116964 research outputs found
Sort by
Mechanisms of deterioration of portland-limestone cement blended systems exposed to external sulfates
Full text linkA comprehensive experimental approach has been developed to examine the effect of different testing and mixture parameters on the rate and mechanism of deterioration of portland-limestone cement (PLC) systems exposed to sulfates. An extensive laboratory database was generated through the evaluation of numerous combinations of materials, curing regimes, and exposure conditions. These results were linked with specimens subjected to real-world exposure conditions. The disparities in expansion rates, mass change, and visual appearance of blended systems exposed to sulfate solutions at different temperatures were analyzed and linked to microstructural changes and to the variations in the phase assemblages as a function of depth and time. Not only has the present work shown that previously published results can be extended to systems with higher limestone contents, but it has also demonstrated that the performance of commercially available PC-SCM blends can be significantly enhanced by adjusting the SO₃/Al₂O₃ and CO₂/Al₂O₃ molar bulk ratios through proper selection of limestone, sulfate, and lower-than-thought SCM levels. In addition, the presented results have highlighted the role that the experimental conditions play in the degradation process, which were shown to be particularly pronounced in systems of low sulfate resistance with high limestone contents, owing to their high propensity for thaumasite formation. Moreover, it was established that the trends in expansion do not always reflect the type, rate, and severity of the deterioration. This result was observed in mortar specimens subjected to different exposure conditions and confirmed by the investigation of laboratory and field concrete samples. In this context, the adoption of testing protocols conducted at 23°C to validate or predict the sulfate resistance of a system that will be exposed to lower temperatures seems questionable. This statement is founded on the severe degradation observed in most of the mortar and concrete specimens exposed to sulfate solutions at 5°C, some of which showed negligible expansion and no signs of macroscopic deterioration when tested according to standard procedures at 23°C. In this regard, testing at 23°C seems definitely suitable to classify non-sulfate resistant systems, but, in its current form and according to standard expansion limits, it cannot guarantee the high sulfate resistance of a system in a low temperature exposure.Civil, Architectural, and Environmental Engineerin
Eating together : race, social relationships and food practices among college educated adults
Full text linkIn this dissertation, I explore social contexts (e.g. workplace environments and romantic relationships) in relation to the food practices of college-educated black and white adults. To do so, I use a critical perspective on race, gender, and class to analyze qualitative data from 40 in-depth interviews with 20 black women, 8 black men, 6 white women, and 6 white men. This dissertation is divided into three article chapters (2-4), each of which explores a different social context and/or social relationship. In chapter 2 (Article 1) I explore how the meanings (e.g. care, obligation) individuals attach to food within the context of romantic relationships shape the processes of overeating, healthy eating, and food choices. This chapter finds that the meanings individuals attach to food within the context of romantic relationships vary by the intersection of race and gender and differentially impact processes of healthy eating, overeating, and food choices. In chapter 3 (Article 2) I explore the relationship between religion, spirituality and food practices among my sample. This chapter finds that the influence of religion and spirituality on food practices is more salient among the black respondents within this sample, but that this influence manifests differently between black women and men. In chapter 4 (Article 3) I explore the relationship between workplace environments and food practices. This chapter finds that workplace environments are central to the transmission of healthy as well as unhealthy food practices. Specifically, aspects such as time scarcity, job type, and access to on and off-site food options shape whether and how individuals in the workplace eat healthily. This dissertation contributes to the literature on food practices and social relationships and does so by paying attention to the intersection of race and gender in particular. By focusing on college-educated adults this dissertation eliminates some of the potential SES bias that could occur with respect to food practices as well as social relationships, thereby allowing for a closer analysis of the intersection of race and gender.Sociolog
Privacy Preserving Recommender Systems: Balancing Personalization with Privacy
Full text linkUniversity of TexasPersonalized recommendation systems have become an essential part of how modern digital
products operate, especially in e-commerce and large retail platforms. These systems rely heavily
on analyzing customer behavior, purchase signals, and historical interactions to deliver
suggestions that feel relevant. In practice, however, most of these pipelines still depend on
centralized storage of detailed customer data. As privacy expectations increase and laws such as
CPRA(California Privacy Rights Act), CCPA(California Consumer Privacy Act) and GDPR
(General Data Protection Regulation) become stricter, this approach is becoming harder to
justify. Organizations now need to rethink how personalization can work without relying on the
unrestricted collection of individual user data.University of TexasComputer Scienc
Would a China War Scenario Break the Insiders’ Hold?
Full text linkElizabeth Saunders has written a chilling book, The Insiders’ Game, showing that the “facts on the ground” or the nation’s longer-term interests have often taken a back seat to partisan political exigencies when it comes to foreign policy. After a string of disastrous wars in recent decades, the public’s trust in policymakers’ capacity to make the right decision has taken a beating. Unless China attacks first, a decision to intervene against it over Taiwan is unlikely to be left up to the foreign policy elite. Not only would any military action threaten a potentially ruinous escalation, but a war between the two largest economic powers would ensure the downfall of the global economy no matter who won militarily. Recent presidents Biden and Trump have sensed that the public has grown increasingly opposed to taking any major military risks.LBJ School of Public Affair
Assessing and optimizing the backup power performance of solar PV and battery systems : case of Texas winter storm Uri 2021
Full text linkThis study assessed the potential of solar photovoltaic-battery energy storage systems (PVESS) to serve as a reliable backup power solution for multi-family residential buildings during severe weather events, specifically focusing on the 2021 Texas winter storm Uri by aiming to offer valuable information for residential customers, industry stakeholders, and policymakers regarding incentivizing these systems as a dependable power source during grid outages. A comprehensive framework is developed, utilizing simulated energy consumption data based on actual historical weather conditions and representative building models, to design an optimized PVESS configuration that balances economic and resilience considerations for each modelled building. This research incorporates the battery dispatch approach featuring critical load characterization to maximize system performance. The system's performance during the outage is evaluated by measuring the percentage of load served on average and the duration of support provided by PVESS across various scenarios for representative buildings from each region of Texas. The analysis revealed that PV system design is tied to roof area constraints and battery design to cost constraints. PVESS performance increased with increasing PVESS power capacity, while savings reduced with high battery energy capacity up to a certain threshold before offsetting the losses incurred by customers during outages. Dispatch strategies focused on either meeting immediate loads entirely or meeting a set of loads for a prolonged duration of outages, with comparable performance under maximum battery capacity conditions. PVESS designed to maximize savings within commercial sizes of 30 kW PV and 20 kWh rendered an average of 23% of load met with 40% supply availability, while those designed to maximize battery capacity rendered 60% of load met on average and 100% supply availability with capacities beyond 150 kW PV and 200 kWh batteries. PVESS performance can drastically improve if served a subset of loads, such as heating, refrigeration, and plug loads, instead of total loads. Thus, adopting PVESS as a backup power resource might be challenging currently. However, policies and initiatives causing declines in battery prices, efficiency upgrades, and critical load management in the future can tilt this landscape in Texas towards reliability of PVESS during weather induced outages.Earth and Planetary Science
Implementation of arbitrary trajectory fast spin-echo sequence on a memory-limited permanent magnet MRI scanner
Full text linkRecent advances in computing and MRI have inspired the development of
new k-space trajectories which can be used to acquire images with higher resolution at faster acquisition times. These trajectories, which are implemented using time-varying gradient waveforms, are often non-Cartesian to provide more flexibility in sampling density and location, allowing for more undersampling and artifact resistance. MRI sequences are typically developed to support a small number of hard-coded trajectories, but a more generalized approach would allow for rapid prototyping and greater flexibility, especially with the increasing popularity of low-field MRI development. This thesis details the implementation of an arbitrary trajectory fast spin echo sequence which abstracts these gradient details from the user, taking a trajectory input for each readout and automatically generating the sequence and its gradients. Approaches for handling memory-limited devices are developed, including segmenting the sequence description into multiple subsequences.Electrical and Computer Engineerin
Earthquake ground motion characterization in West Texas with an emphasis on site amplification and kappa
Full text linkInduced seismicity has emerged as a critical concern in West Texas, where increased earthquake activity driven by oil and gas operations poses risks to infrastructure and communities. Despite this growing hazard, the characterization of earthquake ground motions in induced seismicity regions remains underdeveloped compared to tectonic settings. Traditional ground motion models (GMMs), predominantly derived from ground motion recordings of moderate-to-large earthquakes in active tectonic regions like California and Japan, are ill-suited for the smaller magnitude, shallow, and spatially clustered events typical of induced seismicity. This mismatch creates significant challenges for seismic hazard assessment because we lack comprehensive models and validated data that capture how earthquake source effects, regional attenuation, and local site conditions combine to shape ground motions in induced seismicity regions. This dissertation addresses these challenges by utilizing a comprehensive modeling framework to characterize earthquake ground motions in induced seismicity environments, with a specific focus on West Texas. A central emphasis of this work is on resolving site amplification and high-frequency spectral decay, parameterized by ĸ₀, which together govern how seismic waves are amplified or attenuated at a site. The approach leverages the TexNet seismic monitoring network, which has greatly expanded high-quality earthquake recording coverage in the region since 2017. Using this dataset, the research applies a broadband Bayesian inversion framework to estimate key seismological parameters from acceleration Fourier amplitude spectra (FAS). The inversion jointly resolves source parameters (moment magnitude, stress parameter), path parameters (geometrical spreading, anelastic attenuation), and site parameters (frequency-dependent amplification and ĸ₀), while also quantifying the uncertainties and trade-offs inherent in the inversion process. Using a large-scale dataset of recorded motions, the inversions provide region- specific source and path parameters that are generally consistent with other regions in Central and Eastern North America. The inverted site response parameters across different sites are classified into six groups through spectral clustering, which classifies stations based on their amplification characteristics. The inverted ĸ₀ values systematically vary between clusters but do not correlate well with subsurface characteristics. Posterior distribution analyses reveal strong correlations between some model parameters, highlighting the inherent trade-offs in the inversion process, with the strongest correlation between the stress parameter and ĸ₀. Focusing on the inverted site parameters of site amplification and ĸ₀, the work clarifies why simplified slope-based methods for estimating ĸ₀ often produce biased results. These methods are sensitive to the selected frequency band for the slope calculation, especially in relation to the source corner frequency, and are significantly influenced by assumptions regarding the site amplification. These issues limit the robustness of slope-based ĸ₀ methods compared to inversion-based approaches. This dissertation also considers the influence of the inversion dataset on the resulting seismological parameters. Utilizing only near-source data (≤ 25 km), which can reduce the dataset size by factors of 10 to 20, makes it difficult to separate source and site parameters. In particular, trade-offs between the stress parameter and ĸ₀ are significant. Expanding distance coverage to increase the dataset size mitigates these trade-offs and improves the reliability of source, path, and site parameter separations. The insights and methodologies developed here inform the creation of region- specific GMMs using the inverted seismological parameters and establish pathways for adapting this framework to other induced seismicity areas, including the Midland Basin and Eagle Ford Shale regions in Texas.Civil, Architectural, and Environmental Engineerin
UT Wind Ensemble Collection finding aid
No full textThe UT Wind Ensemble collection spans nearly 20 years (1973-1991) and includes original concert recordings, primarily on reel-to-reel tape with some content on VHS. Conductors represented in the collection include Thomas Lee, Jerry Junkin, and Glenn Richter. Some recordings have limited program information available.UT Librarie
Designing nanocrystal donor : molecular acceptor interfaces for improved charge and energy transfer
Full text linkHybrid 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
Full text linkThis 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