8413 research outputs found
Sort by
Top Down Thermodynamics: Entropy, Form, and the Thermal Turbine
No full textThis monograph addresses a persistent conceptual fracture in thermodynamics and statistical mechanics: the gap between what entropy demonstrably does in real physical systems and how it is commonly interpreted. In particular, it shows how decades of experimental and theoretical work on muscle contraction forced a re examination of entropy, causation, and irreversibility - leading not to a rejection of thermodynamics, but to a return from Clausius to Carnot, now equipped with Boltzmann's mathematics. The central claim is simple but disruptive: irreversible function is governed by macroscopic combinatorial structure, not microscopic disorder. Entropy is not an epiphenomenon of molecules; it is a macroscopic physical body that stores and releases energy. One form of stored energy is mechanical. A second form is thermally sourced and is referred to here as caloric potential. What follows is not speculative philosophy. It is a synthesis grounded in combinatorics, statistical mechanics, and experimental muscle physiology
Quantifying Ungulate–Rangeland Interactions: From Monitoring Free-Roaming Horse Condition to Vegetation Response Following Herbivore Exclusion
No full textReliable assessment of herbivore condition and vegetation response is essential for understanding grazing impacts across arid rangelands. This thesis integrates two complementary studies that address these challenges at different scales. The first develops and validates a quantitative framework for calibrating free-roaming horse body-condition scores from camera-trap imagery, comparing observer and veterinarian assessments to correct qualitative bias. The second analyzes a seventeen-year record of herbivory removal in a winterfat-dominated community in southeast Oregon, modeling long-term vegetation and soil responses to exclusion of ungulates and jackrabbits. Bayesian mixed-effects models reveal that ungulate exclusion increased winterfat, cyanobacteria, lichen, moss, and annual cover while decreasing soil compaction. Rabbit exclusion further increased winterfat and annual forb cover while decreasing annual graminoid cover, and showing diverging results in soil compaction. Together, these studies advance rangeland monitoring by combining methodological rigor with long-term ecological inference, offering practical tools for managing herbivore–vegetation interactions across western landscapes
Development and Catalytic Activity of Half-Sandwich Ruthenium(II) Complexes Featuring Derivatives of PTA (1,3,5-triaza-7-phosphaadamantane)
No full textTwo new upper-rim enamine derivatives of 1,3,5-triaza-7-phosphaadamantane (PTA, an air-stableand water-soluble phosphine ligand), PTA=C(p-C6H4
tBu)NH2 and PTA=C(p-C6H4Ph)NH2, were
synthesized by the addition of the corresponding nitriles across the C–Li bond of 1,3,5-triaza-7-
phosphaadamantan-6-yllithium (PTA–Li). Like the parent PTA, these new ligands exhibit excellent
resistance to P-oxidation by atmospheric O2. However, the hydrocarbon groups render them
completely insoluble in water.
A range of cyclopentadienylruthenium(II) complexes containing these ligands and other enamines
made in our group have been synthesized by treatment of [CpRuCl(PPh3)2] with the ligands in
hot toluene under anaerobic conditions. The bright yellow powders that precipitated during these
reactions were analyzed by 31P NMR spectroscopy and found to be the monodentate, mixed-
phosphine complexes [CpRuCl{κ1-PTA=C(Ar)NH2}(PPh3)] rather than the expected bidentate
species [CpRuCl{κ2-PTA–C(Ar)=NH}]. The attempted abstraction of Cl– from the monodentate
complexes with TlPF6 did not induce chelation.
The PTA–enamine complexes [CpRuCl{κ1-PTA=C(Ar)NH2}(PPh3)] were tested as catalysts
for the atom-transfer radical addition of CCl4 to styrene in deuterated toluene, deuterated methanol,
and deuterated acetonitrile. The insolubility of the catalysts in toluene made them ineffective in
that solvent. For methanol and acetonitrile, wherein thecatalysts are slightly soluble at the reaction
temperature of 60◦C, percent conversions (styrene, 24 h) of 50–78% and yields of 4.0–11.5% were
found. Turnover frequencies ranged from 0.17 to 0.48 h−1 at 1 mol% catalyst loading.
Separately, a range of areneruthenium(II) complexes of water-soluble PTA–pyridyl ligands PTA–CH(2-py)OH and PTA–CH(3-py)OH were tested as catalysts for the aqueous-phase aerobic
hydration of benzonitrile. Percent conversions (7 h) ranged from 5% to 90% and turnover frequencies
from 0.2 to 2.6 h−1 at 5 mol% catalyst loading. The best-performing catalyst containing each ligand
was tested against a wider range of nitriles; water-soluble, electron-rich nitriles were found to be the
best substrates
Integration of Lecture and Laboratory with Implementation of Active Learning Techniques in an Undergraduate Microbiology Course
No full textThis quantitative dissertation explores the impact of an integrated, active-learning instructional design in an undergraduate microbiology course at a community college in Northern Nevada. Most traditional instructional models in science separate lecture and laboratory components; this results in a disjointed learning experience and limits opportunities for students to apply what they learn in meaningful, collaborative ways. To address these limitations, the redesigned course utilized Bybee’s 5E instructional model, merging lecture and lab into a single, cohesive, student-centered environment that emphasized inquiry, reflection, and peer interaction.A quasi-quantitative research design with a control group was used for this study. The experimental group combined lecture and lab components and was taught using active learning strategies to engage students. The control group followed the traditional class format, where lecture and lab were taught separately and traditional didactic lecture methods were used. The research questions for this study included comparisons of the two teaching methods between the experimental and control groups using student exam scores and final grades. Within the experimental group, pre- and post-course student survey data were analyzed to compare student course satisfaction and student self-efficacy. Additionally, the study examined the relationship between these survey measures on exam averages and final course grades in the experimental group.
Grounded in Vygotsky’s (1978) theory of social constructivism, this study analyzed student data collected over five semesters. Quantitative data included exam scores and final grades from students in both traditional and active-learning course sections. Survey responses on course satisfaction and self-efficacy from students enrolled in the modified version of the course were utilized. This study aimed to evaluate differences in students’ academic performance, their self-reported satisfaction with the course, and self-efficacy.
The results demonstrated statistically significant improvements in student outcomes within the active-learning (experimental) group. These students achieved higher exam averages and final grades compared to those in the traditional sections. Survey data showed that students who self-identified as experiencing test anxiety preferred this modified format. The findings suggest that this integrated, inquiry-based course design created a more supportive and engaging learning environment, resulting in improved academic outcomes. This model could be especially beneficial for first-generation and underrepresented students in STEM fields.
This study contributes to the growing body of research supporting active learning and integrated course design within STEM education. The findings emphasize the importance of establishing inclusive and interactive classroom environments that enhance student engagement, deepen comprehension, and promote more equitable academic outcomes.
Keywords: active learning, 5E instructional model, microbiology education, integrated lab-lecture, social constructivism, student confidence, STEM equit
Direct Ion-Temperature Measurements Using High-Resolution Inelastic X-ray Scattering
No full textTemperature in high-energy-density (HED) materials has been a long-standing problem. Direct temperature measurements are challenging because HED samples are often opaque and have extremely short lifetimes. Historically, ion temperature has been inferred from structural measurements that serve only as proxies. This approach becomes especially problematic when studying the evolution of highly nonequilibrium states generated by short-pulse laser–matter interactions. In such states, electrons can reach multi-eV temperatures while the lattice remains essentially unchanged. Understanding the dynamics of non-equilibrium HED systems is critical for laboratory astrophysics, materials science, and inertial fusion energy research. A reliance on inferred ion temperatures has led to disagreements across many thermodynamic processes. For example, within the field of electron–ion equilibration, indirect temperature determination has produced more than an order-of-magnitude variation in predicted equilibration rates. Likewise, experiments investigating interatomic bond strength have reached conflicting conclusions due to uncertainties in inferred ion temperatures. Direct, model-independent temperature measurements are needed to resolve these discrepancies. This dissertation presents the development of a high-resolution inelastic-scattering platform capable of directly measuring ion temperature in HED matter. Designed for free-electron laser facilities, the platform uses a backscattering geometry to measure the ion velocity distribution. When the distribution follows Maxwell–Boltzmann statistics, the temperature can be extracted through standard Doppler-broadening relationships. These truly model-independent lattice-temperature measurements enable unambiguous determination of thermodynamic behavior in metallic samples under extreme conditions. Using this platform, we performed a series of experiments measuring the temporal evolution of ion temperature in laser-irradiated metallic samples. Gold temperature measurements were obtained at the LINAC Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory. Analysis of the resulting temperature profiles provides insight into the thermal properties of gold in a highly nonequilibrium regime. The measurements offer conclusive evidence of extreme superheating—ion temperatures far exceeding the melt point while the material maintains a crystalline structure. The full temporal profiles also allow us to study electron–ion equilibration dynamics directly, addressing the long-standing order-of-magnitude discrepancies in published equilibration rates. Furthermore, by combining the temperature measurements with structural information from X-ray diffraction, we observe changes in interatomic bond strength—a topic of significant debate over the past several decades. The final chapter discusses extending this platform to laser-shock experiments. A model-independent method for determining the temperature behind the shock front is essential for accurately constraining equation-of-state measurements
Can Adaptive Management Increase Pinyon-Juniper Woodland Resilience to Drought? Canopy Dieback and Soil Water in Semi-Arid Woodlands
No full textAccelerated drought-induced tree mortality, driven by increasing aridity and rising temperatures, greatly threatens ecosystem resilience and function in pinyon-juniper woodlands. As reduced snowpack and increased evapotranspiration lead to drier soils in these already water-limited environments, understanding the role of woodland stand structure and density in mediating tree response to drought events becomes crucial. The influence of stand density on tree health is complex. Evidence suggests both density-dependent and density-independent processes occur together in ways that vary with environmental and site characteristics. Silvicultural thinning, which reduces tree basal area or density, is commonly believed to increase drought resilience of dry forests and woodlands by reducing competition for essential resources such as soil water. However, while thinning may alleviate water stress by decreasing plant water use and transpiration, the complex balance of plant water uptake, canopy interception, and soil surface evaporation means that potential impacts on soil moisture and temperature remain inadequately understood.This research addresses these critical gaps through two complementary studies conducted within the same pinyon-juniper woodland field site in southwestern Colorado, United States. The first chapter, utilizing pre-treatment observational data, examines the relationship between stand structure, environmental factors, and canopy dieback to evaluate how structural complexity and density influence woodland health. The second chapter evaluates the short-term ecohydrological responses to various experimental thinning treatments one year post-implementation, assessing treatment effects on soil moisture and surface temperature under both uniform and heterogeneous thinning prescriptions.
Results from the pre-treatment observational study revealed consistent positive density-dependent dieback across multiple spatial scales, suggesting that tree mortality patterns are intrinsically linked to stand density and environmental variability. These findings suggest the potential value of silvicultural practices that reduce stand density to enhance drought resilience. Building on this understanding, the experimental study demonstrated that reduced basal area from thinning increased soil moisture at 23 cm depth across both snowmelt-drawdown and monsoonal seasons. In contrast, soil moisture at 3 cm exhibited minimal treatment effects, likely due to the countering effects of evaporation, interception, and transpiration. Additionally, thinning expanded diurnal soil temperature ranges by reducing canopy thermal buffering.
Collectively, these studies highlight that an understanding of stand structure and ecohydrological processes is crucial for developing effective adaptive management strategies in pinyon-juniper woodlands. Our findings offer valuable insights on soil water availability, woodland health, and the long-term resilience of these semi-arid ecosystems
Long-Term Patterns of Peat Accumulation and Organic Matter Decomposition in Costa Rican Peatlands
No full textTropical peatlands, compared to their boreal counterparts, are vastly understudied despite these ecosystems acting as a significant terrestrial carbon (C) sink, sequestering 100-300 gigatons of carbon. Within tropical ecosystems, Central and South American peatlands are even more overlooked, with most research stemming from Southeast Asia and new emerging data from the Congo Basin. Likewise, although modeling and global predictive studies have been performed on the future of tropical peatland carbon dynamics, there is an alarming lack of field-based studies, again particularly affecting Latin America. For instance, very little is known about the characteristics of peat soils and their carbon stocks. We also lack a mechanistic understanding of why peat develops in certain areas but not in others, both in terms of peat initiation conditions as well as the factors that enable peat to subsist over centuries and millennia. In the face of rapid environmental land-use changes, the carbon-sink capacity of peatlands could be weakened, or even reversed, which would lead to further climate warming through the release of greenhouse gases into the atmosphere. Here, I present extensive, high-resolution laboratory datasets from peat cores that were gathered from four distinct peatland types found within Costa Rica (high-elevation, riverine, coastal palm swamp, and mangrove). A multi-proxy palaeoecological approach was employed to shed light on the successional pathways and past conditions that have allowed these peatlands to form, as well as provide a first estimate of their carbon stock. The performed analyses include radiocarbon dating, loss-on-ignition, carbon and nitrogen content, and plant macrofossils. Fourier transform infrared spectroscopy (FTIR) was additionally utilized to characterize changes in organic matter quality across sites and over time, and the role of recalcitrant material in tropical peat accumulation. This research provides the basis for understanding long-term carbon accumulation within Caribbean tropical peatlands and is critical to advancing knowledge of the structure of tropical peatland ecosystems
From Boussinesq Equation to Porous Medium Equation: Analytical Extensions and Structural Reformulations in Nonlinear Groundwater Flow
No full textThis dissertation develops analytical and semi-analytical methods for the porous medium equation (PME), with emphasis on recharge problems, boundary discontinuities, and extensions of classical groundwater flow models. Beginning with the cylindrical formulation of recharge into an initially dry aquifer, a semi-analytical solution is constructed that clarifies the roles of geometry, initial conditions, and nonlinear diffusion, extending the injection framework of Telyakovskiy et al. (2016) from the Boussinesq setting to the full PME.
The analysis then addresses one-dimensional boundary problems, where step discontinuities are resolved through families of power-law and exponential–polynomial solutions, reformulating and extending the closure approach of Tolikas, Sidiropoulos, and Tzimopoulos (1984) to the PME context.
A further contribution develops a quadratic non-selfsimilar solution as an extension of the framework introduced by Parlange et al. (2000), revealing new analytic solutions to regimes of drainage and infiltration. In each case, the PME-based formulations not only yield new solution forms and boundary treatments but also recover the earlier Barenblatt-based results when the corresponding parameter limits are applied. This ensures that the present work complements and enhances prior models, embedding them within a broader and more flexible analytical structure.
Taken together, these developments broaden the analytical toolkit for nonlinear diffusion in porous media, generalizing existing results across wider parameter ranges and geometries while recasting governing structures to sharpen tractability and physical interpretation. The outcome is a more comprehensive mathematical framework for porous medium flows, bridging classical groundwater theory with contemporary nonlinear diffusion analysis
Characterization of interstitial cells and their role as regulators of motility and neural pathways in the esophageal region
No full textThe esophagus transports ingested contents from the mouth to the stomach where they pass through the high-pressure zone of the gastroesophageal junction (GEJ). Within the GEJ the lower esophageal sphincter (LES) generates tone to increase luminal pressure, meanwhile the distal esophagus generates phasic contractions which may also contribute to high-pressure. During swallowing the GEJ must transiently relax before contracting again to prevent reflux. This entire process of swallowing requires integrated coordination of the activity of smooth muscle cells (SMCs), striated muscle, interstitial cells and nerve fibers. This dissertation investigates the cellular and molecular mechanisms contributing to control of motility in the esophageal region, focusing on the role of intramuscular interstitial cells of Cajal (ICC-IM) and platelet-derived growth factor receptor alpha positive (PDGFRα⁺) cells. Using mouse and non-human primate (Cynomolgus Macaque; monkey) tissue, we demonstrated that the distal esophagus of both species contains a mixture of striated and smooth muscle. This conserved architecture enhances the translational relevance of studies performed in mouse models. We identified dual roles for ICC-IM in regulating phasic contractility in the distal esophagus and tone in the LES via a Ca2+ activated Cl- channel, ANO1. Notably, we described a subpopulation of ICC-IM with a unique Ca2+ signaling behavior that appears to underlie rhythmicity in the distal esophagus; this population is absent in the tone generating LES. We also demonstrate that ICC-IM mediate cholinergic and nitrergic neurotransmission directly by altering intracellular Ca2+ signaling, thereby altering ANO1 activity. We show that PDGFRα+ cells express purinergic receptors and small conductance Ca2+ activated K+ channels (SK3) despite the apparent lack of a functional purinergic neural input. We demonstrate that these purinergic receptors can however be activated pharmacologically suggesting that this pathway may become active in disease whereby there is an increase in LES relaxation. Interstitial cells were often closely associated with nerve fibers throughout the entire esophagus and LES and may regulate neurotransmission in proximal regions in a manner similar to what we show for the LES. Together, the data presented in this dissertation outlines a multifaceted role for interstitial cells in coordinating esophageal motility and neurotransmission. Alterations in these pathways may contribute to motility disorders such as achalasia and gastroesophageal reflux disease, and the identification of ion channel signaling mechanisms (e.g., ANO1) highlights potential therapeutic targets for the development of less invasive, pharmacological treatments for esophageal disease
How Habitat and Observer Access Bias affects eBird Data Coverage in Nevada
No full textOutdoor recreation is popular among Nevada residents and visitors to the state.Bird watching is one such popular activity. Many bird watchers (“birders”) use eBird,
a citizen science project, to track and share their sightings, as well as to plan excursions.
eBird is a global project, run by the Cornell Lab of Ornithology, and is more than just
an online platform for tracking bird observations: The data are also made available
to researchers who use them to perform broad scale studies that would otherwise be
practically impossible to conduct without such a large group of volunteers collecting
data. In this study, using citizen science data from eBird, I seek to quantify discrepancies
in coverage among different habitat types across the state, and address possible sources
of coverage bias, with the goals of (1) helping inform eBird participants who might
want to help fill these coverage gaps in Nevada, and (2) identifying what factors might
be driving these coverage discrepancies. This could lead to better coverage, providing a
more complete data set for birders, scientists, and resource managers. To achieve this,
I first describe the coverage discrepancies across different regions and habitats (EPA
ecoregions) across seasons. Second, I demonstrate differences in several environmental
and access related features between different eBird location types and a set of randomly
generated locations. Finally, I implement spatially explicit classification models to
assess which environmental features are most associated with where eBird users tend
to go birding. These results suggest that ecoregions with major metropolitan areas are
highly over-represented when compared to less populated zones, and that birders favor
areas close to roads, cities, and water that are greener when choosing where to watch
birds