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Optical Distortion in Hypersonic True Flight Enthalpy Flows
No full textA simplified, blunt-nose wedge model was tested over a range of realistic hypersonic flight conditions to evaluate several aero-optic diagnostic measurement techniques. A two-dimensional 10��� half angle wedge of width 0.47 m and blunt-nose radius 1 cm test article was designed and tested in an experimental campaign in Texas A&M University���s hypervelocity expansion wind tunnel. The aero-optic diagnostic techniques employed in this work included schlieren photography, linear array focused laser differential interferometry, Michelson interferometry, and optical emission spectroscopy. Experimental test conditions comprised Mach numbers of 6, 9, 12, and 15, realistic-flight flow enthalpy, and static temperatures between 200 K and 270 K. Hypersonic flow features such as bow shocks, natural light emission, and boundary layers were captured in schlieren recordings. Index of refraction fluctuation power spectral density data were recorded between frequencies of 100 kHz and 10 MHz at multiple points near the surface of the test arti-cle. The data suggested that eddies causing density fluctuations at rates greater than 2 MHz and between 7.30 mm and 10.63 mm tall developed in the boundary layer for unit Reynolds numbers between 11 �� 106 m���1 and 12 �� 106 m���1
Professional Mental Health Help-Seeking Behaviors
No full textThis dissertation examined the mental health help-seeking behaviors of undergraduate students and the retrospective help-seeking experiences of professors, while they were college students. Past research has noted disparate mental health outcomes for minoritized and first-generation students. However, research exploring their help-seeking attitudes, styles, and sources in general college populations is limited. This dissertation aims to address some of those gaps by including the perspectives of traditionally underrepresented groups.
The dissertation employed a mixed-methods approach. The first study used a quantitative approach with over 200 self-identified Black, Latine, and White students through surveys. Data was analyzed via numerous versions of Analysis of variances. The second study employed a qualitative focus group design with 10 students from the first study. The third study used a single case design via an exploratory, qualitative inquiry with 8 self-identified Black and Latine professors. Data collection methods for both qualitative studies included face-to-face interviews. Data for both qualitative studies were also analyzed via the constant comparative method.
Major findings from the first study indicated significantly higher avoidant help-seeking styles scores for first-generation students than their counterparts. Findings from the second study included various themes about generational differences, socioeconomic ideals, and differing help-seeking styles via ethnicity. Findings from the third study included various themes based on values, sociocultural factors, and how professors��� attitudes changed over time.
The data from this dissertation highlights the need for continued exploration and understanding the role that college settings, ethnicity, and first-generation status may or may not play in mental health help-seeking behaviors
Biological Ecosystem Inspired Approaches for Circular Economy Design and Quantification
No full textA cornerstone of sustainable development is the idea of a circular economy, a closed loop system where resources are cycled through a system and waste generated and virgin resource use are minimized. This thesis proposes a new of design tools based on environmental network analysis (ENA) and new design metrics, Ns* and NS, as tools which can be used to design systems in accordance with circular economy principles. NS is the number of nodes which strongly connect to a cycle, thus participating in both donation and acceptance, and Ns* is the proportion of total actors connected to a cycle that have a strong connection to that cycle. To explore these tools, multiple engineered systems were evaluated to benchmark their performance against the performance of biological ecosystems and to investigate the ties between ENA metrics and circular economy strategies. Manufacturing floors were also assessed in their ability to be easily reconfigured and their performance based on ENA metrics. The manufacturing floors with the closest values to biological ecosystems also performed the best at reconfigurabilty. The results showed how the low data metrics were able to guide design decisions of an emerging technology through exploring the potential resource cycling routes in a hypothetical economy. Additionally, a carpet network model was used to understand how the design tools related to circular economy strategies. Ns* and NS were found to be integral in assessing collaboration between industries participating in cycling, while FCI showed to be a good indicator of resource cycling, waste diversion and a decreased reliance on raw materials
Diasporic Imprint on Religious Architecture: Post-1965 South Asian Mosques in Houston
No full textDiaspora plays a role in shaping and reimagining the built environment that ethnic groups establish in a foreign land. Mosques, both as individual buildings and as a part of Islamic centers, function as the space for congregational prayer for Muslim worshippers. Mosques serve as a way for Muslims to express cultural values and identity. When placed in a diasporic environment, mosques combine inherited traditions with the diasporic needs of immigrant Muslims. The objective of this research is to investigate and understand how South Asian immigrants have developed the architecture of mosques and Islamic centers in the Greater Houston Area since the 1965 Hart-Cellar Act was passed, and how they have merged diasporic and traditional design elements in mosque architecture. The research hypothesizes that the architecture of South Asian American mosques in Greater Houston is an attempt to retain cultural identity through the hybridization of traditional and diasporic influences.
An explanatory research method has been implemented to do a comparative case study analysis of three cases of mosques and Islamic centers located in Greater Houston. Data for the research has been collected through literature review, archival studies, and field observation. The thesis is expected to provide a cultural narrative on the development of South Asian American mosque architecture within the diaspora of Greater Houston and add to the existing history of South Asian American religious architecture
Pair Production in Strong Fields
No full textThe correction to the Coulomb energy due to virtual production of e+e��� pairs, which is on the order of one percent of the Coulomb energy at nuclear scales, is discussed. The effects of including a pair-production term in the semi-empirical mass formula and the correction to the Coulomb barrier for a handful of nuclear collisions using the Bass and Coulomb potentials are studied. With an eye toward future work using Constrained Molecular Dynamics (CoMD) model, we also calculate the correction to the Coulomb energy and force between protons after folding with a Gaussian spatial distribution.
In the collision of two heavy ions the strong repulsion coming from the Coulomb field is enough to produce real e+e��� pair(s) from vacuum fluctuations. The energy is provided by the kinetic energy of the ions and the Coulomb interaction at the production point. If, for instance the electron is located at the center of mass (C.M.) of the two ions moving along the z-axis, and the positron at a distance x from the electron, the ions can be accelerated towards each other since the Coulomb barrier is lowered by the presence of the electron. This screening results in the increase of the kinetic energy of the colliding ions and may result in an increase of the fusion probability of light ions above the adiabatic limit.
Nuclear scattering is not the only situation where real pairs can be produced by this mechanism. In particular, the fields involved in �� decay and nuclear fission are strong enough to produce pairs. The energy of the e+e��� pair is related to the relative distance and velocity of the daughter nuclei. Thus, the energy distribution of the produced pairs can give information about the dynamics of the fission and �� decay processes. A neck model of nuclear fission is used to illustrate how the pairs can be used as a probe of the dynamics.
This model of pair production is also applied to situations with strong fields involving lasers. In particular, lasers can fully ionize clusters of atoms, which then expand in a ���Coulomb explosion," and when a laser irradiates the surface of a metal, a shower of protons is ejected in a phenomenon known as Target Normal Sheath Acceleration (TNSA). The fields involved in these cases were found to be too weak to produce pairs with this mechanism. Likewise, no pairs are produced by the gravitational field at the event horizon of a black hole, indicating that this mechanism is different from Hawking radiation
Soil Temperature and Moisture Control in Ground Source Heat Pump Systems
No full textThis numerical study focuses on exploring passive methods to control soil temperature rise and restore favorable thermal conditions in ground source heat pump (GSHP) systems. The three methods investigated were soil moisture control, presence of thermosiphon (TS), and effects of soil type. A single U-loop of a GSHP system was modeled in a soil domain using a finite element analysis (FEA) software Ansys Mechanical. The Backward Euler formulation and the Sparse Direct Solver were used to discretize and solve the governing heat conduction equation. Four moisture contents (high, low-to-high, high-to-low, low) and two soil types (sandy loam, clay loam) were considered, along with the presence (TS case) and absence (non-TS case) of a single thermosiphon. Soil temperature profiles were plotted at multiple points to examine the effects of moisture level and soil type, and the temperature difference between TS- and non-TS cases was plotted to study the thermosiphon effect. Curve-fitting of soil temperature profiles was done to quantify the rate of soil temperature rise at different depths. The results showed that soil temperatures decreased with moisture content. Soil temperatures were lower for TS cases than for non-TS cases, and the TS effect also decreased with moisture content. Moreover, clay loam resulted in higher soil temperatures than sandy loam at all moisture levels considered. In summary, to maintain and restore soil thermal conditions favorable to GSHP systems, moisture control is recommended for GSHPs in high thermal diffusivity soils, while thermosiphon use is preferred for GSHPs in low thermal diffusivity and dry (low moisture content) soils
Nanoscale Functionalization of Graphene-Based and Molybdenum Disulphide Samples via Electrochemical and Thermochemical Methods
No full textOur primary objective was to try to functionalize Graphene-based and Molybdenum Disulphide samples through electrochemical and thermochemical methods. The samples that we experimented with were Graphene, Graphene Oxide, and Molybdenum Disulphide on gold substrates. We chemically functionalized Graphene Oxide with Cyanuric Chloride (2,4,6- trichloro-1,3,5-triazine), assisted by an external heater source to covalently bond the compounds (thermochemical means), which was confirmed by X-ray Photoelectron Spectroscopy (XPS) results.
In the electrochemical method, we attempted to locally functionalize Graphene and Molybdenum Disulphide (MoS2) samples fabricated on a gold substrate via tip-based Local Anodic Oxidation (LAO) using a Conductive Atomic Force Microscope, where the AFM tip is connected to the positive terminal of the source meter and sample connected to the negative terminal. The local chemical changes were analyzed by measuring and comparing scan heights before the LAO. Platinum-coated Silicon tips were used due to their hardness and local corrosion resistance to pattern the 2D materials. Analysis of results and a proposed future work on the chemical functionalization of Molybdenum Disulphide were also discussed due to its surface properties akin to Graphene samples
Phase Field Fracture Simulations of High Burn-Up Uranium Dioxide Under Accident Transients
No full textUranium dioxide stands as the predominant fuel type in contemporary nuclear reactors. Despite its notable utility, there is a desire to enhance its performance in high burn-up scenarios. Such advancements would not only mitigate operational costs within existing reactor fleets but also ensure the long-term sustainability of global nuclear programs. To this end, significant progress has been made concerning the thermal performance of uranium dioxide. One notable advancement has been the use of computer simulations to test the fuel in ways that are difficult to replicate in traditional experiments.
This research introduces a novel variant of the cohesion phase-field fracture model within the Multiphysics Object-Oriented Simulation Environment (MOOSE) framework. This model was used to simulate high burn-up uranium dioxide under two specific transient scenarios. The first involves a transient representative of reactor start-up, serving to verify the model and establish a performance baseline. The second scenario involves a high-power ramp transient, simulating an unforeseen accident that could potentially occur at any point during operation. The resulting crack patterns from these transients were systematically studied and subsequently compared with existing literature.
The study of these transients has yielded several significant results. During reactor start-up, a limited number of discrete radial cracks would form at the edge and propagate toward the center of the fuel pellet. Characteristics of these cracks, such as their length and quantity, exhibit correlations with start-up power and fuel heat rate. Additional cracking was observed later in the transient when the fuel temperature was increased. These additional cracks would branch off existing cracks and move in the circumferential direction.
The morphological features of the cracks generated in these simulations are consistent with observations from historical and contemporary experiments. Moreover, the model employed in these simulations demonstrates competitiveness with contemporary counterparts, distinguishing itself by offering greater flexibility and fewer artificial restrictions
A Novel ML-based Approach for the Prediction of the Oceanic Heat Flux in a Slab Ocean Model Coupled to a Physics-Based Model of the Atmosphere
No full textA slab-ocean model is a thermodynamic model of the ocean mixed layer. It provides a prognostic variable for the sea surface temperature (SST), and when coupled to a model of the atmospheric circulation, it allows for two-way ocean-atmosphere interactions at a low computational cost. The standard formulation of a slab ocean model accounts for the spatially varying thermal effects of the oceanic circulation by a prescribed two-dimensional static estimate of the oceanic heat flux field. A downside to using such a static estimate is that it cannot capture the effects of changes in the ocean circulation. This work presents a methodology to introduce a temporarily changing two-dimensional oceanic heat flux field in a slab ocean model. It also introduces a novel machine learning-based approach to dynamically evolve this field. The approach is tested on the low resolution atmospheric global circulation model SPEEDY, which has an optional slab ocean component. This component is modified to implement the proposed methodology. It is first demonstrated that the static estimate of the oceanic heat flux can be further improved by an iterative method. Then, it is shown that with the temporally varying estimate of the oceanic heat flux the model produces more realistic sea surface temperature variability than with the static estimate. Finally, it is demonstrated that the machine learning-based approach can be used to replace the prescribed estimates with a dynamically evolving field of the oceanic heat flux
General Sizing Relationships for Axial Flux Motors
No full textThis dissertation presents a comprehensive study of the design, optimization, and performance analysis of axial flux motors, focusing on enhancing their performance potential using a multiphysics design approach of the motor���s shared electromagnetic, thermal, and structural geometry. Axial flux motors are known for their compact structure and high power density and are increasingly becoming an item of interest for applications such as aerospace and other traction applications.
The contemporary fractured design process substantially slows novel motor design, with each subsystem designed and optimized separately. A significant contribution of this research is the development of a set of simultaneous performance scaling relationships for axial flux motors, providing a valuable tool for designers to predict motor behavior based on key geometric and system-level parameters in the early stages of design. The resulting method can estimate equivalent finite element results within 8.8% across the range of interest in approximately 1/650th the time, with a maximum error of 16.6%. The final result validation is provided via comparison with commercially available high-performance motors as well as published results relating cooling topology with current density.
The dissertation concludes with a discussion of the potential impacts of the study on the future development of axial flux motors, highlighting the opportunities for further research. This work not only advances the state-of-the-art in axial flux motor technology but also contributes to the broader field of electric machinery by providing valuable insight into how the design of electric machines can be improved to reflect the computational tools available to modern engineers