Physical Sciences and Mathematics Commons^™

Understanding Waveguides In Resonance, Pieter Johannes Daniel Vandenberge

Dissertations and Theses

Several important classes of modern optical waveguides, including anti-resonant reflecting and photonic bandgap fibers, make use of geometries that guide energy in low refractive index material, a property that makes them of significant interest in numerous applications, notably including high-power delivery and guidance. These waveguides frequently exhibit resonance phenomena, in which their ability to propagate an input signal is sharply curtailed at particular operating frequencies. In this work we detail new advances in understanding these resonance effects and their implications for numerical modeling of these structures.

Part 1 focuses on the fields of slab waveguides, relatively simple structures for which …

Mmwave Rat Optimization: Mac Layer Initial Access Design And Transport Layer Integration, Suresh Srinivasan

Dissertations and Theses

MmWave Radio Access Technology (RAT) is a promising technology for wireless communication due its large bandwidth and is already being deployed in 5G cellular and emerging WiFi technologies. MmWave systems use highly directional beams with narrow beamwidths to overcome the high path loss associated with their frequency bands. A mmWave radio can be used either in a standalone mode (where all radios use the same technology) or simultaneously with other technologies such as LTE and low frequency WiFi in a communication mode commonly referred to as integrated mode. This thesis proposes two methods to optimize mmWave RAT performance in both …

How Are Oregon's Rural Indigenous Communities Overcoming Water Access Issues?, Tyren John Thompson

Dissertations and Theses

This study investigates how water insecurity affects Indigenous communities in Grand Ronde, Warm Springs, and Umatilla, Oregon, through loss of clean drinking water, access to culturally significant foods, and exposure to pollution. Each community offers innovative solutions drawing on their Indigenous knowledge to overcome water supply challenges. Communities with more resources are better equipped to cope with water insecurity and environmental degradation.

Tiny Drifters Amidst Global Change: Examining Environmental Drivers, Trophic Impacts, And Management Strategies Of Estuarine Plankton Communities In The Anthropocene, Taylor Nicole Dodrill

Dissertations and Theses

Plankton productivity supports estuarine food webs, and has been tied to the success of fisheries, macroinvertebrates, and cultured shellfish yields. Climate change and alterations to nutrient loads are thought to be influencing plankton assemblages, with toxin-producing harmful algal blooms (HABs) on the rise and nutritional quality of plankton declining globally. These shifts in plankton communities may contribute to low biomass yields and toxin-based closures of important fisheries. The objectives of this dissertation are to identify environmental drivers, trophic impacts, and management strategies to understand and respond to changing estuarine plankton communities. To address these objectives, I used a combination of …

Energy Auction With Non-Relational Persistence, Michael Ramez Howard

Dissertations and Theses

As the current landscape for electric vehicles changes, options for remote charging are expanding to keep up. In the United States alone, sales of electric vehicles grew 85% from 2020 until hitting 450,000 units by the end of 2021. While these growing sales are encouraging, commercial charging stations have a long way to go before they are as ubiquitous as gasoline stations are today. The peer-to-peer energy auction helps fill the gap in underserved areas by allowing private homeowners to share their charging facilities with other electric vehicle drivers. The auction framework wraps existing charging outlets with a Cloud-connected microcontroller. …

Forest Generating Functions Of Directed Graphs, Ewan Joaquin Kummel

Dissertations and Theses

A spanning forest polynomial is a multivariate generating function whose variables are indexed over both the vertex and edge sets of a given directed graph. In this thesis, we establish a general framework to study spanning forest polynomials, associating them with a generalized Laplacian matrix and studying its properties. We introduce a novel proof of the famous matrix-tree theorem and show how this extends to a parametric generalization of the all-minors matrix-forest theorem. As an application, we derive explicit formulas for the recently introduced class of directed threshold graphs.

We prove that multivariate forest polynomials are, in general, irreducible and …

Tidal Bed Stress Asymmetry And Sediment Transport In Estuaries, Austin Scott Hudson

Dissertations and Theses

Rivers and estuaries provide numerous ecological, economic, and cultural resources. The value of these resources is greatly influenced by sediment transport processes, which can be affected by human activities and climate variability. A key driver of sediment transport in tidal rivers and estuaries is tidal asymmetry of velocity and bed stress, which can manifest from both non-linear tidal interactions and linear interactions among astronomical tidal constituents.

In this study, an analytical framework is developed to examine and describe the dynamics of bed stress asymmetry in semidiurnal, diurnal, and mixed-tide estuaries (Chapter 1). While tidal velocity asymmetry has been previously analyzed, …

Cognitive Engagement During Group Learning Activities In Chemistry Courses: An Analysis Of Student Discourse, Safaa Youssef El-Mansy

Dissertations and Theses

As educators, our goal is to help our students be successful, but in order to accomplish this, we need to understand what factors contribute to student success. One factor, small-group active learning, has been correlated to improved academic outcomes; however, the magnitude of this improvement can vary across different courses, different types of group work, and even across courses that use the same group work structure. Therefore, it is important to understand what aspects of group work contribute to its effectiveness. The work presented in this dissertation investigated one specific aspect: students’ cognitive engagement. This was done by analyzing the …

Using Biometrics, Behavioral Observations, And Multiple Molecular Techniques To Assess The Impacts Of Changes In Temperature And Salinity On The Common Bay Mussel (Mytilus Trossulus), Casey Martin

Dissertations and Theses

The intertidal zone is a place of rapid and frequent change that is home to a variety of creatures who are essential to the integrity of the habitat. Mussels are robust sessile bivalves that anchor to the rocks of the intertidal. The prominent species on the Oregon Coast, the Common Bay Mussel (Mytilus trossulus), plays an essential role as a coastal food source, water column filter, and barrier to prevent erosion due to wave action. Mytilus trossulus withstands daily shifts in temperature, salinity, and tide, as well as seasonal changes. Global climate change due to excess carbon emissions …

Forest Fire Effects On Snow Storage And Melt Across Scales Of Forest Recovery In The Western Oregon Cascades, Megan Nicole Guinn

Dissertations and Theses

Snow is the largest component of water storage in the western United States, it serves as a key moisture source for forested ecosystems and is fundamentally linked to streamflow and nutrient cycling. Snow is vulnerable to climatic warming, and a key consequence of declining mountain snowpack is the escalation in wildfire frequency, extent, intensity, and duration across the seasonal snow zone. Fire modifies the spatial extent of snow in watersheds, reducing snow water storage and timing of melt across burned forests. Forested mountain ecosystems and water supplies are facing shifts in their structure, function, and succession. Previous research has focused …

Modeling Leaf-Level Transpiration: Exploring The Consequences Of Assumed Saturated Vapor Pressure In Leaves, Danlyn L. Brennan

Dissertations and Theses

Understanding the dynamics of water transport through leaf intercellular airspaces (IAS) and its impact on transpiration is crucial for accurate predictions of plant water use and ecosystem response to changing climates. This study investigates the implications of assuming undersaturation of water vapor in the IAS for transpiration predictions and explores potential modifications to standard modeling approaches.

A dynamic 1D soil-plant-atmosphere continuum using a stomatal optimization model (SPAC-SOT) framework was used to simulate the response of tree species, P. edulis, to prolonged drought and varying environmental conditions. Comparisons between two model assumptions (saturated vs. undersaturated IAS) reveal notable differences in …

Wasted Space, Ryan Martyn

Dissertations and Theses

This paper performs a spatial analysis of Portland, Oregon, with a focus on identifying and utilizing "wasted space," such as parking lots and vacant land, as strategic opportunities to enhance the completeness of the city. The planning concept of a "complete neighborhood" is defined as a locality that offers residents access to all essential aspects of daily life within a convenient walking distance. This notion encompasses elements, such as walkability, accessibility to essential services and amenities, sustainability, and equity. The objective of this study is to provide a more precise definition of the planning concept of a complete neighborhood and …

The Influence Of Polystyrene Microplastics On Juvenile Steelhead Trout (Oncorhynchus Mykiss), Kaitlyn Marie Baker

Dissertations and Theses

Mass production of plastic within the past decade has led to over 100 billion tons of plastics being added to the world’s oceans through rivers and effluent disposal and decomposition. For marine environments, the sudden and constant growth of microplastics (plastics 1 µm to 5 mm in diameter), is of particular concern to top-predatory fish such as steelhead trout (Oncorhynchus mykiss), who passively or actively uptake microplastics while consuming prey. Previous research has demonstrated clear detrimental impacts of microplastic accumulation in bivalves, seabirds, and zebrafish, including decreased diet, reproduction rates, and metabolism, as well as increased rates of …

Community Adaptations To Wildfire Risk In Central Oregon, Usa: An Empirical Study Of Inclusionary Practices In Collaborative Wildfire Risk Mitigation, Liam Resener

Dissertations and Theses

Adverse impacts of wildfire in Western North America have become increasingly present through the 21^st century, driven by landscape changes imposed by colonists in the 19^th and 20^th centuries. Community adaptations to wildfire will be necessary through the 21^st century to restore landscapes and protect the safety and livelihoods of people who live in at-risk areas. Wildfire risk extends across countless environmental and social systems, and individuals have competing ideas about what constitutes that risk and how to best adapt to it. As resources are being allocated to community adaptations, important questions emerge about the values …

Exploring Nonprofit Views On Water Management And Conservation Strategies, Jillian Marie Farley

Dissertations and Theses

Valuing water resources presents a multitude of methodological and theoretical challenges, including economics, biodiversity, and cultural significance. Information is not readily available on the individuals working every day on water resource management and how they navigate such a complex topic. This project is designed to help all parties better understand the opinions of individuals working for nonprofit organizations and Watershed Councils in the State of Oregon about current methods of water resource conservation. The results reflect respondents’ personal views on the process and practices of valuing water and are designed to prompt deeper discussions between the organizations, communities, and policymakers. …

Structure-From-Motion Derived Snow Cover In Burned Forests Of The Western Oregon Cascades, Siobhan Ciafone

Dissertations and Theses

Forest fire occurrence in the western US has increased rapidly since the 1980s, and most western US fires occur in the seasonal snow zone. Burned forests influence snow accumulation and melt patterns for years following fire, and understanding drivers of variability in snow cover across a burned landscape at the basin-scale is necessary for accurate hazard prediction and water resource forecasting. Basin-scale surveys of snowpack are possible with remote sensing, but accurate sensing methods such as Light Detection and Ranging (LiDAR) are often cost-prohibitive. In the last decade, structure-from-motion (SfM), an optical remote sensing technique, has emerged as an affordable …

Race And Income As Predictors Of Trust In Flood Mitigation Strategies, Wendy Nathaly Sangucho Loachamin

Dissertations and Theses

Trust plays a central role in coastal flooding management because the support or opposition to costly mitigation strategies depends, in part, on how much stakeholders trust in the effectiveness of these strategies. Despite the importance of trust in the approval of flood mitigation strategies, trust is rarely measured. Furthermore, Environmental Justice (EJ) studies have consistently shown that BIPOC (Black, Indigenous and People of Color) and low-income communities are more vulnerable to environmental hazards. Therefore, if these communities are more exposed to flooding, we hypothesize they will have less trust in flood mitigation strategies to protect them; yet trust is understudied …

Multi-Agent Deep Reinforcement Learning For Radiation Localization, Benjamin Scott Totten

Dissertations and Theses

For the safety of both equipment and human life, it is important to identify the location of orphaned radioactive material as quickly and accurately as possible. There are many factors that make radiation localization a challenging task, such as low gamma radiation signal strength and the need to search in unknown environments without prior information. The inverse-square relationship between the intensity of radiation and the source location, the probabilistic nature of nuclear decay and gamma ray detection, and the pervasive presence of naturally occurring environmental radiation complicates localization tasks. The presence of obstructions in complex environments can further attenuate the …

The Radical Relationality Of Complex Partnerships: Community-Member Experiences In Critical Community-Based Learning, Amie Riley

Dissertations and Theses

Through a radical relationality within the social-ecological systems that sustain us, critical community-based learning (CBL) in higher education offers a praxis for engaging the demanding pedagogical and community challenges we face. When CBL is implemented as both a critical and sustainability pedagogy, as a strategy for social change, the relationships created by CBL partnerships have the potential to generate transformational outcomes for all partnership agents. Using a critical complexity theoretical framework, a bricolage of complexity science and critical theory, this critical qualitative study sought to understand the systemic patterns and behaviors of a community-based learning partnership by elevating community-member voices. …

Drivers And Dynamics Of Phytoplankton Communities And Harmful Algal Blooms In Mountain Lakes, Lara Stephanie Jansen

Dissertations and Theses

Harmful cyanobacterial blooms (cyanoHABs) are a complex and widespread disturbance in freshwater water bodies, impacting water quality for wildlife and human populations. While cyanobacteria often bloom in warm lakes impacted by human development like agriculture, blooms are increasingly reported in cooler waters with limited development in the surrounding watershed. As much of cyanoHAB research has focused on lakes in highly developed watersheds, the understanding of factors leading to cyanobacteria dominance and blooms in the absence of major development remains limited. Mountain lakes can serve as ideal systems to study bloom-forming cyanobacteria in watersheds with minimal development. In addition, mountain lakes …

Electrochemical Hydrogen Gas Production And Carbon Dioxide Sequestration Via In Situ Formation Of Nickel (Ii) Tris-(Pyridinethiolate) Derivatives, Dayalis S.V. Brown

Dissertations and Theses

In the research presented, we use electrochemical techniques, such as cyclic voltammetry and controlled potential electrolysis, to study in situ formation of hydrogen evolution catalysts which also reduce carbon dioxide. Using pyridinethiol-based ligands and a nickel (II) precursor, both homo- and heteroleptic complexes were investigated as catalysts to produce alternative fuels while mitigating greenhouse gas emissions. Existing synthetic procedures to obtain these Ni(II) catalysts lead to low yields of the complexes and difficulties in crystallizing samples for further analysis, limiting sample size and restricting the number of studies. While current research is heavily focused on photochemically-driven experiments, given that solar …

The Impact Of Climate Change On Selected Pnw Watersheds Through The Lens Of Western Red Cedar Habitat, Jordan T. Hamann

Dissertations and Theses

Climate change is a real phenomenon that is exacerbating existing natural processes and developing into a new normal for the planet. This change may be devastating for Pacific Northwest populations of Western Red Cedar (WRC) west of the Cascade Mountain range in the states of Oregon and Washington. WRC is a valuable tree species for reasons both economic and cultural. Dieback among WRC is following an accelerating trend. Since dieback is usually followed by tree mortality, understanding its causes and distribution is beneficial to the overall success of the species going into the future.

Through the use of ESRI's ArcGIS …

Spatial Variations In Ancient Meteoric Water: An Investigation Of The Rattlesnake Tuff, Julian Michael Cohen

Dissertations and Theses

Volcanic glass has been used extensively as a paleoclimate proxy. Deuterium (2H) concentrations in glass have been found to be stable over geologic timescales, making δD a reliable proxy for ancient water chemistry. However, continued work revolves around better understanding how different factors affect preserved water in ash. Here, I analyze δD in the Rattlesnake Tuff (RST), a widespread ca. 7 Ma ashflow tuff, and create an isoscape to assess variations in δD across Oregon during that time. Additionally, I examine compositional data from glass shards to explore the relationship between δD and shard composition. The RST exhibits well defined …

Developing And Testing Low-Cost Air Cleaners For Safer Spaces During Wildfires, Brett William Stinson

Dissertations and Theses

Air cleaning reduces indoor exposure to fine particulate matter (PM_2.5) during wildfire events. However, resource and cost restraints may limit access to air cleaning during such an event, as both commercial devices and the high-rated MERV filters that homemade assemblies typically rely upon tend to be expensive and in short supply. With these barriers in mind, we sought to develop and evaluate the potential for air cleaners that use common household fabrics as filtration media. Evaluated designs use a box fan to move air across fabric filters; box fans are inexpensive and readily available to many households. Ultimately, …

A Deep Hierarchical Variational Autoencoder For World Models In Complex Reinforcement Learning Environments, Sriharshitha Ayyalasomayajula

Dissertations and Theses

Model-based reinforcement learning (MBRL) approaches leverage learned models of the environment to plan and make optimal decisions, reducing the need for extensive real-world interactions and enabling more efficient learning in complex domains such as robotics, autonomous systems, and resource allocation problems. They also provide interpretability and insight into the underlying dynamics, facilitating better decision-making and system understanding.

The world model is a model-based RL approach that employs generative neural network models to learn a compressed spatial and temporal representation of the environment. This work explores world models and a simple single-layered RNN model to learn a simple policy based on …

Creating Regression Model For Non-Markov Transition Probability Using Pseudo-Observations, Michael Gray

Dissertations and Theses

A multi-state model is a graphical tool widely used to illustrate a transitional relationship between states in many applications. We will study the transition probabilities of an illness-death model, which is an example of a multi-state model. We will investigate transition probabilities using a counting process approach. Aalen-Johansen estimator is the gold-standard in estimating a transition probability. However, Aalen-Johansen estimator may be biased when the Markov assumption is violated. Therefore, Aalen-Johansen estimator is an unreliable estimator when the Markov assumption is violated. Several papers have published non-parametric estimators that accommodate for non-Markov models using a counting process approach.

Furthermore, there …

Identifying Advantages To Teaching Linear Regression In A Modeling And Simulation Introductory Statistics Curriculum, Kit Harris Clement

Dissertations and Theses

Statistical association is a key facet of statistical literacy: claims based on relationships between variables or ideas rooted in data are found everywhere in media and discourse. A key development in introductory statistics curricula is the use of simulation-based inference, which has shown positive outcomes for students, especially in regards to statistical literacy and conceptual understanding. In this dissertation project, I investigate students from the Change Agents for the Teaching and Learning of STatistics (CATALST) curriculum in activities I designed for learning statistical association and linear regression. First, I analyzed the informal line fitting strategies of CATALST students. Findings suggest …

Implementing A Functional Logic Programming Language Via The Fair Scheme, Andrew Michael Jost

Dissertations and Theses

This document presents a new compiler for the Functional Logic programming language Curry based on a novel pull-tabbing evaluation strategy called the Fair Scheme. A simple version of the Fair Scheme is proven sound, complete, and optimal. An elaborated version is also developed, which supports narrowing computations and other features of Curry, such as constraint programming, equational constraints, and set functions.

The Fair Scheme is used to develop a new Curry system called Sprite, a high-quality, performant implementation whose aims are to promote practical uses of Curry and to serve as a laboratory for further research. An important aspect of …

A Gridded Co2 Emissions Inventory For Portland, Or, James Eckhardt Powell

Dissertations and Theses

Here we develop a new high resolution inventory of CO₂ emissions for the three Oregon counties which comprise the bulk of the City of Portland, Oregon, USA. Locally curated and long-running data collection efforts for on-road traffic activity and emission rates are used to model on-road emissions, and a new survey of the area's natural gas network informs the building energy model. The inventory estimates total emissions of CO₂ for each hour of the year 2018 in the on-road, residential, and commercial building sectors at 1 km² resolution. The onroad inventory compares to within 3% with an …

Phytoplankton Community As An Indicator Of Cyanobacteria Harmful Algal Blooms In High Mountain Lakes, Victoria Elizabeth Avalos

Dissertations and Theses

Cyanobacteria blooms are a growing issue worldwide and can be harmful to both aquatic life and human health. Warm temperatures, nutrient loading, stable water columns, and selective grazing of zooplankton and phytoplankton can contribute to cyanobacteria bloom formation. In this study, I characterized the algal communities and water quality differences in two physiographically similar lakes with relatively little human influences, Odell and Crescent Lakes, Oregon, to better understand potential contributing factors to cyanobacteria harmful algal bloom formation (cyanobacteria bloom) in Odell Lake.

There are three hypotheses in this study:

1. If there was a cyanobacteria bloom in Odell Lake, but not …