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Hydrazone-Based Switches: Communication, Recognition, Transport, and Environmental Effects
No full textBiological systems achieve intricate control over processes such as signal transduction and ion transport through complex intermolecular communication networks. Replicating such dynamic control over synthetic supramolecular systems is a grand challenge. This thesis uses chemically and photochemically activated hydrazone-based switches to try and emulate similar intricate allosteric regulation in synthetic supramolecular systems.
First, we illustrate the conceptual foundation for both chemically and light-activated molecular switches, positioning hydrazones as a robust and tunable platform. Building on this foundation, we developed a hierarchical multistep switching cascade: a Zn(II)-initiated metal and proton relays that propagate a reversible signal between two different hydrazone units via coordination-coupled deprotonation (CCD). A single chemical input thereby drives intermolecular communication, mirroring the layered logic of biological signaling pathways.
The centerpiece of this thesis is a light-driven molecular anion pump employing a trimeric hydrazone receptor to actively transport chloride ions against a concentration gradient. Reversible E/Z photoisomerization modulates the receptor’s binding affinity, enabling directional Cl- uptake and release. This design converts light energy into chemical work, achieving one of the first synthetic anion pumps and underscoring the power of hydrazone switches in active, out-of-equilibrium supramolecular systems.
Finally, we introduce a novel class of photoswitches based on BF2-coordinated hydrazones. These so-called azo-BF2 switches, while highly useful in visible and near-infrared applications, face a stability challenge in the solution-state. We studied how subtle π-system modifications and solvent polarity govern their switching properties, stability, and reactivity. Mechanistic pathways such as intramolecular 1,2-BF2 shift and solvent-induced solvolysis are elucidated, informing strategies to enhance photoswitch performance
Neural patterns reflect semantic representation in novice sign language learners
Get PDFHow do novice language learners represent semantic information in their new language? The extent to which languages are supported by distinct or overlapping neural representations in bilinguals has been the topic of much research, but less is known about how new knowledge is integrated into established representational networks, especially at the earliest stages of language acquisition. Furthermore, most investigations have compared languages which share a modality (spoken). Signed languages can provide insight into language unconfounded by perceptual qualities that spoken languages share. Chapter 1 presents an initial study in which hearing English-speaking non-signers learned a set of nouns in American Sign Language (ASL) before fMRI scanning. Neural patterns which correlate with semantic features in ASL and English (but not an unstudied control language) provide a proof of concept that overlapping cross-language representations emerge after just a few hours of learning. In Chapter 2, I replicate these results in a larger dataset and additionally show that two different data-driven measures of neural correspondence between ASL and English reflect individual differences in comprehension in several frontal, temporal, and occipital regions. Lastly, Chapter 3 presents a longitudinal study which measured ASL learning over several weeks with more complex and dynamic stimuli. Leveraging prior work in which relies on large language models (LLMs) to capture complex semantic features from stimuli, I present initial analyses which suggest that a model trained on neural data during audio-only English listening can estimate neural responses to not only audiovisual English stimuli, but visual clips of sentences in ASL in superior temporal regions. Taken together, these three studies demonstrate the role of frontal and temporal regions, especially bilateral superior temporal sulcus, in representing semantic content across language and modality in novice learners
Hybrid DC-DC Converters for Soft Charging Capacitive Actuators: Modeling, Analysis and Design
Get PDFRecent trends in haptics, microrobotics and ultrasound technology have shown an increasing use of piezoelectric and other electrostatic actuators. These actuators are suited for miniaturized applications due to their high power density and favorable scalability at a small size. Their electrical impedance at lower frequency (their typical operating range) is capacitive, therefore, they can be modeled as capacitive loads.
The driving circuits for capacitive actuators need to deliver and recover (bidirectional) dominantly reactive power, unlike typical power electronics converters for resistive loads which deliver (unidirectional) real power to the load. Therefore, the circuits, operation, and optimization required to drive these capacitive loads differ from traditional DC-DC or DC-AC converter circuits that deliver real power.
Several DC-DC converter architectures have been explored to deliver reactive power to capacitive loads. Past works have been limited by efficiency, power density or voltage regulation. This thesis explores the use of hybrid DC-DC converters to drive capacitive loads where high voltage, high power (energy) density, and high efficiency are important. A hybrid converter merges a magnetic converter and a switched capacitor (SC) converter, using both capacitors and inductors as energy storage and energy processing elements. Hybrid converters leverage the benefits of magnetic converters to soft charge capacitive loads and to regulate the output voltage, and the SC converter benefits of efficient voltage conversion and use of high energy density capacitors. The hybrid topology explored in this thesis merges the multi-step inductive buck-boost converter and the multilevel series parallel SC converter. In this work, modeling, operation, optimization, and implementation of the hybrid soft charging converter are presented, highlighting its benefits as a pathway towards high power density converters for capacitive loads. The integrated circuit implementation of the hybrid converter designed in 180 nm SOI process is presented
Design and Manufacturing of Multifunctional Piezoelectric Composites
No full textPiezoelectric materials possess a unique ability to convert mechanical energy into electrical signals and have broad industrial applications. However, monolithic piezoelectric materials such as piezoceramics and piezopolymers often suffer from inherent trade-offs among mechanical strength, elasticity, and durability. Piezoelectric composites, typically consisting of a polymer matrix with ceramic reinforcements, offer a solution by combining the advantages of each constituent. Nevertheless, maintaining stable mechanical performance in high-temperature environments remains a significant challenge as conventional polymer matrices usually experience structural degradation.
In this thesis, a novel piezoelectric composite is developed using a preceramic polymer (PCP) matrix with barium titanate (BTO) inclusions. PCPs are silicone-based polymers that undergo a unique polymer-to-ceramic phase transition upon heating. The Digital Light Processing (DLP) 3D printing technique is employed to fabricate the composites. The resulting piezocomposites can withstand compressive stress up to 30 MPa and strain up to 20% without structural failure, even at 500 °C. Moreover, repeated thermal cycling enhances the effective longitudinal piezoelectric coefficient (d33) to 6.98 pC/N, a 2.36-fold improvement over single-cycle processing.
To enhance the piezoelectric response beyond the inherent limits of bulk materials, this thesis explores advanced architectural designs. Studies of piezoelectric energy harvesters (PEH) and metastructure-based pressure sensors (MBPS) indicate that controlling strain distribution and deformation mechanisms through architectural design is crucial for improving electro-mechanical performance.
Guided by these insights, a multifunctional compressible piezocomposite sensor (CPS) is developed. Its unique geometry enables high-performance acceleration sensing and dynamic force sensing within a single device – capabilities that are typically incompatible in sensors made from bulk materials. As a low-frequency, triaxial accelerometer, the CPS achieves a sensitivity up to 2628.1 mV/g with an operational frequency up to 18 Hz. As a dynamic force sensor, it demonstrates a sensitivity of 11.53 V/N over a force range up to 3.57 kN. Its extensive strain range (over 600%) also suggests potential for strain sensing. This dual-mode sensor overcomes the inherent sensitivity-range trade-off of conventional devices through its optimized geometry. In addition, its advanced material composition enables reliable performance at high temperatures. Together, these complementary attributes open new avenues for applications in robotics, aerospace, and biomedical technologies
The Role of the Orbitofrontal Cortex in Social Cognition: An Analysis of Betweenness Centrality and Functional Heterogeneity
No full textResearch into the role of the orbitofrontal cortex in social cognition has been dominated by lesion studies. While the OFC has been suggested to organize large neural networks and contribute to appropriate social behavior, this bias towards lesion studies fails to provide positive evidence of the specific function the OFC facilitates. This study utilizes iEEG high gamma data for an analysis of betweenness centrality in the OFC during a social task to bridge the gap in knowledge. The OFC is found to exhibit high centrality across the entirety of a social task as well as during the planning of communicative behavior in comparison to frontal control regions. Further exploration into the networks that the OFC organizes implicates a high frequency circuit connecting the OFC, middle temporal, and other frontal regions. These results provide insight into the network-level dynamics of the OFC and can be helpful in understanding the clinical implications of OFC loss of function.https://digitalcommons.dartmouth.edu/wetterhahn_2025/1006/thumbnail.jp
BOYS IN A BOX: A MIXED METHODS STUDY EXAMINING THE MASCULINITY OF BOYS IN A PRIVATE SCHOOL
Get PDFMy name is Shavar Bernier, and the title of my thesis is Boys in a box: mixed methods study examining boys\u27 masculinity in a private boarding school. I wrote the paper with guidance from my advisors and readers at Dartmouth, Mary Turco, Andrew Garrod, and Douglas Moody.
This mixed-methods study examined masculinity and how it was displayed at a private boarding school in Watertown, Connecticut. The purpose of the study was to use the experiences of students and teaching faculty to understand how masculinity was evident on Taft’s campus. The study participants consisted of 15 former students and forty-five teaching faculty, both past and present. Two primary research tools were used in this study. The first was a 21-question, semi-structured audio interview with the student volunteers. The second was a seven-question electronic survey completed by 45 faculty members.
The student interviews focused on each student’s unique experience at Taft. The primary purpose of the interview was to have male-identifying students discuss masculinity at Taft and how they believe masculinity is displayed on campus. During the interview, each student reflected on societal pressures and norms that could impact their behavior at Taft. The faculty survey focused on the classroom experience for all students but explicitly gathered insights about the education of male-identifying students concerning masculinity(ies).
The student interview findings showed that there exists a toxic form of masculinity on campus and that it is ingrained in mainstream culture. Furthermore, the
students are interested in learning more about masculinity as they believe education would encourage a healthy and positive expression of masculinity within school culture.
From the faculty perspective, the findings show that many teachers have experienced and witnessed displays of toxic masculinity in the classroom, the dorms, and other areas of campus. While this faculty sentiment was not unanimous, most agreed that negative expressions of masculinity cause harm to the larger community. Faculty do not formally educate students on masculinity through curriculum or workshops, despite many believing it would benefit the entire community
Hunting York
No full textIn HUNTING YORK, I used my research on the Amerindian slave-trade between 1715- 1740, and the French Indian Wars from 1740-1765, to paint a canvas of life on the Atlantic coast of North America. Following the escape of a male african captive from a fictional Muscogee village in the everglades, an Apalachee is hired to track him down as they travel north along the coast to an unknown destination. The entire story was not able to be finished in this thesis, however, I was able to highlight the most relevant parts of my research in the story that follows. Is the indication of a man’s respectability the value he brings to the community, or is it the danger he poses to the community; and does a man’s worth really matter in the end? As our protagonist, Hangs Around Fort, pursues York, he is confronted with the consequences of his evils committed long before our story begins. He justifies his actions as necessary for the survival of his clan in the face of colonialism, but begins to doubt as the world around him changes more and more, and as the hope of saving his people’s way of life begins to seem more and more impossible
AIMR-BRAINSTORM: AI-Enhanced Interactive Mixed Reality For Collaborative Ideation
Get PDFThis study investigates the potential of an AI-enhanced Mixed Reality (MR) brainstorming system, named AIMR-Brainstorm, in comparison to traditional sticky notes for creative ideation. By integrating real-time idea extraction through ChatGPT with immersive, physics-based visualizations, the system aims to transform analog brainstorming workflows into dynamic, interactive digital experiences. Using a within-subject experimental design, 30 participants engaged in paired brainstorming sessions with both AIMR and sticky notes. Quantitative measures of efficiency, engagement, creativity, and user satisfaction were collected through between-session and post-study surveys, while qualitative feedback provided additional insights into user experiences. Conclusively, while traditional sticky notes were generally preferred for their simplicity and perceived efficiency, AIMR significantly enhanced user engagement and creative output. Specifically, AIMR’s immersive elements, such as real-time word-to-idea visualization, interactive idea node linking, and physics-based interactions, were shown to elevate the brainstorming experience, although issues such as interface instability and suboptimal AI idea generation were noted. Users who favored AIMR consistently reported higher satisfaction and engagement, whereas those preferring sticky notes valued its ease-of-use and reliability. The study highlights the complementary strengths of both methods, suggesting that an ideal future brainstorming system would combine the intuitive simplicity of sticky notes with the innovative affordances of AI and MR
The Agricultural Contribution to the Land Carbon Sink in Northern New England: the Role of Deep Soil, Soil Fractions, and Carbon Flux
No full textAgricultural lands and managed grasslands cover a large portion of the Earth\u27s surface and serve as a critical interface between climate mitigation and food production. This dissertation investigates how farms in northern New England contribute to the terrestrial carbon sink by examining deep soil carbon stocks, carbon fractions, and carbon fluxes, across croplands and pastures. Using a combination of deep soil sampling, fractionation analyses, and eddy covariance measurements, we assessed how management and environmental factors influence carbon storage and persistence. First, measuring soil organic carbon (SOC) stocks to one meter soil depth across 12 Vermont pastures revealed that deep soils (below 30 cm) contained 30–50% of total SOC, emphasizing the importance of sampling beyond the surface. Surface SOC was a poor predictor of deeper carbon stocks, and accurate quantification required accounting for site-specific factors such as depth to bedrock, bulk density, and inorganic carbon—underscoring the need for direct, deep soil measurements. Second, soil fractionations from 196 agricultural fields across Vermont showed that improved soil health and perennial land use was positively correlated with both particulate and mineral-associated organic carbon (MAOC), with MAOC particularly responsive to management in certain soil textures. This demonstrates the potential to enhance persistent carbon sequestration through soil health practices. Third, establishing and using an eddy covariance tower on a rotationally grazed pasture in southern Maine, we quantified carbon fluxes while monitoring weather and grazing of cows. The pasture was a modest net carbon source for two years, with carbon uptake highest during moderate weather conditions and with carbon release directly after grazing. These results underscore the need for context-specific strategies to balance carbon and productivity goals. Overall, the findings of this dissertation suggest that climate mitigation and agricultural productivity can be mutually supportive, and that maintaining photosynthetically active agricultural landscapes can support both goals
STRUCTURAL AND FUNCTIONAL LESSONS LEARNED ABOUT REGULATION OF ENTEROTOXIGENIC E. coli VIRULENCE REGULATORY FACTOR, RNS
Get PDFAntibiotic resistance has exacerbated the global health crisis of diarrheal diseases caused by enteric bacterial pathogens. Investigating pathogens, such as Enterotoxigenic Escherichia coli (ETEC) and Vibrio cholerae (cholera), helps to uncover mechanisms for the inhibition of virulence gene expression. A notable member of the AraC transcription factor family in ETEC, Rns, regulates virulence factors including pili and fimbriae, which are essential for adherence and colonization of the intestinal epithelial layer. This microbe–host interaction initiates the release of toxins, leading to the water and ion loss in clinically diagnosed as diarrhea.
In the canonical N-terminal domain of Rns, mutagenesis of the binding pocket confirmed that residues R75 and H20 are crucial for coordinating the carboxylate head group of decanoic acid, an inhibitor of Rns activity. Pocket-filling mutations I14F and I17F reduced the pocket volume, blocking binding of the decanoic acid observed in the wild-type RnsWT. Additionally, disruption of the dimerization interface by mutagenizing Y139 prevented pi-pi stacking interactions with residue Y139 of a nearby protomer, resulting in monomeric RnsY139E in solution. The 2.1Å X-ray crystal structure of Rns reveals new interactions between residues E139 and K143 across the crystal lattice, giving rise to a dimer in the crystal. In RnsWT, however, K143 forms a salt bridge with the neighboring protomer residue E121.
Crystallographic studies probing the DNA-binding domain, in the presence of a CS3 promoter sequence containing sticky ends, produced an approximately 3.4Å diffracting crystal with a longer unit cell, consistent with other protein–DNA co–crystal unit cells, suggesting the possible presence of DNA. Preliminary analysis of the complex structure, solved by molecular replacement, suggests that DNA might be present.
Together, this body of work establishes key residues involved in Rns inhibition and advances understanding of the mechanistic inhibitory pathways of AraC–VRs