outstanding qualities to meet the challenging requirements of ILC and CLIC, such as an extraordinary high sensitivity, virtually infinite gain and ultra-fast response time, apart from compatibility with standard CMOS technologies. In particular, GAPD detectors enable the direct conversion of a single particle event onto a CMOS digital pulse in the sub-nanosecond time scale without the utilization of either preamplifiers or pulse shapers. As a result, GAPDs can be read out after each single bunch crossing, a unique quality that none of its competitors can offer at the moment. In spite of all these advantages, GAPD detectors suffer from two main problems. On the one side, there exist noise phenomena inherent to the sensor, which induce noise pulses that cannot be distinguished from real particle events and also worsen the detector occupancy to unacceptable levels. On the other side, the fill-factor is too low and gives rise to a reduced detection efficiency. Solutions to the two problems commented that are compliant with the severe specifications of the next generation of particle colliders have been thoroughly investigated. The design and characterization of several single pixels and small arrays that incorporate some elements to reduce the intrinsic noise generated by the sensor are presented. The sensors and the readout circuits have been monolithically integrated in a conventional HV-CMOS 0.35 μm process. Concerning the readout circuits, both voltage-mode and current-mode options have been considered. Moreover, the time-gated operation has also been explored as an alternative to reduce the detected sensor noise. The design and thorough characterization of a prototype GAPD array, also monolithically integrated in a conventional 0.35 μm HV-CMOS process, is presented in the thesis as well. The detector consists of 10 rows x 43 columns of pixels, with a total sensitive area of 1 mm x 1 mm. The array is operated in a time-gated mode and read out sequentially by rows. The efficiency of the proposed technique to reduce the detected noise is shown with a wide variety of measurements. Further improved results are obtained with the reduction of the working temperature. Finally, the suitability of the proposed detector array for particle detection is shown with the results of a beam-test campaign conducted at CERN-SPS (European Organization for Nuclear Research-Super Proton Synchrotron). Apart from that, a series of additional approaches to improve the performance of the GAPD technology are proposed. The benefits of integrating a GAPD pixel array in a 3D process in terms of overcoming the fill-factor limitation are examined first. The design of a GAPD detector in the Global Foundries 130 nm/Tezzaron 3D process is also presented. Moreover, the possibility to obtain better results in light detection applications by means of the time-gated operation or correction techniques is analyzed too. / Aquesta tesi presenta el desenvolupament d’un detector de píxels de GAPDs (Geiger-mode Avalanche PhotoDiodes) dedicat principalment a rastrejar partícules en futurs col•lisionadors lineals. Els GAPDs ofereixen unes qualitats extraordinàries per satisfer els requisits extremadament exigents d’ILC (International Linear Collider) i CLIC (Compact LInear Collider), els dos projectes per la propera generació de col•lisionadors que s’han proposat fins a dia d’avui. Entre aquestes qualitats es troben una sensibilitat extremadament elevada, un guany virtualment infinit i una resposta molt ràpida, a part de ser compatibles amb les tecnologies CMOS estàndard. En concret, els detectors de GAPDs fan possible la conversió directa d’un esdeveniment generat per una sola partícula en un senyal CMOS digital amb un temps inferior al nanosegon. Com a resultat d’aquest fet, els GAPDs poden ser llegits després de cada bunch crossing (la col•lisió de les partícules), una qualitat única que cap dels seus competidors pot oferir en el moment actual. Malgrat tots aquests avantatges, els detectors de GAPDs pateixen dos grans problemes. D’una banda, existeixen fenòmens de soroll inherents al sensor, els quals indueixen polsos de soroll que no poden ser distingits dels esdeveniments reals generats per partícules i que a més empitjoren l’ocupació del detector a nivells inacceptables. D’altra banda, el fill-factor (és a dir, l’àrea sensible respecte l’àrea total) és molt baix i redueix l’eficiència detectora. En aquesta tesi s’han investigat solucions als dos problemes comentats i que a més compleixen amb les especificacions altament severes dels futurs col•lisionadors lineals. El detector de píxels de GAPDs, el qual ha estat monolíticament integrat en un procés HV-CMOS estàndard de 0.35 μm, incorpora circuits de lectura en mode voltatge que permeten operar el sensor en l’anomenat mode time-gated per tal de reduir el soroll detectat. L’eficiència de la tècnica proposada queda demostrada amb la gran varietat d’experiments que s’han dut a terme. Els resultats del beam-test dut a terme al CERN indiquen la capacitat del detector de píxels de GAPDs per detectar partícules altament energètiques. A banda d’això, també s’han estudiat els beneficis d’integrar un detector de píxels de GAPDs en un procés 3D per tal d’incrementar el fill-factor. L’anàlisi realitzat conclou que es poden assolir fill-factors superiors al 90%.

This thesis presents population dynamics models that can be applied to predict the rate of spread of the Neolithic transition (change from hunter-gathering to farming economics) across the European continent, which took place about 9000 to 5000 years ago. The first models in this thesis provide predictions at a continental scale. We develop population dynamics models with explicit kernels and apply realistic data. We also derive a new time-delayed reaction-diffusion equation which yields speeds about a 10% slower than previous models. We also deal with a regional variability: the slowdown of the Neolithic front when reaching the North of Europe. We develop simple reaction-diffusion models that can predict the measured speeds in terms of the non-homogeneous distribution of pre-Neolithic (Mesolithic) population in Europe, which were present in higher densities at the North of the continent. Such models can explain the observed speeds. / Aquesta tesi presenta models de dinàmica de poblacions que es poden aplicar a la transició del neolític (canvi d’una societat de caçadors-recol•lectors a una societat agrícola) per tal de predir-ne la velocitat d’expansió al continent europeu, que va tenir lloc fa entre 9000 i 5000 anys. Els primers models d’aquesta tesi proporcionen prediccions a escala continental. Desenvolupem models de dinàmica poblacional incloent kernels explícits i dades realistes. També demostrem una nova equació de reacció-difusió amb retard temporal la qual prediu velocitats fins a un 10% més lentes que en demostracions anteriors. També tractem una variabilitat regional: la disminució del ritme d’expansió del front neolític al nord d’Europa. Desenvolupem models de reacció-difusió senzills que tenen en compte la distribució no homogènia de poblacions preneolítiques (mesolítiques) a Europa, les quals eren presents amb majors densitats al nord del continent. Aquests models poden predir les velocitats mesurades.

En la tesis doctoral Convección térmica en un anillo cilíndrico en rotación se estudian diferentes aspectos de la dinámica lineal y no lineal de un fluido Boussinesqconfinado en un anillo cilíndrico, en rotación alrededor de su eje de simetría y sometido a la acción de un campo gravitatorio y de un gradiente de temperaturadesestabilizador en la dirección radial. Su principal objetivo es analizar la influencia de la rotación, de la geometría cilíndrica y de las condiciones de contorno en la dinámica de un sistema físico que constituye un modelo simple de la convección libre en las capasecuatoriales de las atmósferas planetarias y estelares. En eltrabajo, que se enmarca en el campo de la Simulación Numérica en Dinámica de Fluidos, se utilizan técnicas espectrales para hacer una simulación numérica directade las ecuaciones de Navier-Stokes.El estudio se inicia analizando la estabilidad lineal del estado conductivo imponiendo condiciones de contorno stress-free en las superficies horizontales del anillo.Cuando la rotación es alta, la convección se inicia en forma de columnas de Taylor estacionarias, que son soluciones bidimensionales formadas por estructuras alineadas con el eje del anillo. Para rotaciones bajas, existen dos tipos diferentes de modos convectivos: rollosconvectivos bidimensionales estacionarios y celdastridimensionales con precisión. Este último tipo de solución no se puede encontrar si no se tiene en cuenta la curvatura de la capa. La dinámica cambia cuando seconsideran condiciones de contorno no-slip en las tapas. En el caso de rotaciones bajas, las condiciones de contorno fuerzan que los modos críticos seantridimensionales y se produce un aumento en el número de Rayleigh necesario para que se inicie la convección. A medida que la rotación aumenta, las solucionestridimensionales se alargan progresivamente hasta que se forman columnas de Taylor prácticamente bidimension.

Esta tesis se ha estructurado en cuatro partes principales: 1) Introducción. Se ha hecho un repaso de la bibliografía existente referente a incendios de charcos de líquido y equipo sujeto a la acción directa de la llama. Se ha realizado también un análisis histórico basado en incendios. 2) Experimentación. Se describe la instalación experimental utilizada para llevar a cabo experimentos a gran escala (charcos de 4 y 12 m2 bajo un depósito de 3m de longitud y 1’2m de diámetro)3) Análisis de los resultados. Se ha analizado la reproducibilidad de las pruebas, el calor total y de convección emitidos, y la evolución de las temperaturas del depósito durante el estado transitorio. Se ha definido un parámetro llamado “Factor de obstaculización” , para cuantificar el efecto que un obstáculo produce sobre el calor total emitido.4) Modelización. Se ha desarrollado una modelización para calcular la medida de la llama en la altura y tiempo. Se ha propuesto un modelo matemático que permite determinar la radiación incidente sobre la superficie del depósito, así como la temperatura alcanzada por este.

Despite the large amount of research which has been conducted on turbulent flows, a full understanding of their dynamics as well as the mechanisms involved in the onset of turbulence is still missing. Experimental studies of transition to turbulence are generally carried out in setups with simple geometries which allow isolating the physical mechanisms underlying the dynamics. However, in spite of the simplicity of the models, the problem is extremely complex and it is difficult to reach definitive conclusions on many of the observed dynamical features. Since a few decades ago numerical simulations complement laboratory experiments, significantly accelerating the scientific progress and improving the quality of investigations. In order to compare experimental and numerical results, it is essential to carry out a calibration process in which the possible discrepancies are identified and adjustments (typically modifications in the numerical formulation of the problem) are made in order to minimize them as far as possible. The results of this thesis are primarily intended as an aid in the calibration process of rotating flows in presence of a temperature gradient, which are of great interest in multiple industrial, geophysical and astrophysical applications. Numerical simulations of the flow enclosed in rotating cylindrical and annular cavities subjected to either a vertical or horizontal temperature gradient (rotating Rayleigh--Bénard convection and laterally heated Taylor--Couette flows) have been performed. Several techniques of numerical analysis such as direct simulation of the governing equations, linear stability analysis, continuation methods or time--series analysis have been used for the completion of the thesis. Three sources of discrepancies between experimental and numerical results have been investigated. First,we show a detailed study of how symmetry-breaking due to experimental imperfections may modify the dynamics of the idealized systems used in numerical simulations. An example in rotating Rayleigh-Bénard convection is illustrated in which simulations only capture the experimental behavior when this symmetry-breaking is introduced in the formulation of the problem, i.e. through the boundary conditions. Second, we consider the influence of centrifugal effects which are often neglected in theoretical and numerical studies of rotating flows. This may result in substantial differences with experimental results in those ranges of parameters in which centrifugal buoyancy plays a significant dynamical role. To this extent, we provide a straightforward Boussinesq-type approximation which allows for considering centrifugal effects in an inertial reference frame, including secondary effects stemming from differential rotation or strong internal vorticity, which had not been previously considered in any other formulation. Third, the influence of axial end walls in the dynamics of simple models for the study of baroclinic flows is discussed. The objective of this study is to identify the degree to which simulations in axially periodic systems, with a lower computational cost, can be used to reproduce experimental results. A strong stabilizing effect, which increases significantly at high temperature differences between the cylinders, results from the boundary layers and cause large discrepancies with the onset of instability in the case of axially periodic boundary conditions. Finally, a numerical study of a recently reported experimental bifurcation scenario in isothermal Taylor-Couette flow is also presented. We focus on the dynamics of flow patterns characterized by large amplitude oscillations that are localized only in some vortex-pairs. In this case, experimental and numerical results are in full agreement. / A pesar de que se han llevado a cabo numerosos estudios en el ámbito de los fluidos turbulentos, su dinámica así como las causas que originan la turbulencia continúan planteando multiples interrogantes. Los experimentos sobre transición a la turbulencia se realizan generalmente en instalaciones con geometrías sencillas que permiten aislar los mecanismos físicos responsables de los cambios dinámicos en el sistema. Sin embargo, el problema es muy complejo y, a pesar de la simplicidad de los experimentos, es muy dificil alcanzar conclusiones definitivas sobre muchos de los fenómenos que se observan. Desde hace unas décadas las simulaciones numéricas complementan el trabajo de laboratorio, lo que ha acelerado notablemente el progreso de las investigaciones y también mejorado su calidad. Para comparar de una manera eficaz los resultados numéricos y experimentales es esencial llevar a cabo un proceso de calibración, en el cual las posibles discrepancias se identifican y se realizan ajustes (normalmente modificaciones en la formulación del problema) para minimizarlas al máximo. Los resultados de esta tesis pretenden servir de ayuda en el proceso de calibración para el caso de fluidos en rotación y sometidos a un gradiente de temperatura, los cuales son de gran interés en aplicaciones industriales, geofísicas y astrofí­sicas. Se han realizado simulaciones numéricas del flujo contenido en cavidades cilíndricas y anulares, sometidos a gradientes térmicos tanto verticales como horizontales (convección de Rayleigh--Bénard rotativa y flujos de Taylor--Couette con calentamiento lateral). Entre las técnicas de ánalisis numérico que se han empleado para la realización de la tesis se encuentran la simulación directa de las ecuaciones, análisis de estabilidad lineal, métodos de continuación o análisis de series temporales. Se han investigado tres fuentes de discrepancias entre resultados numéricos y experimentales. En primer lugar mostramos un detallado estudio sobre como una rotura de simetrí­a debida a imperfecciones en un experimento fí­sico modifica la dinámica de los sistemas idealizados que se emplean en simulaciones numéricas. Un ejemplo en el caso de convección de Rayleigh--Bénard rotativa es ilustrado en el cual las simulaciones capturan el comportamiento experimental cuando la rotura de simetría se introduce en la formulación del problema a través de las condiciones de contorno. En segundo lugar, consideramos la influencia de los efectos centrífugos, generalmente despreciados en el estudio de fluidos en rotación. Esto puede ocasionar importantes diferencias con los resultados experimentales en aquellos casos dónde las fuerzas centrí­fugas desempeñen un papel relevante. Por este motivo proporcionamos una sencilla aproximación de tipo Boussinesq que permite considerar los efectos centrí­fugos en un sistema de referencia inercial, incluyendo efectos secundarios debidos a la rotación diferencial o una fuerte vorticidad interna, los cuales no habí­an sido considerados en ninguna formulación anterior. Tercero, discutimos la influencia de las tapaderas en la dinámica de modelos simples para el estudio de flujos baroclí­nicos. El objetivo es identificar el grado en que simulaciones axialmente periódicas, con un menor coste computacional, pueden ser usadas para reproducir resultados experimentales. En este problema se observa que las capas lí­mite producen un fuerte efecto estabilizador, que aumenta a medida que se incrementa el gradiente térmico, y provoca grandes discrepancias con respecto al origen de inestabilidad en el caso periódico. Finalmente, se ha realizado un estudio numérico de un escenario de bifurcación que ha sido reportado recientemente en experimentos sobre flujos de Taylor--Couette isotérmicos. La particularidad de este problema es la aparición de estados globales caracterizados por oscilaciones de gran amplitud localizadas en algunos de sus vortices. Los resultados experimentales y numéricos concuerdan.

The atmospheric boundary layer is the part of the troposphere influenced by the presence of the surface, and where most weather phenomena occur. During the day, with fair weather conditions, a convective boundary layer exists. In contrast, during the night, a stable boundary layer appears. It is important to note that the evolution from a convective boundary layer to a stable boundary layer and vice versa happens through two transitional processes. Due to its complexity and the rapid variability, there is a lack of studies about the morning or afternoon/evening transitions. This thesis wants to solve some of the uncertainties related with the morning and afternoon/evening transition of the atmospheric boundary layer. It is based on observations from the project Boundary-Layer Late Afternoon and Sunset Turbulence (BLLAST) and numerical simulation experiments developed with mixed-layer and large-eddy simulation models. In this thesis, we develop an analysis focused on the role played by the residual layer during the morning transition and by the large-scale subsidence on the evolution of the boundary layer. DALES numerical experiments that include the residual layer are capable of modeling the observed sudden increase of the boundary-layer depth during the morning transition and the subsequent evolution of the boundary layer. These simulations show a large increase in the entrainment buoyancy flux when the residual layer is incorporated into the mixed layer. We also examine how the inclusion of the residual layer above a shallow convective boundary layer modifies the turbulent kinetic energy budget. Large-scale subsidence mainly acts when the boundary layer is fully developed and, for the studied day, it is necessary to consider this in order to reproduce the afternoon observations. Finally, we also investigate how CO2 stored the previous night in the residual layer plays a fundamental role in the evolution of the CO2 mixing ratio during the following day. Moreover, we hypothesize that during the evening transition a delay exists between the instant when the buoyancy flux goes to zero and the time when the local gradient of the virtual potential temperature changes sign contradict the assumption in which are base the gradient-based turbulence models. The results from this work confirm and quantify a flux-gradient delay. Specifically, the observed values of the delay are between approximately 30 and 80 min. The existence of the delay and its duration can be explained by considering the convective time and the competition of forces associated with the classical Rayleigh-Bénard problem. This combined theory predicts that the last eddy formed should produce a delay when the sensible heat flux changes sign during the evening transition. It appears that this last eddy is decelerated through the action of turbulent momentum and thermal diffusivity, and that the delay is related to the convective turnover time. Observations indicate that, as horizontal shear becomes more important, the delay time apparently increases to values greater than the convective turnover time. Finally, we study the existence and characteristics of Lifted Temperature Minimum (LTM) during the evening transition. The study shows that LTM can be detected in calm conditions already during day¿night transition, several hours earlier than the usual time of occurrence reported by previous works. These conditions are fulfilled when weak synoptic forcing exists and the local flow shifts from valley to mountain breeze in a relatively complex orography. Under these special conditions, turbulence becomes a crucial parameter to determine the ideal conditions for observing LTM. Additionally, the correlation of longwave radiation measured at 0.8 m and estimated at the ground varies when the LTM is observed. Therefore, LTM is also related to a change in the atmospheric radiative characteristics under calm conditions. / La capa límit atmosfèrica és la part de la troposfera influenciada per la presència de la superfície terrestre, i on es produeixen la majoria dels fenòmens meteorològics. Durant el dia, en condicions de bon temps, es forma una capa límit convectiva. En canvi, durant la nit, apareix una capa límit estable. L'evolució d'una capa límit convectiva a una capa límit estable i viceversa passa a través de dos processos de transició. A causa de la seva complexitat i la ràpida variació, hi ha una manca d'estudis sobre les transicions del dia a la nit o viceversa. Aquesta tesi vol resoldre algunes de les incerteses relacionades amb les transicions de la capa límit atmosfèrica. La tesi es basa en les observacions obtingudes durant la campanya Boundary-Layer Late Afternoon and Sunset Turbulence i simulacions numèriques desenvolupades amb dos models: un model de capa de mescla i un model de tipus large-eddy simulation. Primerament, es desenvolupa una anàlisi centrada en el paper de la capa residual durant la transició entre la nit i el dia i en el paper de la subsidència en l'evolució de la capa límit. Les simulacions que inclouen la capa residual són capaces de modelar l’augment sobtat de l’alçada de la capa límit durant aquesta transició i també la posterior evolució de la capa límit. Aquestes simulacions mostren un gran augment del flux que entra des de la atmosfera lliure quan la capa residual s'incorpora a la capa convectiva. També s’analitza els efectes de considerar la capa residual en el balanç d'energia cinètica turbulenta. La subsidència actua principalment quan la capa límit està totalment desenvolupada i , pel dia seleccionat, cal tenir-la en compte per tal de reproduir les observacions durant la tarda. Finalment, també investiguem com el diòxid de carboni (CO2) emmagatzemat a la capa residual juga un paper fonamental en l'evolució del CO2 durant el dia. En segon lloc, s'analitza el fet de que durant la transició del dia a la nit hi ha una demora entre el moment en què el flux de flotació esdevé zero i el moment en què el gradient de la temperatura potencial virtual canvia de signa. Aquest fet contradiu el supòsit en què estan basats els models de simulació. Els resultats d'aquest treball confirmen i quantifiquen aquest demora. Específicament, els valors observats de la demora són aproximadament d'entre 30 i 80 min. L'existència de la demora i la seva durada es pot explicar a través del temps convectiu i de les forces associades amb el problema de Rayleigh-Bénard. La teoria proposada considera que l'últim remolí format abans de cessament del flux de superfície produeix el retard en el canvi de signe del gradient del flux de calor. Alhora aquest últim remoli es pot frenar a través de l'acció de la viscositat i la difusivitat tèrmica, i el retard està relacionat amb el temps que dura el recorregut del remolí. Les observacions indiquen que, com més important és el cisallament de vent horitzontal, el temps de retard aparentment augmenta a valors més grans que el temps convectiu. Finalment , s'estudia l'existència i característiques d'un Mínim Elevat de Temperatura (LTM) durant la transició entre el dia i la nit. L'estudi mostra que el LTM es pot detectar en condicions de calma durant aquesta transició hores abans de l'hora d’observació descrita en els treballs anteriors. Aquestes condicions de calma es compleixen quan les forces sinòptiques són febles i el vent local canvia de direcció en una orografia relativament complexa (durant el dia prové de la vall i durant la nit de la muntanya). En aquestes condicions especials, la turbulència es converteix en un paràmetre fonamental per determinar les condicions ideals per a l'observació de LTM. A més, la correlació de la radiació d'ona llarga mesurada a 0,8 m i estimada a terra varia quan s'observa el LTM. Per tant, el LTM també està relacionada amb un canvi de les característiques radiatives de l’atmosfera en condicions de calma.

Els aliatges magnètics amb memòria de forma es caracteritzen per presentar tant la transformació estructural austenita – martensita com la magnètica (ferromagnetisme – paramagnetisme). El conjunt de propietats els fa candidats a ser emprats en aplicacions com a sensors, actuadors o en sistemes de refrigeració magnètica. Entre els aliatges tipus Heusler que presenten aquest comportament el sistema més estudiat és el Ni-Mn-Ga. Nogensmenys, els darrers anys s’ha desenvolupat l’interès en aliatges sense gal•li, com ara els del sistemes Ni-Mn-Sn i Ni-Mn-In. A la present tesi s’han produït i caracteritzat aliatges d’ambdós sistemes amb diverses especificitats: a) l’element majoritari és el manganès (a la bibliografia tradicionalment ho és el níquel), b) s’ha treballat amb diferents morfologies (massissa, cinta, pols), c) les cintes han estat sotmeses a tractament tèrmic i d) les composicions dels aliatges amb indi o amb estany són equivalents. Les composicions concretes són: Mn50Ni50-xSnx i Mn50Ni50-xInx(x= 5, 7,5 o 10 % atòmic). Els capítols 4 i 5 recullen el conjunt de resultats experimentals i la seva anàlisi i discussió. L’estudi s’ha centrat principalment en la transformació estructural que és reversible i amb histèresis. La transformació ha estat detectada amb els aliatges produïts en forma massissa o de cinta. En canvi, la mòlta mecànica indueix canvis estructurals que inhibeixen la transformació en els aliatges amb forma de pols. Per altra banda, s’ha constatat una disminució de les temperatures de transformació a mesura que augmenta el contingut en estany o indi (coincideix amb una disminució del paràmetre e/a relacionat amb el nombre d’electrons als orbitals externs). En el sistema amb estany aquesta relació és lineal. Aquest tipus de dependència ha de permetre seleccionar la composició adient per a desenvolupar aliatges amb la transformació dins d’un interval de temperatures desitjat. L’anàlisi calorimètrica ens permet establir que els valors més elevats en les variacions d’entalpia i d’entropia es donen en el massís en els aliatges amb indi i a les cintes sense tractar tèrmicament en els aliatges amb estany. Malgrat la fragilitat de les cintes, a les mostres amb estany ha estat possible realitzar mesures dilatomètriques. Respecte la resposta termomagnètica, aquesta és similar a la dels aliatges dels mateixos sistemes rics en níquel. / Ferromagnetic shape memory alloys are characterized by both the structural austenite to martensite transformation and also by the magnetic transition from ferromagnetism to paramagnetism. The set of properties make them candidates for use in several applications such as sensors, actuators or magnetic refrigeration systems. Among the Heusler type alloys that exhibit this behaviour the most studied system is the Ni-Mn-Ga. However, it has recently been increased the interest for gallium free alloys, such as systems Ni-Mn-Sn and Ni-Mn-In. In the present thesis have been produced and characterized alloys from both systems with different specificities: a) the majority element is manganese (in the literature it is usually nickel), b) alloys with different morphologies were produced (bulk, ribbon, powder), c) the ribbon shave been annealed and d) the compositions of the alloys with indium or tin are equivalent. The specific compositions are: Mn50Ni50-xSnx and Mn50Ni50-xInx (x= 5, 7.5 or 10 atomic %). The set of experimental results are reported in chapters 4 and 5, together with its analysis and discussion. The study has been focused mainly on the structural transformation that is reversible and hysteretic. Transformation has been detected in the massive alloys and also in ribbons. However, the mechanical grinding has induced structural changes which inhibit transformation in alloys with powder morphology. Moreover, it was found a decrease in transformation temperatures with increasing the content of tin or indium (it coincides with a decrease of the parameter/a related to the number of electrons in outer orbits). In the system with tin this relationship is linear. This dependence must allow the selection of the appropriate composition for the production of alloys with transformation within a desired temperature range. The calorimetric analysis has established that the highest values in the entropy and enthalpy changes occur in bulk alloys (indium samples) and in as quenched ribbons (tin samples). Moreover, despite the fragility of the ribbons dilatometry experiments has been performed in tin alloys. With respect to the thermo magnetic response, it is similar to that of alloys of the same systems but nickel rich.

Despite the success of quantum mechanics in predicting the outcomes of experiments in many branches of physics, the foundations of the theory have remained subject of research and dispute. At the basis of this struggle with the theory lie the phenomena of nonlocality and entanglement. Since it was first predicted by Bell in 1964, nonlocality was not only verified in numerous experiments, but also identified as a useful resource for quantum information processing. Thus, the study of nonlocality is important both from a fundamental point of view and with respect to new applications in quantum information theory, such as secure cryptography and randomness generation. The identification of entanglement as a resource for quantum information led to a strong theoretical effort devoted to its characterisation and detection. Many of the resulting mathematical tools find application in several domains of physics. Although the only known way to create nonlocal correlations is to measure entangled quantum systems, it has been shown that entanglement and nonlocality constitute two inequivalent properties. Therefore, in the light of the success of entanglement theory, it is of interest to also devise a resource theory of nonlocality. The task of this thesis is to develop such a theoretical framework for the characterisation of nonlocality as a resource. To gain a better understanding of nonlocal correlations it will be necessary to investigate correlation scenarios that go beyond the situation originally considered by Bell. In doing so, this thesis provides new description of nonlocality that also have implications for the characterisation of quantum correlations and the detection of new forms of nonlocality. The first question we address is how nonlocality can consistently be defined in a scenario of arbitrarily many parties that may collaborate among each other. To this end we recognise which are the allowed physical operations in this situation and then define nonlocality as the resource that cannot be created by these operations. Our approach shows that the conventional definition of multipartite nonlocality, adopted by the community so far, is inconsistent with this operational definition; we further propose and analyse new models that do not suffer from these inconsistencies. Furthermore, we show that our findings have implications for the characterisation of quantum correlations. A recent approach to describe the set of quantum correlation consists in using principles inspired from information theory. By using a special instance of the models we defined earlier we show a fundamental limitation of this approach: no bipartite information principle is sufficient to single out the set of quantum correlations from the set of nonsignalling correlations. We then developed a description of nonlocality in an even more generalised scenario of several parties. Motivated by a result of Popescu we study scenarios where the parties are allowed to perform not only a single but sequences of measurements on their systems. Characterising nonlocality also in this scenario in operational terms and defining local models compatible with this definition, we show that a new form of nonlocality can be detected Lastly, we examine the problem of detecting the presence of nonlocality in a multipartite scenario when one is given only partial access to the global system. We find that one can verify that the total system must display nonlocality, even though the accessible subsystems only exhibit local correlations.