UC Merced

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.

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.

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.

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.

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.

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.

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.

Think before you act may be backward. In childhood, most of us learned a lot about ourselves, the world, and what it means to live a good and happy life by reading children’s books. We gained acceptance of the world and its people as they are rather than try to beat up on, or contest designs for living that differ from our own. Children’s books taught us beautiful universal humanisms, like ‘live and let live’ and ‘love is the answer.’ In adulthood, detached from childlike principles of kindness, everyday life appears to have normalized selfishness. Living by the principle of humanity-for-all learned so long ago is not always easy. The pressures and expectations of contemporary society can block us from taking the right action. What, then, could be a way back to principled and purposeful living that supports all people? My proposition is simple: don’t think, act. This ethnographic project, based on over three years of fieldwork with a youth media organization in California’s Central Valley, highlights a method for staying true to the values and virtues learned in childhood. Specifically, it focuses on the unity of a group of young people acting their way into proper orientation to life. They share their personal stories, document community concerns, organize and participate in social justice events, and publish media projects based on the outcomes of their youth-action work. Taken together, action prior to deliberation supports social-emotional well-being and critical-evaluative skills building. Using the idea of ‘secret sympathy,’ that aura among the group that produces conformity to unity, this field research suggests that a group acting without overthinking produces a sense of belonging that young people need. The hope that permeates this research relates to the journey toward the discovery of one’s true self so that values formed foster an awakening to aspirations beyond the limits presented in contemporary society. Aspiration under neoliberal ideals works either against such an awakening or stagnates growth because it locks children and youth in that status quo at moments when they are beginning to see and sense social injustice. This, in turn, produces negative thoughts such as disidentification and maladjustment to reality. Getting active in the world and taking action on literally anything in support of conformity to unity in the name of community health frees young people from dominating social constraints. This supports and activates aspirational awakening to all of life’s possibilities, uncontrolled by institutionalized demands.

Over two dozen cave shrines are known from the Mimbres Mogollon region, more than have been reported from any other cultural region in the United States Southwest and Northwest Mexico (SW/NW). Despite some variation, the archaeological record of these sites is remarkably consistent and readily allows for their identification as shrines due to the presence of ethnographically recognizable offertory materials such as prayer sticks (pahos), cane cigarettes, and painted wood objects (“tablitas”). It remains difficult to determine, however, whether this phenomenon represents a stronger interest in cave ritual among the Mimbres or is simply the product of more thorough cave survey in that region, especially the work of Harriet and C. Burton Cosgrove in the 1920s and Walter Hough in 1905. Neighboring regions show related patterns but fewer cave shrines. A synthesis of available data, including the few available 14C dates, suggests that cave ritual did indeed reach unprecedented levels during the Mimbres Classic (ca. 1000–1130 CE). Herein I synthesize a wide range of data in order to place Mimbres cave ritual in its spatial and temporal context. Available evidence suggests that this intensification in cave ritual was driven simultaneously by population expansion, and by social, political, and environmental factors.

Currently, anion exchange membrane fuel cells (AEMFC) are gaining strong interests from researchers because it provides great potential for applying non-precious metal in comparison to the proton exchange membrane fuel cells (PEMFC). Compared to PEMFC, AEMFC has faster reaction kinetics for the cathodic oxygen reduction reaction (ORR), which enables the utilization of non-noble catalyst. In addition, the less corrosive alkaline environment allows for low-cost stainless-steel bipolar plate. However, there are still many technical barriers related to material and transport in an AEMFC. In an AEMFC, water is generated during anodic hydrogen oxidation reaction (HOR) and is consumed during the cathodic ORR. Hydroxide ions are formed during ORR and carry water molecules from the cathode to the anode via electro-osmotic drag. During high current density operation, anode flooding can hinder hydrogen transport. Similarly, it may cause cathode drying leading to high ohmic loss due to reduction in membrane and ionomer conductivity. Therefore, optimizing water management in an AEMFC is essential for achieving good cell performance. Based on the HOR and ORR, the transport limitation may occur due to insufficient supply of one or a combination of hydrogen, oxygen, hydroxide ion, and water. This project, as discussed in Chapter 3, aims to examine and identify sources of transport limitations and quantify their effect under various operating conditions. Two types of flow fields are used to study the cell performance and water behavior in the cell. The membrane electrode assembly is made of alkaline membrane with high hydroxide ion conductivity and gas diffusion electrodes are fabricated with alkaline ionomer. Two gas diffusion electrodes (GDE) are prepared with solid (powder) and liquid (dispersion) ionomer binder, GDE-1 and GDE-2 respectively. The dispersion ionomer binder makes a very hydrophobic electrode that makes ion exchange difficult and results in poor performance although the membrane is sufficiently hydrated. Adding ethanol to ion exchange solution helps to improve exchange and consequently performance. It is found that higher RH is helpful to achieve better ohmic performance, but lower RH is preferred to achieve better concentration or high current density performance. So, it is obvious that the AEMFC performance is very sensitive to RH, especially on the anode side. Hydrogen and oxygen mass transport limitations are both observed from the performance measurement. However, the effect of reducing hydrogen concentration on AEMFC performance is greater than that caused by reducing oxygen concentration. Neutron experiments show that cathode gets more water at the beginning of the cell operation, out of which most water is then transported to the anode through electroosmotic drag, the balance shifts towards anode and anode becomes flooded at some point which causes the cell performance to reduce. All these results provide valuable insights on the AEMFC water management strategies for improving cell performance and making a significant impact towards the development of AEMFC technology.

Hydrogen-powered proton exchange membrane fuel cells (PEMFC) have great potential to replace the traditional internal combustion engines due to its inherent advantages of zero greenhouse gas emissions, better fuel efficiency, quick startup, silent operation, less required maintenance, etc. In a PEMFC, oxygen transport is a critical performance limiting factor because of the sluggish oxygen reduction reaction kinetics. Limiting current method is a well-established in-situ diagnostic tool to measure the oxygen transport resistance in a PEMFC. To obtain accurate oxygen transport resistances, a few key assumptions need to be made including: (1) the effect of temperature gradient in the diffusion media is negligible, (2) no convective flow in the porous media, (3) oxygen is diluted in a gas mixture of nitrogen and water vapor, (4) the total oxygen transport resistance combines gas diffusion layer, microporous layer, and catalyst layer, (5) the effect of membrane thickness has negligible effect, and (6) the anode side does not affect the measurement results due to fast hydrogen oxidation reaction. In this project, as discussed in Chapter 4, we perform a systematic study of the effect of membrane thickness and operating conditions on obtaining robust and reliable limiting current measurements. Standard Nafion membranes of two different thicknesses (25 and 85 µm) are tested with Toray 060 and Freudenberg H23C8 diffusion media. In addition, we further study the interaction between membrane thickness and cell temperature, asymmetric pressure and relative humidity and their effects on limiting current results. Our results show that membrane thickness and relative humidity are critical factors in obtaining reliable oxygen transport resistance due to their effect on the overall water balance in the cell.

Fuel cell durability is a key limitation for its commercialization in heavy-duty applications. Cathode catalyst layers need to be designed to demonstrate not only high oxygen reduction reaction (ORR) mass activity and cell performance but also significanlt durability during long-term operation. Ion-conducting polymers, or ionomers, play a crucial role in determining both performance and durability in a PEMFC. A highly oxygen permeable ionomer (HOPI), developed by Chemours, is explored in the project explained in Chapter 5. HOPI is known for higher ORR mass activity and lower oxygen transport resistance through its film covering the active catalyst sites. A fuel cell utilizing the HOPI ionomer in the cathode catalyst layer is compared with one using the conventional Nafion D2020 ionomer. Durability experiments demonstrate the superior durability of the HOPI ionomer. Measurements of cathode proton resistance, oxygen transport resistance, and cell performance before and after accelerated stress tests reveal the superiority of the HOPI cell in all aspects compared to the D2020 ionomer. According to the literature, the improved cell durability and performance attributed to the HOPI ionomer are due to its higher ORR mass activity, enhanced oxygen transport through the ionomer film, and higher oxygen solubility.