The problem with which this investigation is concerned is that of demonstrating the applicability of a particular theory and technique to two materials of different band structure, InSb and HgSe, and in doing so, determining the deformation potentials of these materials. The theory used in this investigation predicts an inversion-asymmetry splitting and an anisotropy of the Fermi surface under uniaxial stress. No previous studies have ever verified the existence of an anisotropy of the Fermi surface of semiconductors under stress. In this work evidence will be given which demonstrates this anisotropy. Although the inversion-asymmetry splitting parameter has been determined for some materials, no value has ever been reported for InSb. The methods presented in this paper allow a value of the splitting parameter to be determined for InSb.

La photoelectrocatalyse de l'eau par rayonnement solaire est une solution communément proposée pour la production propre d'hydrogène. En termes de rendement solaire-à-hydrogène, un tandem dual photosystème est accepté comme la configuration plus efficace concernant les cellules photoelectrocatalytique pour la dissociation de l'eau. Ce travail s'intéresse au trioxyde de tungstène (WO3) et au bismuth vanadate (BiVO4) sous la forme de photoanodes type n en couches minces pour la complétion d'oxydation de l'eau dans la demi-réaction pour la dissociation complète de l'eau dans une cellule tandem dual photosystème photoelectrocatalytique. Ces couches minces sont fabriquées par des méthodes robustes, économiques, et extensibles de sol-gel dip coating, et caractérisées par différentes techniques pour vérifier leurs caractéristiques physiques et leur performance photoelectrochimique. WO3 et BiVO4 sont optimises par nanostructuration, modification des couches interfaciales, et addition des co-catalyseurs de surface pour améliorer les performances et la stabilité, respectivement dans des conditions acides et neutres. Ces matériaux sont couples avec une photocathode de type p en oxyde de cuivre (II) pour compléter la réaction de dissociation de l'eau. La cellule photoelectrocatalytique ainsi construite est inspirée par la littérature concernant les systèmes innovateurs de tandem dual photosystèmes. Ce travail aboutit à l'une des seules cellules de dissociation de l'eau par photoelectrocatalyse à base des oxydes de métaux, fabriquée via des techniques faciles et économiques. L'efficacité de la production solaire-à-hydrogène est de 0.01%, et applied-bias-to-photon efficacité de 0.06%. / Solar water splitting by photoelectrocatalysis is a proposed long term solution for the production of renewable hydrogen. A wired dual photosystem photoelectrocatalytic cell is thermodynamically considered to possess the highest attainable solar-to-hydrogen efficiency. To realize a photoelectrocatalytic water splitting cell for practical application, facile fabrication methods and abundant low cost materials are essential. This research investigates tungsten trioxide (WO3) and bismuth vanadate (BiVO4) as thin film n-photoanodes to complete the oxygen evolution half reaction for water splitting application in a tandem dual photosystem photoeletrocatalyic water splitting cell. These thin films are fabricated by low cost, robust, scalable, sol-gel dip coating methods and characterized by several techniques to verify the physical characteristics and photochemical performance. WO3 and BiVO4 are optimized by nanostructuration, interfacial surface modification, and addition of surface co-catalysts to increase performance and stability in acidic and neutral conditions, respectively. These materials are coupled with a copper (II) oxide p-photocathode to drive the hydrogen evolution reaction in a photoelectrocatalyic cell to complete the water splitting reaction. The photoelectrocatalytic cell constructed is inspired by previous literature reports encompassing an innovative tandem dual photosystem approach. As a result, this research reports one of the only entirely metal oxide based photoelectrocatalytic water splitting cells, fabricated by inexpensive, unexcessive techniques, resulting in a solar-to-hydrogen efficiency of 0.01% and an applied bias to photon efficiency of 0.06%.

In this paper a prototype spectrum-splitting photovoltaic system based on volume holographic lenses (VHL) is designed, fabricated and tested. In spectrum-splitting systems, incident sunlight is divided in spectral bands for optimal conversion by a set of single-junction PV cells that are laterally separated. The VHL spectrum-splitting system in this paper has a form factor similar to conventional silicon PV modules but with higher efficiencies (>30%). Unlike many other spectrum-splitting systems that have been proposed in the past, the system in this work converts both direct and diffuse sunlight while using inexpensive 1-axis tracking systems. The VHL system uses holographic lenses that focus light at a transition wavelength to the boundary between two PV cells. Longer wavelength light is dispersed to the narrow bandgap cell and shorter wavelength light to the wide bandgap cell. A prototype system is designed with silicon and GaAs PV cells. The holographic lenses are fabricated in Covestro Bayfol HX photopolymer by 'stitching' together lens segments through sequential masked exposures. The PV cells and holographic lenses were characterized and the data was used in a raytrace simulation and predicts an improvement in total power output of 15.2% compared to a non-spectrum-splitting reference. A laboratory measurement yielded an improvement in power output of 8.5%.

Dans cette thèse nous présentons dans un premier temps une nouvelle notion de différentiabilité généralisée pour les applications multivoques, faisant intervenir des applications positivement homogènes: la H-différentiabilité. Nous étudions la stabilité de cette notion en utilisant la convergence de Fischer, d'abord dédiée aux ensembles mais que nous avons adaptée aux applications multivoques. Nous nous intéressons ensuite à l'étude de la dépendance continue des ensembles de points fixes d'une application multivoque contractante par rapport aux données. Finalement nous analysons la convergence d'une méthode d'approximations successives de type forward-backward splitting, des zéros de la somme de deux opérateurs multivoques non monotones, jouissants notamment de propriétés de pseudo H-différentiabilité / In this thesis we present at first a new concept of generalized differentiation for setvalued mappings, involving positively homogeneous applications: the H-differentiability. We study the stability of this notion by using Fischer convergence,firstly dedicated to sets but which we have adapted to set-valued mappings. We establish the continuous dependence of fixed points sets of set-valued contraction and finally we study the convergence of a forward-backward splitting method for approximating the zeros of the sum of two non-monotone set-valued mappings, notably using properties of pseudo H-differentiability.

Suite à l’expérience de l’exil, la culture d’un pays, expression artistique de la mémoire, est ramifiée. L’oeuvre de l’exilé n’est alors qu’une partie du rhizome culturel, reflétant l’identité initiale, dont la souche est la même que celle de ceux qui sont restés, mais en ajoutant l’expérience du présent « ailleurs ». Georges Steiner pousse la réflexion jusqu’à concevoir cette expérience comme étant l’élément déclencheur de la littérature actuelle, que nous considérons comme re-production d’un signifiant qui lui pré-existe. Or, le XXème siècle est celui de l’exil, qui s’est vu imposé avec l’apparition de multiples dictatures ou problèmes économiques (le nazisme persécutant les Juifs, les dictateurs d’Afrique ou d’Amérique Latine, etc.). L’objet de l’étude se focalise sur deux romans argentins : Informe de París de Paula Wajsman (1990) et La sombra del jardín de Cristina Siscar (1999). Les auteures mettent en scène l’exil dans leurs fictions. Nous dédions l’étude à l’analyse de ces deux textes dont les styles diffèrent mais dont les thématiques s’apparentent : rapport à l’espace, perte des repères imaginaires, position face à l’Autre et construction identitaire dans un nouvel environnement. Nous nous demandons ainsi sous quelles formes peut s’exprimer l’exil, synonyme d’une perte généralisée / Following the experience of exile, a country's culture, artistic expression of memory, branches forth. The exile's work is thus only part of the cultural rhizome, reflecting initial identity, whose root is the same as those left behind, while adding the experience of the current “elsewhere”. Georges Steiner pushes the idea to the point of conceiving this experience as being the trigger of current literature, something we consider as the pre-existing signifier. As such, the 20th century is littered with exiles, imposed by the emergence of multiple dictatorships or economic difficulties (Nazi persecution of the Jews, dictators of Africa or Latin America, etc.). The study focuses on two Argentinian novels: Paula Wajsman's Informe de París (1990) and Cristina Siscar's La sombra del jardín (1999). The authors bring to light exile in their fiction. The study is dedicated to the analysis of these two texts whose styles differ but whose themes have much in common : relationship with space, loss of imaginary reference points, situating oneself in regards to the Other and the construction of identity in a new environment. Thus we question in what forms can be expressed the general feeling of loss so synonymous with exile

Two main subjects are addressed in this study. The ability of a bright red material with metallic behaviour to be used as a visible light photocatalyst for hydrogen evolution and the feasibility of visible light photocatalytic water splitting using Z-schemes constituted from different kinds of photocatalysts and materials used as mediators. Strontium niobate (Sr₁₋ₓNbO₃) is an A-site deficient perovskite with intense red colour. It is an unusual material that displays both metallic type conduction and- as we present- photocatalytic activity. Specifically, photocatalytic visible light hydrogen production with oxalic acid as a sacrificial reagent is achieved from this material even without the need for a co-catalyst or other alteration. This photocatalytic activity is screened with time and related to different parameters that might influence it, like crystal structure, surface area and surface chemistry. The crystal structure of strontium niobate is A site stoichiometry dependant and the materials acquires a cubic symmetry for Sr≤ 0.92 and orthorhombic for 0.92≤ Sr≤ 0.97. The change of crystal structure from cubic to orthorhombic symmetry seems to have a negative effect on the photocatalytic activity, as the NbO₆ octahedra become distorted and unfavourable for d-orbital overlapping. The highest photocatalytic activity is exhibited at the turning point of one structure to the other. Increase in the photocatalytic activity is also exhibited by enlarging the surface area through ball milling, nevertheless, a clear trend for surface area effect on activity is not obtained among samples with different Sr content. Additionally, an enrichment of Sr on the surface of strontium niobate is observed by XPS, which apart from the fact that seems to be a governing factor improving stability it is also considered a key point for the exhibited photocatalytic activity altogether. Full water splitting under visible light from Z-schemes is studied by fabricating three general categories of systems. These three different categories depend on the mediator used to fabricate the Z-schemes and are: redox couple Z-schemes (with Fe⁺³/Fe⁺²), solid mediator Z-schemes (with GO) and no mediator Z-schemes. The materials used as photocatalysts for the fabrication of the Z-schemes are: Sr₀.₉₂NbO₃ for hydrogen production and both WO₃ and BiVO₄ independently for oxygen production. The photocatalytic activity for water splitting is evaluated in production of hydrogen and oxygen with time and the ratio of their production rates is frequently checked to see whether the ideal hydrogen to oxygen 2:1 is achieved. The general idea acquired from the results of all the three types of systems is that, water splitting with Z-schemes is a complicated process and in most cases governed by many subreactions. More specifically, in all cases of redox couple Z-schemes we got hydrogen to oxygen ratio imbalances and with the most prominent one being the lack of hydrogen production. Thankful is the fact that a certain type of system, the one consisting of WO₃ as oxygen photocatalyst and Fe⁺² as initial mediator species gives results very close to the ideal one and with a high degree of reproducibility indicating this way the probable formation of a Z-scheme that has overcome more of the imbalances. In between the two other categories, solid mediator and no mediator Z-schemes, subreactions seem to be the governing factor hence imbalances are always present. A case study in the no mediator Z-schemes on an attempt to investigate sources of imbalances, reveals that a big source of imbalance is most probably from the trapping of protons from WO₃.

We present new results on absolute stability for BDF-ADI (Backward differentiation formula Alternating Direction Implicit) methods applied to a linear advection and diffusion equations. Unconditional absolute stability of the BDF2-ADI method is proven for advection and diffusion separately, as well as to the BDF3-ADI method for the purely-diffusive case. Conditional absolute stability of the BDF4-ADI is also proven for the purely-diffusive case, and stability regions for BDF3-ADI and BDF4- ADI are given in terms of the PDE coefficients and numerical parameters. Lastly, numerical experiments are presented to support the theoretical results and conjectures. These experiments also suggest future work.

This thesis consists of two parts. We start with some background theory that will be used throughout the thesis. Then, in the first part, we investigate the existence and uniqueness of the solution of the stochastic partial differential equation with two reflecting walls. Then we establish the existence and uniqueness of invariant measure of this equation under some reasonable conditions. In the second part, we study the splitting-up method for approximating the solu- tions of stochastic Stokes equations using resolvent method.

Group living is a social strategy adopted by many species, where individuals can exhibit long-term social affiliation with others, strengthened through cooperative behaviour and often kinship. For highly social mammals, changes in group membership may have significant consequences for the long-term viability and functioning of a population. Detecting significant social events is essential for monitoring the social dynamics of such populations and is crucial to determining the factors underlying these events. Detecting when changes in social organization occur, especially with incomplete data, poses significant analytical challenges. To resolve this issue, I developed and assessed a straightforward, multi-stage and generalizable method with broad utility for ecologists interested in detecting and subsequently investigating causes of changes in social organization. My approach illustrates the frequency and ecological relevance of group fission and fusion events in a population of fish-eating ‘Resident’ killer whales (Orcinus orca). Group fission is a process commonly found in social mammals, yet is poorly described in many taxa, and has never been formally described in killer whales. To address this gap, I provided the first description of matrilineal fission in killer whales, from a threatened but growing Northern Resident killer whale population in which matrilineal fission has been observed for the past three decades. I also undertook the first comprehensive assessment of how killer whale intragroup cohesion is influenced by group structure, demography and resource abundance. Fission in Northern Resident killer whales occurred both along and across maternal lines, where animals dispersed in parallel with their closest maternal kin. I show that fission in this population is driven primarily by population growth and the demographic conditions of groups, particularly those dictating the nutritional requirements of the group. I posit that intragroup food competition is the most likely explanation for group fission in this population, where prey abundance also has ancillary effects. As group fission can have a direct impact on the fitness of group members and the long-term viability of a population, my findings underscore the importance of incorporating studies of sociality into the management of threatened populations of social mammals. / Graduate / 0329 / 0472

[EN] This thesis addresses the treatment of perturbed problems with splitting methods. After motivating these problems in Chapter 1, we give a thorough introduction in Chapter 2, which includes the objectives, several basic techniques and already existing methods. In Chapter 3, we consider the numerical integration of non-autonomous separable parabolic equations using high order splitting methods with complex coefficients (methods with real coefficients of order greater than two necessarily have negative coefficients). We propose to consider a class of methods that allows us to evaluate all time dependent operators at real values of the time, leading to schemes which are stable and simple to implement. If the system can be considered as the perturbation of an exactly solvable problem and the flow of the dominant part is advanced using real coefficients, it is possible to build highly efficient methods for these problems. We show the performance of this class of methods for several numerical examples and present some new improved schemes. In Chapter 4, we propose splitting methods for the computation of the exponential of perturbed matrices which can be written as the sum A = D+epsilon*B of a sparse and efficiently exponentiable matrix D with sparse exponential exp(D) and a dense matrix epsilon*B which is of small norm in comparison with D. The predominant algorithm is based on scaling the large matrix A by a small number 2^(-s) , which is then exponentiated by efficient Padé or Taylor methods and finally squared in order to obtain an approximation for the full exponential. In this setting, the main portion of the computational cost arises from dense-matrix multiplications and we present a modified squaring which takes advantage of the smallness of the perturbation matrix B in order to reduce the number of squarings necessary. Theoretical results on local error and error propagation for splitting methods are complemented with numerical experiments and show a clear improvement over existing methods when medium precision is sought. In Chapter 5, we consider the numerical integration of the perturbed Hill's equation. Parametric resonances can appear and this property is of great interest in many different physical applications. Usually, the Hill's equations originate from a Hamiltonian function and the fundamental matrix solution is a symplectic matrix. This is a very important property to be preserved by the numerical integrators. In this chapter we present new sixth-and eighth-order symplectic exponential integrators that are tailored to the Hill's equation. The methods are based on an efficient symplectic approximation to the exponential of high dimensional coupled autonomous harmonic oscillators and yield accurate results for oscillatory problems at a low computational cost. Several numerical examples illustrate the performance of the new methods. Conclusions and pointers to further research are detailed in Chapter 6. / [ES] Esta tesis aborda el tratamiento de problemas perturbados con métodos de escisión (splitting). Tras motivar el origen de este tipo de problemas en el capítulo 1, introducimos los objetivos, varias técnicas básicas y métodos existentes en capítulo 2. En el capítulo 3 consideramos la integración numérica de ecuaciones no autónomas separables y parabólicas usando métodos de splitting de orden mayor que dos usando coeficientes complejos (métodos con coeficientes reales de orden mayor de dos necesariamente tienen coeficientes negativos). Proponemos una clase de métodos que permite evaluar todos los operadores con dependencia temporal en valores reales del tiempo lo cual genera esquemas estables y fáciles de implementar. Si el sistema se puede considerar como una perturbación de un problema resoluble de forma exacta y si el flujo de la parte dominante se avanza usando coeficientes reales, es posible construir métodos altamente eficientes para este tipo de problemas. Demostramos la eficiencia de estos métodos en varios ejemplos numéricos. En el capítulo 4 proponemos métodos de splitting para el cálculo de la exponencial de matrices perturbadas que se pueden escribir como suma A = D + epsilon*B de una matriz dispersa y eficientemente exponenciable con exponencial dispersa exp(D) y una matriz densa epsilon*B de noma pequeña. El algoritmo predominante se basa en escalar la matriz grande con un número pequeño 2^(-s) para poder exponenciar el resultado con métodos eficientes de Padé o Taylor y finalmente obtener la aproximación a la exponencial elevando al cuadrado repetidamente. En este contexto, el coste computacional proviene de las multiplicaciones de matrices densas y presentamos una cuadratura modificada aprovechando la estructura perturbada para reducir el número de productos. Resultados teóricos sobre errores locales y propagación de error para métodos de splitting son complementados con experimentos numéricos y muestran una clara mejora sobre métodos existentes a precisión media. En el capítulo 5, consideramos la integración numérica de la ecuación de Hill perturbada. Resonancias paramétricas pueden aparecer y esta propiedad es de gran interés en muchas aplicaciones físicas. Habitualmente, las ecuaciones de Hill provienen de una función hamiltoniana y la solución fundamental es una matriz simpléctica, una propiedad muy importante que preservar con los integradores numéricos. Presentamos nuevos integradores simplécticos exponenciales de orden seis y ocho tallados a la ecuación de Hills. Estos métodos se basan en una aproximación simpléctica eficiente a la exponencial de osciladores armónicos acoplados de dimensión alta y dan lugar a resultados precisos para problemas oscilatorios a un coste computacional bajo y varios ejemplos numéricos ilustran su rendimiento. Conclusiones e indicadores para futuros estudios se detallan en el capítulo 6. / [CAT] La present tesi està enfocada al tractament de problemes perturbats utilitzant, entre altres, mètodes d'escisió (splitting). Comencem motivant l'oritge d'aquest tipus de problems al capítol 1, i a continuació introduïm el objectius, diferents tècniques bàsiques i alguns mètodes existents al capítol 2. Al capítol 3, consideram la integració numèrica d'equacions no autònomes separables i parabòliques utilitzant mètodes d'splitting d'ordre major que dos utilitzant coeficients complexos (mètodes amb coeficients reials d'ordre major que dos necesariament tenen coeficients negatius). Proposem una clase de mètodes que permeten evaluar tots els operadors amb dependència temporal explícita amb valors reials del temps. Esta forma de procedir genera esquemes estables i fàcils d'implementar. Si el sistema es pot considerar com una perturbació d'un problema exactament resoluble, i la part dominant s'avança utilitzant coeficients reials, es posible construir mètodes altament eficients per aquest tipus de problemes Demostrem la eficiència d'estos mètodes per a diferents exemples numèrics. Al capítol 4, proposem mètodes d'splitting per al càcul de la exponencial de matrius pertorbades que es poden escriure com suma A = D + epsilon*B (una matriu que es pot exponenciar fàcilment i eficientemente, com es el cas d'algunes matrius disperses exp(D), i una matriu densa epsilon*B de norma menuda). L'algorisme predominant es basa en escalar la matriu gran amb un nombre menut 2^(-s) per a poder exponenciar el resultat amb mètodes eficients de Padé o Taylor i finalment obtindre la aproximació a la exponencial elevant al quadrat repetidament. En este context, el cost computacional prové de les multiplicacions de matrius denses i presentem una quadratura modificada aprofitant la estructura de matriu pertorbada per reduir el nombre de productes. Resultats teòrics sobre errors locals i propagació d'error per a mètodes d'splitting son analitzats i corroborats amb experiments numèrics, mostrant una clara millora respecte a mètodes existens quan es busca una precisió moderada. Al capítol 5, considerem la integració numèrica de l'ecuació de Hill pertorbada. En este tipus d'equacions poden apareixer resonàncies paramètriques i esta propietat es de gran interés en moltes aplicacions físiques. Habitualment, les equacions de Hill provenen d'una función hamiltoniana i la solució fonamental es una matriu simplèctica, siguent esta una propietat molt important a preservar pels integradors numèrics. Presentams nous integradors simplèctics exponencials d'orden sis i huit construits especialmente per resoldre l'ecuació de Hill. Estos mètodes es basen en una aproxmiació simplèctica eficient a la exponencial d'osciladors harmònics acoplats de dimensió alta i donen lloc a resultats precisos per a problemas oscilatoris a un cost computacional baix. La eficiencia dels mètodes s'il.lustra en diferents exemples numèrics. Conclusions i indicadors per a futurs estudis es detallen al capítol 6. / Seydaoglu, M. (2016). Splitting methods for autonomous and non-autonomous perturbed equations [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/71358 / TESIS