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Development of a new laser doppler vibrometer-based non-contact damage detection system for cracks in rail head
Rail defects are one of the dominant causes of train derailments and an essential factor affecting transportation safety. Among the rail defects, transverse defects (TDs), which are cracks located transversely in rail heads, are one of the main causes of derailments. When TDs are left undetected, their size expands, leading to rail breaks. Therefore, the railway transportation community is interested in the detection of such defects at speeds that do not obstruct the routine railroad operation. The goal of this research is to develop a novel LDV-based noncontact damage detection system for TDs. The tasks performed herein to achieve this goal (i.e., the objective of the study) were: (i) extensive literature review and in-situ testing to understand the vibrations resulting from the propagating waves in rail, (ii) numerical modeling of the damage detection system, (iii) rigorous laboratory and in-situ testing to understand the noise in LDV measurements as well as to evaluate the performance of the damage detection system, and (iv) analytical work to develop filters to minimize the noise in the LDV measurements. Accordingly, the configuration of the developed damage detection consists of two LDVs attached vertically in front of a rail car to measure guided waves in the rail head, which are induced by rail-wheel interaction. This system uses the LDV measurements to detect a change in the relative amplitudes of the recorded waves caused by a defect in the frequency range between 30 kHz to 100 kHz. The lower cut-off frequency was selected conservatively since it was shown in the literature that guided waves start to localize in the rail head after approximately 15 kHz. The higher cut-off frequency was selected since (i) the guided waves below 100 kHz can be used for transverse defect detection (as the frequency exceeds 100 kHz, waves are susceptible to surface defects), and (ii) the measurements collected from rail during the passage of operating trains showed that the power of the excitations induced by wheel-rail interactions is dominant up to approximately 100 kHz. The main challenge during the development of the system was speckle noise, which is inevitable due to the inherent nature of the measurements performed by LDVs placed on a moving platform. Consequently, the damage detection framework associated with the system operates as follows: 1) in the pre-processing stage, time-varying mean and impulsive noise in the recorded LDV signals are filtered and then the changes in the LDV signals in the frequency range of interest are quantified and monitored using moving standard deviation, 2) in the post-processing stage, two damage features, which are based on the relative change in the moving standard deviations and transfer functions between two measurement points are combined using multivariate statistical analysis to create a damage index that shows the location of rail segments which are affected by a defect. The goal of impulsive noise filtering and transfer functions in the framework is to minimize the speckle noise. The field tests demonstrated that rail segments consisting of a defect can be identified by the developed system.Civil, Architectural, and Environmental Engineerin
Methods for matrix completion
In this paper, we are going to provide major results for two sorts of Matrix Completion problems. One involves the recovery of a low rank matrix and the other involves the recovery of an approximately low rank matrix based on a small number of observed entries. In the end of the paper, we are going to demonstrate the feasibility of the recovery methods discussed on randomly generated low rank and approximately low rank matrices.Computer Science
Factors associated with food delivery app use in young adults
Food delivery apps are highly popular among young adults and are often used to purchase calorie-dense foods, which are associated with a variety of health issues such as increased risk for obesity. Limited research exists on the use of food delivery apps and the research that has been conducted, focused on adults, suggests that food delivery app use differs by sociodemographic factors. Thus, the purpose of this study is 1) to describe food delivery app use among young adults, and 2) to examine the association between young adult food delivery app use and factors including age, race, ethnicity, sex, SES, food insecurity, living arrangement, financial responsibility, and full-time student status. Data are from the Promoting Young Adult Health Survey, a cross-sectional online survey with 1,038 young adults online from the Qualtrics panel January-February 2022. Poisson regression was used to examine the relationship between food delivery app use and the sociodemographic variables. Our results suggest that participants who reported being non-Hispanic Black and Hispanic had greater food delivery app use frequency as compared to participants who reported being white. Having higher perceived subjective social status, being food insecure, being financially responsible, and being a full-time student were all significantly associated with greater food delivery app use frequency. Living with someone else was significantly associated with lower food delivery app use frequency. Age, sex, and ‘Other’ Race/ethnicity were not associated with food delivery app use frequency. Overall, young adults use food delivery apps approximately twice a week with vulnerable groups such as Black and Hispanic young adults and young adults reporting food insecurity having greater frequency of use. This study provides a first step in understanding the characteristics of young adults who use food delivery apps more frequently. Given that this new technology can both increase access to unhealthy food options as well as healthy food options, future research is needed to better understand the types of food purchased through food delivery apps and the differences by the sociodemographic factors explored in this study.Kinesiology and Health Educatio
Service integration planning assessment for Capital Metropolitan Transportation Authority and Project Connect in Austin, TX
During the summer of 2023, I had the unique opportunity work as a service integration planning intern with the Capital Metropolitan Transportation Authority (CapMetro), the city of Austin’s transportation agency, where I investigated and analyzed the different obstacles the agency faces in successfully integrating its existing bus network with the future light rail transit (LRT) line that is scheduled to be built as part of Project Connect. As the LRT portion of Project Connect begins to take shape, it is imperative that that Austin’s existing bus network is adequately integrated with the light rail service in order to ensure that existing and potentially
new public transit users are enticed to using the new system, and that those who use intend to use both methods of transport will be able to make a smooth transition between the bus and light rail and vice versa. This process of service integration entails a variety of both qualitative and quantitative changes that primarily deal with user experience of public transportation, including the quality of the ride on the bus, how long the trip will take, and the physical transition from one mode of transportation to another. The research methodology in this report – a two-step process consisting of a desktop-based assessment of various ridership and service quality statistics and an in-person survey of station areas to analyze various design elements and amenities – is an analysis framework of my creation. My findings reveal that CapMetro will have an easier time integrating both modes of transit along station areas that are more densely populated and economically developed. For integration to be successful across the system, CapMetro should make necessary improvements to its bus stops and service, and work with the City of Austin to upgrade nearby sidewalks and roads. The report I prepared for CapMetro last summer and the additional research I have completed for this report will hopefully provide valuable insight to the agency as it progresses with Project Connect. Likewise, I hope this report could serve as a model for transportation agencies in other cities embarking on similar projects and exploring how they can better integrate multiple modes of transportation.Community and Regional Plannin
Enhanced connectivity evaluation of heavily faulted reservoirs and numerical simulation of charge over geologic time to predict present-day spatial distributions of fluid composition
Accurate spatial description of petrophysical and fluid properties is paramount for effective fluid-production decisions made during the exploration and development phases of a subsurface hydrocarbon reservoir. Of all the components of hydrocarbon reservoir description, hydraulic connectivity typically carries the highest uncertainty; inaccurate connectivity evaluations routinely cause under-performance of fluid production, hence low recovery factors. Shortcomings are often faced when applying conventional approaches to hydraulic connectivity assessment. Although conventional downhole fluid analysis (DFA) workflows have proven effective in assessing reservoir connectivity, adequate and sufficient DFA data are not always available; uncertainties irremediably arise because of added rock heterogeneity. Additionally, while equilibrated asphaltene gradients -measured through DFA probes- imply connectivity, ongoing reservoir fluid geodynamics (RFG) processes, such as present-day hydrocarbon charging, can preclude fluid equilibration in a connected reservoir. A comprehensive assessment approach that utilizes all available data streams is sorely needed to overcome the interpretation challenges associated with variable fluid properties across spatially heterogeneous reservoirs. This dissertation develops and verifies a new interpretation workflow to quantify the connectivity of a heavily faulted reservoir in the deepwater Gulf of Mexico. The concept of Areal Downhole Fluid Analysis (ADFA) is introduced and applied to assess local connectivity leading to reservoir-scale connectivity. Analyzed data also include pressure-volume-temperature (PVT) reports, pressure surveys, well logs, and geochemical measurements. The study yields a verifiable connectivity description where faults previously regarded as sealing are classified into sealing or partially transmissive; unresolved faults are also detected as part of the interpretation workflow. Additionally, RFG processes are invoked to investigate oil biodegradation in the presence of asphaltene clustering trends toward the bottom of one sandstone. A spatial correlation of oil viscosity with asphaltene concentration is then derived and successfully implemented to estimate oil viscosity. Spatial fluid compositional variations in subsurface reservoirs can be explained via fluid mixing dynamics of hydrocarbon source charges over geologic time. Many reservoirs experience separate gas and oil charges that can lead to a variety of different outcomes for fluid types and their spatial distribution. Subsequent hydrocarbon charges mix with hydrocarbon in-place, leading to the expansion of the original hydrocarbon volume; underlying water is also displaced downward causing leakage at the spill point. For high-pressure basins such as the Gulf of Mexico, fluid mixing processes can lead to increased solution gas, large gas-oil ratio (GOR) gradients, and formation of viscous oil and tar mat at the free oil-water contact. In some reservoirs, the present-day outcome of oil and gas mixing over geologic time can be established by detailed chemical evaluation of reservoir fluids sampled from multiple reservoir locations. Methane carbon isotope analysis can also be used to evaluate the extent of fluid mixing and to infer the origin of solution gas, while oil charges of different maturities give rise to variable geochemical biomarkers. Thermodynamic equilibration in reservoirs is established in this work via Flory-Huggins-Zuo’s equation of state (FHZ EoS), asphaltene gradients, and cubic EoS modeling of solution gas for reservoir fluids. Reservoir simulations of a point gas charge into oil-bearing rocks with various geometries and charge rates is additionally used to establish conditions which lead to excellent fluid mixing vs. those conditions that lead to large disequilibrium gradients. Reservoir simulations over geologic time further predict fluid properties and compositions across tectonic features. The latter predictions depend on (1) reservoir properties such as hydraulic connectivity, (2) the properties and locations of charge fluids, such as density and viscosity, and (3) the time elapsed since the inception of charge. Comparison between predicted and measured spatial fluid distributions enables history matching of reservoir charge. Numerical modeling results coupled with fluid mechanics establish that there is no possibility that the studied reservoirs could have had a gas charge followed by an oil charge; in the three reservoirs examined, oil must have arrived first, followed by a biogenic gas charge. Furthermore, modeling results establish a wide range of charge conditions that can lead to excellent fluid mixing and equilibration. The result obtained that biogenic gas charge can occur after oil charge challenges widely-held conventional thinking. In the first examined reservoir, methane isotope concentrations are invariant along two stacked and poorly connected sandstones, with methane isotope values (δ¹³C) ~ -60‰, indicating that 2/3 of the solution gas is biogenic in nature. It was found that forced convection driven by addition of biogenic gas at the base of the oil column could originate the observed results. Simulation of gas charge into undersaturated oil during more than 100,000 years results in excellent mixing, matching the present-day average GOR of 1000 scf/stb. In the second examined reservoir, significant oil compositional variations across connected sandstones are observed via a bimodal distribution of fluids consisting of an active diffusional gradient together with a quasi-equilibrium gradient evidenced by asphaltene, GOR, and methane isotope gradients. The bimodal distribution of fluids is replicated by history-matching of source-fluid charge where present-day methane (C₁) mole fraction in the top half of the column (up to 70%) reflects the high concentration of biogenic gas present there, compared to approximately 45% in the lower half of the column. This conclusion is also consistent with mole fractions of intermediate and heavy components (C₄-C₆ and C₂₀-C₄₅+) stemming from the numerical simulations. In the third examined reservoir, three stacked sandstones received similar oil and gas source charges, yet they were subject to different RFG processes that led to entirely different present-day spatial fluid distributions: a near-critical condensate in the upper zone, black oil in the middle zone, and dry gas in the lower zone. A gas-washing process leading to the observed fluid distributions is explained where added pure C₁ strips the oil from half of its intermediate components, and where the C₂-C₃ mole fraction decreases from 18% to 10% during 100,000 years of source-fluid charge.Petroleum and Geosystems Engineerin
Ultrafast laser microsurgery for vocal fold scarring therapy
Ultrashort laser pulses can provide unparalleled microsurgical precision. Further, ablation with ultrafast lasers offers the only means to create precise cuts inside bulk tissue without damaging surrounding tissue. Despite numerous clinical applications identified in benchtop studies, ultrafast laser surgery is rarely used outside of ophthalmology as the miniaturized optical systems required to target in vivo tissue structures do not exist. For example, previous studies have shown that vocal fold (VF) scarring may be treated with tightly-focused ultrashort laser pulses to provide an injection space for therapeutic biomaterials, however the large optics and free space delivery of laser light have thus far limited clinical translation. Solving the challenges surrounding optical system miniaturization, while enabling the tight beam focusing and high energy pulse delivery required for ultrafast laser surgery, can provide surgeons with a tool for precise sub-epithelial ablation, potentially allowing for improved localization and retention of therapeutic biomaterials within scarred VF. Thus, this dissertation focuses on the development, testing, and realization of an ultrafast laser surgery system to enable sub-epithelial ablation of scarred vocal folds in vivo towards an improved treatment for vocal fold scarring. We first report the optical scattering properties and damage thresholds of VF tissues which were measured using an image-guided ultrafast laser ablation technique recently developed in our lab. These results provide a baseline assessment of the laser parameters required to produce highly-localized ablation “voids” within VF, and enable selection of appropriate operating parameters when performing surgery in future ex vivo and in vivo studies. We then studied the nonlinear and thermo-optical responses of various optical materials using the z-scan technique. Results obtained here help us identify the most suitable lens substrates for our miniaturized surgery probe. The second part of this dissertation details the design and realization of a miniaturized ultrafast laser surgery probe designed to treat VF scarring. The probe’s high numerical aperture, side-firing architecture, and small form factor facilitate sub-epithelial ablation to aide in localization of injectable biomaterials within VF tissues. We performed ablation studies on freshly excised porcine hemilarynges and found that large voids can be created beneath the vocal fold epithelium by rapidly translating the probe tip across the tissue surface using external stages. We then demonstrated localization of a model biomaterial within these voids, suggesting that the probe may be utilized for the proposed vocal fold scarring treatment. The final part of this dissertation describes ablation and biomaterial injection studies performed with the ultrafast laser surgery probe in a live animal model. We successfully demonstrated sub-epithelial void formation in both healthy and scarred canine VF using the surgery system. Further, we showed that a model biomaterial could be injected into these voids, suggesting that our laser surgery system can be used to treat vocal fold scarring in a clinical setting.Biomedical Engineerin
The selling of authenticity
This research explores the ways organizational communication practitioners perceive and engage with, social media influencers. Specific attention is paid to the potential for influencers to support marketing efforts in ways that are distinct from the value offered by engagement with traditional celebrities. A qualitative study was conducted with 10 marketing specialists who have participated in marketing efforts that utilized social media influencers. Using thematic analysis, five themes were identified reflecting the nature of the relationship between organizations and influencers: brand, influencer, marketing, celebrity, and social media. These themes reveal that marketers may struggle to provide a clear definition of what constitutes an influencer, but view influencers as different from traditional celebrities. Additionally, social media influencers are viewed by marketers as a means of presenting authentic communication to audiences.Communication Studie
Bioinformatic approaches to characterize phenotypic variability in craniofacial development
Congenital birth defects are the leading cause of infant mortality in the United States. These defects vary widely in their penetrance and expressivity, even when the genetic causes for these malformations are identical. Understanding these interactions is a key aspect of developmental biology. I used a zebrafish model of the zinc finger transcription factor gata3 to study the genetic basis of phenotypic variation. Mutation of gata3 in humans causes the highly variable hypoparathyroidism, sensorineural deafness, and renal dysplasia (HDR) syndrome. In zebrafish, point mutation of this gene induces a range of palate defects.
I used an unbiased bioinformatic approach to identify environmental modifiers of gata3 mutant craniofacial phenotypes. RNA-seq data from gata3 knockdown, gata3 overexpression, and control fish were input into the LINCS L1000 database. Of the predicted chemical modifiers, I found two that exacerbated the mutant phenotype and two that lessened it. The combination of these chemicals and GO enrichment analysis suggested multiple potential pathways for Gata3 function, including Wnt signaling and RNA polymerase function. The signaling molecule sonic hedgehog (Shh) has also been shown to modulate the severity of the gata3 phenotype. I exposed zebrafish to a sub-teratogenic dose of Shh antagonist cyclopamine, and another group of zebrafish to both cyclopamine and gata3 knockdown. I performed RNA-seq on these zebrafish, demonstrating the similarity of the Shh- and Gata3-sensitive transcriptomes. To identify the most likely shared targets of these two molecules, I queried genes whose expression patterns mirrored the biological effect of exacerbated misregulation when exposed to cyclopamine as opposed to just gata3 knockdown alone. Using gene-disease association discovery, I was able to refine this gene list to 11 that have published links to clinical outcomes similar to the gata3 phenotype or with craniofacial malformations. I also used weighted gene co-expression network analysis to identify a module of genes the correlate strongly with co-regulation by Shh and Gata3, suggesting links to Wnt signaling. Together, my work yielded multiple methods to delineate candidate genes for further study in a developmental landscape of variation.Cellular and Molecular Biolog
A decision theoretic approach to combining inference across data sources with applications to subgroup analysis in clinical trials
Many research questions can not be answered by a single scientific study or source of data. To address this challenge, researchers develop principled ways to combine information from multiple studies to reach a conclusion. A very common instance of this problem is the combination of results across multiple clinical studies, commonly known as meta-analysis, usually with the understanding that results from individual studies are only available as published summary statistics. In this thesis I consider principled Bayesian decision theoretic approaches to the general problem of combining inference across multiple studies. After a discussion of the general problem I focus on the particular example that arises when the desired inference is subgroup analysis, that is, inference about how results for subpopulations of interest differ from the results of the larger study population. In the last chapter I consider an extension to a typical meta-analysis problem. Methodologically, the proposed solutions start with a decision theoretic approach to combining inference from two studies through the use of a utility function. Building on this foundation I then consider a more complex utility function for Bayesian population finding. Finally, expanding upon the same utility function I then consider more than two studies to propose a similar solution for a general meta-analysis problem.Statistic
On writing "Gothel, a witch's tale"
This report outlines the development process for my thesis feature script Gothel, A Witch’s Tale. The story is a retelling of the fairytale Rapunzel, in which the loner misfit witch Gothel joins forces with the loner misfit Princess Persinette to save each other and the Magical Forest. This report includes the development of the idea, the scene outline, first and final draft of my script.Radio-Television-Fil