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Base Acres Explained: How They Compare to Planting on Nebraska Farms
No full textThe Farm Bill represents an important piece of legislation that, in part, provides commodity price stability through program payments. Approximately 75% of Nebraska’s cropland is supported by Farm Bill program payments (see previous article here). Importantly, the article revealed large differences in base acre coverage (measured by base acre per planted acre) by county, ranging from 0% in Grant and Hooker counties, to 149% in Nance County.
Since the previous article was published, inquiries have come forward regarding the allocation of base acres by commodity. Specifically, how crop-specific base acres stack up to the number of acres planted to the crop. The purpose of this article is to explore base acre-to-planted-acre relationships by commodity and discuss issues related to updating base acres
Robust Quantification of Cortical Hemodynamic Response to Tactile Stimulation: A Comprehensive fNIRS Methodology to Mitigate Physiological Confounds
No full textThis dissertation establishes a quantitative framework for studying somatosensory processing using functional Near-Infrared Spectroscopy (fNIRS), with a focus on applications in neurorehabilitation. The central aim is to investigate how the brain\u27s hemodynamic response is modulated by the velocity of patterned tactile stimulation. While fNIRS is a promising neuroimaging tool, its data quality is often compromised by physiological noise and motion artifacts, challenging the reliability of its findings and hindering the development of effective, quantifiable neurotherapeutics.
Two preliminary investigations informed the final experimental design. The first pilot study confirmed that pneumotactile stimulation of the hand, during both passive (somatosensory) and active (sensorimotor) tasks, could evoke a significant hemodynamic response. However, it did not reveal a consistent pattern of velocity encoding and was confounded by the high variability associated with the sensorimotor task. A second preliminary study used machine learning classifiers to differentiate the stimulus velocities as reflected in the hemodynamic response. While achieving above-chance accuracy, the performance was inconsistent across participants, underscoring that poor signal quality and experimental complexity were obscuring the underlying neural signals. These initial findings highlighted the critical need for a simplified yet comprehensive paradigm with improved noise mitigation strategies.
To address these challenges, an improved experimental paradigm and a robust data analysis pipeline were developed. Patterned stimuli were administered at four distinct velocities (20, 25, 31, and 39~cm/s) to the hands of 22 right-handed and 3 left-handed neurotypical adults. Crucially, the methodology integrated a novel multimodal recording system, acquiring fNIRS data with short-separation channels alongside a comprehensive suite of auxiliary physiological measurements, including head movements, facial and forearm EMG, respiration, and cardiac pulse. These diverse signals were incorporated as regressors within a General Linear Model (GLM) to systematically isolate the stimulus-evoked cortical activity from systemic interference.
The results validate this comprehensive noise regression strategy, which revealed highly specific and localized brain activation patterns that were otherwise obscured. The primary findings include a robust excitatory response in the contralateral primary somatosensory cortex (S1) and a concurrent inhibitory response in the ipsilateral S1. Furthermore, the analysis demonstrated a velocity-dependent modulation of the hemodynamic response. The comprehensive dataset also allowed for a systematic quantification of how experimental factors and participant characteristics, such as hair type and color, may impact fNIRS signal quality.
In conclusion, this work successfully validates a multi-modal fNIRS-based methodology for the reliable quantification of the cortical response to tactile stimulation. By identifying optimal stimulation parameters and providing a validated framework for mitigating noise, this research offers a neurophysiological basis for designing more effective therapeutic interventions. Moreover, the comprehensive nature of the recordings provides a valuable resource for future investigations.
Advisors: Steven Barlow and Gregory Bashfor
Amplifying Mother Leaders’ Voices: A Feminist Inquiry into Gender Inequity in Higher Education Leadership
No full textWomen now comprise more than half of mid- and upper-level administrators in higher education, yet they remain underrepresented in the most senior leadership roles. For mothers in leadership, this underrepresentation is compounded by gendered structures, expectations, and norms that shape their personal and professional lives in distinct ways. While scholarship has examined working motherhood broadly and gender inequity in higher education separately, little research has focused on how mother leaders experience and interpret gender inequity in higher education leadership. This study sought to address that gap by exploring the lived experiences of ten mother leaders working at research-intensive (R1) universities in the United States. Guided by a feminist epistemology and informed by the philosophies of interpretative phenomenological analysis (IPA) and select feminist concepts, this study examined how participants made sense of the gender inequities they faced at the intersection of motherhood and leadership. Data were collected through semi-structured interviews, personal diaries, and an asynchronous group dialogue. A feminist lens was employed during data analysis, which involved iterative coding, reflexive memoing, and thematic interpretation. Findings revealed that participants navigated gendered organizational structures and experienced persistent pressures from the ideal worker norm. In response, these women adapted their behaviors and overcompensated to be taken seriously as leaders. Participants also described carrying the mental and emotional load of caregiving and emotional labor in the workplace, which intensified work-family conflict. Despite these challenges, participants chose to redefine leadership by incorporating empathy, compassion, and care into their leadership approach. Many framed motherhood as an asset to their leadership and used their experiences to model healthier work-life balance, support employees as whole people, and challenge harmful organizational norms. This study contributes to the scholarship on gender inequity in higher education by amplifying the voices of mother leaders and revealing how gendered organizations and structures shape their experiences. The findings from this study have practical implications for institutions regarding improved policy, leadership development, and workplace culture. This study offers insights into how higher education organizations can better support and retain mother leaders amid staffing shortages and political uncertainty.
Advisor: Elvira Abric
Development of a Machine Learning Framework for an Irrigation Decision Support System
No full textCurrently used irrigation scheduling techniques often require significant human intervention and are time consuming, particularly for variable rate irrigation. This research aimed to develop a conceptual framework that incorporates disparate data sources leveraging both mechanistic and machine learning (ML) approaches. The overarching objective is to utilize the growing availability of data and technology to manage irrigation more precisely, which will minimize negative impacts of irrigation on our water resources. An initial irrigation machine learning model was proposed and tested in this study as a key component of an edge-cloud computing and federated learning decision-making framework. The specific objectives were (1) to develop and evaluate ML models based on linear regression and random forest to derive irrigation recommendations using the latest date (LD), which is used to trigger an irrigation event; (2) to compare ML to the SETMI model for irrigation recommendations; and (3) to propose a framework for implementing ML to support variable rate irrigation and real-time irrigation management. Input data included weather variables, weather-based parameters (e.g., growing degree days), soil properties, basic agronomic information, remote sensing imagery (e.g., for soil-adjusted vegetation index), soil water sensor data, and canopy temperature from stationary infrared thermometers. Both linear regression and random forest ML algorithms were trained and evaluated on their ability to generate irrigation recommendations for maize and soybean. The latest date (LD) was defined as the number of days until an irrigation event is necessary to avoid crop stress. The RMSE of the LD when irrigation will be needed was 7 days (linear regression) and 1.5 days (random forest). The three most important variables were found to be accumulated GDDs, solar radiation, and accumulated precipitation. Implementing the model on a different field site in a subsequent year was not successful (R2 = 0.01), although it did show an increase in LD after precipitation and irrigation, as expected. This research highlights the potential of ML techniques in the science of irrigation scheduling and identifies next steps for continued technology development
Synthesis and Study of Stable Organic Radicals for MRI Contrast Agents and New Materials
No full textThe first part of this dissertation focuses on the design, synthesis, and characterization of a thermally robust S =1/2 phototetrazolinyl monoradical and the development of synthetic methodologies for a high-spin (S = 1) phototetrazolinyl diradical. Electrochemical studies of the phototetrazolium cation (precursor to the monoradical) revealed a remarkably narrow electrochemical band gap (Ecell ≈ 0.82 V), suggesting promising electrical conductivity. Thermal analysis of the monoradical demonstrated excellent stability, with the onset of decomposition at 232 °C. Building on the excellent thermal stability and promising properties for electrical conductivity of the monoradical, we developed two condensation-based synthetic routes that provide viable pathways to a high-spin phototetrazolinyl diradical.
In the second part of this dissertation, we discuss the design, synthesis, and characterization of a quartet ground state (S = 3/2) triBlatter triradical with three Blatter radical centers. The synthesis, purification, and recrystallization of the triBlatter triradical were performed and optimized. The resulting triradical was examined using solid-state EPR spectroscopy and electrochemical studies to investigate its magnetic and electronic properties.
In the final chapter, we report the design, synthesis, and characterization of two conjugates of metabolic organic radical contrast agents (mORCAs) developed for magnetic resonance imaging (MRI). The design of the mORCAs constitutes a sterically shielded gem-diethyl nitroxide radical conjugated to a D-mannosamine sugar backbone. These mORCAs can be utilized for direct metabolic glycan labeling, bypassing the need for two-step bioorthogonal reactions followed by metabolic glycan engineering.
In Vivo MRI experiments in mice demonstrated that the paramagnetic nitroxide radical contrast agents shortened the T1 and T2 times in the kidney and the brain by up to ~10% after 3 days. Ex vivo experiments showed that the contrast agents were immobilized and primarily localized in mouse tissues in the kidney, lung, liver, heart, and blood.
Advisor: Andrzej Rajc
Investigating Molecular Rotation and Vibration with Ultrafast Electron Diffraction
No full textUltrafast electron diffraction (UED) has emerged since the late 20th century as a powerful technique for resolving molecular dynamics. With its high spatial and temporal resolution, UED can now measure rotational motion induced by linearly polarized, nonresonant, nonadiabatic laser pulses—one of the fundamental molecular degrees of freedom with broad applications. By combining laser-induced alignment with UED, new capabilities such as three-dimensional structural retrieval and isotope detection have been demonstrated, as discussed in Chapter 2.
In Chapter 3, three symmetry relations in the coefficients of rotational wave packets are identified and derived, reducing the computational cost of simulating asymmetric-top molecular alignment by a factor of eight in both time and memory. Several numerical techniques are also introduced to further improve computational efficiency, enabling simulations of rotational dynamics at room temperature.
Vibrational dynamics induced by nonresonant laser pulses in the impulsive regime share similarities with nonadiabatic rotational excitation, as both involve ultrashort laser “kicks” that coherently excite molecules into superpositions of eigenstates. However, vibrational motion induced by impulsive stimulated Raman scattering (ISRS) has not yet been detected by UED due to the extremely small displacements, where the harmonic oscillator approximation remains valid. In Chapter 4, time-resolved UED signals are simulated using both classical and quantum harmonic oscillator models and compared in detail. Because current UED temporal resolution (~100 fs) is comparable to or longer than the vibrational period (~100 fs), time-averaged diffraction patterns are analyzed. The classical model agrees well with the quantum results at time delays corresponding to the largest signal amplitudes but deviates for time-averaged signals. Quantum simulations further predict that UED with temporal resolution of about half the vibrational period can still capture vibrational dynamics induced by ISRS, yielding similar but weaker signal amplitudes.
Advisor: Martin Centurio
Electrical and Magnetic Properties of Ferroic Oxide Thin Films and Free-standing Membranes
No full textThis dissertation presents a comprehensive study of the electrical, magnetic, and transport properties of epitaxial ferroic oxide thin films and free-standing membranes, including ferroelectric PbZr0.2Ti0.8O3 (PZT) and ferrimagnetic NiCo2O4 (NCO).
We evaluate the effects of electrostatic and mechanical boundary conditions on the ferroelectric properties of free-standing PZT membranes by transferring them on three types of base layers: the metallic Au, strongly correlated oxide La0.67Sr0.33MnO3 (LSMO), and 2D semiconductor MoS2. The coercive field and domain wall roughness depend sensitively on the metallicity and surface roughness of the bottom electrode. We also fabricate MoS2 field effect transistors top-gated by PZT membranes and achieve a nonvolatile current on/off ratio of 2.04 × 105 at room temperature by switching the polarization of PZT.
We combine monolayer MoS2 with PZT thin films or membranes and explore the effects of ferroelectric polarization and domain wall on the second harmonic generation (SHG) signal in the heterostructure. The SHG signal exhibits threefold symmetry at the polar domain regions. The PZT membrane/MoS2 stack allows in-operando tuning of the SHG response, which is promising for developing programmable nano-photonics.
We explore the unconventional magnetotransport behavior of epitaxial NCO thin films deposited on (001) MgAl2O4 (MAO) substrates in the ultrathin limit. The perpendicular magnetic anisotropy (PMA) revealed by anomalous Hall effect can be sustained in films down to 1.5 unit cell (1.2 nm). The sign change in the anomalous Hall conductivity and its scaling behavior with the longitudinal conductivity can be attributed to the competition between band intrinsic Berry phase effect and impurity scattering.
We also investigate the interplay between strain and defects in determining the metallicity, magnetoresistance, and magnetic anisotropy in NCO thin films and membranes. NCO films on lattice compatible MAO substrate exhibit metallic conduction, and two-fold sinusoidal anisotropic magnetoresistance (AMR). In contrast, NCO films on other perovskite substrates exhibit insulating conduction, and emergence of four-fold AMR component, which is attributed to strain-induced tetragonal magnetocrystalline anisotropy. The free-standing NCO membrane exhibits highly consistent magnetotransport properties with the unsuspended NCO film, suggesting the strain and disorder levels are mostly retained.
Advisor: Xia Hon
Integrating Chinese Tradition and Western Techniques in Jiang Zuxin’s Piano Works: A Study of Temple Fair and Mountain Flower Collection
No full textThis document focuses on Jiang Zuxin’s two piano suites, Temple Fair and Mountain Flower Collection, examining how traditional Chinese musical materials interact with Western compositional techniques. Through close analytical readings of selected excerpts, combined with considerations of performance practice and modal context, the research demonstrates that Jiang systematically employs pentatonic collections and their modal configurations (gong, shang, jue/zhi/yu), along with certain altered tones (such as biangong and qingjue), as foundational pitch material. He also draws on folk songs, dances, and theatrical elements from traditional Chinese culture. At the same time, he simulates the timbres and idiomatic playing techniques of Chinese traditional instruments — including pipa, dizi, sheng/lusheng, guqin, and guzheng — through pianistic textures and techniques. This approach preserves local sonic characteristics while fully exploiting the expressive potential of the piano.
Jiang treats Western compositional methods — such as mixed meter, sanban (free rhythm), polyrhythm, tertian and extended harmony, quartal and quintal constructions, whole-tone scales, non-functional dissonance, and polyphonic techniques — not as rigid formulas but as flexible tools. These techniques are carefully intertwined with modal and textural elements, generating a localized, contemporary piano vocabulary. Within this framework, he maintains voice independence, achieves ensemble-like sonority, and allows expressive flexibility.
The document provides empirical evidence of cross-cultural musical practice, showing how pitch, rhythm, timbre, and texture operate collaboratively. It also offers an analytical framework for understanding the localization of twentieth-century Chinese piano music. Although the research is limited to two suites and relies primarily on score-based analysis, the findings contribute to a broader academic understanding of modern Chinese piano composition. Furthermore, they serve as a reference for cross-cultural compositional strategies.
Advisor: Mark Clinto
Exploring Transformative Learning Experiences in Engineering Doctoral and Post-doctoral Education: Developing Non-technical Competencies for Early-career Academic Roles
No full textThis dissertation explores the transformative learning experiences that early-career engineering faculty recounted from their doctoral and postdoctoral training and how these experiences shaped the development of non-technical competencies essential for academic success. Grounded in Mezirow’s Transformative Learning Theory (TLT) and the Competency-Based Professional Development Framework (CBPDF), the study examines how reflection and shifts in frames of reference supported competency growth and faculty readiness. A qualitative holistic single-case study design was employed. Data sources included semi-structured interviews with early-career engineering faculty and program learning objectives drawn from graduate handbooks. Data analysis was both deductive and inductive guided by Mezirow’s ten phases of TLT and the CBPDF domains, while allowing insights from both data sources to reveal additional non-technical competencies beyond the original framework. These included communication, personal development, teaching, research, management and organizational, mentoring and feedback, interpersonal conflict-management, and political and ethical competencies. Findings showed that participants experienced interconnected personal and professional learning transformations involving independence, adaptability, identity formation, and collaborative learning each characterized by critical reflection, adaptation, rational discourse and reintegration. Participants described becoming more self-directed and resilient while developing scholarly confidence, mentoring capacity, and a reflective academic identity. This study links transformative learning processes with non-technical competency development, emphasizing that preparing future engineering faculty extends beyond disciplinary mastery. It calls for doctoral and postdoctoral programs that intentionally integrate mentorship, reflection, and competency-informed training practices to cultivate adaptable, self-aware, and relationally competent graduates prepared for the multifaceted demands of academic life.
Advisor: Logan Perr
Characterization of Mitochondrial DNA Repair Components and Repair Choices at Targeted Double-strand Breaks in \u3cem\u3eArabidopsis thaliana\u3c/em\u3e
No full textPlant mitochondrial genomes are complex when compared to most other eukaryotic mitochondrial genomes. They are large and variable in size, expand and rearrange frequently, abundant in non-tandem repeats, but maintain a very low synonymous substitution rate in the remaining coding regions. Many of these complexities can be explained by the increased use of double-strand break repair for DNA damage. To advance the understanding of mitochondrial genome dynamics as it relates to double-strand break repair, we performed a forward genetics screen to identify proteins involved in DNA repair in plant mitochondrial genomes. Through this screen, we identified an RNA/DNA helicase, Suv3, that when mutated in Arabidopsis thaliana, causes no change in phenotype unless plants are stressed. Further characterization of suv3- mutants in A. thaliana revealed its role in repeat recombination and maintaining the structure of the mitochondrial genome. Many of the known plant mitochondrial DNA repair genes are homologous to those of E. coli, however characterization of the active sites has not been done in these proteins. We attempted to make site-directed mutants of these proteins in A. thaliana to characterize these active sites, in order to compare them to their homologs in E. coli. One hinderance to understanding the mechanism of double-strand break repair in plant mitochondrial genome is the difficulty in making targeted breaks in plant mitochondrial DNA. The most commonly used system to create breaks, CRISPR-Cas9, cannot be employed to mitochondria due to the inability of a gRNA to enter the organelle. Some methods, like mitoTALENs, allow targeted changes but are labor intensive and only allow for a few targets at a time. To get around these issues, we designed a nuclear-encoded, mitochondrial-targeted, inducible restriction enzyme line that creates 35 simultaneous double-strand breaks throughout the mitochondrial of genome of A. thaliana and analyzed the repair choices and consequences on the genome structure. This dissertation contributes to the field of plant mitochondrial genome dynamics by further characterizing a mitochondrial helicase, providing tools to study active sites of mitochondrial DNA repair proteins, and by showing proof-of-concept of a novel method to make targeted changes in A. thaliana mitochondrial DNA.
Advisor: Alan Christense