OSU Theses
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Item Investigation of time-dependent factors affecting concrete bridge decks in laboratory and field conditions(2023-12) Cochran, DillonConcrete bridge decks form the backbone of much of our modern transportation infrastructure. However, these bridge decks can be subject to several quality-control issues that can result in poor ride-quality elevation control, and deck cracking. The concrete properties determine the effect these quality-control issues will have on the deck. These issues are not merely long-term concerns, but can also be present in new bridge decks as well. For this reason, a proper understanding of both the fresh and hardened concrete properties is vital to designing concrete bridge decks that perform effectively throughout their service lives. Achieving high-quality early-age concrete is critical in reducing the effects of these issues, and several factors can significantly impact early-age concrete — primarily, drying shrinkage and creep. Previous investigations concerned with the role of deck shrinkage in elevation control issues highlighted the potential need for further examination of the effects of creep on early-age bridge deck deflections and cracking. This thesis focuses on the study of tensile and compressive creep as well as shrinkage of concrete at early ages (up to 90 days after casting). Through a detailed examination of tensile and compressive creep, as well as drying shrinkage, the research presented provides insight into several factors that can lead to serviceability issues in steel girder bridges with composite deck slabs.Item Do structural changes in brain development mediate the relationship between parenting factors and adolescent psychopathology? Evidence from the ABCD® study(2023-12) Cohen, Zsofia PhoebeAdolescence is a rich period of social, emotional, and physical development. Growing rates of mental health concerns have been documented in this population across recent decades and highlight a growing public health crisis. Factors such parenting characteristics, caregiver psychopathology, and structural brain abnormalities have been associated with emerging adolescent mental health symptomatology. While numerous investigations have demonstrated these associations, none so far have examined these interdependent factors across this developmental period. This thesis aimed to bridge this gap by examining these facets in a prospective, longitudinal design using secondary data analysis of the Adolescent Brain Cognitive Development (ABCD) Study. The present study examined self and parent-reported questionnaires and structural brain data across three timepoints: Baseline (ages 9-10), Year 2 (ages 11-12), and Year 3 (ages 12-13). Study caregivers reported on their mental health via the Adult Self-Report at Baseline. Adolescents reported on parenting characteristics at Baseline via the Children’s Report of Parental Behavior Inventory, Parental Monitoring Questionnaire, and Family Environment Scale. Structural brain development was examined as a percent change from Baseline to Year 2 across global cortical thickness (GCT), white matter volume (WMV), fractional anisotropy (FA), and mean diffusivity (MD). Finally, adolescent mental health was examined at Year 3 via the Brief Problem Monitor. Linear mixed effects modeling and PROCESS Macro were used to conduct a moderated mediation analysis on a final sample of n=3,672. Parent mental health symptoms at Baseline predicted adolescent mental health symptoms at Year 3, β=0.15, t=9.12, p<.001. Parent mental health failed to predict adolescent structural brain changes, ps>.05. FA (t=3.74, p<.001) and MD (t=3.40, p<.001) were positively associated with adolescent mental health symptomatology at Year 3, while GCT and WMV were not, ps>.05. However, no total indirect effects of mediators (abs=0.00) or index of moderated mediation were found. The results of this thesis underscore parent mental health as an important predictor for adolescents’ mental health outcomes. Findings regarding moderation, mediation, and moderated mediation effects of parenting characteristics and structural brain changes were largely non-significant and replicate a multitude of studies of global brain metrics during this developmental span.Item Exploring interactions between black-tailed prairie dogs and grassland taxa to guide working lands management(2023-12) Buehler, Lindsey MorganBlack-tailed prairie dogs (Cynomys ludovicianus) are considered ecosystem engineers due to their burrows facilitating soil ventilation as well as herbivory and vegetation clipping creating early successional habitat and shifting vegetation composition. Despite the important role prairie dogs play in structuring rangeland ecosystems, conflict with livestock has led to control efforts that have reduced the range of this species and plague (Yersinia pestis) has further reduced populations. Given these reductions, an understanding of how management affects prairie dogs and, indirectly, other taxa, as well as ecological relationships between prairie dogs and wildlife, is needed. This thesis tests the effect of one management approach, boundary management, on prairie dogs and associated taxa in Thunder Basin National Grassland of Wyoming (Chapter 1) and explores the relationships between prairie dogs and native ungulates at three management grasslands across their range (Chapter 2). We used a before-after control-impact study design to assess the effects of boundary management with lethal control on prairie dog numbers and explored this management approach as a proxy for density control, which is a recently proposed management approach in Thunder Basin. We found that while treatment reduced pup numbers, there was no treatment effect on adult prairie dogs nor on associated avian communities. Little effect was seen on the vegetation communities aside from an increase of forbs on prairie dog colonies following treatment. In chapter 2, we used game cameras and an occupancy modeling approach to explore the role of prairie dog presence and spatial aspects of colonies on five ungulate species: pronghorn (Antilocapra americana), elk (Cervus canadensis), white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemonious), and bison (Bison bison). Most ungulate species showed a positive association with prairie dog colonies but also varied use with season and amount of precipitation – likely due to the increase in higher quality forage. This research fills the gap for a necessary case study managers can use to reference when making decisions regarding prairie dogs and it represents the first multi-site and multi-season study of the relationship between black-tailed prairie dogs and native ungulates, providing much-needed insight on these ecological relationships at a range-wide scale.Item Critical reflection and the open mind: Students’ transformative learning journey in an agricultural leadership multicultural course(2023-12) Cearley, Cari A.Changing demographics in the agricultural workforce have underscored the significance of possessing diversity consciousness, essential for thriving in both the agricultural sector and a diverse, culturally evolving society. The purpose of this study was to explore the transformative learning experience of students completing an agricultural leadership diversity course, adopting a qualitative research design to assess the level of transformative learning experienced by students completing the course. Phenomenological study (Moustakas, 1994) served as the chosen research methodology, offering a deeper understanding of the essence of students' lived experiences. Meanwhile, qualitative theoretical coding analysis facilitated an exploration of the extent of transformative learning encountered by students throughout the course. Chi-squared analysis provided quantitative measures of association for categorical variables, with the Phi correlation coefficient indicating the effect size of these associations. This research was grounded in Mezirow's Transformative Learning Theory (1991, 2000), which posits that the development of new worldviews occurs by filtering new knowledge through the lens of prior learning and experience. Boyer et al. (2006) operationalized Mezirow's theory through a theoretical coding rubric, employed in this study to interpret student responses from reflective essays assigned at the beginning and end of the course. The findings revealed that students are motivated by the need to succeed in a multicultural workforce, recognizing the importance of diversity consciousness in a globalized world, with a renewed understanding that embracing differences brings new perspectives while enhancing collaborative efforts. An association between gender and the stages of transformative learning moved was identified, suggesting that gender may play a role in how students engage with and progress through the phases of transformative learning. This study focused on the course as the phenomenon, investigating students' experiences with multicultural and diversity consciousness concepts. The results may inform higher education programs in designing effective multicultural and diversity consciousness educational programming, guiding students through cognitive dissonance, and ensuring they experience the various phases of transformative learning, leading to revised perspectives on the world. Future research should continue to explore the transformative learning process to better prepare students for a diverse global workforce.Item Using dietary management to evaluate enteric methane produced by ruminants(2023-12) Womack, AddieIn this thesis two experiments are described investigating enteric methane (CH₄). The first study investigated the effects of chitosan (CHIT), N-acetylglucosamine (GlcNAc), and glucosamine (GlcN) on enteric CH₄ emissions in an in vitro experiment using an automatic gas flow measurement system. Two diet types were measured, a total mixed ration (TMR, Experiment 1) and an all-forage diet of timothy hay (TIM, Experiment 2). Addition of CHIT or chitosan derivatives had no effect (P ≥ 0.11) on any gas or CH₄ production estimates with the either the TMR or TIM diet, including asymptote, passage rate, lag time prior to gas production, hours to 90% of asymptote, CH4 emissions (g/kg of digestible OM) or estimated total CH₄ emissions (g/d). Our results may be due to a low inclusion rate of chitosan, compared to previous research. The second study utilized twelve Charolais steers (BW=222 ± 10 kg) in a 73-d feeding trial. The objective was to determine if CH₄ and CO₂ emissions, and O₂ consumption measured using an automated head chamber system. (AHCS) can be used as biomarkers to estimate energy intake in growing beef cattle fed a high concentrate diet when integrated with backward dietary energy partitioning calculations. Steers were randomly assigned to 1 of 3 treatments according to DMI as multiples of maintenance energy requirements, which were 1.1× (1.1M) 1.4× (1.4M), and 1.8× (1.8M) estimated NEm requirements, respectively. Measured gross energy (GE), digestible energy (DE), and metabolizable energy (ME) intake levels increased with the observed increases in energy retention and heat production. The predicted values for GE, DE, and ME intake rates likewise increased with increasing DMI. Comparison of measured and predicted GE, DE, and ME intake rates agreed closely analyzed by a Pearson correlation and Lin's correlation coefficient with a high degree of precision and accuracy (R2 = 0.99). This experiment shows that together with multiple short-term breath measurements from an AHCS, BW, and an estimate of average daily gain, GE, DE, and ME intakes by cattle consuming a high concentrate diet can be predicted but will be slightly underestimated.