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Grain Boundary Pinning Approach for Manufacturing High-Strength Nanocrystalline Aluminum Alloys
No full textNanostructuring is a commonly employed method to improve the mechanical properties of metals and alloys, but its usage is limited due to the instability of nanocrystalline (NC) materials. To address this challenge, the current study employs doping techniques to obtain a stable NC structure. In the present work, commercially pure aluminum (Al) powders were milled at cryogenic temperatures (a) without magnesium (Mg) and (b) with 5 wt.% of Mg powders for different durations. The unmilled and cryomilled powders were characterized to determine the changes in particle morphology, elemental composition, and crystallite size. The results showed changes in the morphology of powders and a reduction in crystallite size with the increase in cryomilling duration. Thereafter, the bulk samples using cryomilled powders were manufactured using two different methods (a) spark plasma sintering and (b) cold spray processes. The mechanical properties of the bulk samples were assessed by conducting Vickers microhardness, tensile, and fatigue tests. The tests were performed both at the University's laboratory and at an independent testing facility. The test results from both testing sources showed a significant improvement in mechanical properties for the Al-Mg bulk samples as compared to pure Al. The mechanism for the enhancement in mechanical properties as a result of crystallite size reduction and grain boundary strengthening by the addition of Mg dopant is discussed. The current study also examined the total energy consumption and manufacturing costs involved in the production process. The cost analysis revealed that manufacturing a kilogram of nanocrystalline aluminum alloy costs less than $90 inclusive of the energy costs
Spatial Learning and Memory, Cognitive Flexibility, and Rule-Learning in Food-Caching Mountain Chickadees (Poecile gambeli) Across an Elevational Gradient
Get PDFHow and why individuals differ in their cognitive abilities within and across species remain important and unresolved questions in behavioral and evolutionary ecology. Cognitive traits are involved in many critical behaviors, enabling individuals to use past experiences to inform future decisions or to reduce unpredictability in the environment. But most cognitive experiments have been conducted in laboratory conditions without a strong ecological or evolutionary context, and so do not address to what extent environmental factors influence cognitive traits and associated behaviors. Moreover, although many behaviors likely involve multiple cognitive traits, it is still unclear to what extent there may be tradeoffs between cognitive traits or between higher-order executive control functions. Executive control functions are associated with goal-oriented behaviors and may be highly advantageous, as they are involved with rule learning and using abstract, relational concepts; however, they remain highly controversial in nonhuman animals and have rarely been studied outside of a laboratory context. In this dissertation, I designed and conducted several spatial cognitive tasks to investigate individual variation in spatial learning and memory, cognitive flexibility, and rule-learning in wild, food-caching mountain chickadees ( Poecile gambeli ). I found that chickadees updated information about their environments more frequently in harsher, less predictable winter environments than in milder, more predictable ones. I showed that chickadees were capable of learning and using multiple different rules within a foraging context, and I demonstrated some of the first evidence for abstract-rule learning in nonhuman animals in the wild. Moreover, proactive interference associated with learned associations from two cognitive tasks appeared to influence subsequent foraging decisions and varied with individual cognitive ability on two spatial tasks. Altogether, these results provide new insight into the cognitive ecology of mountain chickadees and the cognitive traits that may play a role in shaping information-related behaviors
Stationarity Perception and Virtual Reality Sickness
No full textStationarity perception involves accurately perceiving a stable visual environment, a critical skill for self-motion. This perception relies on evaluating signals from eye and head movements for congruence. Through a series of experiments, we systematically manipulated the consistency between visual and vestibular signals to determine the visual range of gains allowing for the perception of a stable environment. Participants, wearing head-mounted displays, moved their heads (or were moved passively via a rotating chair) and indicated if the visual feedback felt too slow or fast. Analyzing these responses revealed the most compatible visual gain for perceiving stability (accuracy) and how sensitive this perception was to changes in visual gain (precision). Across studies, we varied conditions involving neck motor signals during active and passive movements, the visual stimulus's spatial frequency and location on the retina, and fixation behavior (whether the fixation point was scene- or head-fixed). We also tested this stationarity perception and VR sickness during repetitions of the task over three days and across rotational axes. In our first study, we found that perception was most accurate and precise during scene-fixed fixation and during active motion. In the second study, spatial frequency and stimulus retinal location affected stationarity perception precision, but not accuracy. Additionally, VR sickness was measured using the Simulator Sickness Questionnaire (SSQ) and found associations with perceptual performance. Reduced accuracy was linked to higher nausea scores, while decreased precision aligned with higher oculomotor discomfort, disorientation, and total scores. In our final study, we found improvements to measurements of precision of stationarity perception. We also found some associations between stationarity perception and VR sickness, but only during yaw rotations. These studies have been critical for characterization of the phenomenon of stationarity perception as well as its relationship to VR sickness. These results may guide future research into self-motion and VR sickness mitigation
"Working with Students from Displaced Backgrounds" Teacher Training Workshop
Get PDFAs the world faces multiple crises, an increasing number of people are being forced to leave their homes�"some of whom end up in the US. Compounding the challenges associated with displacement, many of these individuals arrive without much background, if any, in English language. My applied thesis project aims to address this issue by integrating sociological and social justice theories with educational practices of teaching English to speakers of other languages (TESOL). The project focuses on designing, conducting, and improving a professional development workshop for TESOL teachers. The workshop covers the topics of global displacement, cultural awareness, and the oppression of migrant populations in the US. Pre- and post-workshop surveys will be employed in the study. Conducting a pre and post-survey serves a twofold purpose: (1) to collect and analyze data on what the participants already know about the topic, how their knowledge changed after participating in the workshop, and what they plan to apply to their teaching; and (2) to solicit feedback on the workshop itself in order to improve it. The ultimate goal is to develop a research-based workshop for TESOL teachers throughout the US. that would inform said teachers of the unique challenges faced by refugees and promote best practices in the classroom
Elucidation and Characterization of Glycosyltransferases Implicated in Pectic Polysaccharide Biosynthesis in Arabidopsis thaliana
Get PDFThe cell wall is a complex extracellular matrix composed of cellulose, hemicellulose, and pectic polysaccharides that confers multiple functions to plant cells and the plant as an organism. Glycosyltransferases (GTs) are enzymes that catalyze the transfer of a sugar molecule from an activated sugar-nucleotide donor to an acceptor substrate, and these enzymes are responsible for cell wall polysaccharide synthesis. Across plant and metazoan organisms, mutant phenotypes for many GTs result in developmental defects, some of which can be embryonic lethal. This work first describes the expansion upon our laboratory's previous findings that mutation of Arabidopsis thaliana OFUCOSYLTRANSFERASE1 (OFT1) gene resulted in decreased pollen tube penetration through the stigma�"style interface. Here, we demonstrate that second site mutations of Arabidopsis GALACTURONOSYLTRANSFERASE14 (GAUT14) and GALACTURONOSYLTRANSFERASE-LIKE4 (GATL4) effectively suppress the phenotype of oft1 mutants, partially restoring silique length, seed set, pollen transmission, and pollen tube penetration deficiencies in navigating the female reproductive tract. Following this story, this work describes the function of Arabidopsis FRIABLE1 (FRB1; RRT8) as a Rhamnogalacutronan-I: Rhamnosyltransferase (RRT). FRB1 displays robust RRT activity compared to genetically related enzymes, and protein structure-function investigations described here shed light on the catalytic function of RRTs. Broadly, this dissertation elaborates on genetic interactions occurring between GTs that are implicated in cell-cell interactions during pollen-pistil interactions and defines the function of a previously understudied GT with kinetic parameter characterization and identification of critical residues for catalysis. This work provides information for future studies and doctoral projects revolving around cell wall biosynthesis, plant cell signaling, and amino acid conservation among GTs that are critical for catalysis
Integrating Sub-Centimeter Resolution Photogrammetry with a Surface Roughness Correction Factor Applied to PI-SWERL Measurements
No full textThis thesis consists of two chapters that summarize the development and application of a new technique used to quantify surface roughness for dust emission measurements. Chapter 1 begins with a literature review that documents the significance of research pertaining to dust emission. It then presents a summary of the development of the Portable In-situ Wind Erosion Laboratory (i.e., PI-SWERL) along with existing limitations for adjusting dust emission measurements for microtopographic surface roughness. A new method for characterizing the surface roughness correction factor, alpha (α), is introduced to address these limitations. This thesis describes the development of new reference material to assign α and is presented as a new lookup table that relates landform class and surface characteristics. The second chapter presents and discusses results from a case study application of the new approach from Chapter 1. Surface roughness correction factors were computed for landforms within White Sands National Park to study the effects of surface roughness determinations using the new semi-quantitative lookup table approach on resulting dust emission estimates. These results were compared with published literature values using older methodology. As such, the results from Chapter 2 were evaluated to assess the overall uncertainties involved with current techniques. Resulting dust flux measurements from the original dataset were compared with an adjusted version of that dataset, and a statistical analysis was conducted. The statistical analysis indicated that, of each landform evaluated, surface roughness was overestimated only for the sand sheets. As a result, dust flux was significantly underestimated in the previous study compared with this study. This thesis then examines how the recalculated fluxes project into annual dust flux budges, with estimates of annual average fluxes for sand sheets at White Sands increasing from ~277 tons/km2/year to ~329 tons/km2/year based solely on the methodology of assigning α. The new methodology documented in this thesis will help improve reproducibility of PI-SWERL measurements across studies from different researchers. Findings from this thesis will also improve the quality of in-situ field data collected with PI-SWERL that is used to validate larger global or regional scale models
A Case Study to Explore Spirituality Among Service-learning Instructors at a Land Grant University
Get PDFThe purpose of this study is to explore why academic faculty opt to incorporate service-learning into their coursework for students and how individual spirituality at work contributes to SL design in experiences. A qualitative single case study design was used. Publicly available documents, syllabi, and semi-structured interviews with 20 previous and current service-learning instructors were the sources of data for this case. Among the participants, 16 identified as spiritual and eight shared that spirituality influenced their decision to use service-learning. Research Question One asked how spirituality contributed to faculty decision to pursue SL designation. Overall, while instructors identify as spiritual in motivation, they may not differ greatly on the choice to designate their course. Some cited spiritual motivation while others shared that the rigorous academic framework lends itself to effective teaching and course design. Research Question Two asked how spirituality contributed to course design and results reflect that creating SL curriculum aligns with general course design. Those who cited spiritual motivations included the following spiritual aspects infused in course design: practicality, reciprocity, empathy/compassion, helping people, and social justice. Research Question Three asked how spiritual faculty navigate their spirituality in their role in academia. Spiritual faculty reported navigation of academia as categorized into three types of values alignment: alignment, misalignment, and hacking alignment. Instructors shared methods of negative and positive coping regarding misalignment. Hacking alignment was for those who felt misaligned in the academy, but found ways to align their spirituality with their work. A discussion of the above-mentioned findings, implications for practice and recommendations for future research are provided
The Causes and Consequences of Complex Behavioral Trait Variation in a Resident Montane Bird
Get PDFThe causes and consequences of complex trait variation are of broad interest in the field of behavioral ecology. In the wild, animals experience wide ranging environmental conditions, and understanding the impact of this heterogeneity in shaping behavioral traits, such as cognition, is critical to understanding their evolution. Though it is thought that environmental conditions contribute to large inter- and intra-species variation in cognitive abilities, the mechanisms generating this variation remain poorly understood. Past laboratory-based work has shown that energetically expensive cognitive traits are impacted by developmental perturbations such as non-optimal developmental conditions (e.g. poor parental care, low-quality nest environment, etc.), but whether these same patterns are exhibited in natural populations is relatively unstudied. This dissertation provides novel insights into the mechanisms shaping complex behavioral trait variation in wild systems focusing on two behavioral traits, spatial cognitive abilities and nest building, in free-living mountain chickadees ( Poecile gambeli ). Chapter 1 describes the role of directional natural selection acting on spatial cognitive ability using a cohort comparison approach in a wild population. This study showed that spatial cognitive ability does not change within individuals across years, that adult birds on average performed better than first-year birds, and that members of a first-year cohort that performed worse on a spatial cognitive task were less likely to survive than those with better performance. This is some of the first evidence of natural selection acting on a cognitive trait in the wild. Chapter 2 investigates causes and consequences of variation in nest size in chickadees at different montane elevations with different climatic conditions. This study showed a large degree of temperature variation across all nestling developmental periods and between elevations, but this variation was unrelated to nest size or reproductive output in chickadees. This result contrasts results from studies in other populations of cavity-nesting birds that appear to construct nests corresponding to local environmental conditions. However, I found that female chickadees build highly repeatable sized nests across years. High repeatability in behavioral traits implies a heritable component, suggesting that female nest size is controlled by an innate mechanism. Chapter 3 considers variation in nestling immune response, ectoparasite load, and nest composition to determine how these developmental conditions shape behavioral trait variation. Ectoparasites are known to have fitness consequences for their hosts, but there is mixed evidence of how widespread and impactful these effects are on the traits of developing avian nestlings. I found that there was no relationship between greater ectoparasite infestation in the nest and offspring mass or immune response, seeming to indicate that this aspect of nestlings' developmental environment may not drive future behavioral trait variation. However, I did find that nest composition�"including overall size (i.e., mass), amount of plant materials, and amount of animal materials (i.e., animal hair)�"was highly repeatable within individual females, strengthening the evidence that individual variation in nest building behavior is heritable. Identifying potential post-fledging consequences related to parasite load remains understudied. Chapter 4 builds upon the work of my earlier chapters by investigating the underlying mechanisms that result in observed chickadee nest repeatability. I found evidence that apparent non-functional trait variation may be related to variation that is under selection through potential shared physiological mechanisms. In this study, I found that food-caching propensity and nest building propensity are not only highly repeatable behaviors within individual female chickadees but also highly correlated. This suggests that food caching, a trait under selection that has a strong underlying drive, may be directly affecting an unrelated behavioral trait, nest building, through a shared mechanism, resulting in a potential behavioral syndrome. Lastly, chapter 5 presents data testing whether there is a relationship between the physiological burden during offspring development and spatial cognitive abilities, which could explain some of the existing variation in cognitive abilities in wild food-caching mountain chickadees. I used ptilochronology (feather growth rates reflecting nutritional intake) and amount of corticosterone (a hormone associated with broad metabolic processes including stress responses) in feathers (Cortf) of juvenile chickadees to estimate the variation in developmental condition. I found that developmental variation had a limited effect on spatial cognitive abilities, suggesting potential compensatory mechanisms that buffer these specialized cognitive abilities critical for survival in food-caching chickadees from harmful ontological perturbations
2025 Nevada Middle School Youth Risk Behavior Survey
No full textNevada Center for Surveys, Evaluation, and Statistics (CSES) survey about health behavior. It has been developed for Nevada middle school students to tell us what they do that may affect their health. The information they give will be used to improve health education for young people. If you have any questions or comments please contact https://www.unr.edu/public-health/research-activities/nevada-youth-risk-behavior-surve
Understanding post-wildfire debris-flow activity across climates: insights on initiation conditions and flow identification
Get PDFThe size, frequency, and geographic scope of severe wildfires are expanding in the western U.S. and globally, exposing an ever-larger population to fire-related hazards. Compared to unburned areas, recently burned steeplands have an increased likelihood of runoff-generated debris flows, which are triggered by heavy short-duration rainfall and pose hazards to downstream communities. As the geographic and climatic scope of severe wildfire expands, the degree to which the initiation conditions of these flows vary with local hydroclimate is unknown. This research aims to both investigate the relationship between postfire debris-flow initiation and climate at regional and local scales, and to develop tools for accurately identifying recent debris-flow events. I organize this research into three chapters. The first chapter presents a regional analysis of debris-flow initiation across the Western U.S. and use three independent methods to demonstrate that initiation thresholds vary systematically with local rainfall-intensity climatology. The second chapter takes advantage of this variation to develop and test a rainfall anomaly metric which delineates debris-flow locations that we mapped within individual burn perimeters. The third chapter develops and tests a quantitative flow-type diagnostic metric which accurately identifies the type of flow that occurred in a steep catchment, ensuring the reliability of future training datasets for predictive debris-flow models. Together, these chapters address existing knowledge gaps on how postfire debris-flow generation may inherently vary with local climate, how hydroclimate-based metrics may serve as an important predictors of debris-flow location and initiation conditions, and how debris-flow events can be accurately identified through quantitative methods. These findings mark a contribution to our understanding of postfire hydrologic hazards that is essential under modern fire regimes and will only increase in relevance as anthropogenic climate change continues to expose an ever-larger population to these unique hazards