En esta Tesis se propone un modelo de estimación del riesgo de incendios forestales utilizando información proporcionada por imágenes de satélite, en concreto estudiando el estado de la vegetación a partir de los índices de vegetación, y combinándolo con otras variables. Para ello, se lleva a cabo un estudio comparativo de 8 índices espectrales distintos, obtenidos a partir de imágenes del sensor MODIS del periodo 2001-2006, relacionándolos con la frecuencia de incendios de la zona de estudio, la cual comprende las regiones de Galicia y Asturias, para seleccionar el índice más relacionado con los incendios. Se analiza la variación temporal de los índices en dos periodos consecutivos de 16 días comparándola con la frecuencia de incendios del periodo posterior. Se comprueba que el índice más adecuado es el EVI (Enhanced Vegetation Index). Una vez se ha decidido cuál es el mejor índice para la zona de estudio, se utiliza la regresión logística con el fin de obtener un modelo de predicción de incendios en el que se incluyen otras variables además del índice de vegetación, en concreto se incluye el historial de incendios en cada periodo del año, el historial de incendios de cada una de las celdas de 10x10 km en las que se registran los datos de incendios y la comunidad (Galicia o Asturias). El algoritmo que se obtiene de la regresión logística calcula la probabilidad condicional de que ocurra un incendio en función de dichas variables y además permite clasificar todos los casos en presencia o ausencia de incendio, de esta forma se comprueba que el modelo propuesto clasifica correctamente en torno al 70% de los casos analizados. A partir de los resultados de la regresión logística se definen cuatro niveles de riesgo de incendio que permiten obtener mapas de riesgo que ayudan a simplificar las tareas de prevención y extinción. La frecuencia de incendios observada en cada uno de estos niveles es del 10%, 27%, 43% y 66% para los niveles bajo, medio, alto y extremo. / A fire danger model is proposed using remote sensing data, specifically by using vegetation indices as indicators of the vegetation status, and combining these indices with other variables. A comparison of eight different spectral indices is performed from MODIS images of Galicia and Asturias regions for the period 2001-2006, relating the temporal evolution of the different indices to the frequency of fires in 16-day periods. The EVI (Enhanced Vegetation Index) is shown as the best index for fire danger estimation in these regions. Logistic regression is used for obtaining a fire danger model including the EVI and other variables, such as the fire history of each cell and period of year. With this variables a model with an accuracy of 70% is obtained. From the results of the logistic regression four danger levels are defined in order to obtain fire danger maps. Fire frequency obtained in each level is: 10%, 27%, 43% y 66% for low, medium, high and extreme levels.

by K. E. Bett, J. S. Rowlinson and G. Saville. / Includes bibliographical references and index.

Several different methods for the gas phase assay of tritium have been investigated and a simple and rapid assay technique has been developed. This method has been used to measure the partial pressure of water in aqueous dioxan solutions at 18°C and at 25°C, in a concentration range where the partial pressures are too low to be readily measured by other methods. Partial excess thermodynamic functions of mixing have been calculated from the pressure measurements.

The properties of sub-monolayer Helium-3 films adsorbed on two totally different but planar substrates, Mylar^† film and exfoliated graphite have been studied using NMR. The nuclear magnetic relaxation times T₁ and T₂ have been measured as functions of fractional monolayer completion, temperature, substrate plane orientation and Larmor frequency using a specially designed and constructed NMR spectrometer system. The results obtained with a Mylar film substrate are consistent3with the formation of patches of solid ³He at regions of preferential adsorption on the substrate. Measurements of T₂ m very low coverage ³He films on exfoliated graphite also indicate that the adsorbate forms areas of relatively high density solid, in agreement with the thermodynamic analysis of Elgin and Goodstein. Finally, detailed measurements of T₂ as a function of all of the above parameters at low areal densities will help us to characterise the relaxation processes for the fluid phase of ³³He on exfoliated graphite. ^†Mylar is the tradename of poly(ethelene-terephthalate) film, marketed by Du Pont.

This document charts a series of investigations into some basic questions concerning the relationship between life and the physical theories of thermodynamics. While equilibrium thermodynamics represents a foundational component of modern physics, methods for non equilibrium systems have yet to reach the same level of maturity. The first part of this thesis aims to establish the validity of a burgeoning theory of non-equilibrium thermodynamics known as the Maximum Entropy Production Principle (MEPP), in the context of heat transfer by convective fluid motion between heated boundaries. Applying the MEPP to systems with both fixed and negative feedback boundary conditions revealed that in fact, the steady state of convective fluids cannot be accurately predicted from an assumption of maximum entropy production alone. Rather the subtleties of the boundary conditions and the physical properties of the fluid must be properly accounted for. It is thus proposed that the MEPP should not, as has sometimes been suggested, be treated as a universally applicable law of nature. The second part of this thesis investigates the pattern-forming and transport properties of reactive fluid systems. It is found that under thermal driving forces, closed systems utilise the physical processes of reaction and advection to augment their heat transport abilities. Furthermore, the addition of thermal kinetics and fluid flow to the Gray-Scott reaction diffusion system, reveals a new range of phenomena including positive feedback, self-inhibition, competition and symbiosis. Such behaviour can readily be viewed from an ecological, rather than purely physico-chemical, perspective.

Stochastic thermodynamics provides a clear definition of entropy production and the framework of fluctuation theorems has allowed many general results to be obtained for nonequilibrium systems. Notably, relationships for work and free energy in nonequilibrium systems as well as second law-like inequalities have been obtained. A recent extension to this framework has been the addition of feedback and the generalisation of the previously obtained inequalities to incorporate information quantities related to control and feedback. In this thesis we contribute to this framework by first providing a close analysis of the nature of `time-reversal' for feedback systems. Time reversal is a key ingredient in the formulation of the fluctuation relationships from which one obtains the nonequilibrium work functions and so we consider how to meaningfully construct a time-reverse conjugate process for a system with feedback and provide a justification for the Sagawa-Ueda fluctuation relation. We then introduce a simple model of a feedback engine and use it to analyse the fluctuation properties of the information flow between the controlled system and the feedback controller. Finally, we focus on the possibilities for feedback and consider a model whereby feedback is enacted symmetrically between two coupled systems and find that such a system has entropy-reducing dynamics. Since the dynamics appear to violate the second law of thermodynamics, we comment on their validity and argue that mutual feedback may be unphysical.

Condensation is a special class of phase transition which has been observed throughout the natural and social sciences. The understanding of the critical behaviour of such systems is a very active area of current research, in particular a mathematical description of the formation and time evolution of the condensate. In this thesis we study these phenomena in several models. In particular we focus on the recently introduced inclusion process, and we compare it with related classical mass transport models such as zero range processes. We first give a brief review of relevant definitions and properties of interacting particle systems, in particular recent literatures on the condensation and stationary behaviour of a large class of interacting particle systems with stationary product measures, which forms the theoretical basis of this thesis. The second part of this thesis is on the dynamics of condensation in the inclusion process on a one-dimensional periodic lattice in the thermodynamic limit. This generalises recent results which were limited to finite lattices and symmetric dynamics. Our main focus is firstly on totally asymmetric dynamics which have not been studied before, which we compare to exact solutions for symmetric systems. We identify all the relevant dynamical regimes and corresponding time scales as a function of the system size, including a coarsening regime where clusters move on the lattice and exchange particles, leading to a growing average cluster size. After establishing the general approach to study dynamics of condensation in totally asymmetric processes, we extend the results to more general partially asymmetric cases as well as higher dimensional cases. In the third part of this thesis we derive some preliminary exact results on symmetric systems through duality, which recovers heuristic results in previous chapter and allows us to treat coarsening in the infinite lattice directly.

Teniendo en cuenta el rápido aumento de la población y el crecimiento en el consumo de energía como consecuencia de grandes progresos en transporte y tecnología, el desarrollo sostenible es de especial relevancia pues sugiere la búsqueda de formas de mitigar las emisiones de gases de efecto invernadero, incluyendo la captura y almacenamiento de carbono (o utilización), la eficiencia energética, fuentes alternativas de energía y ahorro de energía, como ya se ha sugerido por el protocolo de Kioto y los informes del IPCC. De ahí que en los últimos años se haya dedicado un esfuerzo considerable a desarrollar tecnologías para la captura y almacenamiento de CO2 a partir de fuentes concentradas de emisión. Además de establecer nuevas tecnologías, durante las últimas décadas la ciencia de materiales sólidos porosos se ha convertido en una de las áreas más intensas de investigación y desarrollo para químicos, físicos y científicos de materiales. De hecho, se ha avanzado considerablemente en el desarrollo de nuevos adsorbentes para diversos procesos de separación. Por ejemplo, las estructuras órgano-metálicas (MOFs) han ido ganando considerable atención como materiales prometedores para aplicaciones de almacenamiento y separación de gases, debido a sus propiedades excepcionales. Sin embargo, es necesaria una comprensión a nivel molecular de la adsorción de gases para acelerar el diseño y desarrollo de aplicaciones a la carta. También es fundamental conocer el comportamiento bajo condiciones de humedad e impurezas, como se tiene normalmente en aplicaciones industriales específicas. El trabajo desarrollado en esta Tesis Doctoral destaca el uso de técnicas de simulación molecular para la optimización de procesos relacionados con el medio ambiente. El objetivo general se centra en avanzar en el campo de materiales para la captura y separación de dióxido de carbono a condiciones de proceso. Se considera de manera explícita la influencia del vapor de agua e impurezas, tanto a la luz de los fundamentos de la adsorción como en la aplicación para la captura de CO2 por post-combustión mediante ciclos de adsorción por oscilación. Partiendo de una breve descripción de los fundamentos de la adsorción y de las simulaciones moleculares, se presenta una revisión exhaustiva de estudios recientes de materiales para captura y separación de CO2, proporcionando así información valiosa para su aplicación industrial. Basados en esta revisión, se han estudiado en detalle algunos de los materiales más prometedores para un proceso de adsorción por cambio de temperatura (TSA) basado en simulaciones moleculares, proponiéndose un nuevo procedimiento para la evaluación y optimización de los sistemas de captura en condiciones reales. Dada la gran influencia de trazas de agua en la separación, se investiga también el CuBTC (uno de los MOF más estudiados y estables en agua) en comparación con la zeolita de referencia 13X. Se examina en detalle el efecto de las especies coexistentes, así como la influencia del agua y SO2 en los gases de combustión, con el fin de llegar a una mejor comprensión de la capacidad de adsorción, la selectividad, la localización de las moléculas en el material, las distribuciones de calor isostérico y su relación con el proceso. Asimismo, se han llevado a cabo estudios paramétricos detallados para una investigación comparativa de la separación de mezclas multi-componentes de gases de combustión mediante el uso de otras zeolitas como caolinita y chabacita. Y finalmente, se presenta un trabajo adicional relacionado con otro problema medioambiental: la separación de un contaminante (ibuprofeno) en agua, mediante el uso de carbones activados, usando las mismas técnicas computacionales, demostrando así la versatilidad de las herramientas empleadas para este tipo de sistemas. / Given the rapid increase in population and the growth in energy consumption as a consequence of major developments in transportation and technology, sustainable development is of special relevance, suggesting ways to mitigate greenhouse gases emissions, including carbon capture and storage (or utilization, CCSU), energy efficiency, alternative energy sources and energy savings, as already suggested by the Kyoto’s Protocol and the IPCC reports. Hence, much effort has been devoted in recent years to develop technologies for capture and storage of CO2 from concentrated sources of emission. Apart from establishing new technologies, over the last decades the science of porous solid materials has become one of the most intense areas of research and development for chemists, physicists, and materials scientists. In fact, considerable progress has been made in recent years on the development of novel adsorbents. For instance, Metal Organic Frameworks (MOFs) have been gaining considerable attention as promising nanoporous materials for gas storage and gas separation applications due to their exceptional physical and chemical properties, and have already been demonstrated to be promising materials in the separation of different gases, however, a molecular level understanding of gas adsorption in the pores is crucial to accelerate the design and development of these and other applications. It is also fundamental to know their behavior under moisture conditions and impurities content, as normally found at specific industrial applications. The work developed in this Thesis highlights the use of molecular simulation techniques for optimizing environmental related processes, providing new procedures to assess the use of these materials from their fundamental knowledge until their applications at industrial conditions. The overall objective is to advance in the field of materials for CO2 capture and separation at process conditions. The influence of water vapor and impurities is explicitly considered, both, in the light of the fundamentals of adsorption and in the application for post-combustion carbon dioxide capture by swing adsorption cycles. Starting from a brief description of the fundamentals of adsorption and molecular simulations, a novel throughout review on recent studies of materials for CO2 capture and separation is presented, thus providing valuable information to assess their industrial application. Based on this review, some of the most promising materials for CO2 separation in a Temperature Swing Adsorption (TSA) process have been studied in detail by using molecular simulations (compared to experimental data when available), proposing a new process for the evaluation and optimization capture systems under real conditions. In addition, given the great influence of water as a trace compound on the separation, CuBTC (one of the most studied MOFs, stable in water and with potential for industrial application) has been investigated in comparison to the benchmark zeolite 13X. The effect of the coexisting species as well as the influence of water and SO2 in flue gas is examined in detail in order to reach a better understanding of the adsorption capacity, selectivity, adsorption density location and isosteric heat distributions. And finally, detailed parametric studies have been carried out for a comparative computational investigation for separating of multi-component mixtures of flue gas by using other representative zeolites such as kaolinite and chabazite. Additional work, related to another environmental problem: the separation of a pollutant (ibuprofen) in water, by using activated carbons, is also presented here, demonstrating the versatility of the tools used for these types of systems.

The present and the future expectation in parallel computing pose a new generational change in simulation and computing. Modern High Performance Computing (HPC) facilities have high computational power in terms of operations per second -today peta-FLOPS (10e15 FLOPS) and growing toward the exascale (10e18 FLOPS) which is expected in few years-. This opens the way for using simulation tools in a wide range of new engineering and scientific applications. For example, CFD&HT codes will be effectively used in the design phase of industrial devices, obtaining valuable information with reasonable time expenses. However, the use of the emerging computer architectures is subjected to enhancements and innovation in software design patterns. So far, powerful codes for individually studying heat and mass transfer phenomena at multiple levels of modeling are available. However, there is no way to combine them for resolving complex coupled problems. In the current context, this PhD thesis presents the development of parallel methodologies, and its implementation as an object-oriented software platform, for the simulation of multiphysics systems. By means of this new software platform, called NEST, the distinct codes can now be integrated into single simulation tools for specific applications of social and industrial interest. This is done in an intuitive and simple way so that the researchers do not have to bother either on the coexistence of several codes at the same time neither on how they interact to each other. The coupling of the involved components is controlled from a low level code layer, which is transparent to the users. This contributes with appealing benefits on software projects management first and on the flexibility and features of the simulations, later. In sum, the presented approaches pose a new paradigm in the production of physics simulation programs. Although the thesis pursues general purpose applications, special emphasis is placed on the simulation of thermal systems, in particular on buildings energy assessment and on hermetic reciprocating compressors. / Las expectativas puestas en el uso de la computación en paralelo plantean un cambio generacional en simulación y computación. Las más modernas instalaciones computacionales de alto nivel -High Performance Computing (HPC)- alcanzan ya la capacidad de realizar gran cantidad de operaciones por segundo -hoy del orden de peta-FLOPS (1e15 FLOPS) y dirigiéndose hacia exaFlops (1e18 FLOPS)-. Esto abre la posibilidad de usar la simulación por ordenador en un amplio espectro de nuevas aplicaciones en ciencia e ingeniería. Por ejemplo, los códigos de CFD&HT van a poder usarse de una forma más efectiva en la fase de diseño de dispositivos industriales ya que se obtendrán resultados muy valiosos en tiempos de ejecución razonables. Por el momento, hay muchos códigos disponibles para el estudio individual de fenómenos de transferencia de calor i de masa con distintos niveles de modelización. Sin embargo, estos códigos no se pueden combinar entre sí para abordar problemas más complejos, en los cuales varios fenómenos físicos interactúan simultáneamente. Bajo este contexto, en esta tesis doctoral se presenta el desarrollo de una metodología de estrategia paralela, y su implementación en una plataforma informática, para la simulación de sistemas multi-físicos. De éste modo, ahora los distintos códigos pueden ser integrados para la creación de nuevas herramientas de simulación destinadas a aplicaciones específicas de interés tanto social como industrial. Esto se hace de una manera intuitiva y simple de manera que los investigadores no tienen que preocuparse ni por la coexistencia de varios códigos simultáneamente ni en cómo hacer que interactúen entre ellos. El acoplamiento entre los diferentes componentes involucrados en una simulación se realiza mediante un código más básico con el cual el usuario solamente interacciona a través de una interfase. Esto aporta interesantes beneficios tanto en la gestión de los proyectos de programario como en la flexibilidad y las características de las simulaciones. En resumen, la estrategia que se propone plantea un nuevo paradigma en la producción de programas de simulación de fenómenos físicos. Aunque la tesis persigue aplicaciones de propósito general se ha puesto especial atención en la simulación de sistemas térmicos, en particular en la evaluación energética de edificios y en compresores herméticos alternativos.

Fast scanning chip-calorimetry was used to explore the crystallisation and melting of three semi-crystalline polymers. The heating and cooling rates required to prevent crystallisation on cooling (from above Tm) and on re-heating (from below T\(_g\)) were determined as: 3,000 and 8,000˚C/s respectively in PCL, 75 and 250˚C/s respectively in PEEK and 10 and 100˚C/s respectively in PLA. The effect of the thermal lag was considered using indium as a standard and corrections of >5˚C were required at rates in excess of 5,000˚C/s. As readily observed in conventional DSC (CDSC), PEEK exhibited a double melting endotherm and this was attributed to a melting-recrystallisation-melting process. The absence of recrystallisation above 250˚C allowed a Hoffman-Weeks analysis to be carried out over a broader temperature range than is general possible in CDSC. The interplay between thermal lag and re-crystallisation was analysed using heating rates covering 5 orders of magnitude. At an optimum heating rate of 1,500 ˚C/s, an equilibrium melting temperature of 359˚C was determined. The consideration of thermal lag led to the measurement of diffusivity using the technique of laser flash apparatus (LFA). The high measurement speed in the LFA allowed a time and temperature resolved study of diffusivity in PLA. LFA, chip-calorimetry and CDSC were used in parallel to explore the cold-crystallisation kinetics of PLA and the development of the relatively unstable α’ crystals. A good correlation between chip-calorimetry and LFA was found, showing an Avrami exponent of 2 and nucleation constant of 6.58 x10\(^5\) and 6.87 x10\(^5\) respectively, corresponding to regime III.