Characterization of metallic species on porous materials by in situ XAS

El objetivo de esta tesis es estudiar la agrupación y el crecimiento de especies metálicas confinadas o soportadas en materiales porosos mediante espectroscopia de absorción de rayos X in situ. Para lograrlo, las especies de paladio y plata se han introducido en materiales porosos (¿-alúmina, carbón activo y zeolitas) mediante impregnación vía húmeda y métodos de intercambio iónico, respectivamente. Luego, el agrupamiento de estas especies metálicas se ha controlado mediante tratamientos de activación en diferentes atmósferas (inerte, oxidativa y reductiva) y seguido por XAS de manera detallada. El objetivo principal del trabajo actual es demostrar que tanto XANES como EXAFS pueden proporcionar información valiosa y, en cierto punto, innovadora durante el control de especies metálicas (en términos de tipo y tamaño de las especies). Aprovechando los procedimientos de análisis inusuales, como el análisis de los cumulantes, el ajuste de la parte imaginaria de la transformada de Fourier y otros, es posible obtener información refinada sobre los sistemas investigados. En la sección de introducción, se proporciona una compilación de estudios en los que se ha utilizado XAS como técnica importante para caracterizar especies metálicas en materiales porosos. Conscientes de que las personas pueden usar dicha introducción como base para estudios más complejos en el futuro, la discusión se ha dirigido tentativamente hacia este objetivo. El capítulo 4 se centra en el estudio de la influencia de los precursores de paladio y la naturaleza del soporte en las nanopartículas resultantes. El proceso de activación completo, es decir, la transformación precursor --> nanopartícula, ha sido seguido por XAS in situ. El análisis estuvo compuesto por el punto de partida (material impregnado), calcinación en flujo de O2 y reducción posterior con H2. La consecuencia del uso de diferentes precursores metálicos y soportes se ha discutido en términos del número de coordinación promedio obtenido a partir del análisis de datos de EXAFS, que fue respaldado por técnicas de caracterización de laboratorio. El capítulo 5 está dedicado al estudio de la agrupación de plata durante y después de los tratamientos de activación utilizando zeolitas de poro pequeño intercambiadas con plata como precursores y nanocontenedores. Se ha estudiado la influencia de la estructura y la composición química de los materiales basados en plata sobre las especies metálicas formadas en diferentes condiciones de agrupamiento y redispersión del metal (calcinación usando atmósferas distintas, reducción en H2, redispersión en O2) utilizando métodos de caracterización in situ o ex situ. Después, se discuten las consecuencias catalíticas de las zeolitas que contienen Ag en la reacción de SCO-NH3. En esta sección, la combinación de XAS in situ con varias técnicas de laboratorio ha demostrado ser fundamental para un completo entendimiento del trabajo. Finalmente, una lista de proyectos desarrollados en paralelo a esta tesis se proporciona al final de este documento.The aim of this thesis is to study the clustering and growth of metallic species either confined or supported in porous materials by in situ X-ray absorption spectroscopy. To accomplish this task, palladium and silver species were introduced into porous materials (¿-alumina, activated carbon and zeolites) by wetness impregnation and ion-exchange methods, respectively. Then, the clustering of these metallic species was controlled by activation treatments in different atmospheres (inert, oxidative and reductive) and followed by XAS in a comprehensive way. The principal goal of current work is to demonstrate that both XANES and EXAFS can provide valuable and, at certain point, innovative information during tuning of metallic species (in terms of type and size). Taking advantage of unusual analysis procedures, such as cumulant approach, fitting of imaginary part of Fourier transform and others, it is possible to obtain refined information about the investigated systems. In the introduction section, a compilation of studies in which XAS was used as important technique to characterize metallic species in porous materials is provided. Conscious that people can use such introduction as a basis for more complex studies in the future, the discussion has been tentatively directed toward this goal. The chapter 4 is focused on the study of the influence of palladium precursors and the nature of support on the resultant nanoparticles. The whole activation process, i.e. the transformation precursor --> nanoparticle, was followed in situ by XAS. The analysis pathway was composed by the starting point (as-impregnated), calcination in O2 flow and posterior reduction with H2. The consequence of using distinct metal precursors and supports were discussed in terms of average coordination number obtained from EXAFS data analysis, which was co-supported by laboratory characterization techniques. The chapter 5 is dedicated to the study of silver clustering during and after activation treatments using Ag-containing small-pore zeolites as precursors and nanocontainers. The influence of framework structure and chemical composition of Ag-based materials on formed Ag species at different clustering and metal redispersion conditions (calcination using distinct atmospheres, reduction in H2, redispersion in O2) were studied using either in situ or ex situ characterization methods. After, the catalytic consequences of tuned Ag-containing zeolites in SCO-NH3 are discussed. In this section, the combination of in situ XAS with several laboratory techniques proved to be pivotal to have a full picture of the investigated system. Finally, a list of projects developed in parallel to this thesis is provided at the end of this document.L'objectiu d'aquesta tesi és estudiar l'agrupació i el creixement d'espècies metàl·liques confinades o suportades en materials porosos mitjançant espectroscòpia d'absorció de raigs X in situ. Per a això, les espècies de pal·ladi i plata s'han introduït en materials porosos (¿-alúmina, carbó activat i zeolites) per mitjà de la impregnació via humida i mètodes d'intercanvi iònic, respectivament. Una vegada preparats els materials, l'agrupament de les espècies metàl·liques s'ha controlat fent ús de tractaments d'activació en diferents atmosferes (inert, oxidant i reductora) s'ha estudiat exhaustivament per XAS. L'objectiu principal del treball és demostrar que tant el XANES com l'EXAFS proporcionen informació rellevant i, en certa manera, innovadora per al control d'espècies metàl·liques (en termes de tipus i grandària d'aquestes espècies). Fent ús de procediments de tractament de dades no molt habituals com l'anàlisi de cumulants, l'ajust de la part imaginària de la transformada de Fourier i altres, és possible obtenir informació detallada sobre els sistemes estudiats. En l'apartat de la introducció, es proporciona una recopilació d'estudis en els quals s'ha utilitzat XAS com a tècnica principal per a caracteritzar les anomenades espècies metàl·liques en materials porosos. Aquesta introducció ha estat redactada per a que puga servir com a punt de partida per a futurs estudis que requereixen la utilització de XAS per a la caracterització de les espècies metàl·liques presents en els catalitzadors. El capítol 4 es centra en l'estudi de la influència dels precursors de pal·ladi i la naturalesa del suport front a les nanopartícules resultants. El procés d'activació, és a dir, la transformació precursor --> nanopartícula, ha sigut estudiat per XAS in situ. L'anàlisi per XAS va comprendre els següents passos: punt de partida (material impregnat), calcinació en flux d'O2 i reducció posterior amb H2. La utilització de diferents precursors i suports metàl·lics ha permès dur a terme una discussió, referent al nombre de coordinació mitjà obtingut a partir de l'anàlisi de dades de la zona EXAFS, que ha estat recolzat per altres tècniques de caracterització. El capítol 5 s'ha dedicat a l'estudi de l'agrupació de plata intercanviada en els catalitzadors durant i després dels tractaments d'activació. S'han utilitzat zeolites de porus xicotet, com la CHA i RHO, intercanviades amb plata. L'estudi de la influència de l'estructura zeolítica i la composició química dels materials enfront dels diferents tractaments d'activació (calcinació utilitzant diferents atmosferes, reducció en presència d'H2, re-dispersió en atmosfera d'O2) es va realitzar fent ús de mètodes de caracterització in situ o ex situ. A continuació, es discuteix la influència d'aquestes espècies metàl·liques formades, utilitzant els diferents mètodes d'activació, per a la reacció d'SCO-NH3. En aquest sentit, s'ha demostrat que la combinació de XAS in situ amb diverses tècniques habituals de laboratori és fonamental per al desenvolupament d'aquest treball. Finalment, es presenta una llista de projectes, en els quals també s'ha treballat paral·lelament, on s'ha utilitzat XAS com a tècnica de caracterització.Wittee Lopes, C. (2018). Characterization of metallic species on porous materials by in situ XAS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/10795

Bayesian computation via empirical likelihood

Approximate Bayesian computation (ABC) has become an essential tool for the analysis of complex stochastic models when the likelihood function is numerically unavailable. However, the well-established statistical method of empirical likelihood provides another route to such settings that bypasses simulations from the model and the choices of the ABC parameters (summary statistics, distance, tolerance), while being convergent in the number of observations. Furthermore, bypassing model simulations may lead to significant time savings in complex models, for instance those found in population genetics. The BCel algorithm we develop in this paper also provides an evaluation of its own performance through an associated effective sample size. The method is illustrated using several examples, including estimation of standard distributions, time series, and population genetics models.Comment: 21 pages, 12 figures, revised version of the previous version with a new titl

Geochemical characterization of alkaline gneissic rocks of Alentejo (Portugal)

Geochemical characterization of alkaline gneissic rocks of Alentejo (Portugal) J. Carrilho Lopes1, J. Munhá2, C. Pin3, J. Mata2 1Departamento de Geociências, Universidade de Évora & Centro de Geologia da Universidade de Lisboa, Portugal. 2Departamento de Geologia & Centro de Geologia da Universidade de Lisboa, Portugal. 3Département de Géologie, C.N.R.S., Université Blaise Pascal, France. [email protected] This study presents and interprets, on a petrological/petrogenetic point of view, a set of mineral and whole-rock geochemical data collected from the so called “Alkaline Province of Northeast Alentejo”, a group of gneisses that outcrops in lithostratigraphic domains known as Ossa-Morena Zone and Blastomilonitic Belt. It’s composed by felsic gneissic rocks of (per)alkaline type, represented by syenites with sodic inossilicates (riebeckite and/or aegirine), nefelinic syenites and hastingsitic syenites, as well as hedenbergitic granites. Most of riebeckitic syenites presents (Zr/Nb)<10, (Y/Nb)<0.7 e (Th/Nb)<0.3, while hastingsitic ones and hedenbergitic granites reveal higher values of these ratios (15.0, 2.0 e 0.6, respectively). The highest contents of Zr (4800 ppm) are also observed on peralkaline terms, with minimum values measured on alkaline granites (135 ppm). Maximum contents of F (6100 ppm) and Cl (7233 ppm) have been determined on riebeckitic and nefelino-sodalitic syenites, respectively, and seems that halogenous contents may be correlated with devolatilization processes, deformation/micro-fracturation and REE mobility. Even though irregular crystallization of phases which consume high contents of REE (e.g. allanite) can disturbe the correspondent geochemical signatures, it is still possible to identify, in most of the cases, distinctions between maximum values of (La/Sm)N , (La/Lu)N and (Gd/Lu)N of peralkaline rocks (29.6, 11.6, 2.4), hastingsitic syenites (14.8, 4.8, 2.0) and alkaline granites (4.0, 3.1, 1.7). Riebeckitic and nefelinic facies present, simultaniously, the sharpest negative anomalies of Ti and the less marked negative anomalies of Nb (means of 0.9 and 0.7), which can be interpreted as a result of differentiation processes with small to moderate contributions of crustal contamination; comparatively, this anomaly is higher in hastingsitic (0.6) and granitic terms (0.4). Obtained in a small set of mafic and felsic samples, Rb-Sr and Sm-Nd isotopic data, show the vulnerability of the first system to post-magmatic processes. Peralkaline rocks show (+2.5<eNd480<+4.9) values which reflect the origin of these magmas from timeintegrated depleted mantle sources, that were enriched in LREE at the time of, or shortly before, the igneous episode in an intracontinental rift setting. Sr-Nd petrogenetic modelling adds complementary information: i.) intracontinental alkaline character of (primary) basaltic magmas as precursors of this alkaline province; ii.) low to moderate crustal contamination during differentiation processes, namely 7% to 20% for peralkaline syenites and about 26% for alkaline granites

Stabilization process in Saccharomyces intra- and interspecific hybrids in fermentative conditions

We evaluated the genetic stabilization of artificial intra-(Saccharomyces cerevisiae) and interspecific (S. cerevisiae &times; S. kudriavzevii) hybrids under wine fermentative conditions. Large-scale transitions in genome size and genome reorganizations were observed during this process. Interspecific hybrids seem to need fewer generations to reach genetic stability than intraspecific hybrids. The largest number of molecular patterns recovered among the derived clones was observed for intraspecific hybrids, particularly for those obtained by rare-mating. Molecular marker analyses revealed that unstable clones could change during the industrial process to obtain active dry yeast. When no changes in molecular markers and ploidy were observed after this process, no changes in genetic composition were confirmed by comparative genome hybridization, considering the clone as a stable hybrid. According to our results, under these conditions, fermentation steps 3 and 5 (30&ndash;50 generations) would suffice to obtain genetically stable interspecific and intraspecific hybrids, respectively. [Int Microbiol 2014; 17(4):213-224]Keywords: Saccharomyces cerevisiae &middot; Saccharomyces kudriavzevii &middot; rare-mating in yeast &middot; molecular markers &middot; DNA content evaluation &middot; stabilization of genome

Implications of pinned occupation numbers for natural orbital expansions. II: Rigorous derivation and extension to non-fermionic systems

We have explained and comprehensively illustrated in Part I that the generalized Pauli constraints suggest a natural extension of the concept of active spaces. In the present Part II, we provide rigorous derivations of the theorems involved therein. This will offer in particular deeper insights into the underlying mathematical structure and will explain why the saturation of generalized Pauli constraints implies a specific simplified structure of the corresponding many-fermion quantum state. Moreover, we extend the results of Part I to non-fermionic multipartite quantum systems, revealing that extremal single-body information has always strong implications for the multipartite quantum state. In that sense, our work also confirms that pinned quantum systems define new physical entities and the presence of pinnings reflect the existence of (possibly hidden) ground state symmetries.Comment: Part II of arXiv:1908.1093

Utilização de modelos estatísticos e machine learning para a previsão de vendas no sector do retalho : um estudo comparativo

Mestrado em Ciências EmpresariaisA previsão das necessidades futuras torna-se fundamental para o correto planeamento e operação das empresas de retalho. Ao nível organizacional, as previsões de vendas funcionam como parâmetros de entrada para as diversas áreas funcionais das empresas. Previsões pouco precisas ou ineficientes podem levar à realização de elevado ou baixo nível de inventário, afetando de forma direta a rentabilidade e a posição competitiva das organizações. Os dados de vendas provenientes deste sector, exibem fortes padrões de tendência e variação sazonal, colocando desafios ao desenvolvimento de modelos de previsão eficazes. O objetivo do trabalho assenta na comparação do desempenho da previsão entre os métodos ARIMA e MLP para o estudo de caso de uma empresa portuguesa do sector do retalho, tendo em consideração cinco grupos de produtos. Pretende-se também investigar qual o impacto do pré-processamento dos dados de entrada no rigor das previsões, e de que forma a utilização combinada dos métodos ARIMA e MLP aumenta a eficácia desta previsão. Os resultados apontam para um melhor desempenho do método MLP em comparação com o método ARIMA, quando utilizado o erro de previsão EAM. Foi ainda demonstrado que o pré-processamento dos dados impacta de forma positiva o desempenho da previsão, contribuindo para a redução significativa dos erros de previsão. Também se conclui que a previsão combinada das metodologias ARIMA e MLP produz resultados positivos para duas das cinco categorias de produtos analisadas, mostrando ser um conceito com elevado interesse para uma investigação futura.Forecasting the future needs is one of the most important decisions for the effective planning and operation of the retail industries. At the organizational level, sales forecasts act as input parameters for the several functional areas of the business. Inaccurate or inefficient forecasts can lead to high or low stock levels, directly affecting the organizations profit and competitive position. Retail sales data often exhibit a strong trend pattern and seasonal variation, creating challenges for the development of effective forecast models. The objective of this study is to compare the forecast performance of ARIMA and MLP methods through a case study of a Portuguese retail company, considering five different groups of products. It is also intended to investigate the impact of the data preprocessing on the accuracy of forecasts, and if the combination of ARIMA and MLP methods can increase the effectiveness of this forecast. The results show that the forecasting performance, evaluated via EAM error, of the MLP method is better than the one obtained for ARIMA method. It has also been shown that data preprocessing positively impacts the forecasting performance, contributing to a significantly reduction of the forecasting errors. It is also concluded that the combined forecasting of the ARIMA and MLP methodologies yields positive results for two of the five groups of products, proving to be a concept of high interest for future research.info:eu-repo/semantics/publishedVersio

Spalling e DoP em alvos metálicos : estudos analíticos e numéricos

Mestrado em Engenharia MecânicaAs constantes formas de ameaça requerem o desenvolvimento constante de mecanismos de protecção, capazes de suster ataques de diversos tipos. Estes mecanismos devem possuir qualificações de segurança elevadas, visando a protecção de pessoas, veículos ou infraestruturas. O desenvolvimento tecnológico de sistemas de protecção inovadores permite acompanhar a evolução do tipo, tecnologia e performance das ameaças (armas, projécteis, explosivos, etc.). Consequentemente, é de grande importância o desenvolvimento de meios capazes de avaliar a capacidade de absorção de impacto dos referidos sistemas de protecção, sistemas esses que devem fornecer a resistência necessária ao impacto de ameaça. Neste trabalho procura-se estudar o comportamento ao impacto balístico de sistemas de protecção metálicos. Estudam-se numericamente os factores que influenciam a capacidade de absorção de energia de um alvo. Apresenta-se uma investigação detalhada das características de absorção de impacto de alvos com diferentes espessuras, impactados por projécteis com forma de ponta cilíndrica, hemisférica, cónica e ogival. Analisa-se a influência de vários parâmetros que afectam a capacidade de absorção de energia do alvo, tais como, a energia cinética de impacto, a forma de ponta do projéctil, as espessuras e os modos de cedência dos alvos. Faz-se a caracterização do comportamento mecânico ao impacto do aço Weldox 460 E, recorrendo ao programa de elemento finitos Abaqus. Evidencia-se, através da análise dos resultados numéricos, a dependência do modo de cedência do alvo em relação ao tipo de projéctil utilizado. Verifica-se um aumento da velocidade de limite balístico com o aumento da espessura do alvo, induzindo um aumento da capacidade de protecção deste. Denota-se a influência da forma de ponta do projéctil e da velocidade inicial de impacto na variação da velocidade residual do projéctil. Ilustra-se o aumento de absorção de energia por parte do alvo, com o aumento de espessura deste. É ainda notória uma absorção de energia de forma mais rápida para projécteis com configuração cilíndrica, verificando-se o inverso em projécteis de configuração ogival. ABSTRACT: The constant forms of threat require the constant development of protection systems capable of sustaining various types of attacks. These mechanisms should have high safety qualifications concerning the protection of people, vehicles or buildings. The development of innovative security systems can follow the evolution of type, technology and performance of the threats (weapons, projectiles, explosives, etc.). Therefore it is of extreme importance the development of means capable of evaluating the impact absorption capability of the before mentioned protection systems, which should be able to provide the resistence needed for the impact of a threat. This work presents a study of the behavior of metal protection systems against a ballistic impact where the afecting factors of the energy absorption capability of a target are numerically analysed. A detailed investigation of the impact absorption characteristics of a target with different thickness when collided by projectiles with blunt, hemispherical, conical and ogival noses is presented. Influence of various parameters afecting the energy absorption capability of the target, such as the kinetic energy of the impacting projectile, its nose shape, failure mode and thickness is studied. The mechanical behavior under an impact loading of Weldox 460 E steel is analysed using the finite element program Abaqus. It is possible to verify the dependence of the failure mode of the target on the type of projectile being used. Along with the increasement of the thickness of the target it is observed that the same happens to its energy absorption and to the ballistic limit velocity. The projectile nose shape and the initial velocity of impact affect its residual velocity. It is also noticed a faster absorption of energy by the target for projectiles with blunt noses, with the opposite happening for the ones with ogival noses