The aim of this research project was to assemble an apparatus to measure the electric quadrupole moments of gas molecules using the technique of electricfield- gradient-induced birefringence, or the Buckingham effect. Comprehensive research by various workers in the field has shown that this technique provides the only direct means of obtaining the quadrupole moment of a molecule. Theory has shown that the most accurate determination of the electric quadrupole moment is through a study of the temperature dependence of the effect. This not only allows for the quadrupole moment to be obtained but also enables the temperature-independent quadrupole hyperpolarisability term to be extracted. Both the quadrupole moment and the hyperpolarisabilty provide valuable information in a variety of applications, including intermolecular forces, electrostatic potentials and non-linear optical phenomena. This thesis fully describes the apparatus used in these measurements, including a description of the custom built oven that allowed for measurements to be performed over a temperature range spanning from 25"C up to 200"C. Results for the quadrupole moments and quadrupole hyperpolarisabilities of carbon dioxide, carbon monoxide, nitrous oxide and hydrogen are presented, together with a quadrupole moment for carbonyl sulphide from room-temperature measurements. Wherever possible, the results of this work are compared to previously published experimental and theoretical data. / Thesis (PhD) - University of KwaZulu-Natal, Pietermaritzburg, 2009.

This dissertation consists of three essays concerning the effects of human capital and health capital on the labor market. Chapter 1 presents a structural model that incorporates a health capital stock to the traditional learning-by-doing model. The model allows health to affect future wages by interrupting current labor supply and on-the-job human capital accumulation. Using data on sick time from the Panel Study Income of Dynamics the model is estimated using a nonlinear Generalized Method of Moments estimator. The results show human capital production exhibits diminishing returns. Health capital production increases with the current stock of health capital, or better current health improves future health. Among prime age working men, the effect of health on human capital accumulation is relatively small. Chapter 2 explores the role of another form of human capital, noncognitive skills, in explaining racial gaps in wages. Chapter 2 adds two noncognitive skills, locus of control and self-esteem, to a simple wage specification to determine the effect of these skills on the racial wage gap (white, black, and Hispanic) and the return to these skills across the wage distribution. The wage specifications are estimated using pooled, between, and quantile estimators. Results using the National Longitudinal Survey of Youth 1979 show these skills account for differing portions of the racial wage gap depending on race and gender. Chapter 3 synthesizes the idea of health and on-the-job human capital accumulation from Chapter 1 with the idea of noncognitive skills in Chapter 2 to examine the influence of these skills on human capital and health capital accumulation in adult life. Chapter 3 introduces noncognitive skills to a life cycle labor supply model with endogenous health and human capital accumulation. Noncognitive skills, measured by degree of future orientation, self-efficacy, trust-hostility, and aspirations, exogenously affect human capital and health production. The model uses noncognitive skills assessed in the early years of the Panel Study of Income Dynamics and relates these skills to health and human capital accumulation during adult life. The main findings suggest individuals with high self-efficacy receive higher future wages.

Distraction osteogenesis (DO) is a surgical procedure in which applied strain stimulates new bone growth; however, the underlying mechanisms by which bone cells respond to load are still uncertain. An organ culture model of DO was developed and validated by using linear distraction on the femoral shafts of 5 day old Wistar rats. Two loading regimes were utilized: distracting the bones for 2 hrs on day 1 (GRP I); distracting the bones for 2 hrs on days 1, 3, and 5 (GRP II). After 1 week in culture, the bones were compared to unloaded contralateral controls and assessed for changes. Structural, dimensional, massing, micro-CT, areal, and viability properties were obtained from testing. Relative to paired controls, distracted bones demonstrated an increase in failure load (9.15% GRP I, 18.85% GRP II), increase in stiffness (31.28% GRP I, 53.21% GRP II), increases in areal and polar moments of inertia, and viability (6.21% GRP I, 13.02% GRP II). Our results suggest that DO can be modeled successfully with an organ culture, and continued use of this system will help to gain insight into the mechanisms and pathways by which distraction osteogenesis occurs.

No description available.

Les travaux présentés dans cette thèse portent sur la conception robuste de produit et plus particulièrement sur la phase de pré-dimensionnement dans le cas où un modèle de dimensionnement et un cahier des charges sont déjà définis. Une approche pour réaliser de l'optimisation robuste est proposée pour réduire la dispersion de la fonction objectif du cahier des charges du produit lorsque les paramètres de conception sont sujets aux incertitudes, conserver une bonne performance du produit et assurer une faisabilité des contraintes. Nous proposons ainsi la formulation d'un cahier des charges dit " robuste " transformant la fonction objectif et les contraintes du cahier des charges initial afin d'intégrer une notion de robustesse préalablement définie. La seconde contribution est une analyse des méthodes trouvées dans la littérature pour la propagation d'incertitudes à travers des modèles de dimensionnement. Les variations des paramètres sont alors modélisées par des dispersions probabilistes. L'analyse théorique du fonctionnement de chaque méthode est complétée par des tests permettant d'étudier la précision des résultats obtenus et de sélectionner la méthode utilisée par la suite. L'approche pour l'optimisation robuste de produit proposée dans ce travail est finalement mise en œuvre et testée sur deux études de cas. Elle intègre la méthode de propagation d'incertitudes dans une boucle de l'algorithme d'optimisation de manière à automatiser la recherche d'une solution optimale robuste pour le dimensionnement du produit.

Cette thèse propose des contributions très prometteuses au sujet du choix des primitives visuelles en asservissement visuel utilisant les moments 2D extraits de l'image. Nous avons proposé une nouvelle manière de résoudre un problème important en asservissement visuel, à savoir la commande du mouvement de rotation suivant les axes orthogonaux à l'axe optique. Ce travail représente une amélioration significative des travaux précédents en asservissement visuel basé sur l'utilisation des moments 2D extraits de l'image pour commander les degrés de liberté des robots manipulateurs. La commande la plus utilisée est connue sous le nom de commande cinématique. L'approche emploie un descripteur global d'image basé sur des moments 2D "shifted" dont les invariants calculés à partir de ces moments 2D "shifted" utilisent des moments d'ordre faible connus pour être robustes au bruit. De plus, ces invariants choisis ne dépendant pas de la forme de l'objet, sont invariants au mouvement de translation, de rotation et d'échelle. Cette nouvelle façon de faire vient ainsi résoudre les problèmes vus dans les travaux précédents relatifs aux choix des combinaisons des moments invariants basés sur les moments centrés et qui dépendent de la forme de l'objet considéré. Dans les travaux précédents, ces invariants sont calculés avec des moments dont l'ordre est compris entre trois et cinq qui sont vulnérables aux bruits de mesure. D'un point de vue asservissement visuel, le travail est basé sur la détermination explicite de la matrice d'interaction calculée à partir des moments 2D "shifted" dont le choix des paramètres de décalages respectent les propriétés d'invariances aux mouvements de translation, de rotation et d'échelle. En procédant ainsi, les informations visuelles choisies montrent la capacité de représenter les objets de formes symétriques et non symétriques. Des résultats de simulations sont présentés pour illustrer la validité de notre proposition.

The work presented in this thesis describes an investigation into the properties and behaviour of a new class of nonlinear optical organic chromophores. This study contributes to the optimisation of nonlinear optical molecules through an improved understanding of the relationships between the molecular nonlinear optical properties and the measured macroscopic quantities. A series of highly dipolar non-linear optical chromophores with absorption typically in the range of 350-500 nm have been synthesised by the reactions of amines with tetracyanoquinodimethane (TCNQ). One of the advantages of these materials is the large molecular figure of merit (μβ where μ is the molecular dipole moment and P is the second order polarisability), which theoretically allows large nonlinear optical coefficients to be obtained. The molecular dipole moments of these chromophores were determined both experimentally and theoretically, and were found to agree. The nonlinear optical properties of these compounds in solution were studied using an electric field induced second harmonic generation (EFISH) technique. The measurements of μβ at 1064 nm and 1907 nm in chloroform and acetone are presented. Moderate μβ values were obtained but β is found to be unexpectedly small in chloroform and shows unusual dispersion characteristics in this solvent compared to acetone. Further concentration investigations revealed features that suggest the presence of aggregates within solution. Optical spectroscopy measurements provide evidence of new species whose presence and conformation were found to be solvent-dependent. The results of this work highlight the need for an entire concentration range to be studied if accurate determination of molecular properties of highly dipolar molecules is required. Guest-host polymer films of these materials have been corona poled using a constant current corona triode. Detailed characterisation studies of the second order nonlinearities using second harmonic generation (SHG) were compared to a less dipolar molecule. These investigations showed that the highly dipolar TCNQ derivatives show severe aggregation within the polymer films. The magnitude of the SHG that can be obtained from such systems is therefore limited by this aggregation.

A novel delamination identification technique based on a low-population genetic algorithm for the quantitative characterisation of a single delamination in composite laminated panels is developed, and validated experimentally The damage identification method is formulated as an inverse problem through which system parameters are identified. The input of the inverse problem, the central geometric moments (CGM), is calculated from the surface out-of-plane displacements measurements of a delaminated panel obtained from Digital Speckle Pattern Interferometry (DSPI). The output parameters, the planar location, size and depth of the flaw, are the solution to the inverse problem to characterise an idealised elliptical flaw. The inverse problem is then reduced to an optimisation problem where the objective function is defined as the L2 norm of the difference between the CGM obtained from a finite element (FE) model with a trial delamination and the moments computed from the DSPI measurements. The optimum crack parameters are found by minimising the objective function through the use of a low-population real-coded genetic algorithm (LARGA). DSPI measurements of ten delaminated T700/LTM-45EL carbon/epoxy laminate panels with embedded delaminations are used to validate the methodology presented in this thesis.

The primary subject of this thesis is graphene and how the rudimentary attributes of its charge carriers, and local moments on its surface, can be directly manipulated and controlled with electrostatic potentials. We first consider bilayer graphene subject to a spatially varying electrostatic potential that forms two neighbouring regions with opposite interlayer bias. Along the boundary, 1D chiral `kink' states emerge. We find that these 1D modes behave as a strongly interacting Tomonaga-Luttinger liquid whose properties can be tuned via an external gate. Next, we consider superlattices in bilayer graphene. Superlattices are seen to have a more dramatic effect on bilayer graphene than monolayer graphene because the quasiparticles are changed in a fundamental way; the dispersion goes from a quadratic band touching point to linearly dispersing Dirac cones. We illustrate that a 1D superlattice of either the chemical potential or an interlayer bias generates multiple anisotropic Dirac cones. General arguments delineate how certain symmetries protect the Dirac points. We then map the Hamiltonian of an interlayer bias superlattice onto a coupled chain model comprised of `topological' edge modes. We then discuss the relevance of spatially varying potentials to recent transport measurements. This is followed by another study that considers the effect of a magnetic field on graphene superlattices. We show that magnetotransport measurements in a weak perpendicular (orbital) magnetic field probe the number of emergent Dirac points and reveal further details about the dispersion. In the case of bilayer graphene, we also discuss the properties of kink states in an applied magnetic field. We then consider the implications of these results with regards to scanning tunnelling spectroscopy, valley filtering, and impurity induced breakdown of the quantum Hall effect. Finally, we investigate local moment formation of adatoms on bilayer graphene using an Anderson impurity model. We construct various phase diagrams and discuss their many unusual features. We identify regions where the local moments can be turned on or off by applying a external electric fields. Finally, we compute the RKKY interaction between local moments and show how it too can be controlled with electric fields.

The primary subject of this thesis is graphene and how the rudimentary attributes of its charge carriers, and local moments on its surface, can be directly manipulated and controlled with electrostatic potentials. We first consider bilayer graphene subject to a spatially varying electrostatic potential that forms two neighbouring regions with opposite interlayer bias. Along the boundary, 1D chiral `kink' states emerge. We find that these 1D modes behave as a strongly interacting Tomonaga-Luttinger liquid whose properties can be tuned via an external gate. Next, we consider superlattices in bilayer graphene. Superlattices are seen to have a more dramatic effect on bilayer graphene than monolayer graphene because the quasiparticles are changed in a fundamental way; the dispersion goes from a quadratic band touching point to linearly dispersing Dirac cones. We illustrate that a 1D superlattice of either the chemical potential or an interlayer bias generates multiple anisotropic Dirac cones. General arguments delineate how certain symmetries protect the Dirac points. We then map the Hamiltonian of an interlayer bias superlattice onto a coupled chain model comprised of `topological' edge modes. We then discuss the relevance of spatially varying potentials to recent transport measurements. This is followed by another study that considers the effect of a magnetic field on graphene superlattices. We show that magnetotransport measurements in a weak perpendicular (orbital) magnetic field probe the number of emergent Dirac points and reveal further details about the dispersion. In the case of bilayer graphene, we also discuss the properties of kink states in an applied magnetic field. We then consider the implications of these results with regards to scanning tunnelling spectroscopy, valley filtering, and impurity induced breakdown of the quantum Hall effect. Finally, we investigate local moment formation of adatoms on bilayer graphene using an Anderson impurity model. We construct various phase diagrams and discuss their many unusual features. We identify regions where the local moments can be turned on or off by applying a external electric fields. Finally, we compute the RKKY interaction between local moments and show how it too can be controlled with electric fields.