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(2021)ThesisThis thesis focuses on the investigations of magnetic thin film structure of cubic and perovskite transition metal oxide magnets, particularly when two different magnetic orderings are competing at such interface. The goal is to understand the various effects of an interfaces that exert on the neighboring materials; to understand the role of the layer structure and microstructure on the overall magnetic properties; and to investigate the feasibility to control such interfacial phenomenon by means of strain, ion implantation, and crystal orientation. Four thin film systems are included: MnxOy/Ni80Fe20, La0.7Ca0.3MnO3/CaMnO3, La0.7Ca0.3MnO3 and BiFeO3/SrRuO3. Oxygen ion implantation was performed on MnxOy/Ni80Fe20 bilayers, and the results show an enhancement of exchange bias and coercivity after the implantation. Polarized neutron reflectometry study reveals a significant change in magnetic spin reversal mechanism due to chemical modification. In the La0.7Ca0.3MnO3/CaMnO3 system exchange bias is assisted by the magnetic frustration at the layer interface. Results suggest, the strength of exchange bias is strongly related to the degree of frustration. Controlling the strain state of La0.7Ca0.3MnO3 shows an effective method to alter the frustration property. Further, the magnetic glassy spins in the La0.7Ca0.3MnO3 epitaxial thin film is studied. Combining DC magnetization, AC susceptibility, and polarized neutron reflectometry measurements, the spin-glass nature of the sample is obtained which spins are freeze around 139 K which just below the ferromagnetic transition of the bulk sample. Finally, for the BiFeO3/SrRuO3 system, an enhancement of net magnetization of the canted antiferromagnetic BiFeO3 was probed in (111)-orientated sample. There is possible exchange interaction of Ru4+ and Fe3+ and the strong orbital p-d hybridization of SrRuO3 which could contribute to the enhanced magnetization.
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(2021)ThesisBy their proximity, jovian planets provide the best lab to analyse their unique spectral features contributing further to the improvement of both planetary and exoplanetary atmospheric sciences. In this thesis, VSTAR and ATMOF codes have been modified and performed to suit the spectral modelling of the jovian planets producing accurate telluric models for line removal and fitting the modelled spectra. The spectral model fits here, used for analysing different spectral features in accordance with P-T profiles, chemical composition and cloud parameters, focus on cloud base pressures and opacities in the atmosphere of jovian planets. The line-by-line radiative transfer atmospheric models presented here are innovative and novel in their concurrent analysis of the transmitted, emitted and reflected light capable of using the most powerful modelling software. The models specified here relate to the atmospheric characterisation of the giant planetary worlds in the Solar System, with potential for expanded application to planetary worlds beyond our own neighbourhood. My models spectrally characterised the upper atmosphere of the ice giants in the NIR bands (R ~2400, 5100 and ~17800), determining their cloud optical parameters by applying three of the latest theoretical and empirical methane line datasets. Meanwhile, by calculating their D/H ratios in both methane and hydrogen, I was able to reassess their formation scenario, suggesting the formation of Uranus at a greater distance from the Sun than Neptune. I also analysed and modelled Jupiter’s planetary disk in three NIR bands of J, H and K (R ~2400) using its various cloud particle distribution through their optical depths and base pressure ranges. In total, 153 NIR spectra indicative of 51 spectral regions on Jupiter’s disk have been modelled and characterised. The spectral regions correspond to 9 designated latitudes and 7 specified longitudes, as a function of their cloud opacity and base pressure changes. The analysis produced the global map of clouds/haze variations on Jupiter’s disk resulting in better understanding of its atmospheric characteristics, dynamics and features capable of creating a broader spectral view to contribute to the planet’s future atmospheric studies along with its giant remote cousins.
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(2021)ThesisCeO2-x and CeO2-x-based catalysts are emerging as important functional materials in many energy- and environment-related applications. However, there remain uncertainties and misconceptions in the interpretation of the fundamental function of defects in determining the characteristics of materials. The present work explores this relationship in detail by considering the critical role of defect equilibria in terms of the effects of solid solubility and charge compensation mechanisms on the resultant physicochemical properties and catalytic performance of bulk CeO2-x as well as MoO3-CeO2-x and RuO2-CeO2-x heterojunctions. Electrodeposition was used to synthesise holey nanosheets and heterojunctions were created using wet chemistry. Analyses consisted of XRD, Raman, SEM, HRTEM, EDS, SAED, AFM, XPS, EPR, PL, KPFM, and UV-Vis. DFT was used to calculate the optical indirect band gap (Eg) values for the different solubility mechanisms for the dopant valences. The catalytic performance was assessed by HER and ozonation testing. The combination of XPS data, their detailed and extensive analyses, and consideration of all possible defect equilibria represents a powerful tool to interpret the physicochemical properties and catalytic performance of bulk materials and heterojunction nanostructures based on them. With this information, it is possible to decouple multifarious data for disparate materials such as bulk materials, chemisorbed heterojunction nanostructures, and physisorbed heterojunction nanostructures. A key outcome of the present work is that the primary factor in both the properties and performance unambiguously is Ce3+ ions, not oxygen vacancies. This is manifested through the solubility mechanisms of the dopants, which are interstitial, and the charge compensation mechanisms, which are ionic for Mo doping and ionic + redox for Ru doping. The latter mechanisms may be altered by three F centres (viz., colour centres), which derive from oxygen vacancies, and intervalence charge transfer (IVCT) in the case of Mo doping. The F centres and metal interstitials also are key factors in raising the Fermi level (Ef) of the doped materials, effectively reducing the Eg, particularly for Mo doping. The hydrogen evolution reaction (HER) performance was dominated by the heterojunctions, where the strong bonding from chemisorption, IVCT, and homogeneous and high distribution density of small heterojunction particles with Mo doping resulted in enhancement such that this performance is the best yet reported for CeO2-x-based materials. In contrast, the HER with Ru doping was relatively poor owing to the weak bonding from the inhomogeneous and low distribution density of large physisorbed heterojunction particles. The ozonation performance was outstanding but adversely affected by cerium vacancies. While this performance for Mo doping was improved by reduction owing to IVCT, that for Ru was uniformly poor owing to the high cerium vacancy concentration. The performance for bulk CeO2-x was poor owing to structural destabilisation during reduction, thus suggesting stabilising effects from the heterojunction particles.
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(2021)ThesisMulti-layered waste packaging materials are widely used in the packaging industries due to their flexibility of applications, superior properties, and relatively lower cost. Despite the advantages accomplished by the polymer-metal multilayers packaging materials, recycling the waste in a traditional method is a very difficult task due to the complexities of multi-materials intrinsic behaviours during the processing of cast-off materials. In this study, a newly developed microrecycling technique (thermal disengagement technology, TDT) has been introduced and briefly demonstrated. Several outcomes are: (i) Polymer laminated Al packaging materials available from the local market was thermally disengaged by TDT into several useful products including ~98% pure Al, and graphitic C without any major emission (ii) laminated polymers in multi-layered packaging materials can be degraded into the graphitic C in an inert atmosphere. Degraded C can stay on Al surface to provide well protection against surface oxidation, (iii) TDT was utilised for different types of multilayer packaging materials consisting of multiple polymers and metallic contents (Al, Cu, & Fe) available in the local market. TDT is highly capable to recycle all different types of packaging materials irrespective to their inclusive materials. (iv) Al-containing packaging material was recycled in different media (air, nitrogen, & argon). Argon media was suitable to recycle Al into its original form and polymers into degraded graphitic C. Recycled Al was transformed into microparticles by non-traditional mechanical milling at cryogenic temperature (-196°C) created by liquid N2. Synthesised flake shaped, and micro-sized carbonaceous Al microparticles are contamination-free and thermally stable and can be useful in the fields of additive manufacturing, (v) A rapid transformation process was introduced where thermally disengaged Al from the TDT subsequently thermally transformed in an arc furnace at a very high temperature (~2000°C) in a short time period (~20s) in an inert and vacuum condition. As a result of this rapid transformation, ceramic reinforced Al alloy with an enhanced physical, microstructural, and mechanical properties was synthesised. The overall project of recycling polymer-metal multilayer packaging materials can be concluded with numerous green materials output along with some co-products and metallic alloys.
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(2021)ThesisThis thesis explores topological defects and topological defect transitions in epitaxial ultrathin ferroelectric heterostructures. Geometrical confinements in ultrathin films has enabled the realisation of several nontrivial topological polarisation arrangements in ferroelectrics, categorised as a range of topological defects such as bubble, meron, vortex, flux-closure domain, etc. These ferroelectric topological defects can be engineered by tuning depolarisation field, mechanical and electrical boundary conditions. Our model system is an ultrathin (001) oriented PbZrxTi1-xO3/ SrTiO3/ PbZrxTi1-xO3 heterostructure fabricated on La0.67Sr0.33MnO3 buffered SrTiO3 substrates. Several topological defects are realised under specific mechanical and electrical boundary conditions. Topological defect transitions are also achieved using different routes such as electric field, thickness variation, mechanical pressure and thin film milling. These topological defects have also gained immense technological interest on account of their emergent properties. This thesis further studies the functional properties in topological defects such as electrical conductivity in bubble domains. The motion of these bubble domains is also investigated. The results herein offer new insights on how to engineer topological defects and topological defect transitions in order to design multifunctional ferroelectric/multiferroic devices with enhanced operational speed, sensitivity and energy-efficiencies.
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(2021)ThesisSingle enzyme nanoparticles (SENs), which encapsulate individual enzymes in a thin permeable polymer network offer great control over the chemical and physical environment directly around the enzyme. SENs have exhibited great enzyme stability by restricting enzyme extensive unfolding motion under extreme conditions, like extreme pH and high temperature. However, up to date, the control over the chemistry of the shell is still quite limited. In this thesis, a new SEN formation strategy has been explored. In order to minimize the risk of enzyme deactivation during synthesis of the SENs, the weak electrostatic interaction was utilized to assemble charged polymers around the enzyme. Different lengths of charged polymers were pre-prepared via reversible addition−fragmentation chain-transfer polymerization (RAFT) and then attached to the surface of enzyme via electrostatic interactions. This strategy has been investigated for the different enzyme, including lysozyme, trypsin, protease, horseradish peroxidase, and glucose oxidase. Isothermal titration calorimetry (ITC) and asymmetric flow field-flow fraction (AF4) in combination with multiangle light scattering (MALS) reveal the binding number and strength of polymer chains / enzyme. The strength of binding can be tuned based on the charge density of the bound polymer. In this method, the trithiocarbonate group of a RAFT agent was placed close to the surface of the enzyme and the initiation of a free radical acrylamide / bisacrylamide polymerisation in solution can result in chain extension of the RAFT polymer and direct the formation of the newly formed hydrogel around the outside of the enzyme. AF4-MALS and small-angle X-ray scattering (SAXS) confirm the formation of a thin cross-linked shell around the enzyme. The mild conditions of this method of SEN formation, which avoids any covalent modification of the enzyme, results in no loss in activity on our model enzyme (glucose oxidase), and four-fold increase in thermal stability. The method is then utilized to probe the protective effect of trehalose close to the enzyme. Trehalose is generally assumed to be the most effective sugar to use as a protein stabilizer. In this method, trehalose molecules were placed close to enzyme surface by either assembling enzyme with charged trehalose polymers or crosslinking with trehalose monomer. In order to evaluate the effect of the trehalose in SENs on stabilizing enzyme, another disaccharide sucrose was treated in the same way for comparison. It was found that the core-shell structure, instead of the chemistry of the shell, was more important for stabilizing enzyme structure under heat treatment. This study offers a new technique for synthesis of SENs with ease of design and control of the shell chemistry of SENs, opening up new pathways for enzyme stabilization and application.
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(2021)ThesisThe purpose of my research is mainly focused on the Properties of CaO-Al2O3-based Mould Flux for High-Al Steel Continuous Casting. Mould flux is crucial to the continuous casting process for lubricating the strand as well as controlling the heat transfer between the mould and the steel strand. To reduce vehicle weight and obtain superior mechanical properties, a large amount of aluminium has been added to the steel. However, aluminium tends to react with silica-based mould flux during continuous casting, which could lead to a variety of casting problems, such as breakout prediction alarms, transverse and longitudinal depressions, etc. Therefore, it is crucial to limit the reaction between Al in the steel and SiO2 in the mould flux. This project aims to develop CaO-Al2O3-based mould fluxes for the continuous casting of the high-Al steel. The project will study melting properties, viscosity, structure, crystallisation behaviour and heat transfer of CaO-Al2O3-based mould fluxes to provide some strategy for the design of mould fluxes for the continuous casting of high-Al steel.
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(2021)ThesisBriquetting is a method of particles compaction where fine particles are densified to produce briquette with different sizes and shapes. In briquetting, loose particles are compressed two counter-rotating rolls. The structural and mechanical properties of briquettes are crucial to the downstream operations such as transportation, handling, and coating etc. Therefore, a better insight into those fundamentals governing of briquetting is of great importance to process control and optimization. This work aimed to develop numerical models at different scales to simulate the briquetting behaviour of fine particles. Two numerical techniques, finite element method (FEM) and discrete element method (DEM), were employed in the research. FEM considers compacts as continuum porous materials and can provide full scale simulations. On the other hand, DEM is a particle-based technique and can provide detailed information at the particle scale. The two complementary methods allow to analyse briquettes at different scales. A 2D FEM model was firstly developed to simulate the briquetting process. The Drucker-Prager Cap (DPC) model was adopted to characterize the mechanical response of powders. The model parameters were determined by conducting different experimental tests of die compaction of iron ore fines. The model was validated by comparing the simulation results with experimental data. The relative density and stresses of the briquettes showed inhomogeneous distributions in the flow direction. The parametric studies showed that the feed pressure affected the briquetting process considerably as both relative density and power draw increased almost linearly with increasing feed pressure. However, a non-linear trend was observed with increasing particle-wall friction. The 2D FEM model was later extended to 3D to consider the shape of roll pockets. The 3D simulation results showed that the Von Mises stress and hydrostatic pressure were more inhomogeneous compared to the 2D results. In the roll depth direction, both relative density and Von Mises decreased from the pocket periphery to the centre region. The effects of feed pressure, roll gap and roll speed were analysed. The roll force and relative density increased almost linearly with increasing feed pressure. A non-linear decline in roll force and relative density were observed as roll gap increased. However, roll speed showed limited impact on roll force and briquette mechanical properties. A DEM model with an elasto-plastic adhesion model was developed to simulate briquetting. The DEM model was firstly calibrated by comparing the die compaction results with experiments. In the DEM simulations of briquetting, the force-angular displacement curves showed the oscillatory patterns similar to those observed in the FEM simulations. The relative density at the final stage decreased in comparison with compression stage, and the contact force network was sparser and thinner. The effects of feed pressure and roll speed were studied. The force on the roll increased significantly, and the relative density and strength increased nonlinearly with increasing feed pressure. In contrast, the roll force, relative density, and strength declined as roll speed increased. The formed briquettes were compressed along two different directions to examine the strength and cracking phenomena. When compressed along the roll width, the crack started at the shoulder region and propagated to the centre part of the briquette. With increasing loading, the briquette broke into two parts along the vertical centre line. When compressed on the curve surface, the break force was much lower compared to the roll width direction and the crack initiated at the middle part of briquette and squeezed out vertically. Feed pressure of briquetting showed strong effect on the failure pattern and break force of briquettes. For both cases, the break force increased almost linearly with increasing feed pressure. Multiple cracks were observed for the loading direction along the roll width. However, a more distinct and clearer vertically squeezed crack at the middle periphery region was noticed along the curve surface. The effect of particle shape was investigated by simulating briquetting of tetrahedral particles. The roll force was much lower for the non-spherical particles and a lower relative density was observed for the tetrahedron particles. The force on the roll and the relative density was found to decrease with increasing the non-sphericity. On the other hand, both roll force and relative density increased with increasing feed pressure.
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(2021)ThesisTranscription factors (TFs) are proteins that bind to DNA in a sequence-specific manner and regulate gene transcription. ChIP-seq and other techniques have allowed a study of TF binding genome-wide but have shown that TFs bind to only a subset of in vitro predicted sites. This highlights that it is difficult to accurately predict which sites TF bind in vivo. In this current study, we have uncovered how the functional domains (FD, i.e., non-DNA binding domains) of TFs mediate protein-protein interactions that aid in TF genome localisation and investigate how DNA methylation affects the genomic localisation of TFs. This is important not only to better understand gene regulation but also to be able to develop next-generation artificial TFs. Analysis of ChIP-seq and RNA-seq data showed that disrupting the interaction between TF Krüppel -like factor 3 (KLF3) and its newly discovered FD co-partner WDR5 significantly impacted both KLF3 and WDR5 genomic localisation and gene activation. This demonstrated that protein-protein interactions with the FD can influence genome-wide TF binding. Next, we investigated how this finding translated to a family of TFs, the KLF family which all share a similar DNA binding domain (DBD) but bind and regulate different target genes across different tissues. Using publicly available ChIP-seq data, we showed that KLF family members have vastly different in vivo genome-wide binding profiles in HEK293 cells despite having similar consensus binding motifs. We then showed using ChIP-seq that replacing the KLF3 FD with the KLF1 FD reduces the number of binding sites and impacts genomic localisation. Taken together, these results demonstrate the importance of the FD in genome-wide binding and how FDs, by mediating specific protein-protein interactions, may allow TF families to achieve functional diversity despite their similar DBDs. We also investigated DNA methylation at the β-globin locus which is a model locus for studying transcriptional regulation where methylation has been identified to affect gene expression, but the underlying mechanisms are yet to be described. By measuring DNA methylation levels in human erythroid cell lines that show differential expression of HBG1/2 and HBB, we identified CpG sites at or near these genes that were differentially methylated and were close to regulatory regions and well-known TF binding sites. Future experiments will investigate whether these differences may directly affect TF binding leading to these gene-expression changes. Overall, my project has illuminated novel ways in which TF binding can be regulated in vivo to allow precise patterns of cellular gene expression, both by FD recruitment of partner proteins that regulate genomic localisation and by target site methylation that may alter TF binding.
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(2021)ThesisThis PhD thesis moves beyond conservation genetics/molecular ecology’s traditional consideration of genetic loci acting in isolation from other genetic loci, in a species that is acting in isolation from other species. I use modelling to explore these interactions, and produce some surprising results with implications for evolutionary biology and for conservation management. The first chapter presents a meta-analysis and simulations of recombination with epistatic selection – where a combination of alleles at different loci produces a fitness effect neither could produce alone. Epistasis is ubiquitous in nature, but difficult to detect. Additionally, mathematical models of recombination and epistatic interactions are typically intractable or contradictory. Consequently, epistatic interactions are often ignored. The main conclusion of the first chapter is that in Drosophila melanogaster, and in some models, lethal combinations of alleles at different loci tend to have a low recombination rate and thus break up less easily, though beneficial combinations show a different pattern. The second and third chapters use modelling to study correlations between species diversity and genetic diversity (SGDCs). If strong positive SGDCs are common, it may be possible to use one diversity measure in the place of another. Conversely, if strong negative SGDCs are common, conservation measures which target one diversity will negatively impact the other. There are theoretical arguments in support of positive and negative SGDCs, but little formal algebraic theory. Moreover, despite many SGDC studies, the results are equivocal. The second chapter shows that SGDCs which measure diversity using richness tend to be positive due to the construction of the SGDC as well as sampling bias but that assemblages with the same SGDCs can evolve very differently. Therefore, SGDCs may not be meaningful. However, many SGDC researchers use measures other than richness which weight rare variants differently from common ones. Therefore, the third chapter shows that the choice of weighting can seriously bias the interpretation of SGDC studies. In summary, this thesis lays the groundwork for a version of molecular ecology based upon a more thorough and accurate assessment of interactions of genes with one another, and with other species.