http://repository.aust.edu.ng/xmlui/handle/123456789/353 This sub-community contains all PhD thesis of the five streams offered at AUST 2026-04-05T14:41:47Z http://repository.aust.edu.ng/xmlui/handle/123456789/5177 Dynamics of Bose-Einstein Condensates in Optical Lattice Ratchet Potential Systems Kabir, Salihu Suraj This thesis aims to explore intriguing phenomena observed in Bose-Einstein condensates (BEC) subjected to asymmetric optical potentials. The phenomena of interest here is directed transport, wherein the BEC is made to travel in a specific direction without applying a net force. This phenomenon becomes possible in systems out of equilibrium when certain symmetries are broken. Three different scenarios have been analyzed: (i) Bose-Einstein Condensates with time-dependent interactions subjected to a kicked ratchet potential, (ii) Non-interacting Bose-Einstein Condensates in a non-Hermitian kicked ratchet potential and (iii) Non-interacting Bose-Einstein Condensates in a kicked ratchet potential whose phase is spatially modulated. In the first scenario, the role of atom-atom interaction on the resulting directed current is studied. A notable correlation between the kicking strength K and the interaction parameter ̃g has been uncovered. A critical boundary within the (K, g ̃) space distinguishes between quasi-periodicity and complete chaos, indicating that strong interactions lead to full chaos. Within the realm of full chaos, significant currents and current reversals, emerge, disrupting the symmetry of the current spectrum. Beyond the stability range where |g ̃|≤ 1, directed transport is no longer ensured. In the second scenario, the impact of non-Hermitian kicking on a cold atom exposed to an asymmetric ratchet potential was explored. This non-Hermiticity stems from dissipative interactions influenced by the environment, leading to either atom-gain or loss effects on the atom. It was realized in this study that non-Hermiticity can either impede or enhance the atom’s transport. Additionally, substantial atom-gain may induce reversals in the current direction. Quantum resonance notably emerges as a pivotal factor in dictating these outcomes. Finally, we considered the effect of a spatial modulation on the transport of this system. Before illustrating the influence of this phase, we observed that within the regimes where current reversals can occur, the probability of negative current peaks is consistently lower than that of positive peaks. Furthermore, both probabilities are symmetric around the value 0.5, an intriguing observation that warrants further investigation. With the inclusion of the phase, our calculations of the transport current revealed that transport can be optimized for faster dynamics. Higher current values were achieved compared to the zero-phase scenario. Notably, starting from a zero-phase regime where current reversals are present, such as the regime of full chaos, the phase not only enhances and rectifies the transport current but also allows for its complete suppression (current blockade). From the current landscapes plotted as functions of the spatial phase θ and the potential strength P, regions of optimal currents were identified at critical values of θ and P. 2025-05-20T00:00:00Z http://repository.aust.edu.ng/xmlui/handle/123456789/5161 Pressure Transient Behavior in Horizontal Wells and Hydraulically Fractured Vertical Wells With Non-Newtonian Fluid Flow in Porus Media: Non-Composite and Composite Reservoirs Ologun, Mojeed Olawale Two fluid regions are usually created during either water or polymer injection into an oil reservoir for enhanced oil recovery. The two fluid regions create a composite reservoir system that requires analytical solution that can be used to evaluate the injection performance. This study present a 2D solution for non-Newtonian fluid in the inner Zone coupled with infinite boundary in the outer Zone; using power law model. The outer Zone fluid can either be Newtonian or non-Newtonian. Moreover, the mathematical model is formulated such that either Zone can be with non-Newtonian power law fluid or Newtonian fluid. The infinite conductivity fractured solution obtained was compared with the ones obtained using the radial line source solution that had already been developed in the literatures and a perfect match was obtained. An application was made to three examples that have been presented in a previous work and satisfactory results were obtained. The dimensionless pressure drops during the early linear flow regime for all values of flow indices are the same, but with deviation during radial flow regime. Moreover, the existing work is limited to radial model in a vertical well, infinite conductivity hydraulic fracture, software simulation model and numerical model. Up to date, there has been no analytical work presented for horizontal well using power law model. Power law model best characterizes non-Newtonian rheological properties and the fluid flow in porous media. Today, horizontal well is widely being used in the exploitation of oil and gas in the industry; either as a producer or an injector. A reservoir where the flow of injected polymer solution during enhanced oil recovery and high viscosity crude oil exhibit non-Newtonian behavior, is better characterized with pressure transient with power law model. This fact has been established. This study also presents a 3-D power law model for analyzing pressure transient behavior in a reservoir with fluid flow that exhibits non-Newtonian behavior. The solution provided is semi-analytical and numerically inverted using Stehfest Algorithm. A step-by-step analytical procedure for analyzing each flow regime is developed. In order to validate the 3-D model, type curves were developed and matched with data provided from simulator in previous work. The step-by-step procedure was used to analyze an eclipse simulated data. There was consistency in the results that validated the analytical mathematical model. The 3-D analytical model developed is also applicable to composite reservoir with two distinct zones due to fluid and rock properties. The flow behavior index in both zones can either be 1.0 or less than 1.0. This is unique to this study. Furthermore, finite conductivity hydraulic fracture mathematically gives the general solution for transient pressure behavior in a fractured well. This study presents a semi-analytical solution and a numerical method which can be used to evaluate the performance of an injection operation in a finite conductivity fracture either in a homogeneous reservoir or a naturally fractured reservoir. The solution obtained was subjected to a validation process by comparing the estimated dimensionless wellbore pressure obtained with that of a previous work where numerical method was used. A good match was obtained. An application was also made to field examples that have been presented in a previous work and satisfactory results were obtained. Main Thesis 2024-01-05T00:00:00Z http://repository.aust.edu.ng/xmlui/handle/123456789/5160 Mechanical Biomarkers and LHRH/EphA2-Molecular Biomarkers: A Theragnostic Approach for Triple Negative Breast Cancer Diagnosis/Treatment Ezenwafor, Theresa Chikwuo The adhesive interactions between molecular recognition units (such as specific peptides and antibodies) and antigens or other receptors on the surfaces of tumours are of great value in the design of targeted nanoparticles and drugs for the detection and treatment of specific cancers. In addition, the heterogeneous nature of cancer and difficult challenges in early detection has activated a high interest in the development of mechanical biomarkers for cancer diagnosis. This current study presented Luteinizing Hormone Releasing Hormone (LHRH) and Epherin type A2 (EphA2) as a promising biomarker to design a targeted therapy for diagnosis and treatment. Furthermore, the work provides insights through atomic force microscope (AFM) and Nanoindentation (NI) on the application of adhesion forces, adhesion energy, viscosity and statistical deconvolution as diagnostic tools to detect TNBC as well as to characterize it into different histological grades. To appraise these discoveries, TNBC tissue samples of different histological grades were selected (non-neoplastic or Grade 0) and (neoplastic of Grade I to Grade III). To evaluate the receptor overexpression, and their distributions on the human breast tissue extracts, using Immunohistochemistry (IHC) technique, as well as the actin cytoskeletal structures of non tumorigenic and tumorigenic breast tissues (grade I to grade III), a combination of immunofluorescence and confocal microscopy, and atomic force microscopy was used. The adhesion forces between LHRH or EphA2 and human TNBC breast tissues are measured using force microscopy techniques that account for the potential effects of capillary forces due to the presence of water vapor. A combination of nanoindentation and statistical techniques is then used to measure the deformations/viscoelastic properties of non-tumorigenic and human TNBC of different histological grades. The investigation of the underlying magnitude of antigen – antibody interactions corresponding to adhesion energy are also determined using adhesion contact theories/models. A Standard Fluid Model/Anti-Zener Model II is also used to characterize the viscoelastic properties of the non-tumorigenic and tumorigenic TNBC tissues of different grades. The results show that the pull off forces and adhesion energies associated with higher grades of TNBC are shown to be greater than those associated with normal/non-tumorigenic human breast tissues, which were studied as controls. The observed increase in adhesion forces and adhesion energies are also correlated with the increasing incidence of LHRH/EphA2 receptors at higher grades of TNBC. Moreover, the decrease in the viscoelastic properties as well as the actin cytoskeletal structural density observed to be connected to the TNBC tissue histological higher grade are lower than those of non-neoplastic breast tissues. The implications of the results are discussed for the development of targeted nanostructures for the detection and treatment of TNBC, also the potential application of nanoindentation and statistical deconvolution techniques to the development of mechanical biomarkers for TNBC detection /cancer diagnosis. Main Thesis 2023-02-05T00:00:00Z http://repository.aust.edu.ng/xmlui/handle/123456789/5159 Valorization of Underutilized Lignocellulosic Biomass Wastes for Biofuel Production Uzoagba, Chidiebele Ejikeme The study focuses on utilizing lignocellulose biomass (LCB) as a sustainable feedstock for biofuel production to address fossil fuel depletion, climate change, energy poverty, and environmental issues in Africa. With global energy demand rising and agriculture generating significant waste, the study explores agricultural residues and unconventional biomass sources, such as Prosopis africana, for bioenergy generation. Africa faces severe energy poverty, with millions lacking access to electricity and clean cooking facilities. The research aims to assess the energy potential of these residues and promote circular economy principles through bioenergy production. Methodologically, the study used data from the FAOSTAT database to analyze various crop residues for their suitability in bioenergy generation. It employed empirical analysis and modeling techniques to assess energy potential. For Prosopis africana, proximate, ultimate, and compositional analyses were performed using advanced techniques like scanning electron microscopy, X-Ray diffraction, and thermogravimetric analysis to determine the biomass’s physical, thermal, and chemical properties. Additionally, the hybrid composition of Prosopis africana pod and cowpea husk was evaluated for briquette production, optimizing particle size, binder concentration, and densification pressure using Response Surface Methodology. Results indicate that agricultural residues hold significant potential for bioenergy, supporting sustainable resource utilization and promoting circular economy practices. Prosopis africana exhibited high heating values (15.23 to 20.49 MJ/kg), positioning it as a strong candidate for biofuel production. Optimal briquette properties were achieved with specific particle size, binder concentration, and densification pressure, improving mechanical and combustion characteristics. The study concludes that agricultural residues and Prosopis africana can alleviate Africa’s energy challenges, promote environmental sustainability, and contribute to economic development. The findings offer critical insights into scaling bioenergy production and adopting circular economy principles. Further investigations are ongoing to address socio-economic challenges related to bioenergy adoption. Main Thesis 2024-11-05T00:00:00Z