Abstract This thesis examines the Mid-Pliocene climatic extreme ca. three million years ago (Ma) which was the latest longtime warm period. It is an important topic because the climate back then was warmer compared with the present. The bipolar regions are studied because they represent the largest areas that control the global climate. This study is based on clay mineral research that may significantly improve our knowledge of the Mid-Pliocene climate when combined with other palaeoenvironmental data. The paleoclimatological objectives of this study were: 1) to investigate how clay minerals reflect the Mid-Pliocene Global Warmth event, 2) to study ice sheet development at high latitudes, especially in East-Antarctica, and the history of ice rafting and sea ice, especially in the Arctic Ocean. This thesis deals with the clay mineral distribution and compositional analysis of the Pliocene-aged marine sediment sequences provided by the Ocean Drilling Program (ODP). The first studied site, Site 1165, is located at the continental rise of Prydz Bay, East Antarctica, and the second studied site, Site 911, is located at the Yermak Plateau, north of Svalbard, in the Arctic Ocean. The Pliocene smectite clay minerals at Site 1165 were mainly derived from Antarctic continental sources and transported to the site primarly by bottom currents related to warm events during the last 5 Ma. The evidence obtained in this study shows that the East Antarctic ice sheet may have been a dynamic ice sheet during the past 5 Ma, especially during the Mid-Pliocene. The results from the Mid-Pliocene possibly suggest a general warming trend. Based on the composition of the heavy minerals and clay minerals, at Site 911, the Pliocene smectite clay minerals were mainly transported within sea ice by the Siberian branch of the Transpolar Drift. The results indicate a warming trend at approximately 3 Ma after which they indicate a shift back to glacial conditions. Based on this study, the Mid-Pliocene Global Warmth can be observed in both the Arctic and Antarctic regions.

The aim of this thesis was to investigate how fiber growth of goats is determined by genotype, (purebred Angora and crossbred between Angora and Boer goat), physiological stages of the females from mid pregnancy until fifty days after the kids had been weaned and the plane of nutrition. Twelve Angora (pure bred) and ten Angora x Boer goat doe's with an initial mass of 28.70±4.42, between three and five years of age were used. Half of them received 120% NRC energy requirements and the other half received 80% requirements. Mohair patches of 100cm2 were collected from the animals at parturition, mid-lactation, weaning and fifty days post weaning. The fiber greasy weight started declining with commencement of lactation in crossbred animals of both high and low nutrition. The greasy mass again increased from the period of weaning until fifty days post weaning suggesting that crossbred animals do not produce a lot of fiber at the expense of fetal and kid growth. Since fiber production from the crossbred animals is lower, I recommend that the Angora genotype be increased to gain more fiber and further research be done on the topic. / Dissertation (MInstAgrar)--University of Pretoria, 2010. / Animal and Wildlife Sciences / unrestricted

L’océan Indien est le lieu de processus atmosphériques et océaniques majeurs dont les répercussions en terme climatique peuvent être de grandes importances. Cette thèse se propose de documenter les forçages, les variabilités, les impacts et les interactions de la mousson Indo-asiatique et du courant des Aiguilles à l’échelle orbitale (incluant les conditions glaciaires-interglaciaires) au cours de la période Quaternaire.Si le maximum d’insolation (minimum de précession et maximum d’obliquité) initie les fortes moussons Indo-asiatiques, des forçages internes au système climatique jouent également un rôle majeur pour expliquer leur dynamique (fort vents et précipitations), en particulier le changement de volume de glace de l’hémisphère Nord et l’export de chaleur latente de l’océan Indien Sud. La prédominance de ces forçages internes est propre à la mousson Indo-asiatique et la distingue des moussons boréales Africaines. Ceci indique que le concept de mousson globale n’est pas valable à l’échelle orbitale.Concernant l’hémisphère Sud, les variations de température de surface du courant des Aiguilles exercent un contrôle important sur le climat Sud Africain (la végétation et les précipitations). Ce courant permet également le transfert plus ou moins important de chaleur et de sel vers l’océan Atlantique Sud par l’intermédiaire de la migration de la convergence subtropicale et des vents d’ouest associés. Ce mécanisme, contrôlé fortement par la dynamique des hautes latitudes Sud, affecte la circulation thermo-haline globale et constitue un acteur important des transitions glaciaires-interglaciaires et des changements de mode de variabilité climatique au cours du Quaternaire (Transition Mid-Pleistocène et évènement du Mid-Brunhes). Les changements induits dans le climat de l’Hémisphère Nord, et notamment le volume de glace, pourraient ensuite se répercuter sur la dynamique de la mousson. En revanche, l’effet des moussons sur le courant des Aiguilles parait mineur. Toutefois, les interactions entre la mousson Indo-asiatique, l’ENSO et les éventuels IOD (dipôles climatiques de l’océan Indien) pourraient affecter la dynamique du courant. / The Indian Ocean is the place of major atmospheric and oceanic processes with large potential repercussions on the global climatic system. This thesis investigates forcing, variations, impacts and interactions of the Indo-Asian monsoon and of the Agulhas current at the orbital scale (including glacial-interglacial conditions) over the Quaternary period.Insolation maximum (precession minimum and obliquity maximum) initiates strong Indo-Asian monsoons, but processes internal to the climate system, in particular Northern Hemisphere (NH) ice volume changes and the latent heat export of the south Indian Ocean, play a major role to explain their dynamics (strongest winds and precipitation). The predominance of these internal forcings is a specificity of the Indo-Asian monsoon and distinguishes it from African boreal monsoons. This indicates that the concept of a global monsoon at the orbital scale is a misnomer.Concerning the Southern hemisphere, sea surface temperature variations of the Agulhas current exert an important control upon the South African climate (vegetation and precipitation). This current also participates to the transfer of heat and salt towards the South Atlantic Ocean whose intensity is mainly related to the migration of the subtropical convergence and associated westerlies winds. This mechanism, strongly controlled by high southern latitudes dynamics, affects the global overturning circulation and plays an important role for glacial-interglacial transitions and changes in modes of climate variability during the Quaternary (Mid-Pleistocene Transition and Mid-Brunhes event). Induced Northern hemisphere climate changes, in particular ice volume, could in turn influence monsoon dynamics. On the other hand, the effect of monsoons on the Agulhas current seems to be of minor importance. However, interactions between the Indo-Asian monsoon, ENSO and the possible IOD (Indian Ocean climatic Dipole) could affect the dynamic of the current.

Services are becoming increasingly important. Almost two-thirds of the world’s total economic output is accounted for by services. Moreover, the leisure services industry is one of the fastest growing industries around the world. The global growth rate was more than 6% per year in the last five years. The global leisure services industry is expected to be worth $3.4 trillion by 2010, with a growth rate of 6.1% for the 2005-2010 period. Marketers should focus on value-creating processes that involve customers as co-creators of value, because marketers cannot create or deliver customer value alone. Therefore, assessing consumers’ value perceptions can provide informative feedback that marketers can use to adjust their market offerings and meet consumers’ needs and expectations more effectively. This replication study investigated the application and relevance of Petrick’s (2002:119) SERV-PERVAL scale as a measure of consumers’ perceptions of service value in mid-scale restaurants. The SERV-PERVAL scale measures five dimensions of perceived value, namely perceived quality, emotional response, monetary price, behavioural price and reputation. The results should assist marketers to decide how best to influence overall value perceptions and favourable behavioural intentions amongst target markets through understanding how consumers make purchase decisions based on their perceptions of value. First, a conceptual framework of the relationships between perceived value and its antecedents and consequences was synthesised from the leisure marketing literature. Then the study surveyed students at the University of Pretoria and asked them to report their perceptions of a dining experience at a mid-scale restaurant. Multiple regression analysis was used to analyse the data. Two multiple regression models were tested. The findings provided support for the conceptual framework, as well as evidence for the relevance of utilising the SERV-PERVAL scale to measure the value perceptions of South African restaurant patrons. The significance of the two multiple regression models, analysed in the replicated study, was established. Seven hypotheses were tested. In only two cases, the null hypotheses could not be rejected in favour of the alternative hypotheses. The results of the first multiple regression model indicate that consumers' emotional response is the best predictor of their overall perceptions of value. Thus, mid-scale restaurant managers should enhance the pleasurable attributes of the service experience (e.g., background music; interior decoration and lighting; air-conditioning and scent) in order to enhance the consumer's dining experience. The results of the second multiple regression model indicate that consumers' perceived value is a better predictor of consumers' favourable behavioural intentions than satisfaction. An implication for managers is that they can increase their consumers' perceptions of value by enhancing the pleasurable attributes that consumers' experience, a well as the quality and the monetary price of services as perceived by the consumers. It is also important to maintain the level of the services' behavioural price and reputation perceived by consumers. However, managers need to identify the attributes that add pleasure to their target customers and understand how to employ them effectively. / Dissertation (MCom)--University of Pretoria, 2008. / Marketing Management / MCom / Unrestricted

Ce travail de thèse porte sur la conception, la réalisation et l'étude physique de sources lasers de haute cohérence et de forte puissance émettant dans le proche et le moyen infrarouge. Nous nous intéressons plus particulièrement aux lasers à semiconducteur émettant par la surface en cavité externe verticale (VECSEL), l'objectif étant d'obtenir un fonctionnement laser monofréquence accordables et robustes, de forte puissance à température ambiante et en régime continu dans la gamme spectrale 2-3µm et autour de 1µm, avec des dispositifs pompés optiquement ou électriquement. Nous traitons de la conception et de la caractérisation des VECSEL, depuis l'optimisation du milieu à gain jusqu'à l'élaboration et la caractérisation de prototypes laser fonctionnels, et nous effectuons une étude approfondie des propriétés physiques de l'émission laser en terme de cohérence spatiale et temporelle. / This thesis focuses on the design, realization and physical study of high power and highly coherent laser sources emitting in the near and mid-infrared. We are particularly interested in vertical external cavity surface emitting laser (VECSEL), the aim being to obtain a robust and tunable single frequency operation with high power at room temperature in continuous wave and in the spectral range of 2-3µm and around 1µm, with optically or electrically pumped devices . We discuss the design and characterization of VECSEL, from optimization of the gain medium to the development and characterization of a functional laser prototype, and we conduct a thorough study of the physical properties of the laser emission in terms of spatial and temporal coherence.

Ce travail de thèse porte sur l'étude et la réalisation de Lasers à Emission par la Surface à Cavité Verticale pompés électriquement (EP-VCSELs) à base d'antimoniures émettant dans le moyen-infrarouge au-delà de 2 µm. Ces VCSELs proposent des caractéristiques intéressantes pour la détection de gaz tel qu'une émission monomode et une large accordabilité sans saut de mode. L'objectif de ce travail était de développer de tels composants. La première partie de ce mémoire présente les propriétés des couches qui seront empilés pour former la structure VCSEL. La seconde partie traite des différentes conditions pour obtenir une source laser monomode. La troisième partie présente les procédés de fabrication qui ont étés mis en place. Notamment de la sous-gravure sélective de la Jonction Tunnel (JT), qui est une technique de confinement originale dans le système GaSb. Celle-ci permet de réduire le diamètre de la JT jusqu'à 6 µm, ce qui est la condition pour obtenir une émission monomode.La dernière partie de ce manuscrit présente les caractérisations menées sur les structures monolithiques à JT sous-gravées. La sous-gravure sélective nous a ainsi permis d'obtenir le premier EP-VCSEL monolithique monomode. Ce composant fonctionne au-delà de la température ambiante et en régime continu. Avec des courants de seuils aussi bas que 1,9 mA et un fonctionnement jusqu'à 70°C. Le développement des structures monolithique à zone active (ZA) en cascade a également permis d'augmenter les puissances optiques en sortie de ces composants. Celles-ci sont passées de 300 µW @ 20°C à 950 µW pour la première structure citée classique et la structure à ZA en cascades respectivement. / This thesis deals with study and conception of GaSb-based electrically pumped Vertical Cavity Surface Emitting Lasers (EP-VCSELs) emitting in the mid-infrared range above 2 µm. This VCSELs exhibits suitable characteristics for gas analysis like single-mode emission and a large current tunability without mode-hopping. The objective of this work was to develop such devices. The first part of this work is about properties of the epitaxial stack layers used to form the VCSEL structure. The second parts deal with characteristics and the confinement system to design a single mode cavity. The third part presents manufacturing process which has been set up, like Tunnel Junction (TJ) under-etching, which is an innovate approach on the GaSb system. It allows reducing TJ diameter down to 6 µm, which is a necessary point to demonstrate single-mode operation.The final part of this manuscript presents the characterisations purchased on the under-etched TJ monolithic-VCSELs. Selective under-etching of the TJ allowed the first demonstration of the first single-mode monolithic EP-VCSEL. This device emits around 2.3 µm in continuous regime above room temperature. This device exhibits threshold currents as low as 1.9 mA and operate up to 70°C. The development of bipolar cascaded VCSELs has also allowed increasing the optical power on large diameter multimode, with a maximum output power of 300 µW and 950 µW@20°C for the classic and the bipolar cascaded VCSEL respectively.

Les lasers à cascade quantique sont des sources lasers à semiconducteur compactes et capables de délivrer une forte puissance optique sur une large gamme de longueur d'onde dans l'infrarouge. Les QCLs de la filière InP sont les plus établis. Le système de matériaux InAs/AlSb est une solution alternative encore peu développée mais qui, en vertu de ses propriétés, présente des atouts incontestables pour la réalisation de lasers à cascade quantique. Le travail de cette thèse a apporté une meilleure connaissance du système InAs/AlSb et de ses possibilités pour les QCLs, à la fois sur un plan théorique, expérimental et technologique.Nous avons œuvré à l'amélioration des performances des lasers à cascade quantique sur ce système de matériaux, notamment en cherchant à augmenter la température maximum de fonctionnement dans les courtes longueurs d'onde et le lointain infrarouge. Un modèle de transport électronique a été développé. Ce modèle permet de reproduire de manière relativement précise les résultats expérimentaux. Il est un outil utile pour l'amélioration des designs de zone active et, en conséquence, des performances des lasers.La finalité de ces lasers est leur utilisation pour des applications telles que la spectroscopie moléculaire par absorption. Nous avons donc travaillé à les rendre plus adaptés aux besoins de celles-ci, à savoir que leur émission soit monomode, ce que nous avons rendu possible grâce au développement d'une technologie DFB à haut rendement et très reproductible, et qu'ils puissent fonctionner en régime continu, ce qui a été accompli, autour de 9 µm de longueur d'onde d'émission, jusqu'à une température de 255 K en s'appuyant sur un modèle prédictif basé sur une approche analytique.Afin d'atteindre le fonctionnement en régime continu en dessous de 4 µm de longueur d'onde, nous nous sommes penchés sur l'utilisation d'un substrat alternatif en GaSb, qui nous permet de réaliser des claddings conciliant un faible indice de réfaction et de faibles pertes optiques. Nous avons à cette occasion fait la démonstration du premier QCL fonctionnant sur ce substrat, et ce jusqu'à température ambiante à 3,3 µm de longueur d'onde. / Quantum cascade lasers (QCLs) are unipolar semiconductor lasers employing radiative transitions between electron subbands in multiple quantum well structures. QCLs can deliver high optical powers in a large spectral range from mid-IR to THz. The best QCL performances have been achieved using III-V materials that can be grown on InP substrates. The InAs/AlSb material system represents an alternative solution for the elaboration of QCLs. While it is still much less explored compared with the InP family, some properties of these materials are very attractive for the development of QCLs.This thesis contributed to better understanding of the InAs/AlSb system, as well as to physics and technology QCLs based on these materials.Much attention has been paid to the performance improvement of InAs/AlSb QCLs, especially to the increasing of operation temperature of these lasers. A model of electronic transport in such devices, which is in good agreement with obtained experimental data, has been developed. This model has been used for optimization of the QCL design and, in consequence, to the improvement of the lasers performances.The main application of infrared lasers is molecular spectroscopy requiring high spectral purity of the laser emission. To make InAs-based QCLs suitable for spectroscopic applications we have developed a technology of distributed feedback (DFB) lasers for the 3-10 µm range with single frequency emission. Continuous wave (cw) operation of InAs/AlSb QCLs has been achieved for the first time in lasers emitting near 9 µm at temperatures up to 255 K. These lasers have been optimized for cw operation using predictive modeling of heat balance in the device. In order to improve performances of short wavelength InAs/AlSb QCLs emitting below 4 µm we proposed to replace a plasmon enhanced waveguide employing heavily doped InAs and exhibiting strong free carrier absorption by a low loss dielectric waveguide with AlGaSbAs cladding layers. These lasers grown for the first time on GaSb substrates and operated between 2.8 and 3.3 µm demonstrated performances proving the attractiveness of this approach to achieve further progress in InAs/AlSb QCLs.

Dans le moyen-infrarouge, les barrettes de lasers à cascade quantique sont d’un grand intérêt pour la réalisation de sources large bande intégrables dans les systèmes de spectroscopie laser. Une excellente finesse spectrale, la présence d’un seul mode spatial et une gamme d’accordabilité large sont ainsi rassemblées sur une seule puce, compacte et intrinsèquement stable. Afin de bénéficier de l’ensemble des longueurs d’onde sur une sortie unique, les défis majeurs résident dans l’association de technologies pour rassembler les différentes sorties en une seule via l’utilisation de circuits photoniques intégrés (CPI). Ce CPI peut être séparé en trois briques élémentaires : une filière de guidage passif, un combineur de longueurs d’onde et un coupleur actif/passif. Pour la mise-en-forme du faisceau, nous reportons la fabrication et la caractérisation de guides d’onde en InP/InGaAs/InP gravés profondément, avec des performances proches de l’état de l’art. Nous fabriquons et caractérisons des multiplexeurs basés sur des réseaux de diffraction intégrés, sur filière InP et SiGe. Un multiplexeur de 60-vers-1 voies couvrant la gamme de 7-8,5 µm est réalisé. Une méthode innovante mettant en œuvre des multiplexeurs inter-digités et fonctionnant sur trois ordres de diffraction est démontrée. Finalement, nous réalisons des barrettes de laser à cascade quantique sur InP et sur silicium. Un coupleur adiabatique est dimensionné, fabriqué et caractérisé pour associer efficacement les guides actifs et passifs. Des intégrations de types hétérogène et hybride sont envisagées, avec la première démonstration d’une source accordable utilisant une barrette de lasers et un multiplexeur InP. / In the mid-infrared, arrays of distributed feedback quantum cascade lasers have been developed as a serious alternative to obtain extended wavelength operation range of laser-based gas sensing systems. Narrow-linewidth, single mode operation and wide tunability are then gathered together on a single chip with high compactness and intrinsic stability. In order to benefit from this extended wavelength range in a single output beam, the key challenge resides in the combination of different technologies to merge the output of different sources via the use of mid-IR photonic integrated circuits (PIC). The PIC can be split into three main blocks: the passive waveguide platform, the beam combiner and the active/passive coupler. For beam handling and guiding, we report fabrication and characterization of deeply etched InP/InGaAs/InP waveguides with state of the art performances. We fabricate and characterize multiplexers based on echelle and arrayed waveguide gratings on InP and SiGe platforms. A 60-to-1 spectral multiplexer operating in the 7-to-8.5 µm range is demonstrated. An advanced multiplexing scheme using interleaved and cross-order operations is also exposed. Finally, we realize quantum cascade laser arrays on InP and silicon. We design, fabricate and characterize an adiabatic coupler to efficiently and monolithically integrate active and passive waveguides. Heterogenous and hybrid integration are also considered with the demonstration of a tunable source using laser array and InP-based multiplexer.

A Topological Interlocking Configuration (TIC) is an assembly where the shape and alignment of the blocks define the kinematic constraints. Conventional TICs are single-layered structures made of convex blocks. The interface between the blocks in an assembly is face-to-face contact. The traditional convention disregards the use of joinery, adhesive, or other mechanisms that keep two pieces next to each other. However, TICs require a support structure that prevents the lateral strain of the blocks.<br><br>The generation process of a TIC starts with a surface tessellation that describes a geometric domain. Each tile in the tessellation represents a traversal section of a block. For regular tessellations and uniform generation parameters, such sections lie in the middle of their respective blocks. Additionally, such conditions guarantee the blocks align adequately with each other. If one of such conditions does not hold, then the resultant blocks may not be aligned. Furthermore, there could be overlapping between the blocks, which makes a TIC invalid.<br><br>Traditionally, the generation parameters are angle values set at the edges of the tiles. The angles must match between tiles such that each block in the assembly has a geometry that imposes kinematic constraints to its neighboring blocks. Using the same angle values on regular and semi-regular tessellation produces feasible blocks. That is not the case for non-regular tessellations, curvilinear surfaces, and free-form 3D meshes. In such cases, the generation method must find specific angle values to design the blocks and reduce overlapping.<br><br>In this thesis, we propose a TIC generation framework focused on the generation of valid interlocking assemblies based on multiple types of surface tessellations. We start with the Height-Bisection method, a TIC generation approach that uses the distances from a tile to its respective evolution sections as the generation parameters. The method considers the bisector vectors between two tiles to define the parameters that generate aligned blocks to each other. We expand the generation model to a complete pipeline process that finds feasible generation parameters. The pipeline includes clipping parameters and methods in case that overlapping between blocks cannot be avoided.<br><br>Additionally, we describe a generalization of the mid-section evolution concept to include multiple evolution steps during the generation process. Our approach considers the angles and distances required to generate infinitely many TICs, including shapes that are not possible using the traditional generation method and the Height-Bisection method. Finally, we consider the interlocking assemblies that cannot maintain static equilibrium due to the shape of the surface tessellation. We consider the Structure Feasibility Analysis method to find the location and magnitude of the minimum tension forces that guarantee a TIC will reach a static equilibrium state. We describe how to update the generation parameters according to the results of the feasibility analysis. Our results show that the proposed pipeline generates valid TICs based on different surface tessellations, including closed and free-form shapes.

Laser diagnostics are fast-response, non-intrusive and species-specific tools perfectly applicable for studying combustion processes. Quantitative measurements of species concentration and temperature require spectroscopic data to be well-known at combustion-relevant conditions. Absorption cross-section is an important spectroscopic quantity and has direct relation to the species concentration. In this work, the absorption cross-sections of basic hydrocarbons are measured using Fourier Transform Infrared (FTIR) spectrometer, tunable Difference Frequency Generation laser and fixed wavelength helium-neon laser. The studied species are methane, methanol, acetylene, ethylene, ethane, ethanol, propylene, propane, 1-butene, n-butane, n-pentane, n-hexane, and n-heptane. The Fourier Transform Infrared (FTIR) spectrometer is used for the measurements of the absorption cross-sections and the integrated band intensities of the 13 hydrocarbons. The spectral region of the spectra is 2800 – 3400 cm-1 (2.9 – 3.6 μm) and the temperature range is 673 – 1100 K. These valuable data provide huge opportunities to select interference-free wavelengths for measuring time-histories of a specific species in a shock tube or other combustion systems. Such measurements can allow developing/improving chemical kinetics mechanisms by experimentally determining reaction rates. The Difference Frequency Generation (DFG) laser is a narrow line-width, tunable laser in the 3.35 – 3.53 μm wavelength region which contains strong absorption features for most hydrocarbons due to the fundamental C-H vibrating stretch. The absorption cross-sections of propylene are measured at seven different wavelengths using the DFG laser. The temperature range is 296 – 460 K which is reached using a Reflex Cell. The DFG laser is very attractive for kinetic studies in the shock tube because of its fast time response and the potential possibility of making species-specific measurements. The Fixed wavelength helium-neon (HeNe) laser at 3.39 μm is used to measure the absorption cross-section of the fuels mentioned above. The dependence on temperature, pressure and bath gas (helium, argon and nitrogen) is also examined. The temperature and pressure ranges of this study are 296 – 800 K and 250 – 1000 Torr, respectively. These are the first measured cross-sections at HeNe laser wavelength that are applicable at combustion-relevant conditions.