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A Multiphysics Model for Predicting Spatiotemporal Temperature Profiles in Microwave-Heated CO2 Direct Air Capture Processes
No full textDue to alarming rise in atmospheric CO2 ppm levels, the direct air capture process has been engineered to capture low concentrations of CO2 directly from the atmosphere using chemisorbents. However, the regeneration of chemisorbents is highly energy-intensive and inefficient. To enhance this, microwave is employed for selective and targeted heating of the chemisorbent. Existing measurement techniques struggle to accurately capture the spatiotemporal temperature profile of solvent impregnated polymer (SIP) under microwave heating. Therefore, it becomes crucial to determine the spatiotemporal temperature distribution inside the polymer phase to expedite CO2 desorption, improve energy efficiency, and prevent material degradation. Motivated by these considerations, we propose a 3D-multiphysics model to study the spatiotemporal distribution of temperature inside a hybrid nanoscale multi-functional material. We focus on the microwave heating of a novel heterogeneous system comprising a SIP with a ferromagnetic additive, further solving the heat diffusion and Maxwell���s electromagnetic equations to analyze the temperature variation inside the SIP system. By coupling the physics of electromagnetism and heat transfer, our model allows for a comprehensive analysis of the temperature distribution and heating effects inside the chemisorbent. The proposed model is validated experimentally by the surface temperature findings of the SIP from IR-sensor. Additionally, we conduct sensitivity analysis of spatiotemporal temperature profile on various thermal and dielectric parameters, as well as the size and location of the Fe3O4 layer, to optimize desorption rates and make the regeneration process more energy-efficient
Bayesian Optimization of Coupled Systems
No full textThe field of multidisciplinary design optimization (MDO) addresses the complex challenge of optimizing systems characterized by interconnections or couplings, which significantly increases the computational burden for ensuring reliability in optimization outcomes. Particularly, design challenges involving feedback-coupled systems are notorious for their substantial demands on computational resources. In response to this issue, substantial efforts have been directed towards developing surrogate models that accurately replicate the intricate interconnected nature of these systems. Such models promise to drastically reduce computational expenses while maintaining effectiveness. Although Bayesian Optimization (BO) is traditionally celebrated for its efficiency in querying surrogate models, it encounters significant limitations when applied to constructing surrogate models for interconnected systems. Specifically, the black-box nature of BO struggles to capture the complexities of these systems, often necessitating frequent queries to the actual functions for training set updates. This approach, while potentially reliable, results in prohibitive computational costs.
To address these challenges and enhance the efficiency and reliability of optimization in the context of interconnected systems, we propose a novel methodology. This methodology focuses on the construction and querying of interconnected surrogate models, designed to more effectively and efficiently replicate the behavior of the target systems. By overcoming the limitations of traditional black-box models, our approach aims to provide a viable solution to the computational and practical challenges inherent in multidisciplinary design optimization of feedback-coupled systems. This advancement represents a significant leap forward in the pursuit of computationally efficient and reliable optimization techniques for complex, interconnected systems
Synthesis and Evaluation of Tribological Performance of Mxenes
No full textThis work addresses the challenges associated with the synthesis of MXene (acid etching) using an alternative method of molten salt etching and alteration of interfacial properties. This thesis is part of a thrust to develop acid free synthesis of MXenes at an industrial scale.
The initial part of the thesis is focused on the acid-free synthesis of MXenes via molten salt etching. Despite numerous prior reports of molten salt etching of MAX phases, few of these reports achieved water-dispersible MXene nanosheets and none for Nb-based MXenes. Here, we demonstrate the synthesis and aqueous dispersibility of Nb2CTz nanosheets via molten salt etching and utilizing a KOH wash to add hydroxyl surface groups. However, little is known about the oxidation of molten salt-etched MXenes compared to acid-etched MXenes. This work has indicated the slower oxidation behavior for MXenes etched by molten salts, which may be due to the decreased amount of oxygen-containing terminal groups.
A significant portion of my thesis is focused on utilizing the MXene (acid etched and salt etched) for tribological applications as liquid or solid lubricants. Owing to the high thermal conductivity, electrical conductivity, and mechanical strength of Ti3C2Tz nanosheets, they seem to be a promising candidate as lubricant additives. In this work, we evaluate the performance of Ti3C2Tz as an additive to enhance the heat transfer, rheological properties, and tribological performance of oils. The improved properties (Thermal conductivity) and reduced fluidic drag in viscosity and friction lead to potential applications in (electrical) vehicles that will help attain improved fuel economy.
Although surface terminations (such as ���O, ���Cl, ���F, and ���OH) on MXene nanosheets strongly influence their functional properties, synthesis of MXenes with desired types and distribution of those terminations is still challenging. In my thesis, we demonstrated that thermal annealing helps remove much of the terminal groups of molten salt-etched multilayered (ML) Ti3C2Tz. In this work, the chloride terminations of molten salt-etched ML-Ti3C2Tz were removed via thermal annealing. This thermal annealing created some bare sites of high surface energy and reactivity that are available for further functionalization of Ti3C2Tz. Here, the annealed ML-Ti3C2Tz was re-functionalized by ���OH groups and 3-aminopropyl triethoxysilane (APTES)z, which were evaluated as a solid lubricant, exhibiting ���70.1 and 66.7% reduction in friction compared to a steel substrate, respectively. This enhanced performance is attributed to the improved interaction or adhesion of functionalized ML-Ti3C2Tz with the substrate material. This approach allows for the effective surface modification of MXenes and control of their functional properties.
The ability to control the d spacing of MXene has proved beneficial for energy storage applications such as batteries and supercapacitors, but no one has utilized this control of interlayer spacing for lubrication. In this work, we control the interlayer spacing between the ML-Ti3C2Tz MXene via chemical intercalation. In order to alter the d-spacing, we investigated several different-sized intercalating agents. The increase in the d-spacing of ML-Ti3C2TZ MXene resulted in a drop in electrical conductivity and friction coefficient. Specifically, the enlarged interlayer gap reduced electrical conductivity in the vacuum-filtered ML-Ti3C2Tz MXene films due to increased internal resistance. Additionally, the increased d-spacing or interlayer spacing of ML-Ti3C2Tz resulted in a reduction of the coefficient of friction. This decrease is attributed to the facilitated sliding of individual ML-Ti3C2Tz layers under applied shear forces or load, resulting from the weakened van der Waals interactions due to the increased interlayer spacing
When Modes of Learning Shift Unexpectedly: How Instructors Choose Online Teaching Strategies
No full textThis study examined how in-person instructors selected online teaching and learning strategies when shifting to a different mode of learning during the COVID-19 pandemic. As many in-person instructors have little to no experience with online learning or instructional design, examining how strategies were selected during this time provides an understanding of what strategies worked, the challenges in shifting to a different mode of learning, and practices that were retained moving back to in-person instruction. The findings revealed that instructors selected strategies during these shifts through adapting existing in-person instructional strategies to address the changing circumstance
Addressing the Escalating Impact of Rice Kernel Smut: Insights into Genetic Diversity, Fungicide Resistance, Seed Endophytes, and Cultivar Resistance for Effective Management
No full textOnce considered a minor disease, rice kernel smut, caused by Tilletia horrida, has become one of the most economically important rice diseases in the US. With a lack of resistant rice cultivars, management heavily relies on the midseason preventive applications of propiconazole-based fungicides. However, the effectiveness of fungicide application seldom effective due to gaps in knowledge of the disease���s biology and epidemiology. We address, for the first time, the genetic diversity, fungicide resistance, seed endophytic microbiome, and host resistance, with the target to develop an effective kernel smut management program. We performed multi-locus sequence analysis to explore the genetic diversity of 63 T. horrida isolates collected from across the US. These isolates were grouped into five clades, with 59% of the isolates clustering together. The ITS region phylogeny grouped the 22 Tilletia spp. from eight different countries (Australia, China, India, Korea, Pakistan, Taiwan, The US, and Vietnam) together. Of the 63 US T. horrida isolates tested here, >80% were found to be tolerant at the baseline propiconazole concentration of 0.2 mg/L. While over 60% of the isolates displayed no inhibition at a concentration of 10 mg/L, 22% of the isolates tolerated at 25 mg/L, and one single isolate was not inhibited even at 50 mg/L. The T. horrida genomes sequenced, assembled, and annotated as part of this thesis revealed the presence of a single copy of Cyp51, a target gene for demethylation inhibitors (DMIs). In the cyp51 protein sequences of propiconazole-resistant isolates, five amino acid substitutions, G22A, R183K, V279A, L387I, and G494S, were observed. An efficient artificial inoculation method was established for T. horrida infection. Direct injection with pathogen spores onto developing panicles at the late-boot stage resulted in a higher level of disease infection compared to other inoculation methods evaluated. Field evaluation of 32 rice cultivars identified nine cultivars with partial resistance to kernel smut. An amplicon-based analyses of seed endophytic microbial diversity revealed differences between organic and conventional rice farming systems, with higher bacterial diversity in the latter and increased fungal diversity in the former. In parallel the cultivable endophytic bacteria isolated from rice seeds were identified based on the full-length 16S rRNA gene sequences. Among the 31 unique bacterial isolates tested in vitro, the strains Bacillus sp. ST24, Burkholderia sp. OR5, Pantoea sp. ST25, and Pseudomonas sp. OR4 exhibited antagonistic activities against T. horrida and, three seedling blight pathogens (Marasmius graminum, Rhizoctonia solani AG4, and R. solani AG11). The findings of this study provide insights into genetic diversity, fungicide resistance, and seed endophytes, and cultivar resistance for effective management of kernel smut in rice
Ultra-High Strain Rate Impact Behavior in High Molecular Weight Thermoplastics
No full textThe advent of commercial and military hypersonic vehicles introduces formidable challenges to existing thermal protection systems and ballistic armor. Concurrently, all spacecraft face escalating threats from hypervelocity impacts (HVIs) by micrometeoroids and orbital debris (MMOD). Overcoming these obstacles requires materials/structures capable of withstanding extreme conditions. Yet, a clear knowledge gap exists in the fundamental understanding of the complex multiphysics phenomena generated when materials are subjected to ultra-high strain rate (>10^6 s^ ���1 ) collisions. This is especially true for polymers, despite their capacity for energy absorption and tailorability. This dissertation endeavors to bridge this knowledge gap by exploring the ultra-high strain rate impact behavior of three high molecular weight thermoplastics, ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), and polycarbonate (PC). The primary objective is to help answer fundamental questions about their behavior and illuminate their applications. This goal necessitated a four-pronged strategy: (i) the establishment of an impact testing facility; (ii) the execution of HVI experiments; (iii) the application of numerical simulations to infer impacted target conditions; and (iv) the integration of these findings with existing literature to explain the role a polymer���s microstructure plays in its macroscopic energy absorption. The ensuing findings (i) revealed the difference in UHMWPE and HDPE���s HVI deformation, failure, and energy absorption was governed by an interplay between strain rates and rates of polymer chain disentanglement and reorientation and (ii) demonstrated the viability of threat-optimized protective structures. The dissertation also includes a novel study on similar impact phenomena, generated by decreasing spatial scale instead of increasing velocity. A Laser Induced Projectile Impact Test (LIPIT) apparatus and gas gun were used to launch alumina spheres ranging five orders of magnitude in diameter (3 ��m���10 mm) into scaled PC targets at 550 m/s. Length scale reduction set in motion a remarkable 230% amplification in specific energy absorption and a 240% increase in relative impact deformation area. In all, the dissertation leads to an irrefutable conclusion: while the behavior of polymers at lower rates (<10^3 s^ ���1 ) is well understood, there remains much to discover about their behavior as loading conditions become extreme. Data from lower rates and smaller scales cannot be extrapolated to higher rates and larger scales
Quantifying Complex Grazing Management Practices and Producer Systems Thinking Skills
No full textThe capacity of alternative grazing management strategies to maintain or enhance the production of ecosystem services and ranch profitability continues to be vigorously debated. However, the parameters used to differentiate among alternative grazing systems are inadequate, and standardized methods for comprehensively characterizing grazing systems are lacking. Inconsistent approaches to, and definitions of, adaptive management have likely contributed to the inconsistent findings in grazing management research. Systems thinking has been promoted to enhance decision making in complex natural resource systems but there is a lack of research evaluating the relationship between adaptive management implementation and systems thinking skills. This dissertation (1) develops a rigorous weighted composite index to serve as a standardized approach for more accurately classifying the grazing intensity implemented in grazing management systems; (2) develops an instrument that thoroughly measures the implementation of adaptive management at the ranch level, and; (3) tests the hypothesis that the level of adaptive management is positively associated with a producer���s level of systems thinking skills. The Grazing Intensity Index (GII) characterizes grazing systems differently than characterization efforts that rely on only a few descriptors, which suggests that the GII more objectively and comprehensively captures the cumulative effect of the spatiotemporal distribution of grazing and rest within a grazing system. The Adaptive Management Index (AMI) is positively correlated with perceptions of increased connectedness between grazing system elements, which suggests that the AMI effectively measures the implementation of adaptive management in livestock grazing systems. Gross livestock sales and gender, rather than the AMI, are primary drivers of systems thinking as measured by the systems thinking skills instrument, suggesting that producers who generate a larger volume of sales from their operation have a greater tendency for viewing systems holistically. Implementing the GII and AMI in future grazing management research studies will enable researchers to more precisely characterize contrasting grazing management strategies resulting in more robust findings and enhanced communication among researchers, and between researchers, extension personnel, and producers. Additional research is needed to evaluate the relationship between adaptive management implementation and systems thinking skills
Role of Steroid Hormones and Their Neuroactive Metabolites in Pavlovian Fear Conditioning
No full textIn the United States, one in every three individuals will experience an anxiety disorder in their lifetime. Importantly, there are significant sex differences in the incidence of these disorders. Anxiety disorders are almost twice as prevalent in females than in males, particularly post-traumatic stress disorder (PTSD). This significant sex difference indicates a possible role for gonadal hormones in the development of these disorders. Indeed, progesterone, estrogen, and testosterone have been found to modulate fear and anxiety in clinical populations and in rodent research models. A better understanding of how hormones contribute to the development and maintenance of anxiety disorders is vital to the development of targeted, effective treatments. Here, we use a Pavlovian fear conditioning model in which rats are trained to associate a context and cue with an aversive footshock, which leads to conditioned responding in the absence of the footshock. Using this model, we explore the role of progesterone (PROG), its metabolite allopregnanolone (ALLO), and the testosterone metabolite 3a-androstanediol (3a-diol) on the acquisition, expression, and extinction of conditioned fear. Ovariectomized females were treated systemically with PROG whereas intact males received either ALLO or 3a-diol infusions into the bed nucleus of the stria terminalis (BNST), a sexually dimorphic brain structure shown to modulate anxiety and context-dependent fear. Our laboratory has previously shown that intra-BNST ALLO in male rats and estrous cycle phase in cycling female rats can confer state dependence to contextual fear such that retrieval of the fear memory is optimal when animals are tested in the same hormonal state experienced during conditioning. The results here demonstrate that although acute changes in systemic PROG of ovariectomized females can causes changes in conditioned fear expression, they do not mirror the state-dependent regulation observed in cycling females. In male rats, intra-BNST 3a-diol confers state dependence to contextual, but not cued, fear such that animals trained and tested in different hormonal states exhibit a state-dependent generalization decrement. Finally, we show that in male rats, intra-BNST ALLO can modulate extinction learning but not in a state-dependent manner. The work presented here further demonstrates that hormones and their neuroactive metabolites can influence different aspects of acquisition, expression, and extinction of conditioned fear and supports the consideration of interoceptive cues associated with hormonal state when developing treatments and interventions for anxiety- and trauma-related disorders
Learning from Successful Qatari Women in Corporate Management: Stories of Career Development and Lived Experiences
No full textThe purpose of this study was to explore Qatari women���s career development journey to management within the context of Qatar���s unique culture, honoring ancient traditions while ambitiously entering modernity. For Qatari women to be equally represented in corporate management they must be motivated and aspire to compete for influential positions in gender-mixed environments. This study used a qualitative, life history approach to examine their life experiences that have influenced their career development, in gender-mixed work environments. A two-part data analysis approach was conducted consisting of (a) the construction of a case story that reflected the biographical, life history of each participant as it related to her career development, and (b) inductive, cross-case thematic analysis. The major themes that emerged from this process concerned the critical career development stages that contributed to the personal and professional growth of participants and had a direct impact on their career progression. The four major themes identified were: (a) early beginnings; (b) quest for higher education; (c) establishing and managing career; and (d) strategies for sustained career success.
The participants��� early beginnings centered around their family and were heavily influenced by their father���s support. The love and care shown by their families enabled them to adapt to strong guardianship by showing respect, honor, and obedience to their families. During their quest for higher education, participants were guided by their families��� expectations for educational attainment. They developed resilience in the face of challenges, which altered their original plans for university and caused them to pivot and reconstruct their vision for a university experience. Upon finishing university and entering the workforce, participants��� greatest challenge was assimilating into a gender-mixed work environment. In this new environment the women faced gender bias, ageism, and had to confront societal judgement, which had a strong presence in their work environments. The women worked hard to prove their professional credibility by developing their interpersonal skills and finding their professional voice. Predominant enablers of their success were having a high-risk, growth mindset, managing positive relationships with their supervisors and mentors, and finding a meaningful purpose to drive their ambition and success
John Bickham field notebook: AK5501-AK6000.pdf
No full textBound book, each page corresponds to a karyotype slide data.Data pages for AK6001-AK6500 corresponding to unique identifiers of specimens/samples examined for biological research. Specimens are primarily housed at Texas A&M University; Biodiverstiy Research and Teaching Collection