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A coupled framework for large-scale spacecraft trajectory and system co-optimization
No full textSpacecraft mission design problems often require simultaneous consideration of both the spacecraft’s trajectory and its onboard systems. Traditional optimization approaches, however, typically address these elements in a decoupled manner, which can overlook important interactions and miss opportunities for improved mission performance. While simultaneous optimization can produce more efficient and realistic solutions, it also expands the design space considerably, making the problem more complex to solve. This thesis develops a coupled optimization framework that integrates spacecraft trajectory with system-level modeling to handle these large-scale, interdependent design problems. Within this framework, we first develop a control co-design (CCD) formulation for interplanetary transfers, where trajectory control parameters are optimized simultaneously with propulsion system design variables for a finite chemical rocket. This approach captures the interaction between engine design and trajectory control, enabling more efficient solutions than traditional trajectory-only or decoupled methods. We then extend the framework to consider low-thrust trajectory optimization with discrete flyby options. The approach allows simultaneous optimization of thrust magnitude, direction, and key mission events such as departures, flybys, and arrivals. It supports large-scale problems with thousands of design variables and can handle multimodal solution spaces using multi-start strategies. Finally, we implement a solar electric propulsion (SEP) system model that represents both the propulsion and power subsystems, enabling simultaneous sizing of the engine and associated power generation. The addition of this subsystem further couples the spacecraft’s trajectory and system design, resulting in an even more integrated optimization problem. Together, these contributions advance the state of spacecraft system and trajectory co-optimization by demonstrating the advantages of tightly coupled design for complex missions
Evaluating the Impact of Pavement Condition and Weather on Horizontal Curve-Related Crashes: A State and Local Roadway Analysis in Iowa
No full textHorizontal curves represent one of the most safety-critical elements of roadway design, accounting for a disproportionate share of crashes despite comprising a small fraction of total roadway mileage. This thesis evaluates the combined influence of geometric design, pavement condition, traffic exposure, and environmental factors on crash frequency and severity across Iowa’s state and local roadway systems. A statewide horizontal-curve database is developed using the Iowa DOT’s Crash Analysis Reporting System (CARS), Iowa Pavement Management Information System (PMIS), and county-level pavement inventories for the period 2013–2022. Kernel Density Estimation (KDE) and Getis-Ord Gi* analyses are conducted to identify spatial clustering of crash hotspots.
Crash frequency is modeled using Poisson and Negative Binomial (NB) generalized linear models, with over-dispersion diagnostics confirming the NB specification as the appropriate form. Crash severity is examined using a binary logistic regression framework. Results show that geometric curvature and traffic exposure are the primary predictors of crash frequency on state highways, while on local roads the dominant effects arise from the interaction of pavement condition with adverse weather. Specifically, deteriorated pavement conditions significantly amplify crash risk during wet and wintry periods, even when the main effects of weather exposure alone are small or protective due to behavioral adaptation. Pavement quality (PCI) and geometric characteristics such as curve radius and length also contribute meaningfully to local-road crash variation after adjusting for traffic exposure.
Spatial analyses reveal distinct hotspot corridors across Iowa’s metropolitan regions, rural arterials, and interstate network. The findings provide a comprehensive, data-driven basis for targeted safety interventions, including drainage improvements, surface treatments, enhanced curve delineation, and lighting upgrades at high-risk curve segments
Applications of stellar population synthesis modeling to interacting galaxy systems and local analogs to high-redshift galaxies
No full textGalaxy evolution is a complicated phenomenon that requires a thorough understanding of physical processes occurring inside them. Evolution of galaxies is often tied to galaxy interaction, which can lead to formation of complex structures such as rings, tidal tails and bridges. Hence, an in-depth study as well as knowledge of physical properties associated with such structures are essential for a better understanding of galaxy evolution. In this thesis work, I have implemented stellar population synthesis (SPS) modeling with Code Investigating GALaxy Emission (CIGALE) to model and fit observed spectral energy distributions of galaxies in interacting galaxy systems as well as local analogs to high-redshift galaxies to understand galaxy evolution in different environmental conditions. This work has resulted in three scientific papers. In my first research project, we have constrained the interaction history of the nearby interacting galaxy system Arp 269 or NGC 4485/90. Our analysis reveals that the two galaxies had their latest interaction ∼ 230 Myr ago, and that the bridge connecting them had formed after their most recent encounter. In the second project, we have applied SPS modeling on a sample of potential local analogs to high-redshift (LAHz) galaxies. Our study identifies two confirmed LAHz systems. In addition, we have found instances where our study has either changed or strengthened previous LAHz classifications. In the third project, we have performed SPS modeling to constrain the interaction history of the interacting galaxy system UGC 6944 or NGC 3991/4/5, which reveals that NGC 3991 and NGC 3995 had interacted ∼ 600 Myr ago. In addition, we have discovered a huge clump of neutral hydrogen gas in the bridge connecting the two galaxies and confirmed that UGC 6944 is an evolved splash bridge system. Further, we have identified an asymmetric X-ray distribution associated with NGC 3991 and provided a possible gas heating mechanism capable of producing X-ray emission for an extended period of time
Trust in Tap Water among Alaska Native Communities: A Case Study of a Community within the Norton Sound Region
No full textAccess to safe and reliable water remains a challenge for many Alaska Native communities. Even “served” Alaska Native communities, where at least 55% of homes have in-home piped water, often face service disruptions, unaffordability, and boil water advisories, all of which erode trust in tap water and increase reliance on potentially unsafe alternative sources. However, few studies have investigated how specific experiences with water utility services, including water system aesthetics, service reliability, sensory qualities of tap water, utility communication, and service affordability, influence the user trust in tap water. We administered a survey to 63 residents in a community in the Norton Sound region and used ordered logistic regression to assess the associations between trust in tap water and user experiences. The results showed that trust in tap water is significantly associated with users’ satisfaction with the water treatment method. In small and remote systems, this finding demonstrates that trust in tap water depends not only on perceptions about water quality but also on views of treatment practices. Our results suggest that strengthening treatment performance and communication, particularly through transparent, culturally grounded engagement, can enhance both user confidence and community trust in the safety and reliability of tap water.This article is published as Caleb M. Fiakpui, Cristina Poleacovschi, Joseph A. Charbonnet, Marcus Nartey, Lina Sela, Christina Gish Hill, Matthew Bartos, and Bora Cetin ACS ES&T Water Article ASAP. doi: https://pubs.acs.org/doi/10.1021/acsestwater.5c01349.This material is based upon work supported by the National Science Foundation under Grant No. 2220517
Modeling nitrogen fluxes in a tile-drained cropping system in the Midwest using an enhanced SWAT model
No full textArtificial (tile) drainage systems are extensively implemented across the U.S. Midwest to enhance crop production in poorly drained soils; however, they also pose environmental challenges by significantly altering nitrogen fluxes within agricultural landscapes. In response, sustainable intensification strategies seek to increase agricultural productivity while reducing environmental impacts, often through improved management practices such as cover cropping and conservation tillage. Effectively evaluating the trade-offs and synergies of agricultural management practices demands advanced modeling tools capable of representing coupled biogeochemical and hydrological processes across diverse spatial and temporal scales. This study presents the first application of an enhanced version of the Soil and Water Assessment Tool (SWAT), integrated with Century/DayCent-based biogeochemical modules, to simulate both nitrate (NO3⁻) loss and nitrous oxide (N2O) fluxes in a tile-drained corn-soybean system. The model was applied to long-term field data (2004–2010) from an Iowa site with two treatments: with and without winter rye cover crops. With careful calibration, the model reproduced tile discharge and crop yields well and captured the direction and magnitude of cover-crop reductions in NO3⁻ losses. However, interannual variability in NO3⁻ export and event-scale N2O peaks remained difficult to reproduce, likely due to limited sampling frequency and structural constraints in soil hydrology, solute transport, and vertical resolution. The model simulated a ∼41 % reduction in NO3⁻ leaching with cover crops, close to the observed ∼50 %. In contrast, effects on average daily N2O flux varied by year and conditions, ranging from −30–67 % (observed: −24–28 %). These results support the model’s use for assessing long-term nitrogen-loss responses to cover crops in tile-drained systems, while highlighting priorities for improving event-scale biogeochemical simulations.This article is published as Shahid, Muhammad Rizwan, Junyu Qi, Bryan D. Emmett, Robert W. Malone, Natalia Rogovska, Peter L. O’Brien, John L. Kovar et al. "Modeling nitrogen fluxes in a tile-drained cropping system in the Midwest using an enhanced SWAT model." Agricultural Water Management 326 (2026): 110225. https://doi.org/10.1016/j.agwat.2026.110225The funding support for this study was provided by the U.S. Department of Agriculture, the National Institute of Food and Agriculture (2021–67019–33684 and 2023–67019–39221)
Performance and life cycle assessment of fiber-reinforced concrete mixtures with polypropylene, polyvinyl alcohol, and alkali-resistant glass fibers
No full textThis study investigated the main mechanical, environmental, and economic characteristics of the fiber-reinforced concrete (FRC) mixtures that contained polypropylene (PP), polyvinyl alcohol (PVA), and alkali-resistant glass (ARG) fibers in a range of dosages. The primary objective was to enhance performance attributes, while assessing each fiber’s impact on sustainability and cost-effectiveness. Various FRC mixtures were designed, including individual and hybrid fiber alternatives, with fiber dosages from 0.125% to 0.500% (by volume). Mechanical properties were evaluated through compressive strength, flexural strength, and residual load-carrying capacity, while microstructural details were examined using scanning electron microscopy (SEM). In parallel, a holistic life cycle assessment (LCA) was performed, encompassing production, service life, and end-of-life phases. Economic evaluation then considered initial material costs and long-term maintenance needs under different deterioration scenarios. Based on the wealth of original results, four indices were utilized to integrate mechanical performance, environmental impact, and cost. They included the environmental sustainability index, flexural sustainability index, compressive sustainability index, and economic-mechanical performance index (EMP). The EMP, in particular, enabled a direct evaluation of strength requirements relative to long-term cost implications. Among the tested mixtures, the mixtures that exhibited the highest overall performance were identified, reflecting superior mechanical properties, durability-driven sustainability, and life-cycle cost efficiency. The findings revealed that careful selection of fiber contents (in terms of choice and dosage) can be instrumental in offering proper mixture designs, facilitating their use in applications where long-term performance and environmental considerations are critical.This article is published as Ramezani, Amir, Raymond Pepera, and Behrouz Shafei. "Performance and life cycle assessment of fiber-reinforced concrete mixtures with polypropylene, polyvinyl alcohol, and alkali-resistant glass fibers." Cleaner Materials (2026): 100382. doi: https://doi.org/10.1016/j.clema.2026.100382
Butyrate modulation of porcine monocytes and macrophages
No full textDiet-induced immunomodulation has emerged as a promising alternative to antibiotics for controlling foodborne pathogens in food animals. Microbial fermentation of dietary fibers produces the short chain-fatty acid butyrate in the lower intestinal tract. Elevated levels of butyrate are associated with modulation of host immune responses and reduction of foodborne pathogens, including Salmonella. Salmonella circumvents host immune defenses by invading macrophages and establishing a protected intracellular niche where it can persist. Monocytes and macrophages play essential roles in immune surveillance, pathogen clearance, and maintaining tissue homeostasis. Circulating monocytes migrate into the lamina propria and differentiate into macrophages. Despite studies investigating butyrate interactions with macrophages and Salmonella, little is known about how butyrate directly shapes porcine monocyte and macrophage function or the cellular processes promoting Salmonella clearance in pigs. To first investigate the impact of butyrate on porcine monocyte responses as a model for intestinal macrophages and mechanisms driving butyrate-mediated immunomodulation, primary porcine monocytes were cultured with butyrate +/- LPS for 1, 4, or 24 h. Cytokine analysis via ELISA and gene expression analysis via qPCR revealed low dose (0.25 mM) butyrate decreased LPS-induced cytokine secretion and gene expression of pro-inflammatory cytokines IL-1β and TNF. High dose (1 mM) butyrate increased secretion, but not gene expression of IL-10. Butyrate dose-dependently modified LPS-induced gene expression of butyrate receptors FFAR2 and HCAR2, but not FFAR3. We next sought to understand butyrate receptor expression patterns in porcine cecum and colon mononuclear phagocytic cells from healthy and Salmonella-inoculated animals via qPCR and fluorescent co-detection of mononuclear phagocytes and butyrate receptors using confocal microscopy. To demarcate and identify mononuclear phagocytic cell populations, IBA-1, CSF1R, and/or SIRPA were used as markers for mononuclear phagocytes. FFAR2, FFAR3, and HCAR2 were expressed in IBA-1+CSF1R+ and IBA-1+SIRPA+ cells in healthy cecum and colon. Salmonella was detected in IBA-1+ cells, including instances in which IBA-1+Salmonella+ cells expressed FFAR2, FFAR3, or HCAR2. Salmonella infection also increased expression of each butyrate receptor in cecum and colon. Lastly, the direct effect of butyrate on porcine macrophage responses as it relates to Salmonella clearance is minimally understood. To understand the influence of butyrate on Salmonella infectivity and persistence in porcine macrophages, we exposed porcine macrophages to butyrate during differentiation from monocytes and then utilized a gentamicin protection assay to determine intracellular Salmonella burden. Priming macrophages with butyrate during differentiation reduced susceptibility to Salmonella infection in a dose-dependent manner. Priming with high dose (1 mM) butyrate reduced Salmonella infectivity and persistence. In addition to priming porcine macrophages, we also evaluated whether macrophages treated with butyrate post-Salmonella infection affected Salmonella replication. No differences in the amount of Salmonella were detected with butyrate treatment of Salmonella-infected macrophages. Collectively, our results demonstrated that butyrate exerted a dose and time-dependent effect on monocyte inflammatory responses and macrophage antimicrobial activity
Work values, major choice motivations, and basic need satisfaction in college students
No full textIn this study, need, motivation, and value constructs from self-determination theory
(SDT; Ryan & Deci, 2000) and the theory of work adjustment (TWA; Dawis & Lofquist, 1984)
were explored to determine whether significant relationships exist between college students’
basic psychological need states, academic major motivations, and espoused work values. This
study tested SDT’s assertion that motivational types predict basic psychological need
satisfactions, specifically looking at the motivations at play in students’ choice of academic
major. This study also investigated the relationships between work values and perceived
autonomy, competence, and relatedness satisfaction within the context of students’ academic
major courses. Hypotheses were tested using multiple regression analyses. Findings that basic
psychological need satisfactions were positively predicted by autonomous major choice
motivations and negatively predicted by controlled major choice motivations were consistent
with existent SDT research. Only two of the six work values emerged as significant predictors of
basic need satisfactions within the academic major context. Discussion of the results focused on
implications for future integration of the need, motivation, and work value constructs from SDT
and TWA
Documenting dilemmas: A narrative inquiry of secondary-level building principals addressing sexual harassment in Iowa public schools
Get PDFThis is a study of 14 secondary-level principals in the State of Iowa, who share their experiences navigating the political, social, legal, and moral tensions of the profession each day. This is a public role that is becoming increasingly more political due to the historical and political context of the past 5-10 years, and it is a professional title that comes with ethical standards that must be acknowledged. This project explores the relationship between these experiences and federal, state and local policies related to harmful student behaviors in PK-12 schools, specifically zooming in on sexual harassment. Using narrative inquiry, 14 principals share why they wanted to work as school administrators, how they approach documenting and defining student behaviors, and how they navigate the many stakeholders of both their districts and their communities. Vignettes are included in this study, created from these lived experiences in the field, to illustrate the complexities of specific behavior incidents which may be less easily defined and could involve significant harm to students. Adopting a critical epistemological stance, Chris Linder’s (2018) power-conscious framework and sensemaking theory, the findings explore the role of power and societal expectations in schools and their impact on how behaviors are defined, documented, and, in some cases, prevented each day in districts of varying sizes and ideologies across the State of Iowa. Lastly, it asks critical questions about how principals can navigate sexual harassment incidents in more structured and purposeful ways, leading to positive changes in preventing future harms across the state, especially for Iowa’s most vulnerable students
Engineered micro-nanotechnology platforms for biomedical and biological studies: From platelet behaviors, interactions between neurotransmitters and neurospheroids, to pathogen detections
Get PDFThe incorporation of engineered micro/nanotechnology platforms in biomedical and biological studies has sparked a transformative change in the way researchers approach diagnostics, therapeutics, and fundamental biological studies. This dissertation explores the applications and optimization of these platforms with three key areas of interest: platelet behavior, interactions between neurotransmitters and neurospheroids, and pathogen detection.
Engineered micro/nanotechnology platforms enable the manipulation and monitoring of the biological processes on micro and nano scales, offering detailed insights into complex cellular behaviors and interactions. This work focuses on (1) the dynamic role of platelets in varying flow conditions using microfluidic devices to simulate blood flow and platelet responses, as well as the effects of drugs on platelets; (2) the response of the in-vitro brain model, AHPC neurospheroids, to neurotransmitter treatment using an integrated chip, to improve the understanding of central nervous system functions; (3) the enhancement of pathogen detection sensitivity and point-of-care capability with engineered nanosensors, for rapid disease detection. Methodologically, this dissertation includes three projects combining microfabrication, biological experiments, and quantitative analyses to innovate and enhance the capabilities of micro/nanotechnologies in biological and biomedical settings.
Platelets are crucial to cardiovascular health as they contribute to hemostasis, the process that stops bleeding at the site of an injury. Integrins are key players in platelet adhesion and aggregation. Integrin molecular tensions, the force transmitted by integrin molecules, are regulated by both mechanical and biochemical cues, and both inside-out and outside-in signaling have been widely explored. Although atomic force microscopy, traction force microscopy, and tension sensors can investigate the mechanical properties of the platelets under static condition, the biomechanical characteristics of the platelets under flowing conditions remain enigmatic. Chapter 2 introduces a microfluidic chip grafted with integrin tension sensor that maps the force of the platelets in a flowing condition, revealing how shear stress delays integrin-mediated tension and platelet adhesion. Furthermore, we evaluate the effect of Y27632, a ROCK inhibitor, in a concentration-dependent manner, demonstrating its potential in drug screening applications.
Injury or damage to the central nervous system (CNS) from neurodegenerative diseases can lead to the loss of the specialized cells in stem cell niches or surrounding tissues. To repair or regenerate these cells, strategies often involve using directed differentiation techniques to guide stem cells toward specific neural lineages, with chemical induction being a common method for guiding neural stem cell (NSC) differentiation. Neurotransmitters like dopamine and serotonin can be used as a method to guide the differentiation of NSCs. New experimental approaches are needed to deepen our understanding of CNS functions and neurogenesis. Chapter 3 introduces a study of effects of neurotransmitters on an in-vitro AHPCs brain model using an integrated microfluidic chip, indicating that AHPC neurspheroids remain highly viable and demonstrating cell proliferation and neuronal differentiation following neurotransmitter treatment. Moreover, we demonstrate that adjusting the diffusion barrier’s permeability allows blocking Escherichia coli (E-coli) while permitting neurotransmitters to pass, suggesting the chip’s potential for studying gut-brain interactions.
Potato late blight caused by P. infestans is one of the most economically damaging plant diseases. The development of a rapid point-of-care method allows for the accurate diagnosis of pathogens. Conventional methods, such as ELISA, PCR, and real-time PCR have been developed over the past several decades. LAMP, a nucleic acid isothermal amplification method, has been widely used in plant disease detection due to its high sensitivity and specificity. Chapter 4 introduces a novel label-free LAMP chip featuring a nanopore thin-film sensor, enabling rapid, point-of-care diagnosis, with a limit of detection as low as 1 fg/μL.
These findings highlight the potential of engineered micro/nanotechnologies to deliver diagnostics, evaluation, and treatments, providing a promising advancement in the field. These studies not only contribute to scientific understanding of complex biological processes but also pave the way for future studies and diagnostic tools