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First order sampling methods in gravitational wave parameter estimation
Full text linkThe recent proliferation of algorithmic differentiation and hardware acceleration has made first-order, ensemble-based sampling algorithms highly attractive for a wide range of applications. Algorithmic differentiation enables fast and machine-precision gradient evaluations, while modern hardware acceleration facilities both vectorization and parallelization with ease. Ensemble-based first-order sampling methods offer several notable advantages over traditional approaches. First, they are more
robust in exploring energy landscapes and discovering multiple disconnected energy minima. Second, they can be combined with tempering or birth-death mechanisms to mitigate metastability. Third, they provide a natural framework for constructing robust preconditioners to improve exploration of ill-conditioned energy landscapes. This dissertation adapts a range of recently proposed algorithms in the sampling literature to gravitational wave parameter estimation. We design diffusion-jump process
tailored for GW150914, study interacting diffusion processes to enhance parameter space exploration, and propose quasi-Newton methods to address the challenges arising from the degeneracy and ill-conditioning of the Bayesian potential.Physic
Characterization of the normal and shear interactions between bilayer graphene and sapphire following a novel CVD growth process
Full text linkBeing the pioneer 2D material, graphene has been extensively researched owing to its excellent electronic, mechanical, thermal, and optical properties. Copper foil, which is one of the most common substrates employed in graphene CVD (chemical vapor deposition), provides a catalytic surface for the large-area growth of graphene. However, graphene cannot be directly used on copper and needs to be transferred to suitable substrates. Wet transfer methods, which use polymeric support, pose serious challenges such as long processing times, residual organic contamination, and doping from copper
etchants. Dry transfer methods that rely on mechanical delamination, on the other hand, allow for recyclability of the growth substrate, eliminate the use of etchants, and provide interfacial mechanical properties between graphene and substrates. Using dry transfer for Cu/graphene has been challenging due to the high adhesion between graphene and copper, and the lack of mechanical rigidity of the foils. To circumvent these challenges, this study
focuses on the use of sapphire for the direct, metal-free growth of graphene.
An atmospheric pressure CVD process was optimized for obtaining uniform bilayer graphene on sapphire. It was found that thermally annealing the sapphire prior to growth is a key factor in obtaining a suitable surface reconstruction required for growing high quality graphene at conventional metal CVD temperatures. The growth and annealing parameters were optimized, and the graphene was characterized using Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM).
Additionally, the number of layers of synthesized graphene was determined using Raman mapping and high-resolution transmission electron microscopy. Following growth, dry transfer was carried out on laminated beam specimens using a dual actuator loading device. The transfer was carried out under both nominally mode I and mixed mode loading conditions, and the quality and yield of transfer were determined using Raman, SEM and AFM. Using a beam-on-elastic foundation analysis, the adhesion energy and strength of the graphene-sapphire interface was determined experimentally, and it was found that the overall toughness decreased in going from Mode I to Mode II loading. This is the first-time dry transfer of graphene has been carried out under such a range of mixed-mode conditions, and while the current studies have been carried out on strips, these results have significant implications in employing other loading configurations for the transfer which may be easier to employ at wafer-scales. To explore other loading configurations, normal and shear
interactions were first experimentally determined at the transferred graphene-silicon interface. A cohesive surface based finite element model was developed on Abaqus to obtain a Mode I transfer map that showed that with competing interfaces, the crack grew along the interface with lower strength rather than lower fracture energy. Finally, using the mixed-mode results of graphene-sapphire and graphene-silicon interfaces, a three-point bending model was proposed on Abaqus to explore the feasibility of a direct, polymer-free, one-step dry transfer of graphene from sapphire to silicon.Materials Science and Engineerin
Same-sex relationships and health : how gender, stress, and relationship dynamics shape health over time
Full text linkAlthough the United States has witnessed significant social, legal, and demographic changes concerning sexual minority families over the past several decades, critical gaps remain in our understanding of relationship dynamics and well-being of sexual minority families. Despite a long-standing literature demonstrating the importance of intimate relationships for health, most of this work has focused solely on heterosexual populations. This dissertation takes a life course approach to develop a comprehensive understanding of sexual minority relationship status, relationship transitions, relationship dynamics, and their implications for health. Drawing upon three longitudinal datasets—namely, the Survey of Income and Program Participation (SIPP), the National Longitudinal Study of Adolescent Health (Add Health), and the Health and Relationships Project (HARP)— this project investigates (1) same-sex union and health changes; (2) union transitions and health among sexual minorities; and (3) worries about dementia and marital quality in midlife same-sex and different-sex marriages. Results from this dissertation demonstrate the complexity and diversity in relationship formation and dissolution processes of sexual minority populations and highlight the importance of examining health in relation to relationship experiences from a dynamic point of view. The results also reveal the gendered dyadic processes that shape health-related marital experiences. Together, this dissertation provides new insights that contribute to our ongoing quest to understand the association between union experiences and health, specifically by incorporating the diverse experiences of sexual minorities.Sociolog
Restorying Queer Land Education
Full text linkThis collaborative project is a culmination of stories, memories, testimonios, dreams, life histories, and experiences of Two-Spirit, Queer, and Trans Indigenous educators. I engage with what Opaskwayak Cree Nation Two-Spirit scholar Alex Wilson poses as Queer(ing) Land Education. Queer(ing) Land Education disrupts the gender-based essentialisms ubiquitous within environmental and nature educational discourses by attending to non-binary approaches of human and more-than-human worlds and Indigenous gender and sexual diversity within pedagogy, curriculum, and educational praxis. The project is both ethnographic and autoethnographic as Indigenous paradigms in education argue that Indigenous researchers cannot be disentangled from the community since that would be severing already formed relationships imperative to Indigenous knowledges and ways of being. I hosted individual story-sharing sessions, attended ceremonies, and engaged in inter-reflexive work throughout one year to focus on how Two-Spirit, Queer, and Trans Indigenous educators in Central and South Texas create pedagogical and curricular hubs guided by their relationship to their Indigenous communities, ancestors, and Land. I deploy Land education as a theoretical guide and the “hub” as an organizational theory to make sense of the curriculum-building capacities of Two-Spirit, Queer, and Trans Indigenous educators. The following questions guide this work to foreground a Queer Land Education: How are Two-Spirit and Queer Indigenous educators (re)storying their Land relations by creating queer Indigenous hubs that center Land-based pedagogies and curriculum? How does centering Two-Spirit and Queer Indigenous educator voices provide avenues to re-imagine curriculum building, gender fluidity, and community epistemologies? Ultimately, the knowledge embedded within the stories that my co-theorists shared suggests how Two-Spirit, Queer, and Trans Indigenous educators move through moments of severance, of letting go or being let go of, to emplace worlds of Queer Indigenous freedom, a suggestion that is called severed Queer cartographies. Lastly, my co-theorists expressed how being in relation with Land encouraged them to gather as gender diverse Indigenous people, a process that is called (re)charging Queer Indigenous zones and create a pedagogical hub that centered the voices of Two-Spirit, Queer, and Trans Indigenous people while foregrounding the epistemological importance of honoring the Lands and waters, community, and ancestors.Curriculum and Instructio
Lateral epitaxial overgrowth for monolithic 3D integration of III-V optoelectronic devices
Full text linkWe present a method for selective-area doping and epitaxial lateral overgrowth of III-V semiconductors by MBE toward 3D integration of novel embedded device structures, mid-IR metamaterials, and self-aligned active devices. Metals and dielectrics have historically been relegated to the periphery of conventional III-V devices due to the challenges associated with integrating amorphous/polycrystalline material with crystalline semiconductor growth. Epitaxially-embedded patterned metals and dielectrics could be useful in a wide variety of photonic and electronic devices to introduce both passive (e.g. polarizers, mirrors, or waveguides), and active (e.g. buried Ohmic contacts and enhanced optical emitters) functionality. Monolithic integration of semiconductors, dielectrics, and metals would allow for 3D integration of optoelectronic devices and photonic integrated circuits. Periodic supply epitaxy (PSE), a growth technique that utilizes pauses in the group III flux to increase the desorption and diffusion of adatoms on a dielectric mask, allows for the selective area growth of GaAs and InAs without detrimental polycrystal formation. By combining PSE with conventional growth, we have demonstrated that both metal and dielectric microstructures can be embedded in an epitaxial layer stack and recover a planar, epi-ready surface for further growth. Furthermore, we present GaAs photodiodes grown selectively by PSE which show performance similar to conventionally grown control devices and indicate possible improvement in sidewall passivation. Future work will focus on better understanding the interfaces formed by this growth technique and expanding it to include additional optoelectronic devices such as LEDs and lasers.Electrical and Computer Engineerin
From spectacle to comics : Italian representations of Native Americans from press coverage of Buffalo Bill’s Wild West to Tex and Storia del West
Full text linkIn this dissertation, I argue that Italian representations of Native Americans have been profoundly shaped by a persistent conflation of reality and fiction rooted in colonial and white-centered discourses. Through three case studies – Italian press coverage of Buffalo Bill’s Wild West tours in Italy, and the two Italian western comic series Tex, written by Gianluigi Bonelli, and Storia del West, authored by Gino D’Antonio – I demonstrate how Italian cultural production has repeatedly constructed stereotyped images of Native peoples which, although historically and stylistically different, define Nativeness through categories imposed by whiteness.
My analysis begins with Corriere della Sera and Gazzetta Piemontese/La Stampa’s extensive coverage of Buffalo Bill’s Wild West Italian tours (in 1890 and 1906), showing how these newspapers validated the show’s claims to authenticity and contributed to blurring the boundary between spectacle and truth in relation to both Native Americans and the American West more generally, thus legitimizing the idea that entertainment could provide real knowledge about them. I then move to Tex, the longest-running Italian western comic, showing how its seemingly sympathetic portrayals of Native peoples are embedded in a paternalistic and ultimately colonial discourse. Indeed, through Tex’s authority, leadership over the Navajo, and privileged access to Nativeness, the series reproduces racial hierarchies even while professing solidarity with Native Americans. Finally, I analyze Storia del West, a historically grounded comic that sought to correct earlier romanticizations of the American West. While more attentive to historical detail and Native perspectives than its predecessors, the series nonetheless perpetuates the white-centered trope of the “vanishing Indian,” representing Native peoples as figures belonging to a bygone era and reinforcing the notion that “authentic” Nativeness exists only in the past.
Across the three case studies, the dissertation also identifies recurring stereotypes – the “savage,” the “good/infantilized” Native, and the above-mentioned “vanishing Indian” – which, although articulated with different nuances over time, continue to shape the ways Italian people imagine Native Americans.French and Italia
Mesozoic-Cenozoic broken foreland basin evolution in Northern Patagonia, Argentina (~42-48°S) : integrating sedimentation, magmatism, and subduction dynamics
Full text linkThe 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
Full text linkPermafrost 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
Full text linkBimanual 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
Full text linkUrban 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