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The notion of a categorical semidirect product was introduced by Bourn and Janelidze as a generalization of the classical semidirect product in the category of groups. The main aim of this work is to study the general properties of semidirect products of groups with operators, describe them in various classical varieties of such algebraic structures and apply the results to homological algebra and related areas of modern algebra. The context in which the study is done is a semiabelian category (that is, a pointed, Barr-exact and Bourn-protomodular category). The main result in the thesis is the construction of the semidirect product in a variety -RLoop of right -loops as the product of underlying sets equipped with the -algebra structure. A variety of right -loops is a variety that is pointed, has a binary + (not necessarily associative or commutative) and a binary satisfying the identities 0 + x = x, x + 0 = x, (x + y) y = x and (x - y) + y = x. Thus, -RLoop is a generalization of the variety of -groups introduced by Higgins and the results obtained are valid for varieties of -loops. We also describe precrossed and crossed modules in the variety -RLoop. The theory of crossed modules developed is independent of that developed by Janelidze for crossed modules in an arbitrary semiabelian category and gives simplified explicit formulae for crossed modules in -RLoop. Finally, we mention that our constructions agree with the known ones in the familiar algebraic categories, specifically the categories of groups, rings and Lie algebras.

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Bibliography: pages 58-61. / This thesis is devoted to a study of the relationship between separability and metrisability in the context of locally convex spaces. The duality between sep- arability and weak*-metrisability does not carry over to non-metrisable locally convex spaces; the best that can be said in this case is that the equicontinuous subsets in the dual of a separable locally convex space are weak*-metrisable. To get around this difficulty, we often prefer to use the idea of separability by seminorm: a locally convex space E is separable by seminorm if and only if the equicontinuous subsets of its dual are weak*-metrisable. On any locally convex space E there is a finest topology Tχ which is coarser than the given topology and which makes E separable by seminorm. A question that arises is under what conditions a space E is Tχ-complete. In trying to answer this question, we are led to an intriguing binary relation which G.A. Edgar originally defined on the class of Banach spaces. In the first two Chapters of this thesis, we show that many of the results in Edgar's paper can be expressed in terms of the completeness of a space with respect to various topologies.

Includes abstract. Includes bibliographical references.

The dynamics of complex fluids under various conditions is a model problem in bio-fluidics and in process industries. We investigate a class of such fluids and flows under conditions of heat and/or mass transfer. Experiments have shown that under certain flow conditions, some complex fluids (e.g. worm-like micellar solutions and some polymeric fluids) exhibit flow instabilities such as the emergence of regions of different shear rates (shear bands) within the flow field. It has also been observed that the reacting mixture in reaction injection molding of polymeric foams undergoes self-expansion with evolution of heat due to exothermic chemical reaction. These experimental observations form the foundation of this thesis. We explore the heat and mass transfer effects in various relevant flow problems of complex fluids. In each case, we construct adequate mathematical models capable of describing the experimentally observed flow phenomena. The mathematical models are inherently intractable to analytical treatment, being nonlinear coupled systems of time dependent partial differential equations. We therefore develop computational solutions for the model problems. Depending on geometrical or mathematical complexity, finite difference or finite volume methods will be adopted. We present the results from our numerical simulations via graphical illustrations and validate them (qualitatively) against' similar' results in the literature; the quotes being necessary in keeping in mind the novelties introduced in our investigations which are otherwise absent in the existing literature. In the case where experimental data is available, we validate our numerical simulations against such experimental results.

Bibliography: leaves 99-106. / We introduce and investigate the concept of a nearness structure on a σ-frame. Analogues of the Samuel Compactification, Uniform Coreflection and Completion in the nearness σ-frame setting are obtained. Convergence in uniform frames is also a subject of this thesis integrating compactness, precompactness and paracompactness. Finally, the notion of uniform paracompactness is introduced and its relation with convergence is investigated.

Includes abstract. / Includes bibliographical references (p. 131-140). / In this thesis we study extended theories of gravity in the context of cosmology. The first part is dedicated to the application of the theory of dynamical systems, which allow us to investigate the global dynamics of some cosmological models resulting from scalar-tensor and higher-order theories of gravity. We use the dynamical systems approach with non–compact expansion normalised variables to study the isotropisation of Bianchi type I models in Rn–gravity. We find that these type of models can isotropise faster or slower than their general relativity counterparts. We extend this analysis to the full class of orthogonal spatially homogeneous Bianchi models to study the effect of spatial curvature on the isotropisation of these models. A compact state space is constructed by dividing the state space into different sectors, that allows us to also investigate static solutions and bouncing or recollapsing behaviours which is not possible when using non-compact expansion normalised variables. We find no Einstein static solutions, but there do exist cosmologies with bounce behaviours. We also find that all isotropic points are flat Friedmann like. We discuss the advantages and disadvantages of compactifying the state space, and illustrate this using two examples. We next study the phase-space of Friedmann models derived from scalar-tensor gravity where the non-minimal coupling is F(φ) = ξφ2 and the self-interaction potential is V (φ) = λφn. Transient almost-Friedmann phases evolving towards accelerated expansion and unstable inflationary phases evolving towards stable ones are found. In the last part of this work, we set out a framework to analyse tensor anisotropies in the cosmic microwave background of scalar-tensor cosmologies. As an example, we consider one of the exact solutions found for the class of scalar-tensor theories considered above.

Includes abstract. Includes bibliographical references.