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A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Chemistry. University of the Witwatersrand, Johannesburg. May 2016 / In this research project, the morphogenesis and polymorphism of calcium carbonate (CaCO3) and its subsequent use as a template in the fabrication of hollow carbon spheres (HCS) is reported. A series of ratios (i.e. 5:0, 5:1, 5:2, 5:3, 5:4, 5:5, and 0:5) of binary solvent mixtures consisting of polar aprotic (dimethylformamide and dimethyl sulfoxide) and polar protic (methanol, ethanol, isopropanol, and 2-butanol) solvents, with 10% PEG200 as a crystal modifier, were used to influence the morphogenesis and polymorphism of precipitated CaCO3 (PCC). The PCC products were characterised using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), and laser Raman spectroscopy. An increase in the ratio of the polar protic solvent (methanol, ethanol, isopropanol, and 2-butanol) relative to the polar aprotic solvent (DMF & DMSO) within the binary solvent mixture favored the formation of vaterite particles of different morphologies, while an increase in the ratio of polar aprotic solvent (DMF & DMSO) within the binary solvent mixture favored the precipitation of rhombohedral calcite crystals. Time-resolved ex situ PXRD and SEM measurements revealed that the nucleation and phase transformation of the CaCO3 under polar protic and aprotic solvents followed the dissolution-reprecipitation mechanism. The major phase transformation occurred within 3 hours after mixing the precursor solutions. The effect of poly (4-styrenesulfonic acid) (PSSA) as an additive in the crystallisation of CaCO3 at different temperatures (i.e. 30, 40, 75, and 100 °C) and different crystallisation times (3, 6, 12, and 24 hrs) was investigated. The as-synthesised CaCO3 products were subjected to: SEM, laser Raman spectroscopy, PXRD, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The crystallisation of CaCO3 in the presence of PSSA resulted in the self-assembly of vaterite particles into spherical bulk crystals. Varying the crystallisation temperature led to different particle attachment (CPA) pathways, which in turn resulted in bulk crystal morphologies that varied. Changes in the crystallisation temperature were found to not have changed the polymorphism of the precipitated CaCO3 due to the kinetic stabilisation effects of PSSA, instead hollow vaterite spheres formed at 75 and 100 °C. The possibility to synthesise HCS using CaCO3 as a template under chemical vapour deposition (CVD) at different temperatures (i.e. 600, 700 and 800 °C) was, for the first time, demonstrated. The evolution of CO2(g) from the decomposition of the template during CVD resulted in the formation of a rough surface topography on the carbon shell of the HCS. This surface roughness increased with the increase in the reaction temperature due to the increased rate of CaCO3 decomposition. The structural integrity of the spherical template was not affected by the CO2(g) evolution during carbonisation at all the reaction temperatures. The as-synthesised HCS at 600, 700, and 800 °C gave specific BET surface areas of: 193, 55, and 51 m2/g, respectively. / MT2016

Thesis presented in fulfilment of the requirements far the degree of Master of Science in the University of the Witwatersrand. / Every organism, whether it he plant or animal, worm or man, propagates Itself with a definable degree of constancy* Such constancy cannot be entirely related to the ever-changing external environment; it becomes,of necessity, mainly an inherent function of the organism itself* Somewhere in the organism, there exists a system which determines, controls, or regulates the visible expressions of organlsmal constancy. / WHSLYP2017

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La comparaison, à différents niveaux (systèmes de villes, villes, quartiers), de l'organisation spatiale et hiérarchique des systèmes urbains dans le monde fait apparaître des propriétés universelles (loi rang-taille, structure centre-périphérie des villes, etc.) mais également une grande variété de formes (répartition des populations, densités, prix, activités, etc.). Si les théories évolutionnaires urbaines et celles d'économie spatiale offrent des schémas explicatifs de cette émergence de formes, les modèles qui en sont issus se sont jusqu'à présent focalisé sur un seul niveau d'organisation spatiale, qu'il soitintra ou inter-urbain. Dans une optique d'aménagement durable, il est crucial de disposer de modèles permettant de raisonner sur les inter-dépendances qu'entretiennent ces niveaux d'organisation du peuplement. Cette thèse présenteune famille de modèles entités-centrés et d'outils dédiés à l'étude de cette problématique par la simulation à base d'agents. Ils s'inscrivent dans le projet Simpop et sont mis en oeuvre sur la comparaison des morphogenèses urbaines en Europe et aux Etats-Unis, sur la période 1800-2000. Ils incluent notamment le simulateur simpopNano, accompagné d'un environnement modulaire construit autour d’un SIG pour une exploitation systématique, intelligente et collective de modèles spatiaux. Ensemble, ils confortent l'idée que la seule différence des maillages des réseaux viaires des villes suffit à exprimer des répartitions spatiales plus diffuses sur les grilles américaines que sur les plans radioconcentriques européens. Ce modèle intra-urbain est ensuite articulé avec le modèle de systèmes de villes Simpop2 dans un modèle multi-niveaux. / The multilevel comparison of spatial and hierarchical organisations of urban systems over the world highlights some universal properties (rank-size law, center-periphery structure) but also a variety of more specific patterns (in terms of spatial repartition of populations, densities, prices, activities, etc.). The spatial economy and the urban evolutionnary theory both offer explanations of the emergence of such patterns, but the simulation models they support generally consider one level of spatial organisation only. Understanding and reconstructing those levels' interdependancies is a crucial issue for long-term sustainable urban planning. This thesis presents a set of models and tools that are dedicated to the study of this question through agent-based simulation. They have been developed in the context of the Simpop project, and particulary focus on the comparison of the morphogenesis of urban systems in Europe and in the United States over the period 1800-2000. These tools include the simpopNano agent-based model, and some experimentation modules integrated in an extensible, generic, GIS-based platform dedicated to a systematic, collective and intelligent exploration of spatial simulation models. Together, they reinforce the idea that difference of topology of the streets networks could be sufficient to generate some more diluted spatial repartitions, as observed in US cities when compared to european ones. This intra-urban model is then articulated with an inter-urban one, Simpop2, in a multilevel model. The latter serves to engage a comparison among a variety of approaches in agent-based simulation for coupling models of various levels of abstraction.

The myotome is a segmented skeletal muscle developing along the axis and is the first muscle to differentiate in every vertebrate. While fish and tadpole myotomes persist during development, myotomes of amniote embryos disappear during embryogenesis and are replaced by the long and complex epaxial muscles. Whereas the initial development of the myotome has been intensely investigated, very little is known about the fate of the myotome and the morphogenesis of the epaxial muscles in mammals. This study firstly examined epaxial muscle morphogenesis. Myotomal fibres and cell death in muscle fibres were followed by immunohistochemistry during rat embryogenesis. Results showed that the morphogenesis of epaxial muscles occurs through the movement of the differentiated myotomal muscle fibres rather than by de novo fusion of myoblasts after apoptosis of the initial myotomal myofibres. The myotomal muscle masses undergo progressive transformation and segregation that result in the formation of the distinct groups of epaxial muscles. Next, the mechanisms of epaxial muscle morphogenesis were investigated in rat embryos, by following muscle progenitor cells expressing the transcription factors Pax7 and Pax3 during epaxial muscle morphogenesis using immunohistochemistry. This demonstrated that the myoblasts responsible for epaxial muscle growth derive from a population of progenitors mingled within the epaxial muscle masses as they segregate from the myotome. No migration of precursors is involved. Transgenic ScxGFP mouse embryos, carrying a marker green fluorescent protein under the control of scleraxis (a transcription factor specific to tendons and muscle connective tissues), permitted the tracing of the connective tissues during myotome transformation. Results strongly suggest that connective tissues associated with epaxial myofibres could be actively involved in creating the displacement of the myotomal myofibres during the transformation process. Finally, to test whether the mammalian myotome has a function as a neurally-controlled muscle during development, innervation of the myotome was studied using immunohistochemistry in comparison with the innervation of the forelimb muscles of rat embryos. The results were striking, showing that whereas the migratory limb muscles are contacted by nerves from the beginning of their differentiation, the myotome differentiates and then develops over more than two days without nerves. As revealed by the appearance of acetylcholine receptors clusters, functional innervation only occurs in the epaxial muscles when the myotome has started its transformation. The true mammalian myotome is therefore never innervated and seems to have lost its role as a neurally-controlled muscle in contrast to the myotomal muscle of fish and amphibian tadpoles. Overall the results indicate that the development of the epaxial muscles is strikingly different from that of the muscles originating from migratory myoblasts. Contrary to the migratory muscles, the myotome develops in the absence of nerves and its differentiated muscle fibres are transformed in position and orientation to create the epaxial muscles. The development of mammalian epaxial muscles upon a template of embryonic muscle resembles the development of some adult muscles in Drosophila, developing from the larval muscles. This suggests that the mammalian myotome could be of a larval nature but with the loss of innervation.

Shrews previously recognized as Sorex monticolus were classified into two species (one with 14 subspecies, the other monotypic) on the basis of a morphometric analysis of 3610 individuals from throughout their range. Sorex m. neomexicanus has been recognized previously as a subspecies of Sorex monticolus but is recognized herein as a distinct species. This taxon occurs in the Sacramento and Capitan mountains of New Mexico. This region possibly acted as a boreal-forest refugium for S. monticolus-type shrews during the Pleistocene glaciation, and during the warmer interglacial period, after the most recent glaciation, the valleys became too arid for survival and these shrews survived in forested, montane regions of New Mexico. These mountains are sufficiently isolated from other mountainous regions in the state to reduce or eliminate gene flow between these populations of shrews. S. monticolus as defined herein exhibits relatively little morphometric variation. Even among nominate races, the only obvious morphometric variation is a north-south cline in greatest length of skull. There is a general trend of increasing size from south to north. The southern subspecies restricted to isolated mountains (S. m. monticolus and S. m. parvidens) have the shortest skull lengths of all S. monticolus. The subspecies found in the northern coastal and insular areas of southeast Alaska and British Columbia (S. m. longicaudus, S. m. prevostensis, S. m. malitiosus, S. m. insularis, S. m. calvertensis, S. m. alascensis, and S. m. elassodon) have the longest skulls. S. m. setosus, S. m. isolatus, S. m. soperi, S. m. obscurus and S. m. shumaginensis all have skulls of intermediate length. Insular and coastal populations of S. monticolus have longer skulls than the S. monticolus that occupy the mainland. Shrews with long skulls that occur on the mainland (S. m. longicaudus and S. m. alascensis) also occur on some islands, and the mainland portion of their distributions are restricted to a narrow band along the coasts of Alaska and British Columbia. The southernmost subspecies of S. monticolus with short skulls are restricted to small montane islands. The morphometric variation among nominate races is sufficient to warrant continued separation at the subspecies level of all taxa except S. m. calvertensis and S. m. elassodon. Were it not for differences in pelage color, based on my morphometric analysis, S. m. calvertensis and S. m. elassodon should be synonomyzed. / Graduation date: 1994

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 108-118). Also available in electronic version.