La neige est un matériau poreux dont la microstructure change en permanence. L'ensemble de ces transformations, qui prend le nom de ``métamorphisme", est susceptible d'affecter les propriétés thermiques, mécaniques et électromagnétiques de la neige au niveau macroscopique. En particulier, les échanges d'énergie et de matière à l'intérieur du manteau neigeux et entre la neige et l'atmosphère sont fortement influencés par l'évolution au cours du temps de la microstructure de la neige. Une représentation adéquate du métamorphisme dans les modèles de manteau neigeux s'avère donc cruciale. La microstructure d'un matériau poreux peut être raisonnablement décrite en se servant d'un nombre réduit de variables. En effet, la masse volumique, la surface spécifique (SSA) et la distribution de courbure permettent de caractériser la microstructure d'un matériau. Cependant, dans le cas de la neige cette approche n'en est qu'à ses débuts et n'a pas encore été appliquée de façon systématique. Des variables semi-empiriques, difficiles à mesurer et dépourvues de lien direct avec d'autres propriétés physiques, sont encore largement utilisées dans les modèles détaillés de manteau neigeux. Ce travail de thèse s'inscrit dans cette tentative de représenter la microstructure de la neige au cours du temps à l'aide de variables bien définies et mesurables sur le terrain. Parmi ces variables, nous nous sommes attachés notamment à la SSA, qui constitue une grandeur essentielle pour l'étude du manteau neigeux et de son évolution temporelle. Différentes lois d'évolution de la SSA ont été étudiées, à partir de relations empiriques basées sur des ajustements de données expérimentales jusqu'aux modèles physiques qui représentent le flux de la vapeur d'eau entre les grains de neige. Ces lois ont été dans un premier temps testées à l'aide d'un modèle simplifié de manteau neigeux et puis introduites directement dans le modèle SURFEX/ISBA-Crocus. Pour ce faire, la SSA dans Crocus a été transformée en variable prognostique, en remplaçant d'autres variables semi-empiriques préexistantes. Les différentes formulations de l'évolution temporelle de la SSA ont été comparées à des mesures de terrain, acquises lors de deux campagnes à Summit (Groenland) et au Col de Porte (France). Ces mesures ont été effectuées en utilisant de nouvelles techniques optiques et ont permis d'obtenir un riche jeu de données avec une grande résolution verticale. Les résultats montrent que les différentes formulations sont comparables et reproduisent bien les mesures, avec un écart quadratique moyen entre les valeurs de SSA simulées et observées inférieur à 10 m^2/kg. Enfin, nous avons contribué à faire le pont entre la microstructure de la neige et ses propriétés macroscopiques. En particulier, nous nous sommes intéressés au lien entre, d'une part, la SSA et, d'autre part, les propriétés mécaniques et optiques. Dans le premier cas, nous avons investigué la corrélation entre la SSA et la résistance à l'enfoncement mesurée avec un Snow Micro Pen (SMP). Les résultats encore préliminaires semblent indiquer que la SSA peut être dérivée de la masse volumique et de grandeurs micro-mécaniques estimées à partir du signal du SMP avec un modèle statistique. Dans le deuxième cas, nous avons simulé l'albédo de surface à Summit à partir des profils mesurés de masse volumique et de SSA et du contenu en impuretés. Les résultats de cette étude ont démontré que l'albédo spectral peut être correctement simulé à l'aide d'un modèle de transfert radiatif et l'énergie absorbée par le manteau neigeux peut être estimée avec une précision d'environ 1%. / Snow is a porous medium whose microstructure is constantly subjected to morphological transformations. These transformations, which take the name of ``metamorphism", are likely to affect the thermal, mechanical and electromagnetic properties of snow at the macroscopic level. Specifically, the exchange of energy and matter within the snowpack and between the snow and the atmosphere above are strongly impacted by the evolution over time of the snow microstructure. Therefore, an adequate representation of metamorphism in snowpack models is crucial. The microstructure of a porous medium can be reasonably described using a reduced number of variables. Indeed, the density, the specific surface area (SSA) and the curvature distribution are able to characterize the microstructure of such a material. However, in the case of snow this approach is still in its infancy and has not yet been systematically applied. Semi-empirical variables, difficult to measure and not directly linked to other relevant physical properties, are still widely used in so-called detailed snowpack models. This work contributes to the attempt to represent the state of the snow using well-defined and easily measurable microstructural variables. Among these variables, we focused particularly on the SSA, which is a key quantity for the study of snow and its temporal evolution. Different evolution laws of SSA were studied, starting from empirical relationships based on experimental data adjustments to physical models that represent the flow of water vapor between snow grains. These laws were initially tested using a simplified snowpack model and then introduced directly into the SURFEX/ISBA-Crocus snowpack model. To this end, the SSA in Crocus was turned into a prognostic variable, replacing other preexisting semi-empirical variables. The different formulations of the temporal evolution of the SSA were compared with field measurements, acquired during two campaigns at Summit (Greenland) and the Col de Porte (France). These measurements were carried out using new optical techniques and yielded a rich dataset with high vertical resolution. The results show that the different formulations are comparable and reproduce well the observations, with an average root-mean-square deviation value between simulated and measured SSA lower than 10 m^/kg. Finally, we contributed to bridge the gap between snow microstructure and macroscopic properties. In particular, we investigated the link between the SSA on the one hand and the mechanical and optical properties on the other hand. In the first case, we investigated the correlation between the SSA and the penetration resistance measured with a Snow Micro Pen (SMP). The preliminary results suggest that the SSA can be retrieved from the snow density and the micro-mechanical parameters estimated from the SMP signal using a statistical model. In the second case, we simulated the surface albedo at Summit from the measured profiles of density, SSA and impurities within the snowpack. The results of this study showed that the spectral albedo can be simulated successfully using a radiative transfer model and the energy absorbed by the snowpack can be estimated with a good accuracy (about 1%).

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Este trabalho investigou a técnica de solução coloidal(gelcasting) em meio polimérico para a obtenção de partículas de óxido de cério, visando seu emprego como catalisadores na combustão do metano. A formulação do sistema coloidal foi baseada na hidrólise de sais, como acetilacetonato de cério e nitrato de cério em presença de aditivos tais como polivinilbutiral (PVB), polivinilpirrolidona (PVP) e polivinilacetato (PVA), nas concentrações de 5, 10 e 15%, em meio alcoólico ou aquoso. Essas soluções, contendo os íons de interesse, foram submetidas a um tratamento térmico a 650°C, por 30 minutos, com taxa de aquecimento de 2°C/min. Após o tratamento térmico, os produtos obtidos foram caracterizados quanto a sua morfologia, área superficial, cristalinidade, perda de massa e atividade catalítica. As amostras obtidas a partir de acetilacetonato de cério mostraram-se mais reativas do que as obtidas a partir de nitrato de cério na catálise da combustão do metano, pois apresentaram maiores conversões e atingiram maiores temperaturas durante o processo, o que é de extrema importância uma vez que a combustão catalítica do metano é utilizada para a geração de energia térmica. Durante o processo de combustão, utilizando-se as partículas obtidas a partir de acetilacetonato de cério, observou-se a liberação de grandes quantidades de compostos nitrogenados quando comparado aos resultados dos ensaios com as partículas obtidas com nitrato de cério. Após a combustão do metano, as amostras sofreram significativa alteração na área superficial, provavelmente devido à intensidade do calor liberado, o que deu origem a maior aglomeração dos particulados. / This study investigatedto obtainparticles ofcerium oxide, for use as catalysts for thecombustion of methaneusing the techniqueofthroughpolymericcolloidal solution (gelcasting).Obtaining thecolloidal systemisbased onhydrolysis ofsalts such asceriumacetylacetonate,cerium nitratein the presence ofadditives such aspolyvinylbutyral(PVB),polyvinylpyrrolidone (PVP) and polyvinyl acetate(PVA),at concentrations of 5, 10 and 15% inaqueousoralcoholic medium. Thesesolutions containingionsof interestwere subjected to aheat treatment at 650°C for30 minutes, with heating rate of2°C/min.After heat treatment, the fibers were characterized accordingto their morphology, surface area, crystallinity, weight loss andcatalytic activity. Samplesobtained fromceriumacetylacetonatewere morereactivethan theceriumnitrateto thecombustion of methane, as showed greaterconversions andhigher temperaturesreachedduring the process, which is of utmost importancesince thecombustioncatalyticmethaneis usedfor generatingthermal energy.Duringthe combustion processusing theobtained fromparticlesof ceriumacetylacetonate, there was the release of largequantities ofnitrogencomparedto the results ofassays withthe particles obtainedwithcerium nitrate.Afterthe reactionwith methane, the samples underwentsignificantchange insurface area, probably dueto the intensity of heat of this reaction, which helps to agglomerate the particles.

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Despite extensive research in the field of aging neuroscience, it still remains unclear whether age related cortical changes can be detected in different functional networks of younger adults and whether these networks respond identically to healthy aging. We collected high-resolution brain anatomical data from 56 young healthy adults (mean age = 30.8 +/- 8.1 years, 29 males). We performed whole brain parcellation into seven functional networks, including visual, somatomotor, dorsal attention, ventral attention, limbic, frontoparietal and default mode networks. We estimated intracranial volume (ICV) and averaged cortical thickness (CT), cortical surface area (CSA) and cortical volume (CV) over each hemisphere as well as for each network. Averaged cortical measures over each hemisphere, especially CT and CV, were significantly lower in older individuals compared to younger ones (one-way ANOVA, p < 0.05, corrected for multiple comparisons). There were negative correlations between age and averaged CT and CV over each hemisphere (p < 0.05, corrected for multiple comparisons) as well as between age and ICV (p = 0.05). Network level analysis showed that age was negatively correlated with CT for all functional networks (p < 0.05, corrected for multiple comparisons), apart from the limbic network. While age was unrelated to CSA, it was negatively correlated with CV across several functional networks (p < 0.05, corrected for multiple comparisons). We also showed positive associations between CV and CT and between CV and CSA for all networks (p < 0.05, corrected for multiple comparisons). We interpret the lack of association between age and CT of the limbic network as evidence that the limbic system may be particularly resistant to age-related declines during this period of life, whereas the significant age-related declines in averaged CT over each hemisphere as well as in all other six networks suggests that CT may serve as a reliable biomarker to capture the effect of normal aging. Due to the simultaneous dependence of CV on CT and CSA, CV was unable to identify such effects of normal aging consistently for the other six networks, but there were negative associations observed between age and averaged CV over each hemisphere as well as between age and ICV. Our findings suggest that the identification of early cortical changes within various functional networks during normal aging might be useful for predicting the effect of aging on the efficiency of functional performance even during early adulthood.

Nickel-based catalysts in aqueous alkaline media are low-cost electrode materials for electrolytic hydrogen generation, a renewable method of producing fuel and industrial feedstock. However, further work is necessary to develop inexpensive electro-catalyst materials with high activity and long-term stability. This thesis employs spectroscopic and electrochemical methods to directly address specific research problems for the development of improved materials and devices with commercial or industrial value. The first chapter reviews the applications of nickel electrodes; the structures of nickel, nickel hydroxides, and nickel hydrides; and techniques for measuring the electrochemically active surface area (AECSA) of nickel. In the second chapter, electrochemically precipitated nickel hydroxide materials are fully characterized by Raman spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). This work unifies and simplifies the large body of literature on the topic by considering two fundamental phases, α- and β-Ni(OH)2, and various types and extents of structural disorder. The third chapter examines and demonstrates the potential applications of in situ Raman spectroscopy by monitoring the spontaneous ageing of α-Ni(OH)2 to β-Ni(OH)2 in pure water at room temperature. The fourth chapter considers the longstanding problem of electrode deactivation, the gradual decrease in nickel electro-catalyst activity during prolonged hydrogen production. Voltammetric and XRD evidence demonstrates that hydrogen atoms can incorporate into the electrode material and cause structural disorder or the formation of α-NiHx and β-NiHx at the surface. The voltammetric formation of NiOx, α-Ni(OH)2, β-Ni(OH)2, and β-NiOOH surface species are examined by electrochemical and XPS measurements. The fifth chapter of this thesis presents a new method to measure the AECSA by adsorption of oxalate to the (001) surface of the surface Ni(OH)2, as evidenced by voltammetric and attenuated total reflectance (ATR) FT-IR spectroscopy measurements. The adsorbed oxalate limits the surface hydroxide to a single layer. The surface NiOOH/Ni(OH)2 reduction peak during the reverse scan may be used to accurately and precisely measure the AECSA. The error of this method is estimated at < 10 %.

O processo de adsorção vem sendo utilizado como uma técnica eficaz para a remoção de íons metálicos em efluentes. Neste trabalho são apresentados os estudos para avaliar da capacidade de adsorção de cobalto em caulinita, um adsorvente de baixo custo, visando à remoção deste íon de soluções aquosas. Foi analisada a área superficial específica (S) em 25 amostras de materiais preparadas de diferentes modos: caulinita, bentonita e carvão ativado e, misturas de caulinita-bentonita e caulinita-carvão ativado. Estas misturas foram preparadas pela adição de 10, 20, 30, 40 e 50% de carvão ativado ou bentonita à caulinita. As amostras de caulinita-carvão ativado e caulinita in natura foram calcinadas a 600 e 1000 °C por 4 horas. Foi escolhida para os testes de adsorção a mistura de caulinita com 10% de carvão ativado por apresentar a melhor relação custo benefício em relação à S. Os parâmetros de adsorção investigados nesta mistura foram: tempo de contato, pH, concentração inicial de soluto, competição iônica e força iônica. Verificou-se que o tempo de contato e o pH otimizados para o propósito do trabalho foram 30 min e pH 6. Nestas condições a eficiência de remoção do íon cobalto da solução foi superior a 80%. Verificou-se que a presença de íons Cr e Zn, bem como o aumento da força iônica diminuem a capacidade de adsorção do Co na mistura adsorvente. As isotermas de Langmuir e Freundlich apresentaram R2 iguais a 0,906 e 0,597, respectivamente. Os parâmetros determinados nestas isotermas indicaram um processo espontâneo, ou seja, energeticamente favorável, para a adsorção do Co nas condições e que foram realizadas este trabalho. / The adsorption process has been used as an efficient technique for the removal of metallic ions in industrial effluent. In this work, it is presented the studies to evaluate the adsorption capacity of cobalt in kaolinite, a low cost adsorbent, aiming at the removal of this ion from aqueous solutions. The specific surface area (S) was analyzed in 25 samples prepared in different ways: kaolinite, bentonite and activated carbon and, mixtures of kaolinite-bentonite and kaolinite-activated carbon. These mixtures were prepared by adding to kaolinite 10, 20, 30, 40 or 50% of activated charcoal or bentonite. Samples of kaolinite-activated charcoal mixture and raw kaolinite were also calcined at 600 and 1000 °C for 4 hours. The adsorption parameters investigated for these adsorbents were: contact time, pH, solute initial concentration, ionic competition and ionic strength. It was found that the optimized contact time and pH, for the purpose of this work, were 30 min and pH 6. Under these conditions the cobalt ion removal efficiency was greater than 80%. It was verified that the presence of Cr and Zn ions, as well as the increase in ionic strength caused a decrease in the adsorption capacity of Co in the adsorbent mixture. The Langmuir and Freundlich isotherms presented R2 equal to 0.906 and 0.597, respectively. The parameters determined by these isotherms indicated a spontaneous process, i.e., energetically favorable, for the adsorption of Co under the conditions that this work was carried out.

The diploma thesis deals with the heterogeneous technique of preparation of grafted polypropylene g maleic anhydride (PP-g-MAH). The knowledge of the course of the reaction and its impact on the PP grafting process are summarized in the theoretical part. The preparation of the grafted PP was carried out in a fluidized polymerization reactor at 115 °C, speed of mixing 210 rpm, reaction time 60 min and pressure 6 bar. The amount of grafted MAH was monitored by using a MAH concentration 3 and 5 wt% and an initiator concentration 0.25; 0.5; 1; and 1.5 wt%. Modification efficiency was compared by using 3 types of PP with different particle morphology and specific surface area. By creating the theoretical model, the maximum surface concentration of MAH was calculated and compared with experimental data. Characterization of PP materials was performed by Electron Scanning Microscopy (SEM), Differential Scanning Calorimetry (DSC) and particle surface analysis by BET. Quantitative analysis of grafted MAH was determined by FTIR spectroscopy and acid-base titration.

Porous ceramic materials are an interesting group of materials due to a wide range of physical properties, low density, and good permeability. Production of a monolith with a shape stability that would also have a high specific surface area and high porosity is a common problem with porous ceramics. The goal of this work was to maintain the high specific surface area and to produce a monolith with a shape stability. Two forms of porous silica nanofibers (as prepared and milled) were used and partially sintered using the Spark Plasma Sintering method (SPS). Different sintering times and temperatures for SPS were tested. The findings revealed that the best SPS conditions were as follows: temperature: 600 °C, sintering time: 5 minutes, pressure: 3 MPa, and the heating rate: 144 °C/min. These sintering conditions resulted in a stable silica based machinable monolith made from fibers or milled fibers. The monoliths have the specific surface area of up to 470 m^2/g and porosity of 72 %, or the specific surface area of up to 422 m^2/g and porosity of 69 % for as prepared fibers and milled fibers, respectively.

The effect of papaverine on the albumin permeability-surface area product (PS), reflection coefficient (σ), and capillary filtration coefficient (K(f)) was examined in isolated rabbit lungs. Because PS and K(f) are functions of vascular surface area and permeability, we also compared papaverine with two other means of maximizing lung surface area: isoproterenol (1 x 10-7 M) and a mild increase in vascular pressure. Only lungs perfused with 0.1 mg/ml papaverine were significantly different from control. PS increased from control (2.80 ± 0.16 to 5.53 ± 0.20 ml · min-1 · g dry lung-1 x 10-2), whereas σ decreased from control (0.92 ± 0.01 to 0.78 ± 0.03). K(f) after papaverine was significantly lower than baseline predrug K(f) (5.60 ± 0.78 to 4.56 ± 0.53 ml · s-1 · cmH2O-1 · g dry lung-1 x 10-3). However, this group's predrug K(f) was higher than that of any other group. Our results indicate that papaverine increases albumin permeability and decreases endothelial selectivity. The isolated perfused lung appears fully recruited, because K(f) and PS did not increase with isoproterenol or increased vascular pressure. Papaverine should be used with caution in the Ringer-perfused lung.