UC Merced

Decisions on water allocation to humans and the environment depend on physical engineering structures, various operations and allocation policies, supplies, and demands of numerous end-users. Different assumptions of current and future scenarios can anticipate decisions that best meet human and environmental objectives, under different stressors (e.g., climate change, increased demands). Environmental water allocation especially presents intricate challenges, given the interplay of various regulations and the complexities of managing water resources across different regions. Therefore, the goal of this collection of studies is to provide new insights on reservoir operations, hydropower generation and water management in the Central Sierra Nevada, California, aiming to balance human demands, while achieving greater environmental benefits. This work involves the use of a novel method for water-power modeling with a specific application to the Central Sierra Nevada, California introduced in Chapter 1, and used in Chapters 2 and 4. The modeling framework includes more detailed and facility-specific information to provide a more comprehensive and finer temporal resolution (daily time-step) of water allocation decisions than those found in most modeling efforts. This is a potentially crucial method for modeling water management, due to the reconciliation of water and power systems through the integration of hydroeconomic needs (e.g., hydropower operations) and rule-based simulation (e.g., instream flow requirements), which is one of the biggest challenges in modeling water systems. Better representation of real-world systems is essential to address the difficulties in water management and to analyze solutions. These models are made available for use in a broad range of scenario analyses, including different hydrological inputs (historical and future climates), electricity prices, and a variety of management objectives. Chapter 2 delves into the nuanced landscape of environmental flow (e-flows) requirements, primarily anchored on water year types (WYTs), to understand the efficacy and adaptability of current strategies. Through an extensive examination of pertinent hydropower licensing documents, the research identifies a lack of standardized adoption of WYTs in many river reaches, manifesting as minimal variation across different year types and limited seasonal fluctuations. Incorporating climate change projections from multiple Global Circulations Models, the study reveals significant variability in WYT distributions under existing management strategies. This variability has led to inconsistencies in e-flow management, exacerbating potential conflicts among stakeholders. To address these challenges, an adaptive strategy is proposed, employing a method to recalibrate WYT thresholds, aiming to bolster the reliability and resilience of e-flows. As a result, Chapter 3 critically analyzes the systemic barriers hindering the effective implementation of e-flows. A comprehensive systematic review and bibliometric analysis were conducted, yielding insights into the major impediments such as competing priorities of human water uses, data deficiencies, and resource and capacity limitations. To enhance the successful implementation of e-flows, the dissertation recommends a system analysis approach, utilizing modeling tools to navigate competing demands and foster holistic flow allocations based on hydroecological principles. In turn, Chapter 4 evaluates the resilience of water systems and hydropower against climate whiplash. Through 200 synthetic hydrologic sequences of different lengths of dry-wet-dry combinations, the research underscores the vulnerability of water storage and the implications for water resource management, offering policy suggestions to enhance system flexibility and resilience against climatic shocks. Finally, Chapter 5 concludes by providing policy insights and recommendations based on these studies to help inform stakeholders and decision-makers in the search for sustainable solutions to water management problems.

Microfluidic devices present a versatile means of working with microscale objects. Here we present a new class of microfluidic design and devices that enable control of small objects without the use of traps. The chosen geometry enables symmetry-protected functionality, separating out 3D directional control from straining flow. An experimental implementation of this device allows for strainless, arbitrary path generation both with and without feedback control. Overall, the device provides a new means of micromanipulation to address experimental needs for precise motion and strain control.

Developing vascular cells have been shown to self-organize into unique structures in both two and three dimensions. Depending on the conditions, these cells may develop micropatterns with spatial segregation of different cell types in 2D or develop into perfusable vascular vessels in 3D. This self-organization arises from the interplay of motility, proliferation, differentiation, and cellular signaling; with the relative importance of these factors remaining unclear. In this dissertation, I report the development and use of a computational model to explore how motility, proliferation, and differentiation rates affect the emergence of micropatterns from differentiating vascular cells in a 2D in silico environment. Later, I explore the in vitro vascular development, via a microfluidic platform, of vascular networks that are functional, perfusable, and stable for more than two months. Firstly, I developed a stochastic on-lattice population-based model to study the emergence of vascular patterns from a starting distribution of stem cell induced vascular progenitor cells capable of differentiating into both endothelial cells and smooth muscle cells that are motile and proliferative. Our model yielded patterns that were qualitatively and quantitatively consistent with our experimental observations, for physiologically reasonable parameters. Our results suggest that, for such parameter values, it is the post-differentiation motility and proliferation rates that drive the formation of vascular patterns more than differentiation alone. This was shown to be true even when higher order effects like density dependent adhesions and paracrine signaling were considered. Secondly, microfluidic devices and organ-on-a-chip models have become good solutions for studying 3D cell cultures that more closely mimic physiologically relevant lengths and timescales. These devices allow for the incorporation of height into cultures by suspending cells in extracellular matrices, such as fibrin, that more closely mimic in vivo microenvironments. Here I also report the use of endothelial cells in culture with mural cells, smooth muscle cells and pericyte cell cultures, as ideal conditions for the successful development of perfusable vasculature within a three-channel microfluidic device. We found the use of these cells, in tri-culture, to lead to the development of physiologically narrow vessels that were functional and perfusable for more than two months. These findings hint at methods that could be employed for directing specific micropatterns or 3D structures that focus on controlling the motility and proliferation rates of differentiating stem cells. Furthermore, these studies aim to advance the field of organoid development, by providing a reliable method for developing fully vascularized organoids and organs that are stable for long time-scales.

As the healthcare profession has become more diverse, physicians may encounter patients who discriminate against them based on their group identity. Most past research has focused on addressing healthcare workers’ negative bias toward patients, yet incidents of patient bias toward healthcare workers also occur. Patient bias is prejudice, racism, and/or discrimination against healthcare workers by patients experienced during patient-provider interactions and decision-making. Experiencing discrimination due to these biases can negatively influence healthcare workers’ health and well-being and reduce their persistence in their careers. Yet, to my knowledge, no studies have measured patients’ implicit bias toward healthcare workers. Thus, in two studies, I examined patients’ implicit bias toward Hispanic physicians and two important qualities for physician-patient interaction: trustworthiness and competence. I also examined how these biases related to whether people chose a Hispanic physician, their perceptions of care by a Hispanic physician, and their intentions to adhere to medical advice from Hispanic physicians. Across both studies, participants implicitly rated White physicians more favorably (i.e., more implicitly trustworthy and competent) than Hispanic physicians. Results suggested that people were more likely to choose a Hispanic physician to the extent that they implicitly associated Hispanic physicians with competence and more likely to adhere to physicians to the extent that they rated Hispanic physicians as implicitly competent and trustworthy. Additionally, results suggested Hispanic participants were more sensitive to physician ethnicity than were White participants. Specifically, Hispanic participants who were assigned a Hispanic physician were more likely to be confident in the diagnosis to the extent they reported implicit trustworthiness and competence ratings for Hispanic physicians. Additionally, Hispanic participants who were assigned a Hispanic physician were more likely to believe the diagnosis to the extent they reported implicit trustworthiness ratings for Hispanic physicians. Finally, Hispanic participants assigned a White physician were more likely to request a second opinion and less likely to be confident in the physician’s diagnosis to the extent they reported implicit trustworthiness ratings for Hispanic physicians.

The escalating frequency and severity of wildfires in California have precipitated substantial economic losses and social strains, underscoring the imperative to comprehend the dimensions of wildfire management. This dissertation amalgamates three pivotal research endeavors focusing on different dimensions of wildfire risk: perceptions among wildland-urban interface residents, predictions of wildfire burn severity, and visualization of uncertainty. The surge in wildfires, coupled with the increasing population moving to Wildland-Urban Interface (WUI) areas, highlights the urgency of understanding both the physical and human dimensions of wildfire risk management. While various management practices involving communities have emerged as favored solutions, barriers to their implementation persist. Understanding public attitudes and perceptions regarding these practices is essential for successful fire management efforts.Furthermore, the warming climate and increasing fuel loads due to fire exclusion, compounded by climate change and drought, have led to more frequent, extensive, and severe wildfires. Burn severity, a metric that measures the ecological impact of fire on vegetation, is crucial for post-fire management. The Composite Burn Index (CBI) emerges as a preferred method of characterizing fire effects due to its comprehensive approach, offering a systematic and visually intuitive estimation of ecological impacts following a fire. Effective wildfire severity and risk information to stakeholders is paramount for enhancing understanding and promoting resilience. However, conveying complex information poses significant challenges. Visualization techniques play a vital role in conveying risk information and aiding comprehension of complex wildfire-related information. This research introduces a scalable visualization model for a use in predicting and managing the complex dynamics of wildfire occurrences. This dissertation advances our understanding of wildfire management by elucidating the complex interplay between public perceptions, burn severity estimation, and risk visualization. By integrating social perspectives with empirical modeling and visualization techniques, it offers multifaceted approach to addressing the challenges posed by wildfires in California. The insights garnered from this dissertation are crucial for informing policy decisions, guiding mitigation efforts, and fostering community resilience in the face of escalating wildfire threats.

Hematopoiesis depends on complex interactions between hematopoietic stem cells (HSCs) and the bone marrow (BM) microenvironment. However, alterations in this regulated system can lead to malignant transformation and hematopoietic diseases. Acute myeloid leukemia (AML) is characterized by uncontrolled growth of leukemic blasts in the BM and is the most common acute leukemia in adults. Tumor survival after cytotoxic treatment of AML patients remains a major therapeutic challenge, contributing to disease relapse. Fine-tuning the cytotoxic conditioning regimen to discover the most effective treatment plan has the potential to significantly improve outcomes in AML patients, thereby reducing the risk of relapse. The mechanism by which conditioning achieves therapeutic outcomes is through BM ablation. Additionally, conditioning can impact different compartments of the BM microenvironment. In this study, we investigated the impact of busulfan conditioning on the BM niche, focusing on how the intensity of cytotoxic conditioning regimens and animal age influence this dynamic process. We later expanded our findings to an AML mouse model to evaluate the BM niche around resistant tumor cells after cytotoxic therapy.

By examining the impact of varying dosages and recipient age factors on treatment response as well as BM microenvironment adjacent to the residual tumor cells after therapy, we sought to optimize chemotherapy regimens and establish the groundwork for tailoring treatment strategies to AML cancer patients.

Existing literature examining perceptions of nicotine addiction are largely surface level questions or fail to align with diagnostic criteria of tobacco use disorder. The disentanglement of the physical, psychological, and social components of nicotine addiction are needed to better understand what addiction means to people. Understanding how the lay person views and thinks about nicotine addiction may provide insight into non-smokers initiation intentions, smokers consumption habits, and quit intentions. This study developed and validated a novel scale assessing perceptions of nicotine addiction that comprehensively aligns with the clinical dimensions of nicotine addiction. To establish the scale’s construct validity, this study utilized cognitive interviews for item development, exploratory and confirmatory factor analysis and psychometric evaluation for scale development, and assessed convergent, discriminant, and criterion validity for scale evaluation. The proposed scale returned adequate diagnostics using psychometric evaluation and its construct validity was established using three assessments of validity. The findings from this study suggest that perceptions of nicotine addiction may not align with clinical dimensions of addiction, and that public health education efforts should focus on the experiences of addiction rather than emphasizing the consequences of addiction.

Many chemical reactions occurring at aqueous interfaces show different kinetics and thermodynamics than the same reactions occurring in the bulk. The nature of these chemical reactions is central in understanding environmental, industrial, and biological processes; but remains incompletely understood due to its complexity and experimental difficulties in tuning and characterizing reactions at aqueous interfaces. In this dissertation, different experimental approaches are utilized to generate large, well-characterized aqueous interfaces for kinetic studies of chemical reactions. Chapter 1 introduces deviations of chemistry at aqueous interfaces that can alter physiochemical properties of chemical processes. In chapter 2, I study mechanistic rate accelerations of organic reactions at the organic-water interface and find that free OH groups of interfacial water molecules play an essential role in catalysis. In chapter 3, I revisit the effects of electric fields at the air-water interface of water microdroplets on directly converting water into hydrogen peroxide which is thermodynamically unfavorable in solution. Contrast to previous reports, no hydrogen peroxide production is observed in water microdroplets when tuning the electric fields at droplet surfaces. In chapter 4, I discuss claims of spontaneous hydrogen peroxide formation at the air-water interface and pinpoint potential experiments that can help to clarify them. Chapter 5 is the conclusion of the work presented in this dissertation.

This dissertation examines how Latinx families talk about racial and cultural identity and racism and how these conversations about and experiences with racial and ethnic inclusion and exclusion vary by family and community resources. I conducted 65 in-depth, semi-structured interviews with U.S.-born Latinx children of immigrants from Florida and California, young adult siblings, and parents. My dissertation contributes to research on race and ethnicity by developing the processes of how structural racism unfolds in Latinx families through racial and ethnic socialization and how individual, family, and community resources can help resist racial oppression.

Giant unilamellar vesicles (GUVs) are spherical structures composed of an aqueous compartment enclosed by a bilayer membrane. They are often seen as a simplified analog of a cell membrane and can be utilized as minimal cell models for studying cellular systems due to their cell-like sizes and capacity to mediate membrane interactions. A paper-based diffusive loading technique termed, OSM-PAPYRUS, is shown to assemble GUVs in physiologically relevant salt solutions with gentle loading of proteins. Characterization of this loading process reveals cell-like variation of encapsulated protein concentrations and a gamma distribution often cited for protein distributions in the cell. This ability to mimic cellular variability in vitro reveals potential in bridging the gap between in vitro and in vivo experimentation. The highly controlled environment of in vitro experiments can be combined with cell-like volumes, phospholipid bilayer, and cellular variation in GUVs. A practical application is explored, encapsulating the post-translation oscillator (PTO) of the cyanobacteria circadian clock system which shows membrane interactions in vivo. The results showed that cellular variation and membrane binding significantly hampers the fidelity of the clock, in contrast to bulk experiments where concentration did not matter once a critical concentration is met. An increase in concentration to cellular levels helps counteract the effect of variation. Modeling the clock reaction using expected distributions and variation of encapsulated proteins, corroborated with the hypothesis that intercellular variation and membrane binding were responsible for trends in the experimental data. The experimental data and model showed that the PTO by itself was not capable of achieving the near 100% fidelity observed in the native cyanobacteria, instead, other cellular components, like SasA and CikA or transcriptional-translational feedback loop (TTFL) would be necessary to achieve in vivo clock fidelity. The GUV model demonstrated advantages over in vivo studies, particularly in the isolation of the PTO, which allowed for the determination that large period variations seen in vivo cannot be produced by the PTO even under cell-like variability and volumes. This demonstrates the ability of GUV in vitro models to obtain context on behaviors not appreciated by either previous bulk in vitro or in vivo studies.