Thesis (Ph.D.)--Mississippi State University. Department of Mechanical Engineering. / Title from title screen. Includes bibliographical references.

In this thesis, we aim to create a framework for the derivation of thermodynamically consistent anisotropic viscoelastic models. As an example we propose simple models extending the isotropic Oldroyd-B and Giesekus models to illustrate the models' behavior and the process of finding the correct equations. We show what behavior in sheer we can expect and continue with a 3D simulation inspired by the experiment on a real liquid crystal mixture. Finally, we compare the simulation and the experiment to find similarities and possible further research topics.

<p dir="ltr">Managing transient heat loads has become more challenging with the increasing electrification of ground, air, and marine vehicles. Doing so requires novel designs of thermal management systems, or in some cases, novel retrofits of legacy TMSs to accommodate the addition of more electrified subsystems. However, design tools that are well suited for examining and optimizing the dynamic response of TMS over candidate operation or mission profiles are limited. In this thesis, a principled methodology and associated tools for the enumeration and dynamic optimization of all feasible architectures of an air cycle machine are presented. Graph-based modeling is pivotal for exploring and optimizing ACM architectures, providing a structured representation of system components and interactions. By modeling the ACM as a graph, with vertices and edges representing components and interactions, respectively, various component configurations and performance metrics can be systematically analyzed. This approach enables efficient exploration of design alternatives and consideration of dynamic boundary conditions (representing, for example, a complex mission profile) during optimization. Another unique contribution of this thesis is a novel application of a multi-state graph-based modeling approach for developing dynamic models of turbomachinery components. By representing multiple states within each control volume or component and connecting them through power flows, this approach accurately captures both first and second law dynamics, enabling the computation of dynamic entropy generation rates. A detailed case study demonstrates the optimization of ACM architectures based on entropy generation minimization and dynamic bleed air flow rate minimization. This study highlights the trade-offs between different optimization criteria and the potential for generalizing the tool to more complex thermofluid systems in thermal management applications. The results underscore the importance of entropy-based analysis in comparing the thermodynamic losses across various system architectures.</p>

School science education prepares learners to study science at a higher level, prepares them to follow a career in science and to become scientific literate citizens. It is the responsibility of the educator to ensure the learners’ conceptual framework is developed to the extent that secures success at higher level studies. The purpose of this study was to test the effectiveness of conceptual change teaching strategies on the conceptual development of grade 11 learners on Newton’s second law of motion. The two strategies employed were the cognitive conflict strategy and the development of ideas strategy. A sequential explanatory mixed-method research design was used during this study. The qualitative data were used to elucidate the quantitative findings. The quantitative research consisted of a quasi-experimental design consisting of a single-group pre-test–post-test method. During the qualitative part of the research a phenomenological research approach was utilised to gain a better understanding of participants’ learning experiences during the intervention. The quantitative research made use of an adapted version of the Force Concept Inventory (FCI). The data collected from the pre-test were used to inform the intervention. The intervention was videotaped and the video analysis or qualitative data analysis was done. After the intervention the post-test was written by the learners. Hake’s average normalised learning gain <g> from pre- to post-scores was analysed to establish the effectiveness of the intervention. The two sets of results (quantitative and qualitative) were integrated. Information from the qualitative data analysis was used to support and explain the quantitative data. The quantitative results indicate that there was an improvement in the students’ force conception from their initial alternative conceptions, such as that of an internal force. Especially the learners’ understanding of contact forces and Newton’s first law of motion yielded significant improvement. The qualitative data revealed that the understanding of Newton’s second law of motion by the learners who partook in this study did improve, since the learners immediately recognised the mistakes made when confronted with the anchor concept. The cognitive conflict teaching strategy was effective in establishing the anchor concept of force which proved to be useful as bridging concept in the development of ideas teaching strategy. The data from both datasets revealed that the cognitive conflict teaching strategy for the initial part of the intervention was effective. It was evident that for development of the idea teaching strategy the two data sets revealed mixed results. Recommendations were made for future research and implementation of conceptual development teaching strategies. / MEd (Natural Sciences Education), North-West University, Potchefstroom Campus, 2014

School science education prepares learners to study science at a higher level, prepares them to follow a career in science and to become scientific literate citizens. It is the responsibility of the educator to ensure the learners’ conceptual framework is developed to the extent that secures success at higher level studies. The purpose of this study was to test the effectiveness of conceptual change teaching strategies on the conceptual development of grade 11 learners on Newton’s second law of motion. The two strategies employed were the cognitive conflict strategy and the development of ideas strategy. A sequential explanatory mixed-method research design was used during this study. The qualitative data were used to elucidate the quantitative findings. The quantitative research consisted of a quasi-experimental design consisting of a single-group pre-test–post-test method. During the qualitative part of the research a phenomenological research approach was utilised to gain a better understanding of participants’ learning experiences during the intervention. The quantitative research made use of an adapted version of the Force Concept Inventory (FCI). The data collected from the pre-test were used to inform the intervention. The intervention was videotaped and the video analysis or qualitative data analysis was done. After the intervention the post-test was written by the learners. Hake’s average normalised learning gain <g> from pre- to post-scores was analysed to establish the effectiveness of the intervention. The two sets of results (quantitative and qualitative) were integrated. Information from the qualitative data analysis was used to support and explain the quantitative data. The quantitative results indicate that there was an improvement in the students’ force conception from their initial alternative conceptions, such as that of an internal force. Especially the learners’ understanding of contact forces and Newton’s first law of motion yielded significant improvement. The qualitative data revealed that the understanding of Newton’s second law of motion by the learners who partook in this study did improve, since the learners immediately recognised the mistakes made when confronted with the anchor concept. The cognitive conflict teaching strategy was effective in establishing the anchor concept of force which proved to be useful as bridging concept in the development of ideas teaching strategy. The data from both datasets revealed that the cognitive conflict teaching strategy for the initial part of the intervention was effective. It was evident that for development of the idea teaching strategy the two data sets revealed mixed results. Recommendations were made for future research and implementation of conceptual development teaching strategies. / MEd (Natural Sciences Education), North-West University, Potchefstroom Campus, 2014

Biological signal processing can help us gain knowledge about biological complexity, as well as using this knowledge to engineer better systems. Three areas are identified as critical to understanding biology: 1) understanding DNA, 2) examining the overall biological function and 3) evaluating these systems in environmental (ie: turbulent) conditions. DNA is investigated for coding structure and redundancy, and a new tandem repeat region, an indicator of a neurodegenerative disease, is discovered. The linear algebraic framework can be used for further analysis and techniques. The work illustrates how signal processing is a tool to reverse engineer biological systems, and how our better understanding of biology can improve engineering designs. Then, the way a single-cell mobilizes in response to a chemical gradient, known as chemotaxis, is examined. Inspiration from receptor clustering in chemotaxis combined with a Hebbian learning method is shown to improve a gradient-source (chemical/thermal) localization algorithm. The algorithm is implemented, and its performance is evaluated in diffusive and turbulent environments. We then show that sensor cross-correlation can be used in solving chemical localization in difficult turbulent scenarios. This leads into future techniques which can be designed for gradient source tracking. These techniques pave the way for use of biologically-inspired sensor networks in chemical localization.

<p dir="ltr">In holographic quantum field theories, a bulk geometric semiclassical spacetime emerges from strongly coupled interacting conformal field theories in one less spatial dimension. This is the celebrated AdS/CFT correspondence. The entanglement entropy of a boundary spatial subregion can be calculated as the area of a codimension two bulk surface homologous to the boundary subregion known as the RT surface. The bulk region contained within the RT surface is known as the entanglement wedge and bulk reconstruction tells us that any operator in the entanglement wedge can be reconstructed as a non-local operator on the corresponding boundary subregion. This notion that entanglement creates geometry is dubbed "ER=EPR'' and has been the driving force behind recent progress in quantum gravity research. In this thesis, we put together two results that use Tomita-Takesaki modular theory and quantum ergodic theory to make progress on contemporary problems in quantum gravity.</p><p dir="ltr">A version of the black hole information loss paradox is the inconsistency between the decay of two-point functions of probe operators in large AdS black holes and the dual boundary CFT calculation where it is an almost periodic function of time. We show that any von Neumann algebra in a faithful normal state that is quantum strong mixing (two-point functions decay) with respect to its modular flow is a type III₁ factor and the state has a trivial centralizer. In particular, for Generalized Free Fields (GFF) in a thermofield double (KMS) state, we show that if the two-point functions are strong mixing, then the entire algebra is strong mixing and a type III₁ factor settling a recent conjecture of Liu and Leutheusser.</p><p dir="ltr">The semiclassical bulk geometry that emerges in the holographic description is a pseudo-Riemannian manifold and we expect a local approximate Poincaré algebra. Near a bifurcate Killing horizon, such a local two-dimensional Poincaré algebra is generated by the Killing flow and the outward null translations along the horizon. We show the emergence of such a Poincaré algebra in any quantum system with modular future and past subalgebras in a limit analogous to the near-horizon limit. These are known as quantum K-systems and they saturate the modular chaos bound. We also prove that the existence of (modular) future/past von Neumann subalgebras also implies a second law of (modular) thermodynamics.</p>

<p dir="ltr">This thesis explores the thermodynamics and mechanics of reaction-diffusion interfaces in solid materials, focusing on configurational forces for bulks and surfaces, which are essential in understanding phenomena like electromigration, phase separation, and void evolution. The work is divided into four themes: bulk and surface configurational mechanics, electromigration in solder joints, and solid mixture theory. The thesis develops theories based on continuum mechanics and configurational forces, deriving Eshelby stress tensors and balance laws for interfaces. Experimental work on electromigration in SnBi solder joints is used to validate the theory. The research contributes to advancing the understanding of solid-state diffusion and phase evolution in engineering materials.</p>