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Cold-formed steel roof truss systems that use complex stiffener patterns in existing hat shape members for both top and bottom chord elements are a growing trend in the North American steel framing industry. When designing cold-formed steel sections, a structural engineer typically tries to improve the local buckling behavior of the cold-formed steel elements. The complex hat shape has proved to limit the negative influence of local buckling, however, distortional buckling can be the controlling mode of failure in the design of chord members with intermediate unbraced lengths. The chord member may be subjected to both bending and compression because of the continuity of the top and bottom chords. These members are not typically braced between panel points in a truss. Current 2001 North American Specifications (NAS 2001) do not provide an explicit check for distortional buckling. This dissertation focuses on the behavior of complex hat shape members commonly used for both the top and bottom chord elements of a cold-formed steel truss. The results of flexural tests of complex hat shape members are described. In addition, stub column tests of nested C-sections used as web members and full scale cold-formed steel roof truss tests are reported. Numerical analyses using finite strip and finite element procedures were developed for the complex hat shape chord member in bending to compare with experimental results. Both elastic buckling and inelastic postbuckling finite element analyses were performed. A parametric study was also conducted to investigate the factors that affect the ultimate strength behavior of a particular complex hat shape. The experimental results and numerical analyses confirmed that modifications to the 2001 North American Specification are necessary to better predict the flexural strength of complex hat shape members, especially those members subjected to distortional buckling. Either finite strip or finite element analysis can be used to better predict the flexural strength of complex hat shape members. Better understanding of the flexural behavior of these complex hat shapes is necessary to obtain efficient, safe design of a truss system. The results of these analyses will be presented in the dissertation. / Ph. D.

Sistemas diferenciais quadráticos planares estão presentes em muitas áreas da matemática aplicada. Embora mais de mil artigos tenham sido publicados sobre os sistemas quadráticos ainda resta muito a se conhecer sobre esses sistemas. Problemas clássicos, e em particular o XVI problema de Hilbert, estão ainda em aberto para essa família. Um dos objetivos dos pesquisadores contemporâneos é obter a classificação topológica completa dos sistemas quadráticos. Devido ao grande número de parâmetros (essa família possui doze parâmetros e, aplicando transformações afins e reescala do tempo, reduzimos esse número a cinco, sendo ainda um número grande para se trabalhar) usualmente subclasses são consideradas nas investigações realizadas. Quando características específicas são levadas em consideração, o número de parâmetros é reduzido e o estudo se torna possível. Nesta tese estudamos principalmente duas subfamílias de sistemas quadráticos: a primeira possuindo um nó triplo semielemental e a segunda possuindo uma selanó semi elemental finita e uma selanó semielemental infinita formada pela colisão de uma sela infinita com um nó infinito. Os diagramas de bifurcação para ambas as famílias são tridimensionais. A família tendo um nó triplo gera 28 retratos de fase topologicamente distintos, enquanto o fecho da família tendo as selasnós dentro do espaço de bifurcação de sua forma normal gera 417. Polinômios invariantes são usados para construir os conjuntos de bifurcação e os retratos de fase topologicamente distintos são representados no disco de Poincaré. Os conjuntos de bifurcação são a união de superfícies algébricas e superfícies cuja presença foi detectada numericamente. Ainda nesta tese, apresentamos todos os retratos de fase de um sistema diferencial conhecido como modelo do tipo SIS (sistema suscetívelinfectadosuscetível, muito comum na matemática aplicada) e a classificação dos sistemas quadráticos possuindo hipérboles invariantes. Ambos sistemas foram investigados usando de polinômios invariantes afins. / Planar quadratic differential systems occur in many areas of applied mathematics. Although more than one thousand papers have been written on these systems, a complete understanding of this family is still missing. Classical problems, and in particular Hilberts 16th problem, are still open for this family. One of the goals of recent researchers is the topological classification of quadratic systems. As this attempt is not possible in the whole class due to the large number of parameters (twelve, but, after affine transformations and time rescaling, we arrive at families with five parameters, which is still a large number), many subclasses are considered and studied. Specific characteristics are taken into account and this implies a decrease in the number of parameters, which makes possible the study. In this thesis we mainly study two subfamilies of quadratic systems: the first one possessing a finite semielemental triple node and the second one possessing a finite semielemental saddlenode and an infinite semielemental saddlenode formed by the collision of an infinite saddle with an infinite node. The bifurcation diagram for both families are tridimensional. The family having the triple node yields 28 topologically distinct phase portraits, whereas the closure of the family having the saddlenodes within the bifurcation space of its normal form yields 417. Invariant polynomials are used to construct the bifurcation sets and the phase portraits are represented on the Poincaré disk. The bifurcation sets are the union of algebraic surfaces and surfaces whose presence was detected numerically. Moreover, we also present the analysis of a differential system known as SIS model (this kind of systems are easily found in applied mathematics) and the complete classification of quadratic systems possessing invariant hyperbolas.

Sistemas diferenciais quadráticos planares estão presentes em muitas áreas da matemática aplicada. Embora mais de mil artigos tenham sido publicados sobre os sistemas quadráticos ainda resta muito a se conhecer sobre esses sistemas. Problemas clássicos, e em particular o XVI problema de Hilbert, estão ainda em aberto para essa família. Um dos objetivos dos pesquisadores contemporâneos é obter a classificação topológica completa dos sistemas quadráticos. Devido ao grande número de parâmetros (essa família possui doze parâmetros e, aplicando transformações afins e reescala do tempo, reduzimos esse número a cinco, sendo ainda um número grande para se trabalhar) usualmente subclasses são consideradas nas investigações realizadas. Quando características específicas são levadas em consideração, o número de parâmetros é reduzido e o estudo se torna possível. Nesta tese estudamos principalmente duas subfamílias de sistemas quadráticos: a primeira possuindo um nó triplo semielemental e a segunda possuindo uma selanó semi elemental finita e uma selanó semielemental infinita formada pela colisão de uma sela infinita com um nó infinito. Os diagramas de bifurcação para ambas as famílias são tridimensionais. A família tendo um nó triplo gera 28 retratos de fase topologicamente distintos, enquanto o fecho da família tendo as selasnós dentro do espaço de bifurcação de sua forma normal gera 417. Polinômios invariantes são usados para construir os conjuntos de bifurcação e os retratos de fase topologicamente distintos são representados no disco de Poincaré. Os conjuntos de bifurcação são a união de superfícies algébricas e superfícies cuja presença foi detectada numericamente. Ainda nesta tese, apresentamos todos os retratos de fase de um sistema diferencial conhecido como modelo do tipo SIS (sistema suscetívelinfectadosuscetível, muito comum na matemática aplicada) e a classificação dos sistemas quadráticos possuindo hipérboles invariantes. Ambos sistemas foram investigados usando de polinômios invariantes afins. / Planar quadratic differential systems occur in many areas of applied mathematics. Although more than one thousand papers have been written on these systems, a complete understanding of this family is still missing. Classical problems, and in particular Hilberts 16th problem, are still open for this family. One of the goals of recent researchers is the topological classification of quadratic systems. As this attempt is not possible in the whole class due to the large number of parameters (twelve, but, after affine transformations and time rescaling, we arrive at families with five parameters, which is still a large number), many subclasses are considered and studied. Specific characteristics are taken into account and this implies a decrease in the number of parameters, which makes possible the study. In this thesis we mainly study two subfamilies of quadratic systems: the first one possessing a finite semielemental triple node and the second one possessing a finite semielemental saddlenode and an infinite semielemental saddlenode formed by the collision of an infinite saddle with an infinite node. The bifurcation diagram for both families are tridimensional. The family having the triple node yields 28 topologically distinct phase portraits, whereas the closure of the family having the saddlenodes within the bifurcation space of its normal form yields 417. Invariant polynomials are used to construct the bifurcation sets and the phase portraits are represented on the Poincaré disk. The bifurcation sets are the union of algebraic surfaces and surfaces whose presence was detected numerically. Moreover, we also present the analysis of a differential system known as SIS model (this kind of systems are easily found in applied mathematics) and the complete classification of quadratic systems possessing invariant hyperbolas.

The thesis presents an experimental investigation of combustion performance and emissions of waste cooking oil (WCO) based biodiesel. To evaluate the comparative performance of biodiesel and diesel, combustions tests were conducted using Continuous Combustion rig (CCR) and Land Rover VM diesel engine. Firstly, physical properties of WCO biodiesel and diesel samples were measured in the laboratory. Elemental analysis of WCO biodiesel showed that there are differences between the functional groups in diesel and biodiesel which lead to major differences in the combustion characteristics of the two fuel types. It was found that biodiesel had 10% lower carbon content, almost no sulphur content for biodiesel and up to 12% more oxygen content compared with diesel. This explains the lower caloric value for WCO biodiesel (up to l8 %) compared with diesel. However, higher oxygen content and double bounds in WCO biodiesel increase its susceptibility to oxidation. The CCR test results showed an increase in combustion gas temperature with the increases in biodiesel blend ratio in diesel. This was due to a faster reaction rate for biodiesel than that of diesel leading to a faster brakeage of the hydrocarbon chain to release more heat. The engine tests were performed to measure the torque and emissions for different engine speeds and loads. In general a decrease in engine torque with up to 9% for biodiesel was observed, which was due to the lower calorific value of biodiesel compared with that of diesel. The brake specific fuel consumption (BSFC) increased as the biodiesel blend ratio in diesel increases due a greater mass of fuel being injected at a given injection pressure, compared with diesel. Using WCO blends ratio up to 75% in diesel showed a reduction in exhaust emission compared with diesel, however, at the cost of increased fuel consumption. A common conclusion can be drawn in favour of the WCO biodiesel as being a greener alternative to petro-diesel when used in blend with diesel. However, due to large variations in the biomass used for biodiesel production could lead to variations in physical and chemical properties between biodiesel produced from different biomass. Therefore more stringent standards need to be imposed for biodiesel quality in order to diminish the effect of variation in physicochemical properties on engine performance and emissions. The future work in developing standard test procedures for establishing fuel properties and limits/targets would be beneficial in using a large amount of waste cooking oil in the production of biodiesel, thus contributing to reduction in CO2 and waste minimisation.

Esta investigación tiene como propósito comprender, documentar y describir cómo ampliar la participación del alumnado a través del análisis en profundidad de cinco experiencias desarrolladas en centros de educación infantil y primaria de la Comunidad de Cantabria. Utilizamos la expresión de voz como metáfora para reivindicar el derecho de los alumnos/as a participar en la toma de decisiones de los aspectos relevantes de la vida de la escuela, de su aprendizaje y de los procesos de mejora educativa y social (Fielding, 2004, 2011; Cook Sather, 2006; Rudduck y Flutter, 2007; Gunter y Thomson, 2007; Susinos y Ceballos, 2012; Grion y Cook-Sather, 2013). Atendiendo a este propósito se ha diseñado una investigación cualitativa-etnográfica (Hammersley and Atkinson, 1994) que atiende a tres momentos: la fase extensiva busca construir una mirada amplia de las experiencias de participación del alumnado existentes en los centros educativos de Cantabria a través del discurso de informantes claves: orientadores educativos y asesores de formación. La fase intensiva supone el análisis de cinco experiencias de voz del alumnado en las etapas de educación infantil y primaria. Y, por último, la elaboración de una guía para el desarrollo de experiencias de voz del alumnado que busca inspirar a profesionales en ejercicio para la puesta en marcha y desarrollo de experiencias de voz del alumnado. / The aim of our research is to understand, document and describe how pupil participation can be increased in schools through the in-depth analysis of five experiences developed in nursery and primary schools in the Autonomous Community of Cantabria, Spain. When the term the student voice is used in this research it is used as a metaphor for recognizing and asserting the right of students to participate and be involved in making decisions on areas relevant to school life, their learning and educational and social transformation (Fielding, 2004, 2011; Cook Sather, 2006; Rudduck and Flutter, 2007; Gunter and Thomson, 2007; Susinos and Ceballos, 2012; Grion and Cook-Sather, 2013). In order to do this, our research has been carried out within the paradigm of qualitative research based on an ethnographic perspective (Hammersley and Atkinson, 1994) and it was designed to address three moments or phases: the extensive phase aims to create a broad view of the experiences of existing pupil participation in schools in Cantabria through the discourse of key informants: educational counsellors and training advisors. The intensive phase involves the direct analysis of five experiences of the student voice in nursery and primary education. We have paid attention to the different strategies of participation used in them. The third phase is the elaboration of a guide for the development of student voice experiences in order to inspire professionals in their work in the implementation and development of these types of experiences.

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Science), Vaal University of Technology / Cadmium and cobalt complexes of urea and thiourea were synthesized using ethanol as a solvent. All complexes were refluxed at 70 - 80 °C, left to cool at room temperature, washed with methanol and acetone to remove impurities and dried at an open environment. The characterization of complexes was done using FTIR spectroscopy, elemental analysis and TGA. The complexes were found to coordination with the ligands through sulphur and oxygen atoms to the metal, instead of nitrogen. These were as results of wavelength shifting from high to low frequency from spectra of the complexes as compare to their free ligands. These observations make these complexes good candidates for the possible use in synthesis of metal sulphides or oxides nanoparticles. Thermogravimetric analyses of all the complexes were conducted to check the stability of use as precursors for nanoparticles at low and high temperature. A number of thiourea and urea complexes with cadmium and cobalt have been prepared and used in the preparation of metal sulphides/oxides nanoparticles. Complexes start to decompose at low temperature about 100°C and the last decomposition step was at about 800-900°C, which is convenient to thermal decomposition of precursors in the high boiling solvents or capping agent to prepare surface capped metal sulphides/oxides nanoparticles. The complexes were easy to synthesize, low cost and stable in air and were obtained in reasonable yields. All the complexes reported in this study have been used as single source molecular precursor in the preparation of cadmium oxide, cadmium sulphide, cobalt oxide, cobalt sulphide nanoparticles (normal) and as mixture of any two complexes to form core-shells nanoparticles. Quality nanoparticles synthesis requires three components: precursors, organic surfactants and solvents. The synthesis of the nanoparticles can be thought of as a nucleation event, followed by a subsequent growth period. Both the nucleation and growth rates were found to be dependent upon factors such as temperature, growth time, and precursor concentration. For a continuous flow system the residence time (at nucleation and growth conditions) was also found to be important. In order to separate the nucleation and growth events, injection techniques were employed to achieve rapid nucleation of nanoparticles with final size dictated by the growth temperature and/or residence time through the growth zone of the reaction system. Good crystalline normal nanoparticles were obtained from thermolysis of the precursors in hexadecylamine (HDA) as the capping agent at fixed concentrations, temperature and time. All nanoparticles showed a blue-shift in band edges with good photoluminescence behaviour which is red-shifted from their respective band edges and XRD patterns, the crystal structure are in hexagonal phase. The particles showed rods, spheres and hexagonal shapes. Nucleation and growth mechanism brings new avenue in nanostructures called core-shells, which have been reported to have improved luminescence, quantum yields, decreased fluorescence lifetimes, and benefits related to the tailoring of the relative band-gap positions between the two materials. In this study cadmium and cobalt complexes of urea and thiourea were separately dispersed in TOP and injected separately (allowing nucleation/core to occur, followed by the shell) in hot HDA at 180ºC for 1hour to yield core-shell nanoparticles. Parameters, such as concentration, temperature and capping molecule as factor affecting nucleation and growth of the core-shells were monitored. The core-shell nanoparticles were characterized by UV/Vis spectroscopy, XRD and TEM. We observed spherical, tripod, bipods, hexagonal and irregular shaped nanoparticle as the concentration of the precursors was increasing, however we were able to form core-shells nanoparticles in one set of experiment 1:3 CdS-CdO, which are assumed to be a reverse type I coreshells nanoparticles. Exciton absorption peaks at higher energy than the fundamental absorption edge of bulk indicate quantum confinement effect in nanoparticles as a consequence of their small size. XRD patterns, crystals range from hexagonal, cubic and mixture of hexagonal and orthorhombic. A low temperature studies were also conducted a mixture of hexagonal and sphererical shapes with sheets like onion morphology were observed. / NRF HUB & SPOKES (VUT)

Cette étude est consacrée aux monnaies d’or et d’argent lagides comme moyen de l’action des rois d’Alexandrie entre l’avènement de Ptolémée V en 204 et la mort de Ptolémée IX en 81. Ce grand deuxième siècle est habituellement considéré comme un temps de crise profonde du pouvoir royal, alors aux prises avec des révoltes en Égypte, des luttes dynastiques et affaibli par la perte de la plupart des territoires extérieurs hormis Chypre et Cyrène. Dans ce contexte, la place et le rôle des émissions ptolémaïques dans la gestion du royaume par les Ptolémées peuvent être questionnés. Pour cela, nous avons répertorié 6 413 pièces au sein d’un catalogue dans le but de collecter un maximum d’informations ainsi que pour réaliser une étude des niveaux de production tout au long de la période. A cela s’ajoute l’établissement d’un catalogue des trésors et trouvailles isolées remis à jour. Une deuxième partie est dédiée à l’importance ainsi qu’aux classements de ces émissions qui sont discutés et parfois révisés au regard des informations réunies. Pour cela, les 380 analyses élémentaires de monnaies d’or et d’argent réalisées à l’IRAMAT fournissent une somme d’informations inédites. Enfin, nous tentons d’insérer les nouvelles données produites dans les connaissances générales de l’histoire du royaume des Ptolémées au IIe siècle. L’enjeu est de déterminer dans quelle mesure l’usage de la monnaie peut être un révélateur des politiques royales. Il convient également de définir l’importance de ce moyen de paiement et dans quels cas il est employé. Ainsi, le témoignage des monnaies permet d’analyser certains aspects de la réaction du pouvoir royal lagide face aux difficultés rencontrées au IIe siècle. / This study is dedicated to the Ptolemaic gold and silver coins as means of action of kings of Alexandria from the advent of Ptolemy V in 204 until the death of Ptolemy IX in 81. This expanded second century is usually considered as a time of deep crisis of the royal power, then battling against internal revolts in Egypt, dynastic fights and weakened by the loss of most of the foreign territories except Cyprus and Cyrene. In this context, the place and the role of the Ptolemaic issues in the management of the kingdom by the Ptolemies can be questioned. We listed 6 413 coins within a catalog to collect a maximum of information there as well as to realize a study of the levels of production throughout the all period. Then, an updated catalog of hoards and isolated finds is added. The second part is dedicated to the whole importanceas well as to the classifications of these broadcast issues which are discussed and sometimes revised with regards to the information gathered. For that purpose, the contribution of 380 elemental analysis of gold and silver coins achieved in the IRAMAT laboratory supplies a sum of new information. Finally, we try to insert the new data produced intothe general knowledge of the history of the Ptolemaic kingdom in the second century. The stake is to determine to what degree the use of coins can reflect the royal policies. It is also advisable to define the importance of this means of payment and in which cases it is used. In the end, the testimony of coinage allows us to analyze certain aspects of the reaction of the Ptolemaic royal power confronting difficulties met in the second century.

PIXE, Particle Induced X-ray Emission, est une méthode d’analyse multiélémentaire, rapide, non destructive, basée sur la détection des rayons X caractéristiques émis suite à l’interaction de particules chargées avec la matière. Cette méthode est usuellement utilisée avec des protons accélérés à une énergie de l’ordre de quelques MeV dans des domaines d’applications variés, atteignant une limite de détection de l’ordre de quelques μg/g (ppm). Cependant, la profondeur d’analyse est relativement limitée. Grâce au cyclotron ARRONAX, nous pouvons utiliser des protons ou des particules alpha jusqu’à une énergie de 70 MeV pour mettre en œuvre la technique PIXE à haute énergie. Avec de telles énergies, nous excitons préférentiellement les raies X K, plus énergétiques que les raies L utilisées dans la PIXE classique pour l’analyse des éléments lourds. L’analyse d’échantillons épais, en profondeur, est ainsi accessible. Pour l’analyse des éléments légers, nous pouvons utiliser la détection de rayons gamma émis pas les noyaux excités en combinant les méthodes PIGE et PIXE. Nous allons tout d’abord présenter les caractéristiques et les principes d’analyse de la méthode PIXE à haute énergie que nous avons développée à ARRONAX. Nous détaillerons ensuite les performances atteintes, notamment en termes de limite de détection dans différentes conditions expérimentales. Enfin, nous présenterons les résultats obtenus pour l’analyse d’échantillons multicouches et la quantification d’éléments traces dans des échantillons épais. / Particle Induced X-ray Emission (PIXE) is a fast, nondestructive, multi-elemental analysis technique. It is based on the detection of characteristic X-rays due to the interaction of accelerated charged particles with matter. This method is successfully used in various application fields using low energy protons (energies around few MeV), reaching a limit of detection of the order the μg/g (ppm). At this low energy, the depth of analysis is limited. At the ARRONAX cyclotron, protons and alpha particles are delivered with energy up to 70 MeV, allowing the development of the High Energy PIXE technique. Thanks to these beams, we mainly produce KX-rays, more energetic than the LX-rays used with standard PIXE for the heavy elements analysis. Thus, in depth analysis in thick materials is achievable. For light element analysis, the PIGE technique, based on the detection of gamma rays emitted by excited nuclei, may be used in combination with PIXE. First of all, we will introduce the characteristics and principles of high energy PIXE analysis that we have developed at ARRONAX. Then we will detail the performance achieved, particularly in terms of detection limit in various experimental conditions. Finally, we present the results obtained for the analysis of multilayer samples and quantification of trace elements in thick samples.