Theses and Dissertations
Permanent URI for this collection
Browse
Search Collection
1 - 5 of 33300
-
ArticleSynthesis of pyrones and monomers from biobased materials( 2024-12)There are different scientific challenges that have risen in the last few decades that require our immediate attention. An approach to tackle these challenges is the use of different biobased molecules to address the different needs that may arise from our ever-expanding world. In this dissertation we discuss work to try to address some of these challenges. The second chapter will cover the use of the biobased molecule triacetic acid lactone to form salinaphthoquinones an organic molecule with interesting antibacterial activity. The third chapter will cover our collaboration with the Cochran group in chemical engineering. With the Cochran group we have used different bio-based molecules such as hydroxycinnamic acids and Myo inositol for different polymer applications. These molecules were used to either make biobased polymers or enhance the rate of hydrolysis of PET. The fourth chapter will cover our collaborative work with the Shanks and Tessonnier group in chemical engineering. In this work we studied indole-based molecules and their use as corrosion inhibitors. This work is important to try to mediate the use of toxic corrosion inhibitors in different industries like the field of oil and gas.
-
Article“What a wild thing to think!”: The effects of attitude expression on perceptions of attitude extremity( 2024-12)Despite the existence of a prolific field of research concerned with attitudes and their various properties, there is a glaring lack of understanding of what it means for attitudes to be extreme conceptually. The typical definition simply refers to an attitude’s distance from a scale midpoint (also known as polarization) but makes no indication towards lay definitions or a conceptual understanding. The metrics that one uses to gauge the extremity of an attitude of their own or another’s have not been formally investigated to my knowledge. The current research tested three different conceptualizations of attitude extremity: intensity of feeling, attitude qualifiedness, and the lengths an individual is willing to go to defend their position as indicators for extreme attitudes. Using an experimental design, this study manipulated presence of these qualities (high vs. low vs. control) in counter-attitudinal statements to test for their effects on perceptions of attitude extremity. In addition, individual differences in need to evaluate (the tendency to make more evaluative judgments of situations and stimuli) and need for affect (the tendency to approach or avoid emotional situations and stimuli) were measured in search of general tendencies towards higher or lower extremity judgments, as well as higher or lower willingness to engage in conversation and/or debate with hypothetical peers with opposite beliefs. Support was found for all three hypothesized extremity cues influencing perceived extremity in both directions compared to control groups. Willingness to engage showed an opposite pattern to perceived extremity as expected, though differences from control were not always significant. Insufficient evidence was found for the individual differences’ effects on most outcomes, with the exception of need to evaluate predicting willingness to engage. An interesting multicollinearity between manipulation checks for intensity and lengths, as well as implications for the future of attitudes and social cognition research are discussed.
-
ArticleSpatial, temporal, and environmental associations of ichthyoplankton assemblages and sampling success in an agricultural landscape( 2024-12)Anthropogenic modifications of lotic environments for agriculture, such as the conversion of floodplain habitat to row crops or streambed channelization for livestock, are major threats to North American prairie stream fishes. Disturbed land influences the chemical composition of adjacent lotic systems through the introduction of nutrients, sediment, and inorganic salts, along with removal of in-stream habitat like woody debris or gravel beds. Early life stages of fishes in particular are highly sensitive to the environment of rivers, and changes in the in-stream environment can result in assemblage shifts from increased mortality of larvae and young fishes. For successful reproduction, instream conditions must align with species’ reproductive strategies, larval microhabitat needs, and ontogenetic niche spaces. River modification greatly increases the risk for environmental bottlenecks to recruitment, beginning at the earliest life stages of fishes. In addition to exogenous threats from river alteration and agricultural land conversion, stream fishes in the Midwestern U.S. must contend with the introduction of exotic species such as invasive carp (Silver Carp Hypophthalmichthys molitrix, Bighead Carp H. nobilis, and Grass Carp Ctenopharyngodon idella). However, the range and reproductive requirements of invasive carp in North America are more flexible than they are in the native range of these fishes, leading to the need for further research into how degraded river conditions affect invasive carp reproduction in comparison to native fishes, if at all. Here, we evaluated larval fish communities in a suite of highly agriculturalized rivers in northwestern Iowa in relation to temporal and environmental variables. Our findings, based on 5,878 collected larvae from the Big Sioux, Floyd, Little Sioux, and Boyer rivers in 2022 and 2023, indicated the presence of both invasive carp and several common native fish taxa across a wide range of environmental conditions. Larval community composition was significantly associated with ten-day average river discharge, water temperature, pH, and the proportion of shrubland in the upstream riparian corridor. Taxa were typically clustered together in the mid-ranges of these variables, suggesting a high degree of similarity in spawning conditions, adult assemblages, and larval habitat preferences. Notably, Catostomidae were associated with slightly cooler waters, higher discharge, and lower pH than other taxa. Spatially, native fish communities were relatively homogeneous among rivers but varied longitudinally within each river. Cyprinidae, Catostomidae, and Percidae were major contributors to dissimilarities between upstream, middle, and downstream river reaches. We also captured rare instances of the large-river fish families Hiodontidae and Sciaenidae. Invasive carp larvae were captured in multiple reaches of the studied rivers, including reaches where they were previously undetected, suggesting potential suitability for spawning and reproductive success. To complement our larval sampling, we assessed the power and precision of an existing larval invasive carp monitoring program to detect changes in ichthyoplankton densities across time and space, a primary goal of many long-term monitoring programs for invasive species. Variability in catches during early life stages of riverine fishes, especially flexible spawners like invasive carp, presents significant challenges for precise and efficient sampling. We assessed the precision of invasive carp (Silver Carp and Bighead Carp) larval surveys in the Upper Mississippi River basin using a seven-year database. Our analysis revealed highly variable larval densities and low precision with existing sampling protocols. Achieving acceptable precision required levels of sampling effort likely infeasible to many managers. However, sampling precision was negatively influenced by high river discharge and positively influenced by warming water temperatures. Our results offer both implications for practical ichthyoplankton monitoring along an invasion front of a riverine invasive species and reveal patterns of native larvae in response to characteristics of river degradation and homogenization.
-
ArticleDecision support tools for farm management by integrating domain knowledge with machine learning and optimization techniques( 2024-12)By 2050, the global population is expected to reach 10 billion, while arable land remains unchanged. Meanwhile, food prices have been rising in recent years, highlighting the need for innovative solutions to ensure an affordable food supply. Inefficient farming systems may either reduce productivity or increase production costs. This dissertation proposes tools to aid farming decisions by utilizing historical data, machine learning models, and optimization techniques. Inadequate farming strategies result in significant food wastage, with approximately 30-40% of produced food being wasted after harvest yearly. In the second chapter, a planting scheduling tool was developed to minimize this wastage. Random planting causes uneven weekly harvests, sometimes exceeding storage capacity, leading to waste. The tool predicts Growing Degree Units (GDUs) to determine harvest readiness and uses this information in an optimization model to create a planting schedule and determine optimal storage capacity. Applied to the Syngenta Crop Challenge 2021, the GDU prediction model achieved a relative root mean square error (RRMSE) of 7-8%, and the scheduling model ensured uniform weekly harvests with no food wastage. A key component of precision farming is the accurate prediction of crop yields and understanding the interactions among various factors. This insight aids in making informed decisions and ensuring a sustainable food supply. The third chapter of the dissertation developed a crop yield prediction model for the US corn belt at the county level. This model combined APSIM, a crop simulation model, with a machine learning model to create an optimized weighted ensemble model (RRMSE 9%) using weather, soil, and management information. The concept of yield prediction was further extended in the fifth chapter to the field level by incorporating genotype data. A multimodal CNN-DNN model was designed using genotype, environment, and management interaction. Further analyses were conducted to understand how these factors interact, leading to recommendations for increasing productivity. Applying fertilizer is essential in crop production; insufficient amounts lower productivity, while excessive amounts raise costs. The production cost needs to be optimized to ensure food remains affordable and profitability is sustained. In the fourth chapter, we developed a tool to recommend the economic optimum nitrogen rate (EONR). This tool used APSIM simulations to train a machine learning (ML) model to predict yield responses for different nitrogen rates. The quadratic plateau model fits these predictions into a closed form of yield response, which was used in an optimization model to recommend EONR (192KgN/ha ± 48KgN/ha) for various scenarios. In brief, this dissertation presents a planting schedule tool to reduce food waste, yield prediction models considering G × E × M interactions for county and field levels, and an optimal fertilizer tool using machine learning, neural networks, and optimization methods. These tools aim to enhance farming decisions and ensure global food security.
-
ArticleHybrid RANS-LES modeling of high-speed shock turbulent boundary layer interactions( 2024-12)Three hybrid RANS/LES studies of supersonic and hypersonic shock turbulent boundary layer interactions (STBLIs) are considered. The first simulation studies an attached hypersonic turbulent boundary layer at Mach $7.2$ and $Re_\theta \approx 3300$ through $8^{\circ}$ compression corner with cold walls $(T_w/T_r) = 0.53$. The second and third simulations study a Mach $2.9$ (and $Re_\theta \approx 2300$) supersonic shock-induced separation through a $24^{\circ}$ interaction and $12^{\circ}$ incident shock configurations, both with slightly hot walls ($T_w/Tr = 1.14$). Results are described based on flow visualizations, distributions of wall quantities, as well as mean and fluctuating fields. Hybrid RANS/LES results are compared to DNS and experiments performed at similar flow conditions. Results are assessed with close attention to the size of the separation bubble, the separation and reattachment points, the mean wall-pressure distribution, and velocity profiles both upstream and downstream of the interaction region. Excellent agreement between Hybrid RANS/LES results and the DNS data is observed in the attached hypersonic STBLI configuration with a cold wall condition. This confirms the applicability of the $k-\omega$ RANS model compressibility correction to flows with strong discontinuities. Configurations with shock-induced separation are more challenging for the Hybrid RANS/LES model, especially the $24^{\circ}$ compression corner case. This can be attributed to the shielded length scale $\ell_s$, originally calibrated to address early RANS to LES model transition for hypersonic turbulent boundary layers with cold walls. Results for shock-induced separation via a $12^{\circ}$ incident shock are generally better compared to DNS. However, numerical flows fundamentally differ from the actual experimental flow, which is three-dimensional. On the other hand, numerical flows use periodic boundary conditions, assuming flow homogeneity in the spanwise direction.