UT Electronic Theses and Dissertations

Permanent URI for this collectionhttps://hdl.handle.net/2152/11

This collection contains University of Texas at Austin electronic theses and dissertations (ETDs). The collection includes ETDs primarily from 2001 to the present. Some pre-2001 theses and dissertations have been digitized and added to this collection, but those are uncommon. The library catalog is the most comprehensive list of UT Austin theses and dissertations.

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    Delineating the interfacial interactions and gas evolution in low-cobalt, high-energy density lithium-based batteries
    (December 2023) Sim, Richard, Ph. D.; Manthiram , Arumugam; Yu, Guihua; Hwang, Gyeong; Subramanian, Venkat
    Layered oxides (LiNi₁₋ [subscript x] M [subscript x] O₂; M = Co, Mn, Al) are promising cathode materials that can achieve key performance metrics with their high energy densities and rate performance. However, these materials suffer from a series of surface and bulk degradations during charge-discharge that may compromise the performance and safety of the battery. This dissertation focuses on elucidating the surface and bulk degradation mechanisms that result from electrode-electrolyte incompatibility for high-energy layered-oxide cathodes and lithium-metal anodes. Extensive discussions are provided on the set-up of specialized instrumentation for advanced gas detection and application of advanced characterization tools to elucidate the surface interfacial reactions at the electrode-electrolyte interface for the development of sustainable, safe, and long-lasting lithium-based batteries. An evaluation of the influence of calendering on cobalt-free LiNi₀.₉Mn₀.₀₅Al₀.₀₅O₂ (NMA-90) cathodes is explored as a facile method to minimize the degree of electrode-level effects on cell performance for future projects. Calendered NMA-90 | graphite full cells exhibit lower cell impedance, enhanced cyclability, and pulse-power performance. Overall, calendering is demonstrated to be a crucial post-processing technique for commercial high-nickel cathodes. Gas evolution from the cathode at high voltages remains a pervasive issue for practical batteries. The details of the design and set-up of an online electrochemical mass spectrometry system (OEMS) that operates well for cells with lean and volatile electrolytes is provided. This system is applied to a broad series of cathode-electrolyte systems and charging conditions to elucidate the factors leading to gas release from the cathode. Important topics to gas evolution from the layered-oxide cathode, including voltage, state of charge, cathode composition, electrolytes, and surface coatings are discussed. A separate pathway to achieving high energy densities with the cathode is to increase the upper cut-off voltage of the battery to 4.6 V from the standard 4.4 V vs Li/Li⁺. A localized saturated electrolyte (LSE) is employed to enable the stable cycling of a cobalt-free, low-nickel LiNi₀.₇Mn₀.₂₅Al₀.₀₅O₂ in lithium-metal half-cells. It is found that the improvements to the cycling performance are due to a beneficial interphase layer, reduced degree of rock-salt phase formation, and reduced gas evolution from the cathode. Transition-metal dissolution from the cathode is exacerbated at high voltages, which will influence solid-electrolyte interphase (SEI) formation at the anode. Secondary-ion mass spectrometry (SIMS) is employed to track the distributions of common products found in the SEI. Spatial correlations between deposited transition-metals, organic/inorganic electrolyte decomposition products, and lithium metal on the lithium-metal anode are established and quantified for a variety of anodes cycled with different cobalt-free cathodes and electrolytes. Critical insights into the effects of spatial heterogeneity and SEI localization on cell cyclability are provided.
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    Doctoral thesis recital, opera coaching (lecture)
    (2024-02-28) Moiseeva, Ana; Unable to determine
    Lecture: A guide to the interpretation of Georgian operatic music for non-native speakers
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    Doctoral thesis recital, collaborative piano
    (2024-02-27) Branco, Renan; Unable to determine,
    Violin sonata no. 1 in F minor / Sergei Prokofiev -- Three sonnets by Petrarach : S. 270 [for voice and piano] / Franz Liszt -- Legende for trumpet and piano / Georges Enesco.
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    Skarn and epithermal vein mineralization in the San Carlos Caldera region, northeastern Chihuahua, Mexico
    (1981) Immitt, James Peter; Kyle, J. Richard
    The San Carlos Pb-Zn-Ag skarn deposit and several Pb-Zn-Cu-fluorite epithermal vein prospects are located along the boundary of the San Carlos caldera near Manuel Benavides (San Carlos) in northeastern Chihuahua, Mexico. The skarn deposit is at the crest of a Laramide anticlinal fold in the Sierra Azul. The anticline was intruded and uplifted by a granitic pluton related to caldera development at 31 mybp. Detailed mapping and petrography reveal that Lower Cretaceous dolomitic limestone and calcareous siltstone have been metamorphosed and metasomatized to form a well-defined zonal alteration pattern around the intrusive core of the fold. Prograde calc-silicate metamorphism resulted in a sequence, with increasing distance from the heat source, of forsterite or diopside, tremolite, and recrystallized carbonate zones. Within the forsterite zone the pre-mineralization calc-silicate assemblage has been replaced by a metasomatic assemblage consisting mainly of magnetite, calcite, galena, and sphalerite. Precipitation of ore minerals took place when acidic magmatic hydrothermal fluids interacted with the dominantly carbonate country rocks. Retrograde serpentine alteration of forsterite and diopside is the only indication of the pre-mineralization metamorphosed lithologies. The epithermal vein prospects occur near the northwestern margin of the caldera mainly along normal faults near the apex of the La Consolacion dome. This dome was probably formed during emplacement of another peripheral intrusion believed to be present at depth. Veins occur in marbleized Lower Cretaceous shale and argillaceous limestone and in a hydrothermally altered caldera-related Tertiary rhyodacite flow. Ore deposition resulted from circulation and cooling of metal- and fluorine-bearing hydrothermal fluids. Fluid inclusion data indicate a range in temperature from 317-142°C and in salinity from 5.7-2.8 equivalent weight percent NaCl , with both generally decreasing in younger minerals. Mineralization in the San Carlos area is spatially, and may have been temporally associated with development of the San Carlos caldera. It may have been controlled by the availability of heat and hydrothermal fluid from caldera-related igneous activity, ease of fluid movement along caldera-related structures, and the presence of reactive host rocks
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    Computer analysis of reinforced concrete cross-sections
    (1983) Farahany, Mohsen M.; Not Available
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    Painted pottery from the Galaz ruin : figurative style in Mimbres art
    (1986) Farmer, James (James D.); Not available
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    Stratigraphy, sedimentology, and paleontology of Upper Cretaceous (Campanian-Maastrichtian) sedimentary rocks in Trans-Pecos Texas
    (1985) Lehman, Thomas Mark; Kocurek, Gary; Langston, Wann, Jr., 1921-2013
    Marine, paralic, and continental sedimentary rocks of Late Cretaceous (Gulfian) age are exposed in three major areas along the Rio Grande valley in Trans-Pecos Texas and adjacent Mexico. Although different stratigraphic nomenclature has been applied to strata exposed in each area (Sierra Vieja, Ojinaga, and Big Bend), the general succession and similarity of lithologies, biostratigraphic correlation, and paleocurrent data suggest that these strata are parts of the same genetic units and were formerly contiguous. In general, marine shale and limestone of the Ojinaga Formation is equivalent to that of the Boquillas and Pen formations, paralic sandstone of the San Carlos Formation is equivalent to that of the Aguja Formation, and variegated continental mudstone of the El Picacho Formation is equivalent to that of the Javelina Formation. Both Aguja and San Carlos formations are informally subdivided in this report. The entire sedimentary pile thins dramatically northeastward from the Chihuahua Trough onto the Coahuila Platform. Three major transgressive-regressive cycles are recorded in the paralic deposits, with progradational episodes occurring in Middle Turonian, Early Campanian, and Late Campanian time. The strandline migrated northeastward across the Trans-Pecos region, and sediment was derived primarily through erosion of a volcanic arc terrane in western Mexico. Progradational deposits consist of fluvial-dominated deltaic and laterally continuous sandy shoreface accumulations. Increase in thickness and continuity of shoreface deposits in the Sierra Vieja area suggests that a major deltaic headland may have existed to the north, and that much of the Trans-Pecos region occupied a broad interdeltaic embayment. An abrupt change in sedimentation occurred in Maastrichtian time with the onset of Laramide tectonism and initial development of the Tornillo Basin. Sediment transport shifted to the southeast, concurrent with an influx of coarse volcanic detritus, chert pebbles reworked from Lower Cretaceous rocks, and the widespread cannibalization of Upper Cretaceous sediments. Stream channel aggradation and incision events, and alternating periods of podzolization and calichification in floodplain paleosols, suggest that long term humid - semi arid climatic cyclicity prevailed during deposition of these sediments
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    Holding loss at its center : age value at Missions Concepción & San José
    (2019-05) King, Meghan Elizabeth; Holleran , Michael; Ibarra Sevilla, Benjamín
    Mission Concepción and Mission San José in San Antonio, Texas belong to a collection of five eighteenth century Spanish Colonial Missions founded along the San Antonio River. The churches of Concepción and San José are of analogous construction, built of local tufa limestone with corresponding layers of lime stucco. The history of these buildings has seen several eras of preservation approaches, or lack thereof, up to and including abandonment. This thesis considers the state of the exterior stucco of both buildings as a means by which to contemplate the value preservation places on loss and look of age. In honoring all periods to the building of a monument, the preservation of the churches' picturesque and semi-ruinous appearances emerges at odds with the material needs of the buildings and presents a limited framework of interpretation. This analysis investigates the "why" of this preservation scenario why does loss prefigure so centrally in preservation? And from where does this value emerge? In investigating the ideological framework of the Venice Charter and the Secretary of the Interior's Standards, an inherently broken notion of time reveals itself at their roots. In practice this produces a binaristic notion of loss and wholeness that are an inherent expression of age value's priority above all else. In applying this analysis against the Missions, this thesis seeks to redress the limits of this framework and locates a space for an alternative preservation discourse of capacious interpretations.
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    The impacts of sustainable development policy on facility maintenance management
    (2023-08) Matthews , Audrey (Audrey Alice); Lieberknecht, Katherine E.; Paterson, Robert G.
    This paper discusses how maintenance at a municipal level is impacted by public mandates, policies and initiatives that address climate change mitigation or adaptation. First the paper discusses how climate change will impact communities and a municipal response to the regional internal climate issues it will cause, and some of the solutions governments have undertaken to alleviate or mitigate those impacts. It looks at Austin, Texas, as a case study to understand and analyze the effects that the municipal climate change related policies have on the ability of maintenance management to achieve their goals. Because maintenance is extremely important for sustainable building goals, this thesis looks to understand that connection. Through the results the paper found that most of the success for sustainable building policy comes from the city staff working to connect ideas and people to achieve sustainable goals that they find important and ordinances from the city requiring city-owned properties to create sustainable building. However, new technologies without seeing the whole project maintenance, a continuing and common lack of communication and involvement of maintenance stakeholders in the design and implementation stage, and budgeting that requires catastrophic emergency systems to be most important hold back sustainable policies and initiatives from being as compatible with facility maintenance management than it could be.
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    Doctoral thesis recital, viola
    (2024-02-23) Lee, Gwanji; Unable to determine
    Sonata op. 36 in B♭ major for viola and piano / Henri Vieuxtemps -- Sonata no. 1 in C minor for viola and piano / York Bowen.
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    Doctoral thesis recital, conducting (lecture)
    (2024-02-22) Eary, Drew; Unable to determine
    Lecture on the orchestral work Oceans by Maria Huld Markan Sigfúsdóttir. Includes a performance of a transcription of the work for wind ensemble, conducted by Drew Eary
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    Getting in the way : new approaches to rape joke discourse and women’s comedy about sexual violence
    (2023-08-03) Cacace, Katharine M.; McClearen, Jennifer; Fuller-Seeley, Kathy; Scott, Suzanne; Haggins, Bambi
    One of the most visible pop culture discussions about the relationship between comedy and sexual violence is the construct of the rape joke, a discourse of power and gender that—to use a phrase plucked from stand-up comic Cameron Esposito’s special on this topic—gets in the way of fully understanding how feminism shapes comedy, and obscures novel ways that women speak about their lives. This dissertation builds upon a definition, advanced by Nicola Gavey and Jane Ward, of sexual violence as ingrained within the practices of heterosexuality and develops a feminist ethical framework I call “walking together” to explore rape jokes in women’s stand-up specials, albums, and joke books that sit outside the boundaries of typical rape joke discourse. I examine Phyllis Diller’s books about housework and marriage in the white midcentury American middle-class home as an example of subtle, sneakily feminist, possibly liberating comedy about sexual violence, while my analysis of Iliza Shlesinger’s self-declared feminist stand-up comedy specials finds damaging rape myths. Further, using Sienkiewicz and Marx’s theory of the interconnected right-wing comedy complex, I question whether Shlesinger’s comedy might serve a possible point of entry into political conservatism for white women who are open to something that sounds like popular feminism. Finally, I dissect the common comedy metaphor of punching up and punching down that is so often used to analyze the ethics of a joke and, working instead from comedy about sexual assault and sexual coercion by Wanda Sykes, Cameron Esposito, and Natalie Palamides, I offer shadowboxing as an alternative way to view what comedy is and what it can do.
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    Timely information sharing in communication constrained systems
    (2023-08-07) Abou Rahal, Jean; De Veciana, Gustavo; Caramanis, Constantine; Hasenbein, John; Shakkottai, Sanjay; Vikalo, Haris
    In the near future it is envisaged that there will be a proliferation of disruptive applications combining sensing capabilities with cutting-edge wireless technologies. The wide deployment and availability of sensing nodes as well as the large amounts of data being collected will call for the design of "smarter" ways of gathering and processing such data. Such networks will be driven by the need to extract the most relevant data/information that is of interest to possibly multiple agents/nodes, while optimizing the allocation of the shared limited available resources to adapt to the heterogeneity of the interests of the different nodes as well as the heterogeneity in their network conditions. Indeed, the timely sharing of relevant information is shaping to be crucial in applications where real-time decisions are to be constantly made. In the automotive industry for example, it is expected that vehicles equipped with sensing nodes could collaborate by sharing sensed information which would allow for vehicles with obstructed views to make safer decisions and/or enhance the capacity of roadways. In the infotainment industry, and more specifically in the case of Virtual Reality (VR) applications that require large amounts of data to be constantly streamed, users at proximity of each other and that are part of the same VR experience may largely benefit from sharing resources such as edge caches that could be leveraged for the timely computation and delivery of the needed data especially in settings where different users may request the same data. The optimization of information sharing in communication constrained systems will thus be a fundamental problem underlying such systems. The focus of our work is on the modeling and analysis of these classes of problems and their implications in practical sensing systems. This thesis is composed of two main parts. In the first one, we explore the optimization of applications where timely sharing of information leads to enhanced safety and more accurate real-time decisions. We investigate novel metrics and algorithms aimed at achieving a high degree of real-time situational awareness in applications with distributed sensing nodes. In the second part of this thesis, we explore the timely sharing of information in a multi-user VR setting that would provide immersive VR experiences among the users. In particular, we explore how to support 360° VR video applications where the prediction of users' future viewings orientation is a major component as well as how to leverage overlaps in users' predictions in order to relieve the load on the shared communication network resources. Such applications face major challenges mainly tied to the heterogeneity in users' devices, predictions, network conditions, etc., which we propose to tackle through the careful design of metrics and policies robust to such heterogeneity and aimed at enhancing while achieving fair VR performance among the users.
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    Microstructural design principles for stable interphases in alkali-metal and anode-free batteries
    (2023-07-31) Wang, Yixian, Ph. D.; Mitlin, D. (David); Yu, Guihua; Warner, Jamie; Henkelman, Graeme; Watt, John
    The pursuit of reliable and high-energy storage devices with enhanced safety has attracted significant research interest in recent decades. Alkali metals like lithium and sodium have shown promise as anode materials but suffer from limitations such as dendrite growth and interfacial instability, which pose safety risks and hinder their widespread applications. To overcome these challenges, an anode-free battery (AFB) design offers increased energy density and enhanced safety. However, AFBs often experience rapid capacity decay due to the lack of a reservoir for active ion loss during cycling. Additionally, solid-state batteries utilizing non-flammable inorganic solid electrolytes address safety concerns and potentially provide higher energy density but face interfacial obstacles such as dendrite growth and unstable solid electrolyte interphase (SEI). This dissertation focuses on microstructural design of stable interphases to address the interfacial challenges and improve the performance of alkali-metal and anode-free batteries. To start with, electrochemically stable intermetallics are introduced as effective coating layers on copper foam current collectors, improving metal wetting and subsequent cycling. Unlike conventional alloys, the introduced intermetallics (Na₂Te and Na₂S) do not undergo reversible alloying – dealloying reactions that cause remarkable volumetric change, therefore enhancing mechanical integrity throughout the cycling process. Building upon this design strategy, the dissertation further investigates the application of intermetallic coatings in solid-state electrolyte systems. A thin layer of Li₂Te intermetallic coating is fabricated onto commercial copper foil current collectors, which significantly reduces the electrodeposition/electrodissolution overpotentials, improves Coulombic efficiency (CE), and enables stable cycling of anode-free all-solid-state batteries. Additionally, this dissertation introduces a novel metallurgical composite composed of ternary sodium-antimony-tellurium (NST) intermetallic, which demonstrates remarkable sodiophilic properties, effectively facilitating uniform sodium electrodeposition and electrodissolution for enhanced cycling stability. An anode-free cell consisting of an NST-coated current collector and Na₃V₂(PO₄)₃ (NVP) cathode demonstrates significantly improved cycling performance compared to using a baseline copper collector. In this dissertation, various state-of-the-art characterization techniques are utilized to investigate the microstructural evolution occurring at interfaces, offering new insights into the intricate connection between wetting behavior and electrochemical performance. Furthermore, multidimensional modelling and simulation approaches are employed to gain a further understanding of the underlying mechanisms.
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    Design principles and structure-function relations of nitrogen-rich nanoporous carbons
    (2023-08-11) Burrow, James N.; Mullins, C. B.; Korgel, Brian A; Lynd, Nathaniel A; Yu, Guihua
    Efficient separation of CO₂ from post-combustion flue gas remains a significant engineering challenge central to the energy transition. Swing adsorption processes, operating on the principle of selective physisorption, have garnered considerable interest as a potentially sustainable solution for post-combustion carbon capture. This dissertation focuses on understanding synthetic processes, design principles, and structure-function relationships of N-enriched nanoporous carbon adsorbents for the selective capture of CO₂. Using a multimodal material characterization approach centered around gas porosimetry and X-ray techniques, this work has revealed 1) how to alter syntheses to tune porosity, surface chemistry, and nanostructure of carbon adsorbents and 2) which material properties should be targeted for increased CO₂ capacity and selectivity toward practical utility. We showed that the presence of N during synthesis can significantly alter traditional mechanistic pathways of porosity generation, and that the use of molten salts as high-temperature solvent analogues enables precise control of carbon material properties. Further, we found a compensation relationship between the entropy loss and enthalpy gain of CO₂ adsorption, stemming from confinement in carbon nanopores. We revealed that N-rich surface chemistries can effectively break this exchange relation by enhancing the interaction between the sorbent surface and polarizable CO₂ while impacting the configurational entropy to a lesser extent. As such, we identified that the heat of CO₂ adsorption on nanoporous carbons is tunable from approximately 20 – 50 kJ/mol at typical flue gas conditions by manipulating nanostructure and N content. Additionally, we discovered that increases to the CO₂/N₂ adsorption selectivity, indirectly associated with increased N-content, are in fact derived from a molecular sieving effect between turbostratic sheets of carbon that pack tightly enough to exclude N₂ but simultaneously allow for high-affinity CO₂ adsorption. We also emphasized that commonly-pursued design goals of enhancing CO₂ capacity by maximizing (N₂-accessible) microporosity and surface area are in practice associated with deleterious increases in N₂ adsorption and diminished CO₂/N₂ selectivity. As a result, nanoporous carbons with both high capacity and sufficient selectivity for utility in post-combustion carbon capture must present only moderate N₂-accessible surface area with a semi-crystalline nanostructure amenable to molecular sieving, with an interlayer d-spacing (i.e., critical ultramicropore width) between 3.30 and 3.64 Å (the kinetic diameters of CO₂ and N₂, respectively). With a data-driven approach to molten salt synthesis of these size-sieving turbostratic carbons, we employed inverse design to create N-rich carbon adsorbents that satisfy these requirements and obtain predicted performance for carbon capture from natural gas combined cycle flue gas that rivals benchmark metal-organic frameworks (i.e., Mg-MOF-74, UTSA-16). Additionally, we report the discovery of calcium poly(heptazine imide), a covalent organic framework allotrope of carbon nitride. We found that exchanging framework-complexed cations with protons resulted in an amine-rich porous material that selectively captures a large quantity of CO₂ from dilute conditions through enhanced physisorption (and not chemisorption), most likely mediated by H-bonding with acidic protons.
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    Assessing workers’ decision quality with scarce ground truth data
    (2023-06-26) Dong, Wanxue; ​Saar-Tsechansky, Maytal; De-Arteaga, Maria; Geva, Tomer; Barua, Anitesh
    Accurately assessing workers’ decision quality is fundamental for management, and the efficiency of expert and crowd-sourcing markets. This paper establishes novel ML and AI methods to accurately evaluate workers’ decision accuracy and bias with scarce ground truth (GT or gold standard GS) data, and to further improve accuracy assessment through costly effectively acquiring GT if given an acquisition budget. Without the proposed methods, assessing workers’ decision quality typically requires GT data to compare with workers’ noisy decisions. However, GT is often prohibitively costly to acquire for even a small fraction of each worker’s decisions. For example, physicians may determine a diagnosis and initiate a treatment, yet the correct decision, such as the one that can be established by a panel of physicians. Consequently, in practice, there is often poor transparency regarding physicians’ decision quality. In my dissertation, I collaborating with my coauthors developed the groundwork for achieving scalable and inexpensive assessments of workers’ decision accuracy and bias. The empirical results show that the decision accuracy assessment with very limited GT improves the best available approach by 60% to 93%; my bias assessment produces either comparable to or outperforms the commonly used existing approach; my cost-effective GT acquisition strategy applied in Amazon Mechanical Workers’ accuracy assessment achieves the same performance only using 1/3 of the GT or improve the assessment by 24%. All proposed methods have significant implications in many impactful domains including health care, fraud detection, fact checking, and online labor markets. The methods proposed in this dissertation address the problem of estimating workers’ decision accuracy and bias from historical data with scarcely available ground truth, and achieve the state of the art performance. This dissertation lays the groundwork towards increasing transparency in workers’ (sources’) decision quality.
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    Essays on nonparametric identification and production function estimation
    (2024-02-07) Pan, Qingsong; Ackerberg, Daniel A.; Kline, Brendan; Xu , Haiqing; Ordin, Andrey
    This dissertation consists of three chapters on applied econometrics and econometric theory. The first two chapters propose new estimating approaches to nonparametric production functions, and the third chapter studies the partial identification of treatment effects in a nonparametric setting. In the first chapter, we study the nonparametric identification of gross output production functions with a nonseparable productivity shock when output markets are perfectly competitive. Our nonseparable specification relaxes the traditional assumption of Hicks neutrality that has been shown to be inconsistent with a number of data sets. It can thus capture the bias in technical change, which recent research has found relevant to many important economic questions. We first generalize the identification approach of Gandhi et al. (2020) to nonseparable models and show the identification of output elasticities. To identify the entire production function, we then impose a homogeneity assumption, which is supported by the data. Given the fact that our nonseparable models nest Hicks-neutral models, we are able to document the misspecification bias of the latter. Using Chilean and Colombian plant-level data, our estimates suggest that Hicks-neutral models overestimate returns to scale, overestimate output elasticities of labor, and generate biased estimates of capital intensity. Our estimates also indicate that technological change is predominantly biased toward capital over labor and intermediate inputs. In the second chapter, we extend the identification approach in chapter 1 from perfect competition to imperfect competition. When physical quantities of output are observed, we follow Flynn et al. (2019) and replace the assumption of perfect competition with a constant-returns-to-scale (CRS) condition. When only revenue instead of physical output is observed, we follow Kasahara and Sugita (2020) and combine a first-order condition with a CRS condition to show identification of output elasticities and markups. In the third chapter, we derive a set of partial identification results for the mean treatment response and the average treatment effect when the μ-strong concavity assumption is combined with the monotone treatment response (MTR) assumption or the MTR-MTS (monotone treatment selection) assumption. μ-strong concavity is a generalization of the usual concavity assumption and the parameter μ can be seen as a measure of the strength of concavity. By tuning the value of the parameter μ, a practitioner can conduct sensitivity analyses with respect to the concavity assumption. We illustrate my findings by reanalyzing the return to schooling example of Manski and Pepper (2000).
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    Birthing while Black : a qualitative exploration into the experiences and implications of the COVID-19 pandemic on Black maternal health and care in Texas
    (2024-02-07) Wright, Jaylen; Nydegger, Liesl; Pinedo, Miguel (Pinedo Bañuelos); Bartholomew, John; Burse, Nakeitra
    Given the implications of the COVID-19 pandemic on vulnerable and marginalized communities, it is essential that the unique implications of additional significant life stressors for Black women and birthing communities are carefully considered. These implications include addressing the complex intersectionality of pregnancy, gender, race, and social class and how structural inequalities which existed before the pandemic have been magnified in the COVID-19 era. Guided by an adapted stress process model, Black feminist thought, and the reproductive justice framework, this dissertation sought to qualitatively explore the lived and observed experiences of stress and perinatal care among Black mothers (Study 1; n=35) and maternity care professionals (Study 2; n=29) during the COVID-19 pandemic. Following a qualitative descriptive research design, in‐depth, semi-structured, virtual interviews were conducted with a total of 64 individuals between May and August of 2022. For Study 1, mothers recounted experiences of discrimination stress, trauma, support, and well-being as it related to the stigmas around their pregnancies and evolving motherhood. For Study 2, in addition to providing sentiments that validated the perinatal experiences shared by Black mothers in Study 1, maternity care professionals reflected on their journeys to, challenges of, and outlook for birthwork, including implications for Black maternal health. In addition to prompting dramatic changes to the delivery of maternal healthcare in the United States, findings from this dissertation have highlighted major dimensions of well-being, safety, and respectful maternity care described by Black mothers and care practitioners. Therefore, Future research should continue to center the experiences of Black mothers and include the voices of birthwork professionals around their roles in Black birth justice and maternal health equity.
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    Ab initio electronic transport : from two-dimensional semiconductors to nanoscale metals
    (2024-02-07) Zhang, Chenmu; Liu, Yuanyue; Akinwande, Deji; Wang, Yaguo; Zheng, Yuebing
    Over the past few decades, Moore’s Law has been a driving force behind the exponential increase in integrated circuits capabilities, significantly transforming people’s lives. However, the continuation of Moore’s Law is being called into question as the continuous shrinking of electric circuits is approaching physical limitations. Currently, the size of transistors and interconnects, two fundamental components in modern chips, has reached the tens of nanometers. Further downscaling leads to circuit delay, heat dissipation and poor performance of microchips, ultimately prohibiting Moore’s Law. One of the biggest challenges is the materials: conventional semiconductors and metals in transistors and interconnects exhibit undesirable resistivity increases when reduced to the nanoscale. Thus, the need for 2D semiconductors and better metals with fewer dimensional impacts has become increasingly urgent. This underscores the critical importance of understanding electronic transport in small system, which is the focus of this thesis. By utilizing first-principles calculations, the mobility and conductivity of 2D semiconductors and finite-size metals can be predicted, leading to physical insights and high-throughput screening for best candidates for electronic transport. This dissertation is organized as follows: Chapter 2 describes the Boltzmann transport equation (BTE) to study electronic transport in materials. Chapter 3 demonstrates how to obtain the transition rates, necessary for solving the BTE, from first principles. In particular, we developed an efficient approach to interpolate the electron-phonon-coupling matrix in 2D materials, which can also include the effect of free carrier screening. Based on the state-of-the-art calculations, Chapter 4 shows that reduced dimensionality results in a larger “density of scattering” in 2D semiconductors, leading to generally lower carrier mobility. We predict several high-mobility (>1400 cm²V⁻¹s⁻¹) 2D semiconductors with extremely small effective mass and/or weak EPC, thus avoiding the “dimensional curse”. Chapter 5 and 6 demonstrate the computational approaches to high-field transport properties and remote phonon scattering for 2D semiconductors, respectively. Finally, for metal in interconnects, we develop an ab initio approach to incorporating electron-phonon/surface scattering for electronic transport in finite-size metals and demonstrated it in copper films with different surfaces in Chapter 7.
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    Estimation and control for autonomous directional drilling with rotary steerable systems
    (2022-12-02) Keller, Alexander M.; Chen, Dongmei, Ph. D.; Demirer, Nazli; LI, WEI; SENTIS, LUIS; LONGORIA, RAUL G; FAHRENTHOLD, ERIC P
    Accessing difficult to reach hydrocarbon reservoirs while simultaneously reducing risk and increasing efficiency has driven demand for precise autonomous directional control of rotary steerable systems (RSS). Despite advances in RSS technology, precise control remains difficult primarily because the tool is located deep underground which introduces challenges that require advanced methods to overcome. In the deep subsurface environment, many parameters are difficult or impossible to measure. One consequence of this fact is model mismatch is often encountered which degrades control performance. Another consequence, resulting from the fact that the position of the tool cannot be measured underground, is that trajectory control is implemented on the surface imposing large communication delays on the control loop. This dissertation investigates methods to overcome these challenges and improve the accuracy and reliability of automated directional drilling. A Markov Chain Monte Carlo (MCMC) based method is proposed to estimate time-varying model parameters in real-time using only measurements commonly obtained while drilling. The method is evaluated on historical field data and in closed-loop simulation. Also, the utility of estimation for human-in-the-loop operation is explored through the design of an early warning system. In order to incorporate information of the model uncertainty into the control framework, a stochastic model predictive controller (SMPC) is designed. As part of this development, a series of approximations are made to a first-principles model of directional drilling that significantly reduces the computational complexity of the controller. The SMPC is posed as a convex second-order cone optimization problem that is solved efficiently and enables real-time directional control. In open-loop, the controller is optimal and satisfies state and input constraints probabilistically. In closed-loop, it satisfies input constraints, is approximately optimal, and has minimal violation of state constraints as demonstrated by simulation-based experiments. Lastly, to address the challenge of unobservable position downhole, a machine learning (ML) based estimation method is developed, and several algorithms are compared in terms of accuracy and computational demand, which is critical to practical implementation. The impact of estimation errors on control performance is analyzed, and the results are used as metrics in the evaluation of the models on historical drilling data.

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