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Topics in Applied Statistics
No full textOne of the fundamental goals of statistics is to develop methods which provide improved inference in applied problems. This dissertation will introduce novel methodology and review state-of-the-art existing methods in three different areas of applied statistics. Chapter 2 focuses on modelling subcommunity dynamics in gut microbiome data. Existing methods ignore cross-sample heterogeneity in subcommunity composition; we propose a novel mixed-membership model which models cross-sample heterogeneity using the phylogenetic tree and as a result is robust to mispecifying the number of subcommunities. Chapter 3 reviews state-of-the-art methods in recommender systems, including collaborative filtering, content-based filtering, hybrid recommenders, and active recommender systems. Existing literature has focused primarily on bespoke applications; statisticians have an opportunity to build recommender system theory. Chapter 4 proposes a novel method of accounting for time-based design inconsistencies in Bayesian network meta-analysis models and discovers non-linear time trends in the effectiveness of vancomycin as a MRSA treatment. Chapter 5 provides some concluding remarks.</p
Team-Based Qualitative Rapid Analysis: Approach and Considerations for Conducting Developmental Formative Evaluation for Intervention Design.
No full textQualitative rapid analysis is one of many rapid research approaches that offer a solution to the problem of time constrained health services evaluations and avoids sacrificing the richness of qualitative data that is needed for intervention design. We describe modifications to an established team-based, rapid analysis approach that we used to rapidly collect and analyze semi-structured interview data for a developmental formative evaluation of a cardiovascular disease prevention intervention. Over 18 weeks, we conducted and analyzed 35 semi-structured interviews that were conducted with patients and health care providers in the Veterans Health Administration to identify targets for adapting the intervention in preparation for a clinical trial. We identified 12 key themes describing actionable targets for intervention modification. We highlight important methodological decisions that allowed us to maintain rigor when using qualitative rapid analysis for intervention adaptation and we provide practical guidance on the resources needed to execute similar qualitative studies. We additionally reflect on the benefits and challenges of the described approach when working within a remote research team environment.ClinicalTrials.gov: NCT04545489
Investigation of 2D Hybrid Organic-Inorganic Perovskite Thin Films Deposited by RIR-MAPLE for Heterostructure Integration
No full textThe power conversion efficiency of perovskite solar cells has increased significantly in the past 10 years from around 13% to over 25%. However, the most common perovskite absorber materials, three-dimensional (3D) perovskites, are challenged by moisture stability which hinders their more widespread commercialization. One approach to increase moisture stability is to incorporate a layer of hydrophobic ligands on top of the absorber layer in the form of a two-dimensional (2D) perovskites, thereby forming a 2D-on-3D heterostructure, however there are significant processing challenges. This dissertation conducts a careful investigation of n = 1 2D perovskite thin films deposited using a technique called resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) to better understand and then improve the heterostructure. The major conclusions of this work are that any halide mixing likely occurs in the 3D layer only at the heterostructure interface due to the site preferences that bromine and iodine have in the octahedra. Several supplemental processing parameters – deposition scheme, growth temperature, and solvent ratio (DMSO:MEG) – were used to successfully increase the average grain size, increase the amount of vertically oriented grains, modify the morphology, and decrease the Stokes shift in (PEA)2PbI4 thin films. Ultimately, out-of-plane conductivity in (PEA)2PbI4 thin films was successfully improved using the sequential deposition scheme, elevated growth temperature, and decreased amount of matrix solvent. The structural improvements and improved out-of-plane conductivity were also demonstrated for the heterostructure when modified processing conditions were used to deposit the 2D layer. The process-structure-property relationships investigated in this work serve as guidelines for tailoring 2D-on-3D heterostructures.</p
An <i>In Vitro</i> Microfluidic Alveolus Model to Study Lung Biomechanics.
No full textThe gas exchange units of the lung, the alveoli, are mechanically active and undergo cyclic deformation during breathing. The epithelial cells that line the alveoli contribute to lung function by reducing surface tension via surfactant secretion, which is highly influenced by the breathing-associated mechanical cues. These spatially heterogeneous mechanical cues have been linked to several physiological and pathophysiological states. Here, we describe the development of a microfluidically assisted lung cell culture model that incorporates heterogeneous cyclic stretching to mimic alveolar respiratory motions. Employing this device, we have examined the effects of respiratory biomechanics (associated with breathing-like movements) and strain heterogeneity on alveolar epithelial cell functions. Furthermore, we have assessed the potential application of this platform to model altered matrix compliance associated with lung pathogenesis and ventilator-induced lung injury. Lung microphysiological platforms incorporating human cells and dynamic biomechanics could serve as an important tool to delineate the role of alveolar micromechanics in physiological and pathological outcomes in the lung
Automorphic-twisted summation formulae for pairs of quadratic spaces
No full textConjectures of Braverman-Kazhdan, L. Lafforgue, Ngô and Sakellaridis imply that all affine spherical varieties admit generalized Poisson summation formula. In this dissertation we establish a generalized Poisson summation formula for certain spaces of test functions on the zero locus of a quadratic form. The functions are built from the Whittaker coefficients of automorphic representations on GL_n. We also give an expression of the local factors where all the data is unramified. </p
Network-level dynamics underlying a combined rTMS and psychotherapy treatment for major depressive disorder: An exploratory network analysis.
No full textBackgroundDespite the growing use of repetitive transcranial magnetic stimulation (rTMS) as a treatment for depression, there is a limited understanding of the mechanisms of action and how potential treatment-related brain changes help to characterize treatment response. To address this gap in understanding we investigated the effects of an approach combining rTMS with simultaneous psychotherapy on global functional connectivity.MethodWe compared task-related functional connectomes based on an idiographic goal priming task tied to emotional regulation acquired before and after simultaneous rTMS/psychotherapy treatment for patients with major depressive disorders and compared these changes to normative connectivity patterns from a set of healthy volunteers (HV) performing the same task.ResultsAt baseline, compared to HVs, patients demonstrated hyperconnectivity of the DMN, cerebellum and limbic system, and hypoconnectivity of the fronto-parietal dorsal-attention network and visual cortex. Simultaneous rTMS/psychotherapy helped to normalize these differences, which were reduced after treatment. This finding suggests that the rTMS/therapy treatment regularizes connectivity patterns in both hyperactive and hypoactive brain networks.ConclusionsThese results help to link treatment to a comprehensive model of the neurocircuitry underlying depression and pave the way for future studies using network-guided principles to significantly improve rTMS efficacy for depression
Understanding the Crime Gap: Violence and Inequality in an American City
No full text The United States has experienced an unprecedented decline in violent crime over the last two decades. Throughout this decline, however, violent crime continued to concentrate in socially and economically disadvantaged urban neighborhoods. Using detailed homicide records from 1990 to 2010, this study examines the spatial patterning of violent crime in Chicago to determine whether or not all neighborhoods experienced decreases in violence. We find that while in absolute terms nearly all neighborhoods in the city benefited from reductions in homicide, relative inequality in crime between the city's safest and most dangerous neighborhoods actually increased by 10 percent. This increase was driven by a greater rate of decline in the city's safest neighborhoods. This crime gap can be partly attributed to the decreasing association between concentrated disadvantage and homicide in the safest neighborhoods. We also find that the decline did not significantly alter the spatial distribution of crime, as homicides remained concentrated in the initially most dangerous neighborhoods and their adjacent areas. </jats:p
Patient satisfaction after multiple revision surgeries for adult spinal deformity.
No full textObjectiveRevision surgery is often necessary for adult spinal deformity (ASD) patients. Satisfaction with management is an important component of health-related quality of life. The authors hypothesized that patients who underwent multiple revision surgeries following ASD correction would exhibit lower self-reported satisfaction scores.MethodsThis was a retrospective cohort study of 668 patients who underwent ASD surgery and were eligible for a minimum 2-year follow-up. Visits were stratified by occurrence prior to the index surgery (period 0), after the index surgery only (period 1), after the first revision only (period 2), and after the second revision only (period 3). Patients were further stratified by prior spine surgery before their index surgery. Scoliosis Research Society-22 (SRS-22r) health-related quality-of-life satisfaction subscore and total satisfaction scores were evaluated at all periods using multiple linear regression and adjustment for age, sex, and Charlson Comorbidity Index.ResultsIn total, 46.6% of the study patients had undergone prior spine surgery before their index surgery. The overall revision rate was 21.3%. Among patients with no spine surgery prior to the index surgery, SRS-22r satisfaction scores increased from period 0 to 1 (from 2.8 to 4.3, p 0.3). Among patients with multiple revisions, 40% experienced rod fracture, 40% proximal junctional kyphosis, and 33% pseudarthrosis.ConclusionsAmong patients undergoing ASD surgery, revision surgery is associated with decreased satisfaction, and multiple revisions are associated with additive detriment to satisfaction among patients initially undergoing primary surgery. These findings have direct implications for preoperative patient counseling and establishment of postoperative expectations
Accumulation and Distribution of Trace Elements and Radionuclides in Agricultural Soils Impacted from Long-term Phosphate Fertilizer Application
No full textExcessive application of phosphate fertilizers can result in the accumulation of both phosphorus (P) and trace metals (U, Cd) in agricultural soils, which could end up in crops and cause chronic harms to the environment. Here we investigate the quality of soils in a long-term trial corn/soybean field at the Tidewater Research Station, North Carolina, where both surface soils (top 20 cm) and subsurface soils (up to 150 cm) were collected from five plots with different application rates of P-fertilizer since 1966. We analyzed a broad range of major nutrients and trace elements with focus on metals and metalloids including Cd, U, V, Cr, As, and Sr, which are notably enriched in the used P-fertilizer relative to local background soil. The study aims to investigate the trace elements accumulation, distribution, and mobilization in the soils. The results show that the impact of long-term P-fertilizer application was mostly manifested in the top layers of the soils compared to deeper soils, with the exception of As showing accumulation in the deeper soils. Among the five plots, bulk soils applied with higher rates of P-fertilizers had higher concentrations of P and trace elements than soils without using P-fertilizers. The concentration of Cd was significantly correlated with that of P (r = 0.97, p = 0.005) in the bulk surface soils, indicative of its direct contribution from P-fertilizer and accumulation in the soil. In contrast, other trace elements exhibited weaker or little correlations with P in the bulk surface soils. The potential bioavailability of elements in soils was assessed via the Mehlich III extraction method, showing that the higher application rate of P-fertilizer, the higher percent of bioavailability was found for Cd (up to 65% of the bulk soil) and P (up to 56%), whereas the other trace elements had much lower bioavailable fractions (0.4 – 12%). Strong correlations (r > 0.9, p < 0.05) were observed between the bioavailable concentrations of P and that of Cd, U, Cr, V, As, Sr in the surface soils. This indicates that the bioavailable form of trace elements is more sensitive in reflecting the impacts from P- fertilizer on surface soils. Four-step sequential leaching tests (i.e., F1: exchangeable, F2: reducible, F3: oxidizable, and F4: residual) conducted for the surface soils indicated differential mobilization of trace elements under different P-fertilizers application rates. Greater portions of Cd were found in the mobile fractions (F1 – F3) of soils with higher P-fertilizer input, while Sr was dominantly present in the residual fraction (F4: 95 – 97%), and redox-sensitive elements were higher in the reducible (As, V) and oxidizable (U, Cr) fractions than Sr, reflecting their redox-dependent mobilization potential. Overall, our systematic data analysis shows the effect of long-term P-fertilizer application on the accumulation of trace elements in soils. Further studies should evaluate the uptake of trace elements by crops and their mobilization to the underlying groundwater resources