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Mesozoic-Cenozoic broken foreland basin evolution in Northern Patagonia, Argentina (~42-48°S) : integrating sedimentation, magmatism, and subduction dynamics
Get PDFThe Andean retroarc basin between 42-48°S is enigmatic in its structural configuration and early development. The ‘Patagonian broken foreland’ hosts basement blocks >500 km inboard the trench. Here, Andean shortening was accommodated across much of the upper plate, possibly in response to flat slab subduction. This work interrogates conflicting hypotheses on the tectonic evolution of the region, including: the subsidence mechanism that accommodated >8 km of Cretaceous sediment; the timing of broken foreland development and initial Andean shortening; and if transitions in shallowing and resteepening of the down going slab drove deformational conditions and broken foreland basin development. Low shortening (<20 km) in the region preserves the record of (1) Andean arc magmatism used as a proxy for subduction dynamics and (2) the earliest stages of broken foreland basin and fold-thrust belt development. A basin analysis and sedimentological approach is used to evaluate the drivers and earliest stages of Andean orogenesis in northern Patagonia.Earth and Planetary Science
Determining soil water and soil organic carbon storage patterns using InSAR in the Arctic Foothills, Alaska
Get PDFPermafrost stores twice the amount of carbon (C) found in the atmosphere. As the temperature rises in the Arctic , thawing of permafrost may enhance subsurface storage and flow of waters and release huge amounts of previously frozen C within the cryosphere to the hydrosphere and atmosphere, exacerbating climate change. However, studying the remote permafrost region using limited field measurements is difficult, and my goal is to advance the application of satellite remote sensing, specifically Interferometric Synthetic Aperture Radar ( InSAR ) techniques, for observing and characterizing permafrost hydrology and C dynamics. This study focuses on determining the relationship between InSAR -observed thaw subsidence and physical and chemical properties of the active layer soils. I developed an InSAR processing strategy for estimating surface deformation associated with the freeze-thaw process over permafrost terrain. This algorithm effectively retrieved two signals of deformation: the long-term subsidence trend caused by an in crease in the soil surface layer water storage over multiple years and the seasonal deformation related to the annual freeze-thaw cycle. The algorithm is robust even when only a limited number of radar acquisitions are available. Additionally, I assessed and quantified InSAR measurement errors, including orbital errors, decorrelation, tropospheric noise, and DEM errors. To validate and calibrate the InSAR seasonal surface deformation observations, I developed a stochastic method to assimilate filed data, and robustly characterized the regional statistics of Arctic soil properties. This allowed us to jointly analyze field and remote sensing observations acquired at very different scales. This study is the first analysis that integrates spaceborne InSAR deformation data with a large number of field measurements that contain relevant information on water -holding capacity. This allowed showing that the amplitude of the maximum seasonal thaw subsidence is proportional to the soil water equivalent depth in the active layer near the end of the thaw season. Based on this finding, I mapped regional soil water equivalent depth in the soil surface layer over a 6500 km² region around the Toolik Field Station on the North Slope of Alaska with a spatial resolution of ∼ 100 meters using InSAR . Furthermore, several years of fieldwork led to a large and methodologically consistent dataset on the amounts of C stored in the Arctic surface soil layer, allowing a regional estimate of soil organic C storage for the soil surface layer of the entire Arctic Foothills region of Alaska . Estimates show that the permafrost active layer (usually < 1 m depth) stores as much C as previously estimated for deeper permafrost. Because the seasonally-thawed surface soils in Arctic landscapes are currently vulnerable to climate change, more C may be lost to the atmosphere in pulse disturbances such as fire or the rmal erosion. My research also analyzed the relationship between thaw subsidence and soil environmental properties, particularly soil C content. I demonstrate that the thickness of the second soil surface layer, known as the catotelm, is the most important layer in predicting the magnitude of thaw subsidence and serves as a strong indicator of the amount of soil C content.Aerospace Engineerin
Bimanual coordination classification, influence, and haptic augmentation for human-operated robotic systems
Get PDFBimanual coordination is an intrinsic feature of human behavior and a critical element in the design of intelligent, human-operated robotic systems. From upper-limb exoskeletons to surgical robots, the coordination of an operator’s bimanual limbs can determine task performance and training. Bimanual coordination is a well-studied topic of human motor control; however, researchers have yet to fully leverage it in human-operated robots to monitor and augment bimanual tasks. A primary reason for this gap is the lack of mathematically objective and comprehensive taxonomies of bimanual coordination. Such a taxonomy would generalize to many bimanual tasks, correlate with human performance, and lend itself intuitively to robotic augmentation. To bridge this gap, this dissertation is split into three aims. Aim (1) produces a rigorous, high-level classification of bimanual coordination based on kinematics and geometric properties. We devise metrics to classify movements continuously and in near-real time according to sequence, scaling, number of targets, direction, and symmetry. We then validate the classification on data from a 2D bimanual path following experiment and show extended applicability to data from robotic surgical training tasks. Results show important overlap within classes of bimanual coordination, high classification accuracy by using statistical methods, and task-specific coordination labels for surgical gestures and surgical expertise. Aim (2) evaluates performance of bimanual motor tasks as related to the taxonomy by using three outcome measures that reflect movement accuracy and smoothnessthe correlation. We also evaluate several kinematic, human-centric measures, similar to biomechanical signals, to aid in classification. Results show human-centric measures may inform bimanual movement classification in systems with limited sensing and the interaction of bimanual coordination factors has greater effect on performance outcomes. Aim (3) implements virtual, bimanually-dependent haptic forces in robotic systems to shape bimanual movement for improved performance or training. Haptic forces include virtual springs and dampers set between the hands to resist deviation from classes of bimanual movements. Results show improved movement shape for bimanual path following and improved temporal-efficiency for a surgical training peg transfer task. This aim highlights the intuitiveness of the bimanual taxonomy for robotic-augmentation development. Moreover, the work of this dissertation may impact and improve the design and control of human-operated robotic systems for bimanual motor performance.Mechanical Engineerin
Optimizing instrument signal to quantify urban volatile compound concentrations and emission sources
Get PDFUrban air pollution is incredibly complex, with thousands of trace gases (volatile organic compounds, VOCs) being formed by direct emissions and photochemical processes, and removed by regional wind transport, chemical transformations and deposition. VOCs are pre-cursors to ground-level ozone and secondary organic aerosol which have known human health effects and are of regulatory importance in the United States. As tailpipe emissions have decreased, other emission sources in urban areas have gained importance over the last few decades. The vast array of emission sources and urban air chemistry are still poorly characterized. This uncertainty is due to the lack of sufficiently resolved data in urban regions and due to challenges in nontargeted VOC real-time measurements. Specific challenges include compound attribution of ions in chemical mass spectrometry techniques used to measure urban VOCs due to potential effects from fragmentation and clustering processes within the ion-molecule reactor. To characterize and control for the fragmentation and clustering tendencies of chemical ionization mass spectrometry (CIMS), I measured a constant concentration of a 14-compound gas standard tank with a Vocus proton transfer reaction time-of-flight mass spectrometry (Vocus PTR-ToF-MS) in both H₃O⁺ and NH₄⁺ ionization modes and automatically varied voltage and pressure parameters, which caused substantial changes in ion sensitivity. NH₄⁺ mode resulted in a higher signal for oxygenated compounds although other compound classes had poorer detection. Using the Vocus PTR-ToF-MS in field measurements, I conducted three mobile VOC measurement campaigns around central Austin, TX. The Vocus captured many plumes, often from tailpipe emissions but also from personal care products, cooking and other sources. To find novel emissions sources and compounds being emitted, I developed an approach to compare the VOC mobile GPS data with proximity to buildings with suspected emission sources such as restaurants, bars, and gas stations. I found that urban emission sources are very complex, but overall my approach was able to confirm the presence of specific VOC profiles including various chemical classes such as carbonyls and acids related to specific emissions across the study domain. To investigate the fate and reactivity of VOC concentrations in an urban environment, I conducted field measurements at a rooftop site in Manhattan, New York City. I proposed bulk emission sources of some compounds by evaluating measured concentrations with respect to wind directions and found that concentration profiles of VOCs in Manhattan differed from past campaigns in other urban areas due to the magnitude of fresh emissions detected. I also compared Manhattan concentrations of VOCs and other pollutants such NOx and CO to EPA PAMS sites in the Bronx and Flax Pond. By calculating the summed OH reactivity and SOA potential contributed by VOCs, I found that oxygenates are a major part of Manhattan’s OH and SOA potential budget.Civil, Architectural, and Environmental Engineerin
On the boundaries of STEM makerspaces
Get PDFMakerspaces are an increasingly popular venue for informal, opt-in, STEM educational experiences, and many have lauded their potential to increase student engagement within STEM (e.g., Martin, 2015; Roldan et al., 2018). However, STEM is a domain in which non-dominant populations have been repeatedly denied equitable experiences, and makerspaces may be another STEM space that recreates and reinforces this marginalizing environment. Scholars have critiqued the modern movement as a white, male, middle-class pursuit and have warned against an uncritical adoption of the narrow, STEM-oriented, techno-centric framing of making activities (e.g., Vossoughi et al., 2016; Worsley & Bar-El, 2020). Following these critiques, I investigate perceptions of making and makerspaces amongst undergraduate students who do not visit the space. Specifically, I explore why some STEM students choose not to visit makerspaces by asking: 1. How do students describe the visual design of a STEM makerspace in relation to their interest in visiting the space? 2. What repertoires of practice do students see as valid within a STEM makerspace? 3. How do students decide whether to cross the boundary into a STEM makerspace? To answer these questions, I interviewed students on the boundaries of a STEM makerspace about their perceptions of making, view of the makerspace, and their interest in visiting the facility. I found evidence supporting the critiques of the modern making movement throughout my dataset. Most students have a narrow definition of making that is restricted to creating something physical. Students differentiate between practices they see as “more technical” and more “artsy craftsy,” positioning the latter as lesser than or not appropriate within the bounds of a STEM makerspaces. This perception that certain practices are not validated in the makerspace acts as a barrier towards participation for many students, regardless of if they have prior experiences with making practices. Even if students do engage with the makerspace, they can face marginalizing experiences there that influence their interest in further participation and mediated the forms in which they were willing to engage with other makerspace participants. Implications for expanding and validating forms of making practices not currently valued in STEM spaces are discussed.Science, Technology, Engineering, and Mathematics Educatio
Advanced control of roll-to-roll mechanical dry transfer
Get PDFRoll-to-roll (R2R) manufacturing enables continuous, high-throughput processing of flexible substrates used in technologies such as printed electronics, energy storage devices, and two-dimensional (2D) materials. Within this framework, R2R mechanical dry transfer is an efficient, eco-friendly transfer method, where materials are continuously peeled and transferred between webs without the need for solvents or other liquids. Despite its advantages, this process presents substantial control challenges due to the strongly nonlinear dynamics at the peeling interface, sudden variations in adhesion energy, and abrupt transitions in material properties—especially when dealing with patterned materials or devices. Achieving uniform and defect-free transfer requires precise regulation of web tension and peeling geometry, as even small deviations can significantly degrade transfer quality.
Existing control approaches for R2R mechanical dry transfer rely on simplified linearized models that overlook critical nonlinear effects, parameter uncertainties, and actuator constraints. Consequently, these methods often fail to maintain robust performance under varying operating conditions or when processing patterned substrates, where adhesion and tension dynamics can change abruptly. The lack of control frameworks capable of systematically handling these complexities limits both the precision and scalability of R2R mechanical dry transfer, representing a major obstacle to its adoption in high-yield industrial manufacturing environments that demand consistent material quality and process reliability.
This dissertation develops a unified control framework to address the nonlinear, uncertain, and constrained nature of the R2R mechanical dry transfer process. The proposed methods include: 1) Full-state feedback control using linear differential inclusion (LDI) modeling to manage nonlinearities and uncertainties, 2) switched-system control for patterned materials using an uncertain almost periodic piecewise linear system (APPLS) framework to capture abrupt changes in adhesion and system dynamics, 3) a nonlinear model predictive control (MPC) strategy that incorporates input constraints and peeling pattern predictions for real-time control, 4) a repetitive learning MPC (RLMPC) strategy that leverages the repetitive nature of some peeling processes to match the performance of the full nonlinear MPC over successive cycles while substantially reducing computational cost, and 5) an iterative learning control (ILC) strategy for sequential transfers of identical samples, achieving MPC-level performance with minimal online computation. Collectively, these methods establish a scalable foundation for high-precision control of R2R mechanical dry transfer, substantially enhancing process stability, repeatability, and material quality.Mechanical Engineerin
Improvement and applications of field seismic SASW testing and investigation of the influence of water content changes on small-strain dynamic rock properties using laboratory free-free testing
Get PDFThe importance of seismic field and dynamic laboratory measurements in geotechnical engineering is undeniable. The dynamic parameters determined from these testing methods are used as key parameters in earthquake analyses and as essential data for characterizing the stiffnesses of geotechnical sites. Therefore, to enhance our understanding of geotechnical sites, improving the measurement techniques and increasing the applications in both seismic field testing and dynamic laboratory testing are very important. The Spectral-Analysis-of-Surface-Waves (SASW) method is a field testing method involving surface waves. This method is cost effective compared to other methods due to the nonintrusive and nondestructive characteristics of the method. Traditionally, SASW testing has been performed in only one direction to determine Vs profiles at sites. However, the measurement can be improved by performing an additional set of tests in the reverse direction at the same site with only a small increase in cost. The first part of this research introduces and discusses the benefits of the improved SASW method, using a case study performed on the crest of a dam. The SASW testing has accomplished very powerfully also cost-effective works at various geotechnical sites. For example, the SASW testing was performed to identify a vulnerable location for dam repair, estimate the burial depth in landfills, provide basic parameters for earthquake modeling. Furthermore, in this second part of the research, the SASW testing was performed on the differently compacted embankment as one of the application examples. The SASW testing was performed to evaluate the compacted embankment and to understand the natural ground of the site, and testing results at this site are presented and discussed. The last part of this research focuses on the influence of changes in water content on small-strain dynamic rock properties using free-free testing, which has not been effectively considered in the previous testing. Changes in the material damping ratios and Poisson’s ratio values due to the changes in the water content are mainly discussed. The water influence is a significant factor in small-strain dynamic rock properties measurements. The influence of the water was studied using free-free testing on the 23 different rock samples.Civil, Architectural, and Environmental Engineerin
Chemical solutions to concrete durability problems
Get PDFGiven recent changes in energy production that have significantly reduced the availability of fly ash, there is an increasing need for alternative materials that can provide similar levels of durability performance as fly ash. The objective of the project was to evaluate the use of commercially available chemical admixture products in improving concrete durability. Numerous products were tested across the major durability issues including corrosion of reinforcing steel, classical sulfate attack, delayed ettringite formation, and alkali-silica reaction. Testing parameters investigated included early-age hydration, compressive strength, expansion, electrical resistivity, corrosion potential, chloride diffusivity, and surface sorptivity. Lab samples included accelerated forms of testing to assess performance more quickly, while corresponding field samples were also cast to provide valuable long-term data and to correlate results with lab samples. This study found that some of the chemical admixtures evaluated improved the durability of concrete, while others were found to have insignificant impacts -- none of the products tested were able to achieve all the benefits imparted by Class F fly ash.Civil, Architectural, and Environmental Engineerin
Designing nanocrystal donor : molecular acceptor interfaces for improved charge and energy transfer
Get PDFHybrid materials comprised of semiconductor nanocrystals and surface-bound molecular chromophores are an emerging platform for addressing challenges in solar energy and catalysis. Nanocrystals have size-tunable optical properties, allowing them to readily capture light and transfer that energy in the form of excitons or single charges to a surface-bound molecular acceptor bound. The excited acceptor can then be utilized for catalysis, improved solar energy conversion efficiencies or high resolution 3D printing. However, nanocrystal-to-molecule transfer takes place in a complex, heterogenous ligand shell of solubilizing native ligands and charge or exciton accepting ligands, wherein intermolecular interactions can direct transfer. At present, these materials are synthesized without a framework for efficiently transferring energy or charge.
To address this issue, we have identified methods of tuning nanocrystal-to-molecule transfer at the nanocrystal-molecule interface. This was achieved by systematically varying components of the ligand shell during synthesis, measuring photoinduced charge or energy transfer using transient absorption spectroscopy and using computational methods to describe our observations. First, we examined the surrounding environment of native ligands by exchanging oleic acid for a series of cinnamic acid derivatives containing static dipoles that alter the local dielectric environment. We found that solubilizing ligands induced electrostatic interactions that altered the nanocrystal-molecule distance and donor-acceptor electronic coupling resulting in a 4x rate variation.
Next, we explored the role of inter-acceptor interactions on transfer, which can result from self-assembled acceptor aggregation at high surface acceptor concentrations. We found that electron transfer could be tuned by nearly an order of magnitude solely from acceptor concentration due to a change in acceptor orientation at the nanocrystal surface. Next, we explored the binding group position that secures acceptors to the NC. We find that positioning of the binding group can affect triplet exciton transfer and applications such as photon upconversion. The results from the acceptor aggregate work led us to explore new acceptor structures that utilize directed acceptor interactions through the use of covalent tethers. We investigated the excited-state electronic structure of covalently tethered one-dimensional aggregates of acceptor molecules using transient absorption spectroscopy. We found that covalent tethers tune the amount of excited-state Frenkel exciton and charge transfer character. Further, the tether in one-dimensional aggregates enhances exciton diffusion along the long axis of the structure. In summary, this work has developed a set of design principles for tuning charge or energy transfer via parameters at the nanocrystal-molecule interface.Chemistr
Trans* stellar knot-works : transitioning archives, Afro trans vivências and transtopias
Get PDFThis dissertation investigates the embodied experiences of black trans women in the African Diaspora, departing from the diaspora in Brazil, as we participate in movements whose agendas fight against transphobia, anti-blackness, police brutality and state bureaucracy in order to define and achieve freedom in our own terms. I discuss how those experiences reassemble the ways black bodies are imagined, gendered, sexualized and racialized. I use a methodology that combines what I am calling papo-de-mana, roughly translated as sista talk, and Trans* stellar knot-works. The former foregrounds conversations with and from, as well as putting in conversation, black women’s voices, be them trans or cis, as a site of dialogic theorizing. The latter is a process of knowledge production that consists of multisited archives that are comprised of, but not limited to, the ways we care for ourselves, and for our communities, our relation to our landscapes, the discourses we create, the artistic work we produce in different media, the imaginaries and emotions that are precariously disembodied into language. I use the metaphors of the knot and thread to trace the sartorial, digital, spiritual, political and imaginative connections between the experiences of black trans women in Brazil and in parts of the diaspora such as the United States and Angola. I argue that what ties those experiences in a Trans* Stellar knot-work is a praxis of fugitivity, which consists of the refusal of black trans women in accepting premature death as destiny. Their theorizing on the creation of possibilities of abundance of life and futurity is the thread that connects those embodied movements for justice. Some of the themes I investigate to articulate those concepts are: black trans people’s embodied artful strategies against surveillance as the colonial gaze, the legacies of the Brazilian trans organizations ASTRAL in relationship to the US trans organization S.T.A.R., black trans women’s everyday practices of resistance through a strong work ethics, abolitionist archives against the pathologization and criminalization of non conforming bodies and the initiatives to create accessible futures.African and African Diaspora Studie