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D-Optimal Joint Best Linear Unbiased Predictors In Progressively Type-Ii Ordered Statistics
No full textReliability and life-testing experiments play a crucial role in understanding the longevity and performance of systems and components, particularly in high-stakes applications such as engineering, manufacturing, and quality control. In this thesis, we focus on the prediction of future unobserved failure times by employing joint predictors based on progressively Type-II censored data obtained from such life-testing experiments. Specifically, we derive explicit analytical expressions for the joint best linear unbiased predictors (BLUPs) of two future order statistics under the D-optimality criterion. The derivation involves minimizing the determinant of the variance-covariance matrix of the predictors within the context of progressively Type-II censored schemes. This approach ensures that the resulting joint predictors are D-optimal, establishing them as a highly efficient choice for predicting unobserved future data points.
One of the primary contributions of this work is the detailed comparison between joint predictors and marginal predictors, which is accomplished by analyzing the design efficiency in various scenarios. By evaluating efficiency measures such as D-efficiency and Trace-efficiency, the analysis highlights the strengths of joint prediction approaches over marginal predictions in terms of gaining efficiency and thus improving reliability outcomes. This comparison provides valuable insights into the practical benefits of employing joint predictors when analyzing reliability data from life-testing experiments on progressively Type-II censored data. Additionally, the study also investigates the conditions under which joint BLUPs do not exist, demonstrating the inherent limitations and challenges of using such predictors under specific situations
Evolutionary History Of A Specialized And Diverse Highland Snake Complex (crotalus Willardi)
No full textThe Ridgenosed rattlesnake (Crotalus willardi) is a highly unique group of small rattlesnakes consisting of 5 subspecies that inhabit the high elevation pine oak woodlands of the Sierra Madre Occidental and the Madrean Archipelago. They remain one of the most understudied groups of rattlesnakes with little understanding of the relationships between the subspecies. I utilize genomic level genetic data collected using ddRAD-seq methodology on 60 individuals encompassing all 5 subspecies and the majority of the range. Utilizing co-ancestry analysis, Admixture, and Phylogenetic analyses (both maximum likelihood and Bayesian approaches) we uncovered seven separate genetic groups. Of these, three consisted of a single described subspecies with the remaining two subspecies being paraphyletic. One integrade was uncovered by our analysis but Treemix modeling indicated that 98% of variation in the gene trees could be explained without geneflow. Admixture, however, should slight mixing in some groups which may be indicative of ancestral gene flow. The deepest divergences occur in the southernmost subspecies with some strange patterns occurring where sister lineages were not the closest to each other geographically. These results suggest that current taxonomy may not be adequate in explaining the variation in the complex. They also suggest that there has been little to no recent gene flow with the group first evolving in the south and moving north
Examination Of The Role Of Ovarian Hormones On Nicotine Withdrawal Severity In Females
No full textWomen are more susceptible to the long-term consequences of chronic nicotine exposure, and clinical evidence has shown that abstinence from nicotine exposure produces a withdrawal syndrome that is intensified by estrogen (E2 in rats) and progesterone (PR) in females. The goal of this Masterâ??s thesis was to determine the mechanisms by which E2 and PR promote withdrawal from nicotine vapor inhalation in female rats. Prior work in male rodents has revealed that nicotine withdrawal is modulated in the medial habenula-interpeduncular nucleus (MHb-IPN) pathway. Our hypothesis is that females experience greater inhibition of the IPN via local interneurons that release the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Also, we hypothesize that E2 and PR promote inhibition of the IPN during withdrawal in females. To address our hypotheses, we examined withdrawal-induced changes in the expression of GABAergic genes (Aim 1) and the impact of ovarian hormones on the expression of GABAergic genes (Aim 2) in the IPN of intact and ovariectomized (OVX) female rats. Rats received 14 days of nicotine vapor inhalation. Withdrawal was then precipitated following administration of the nicotinic receptor antagonist mecamylamine (3.0 mg/kg, sc), and the physical signs of withdrawal were assessed for 10 minutes. After testing, vaginal lavage and cytology procedures were conducted to determine the phase of the estrous cycle they were tested in. Gene expression analyses were then performed to evaluate mRNA levels of various markers of GABAergic inhibition and hormones in the IPN. Intact female rats displayed greater physical signs of nicotine withdrawal compared to controls and OVX females. Additionally, we observed a withdrawal-induced increase in GABAergic and hormone receptor gene targets in the IPN of intact females, and these effects were obliterated in OVX females. These results suggest that ovarian hormones promote nicotine withdrawal severity via increasing inhibition of the IPN
A Computational And Conceptual Study On The Effect Of Molecular Structure On The Excited State Lifetime And Redox Energetics Of Iridium And Ruthenium Photoredox Catalysts
No full textThis work investigates the effect of ligand structure on the photophysical and redox properties of iridium and ruthenium photoredox catalysts. Using density functional theory (DFT) and intuitive theoretical tools, we systematically analyze how structural isomerism, cyclometallation, nitrogen-containing heterocycles, and ligand substitution impact the performance of [Ir(ppy)2(bpy)]+ and Ir(ppy)3-based catalysts.
First, this dissertation explores structural isomerism, revealing that while ground-state and excited-state redox potentials remain stable across isomers, variations in transition dipole moments and spin-orbit coupling lead to significant changes in excited-state lifetimes. These findings highlight the importance of isomeric orientation for controlling decay rates. Then, this study investigates the role of cyclometallation in extending the excited-state lifetimes of iridium and ruthenium complexes, demonstrating the role of metal-carbon bonds in radiative and non-radiative decay pathways. This work also studies the effect of nitrogen-containing heterocycles, showing that incorporating pyrazine and pyrimidine groups can increase lifetimes and shift reduction potentials, thus improving photoredox efficiency. Furthermore, this study examines how electron-withdrawing and electron-donating substituents, located on redox-active and cyclometallating ligands, shift redox potentials and extend excited-state lifetimes, depending on their position. Finally, this dissertation investigates temperature-dependent decay pathways, demonstrating how modifying the ligand environment around the metal center can change the energy barriers throughout the 3MLCT → 3MC → S0 pathway, thus reducing non-radiative decay and improving catalyst stability. Collectively, this work provides a framework for the rational design of iridium photoredox catalysts, paving the way for more efficient applications in synthetic chemistry and sustainable energy
Environmental change as a driver of the evolution of migratory behavior in suboscine birds
No full textAvian migration, particularly long-distance seasonal migratory movement, has long captured the attention of researchers and the public alike. However, the evolutionary origins of migratory behavior are poorly understood, in part due to limited understanding of the full range of migratory strategies including short-distance and intra-tropical movements. We examine the climatic drivers of migration across suboscine birds, a group of roughly 1,300 primarily Neotropical species with a complex array of migratory strategies. Our reconstructions of the evolutionary history of suboscine migration reveal that migratory behavior is labile and is lost approximately twice as often as it is gained. We find that the evolution of migratory behavior in temperate-breeding, long-distance migrant suboscines is driven by temperature seasonality, presumably associated with departure from high latitudes to avoid resource drought in winter. Short-distance migration in tropical-breeding species, however, evolved in association with seasonality in precipitation. Tropical regions with high precipitation seasonality contain a mix of migrant and non-migrant suboscines, but a higher proportion of species vacates these areas compared to tropical regions with stable seasonal precipitation. Further, when we examine projected future climates under two scenarios, we find that while temperature seasonality is projected to decrease across the breeding ranges of most suboscines, precipitation seasonality demonstrates a more complex response that differs between future climate scenarios. The contrasting impacts of climate on the evolution of different migratory strategies highlights the complexity of climate-movement associations and the challenges associated with identifying how future climate change might impact organisms with disparate migratory strategies
Thermal analysis of combustion synthesis of FeAlxOy catalysts for dehydrogenation of fossil fuels
No full textThe growing demand for hydrogen as a clean energy carrier highlights the need for its alternative production method with reduced CO₂ emissions. Microwave-assisted thermocatalytic dehydrogenation of fossil fuels offers a promising solution for clean hydrogen production, with FeAlxOy nanocomposites acting as efficient catalysts due to their thermal stability, catalytic activity, and microwave-absorption properties. FeAlxOy nanocomposites, fabricated by solution combustion synthesis (SCS), have shown good microwave-absorption and catalytic properties. However, the effects of synthesis parameters such as fuel type and Fe:Al molar ratio on the SCS process and properties of the final material are not well understood. The SCS process involves vaporization of water, thermal decomposition of the mixture components, and oxidation – reduction reactions. In the present work, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were utilized to study the SCS mechanism, with a focus on understanding decomposition processes. TGA provided insights into the thermal stability and mass loss profiles of the mixtures, while DSC quantified the heat release and identified reaction onset temperatures. Results demonstrated that the choice of fuel significantly influenced the thermal behavior and properties of FeAlxOy nanocomposites. Glycine-based mixtures exhibited superior thermal stability and complete decomposition in a single step with high heat release compared to citric acid-based mixtures, which required higher synthesis temperatures and experienced slower, two-step decomposition processes. These findings emphasize the effectiveness of glycine-fueled SCS in producing thermally stable and catalytically active FeAlxOy nanocomposites
Investigating A Study Abroad Program As A Reflective Development Of Intercultural Competence For Students In A Hispanic-Serving University
No full textThis dissertation project investigates the broad problem of evaluation and effectiveness that have diminished the opportunities that study abroad can potentially offer as part of higher education in the U.S. The research aim was to develop a reflective plan of implementing study abroad to achieve the transformation of intercultural competence of students of higher education in a Hispanic university. The research questions were deduced from a combination of views from literature since the 1920s affirming study abroad as elitist endeavor, female, liberal arts and academically weak. Using a quantitative data methodology, the study were collected data from students who participated in study abroad and returned to campus using a retrospective method known as post-then-pre data collection. The sample universe was over 300 students with a 12 percent response rate. The findings reveal language was not a predictor variable in the development of intercultural competence; however, the study affirmed that study abroad assists students to develop intercultural competence suggesting that there were other variables missing in study abroad such as block-time for immersion. These results builds towards accountability for effective evaluation of study abroad as a legitimate and valuable part of U.S. higher education in the era of globalization
Ni Uno Mas: A Critical Examination of Zero Tolerance Policies
No full textThis study investigates the impact of zero-tolerance policies on minority students, emphasizing the school-to-prison pipeline (STPP). Using a qualitative methodology and testimonios, the study reveals how these policies, initially aimed at severe offenses, have disproportionately targeted minor infractions among ethnic minority students, exacerbating systemic inequities. Through a comprehensive literature review and personal narratives, the research highlights the cultural mismatch between strict disciplinary measures and the lived realities of these students, shedding light on the profound consequences these policies have on their educational journey and personal development. The findings underscore the urgent need for policy reform, advocating for restorative justice practices over exclusionary discipline. By amplifying student voices, the study aims to inform policymakers, educators, and stakeholders about the detrimental effects of current policies and the necessity for an equitable and inclusive educational environment. This work contributes to the discourse on educational equity, calling for a policy reform and reevaluation of disciplinary practices to dismantle the STPP and foster a supportive environment conducive to the academic and personal growth of all students. The research ultimately seeks to drive transformative change in the educational system, ensuring fairness and justice for all students, regardless of their background
The Flexible Pathways Model Of Writing Assessment: A Plan For Equity And Agency In The Writing Classroom
No full textThis project is a qualitative study in which I seek to understand how my new model of writing assessment, The Flexible Pathways Model, or FPM, functions when piloted in three First-Year Writing classrooms at a border and Hispanic-Serving Institution. This research builds on the work of composition scholars Peter Elbow and Pat Belanoff, Elbow and Jane Danielewicz, Asao B. Inoue, Ellen Carillo, and Edward White as well as education scholar Benjamin Bloom. The model also incorporates concepts from Universal Design scholarship of Tara Wood, Stephen Dolmage, and Anne-Marie Womack. In the FPM, students learn about four different methods of writing assessment and pedagogy. Each student then selects which method they would like the instructor to use to assess their work. Depending on the student\u27s selection, their choice of assessment method also shapes how they will proceed through the curriculum as they may choose a model with hard or flexible deadlines, deferred grades, multiple versions of assignments, or move at their own pace. Individual interviews and a focus group with the instructors who used the FPM indicated the FPM has great flexibility, functioning as a framework in which teachers are free to be creative. The teachers also showed a strong willingness to collaborate with me and each other, showed significant concern for their students, and this concern for students seemed to be the root from which greater flexibility, increased student choice, and increased equity and agency grew in the classroom. The teachers thought that the FPM gave students more agency and helped to create a grading ecology of greater equity for virtually all students than more traditional one-size-fits-all approaches and can foster composing environments conducive to the success of an increasingly diverse student population in our writing classrooms
Why Geological Angular Unconformity Is Usually Horizontal: A Geometric Explanation
No full textIn several locations, geologists have observed the presence of two differently oriented rock masses, one horizonal (or almost horizontal) and the other somewhat inclined; this phenomenon is known as angular unconformity. Based on the detailed analysis of geophysical processes, geologists conclude that usually, horizontal rock masses are much newer. This is known as the law of original horizontality. From the fundamental viewpoint, it is desirable to take into account that geophysics is a developing science, its models get modified and adjusted as time progresses. It is therefore desirable to come up with an explanation of this phenomenon that would be maximally independent on any specifics of a geophysical model. In this paper, we show that the law of original horizontality can be derived by using only the general geometric symmetry ideas