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How the Presence of In-Group Peers and Experts Influence Stem Undergraduate���s Identity, Persistence, and Academic Success
No full textEfforts to confront complex societal challenges are hindered by the lack of diversity in the science, technology, engineering, and mathematics (STEM). As education is a social enterprise, investigating how social interactions support or hinder belonging and persistence is crucial for the success and retention of historically underrepresented (HU) students. This three-article dissertation sought to understand and quantify how the presence (or lack thereof) of ingroup peers and experts in a student���s network influences domain-specific motivation and persistence intentions for HU STEM students. Study 1 uses ego-centric social network analyses to evaluate how the characteristics of mentees and mentors relate to the content of support and structure of mentor networks in a large sample of White and Hispanic/Latino(a) STEM undergraduates. Mentee perceived psychological similarity with their mentor(s) predicted both dyadic and network average levels of mentor support (i.e., psychosocial, career, role modeling) and relational satisfaction. Additionally, demographic homophily and engagement in undergraduate research were related to some mentor network structures. Study 2 extended this work by evaluating how characteristics of mentees, including if they have a mentor, and the quality and structure of their individual networks related to social integration, well-being, academic success, and persistence in STEM over two years. Having a high-quality mentor network, rather than the absence or presence of one or multiple mentors, was an important predictor of domain identity and well-being for students, which ultimately led to persistence in their STEM major. Finally, Study 3 narrowed the scope of social supports by analyzing patterns of demographic and psychological factors between students in one sophomore- and junior-level undergraduate Engineering and Computer Science (ECS) classroom. LNAM results revealed the presence of network clustering based on similar levels of domain identity. Additionally, domain values were positively related to STEM persistence intentions. This work critically addresses several significant gaps in the literature at the intersection of motivation and social networks for HU STEM undergraduates. Results inform best practices for developmental mentor network support, program developments, and interventions at the classroom level aimed to enhance social supports for students, ultimately addressing the nation���s goals to broadening participation in STEM fields
A Primer on Tariffs
Get PDFTariffs are taxes explicitly on imported goods, either broad-based or product-specific, often used to manage trade, protect domestic industries, or as a negotiation tool in international relations. In this issue of PERCspectives on Policy, PERC's Montgomery Professor Dennis Jansen discusses the purpose and past U.S. history of tariffs, and their role in modern day trade policy
Optimizing Markov Decision Process Models of Intermittently-Observed Multi-Agent Systems
No full textA challenging category of robotics problems arises when sensing incurs substantial costs. This thesis examines settings in which a robot wishes to limit its observations of state, for instance, motivated by specific considerations of energy management, stealth, or implicit coordination between multiple agents. We consider the problem of planning under uncertainty when a robot���s observations are intermittent under two specific circumstances. In one, their timing is known via a pre-declared schedule, whereas in the other the timing arises dynamically from multiple robots working together to generate observations.
After establishing the appropriate notion of an optimal policy for each setting, we find that the pre-declared case requires tackling the problem of joint optimization of the cumulative execution cost and the number of state observations, both in expectation under discounts. To approach this multi-objective optimization problem, we introduce an algorithm that can identify the Pareto front for a class of schedules that are advantageous in the discounted setting. The algorithm proceeds in an accumulative fashion, prepending additions to a working set of schedules and then computing incremental changes to the value functions. Because full exhaustive construction becomes computationally prohibitive for moderate-sized problems, we propose a filtering approach to prune the working set. Empirical results demonstrate that this filtering is effective at reducing computation while incurring only negligible reduction in quality. In summarizing our findings, we provide a characterization of the run-time vs quality trade-off involved.
We explore as well the dynamic observation scenario, by developing a formulation for renegotiation of observations throughout execution. The formulation is additionally expanded to support the navigation of multiple agents in a single, joint MDP. We conclude with a hardware demonstration featuring two robots maintaining formation whilst moving down a corridor, subject to motion uncertainty and turning to look at each other intermittently to gauge their states
Self-Healing of Bulk Vitrimers as a Function of Thermomechanical Boundary Conditions
No full textThe subject of this study is vitrimers, a class of thermoset polymers with exchangeable covalent bonds, with a focus on their ability to improve material durability in the aerospace, civil infrastructure, and elastomer technology industries while requiring minimal intervention. The material used in this study was procured from ATSP Innovations, provided as a bulk block with the specified dimensions to meet our testing requirements. The selected material, a variant of ATSP characterized as CBAB, was chosen strategically owing to its unique availability in bulk form from the manufacturer at this juncture. This characteristic of CBAB was pivotal for our study as it is allowed for a consistent and uniform sample preparation, an essential factor for the integrity of our fracture mechanics analysis.
To evaluate the bulk fracture, compact tension (CT) tests were done on samples cut out of a panel. The samples were then mended by putting the two halves of the sample together and applying heat and mechanical pressures to study the kinetics of bond formation and their selfrepair mechanisms. Pre- and post-healing fracture toughness measurements were methodically performed, demonstrating a significant restoration of mechanical strength, confirming the effectiveness of the repair procedure. Furthermore, the study investigated the interplay between time and temperature influencing vitrimers ability to self-heal, offering light on the best circumstances for maximal healing efficiency. The time and temperature dependence of the healing mechanism was explained quantitatively by means of an Arrhenius relationship, and the activation energy of the bond reformation was assessed. Furthermore, by revealing the intricate link between stress levels and the healing process, this study sheds light on the fundamental mechanisms governing vitrimer self-repair, paving the path for improved material design and application. A comparison was made between the healing performance of bulk samples and ATSPcarbon fiber reinforced composites, obtained from other studies, to shed light on the effect of confinement (in the composite) on the healing performance of the vitrimers. Crucially, this study emphasizes the critical roles that temperature, time, and stress levels play in shaping the dynamics of self-healing, providing invaluable insights for both advancing our understanding of vitrimers and facilitating their wider adoption in the field of self-repairing materials
Essays on Social Preferences
No full textThis dissertation includes three essays in the field of behavioral economics, with a special focus on social preferences using laboratory experiments. The first essay investigates the influence of patient autonomy on doctors��� performance. Using a theory-driven laboratory experiment, I find that when the patient is not able to assess the doctor���s diagnostic precision, for those patients who are not fully compliant with doctors��� advice, doctors will reduce their investment of effort in the diagnosis. This reduction is the largest among those doctors who prioritize patients��� well-being. The experiment also investigates two institutional changes, communication and reputation, which both effectively improve patients��� well-being. This study contributes to experimental health economics by uncovering the potential detrimental effect of patient autonomy on a doctor���s performance and the patient���s health status.
The second essay explores the effectiveness of two punishment strategies for addressing the free-rider problem in public goods production. By varying the timing of punishment in a public good game, we differentiate between the Post-Punishment rule, expected to induce emotional arousal, and the Pre-Punishment rule, aimed at strategic considerations with minimal emotional impact. Pupil dilation data from eye trackers support our hypotheses, revealing that the Post-Punishment rule���s success relies on negative emotions, while the Pre-Punishment rule does not. This study sheds light on the role of negative emotions in punishment efficacy and introduces a novel punishment rule that operates independently of negative emotional responses within a group.
The third essay examines the trade-offs individuals make between money, honesty, and altruism through a sender-receiver game that allows truth-telling, selfish lies, and altruistic lies. We propose a theoretical model identifying five unique types of senders. Experimental findings show prevalent yet diverse patterns of trade-offs among these three domains of concern. This research adds to the literature on lying behavior by revealing varied preferences across moral domains and a widespread
propensity for costly altruistic lies
Phylogeography and Systematics of the Sand Shiner, Notropis stramineus (Cope, 1865)
No full textNotropis Rafinesque, 1818 is a species-rich genus of North American minnows that has been demonstrated to harbor ���cryptic��� diversity. The Sand Shiner, Notropis stramineus, is one of the most widespread North American minnows. Various subspecific classifications have been proposed for the Sand Shiner, the most widely accepted of these comprising two subspecies, N. s. stramineus and N. s. missuriensis, based largely on minor differences in scale-row counts between individuals inhabiting tributaries to the Great Lakes, upper Mississippi River and Texas Gulf Coast river systems (N. s. stramineus) and those inhabiting the Missouri and Arkansas River systems (N. s. missuriensis). Analysis of three loci revealed that the Sand Shiner, N. stramineus comprises five clades, and further, other members of Notropis were recovered between clades of N. stramineus, though gene tree discordance created difficulties for determining species boundaries. Ultra-conserved elements (UCEs), enriched from each clade of N. stramineus, related species, and several outgroup taxa, were then analyzed. All least-inclusive clades recovered were identical across analyses and corresponded to clades recovered in Chapter II, however, relationships between the clades differed. In contrast to Chapter II, most clades comprising N. stramineus were monophyletic, and are here termed the N. stramineus species complex. As in Chapter II, a separate clade of N. stramineus was recovered outside of the clade containing the N. stramineus species complex as the sister taxon to a species of Notropis not previously considered to be closely related (N. chihuahua). These results demonstrate that N. stramineus is likely comprised of five distinct evolutionary lineages, which are diagnosed and described (clades B1, B2 and D) or redescribed (clades A and C) in the final chapter, with species diagnosed using characters derived from aspects of pigmentation, body and head shape, tuberculation, and osteology
Effects of Horizontal Resolution on Precipitation Simulations
No full textPrecipitation simulated by climate models in different resolutions, including the mean state of global precipitation, regional precipitation response to mesoscale SST variability, global extreme precipitation in present-day and its future projections, are investigated using both observational (reanalysis) data and global climate model simulations.
The hydrological cycle and its anticipated alterations in the face of global warming are analyzed and compared based on observations, reanalysis datasets, and climate models with different horizontal resolution. Notably, CESM-HR demonstrates a remarkably more robust oceanic water cycle than CESM-LR, a difference possibly stemming from the warmer SSTs in CESM-HR in contrast to CESM-LR. Under global warming, the impact of increased horizontal resolution on future projected changes in the hydrological cycle becomes apparent. Specifically, CESM-HR exhibits a slightly higher percentage increase in ocean-to-land water vapor transport. Therefore, it plays a role in the amplified increase in precipitation over land under climate change.
Precipitation and associated atmospheric response to mesoscale SST forcing is explored. By filtering out mesoscale SST variability, CESM-HR produces a realistic precipitation response as observed, while CESM-LR fails to capture such a response because of absent mesoscale SST variability. Further analyses in CESM-HR and ERA5 reveal a similar vertical velocity response extending up to 500hPa, suggesting a possible free-atmosphere response to mesoscale SST anomalies. Composite analysis further validates this local deep response. The poor representation of mesoscale SST variability in CESM-LR hampers model���s ability to simulate precipitation and associated circulation response.
A comprehensive overview of the impact of horizontal resolution on presenting extreme precipitation shows that, CESM-HR not only replicates the observed spatial distribution of extreme precipitation but also accurately captures the intensity across the global land. Significantly, the discernible influence of horizontal resolution on precipitation extremes predominantly manifests itself through its effect on the representation of resolved large-scale precipitation. Under global warming, extreme precipitation over most of the global land is shown to be intensified. After decomposing projected changes of extreme precipitation by moisture budget analysis in CESM-HR, we find that across most of the global land area, the projected changes are predominantly attributed to shifts in atmospheric circulation features, rather than contributions from thermodynamics
An Evaluation of Alternatives for Updating Base Acres in the 2024 Farm Bill
No full textGiven that the income-support provisions in the farm bill have been decoupled from production for more than two decades, base acres are no longer reflective of planted acres in the United States. Three alternatives are currently being discussed to better align base acres with current plantings in the next farm bill: 1) a reallocation of bases to current plantings, 2) a forced update to current plantings, and 3) a rolling average of the plantings from the previous two years. There undoubtedly will be winners and losers across individual operations, crops, and regions. Knowing who will be impacted would enable Congress to make more informed decisions regarding base updates. To comprehensively evaluate the alternatives, this study undertook a farm-level and national analysis.
The farm-level analysis was implemented by collecting data from four representative farms maintained by the Agricultural and Food Policy Center at Texas A&M University. For each farm, base acres were calculated for the three alternatives, and stochastic simulation was used to determine a five-year forecast of average government payments, ending cash, and ending real net worth. The national analysis was conducted by collecting public data from the Department of Agriculture���s Farm Service Agency for nine covered commodities and calculating new base acres per county to determine absolute gains and losses. The absolute change per crop per county was totaled to determine the deviations between the current baseline and each scenario being analyzed.
The results from the farm-level and national analysis indicate a wide variety of impacts on individual farms, crops, and regions. While maintaining current base acres might be the optimal solution for one location or commodity, it is apparent that the same scenario would be less preferred by others. One universal option (e.g., to reallocate base acres) might not be the best solution; in fact, allowing producers to choose amongst several options might be the best route for baseline modification in the next farm bill, recognizing that approach will also cost the most
Teacher Motivations for Field Trips to Small Museums
No full textThis study explored what components are most valued by teachers during the planning phase of field trips to small museums. It identified teachers' motivations and constraints when planning a field trip to a small museum. In addition, it examined the influence of motivations and constraints on the likelihood of teachers taking a field trip and teachers��� willingness to put in effort to take a field trip after the planning phase. Past research on teacher motivations for field trips, however, reveals a need to improve in the area of small museums. Small museums are significant contributors to society by providing local access to education, creating job opportunities, promoting sustainability, and more. This study sought to find teachers' motives and constraints during field trip planning and the intention of taking a field trip after planning through survey data collected from teachers ranging from kindergarten to twelfth grade. The data analyzed were grouped into motives, constraints, likelihood, and willingness. The findings offer insight to small museums to make the necessary investments in school field trips that may increase revenue, enhance community engagement, and create better educational experiences
Shaping Human Capital and Socioeconomic Outcomes: The Impacts of Grade Retention, Lead Exposure, and Social Media Rhetoric
No full textMy dissertation consists of three essays on the topics of grade retention, lead exposure, and social media rhetoric. In the first chapter, I provide the first causal evidence of the effects of grade retention on the labor market outcomes using Texas��� policy of retaining third graders who fail a reading test. The fuzzy regression discontinuity design estimates show that third-grade retention significantly reduces adult earnings. Although the policy aims to improve academic achievement, the results demonstrate that third-grade retention lowers high school graduation rates without improving college outcomes and aggravates absenteeism and violent behavior.
In the second chapter, coauthored with Andy Cao and Jason Lindo, we investigate whether Donald Trump���s "Chinese Virus" tweets contributed to the rise of anti-Asian incidents. We find that the number of incidents spiked following Trump���s initial ���Chinese Virus��� tweets and the subsequent dramatic rise in internet search activity for the phrase. Difference-in-differences and event-study analyses leveraging spatial variation indicate that this spike in anti-Asian incidents was significantly more pronounced in counties that supported Donald Trump in the 2016 presidential election relative to those that supported Hillary Clinton. We estimate that anti-Asian incidents spiked by 4000 percent in Trump-supporting counties, over and above the spike observed in Clinton-supporting counties.
In the third chapter, coauthored with Thao Duong, we analyze the long-term effects of low-level lead exposure during early childhood from Kindergarten through grade three on educational achievement and earnings. Utilizing the unexpected decline in lead emissions following the reduced operation of piston-engine aircraft after the 9/11 attacks as a natural experiment, combined with detailed individual-level administrative data from Texas ERC, we employ both difference-in-differences and instrumental variable techniques to identify the causal impact of lead exposure on various student outcomes. Our findings reveal that even minimal increases in lead exposure, measured in micrograms per cubic meter, are associated with significantly decreased probabilities of high school graduation and post-secondary enrollment in public universities or community colleges. Moreover, we observe that lead exposure adversely affects children by diminishing their future earnings in the labor market