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Firn Velocity Structure from Distributed Acoustic Sensing on Thwaites Eastern Ice Shelf, Antarctica
No full textThis study presents a Distributed Acoustic Sensing (DAS) investigation of the firn structure on Thwaites Eastern Ice Shelf (TEIS), a critical and rapidly evolving region of the West Antarctic Ice Sheet. TEIS is vulnerable to both oceanic and atmospheric changes and thus has the potential to be one of the largest contributors to sea level rise. Given the accelerated thinning and anticipated detachment from its pinning point, understanding the structural integrity of TEIS is paramount for predicting the future stability of Thwaites Glacier. A 340-meter horizontal DAS experiment was deployed at the Automated Meteorology Ice Geophysics Observation System III station on TEIS as part of the International Thwaites Glacier Collaboration. Both active and passive seismic energy were recorded to develop 2D P- and S-wave velocity models of the firn column. These models aim to provide high-resolution estimates of firn depth and identify velocity heterogeneities indicative of variations in structural and physical properties, including potential ice lenses and melt features. The results demonstrate the efficacy of DAS in acquiring high-quality seismic data in the cryosphere. The derived velocity models generally agree with firn depths and velocities estimated with other geophysical techniques on Antarctic ice. The resulting S-wave velocity model constrains the pore closeoff depth to 45-55 m and shows the presence of sharp vertical velocity gradients. The P-wave model, with its higher sensitivity to fluid content, provides a more detailed view of potential heterogeneities, including an observed high-velocity anomaly. This study highlights the potential of DAS as a rapidly deployable method for characterizing 2D firn structure over large distances. This study contributes to a better understanding of the processes that may influence Thwaites’ stability and vulnerability to collapse
Writing an Annotated Bibliography - Handout
No full textThis document provides information on annotated bibliographies and their uses
IDENTIFICATION AND QUANTIFICATION OF QUINONES IN ENVIRONMENTAL SAMPLES
No full textQuinones represent an important class of compounds, widely recognized redox-reactive organic substances in natural organic matter (NOM). Despite their critical importance in biogeochemical cycles, degradation of pollutants, and greenhouse gas (GHG) emission, their precise structure and abundance in environmental samples have puzzled environmental geochemists for decades due to the complexity of environmental samples. To tackle the grand challenge of identifying and quantifying quinones, this study aimed to: 1. Develop a chemical tagging method for quinone identification; 2. Identify quinones in complex environmental samples by integrating chemical tagging with metabolomic analysis; 3. Screen and isolate quinones through coupling chromatography separation with redox reactivity screening; and 4. Establish a method for quantifying the total quinone concentrations in environmental samples. A selective chemical tagging method for quinones was developed by using Michael addition reactions with cysteine (Cys) and cysteine-containing peptides (CCPs), and validated by UV and mass spectra (MS) analysis using model quinones. Quinones in biochars were identified by coupling chemical tagging with Cys and/or CCPs to metabolomic analysis based on high-performance liquid chromatography-high resolution tandem mass spectrometry (HPLC-HRMS/MS) analysis. Total quinones in water extraction of environmental samples were measured by integrating specific tagging with non-aromatic CCPs with size exclusionary chromatography (SEC) analysis. Analysis of Swiss biochar shows a diverse pool of quinones (390 candidates) tagged with Cys or CCPs. Benzoquinone and methyl-p-benzoquinone were confirmed, and additional high-confidence candidates include C7H6O5, C11H10O3, C12H12O3, and C12H12O4. Redox reactivity screening-based chromatography separation isolated new quinones with two quinone functional groups, i.e., doxorubicin derivatives. From quinone quantification analysis, pyrogenic carbon from wildfires showed three times higher quinone concentration (1 – 14 μM) and reactivity than background soils. In summary, this study developed innovative methodologies for identifying quinones and quantifying their concentrations in complex environmental media. These methods identified the chemical structures of quinones in complex biochar extracts, and novel quinones were isolated. Future investigations using the methods developed herein may replace the enigmatic black box of redox-reactive NOM with compounds characterized by their structures and concentrations
Two-Dimensional van der Waals Bilayer Heterostructure Towards Band-to-Band Tunneling and Photocatalytic Water Splitting Applications
No full textThe potential of van der Waals (vdW) heterostructure to incorporate the outstanding features of stacked materials to meet various application requirements has drawn considerable attention. According to the band alignments, vdW heterojunctions can be divided into three types: type I (straddling), II (staggered), and III (broken-gap). In this dissertation, three novel vdW bilayer heterostructures with staggered and broken-gap band alignment are proposed based on layered gallium oxide (Ga2O3), silicon carbide (SiC), germanium carbide (GeC) and aluminum nitride (AlN) by means of first principles density functional theory. The exceptional quantum tunneling mechanisms of type-III heterostructures make them a promising design strategy for tunneling field-effect transistors. A unique Ga2O3/SiC vdW bilayer heterostructure with inherent type-III broken gap band alignment has been revealed through first-principles calculation. Due to the overlapping band structures, a tunneling window of 0.609 eV has been created, which enables the charges to tunnel from the VBM of the SiC layer to the CBM of the Ga2O3 layer and fulfills the required condition for band-to-band tunneling. External electric field and strain can be applied to tailor the electronic behavior of the bilayer heterostructure. Positive external electric field and compressive vertical strain enlarge the tunneling window and enhance the band-to-band tunneling (BTBT) scheme. Under external electric field as well as vertical and biaxial strain, the Ga2O3/SiC vdW hetero-bilayer maintains the type-III band alignment, revealing its capability to tolerate the external electric field and strain with resilience. All these results provide a compelling platform for the Ga2O3/SiC vdW bilayer to design high-performance tunneling field effect transistor.
Besides, the structural, electronic and optical properties of a novel SiC/AlN vdW bilayer heterostructure have been systematically investigated through first-principles calculations. Notably, the heterostructure presents an inherent type-II band orientation wherein the photogenic holes and electrons are spatially separated in the SiC layer and the AlN layer, respectively. Our results indicate that the SiC/AlN heterostructure occupies a suitable band-gap of 2.97 eV, straddling the kinetic overpotentials of the hydrogen and oxygen production reactions. The heterostructure has an ample absorption profile ranging from the ultraviolet to the near-infrared regime, while the absorption intensity reaches up to 2.16×105 cm-1. In addition, external strain modulates the optical absorption of the heterostructure effectively.
Moreover, this dissertation reports the intriguing potential of a novel 2D van der Walls hetero-bilayer consisting of GeC and AlN in the photocatalytic water splitting method to generate hydrogen. The GeC/AlN heterostructure has an appropriate band gap of 2.05 eV, wherein the band edges are in proper energetic positions to provoke the water redox reaction to generate hydrogen and oxygen. The type-II band alignment of the bilayer facilitates the real-space spontaneous separation of the photogenerated electrons and holes in the different layers, improving the photocatalytic activity significantly. Analysis of the electrostatic potential and the charge density difference unravels the build-up of an inherent electric field at the interface, preventing electron-hole recombination. The ample absorption spectrum of the bilayer from the ultra-violet to the near-infrared region, reaching up to 8.71×105 /cm, combined with the resiliency to the biaxial strain, points out the excellent photocatalytic performance of the bilayer heterostructure. On top of rendering useful information on the key features of the GeC/AlN hetero-bilayer, the dissertation offers informative details on the experimental design of the van der Walls bilayer heterostructure for solar-to-hydrogen conversion applications
Analysis of Favorable Structural Settings and Step-Overs in Normal Fault Systems in the Great Basin Region: Implications for Geothermal Exploration and Development
No full textThe Great Basin region (GBR) in the western U.S. may host vast amounts (~10 GWe) of undiscovered geothermal resources. Although ~39% of the known geothermal systems in the GBR lack visible hot springs or fumaroles, up to 75% of the geothermal resources in the area may be blind or hidden. Nearly all geothermal systems in the GBR reside in six types of favorable structural settings, including normal fault terminations, step-overs (i.e., relay ramps) in normal faults, fault intersections, accommodation zones, displacement transfer zones whereby strike-slip faults end in arrays of normal faults, and pull-aparts in strike-slip fault systems. Although the affinity between geothermal systems and these structural settings is widely known, little research has been conducted to distinguish which geometries of a particular structural setting are more conducive for geothermal activity. Distinguishing the most favorable geometries is crucial to improving exploration strategies for hidden systems, selecting optimal drilling targets, and increasing the efficiency of existing power plants. Through field observations, Quaternary fault data, LiDAR, and regional geophysical surveys (e.g., gravity, magnetics, and magnetotellurics), a detailed inventory identified 1,087 favorable structural settings within the GBR. Step-overs in Quaternary normal fault zones are the most common favorable structural setting identified in the GBR, accounting for ~42% (454) of all settings. Complex fault geometries within the step-overs, including multiple minor faults connecting the major overlapping fault strands, enhance permeability and generate efficient pathways for hydrothermal fluid flow. Step-overs are common in normal fault zones, and thus it is difficult to distinguish which step-overs might host a blind geothermal system. However, step-overs come in a variety of geometries depending on the relative overlap, underlap, and spacing between the major fault strands. In addition, the geometry of the minor faults that breach the step-over can vary from relatively major oblique-slip faults that directly connect the major fault strands to systems of en échelon faults that parallel the major fault strands. Step-overs were therefore further classified based on orientation, sense of stepping (right vs. left), amount of overlap and spacing between main fault strands, and linkage style (hard vs. soft). Of the step-overs identified, ~54% are right stepping, ~51% hard linked, and ~50% are underlapping. Relay ramp width ranged from 0.1-14.6 km, with an average of 2.8 km. Step-overs associated with higher-temperature (>120°C) geothermal systems are ~56% right stepping, ~70% hard-linked, ~56% overlapping, and ~74% lie between fault strands oriented north to north-northeast. Average relay ramp width for these higher-temperature step-overs is 3.3 km. Producing systems (i.e., contain operating power plants) in step-overs preferentially step left (~64%), are hard-linked (~73%), overlap (~55%), and have an average relay ramp width of 3.4 km. These data suggest that higher-temperature systems favor left-stepping, overlapping, hard-linked geometries in the GBR. Step-overs with hard-linked and overlapping fault strands have relative high densities of fractures, faults, and fault intersections, all of which serve to enhance permeability. Additional structural complexity provides subvertical conduits of enhanced permeability that facilitates transport of hot fluids from greater depths. These attributes combined with faults optimally oriented to experience dilation in the current stress field provide long-lived permeable pathways that can host higher-temperature geothermal systems. This information will aid in more efficient exploration of hidden geothermal systems across the GBR
EXPLORING THE USAGE OF LITHIUM MINING TAILING CLAY (LMTC) IN CONSTRUCTION MATERIALS
No full textAsphalt binders and Portland cement are the most expensive constituents in paving materials. Efforts to reduce costs while minimizing the carbon footprint have driven research into alternative materials. This preliminary study explores the properties of asphalt binders and Portland cement concrete mixtures modified with varying percentages of lithium mining tailing clay (LMTC), a by-product of lithium extraction. LMTC was also evaluated as a substitute modifier to calcium carbonate (CaCO3) in air-blown binders. To prepare the LMTC-modified binders, a mechanical mixer set at 5000 rpm was used, and the optimal mixing time was determined. Asphalt binders with performance grades (PG) 58-28 and 64-28M were blended with four different percentages of LMTC. Similarly, the air-blown binder was modified with two percentages of LMTC and CaCO3. The rheological properties of the modified binders were analyzed, and the results showed that LMTC and CaCO3 decreased the penetration values and increased the viscosity. Performance tests such as the IDEAL CT and Hamburg Wheel Tracking Tests (HWTT) showed that LMTC enhanced rutting resistance but reduced cracking resistance. Dynamic Shear Rheometer (DSR) testing indicated improvement in the PG, leading to higher resistance to permanent deformation.
The use of LMTC in concrete mixtures was also investigated by substituting a portion of cement with LMTC at three different percentages. Tests were conducted to evaluate the concrete slump, compressive, and flexural strength. Results showed that increasing LMTC content decreased compressive strength and slump height. However, the flexural strength for the 5% LMTC concrete mix was comparable to the control mixture and increased slightly at higher LMTC levels.
Overall, the findings highlight the potential use of LMTC as an alternative material in asphalt binders and concrete mixtures with promising effects. However, further optimization is needed to balance performance. Once performance enhancements are achieved, it will be essential to quantify the environmental benefits through a comprehensive evaluation, ensuring its contribution to sustainable paving materials
AI Integration in Higher Education: A Content Analysis on AI Sophistication and Student Outcomes/Skill Development as Reported in Empirical Studies (2019-2024)
No full textThis study investigated the integration of Artificial Intelligence (AI) in higher education to enhance student outcomes, focusing on AI complexity, student outcomes, and effect sizes. Through a content analysis of 47 peer-reviewed empirical articles from 2019 to Mid 2024, the research identified various AI applications, including chatbots, ChatGPT, Intelligent Tutoring Systems (ITS), virtual reality, augmented reality, language bots, writing bots, and recommender and search engines. The significant distribution of effect sizes across the four categories (small, medium, large, not reported) suggests that the impact of AI on learner outcomes is diverse, indicating that while some AI applications have a substantial impact, others have a more modest effect. The lack of a strong association between AI complexity and student outcomes underscores the necessity for a comprehensive approach to AI integration in education, where the focus is not just on the technology but on how it is used to support teaching and learning practice. The study concluded that contextual factors may significantly impact the relationship between AI complexity and student outcomes. These factors include (a) AI-related elements such as the user interface and adaptability, (b) teacher-related aspects like AI literacy and training, (c) student-related components including prior knowledge and motivation, and (d) technology-related factors such as infrastructure, resources, and support systems. Understanding these factors is essential for assessing the impact of AI complexity on student outcomes and informing effective strategies for AI integration in education. A balanced, quality-driven approach to AI integration is essential for optimizing its benefits in all learning modalities
Pd-Ag Catalyzed Aza-Piancatelli Reaction: From Synthesis to Mechanistic Investigations
No full textThis work demonstrates a cocatalytic approach using Pd(OAc)2 and AgSbF6 at room temperature for synthesizing trans-substituted cyclopentenones derivatives utilizing the Piancatelli reaction. The methodology resulted in a broad substrate scope across ortho-substituted anilines but shows limited reactivity with para-substituted anilines at room temperature. Oxygen nucleophiles were found to be unsuccessful. At elevated temperature of 80°C, para-substituted anilines showed improved reactivity with silver catalyst alone being sufficient for the transformation. The possibility of dual mechanistic pathways was explored, one requiring both palladium and silver at room temperature and another involving only silver at an elevated temperature of 80°C. Particularly for the electron-rich substrates at high-temperature conditions the formation of Friedel-Crafts product as a byproduct is observed. The third chapter examines the nature of catalysts used in the current work. As no single definitive experiment could conclusively differentiate between homogeneous or heterogeneous catalysis, multiple tests were conducted to investigate the nature of catalysis in a Pd-Ag co-catalyzed system and suggested the possibility of a homogeneous catalytic system. To further reveal insights into the mechanism of the reaction, two analytical methods ReactIR and GCMS reaction monitoring were explored in chapter 4. While the ReactIR studies proved unsuccessful due to metallic deposition on the probe and baseline drift in spectra, further GCMS based investigations revealed the presence of an N-substituted intermediate. At elevated temperature, a faster reaction rate was observed compared to room temperature. The Hammett plot analyses resulted in a non-linear relationship at room temperature. Although at an elevated temperature, more linear trends were observed, revealing further clues into the intricate mechanism of the proposed reaction. This research provides insights into transition metal-catalyzed heterocycle synthesis and opens new directions for methodology development
Understanding the Timing and Extent of Glaciers in the El Tatio Geothermal Field During and Prior to the Last Glacial Maximum Using Cosmogenic Dating
No full textThe Chilean Atacama-Altiplano, in the subtropical Andean Region, is an elevational plateau of >4000 masl, but the current annual precipitation is too low (e.g., <100 mm/yr) to sustain glaciers. However, geomorphic evidence including moraines indicates the past presence of alpine glaciers in the area. Previous studies exist in Chile and nearby Bolivia, but the datasets are still too limited to produce good glacial chronologies. Additionally, in South America and elsewhere, it is still uncommon to find dateable reconstructions of alpine glaciers before Marine Isotope Stage 2 (MIS 2 ~29 ka to 14 ka). In order to advance the understanding of past glaciations in the subtropical Andes, we collected 14 samples from andesite boulders of at least 3 well-preserved moraines from the El Tatio Geothermal Field in the Chilean Altiplano (~21-23॰S, ~68-69॰W). For constraining the ages, we utilized 3He cosmogenic dating in pyroxene, a well-established method, which is not a common practice for the subtropical Andean Region. Our results show at least three stages of glacial expansion in the El Tatio area ca. 22-30 ka (MIS 2), 58-59 ka (MIS 4), and 155-200 ka (MIS 6). Considering other glacial chronologies and paleoclimatic proxies in the Andes, our ages align well with climatic cold stages. Additionally, although prior research in other parts of South America have typically identified glacial expansions during MIS 2 and MIS 4, our data reveals evidence of a previously underexplored glacial expansion during MIS 6. Our research focuses on dating moraines in the arid, subtropical Andes, offering valuable insights into the timing and extent of glaciation, which can enhance paleoclimate reconstructions in the Southern Hemisphere. This work assists with future research on the local effects of glacial accumulation and retreat in and around the El Tatio Geothermal Field
Land Lines
No full textI like to tell stories through undervalued materials. In Land Lines I created sculpture and installations from found objects and obsolete technologies to explore the costs of our relentless drive to solve problems via technology. My exhibit used reclaimed utility posts, industrial wool insulation batts, hand processed wool, analog telephones, photos, upcycled furniture, and many found objects. The first gallery room contained large sculptures ("Land Lines," "Unknown Caller" and "Disconnected") and an installation of sand and large format b&w digital photos printed on plain printer paper displaying tracks and traces of animals at the Nevada giant sand dunes: Sand Mountain, Lava Dune and Big Dune ("Hourglass"). The middle gallery room "Busy Signal", was an installation of noisy, obsolete analog telephones and other communication devices surrounding a floor to ceiling sculpture made of stacked industrial wool insulation batts and braided wool. "Listening Lounge," a performative installation and community space, filled the final room, and female-identifying visitors read aloud from female writings in the areas of natural science, history and art. A female "silent reader" also read constantly in the room. The Listening Lounge contained books related my research, carpets, mounted plant specimens, and a selection of scarab beetle specimens. I work to create impactful installations that engage my viewers. I direct my viewers' path, and envelop the viewer in artwork throughout the exhibit. Viewers were encouraged to touch, explore and play with the elements of the exhibit, especially the analog phones, which rang constantly and enabled visitors to communicate between rooms.Our personal and collective histories are not only transmitted by our communication tools but shaped by them. Once we phoned, corresponded, and read the paper; today we text, follow, and stream. We measure the mysterious mycorrhizal exchange of trees and record the songs of bats, birds, and whales and their full meanings elude us. We struggle to make deep connections with each other despite a growing rubbish pile of promising devices. My project Land Lines questions the cost of our relentless drive to solve communication problems via technology and explores the value of embodied communication. Does a human touch add meaning to communication? I embrace the handmade, engage directly with the more than human world. I hike sand dunes examining tracks and traces. I wash, card, felt, braid, and dye raw wool. I collect objects that are forgotten but not gone, and I join all these stories with mine. Low tech processes and materials connect me to other histories, communities, and traditions. Communicating well is neither quick nor easy. Some voices of human and more than human communities are soft, even mysterious. Yet meaning is made, since long before cables gridded the sky, landscape, and ocean floor. I invite viewers to slow down, listen carefully, and consider the complexity of communication, perhaps even make some new connections