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Yes / Numerical simulation of wet granulation in a continuous granulator is carried out using Discrete Element Method (DEM) to discover the possibility of formation of seeded granules in a continuous process with the aim of reducing number of experimental trials and means of process control. Simple and scooped drum granulators are utilized to attain homogenous seeded granules in which the effects of drum rotational speed, particles surface energy, and particles size ratio are investigated. To reduce the simulation time a scale-up scheme is designed in which a dimensionless number (Cohesion number) is defined based on the work of cohesion and gravitational potential energy of the particles. Also a mathematical/numerical method along with a MATLAB code is developed by which the percentage of surface coverage of each granule is predicted precisely. The results show that use of continuous granulator is promising provided that a high level of shear is considered in the granulator design, e.g. it is observed that using baffles inside the drum granulators is essential for producing seeded granules. It is observed, moreover, that the optimum surface energy for scooped granulator with rotational speed of 50 rpm is 3 J/m2 which is close to the number predicted by Cohesion number. It is also shown that increasing the seed/fine size ratio enhances the seeded granulation both quantitatively (60% increase in seeds surface coverage) and qualitatively (more homogeneous granules).

The Greenland ice sheet is the largest Northern Hemisphere store of fresh water, and it is responding rapidly to the warming climate. In situ observations document the changing ice sheet properties in the lower accumulation area, Southwest Greenland. Firn densities from 1840 meters above sea level retrieved in May 2012 revealed the existence of a 5.5-meter-thick, near-surface ice layer in response to the recent increased melt and refreezing in firn. As a consequence, vertical meltwater percolation in the extreme summer 2012 was inefficient, resulting in surface runoff. Meltwater percolated and refroze at six meters depth only after the end of the melt season. This prolonged autumn refreezing under the newly accumulated snowpack resulted in unprecedented firn warming with temperature at ten meters depth increased by more than four degrees Celsius. Simulations confirm that meltwater reached nine meters depth at most. The refrozen meltwater was estimated at 0.23 meters water equivalent, amounting to 25 % of the total 2012 ablation. A surface energy balance model was used to evaluate the seasonal and interannual variability of all surface energy fluxes at that elevation in the years 2009 to 2013. Due to the meltwater presence at the surface in 2012, the summer-averaged albedo was significantly reduced (0.71 in 2012; typically 0.78). A sensitivity analysis revealed that 71 % of the subsequent additional solar radiation in 2012 was used for melt, corresponding to 36 % of the total 2012 surface lowering. This interplay between melt and firn properties highlights that the lower accumulation area of the Greenland ice sheet will be responding rapidly in a warming climate. / Stability and Variations of Arctic Land Ice (SVALI) / Programme for Monitoring of the Greenland Ice Sheet (PROMICE) / Greenland Analogue Project (GAP)

The reliance on freshwater released by mountain glaciers and ice caps demands that the effects of climate change on these thermally-sensitive systems are evaluated thoroughly. Coupling climate variability to processes of mass and energy exchange at the glacier scale is challenged, however, by a lack of climate data at an appropriately fine spatial resolution. The thesis addresses this challenge through attempting to reconcile this scale mismatch: glacier boundary-layer observations of meteorology and ablation at Vestari Hagafellsjökull, Iceland, and Storglaciären, Sweden, are related to synoptic-scale meteorological variability recorded in gridded, reanalysis data. Specific attention is directed toward synoptic controls on: i) near-surface air temperature lapse rates; ii) stationarity of temperature-index melt model parameters; and iii) glacier-surface ablation. A synoptic weather-typing procedure, which groups days of similar reanalysis meteorology into weather categories , forms the basis of the analytical approach adopted to achieve these aims. Lapse rates at Vestari Hagafellsjökull were found to be shallowest during weather categories characterised by warm, cloud-free weather that encouraged katabatic drainage; steep lapse rates were encountered in weather categories associated with strong synoptic winds. Quantitatively, 26% to 38% of the daily lapse-rate variability could be explained by weather-category and regression-based models utilizing the reanalysis data: a level of skill sufficient to effect appreciable improvements in the accuracy of air temperatures extrapolated vertically over Vestari Hagafellsjökull. Weather categories also highlighted the dynamic nature of the temperature-ablation relationship. Notably, the sensitivity of ablation to changes in air temperature was observed to be non-stationary between weather categories, highlighting vulnerabilities of temperature-index models. An innovative solution to this limitation is suggested: the relationship between temperature and ablation can be varied as a function of weather-category membership. This flexibility leads to an overall improvement in the simulation of daily ablation compared to traditional temperature-index formulations (up to a 14% improvement in the amount of variance explained), without the need for additional meteorological data recorded in-situ. It is concluded that weather categories are highly appropriate for evaluating synoptic controls on glacier meteorology and surface energetics; significant improvements in the parameterization of boundary-layer meteorology and ablation rates are realised through their application.

Les solides divisés, ou poudres, sont très utilisés dans de nombreux secteurs industriels. Dans l'industrie pharmaceutique les poudres peuvent être granulées et/ou comprimées pour la mise en oeuvre de formes galéniques solides et elles peuvent également être dispersées pour formuler des suspensions buvables par exemple. En cosmétique, le mélange des poudres ou la mise en suspension sont des étapes cruciales pour certains produits. Le secteur agro-alimentaire génère et formule de nombreux produits sous la forme de solides divisés. Dans le domaine des peintures, la dispersion des pigments dans la phase liquide est primordiale. Dans ces différents cas, les interactions interfaciales solide-solide et solide-liquide régissent très fortement les différents procédés industriels. C'est le cas de la dispersion d'une poudre dans un liquide qui est fortement influencée par l'énergie interfaciale entre la poudre et le liquide, composante directement liée à la tension de surface du liquide et l'énergie de surface de la poudre par l'intermédiaire de l'angle de contact (équation de Young). Dans cette étude, la dispersion de talc, hydrophobe, largement utilisé dans l'industrie notamment papetière, est étudiée dans une phase aqueuse. Afin de modifier les interactions solide-liquide (et solide-solide), la surface du talc est modifiée par enrobage à sec avec de la silice nanométrique hydrophobe (Aérosil® R972). Pour cela, deux dispositifs d'enrobage ont été utilisés : un mélangeur à haut cisaillement (Cyclomix®) et un broyeur à billes planétaire (BBP). L'objectif de ce travail est d'étudier l'influence des modifications des interactions solide-liquide sur la dispersibilité des particules. Les modifications de surface des particules enrobées ont été analysées par la méthode de la goutte posée, par montée capillaire, par chromatographie gazeuse inverse (CGI) et par sorption dynamique de vapeur (DVS). Ces modifications ont ensuite été mises en parallèle avec la vitesse de dispersion des particules dans l'eau. Des relations ont été établies entre la vitesse de dispersion des particules et le travail d'adhésion particules / eau. En plus des interactions solide-liquide, le passage dans les appareils d'enrobage modifie d'autres paramètres du talc comme sa densité, sa rhéologie, sa flottabilité etc., autant de paramètres modifiant également sa dispersibilité. Enfin, la puissance d'agitation de la phase aqueuse est un paramètre également étudié. / Powder technology concerns the phenomena encountered in industrial processes involving divided solids. Such processes are found in the pharmaceutical, cosmetics, and food industries (where many products are based on powders; tablets, granules, suspensions), and in the paint industry where solid pigments are dispersed in liquids. In particular this thesis examines the dispersion of powders in liquids which depends strongly on the interactions between solids and liquids and can be assessed by the solid-liquid interfacial energy. This energy is directly linked to the surface tension of the liquid and the surface energy of the solid through the contact angle in the Young equation. The contact angle is used to calculate the work of adhesion between a powder and a liquid and characterises the wettability of the powder. Talc powder, mainly used in paper industry, is used in this study. The surface of talc powder has been modified by dry coating with hydrophobic nano-silica (Aerosil® R972) using two different devices: a high shear mixer (Cyclomix®), and a planetary ball mill. The aim being to observe the effect of surface modification on the wettability and surface energy of coated talc particles and the effect of these surface energy changes on the dispersability of particles. Different parameters have been considered: the concentration of hydrophobic silica, the duration of processing without silica and with 3 % silica. Surface modifications have been assessed using the sessile drop method, capillary rise, inverse gas chromatography (IGC) and dynamic vapour sorption (DVS). This study shows that not only the surface wettability is modified by the treatment of particles in the coating devices, but also their physical characteristics such as their bulk density, their rheology, their buoyancy and thus their dispersibility. Finally, a study is made of the effect the stirring power of the aqueous phase on the dispersibality of talc powders coated with different concentrations hydrophobic silica.

Doctor of Philosophy / Department of Agronomy / P.V. Vara Prasad / Agriculture is the largest (90%) consumer of all fresh water in the world. The consumptive use of water by vegetation represented by the process evapotranspiration (ET) has a vital role in the dynamics of water, carbon and energy fluxes of the biosphere. Consequently, mapping ET is essential for making water a sustainable resource and also for monitoring ecosystem response to water stress and changing climate. Over the past three decades, numerous thermal remote sensing based ET mapping algorithms were developed and these have brought a significant theoretical and technical advancement in the spatial modeling of ET. Though these algorithms provided a robust, economical, and efficient tool for ET estimations at field and regional scales, yet the uncertainties in flux estimations were large, making evaluation a difficult task. The main objective of this study was to evaluate and improve the performance of widely used remote sensing based energy balance models, namely: the Surface Energy Balance Algorithm for Land (SEBAL), Mapping Evapotranspiration at high Resolution and with Internalized Calibration (METRIC), and Surface Energy Balance System (SEBS). Data used in this study was collected as part of a multi-disciplinary and multi-institutional field campaign BEAREX (Bushland Evapotranspiration and Agricultural Remote Sensing Experiment) that was conducted during 2007 and 2008 summer cropping seasons at the USDA-ARS Conservation and Production Research Laboratory (CPRL) in Bushland, Texas. Seventeen high resolution remote sensing images taken from multispectral sensors onboard aircraft and field measurements of the agro-meteorological variables from the campaign were used for model evaluation and improvement. Overall relative error measured in terms of mean absolute percent difference (MAPD) for instantaneous ET (mm h[superscript]-[superscript]1) were 22.7%, 23.2%, and 12.6% for SEBAL, METRIC, and SEBS, respectively. SEBAL and METRIC performances for irrigated fields representing higher ET with limited or no water stress and complete ground cover surfaces were markedly better than that for dryland fields representing lesser ET and greater soil water deficits with sparser vegetation cover. SEBS algorithm performed equally well for both irrigated and dryland conditions but required accurate air temperature data. Overall, this study provides new insights into the performance of three widely used thermal remote sensing based algorithms for estimating ET and proposed modifications to improve the accuracy of estimated ET for efficient management of water resources.

Nanotechnology builds devices from the bottom up with atomic accuracy. Among the basic nano-components to fabricate such devices, semiconductor nanoparticle quantum dots (QDs), metal nanocrystals, proteins, and nucleic acids have attracted most interests due to their potential in optical, biomedical, and electronic areas. The major objective of this research was to prepare nano-components in order to fabricate functional nano-scale devices. This research consisted of three projects. In the first two projects, we incorporated two desirable characteristics of QDs, which are their abilities to serve as donors in fluorescence energy transfer (FRET) and surface energy transfer (SET) as well as to do multiplexing, to engineer QD-based nanoconjugates for optical and biomedical applications. Immobilizing luminescent semiconductor CdSe/ZnS QDs to a solid platform for QD-based biosensors offers advantages over traditional solution-based assays. In the first project, we designed highly sensitive CdSe/ZnS QD SET-based probes using gold nanoparticles (AuNPs) as FRET acceptors on polystyrene (PS) microsphere surfaces. The emission of PS-QD was significantly quenched and restored when the AuNPs were attached to and then removed from the surface. The probes were sensitive enough to analyze signals from a single bead and for use in optical applications. The new PS-QD-AuNP SET platform opens possibilities to carry out both SET and FRET assays in microparticle-based platforms and in microarrays. In the second project, we applied the QD-encoded microspheres in FRET-based analysis for bio-applications. QDs and Alexa Fluor 660 (A660) fluorophores are used as donors and acceptors respectively via a hairpin single stranded DNA. FRET between QD and A660 on the surface of polystyrene microspheres resulted in quenching of QD luminescence and increased A660 emission. QD emission on polystyrene x microspheres was restored when the targeted complementary DNA hybridized the hairpin strand and displaced A660 away from QDs. The third project involved fabrication of different nanoconjugates via self-assembly of template-based metal nanowires and metal nanoparticles using oligonucleotides as linkers. These nanoconjugates can serve as building blocks in nano-electronic circuits. The template method restricted the oligonucleotides attachment to the tip of the nanowires. Nanowires tagged with hybridizable DNA could connect to complementary DNA-modified metal crystals in a position-specific manner.

Orientador: João Manuel Marques Cordeiro / Resumo: O chumbo, em função de sua alta resistividade é mau condutor de eletricidade, sendo classificado como um metal semicondutor. Já os seus óxidos são muito utilizados na confecção de baterias automotivas, pelo seu comportamento condutor. Dos vários óxidos de chumbo que existem, o dióxido de chumbo (PbO2) é um dos que mais se destacam devido a suas aplicações. O β-PbO2 é um semicondutor com band gap estreito, que recebeu uma grande atenção ultimamente devido à sua potencial utilização como óxidos condutores transparentes (TCO). Os TCO são compostos que combinam as propriedades normalmente mutuamente excludentes da transparência e da condutividade. O desempenho óptico e elétrico dos TCO está intimamente ligado à estrutura de bandas e, desta forma, a distribuição periódica de potencial em um cristal. Neste trabalho procura-se compreender os fundamentos das propriedades elétricas macroscópicas do material β-PbO2 na forma de filmes finos. Para tanto, adotou-se abordagem da mecânica quântica baseada na Teoria do Funcional Densidade (DFT), com potencial híbrido B3LYP, implementada no código CRYSTAL09. Cálculos de estrutura de bandas e densidade de estados mostram que o band gap de filmes de β-PbO2 tendem para o gap do material na forma de bulk e cálculos de energia de superfície permitem concluir que sua face mais estável é a (110). / Mestre

Devido à elevada razão superfície/volume dos nanomateriais, estes apresentam propriedades únicas que são consequência das propriedades de suas superfícies. Para estabilizar as nanopartículas, as quais tendem ao crescimento para reduzir o excesso de energia, uma estratégia é a introdução de aditivos que segreguem na superfície e reduzam a energia de superfície. Neste trabalho, o sistema de importância tecnológica SnO2-TiO2 foi estudado. Nanopartículas de Sn1-xTixO2 (0,00 x 1,00) foram sintetizadas pelo método dos precursores poliméricos. Difratogramas de raios X mostram que uma solução sólida com estrutura do tipo rutilo é obtida para x 0,90. A evolução dos parâmetros de rede, os espectros obtidos por perda de energia de elétrons (EELS) e os espectros no infravermelho coletados no modo de refletância difusa (DRIFT) sugerem a segregação do Ti4+ na superfície, que justifica a elevada solubilidade do Ti4+ no SnO2. Os espectros Raman são coerentes com a segregação, mostrando que, mesmo sem a formação de segunda fase, ocorrem regiões ricas em Ti. A segregação está relacionada também à redução do tamanho de cristalito e ao aumento da área de superfície específica devido à redução da energia de superfície (de 1,40 Jm-2 em x = 0,00 até 1,08 Jm-2 em x = 0,50) determinada por calorimetria de adsorção de água e coerente com os dados da calorimetria de dissolução. Para x 0,90, ocorre a formação da fase anatásio além do rutilo e os fenômenos de estabilização dos polimorfos podem ser explicados pela modificação da energia de superfície. Com base na caracterização feita, as atividades fotocatalíticas das nanopartículas foram avaliadas e foi verificado um aumento da eficiência devido à superior área de superfície das amostras aditivadas em relação às amostras puras. / Due to the high surface/volume ratio, nanomaterials have unique properties as a consequence of their surface properties. In order to stabilize the nanoparticles, which tend to grow to reduce their excess energy, one can introduce additives that are prone to segregate at the surfaces and reduce the surface energy. In this work, the technologically relevant SnO2-TiO2 system was studied. Sn1-xTixO2 (0.00 x 1.00) nanoparticles were synthesized by polymeric precursors method. X-ray diffraction patterns show that a rutile-structured solid solution is formed for x 0.90. Lattice parameters evolution, electron energy loss spectra (EELS) and diffuse reflectance infrared spectra (DRIFT) suggest a Ti4+ surface segregation, which explains the high Ti4+ solubility in SnO2. Raman spectra are in accord with the segregation, showing Ti-rich sites in the absence of a second crystalline phase. The segregation is also related to a decrease in the crystallite size and an increase in the surface area due to a decrease in the surface energy (from 1.40 Jm-2 for x = 0.00 to 1.08 Jm-2 for x = 0.50) determined by water adsorption calorimetry and consistent with drop solution calorimetry data. For x 0.90, the formation of anatase occurs in addition to rutile, and the polymorphic stability can be explained according to the surface energy modification. Based on these results, photocatalytic activity of the samples were evaluated, and an increase in the efficiency due to a higher surface area was observed for the samples containing additive compared to pure samples.

An experimental study of phase transitions of long-chain n-alkanes induced by the effect of interfaces is described. ¶ The phase behaviour of long-chain n-alkanes (carbon number 14, 16, 17, 18) adsorbed at isolated mica surfaces and confined between two mica surfaces has been studied in the vicinity of and down to several degrees below the bulk melting points, Tm. Using the Surface Force Apparatus we have measured the thickness of alkane films adsorbed from vapour (0.97 [equal to or greater-than] p/p[subscript o] [equal to or greater-than] 0.997), studied capillary condensation transition, subsequent growth of capillary condensates between two surfaces, and phase transitions in both the adsorbed films and the condensates. By measuring the growth rate of the capillary condensates we have identified a transition in the lateral mobility of molecules in the adsorbed films on isolated mica surfaces. This transition to greater mobility occurs slightly above Tm for n-hexadecane, n-heptadecane and n-octadecane but several degrees below Tm for n-tetradecane, and is accompanied by a change in wetting behaviour and a measurable decrease in adsorbed film thickness for n-heptadecane and n-octadecane. Capillary condensates that form below Tm remain liquid, but may freeze if the degree of confinement is reduced by separation of the mica surfaces. An increase in the area of the liquid-vapour interface relative to that of the liquid-mica interface facilitates freezing in the case of the long-chain alkanes, which show surface freezing at the liquid-vapour interface. ¶ Although thermodynamic properties of the surface freezing transition have been rather well documented, the kinetics involved in formation of such ordered monolayers has so far received very little attention. We studied the surface tension of n-octadecane as a function of temperature in the vicinity of Tm, using the static Wilhelmy plate and the dynamic maximum bubble pressure methods. The two methods give different results on cooling paths, where nucleation of the surface ordered phase is involved, but agree on heating paths, where both methods measure properties of the equilibrium surface phase. On cooling paths, the surface of bubbles may supercool below the equilibrium surface freezing temperature. The onset of surface freezing is marked by a sharp drop in the surface tension. The transition is accompanied by an increased stability of the films resulting in longer bubble lifetimes at the liquid surface, which suggests that the mechanical properties of the surfaces change from liquid-like to solid-like. Our results suggest occurrence of supercooling of the monolayer itself.