L'objectif de cette thèse est de comprendre la structure des binaires gamma, binaires à collision de vents composées d'une étoile massive et d'un pulsar jeune. Ces binaires possèdent probablement une structure similaire aux binaires à collision de vents composées de deux étoiles massives, avec des particularités liées à la nature relativiste du vent de pulsar. L'interaction de deux vents supersoniques d'étoiles massives crée une structure choquée qui présente des signatures observationnelles du domaine radio aux rayons X. Plusieurs instabilités ainsi que le mouvement orbital des étoiles influent sur la structure choquée. Afin de comprendre leur impact, j'ai effectué des simulations à haute résolution de binaires à collision de vents à l'aide du code hydrodynamique RAMSES. Ces simulations sont numériquement coûteuses à réaliser, surtout lorsque un des vents domine fortement l'autre. A petite échelle, les simulations soulignent l'importance de l'instabilité de couche mince non-linéaire dans les collisions isothermes alors que l'instabilité de Kelvin-Helmholtz peut fortement modifier la structure choquée dans une collision adiabatique. A plus grande échelle, cette instabilité peut parfois détruire la structure spirale à laquelle on s'attend si la différence de vitesse entre les vents est trop importante. WR 104 est une binaire dont on observe la structure spirale grâce à l'émission de poussières. Les simulations de ce système montrent un bon accord avec la structure observée et indiquent que des processus de refroidissement du gaz sont nécessaires à la formation de poussières. Pour modéliser les vents de pulsar dans les binaires gamma, RAMSES a été étendu à l'hydrodynamique relativiste. J'utilise ce nouveau code pour réaliser des simulations préliminaires de binaires gamma. Elles montrent effectivement une structure similaire aux binaires stellaires, avec de légères corrections relativistes . Ce code est adapté à l'étude de divers systèmes astrophysiques tels que les jets relativistes, les sursauts gamma ou les nébuleuses de pulsar et fera partie de la prochaine version de RAMSES qui sera rendue publique. / The aim of this thesis is to understand the structure of colliding wind binaries composed of a massive star and a young pulsar, called gamma-ray binaries. They are expected to display a similar structure to colliding wind binaries composed of massive stars, with some particularities due to the relativistic nature of the pulsar wind. The interaction of the supersonic winds from massive stars creates a shocked structure with observational signatures from the radio domain to the X-rays. The structure is affected by various instabilities and by the orbital motion of the stars. To understand their impact, I carried out high resolution simulations of colliding wind binaries with the hydrodynamical code RAMSES. They are computationally demanding, especially when one of the winds strongly dominates the other one. Small scale simulations highlight the importance of the Non-linear Thin Shell Instability in isothermal collisions while the Kelvin-Helmholtz instability may strongly impact the dynamics of adiabatic collisions. I found that, at larger scales, this instability can destroy the expected large scale spiral structure when there is an important velocity gradient between the winds. WR 104 is a system that displays a spiral structure with important dust emission. The simulation of this system shows a good agreement with the observed structure and indicates cooling processes are necessary to enable dust formation. To model the pulsar wind in gamma-ray binaries, an extension of RAMSES has been developed, that incorporates relativistic hydrodynamics. I used this new relativistic code to perform preliminary simulations of gamma-ray binaries. They display a similar structure to colliding wind binaries with small relativistic corrections. We expect to use this code to perform large scale simulations of gamma-ray binaries. It will be part of the next public release of RAMSES and is suited for the study of many astrophysical problems such as relativistic jets, pulsar wind nebulae or gamma-ray bursts.

No description available.

The sorption of humic acid (HA) and HA size fractions onto magnetite has been studied. There is considerable irreversibility in the interaction of the humic with the magnetite surface, but the presence of Eu3+ ions has no effect on the sorption of humic onto magnetite. The magnitude of the sorption to magnetite increases with HA fraction size for all ionic strengths between 0.01 and 3 mol dm-3. Increasing ionic strength also increases sorption. Asymmetric Flow Field Flow Fractionation analysis of HA sorption to magnetite after 1 day revealed preferential sorption of lower molecular weight material. Eu3+ sorption onto magnetite was studied as a function of Eu concentration, which showed an increase in relative sorption as Eu concentration decreased. The behaviour of Eu3+ in ternary (HA/Eu3+/magnetite) systems is heavily influenced by HA, and from the data there is direct evidence for ternary complex formation. Larger HA size fractions retain more Eu3+ in solution than the smaller fractions. The binding strengths of HA size fractions were determined through ion exchange resin experiments: generally the larger fractions (> 10 kDa) showed stronger binding than the smaller components, but the unfractionated sample showed the strongest binding.First order dissociation rate constants have been determined for the whole HA and HA size fractions. The dissociation rate constants are independent of HA fraction size, but the larger species bind more Eu non-exchangeably. Time series ultrafiltration of Eu3+/whole humic mixtures has shown a shift in the distribution of metal ions to larger size fractions after a few days. Two ternary system kinetic speciation models have been developed to predict the behaviour of HA and Eu3+ in ternary systems. The two differ in their description of the multi-component behaviour of the binary HA-mineral interaction. The first assumes a single HA species and two surface binding sites and was found to perform better overall than the second, which has a single surface sorption site and two HA species in solution. The exchangeable binding strengths for the different HA samples calculated from both models showed similarities to those measured experimentally.

The current study focuses on phase stability and evolution in the titanium-zinc titanium-copper and titanium-antimony systems. The study utilized the Laser Engineering Net Shaping (LENS™) processing technique to deposit compositionally graded samples of three binary system in order to allow the assessment of phase stability and evolution as a function of composition and temperature the material is subjected to. Through LENS™ processing it was possible to create graded samples from Ti-xSb (up to 13wt%) and Ti-xCu (up to 16wt%). The LENS™ deposited gradient were solutionized, and step quenched to specific aging temperature, and the resulting microstructures and phase were characterized utilizing XRD, EDS, SEM, FIB and TEM. The Ti-Zn system proved incapable of being LENS™ deposited due to the low vaporization temperature of Zn; however, a novel processing approach was developed to drip liquid Zn onto Ti powder at temperatures above β transus temperature of Ti (882 ◦C) and below the vaporization temperature of Zn (907 ◦C). The product of this processing technique was characterized in a similar way as the graded LENS™ depositions. From measurements performed on Ti-Sb it seems that Sb could be a potential α stabilizer in Ti due to the presence of a mostly homogeneous α grains throughout the gradient; however, from XRD it can be understood that a titanium antimonide phase is present. From results obtained from the Ti-Zn samples, it can be surmised that the eutectoid reaction seems to be active, i.e. The eutectoid reaction is kinetically fast, as concluded by the presence of pearlitic structures. Finally, for the Ti-Cu system this work has been attempted to prove or disprove the existence of the Ti3Cu through the use of XRD and TEM SAD patterns. From XRD spectra collected there are peaks belonging to the Ti3Cu orthorhombic phase along with Ti2Cu and α-Ti phase. In addition to the Ti-Cu system displayed structures associated with divorced eutectoid decomposition mechanism, and at low undercooling seems to be prone to forming solid state dendrites.

D. Tech. Chemical, Metallurgical and Materials Engineering / Discusses the objective of this present study is to manufacture particulate-strengthening Zn-Al-SnO2-TiO2 composite alloy on mild steel from chloride and sulphate baths with the target of improving mechanical and anti-corrosion, wear properties for automotive and decorative applications. Sub-Objectives:To study the effect of Zn-Al-SnO2-TiO2 composite properties on mild steel substrate To investigate the novel multifunctional thin films evolution formed on mild steel and their tribological properties. To investigate thermo-mechanical recrystallization behaviour and its thermal instability.To study the anti-corrosion resistance performance of the electrofabricated quaternary Zn-Al-SnO2-TiO2 coatings.To draw attention to the functional processing parameters of Zn-Al-SnO2-TiO2 produced coatings for high durability.

Ces dernières années, les coûts et la demande en énergie n’ont cessé d’augmenter. Par conséquent, l’humanité fait face à de graves menaces environnementales telles que l'augmentation des rejets de CO2. À cet égard, la communauté internationale doit parvenir à réduire de son empreinte carbone et à veiller à ce que les besoins en énergie thermique soient couverts de manière durable. D’importantes quantités de chaleur résiduaire à basse température (60 - 100°C) sont libérées quotidiennement dans l'atmosphère par de nombreuses installations industrielles. Les thermo-transformateurs de chaleur à absorption constituent un outil intéressant car ils peuvent revaloriser des chaleurs résiduaires pour produire de la chaleur utile pour le chauffage et la production d’eau chaude. Actuellement, les mélanges de travail utilisés dans les pompes à absorption sont les systèmes {ammoniac + eau} et {eau + bromure de lithium}. Cependant, ces deux fluides de travail présentent certains inconvénients tels que la toxicité, la cristallisation et la corrosivité. Par conséquent, il est important de rechercher de nouveaux mélanges de travail. Cette étude a pour objectif d’évaluer l’intérêt d’utiliser des mélanges constitués de liquides ioniques et d'eau au sein de thermo-transformateurs à absorption. Tout d'abord, les propriétés thermodynamiques de ces systèmes binaires (pression de vapeur, densité, capacité thermique et enthalpie d’excès) ont été mesurées dans un large domaine de température et de composition. Ces données expérimentales ont été corrélées à l’aide de modèles thermodynamiques adéquats. Ensuite, les performances de ces fluides de travail ont été évaluées. Les résultats montrent que les systèmes binaires {H2O + Ils} sont une alternative prometteuse aux fluides de travail traditionnels tels que {H2O + LiBr} / Recently, the cost and use of energy continually rise. Hence, humans are close to face serious environmental problems such as increasing CO2 discharges. In this regard, global community is to achieve the ambitious objective of reducing carbon footprint and to ensure that the heating demand is covered in a sustainable manner. Since, enormous amounts of low-temperature waste heat are released on daily bases from many industrial plants to the atmosphere at temperatures between 60 - 100°C. Absorption heat transformers (AHT) are interesting because they can recover low temperature waste heat from different industrial activities and renewable energy sources such as solar and geothermal. AHT can be used to upgrade waste heat to produce useful heat for heating and hot water supplies. Nowadays, the standard working pairs used for AHTs are {ammonia + water} and {water + lithium bromide}. However, both of the working pairs show questionable behavior such as toxicity, crystallization and corrosiveness. Therefore, exploring new working pairs which do not exhibit limitations become of great importance. This work includes an investigation to analyze the AHT systems using {water + ionic liquids} binary systems as working fluids. First, basic thermodynamic properties including vapor pressure, density, heat capacity as well as excess enthalpy of these binary systems were measured at various temperatures with different ionic liquid concentrations. The thermodynamic properties data were correlated by different equations, respectively. The correlated values were significantly consistent with the experimental data. Next, simulation of the AHT performance based on the thermodynamic properties of the new working pairs and on the mass and energy balance for each component of the system were performed. Results show that the {H2O + ILs} binary systems are promising alternatives to replace the already used {H2O + LiBr} working pairs

L’objectif principal de ce travail de thèse est de développer un modèle thermodynamique de type équation d’état cubique, permettant de prédire avec un maximum de précision les propriétés thermodynamiques des corps purs (des comportements de phases aux propriétés énergétiques - enthalpie, capacité calorifique - en incluant les propriétés volumiques) et des mélanges (équilibres de phases dans les régions sub- et supercritiques, points critiques, propriétés énergétiques, densités …), y compris les plus complexes. Concernant les corps purs tout d’abord : en nous appuyant sur la connaissance acquise par les études publiées pendant près d’un siècle et demi sur les équations d’état cubiques, nous avons identifié deux leviers pour accroître la précision de ces modèles. Le premier concerne la sélection d’une fonction α optimale (cette fonction est une quantité clef apparaissant dans le terme attractif du modèle) dont le bon paramétrage permet de représenter précisément les propriétés à saturation des corps purs, telles que la pression de saturation, l’enthalpie de vaporisation et la capacité calorifique du liquide à saturation. Afin que la fonction α puisse être extrapolée au domaine des hautes températures, nous avons défini les contraintes mathématiques que celle-ci doit respecter. Le second levier est le paramètre de translation volumique, paramètre clef pour la bonne représentation des densités liquides. Ces réflexions et les études associées sont à la base du développement des modèles tc-RK et tc-PR, utilisant une fonction α extrapolable à haute température ainsi qu’un paramètre de translation volumique, garantissant une précision jusqu’alors inégalée des propriétés sub- et supercritiques des corps purs prédites par des équations d’état cubiques. Afin d’étendre les modèles tc-RK et tc-PR aux mélanges, il a été nécessaire de développer des règles de mélange appropriées pour deux paramètres de l’équation d’état des mélanges : le covolume et le paramètre attractif. Des règles de mélanges récemment proposées qui combinent équation d’état et modèle de coefficient d’activité ont été adoptées. Les valeurs optimales des paramètres universels de ces règles de mélange ont été identifiées dans le cadre de cette thèse. Une règle de mélange linéaire pour le paramètre de translation volumique du mélange a été sélectionnée ; il a été prouvé que cette règle de mélange garantit l’invariance des propriétés d’équilibre de phases et des propriétés énergétiques entre les modèles translatés et non translatés. Afin de définir le modèle de coefficient d’activité optimal à intégrer dans la nouvelle règle de mélange, une base de données de 200 systèmes binaires a été développée. Ces systèmes binaires ont été sélectionnés afin d’être représentatifs des différents types d’interactions qui peuvent exister dans les mélanges non électrolytiques. La base de données accorde une place significative aux systèmes dits associés, qui sont certainement parmi les plus difficiles à modéliser par une équation d’état. In fine, cette thèse pose toutes les bases du développement d’une équation d’état cubique des mélanges. Le choix du modèle de coefficient d’activité optimal, la détermination des paramètres d’interactions binaires des 200 systèmes de la base de données et leur prédiction constituent des suites possibles de ce travail / The main objective of this thesis work is to develop a cubic equation of state thermodynamic model able to accurately predict the thermodynamic properties of pure compounds (from phase equilibrium data to energetic properties – enthalpy, heat capacity – and volume properties) and mixtures (phase equilibria in sub- and supercritical regions, critical points, energetic properties, densities…), including the most complex ones. Starting with pure compounds: relying on the knowledge collected all through the years from Van der Waals seminal work about cubic equations of state, we identified two levers to increase cubic-model accuracy. First is the selection of the optimal α function (this function is a key quantity involved in the model attractive term) the proper parameterization of which entails an accurate representation of pure-compound saturation properties such as saturation pressure, enthalpy of vaporization, saturated-liquid heat capacity. In order to safely extrapolate an α functions to the high temperature domain, we defined the mathematical constraints that it should satisfy. The second lever is the volume translation parameter, a key parameter for an accurate description of liquid densities. These studies led to the development of the tc-PR and tc-RK models, using an α function that correctly extrapolates to the high temperature domain so as a volume translation parameter, ensuring the most accurate estimations of pure-compound sub- and supercritical property from a cubic equation of state. In order to extend the tc-PR and tc-RK models to mixtures, it was necessary to develop adequate mixing rules for both equation of state parameters: the covolume and the attractive parameter. Recently proposed mixing rules combining an equation of state and an activity coefficient model have been retained. Optimal values of the mixing rules universal parameters have been identified in the framework of this thesis. A linear mixing rule for the volume translation parameter has been selected; it has been proven that this mixing rule does not change the phase equilibrium and energetic properties when switching from a translated to an untranslated model. In order to define the optimal activity coefficient model to include in the new mixing rule, a 200 binary-system database has been developed. These binary systems have been selected to be representative of the different kinds of interactions that can exist in non-electrolytic mixtures. The database includes in particular systems containing associating compounds, which are certainly among the most difficult ones to model with an equation of state. In fine, this thesis sets all the bases for the development of a cubic equation of state for mixtures. The selection of the optimal activity-coefficient model, the estimation of binary interaction parameters for the 200 binary systems from the database and their prediction are possible continuations of this work

M. Tech. (Department of Metallurgical Engineering, Faculty of Engineering Technology), Vaal University of Technology. / This work is an investigation in the development and characterisation of porous Ti-Sn-SiC and Ti-Nb-SiC composites. Pure Titanium (Ti), Tin (Sn), Niobium (Nb) and Silicon carbide (SiC) powders were used as starting materials. The Ti-Sn-SiC and Ti-Nb-SiC composites were produced by powder metallurgy (PM) press-and-sinter route. The Sn is an α-phase stabilizer while Nb is a β-phase stabilizer in Ti alloys. A systematic study of binary Ti-Sn and Ti-Nb alloys was conducted with the addition of SiC particles. The addition of Sn influences the microstructure of the titanium alloy. With increasing the percentage of Sn content, the density of the samples decreases on the Ti-Sn alloys. An increase in the Sn content from 10 to 25 wt. % content resulted in decreased hardness. The Ti-Sn binary revealed stability of the HCP phase with increasing composition of the Sn content. The porous structures of the Ti-Sn-SiC composites were evenly distributed throughout the materials. The sintered densities increase from 94.69% to 96.38%. XRD analysis detected the HCP crystal lattice structure for the Ti5.4Sn3.8SiC and Ti5.6-Sn3.8-SiC composites. XRD pattern of the Ti5.8-Sn3.8-SiC reveals both the HCP and FCC crystal structures. The HCP phase has lattice parameters a= 2.920 Å; c=4.620 Å with smaller c/a ratio of 1.589. Additionally, FCC lattice parameter a=5.620 Å Fm-3m # 225 was obtained both for Ti5.8Sn3.8SiC and Ti6.0Sn3.8SiC XRD patterns. On the other hand, Optical microscopy analysis of the Ti-Nb alloys revealed the equiaxed grains composed of the light β-phase segregating on the grain boundaries. The Ti9Nb1 has low Vickers hardness of all alloys while Ti8Nb2 and Ti7.5Nb2.5 alloys are harder due to high amount of Nb content. Generally, the densities of the Ti–Nb alloys increased with increasing Nb content. HCP and BCC phases have the lattice parameters a = 2.951 Å, c = 4.683 Å and 3.268 Å, respectively. An HCP (α′) phase was detected in the Ti8.5Nb1.5 alloy with lattice parameters a = 5.130 Å, c = 9.840 Å while a BCC phase had a = 3.287 Å. The sintered Ti8Nb2 alloy also had the α′-phase with a = 5.141 Å, c = 9.533 Å and BCC phase with a = 3.280 Å lattice parameters. On the contrary, the Ti7.5Nb2.5 alloy formed the α′-phase of a = 5.141 Å, c = 9.533 Å and BCC with a = 3.280 Å lattice parameters. For the 10 and 15 wt.% Nb alloys, very porous structures were observed. The pores appear spherical and widely distributed. As the Nb content is increased to 20 wt.% (Ti7Nb2SiC) and 25 wt.% (Ti7Nb2.5SiC), porosity was minimized. The sintered densities of the Ti-Sn alloys are decreasing from 95.90% to 92.80% with increased amount of Sn in the Ti, while the sintered densities of Ti-Sn-SiC are increasing from 94.69% to 96.38%. The high porosity, which developed in Ti7Nb1SiC and Ti7Nb2.5SiC, affected the densities of these composites. The sintered densities of Ti-Nb alloys are increasing from 92.08% to 97.65% with increased amount of Nb in the Ti. In terms of hardness Ti7Nb1SiC and Ti7Nb2.5SiC resulted in the lowest while Ti7Nb1.5SiC and Ti7Nb2SiC composites were 511.74 HV and 527.678 HV. The porosity levels were increased by the addition of SiC in the Ti-Sn-SiC and Ti-Nb-SiC composites. The XRD analysis revealed phase transformation on the Ti-Nb alloys and Ti-Nb-SiC composites.

Lisozima mostrou-se capaz, quando dispersa em certos meios orgânico-aquosos, de gerar sistemas pseudoplásticos que evoluem espontaneamente para redes de caráter viscoelástico. Esse fenômeno foi investigado neste estudo, para lisozima dispersa em uma série de misturas binárias contendo derivados de uréia como componente orgânico. Devido aos notáveis efeitos observados para um de tais derivados, a saber, tetrametiluréia (TMU), especial atenção foi dedicada aos sistemas contendo esse composto. O enfoque experimental incluiu espectroscopia Raman, microcalorimetria, reologia e espalhamento de raios X a baixo ângulo (SAXS). O trabalho envolveu o estudo dos sistemas orgânico-aquosos isolados e na presença de proteína. No primeiro caso, foi feita uma investigação espectroscópica e microcalorimétrica dos sistemas quanto a aspectos relativos à segregação de microdomínios na fase liquida e sua conseqüente relação com a deflagração da transição viscoelástica na proteína. Foram observadas descontinuidades nos valores de entalpias de excesso de mistura para o sistema TMU/água em torno de wTMU = 0,6, assim como padrões peculiares de comportamento espectral em torno dessa concentração da mistura binária. No segundo caso, os sistemas complexos de proteínas gerados foram investigados sob o ponto de vista morfológico e dinâmico, através das técnicas reológicas e de SAXS. Energias de ativação de fluxo determinadas na região sub-crítica, de comportamento Newtoniano, mostraram uma dependência exponencial direta com wTMU, indicando que mudanças estruturais nos fluidos complexos já ocorrem em regiões de composição do solvente bem abaixo da região de transição em wTMU = 0,6. Na região viscoelástica, 0,6<wTMU<0,9, ensaios de relaxação indicaram a presença de duas populações distintas. A tangente de perda (tg &#948; = G\"/G\') apresentou valores menores que a unidade para todos os casos, indicando o caráter \"solid-like\" das redes nas condições de ensaio. Apesar de seu caráter sólido, as redes mostram-se bastante flexíveis, suportando grandes deformações antes da ruptura, como inferido a partir da larga região viscoelástica linear. A variação nos módulos elástico (G\') e de perda (G\") com a composição do solvente indica a dependência do caráter viscoelástico com a fração de massa de TMU na mistura binária. Na região de baixo conteúdo de água (wTMU = 0,9), um aumento em G\" após a região viscoelástica linear é observado, indicando aumento da estruturação antes da ruptura da rede. As curvas de SAXS foram modeladas em seus fatores de forma e de interferência com uma equação unificada para objetos aleatoriamente distribuídos em um continuum. Os resultados permitiram a construção de um modelo, compatível com as demais evidências experimentais, segundo o qual as moléculas de lisozima encontram-se em duas conformações distintas nas matrizes: uma de conformação estendida e caráter fractal, predominante em wTMU > 0,6, com dimensão máxima de ca. de 160 &#197;, responsável pela interdigitação com espécies fractais vizinhas e uma espécie compacta, minoritária em wTMU > 0,6 (porém predominante em wTMU <0,6), com raio de giro de ca. 48 &#197;, presente nos microdomínios intersticiais aquosos da matriz. Verificou-se ainda a viabilidade de incorporação homogênea de uma metaloproteína, o citocromo-c, às matrizes de lisozima, sem perturbação significativa de sua morfologia, o que constitue um evento de potencial interesse biotecnológico. Os resultados deste trabalho trazem novos suportes experimentais à hipótese de correlação entre inversão na microconfiguração do meio solvente binário e deflagração do processo de transição sol-gel da proteína. / Lysozyme was found to be able, when dispersed in certain organic/aqueous media, to generate pseudoplastic systems that spontaneously evolve to three-dimensional networks with viscoelastic character. This phenomenon was investigated in this study, for lysozyme dispersed in a series of binary mixtures containing urea derivatives as the organic component. Due to the remarkable effects obtained in one of such derivatives, namely, tetramethylurea (TMU), special attention was given to systems containing that compound. The experimental approach included Raman spectroscopy, microcalorimetry, rheology and small angle X ray scattering (SAXS). The work involved the study of the organic/aqueous systems on their own and in the presence of protein. The former consisted of binary liquid mixtures that were spectroscopically and microcalorimetrically investigated as to aspects concerning microdomain segregation in the liquid phase and its consequent relationship with the threshold of the protein viscoelastic transition. Discontinuities in the excess enthalpy of mixture were observed for TMU/water system around wTMU=0.6, as well as peculiar spectral patterns around that same binary mixture concentration. The latter comprised complex protein systems that were investigated both under a morphological and dynamical point of view. Flow activation energies determined in the sub-critical (Newtonian) region showed an exponential increase with wTMU, indicating that structural changes in the comp]ex fluids are under way at solvent concentration regions well below that of the transition, at wTMU = 0.6. In the viscoelastic region, 0.6<wTMU<0.9, relaxation studies indicated the presence of two distinct populations. The loss tangent (tan &#948; = G\"/G\') presented values lower than the unity for all cases, indicating the solid-like character of the matrices, in the assay conditions. Despite their solid character the networks are quite flexible, standing large strains before rupture, as inferred from the large linear viscoelastic region. The variation in elastic (G\') and loss (G\") moduli with solvent composition indicates a dependence of the viscoelastic character on TMU mass fraction in the binary mixture. In the region of low water content (wTMU = 0.9), an increase in G\" after the LVR is observed, indicating increase in network structuring before rupture. SAXS curves were modeled with a unified equation for randomly distributed objects in a continuum. Results allowed the proposal of a model, which is compatible with the experimental evidence obtained through the other techniques in this work, according to which lysozyme molecules occur in two distinct conformations: one expanded and with fractal character, prevailing at wTMU > 0.6, with maximum dimension ca. 160 &#197; and interdigitated with neighbouring fractal species; and a compact conformation, of minor prevalence at wTMU>0.6 (but prevailing at wTMU < 0.6), with radius of gyration ca. 48 &#197;, present in the matrix microdomain interstices. It has also been verified the feasibility of homogeneous incorporation of cytochrome-c into the lysozyme matrices, an event of potential biotechnological interest. Results from this work bring further experimental support to our hypothesis on the correlation between microconfigurational inversion in the binary solvent medium and the sol-gel transition in the protein.

The theory of stellar evolution and stellar structure relies on the observation of stars in di erent phases of their evolutionary cycle. The relation between observations and theory can be strengthened by obtaining observational data of a large sample of stars in a particular evolutionary phase. The search for Cephei stars, as conducted in this study, can contribute to the sample of known Cephei stars, where these interesting stars are massive non-supergiant early B-type stars, displaying pulsating behaviour which is not well understood. Stars tend to form in clusters where it can therefore be expected that young massive stars can be found in open clusters. For this reason two young southern open clusters were observed in order to search for B-type pulsating stars. The region of NGC 6204 and Hogg 22 was observed over a period of thirteen nights in Johnson B, V and I bands. NGC 6204 is believed to be the oldest cluster of the two at a distance of 0.8 kpc while the much younger Hogg 22 is more distant at 2.8 kpc. These two open clusters are located 6 arcminutes apart which made it possible to observe them simultaneously with a 12.8 12.8 arcminute eld of view. The observations were done with the newly installed 1600 telescope of the North-West University, South Africa. In order to do a variability search, periodic stars need to be identi ed from the cluster data, where a typical data set may contain thousands of scienti c images. In addition to the main motivation for this study, a pipeline was created in order to automate the photometry and data reduction processes. A Lomb-Scargle transform was applied to the stellar light curves in order to identify periodic sources. 354 signi cantly periodic stars were identi ed from the 3182 observed stars. Amongst them, two new possible Cephei stars were found together with a possible slowly pulsating B star (SPB), and numerous eclipsing binary systems. By using photometry of this region obtained by Forbes & Short (1996), instrumental magnitudes were transformed to a standard system in order to compare photometry results. From the constructed colour magnitude diagram of the two clusters, it could be seen that some stars, indicated by Forbes & Short (1996) to be cluster members, were in fact eld stars belonging to neither cluster. The reduction and photometry pipeline was implemented successfully on the data set, which also highlighted the importance of instrumentation and correct data analysis procedures. Possible improvements were identi ed in order to overcome di culties experienced during this study. / Thesis (MSc (Space Physics))--North-West University, Potchefstroom Campus, 2013