Bayesian Analysis of Binary Diagnostic Tests and Panel Count Data

This dissertation mainly explores several challenging topics that arise in diagnostic tests and panel count data in the Bayesian framework. Binary diagnostic tests, particularly multiple diagnostic tests with repeated measures and diagnostic procedures with a large number of raters, are studied. For panel count data, most traditional methods only handle panel count data for a single type of recurrent event. In this dissertation, we primarily focus on the case with multiple types of recurrent events. In Chapter 1, an introduction to the binary diagnostic tests data and panel count data is presented and related literature works are briefly reviewed. To make the dissertation more coherent for the later chapters, some preliminary theories and algorithms, for instance the Metropolis Hastings algorithm, are presented. Finally, an outline of the dissertation organization is put forward. In Chapter 2, a model for multiple diagnostic tests, applied repeatedly over time on each subject, is proposed; gold standard data are not required. The model is identifiable with as few as three tests; and correlation among tests at each time point in the diseased and non-diseased populations, as well as across time points is explicitly included. An efficient Markov chain Monte Carlo (MCMC) scheme allows for straightforward posterior inference. The proposed model is broadly illustrated via simulations and scaphoid fracture data from a prospective study (Duckworth et al., 2012) is analyzed. In addition, omnibus tests constructed from individual tests in parallel and serial are considered. In Chapter 3, a Bayesian hierarchical conditional independence latent class model for estimating sensitivities and specificities for a large group of tests or raters is v proposed, which is applicable to both with-gold-standard and without-gold-standard situations. Through the hierarchical structure, not only are the sensitivities and specificities of individual tests estimated, but also the diagnostic performance of the whole group of tests. For a small group of tests or raters, the proposed model is further extended by introducing pairwise covariances between tests to improve the fitting and to allow for more modeling flexibility. Correlation residual analysis is applied to detect any significant covariance between multiple tests. Just Another Gibbs Sampler (JAGS) implementation is efficiently adopted for both models. Three real data sets from literature are analyzed to explicitly illustrate the proposed methods.. In Chapter 4, a Bayesian semiparameteric approach is proposed to analyze panel count data for multiple types of recurrent events. For each type of event, the proportional mean model is adopted to model the mean count of the event, where its baseline mean function is approximated by monotone I-splines (Ramsay et al., 1988). Correlation between multiple events is modeled by common frailty terms and scale parameters. Unlike many frequentist estimating equation methods, our approach is based on the observed likelihood and makes no assumption on the relationship between the recurrent processes and the observation process. Under the Poisson process assumption, an efficient Gibbs sampler based on a novel data augmentation is developed for the MCMC sampling. Simulation studies show good estimation performance of the baseline mean functions and the regression coefficients; meanwhile the importance of including the scale parameter to flexibly accommodate the correlation between events is also demonstrated. Finally, a skin cancer data example is fully analyzed to illustrate the proposed methods. In Chapter 5, a brief summary of the studies we have completed in the previous chapters is delivered and at the same time we put forward some ideas for future work in each topic covered

Study of the Effect of Centrifugal Force on Rotor Blade Icing Process

In view of the rotor icing problems, the influence of centrifugal force on rotor blade icing is investigated. A numerical simulation method of three-dimensional rotor blade icing is presented. Body-fitted grids around the rotor blade are generated using overlapping grid technology and rotor flow field characteristics are obtained by solving N-S equations. According to Eulerian two-phase flow, the droplet trajectories are calculated and droplet impingement characteristics are obtained. The mass and energy conservation equations of ice accretion model are established and a new calculation method of runback water mass based on shear stress and centrifugal force is proposed to simulate water flow and ice shape. The calculation results are compared with available experimental results in order to verify the correctness of the numerical simulation method. The influence of centrifugal force on rotor icing is calculated. The results show that the flow direction and distribution of liquid water on rotor surfaces change under the action of centrifugal force, which lead to the increasing of icing at the stagnation point and the decreasing of icing on both frozen limitations

From China to the US: nutrition, diet and acculturation of Chinese employed in high-tech industries - Results from a web-based survey

Background: Due to the fast development of economies in China and the great needs of professionals in the US, the population of highly educated young Chinese professionals working in high-tech industries has grown very fast in both countries. This population was suggested to have risk of consuming high energy and fat diet in both countries. Objectives: This study aimed to investigate the associations of dietary intake with nutrition knowledge, attitude, dietary self-efficacy and acculturation among Chinese working in high-tech industries in China and in the US. Methods: This study was a cross-sectional self-administered online survey. We studied 925 Chinese aged 20-45 years, who worked in high-tech industries and had at least a bachelor degree in four sub-groups: employees of Chinese companies in China; employees of American companies in China; Chinese-born immigrant in the US; and American-born Chinese in the US. A web-based questionnaire including a food frequency questionnaire (FFQ) was developed to assess total energy and fat intakes, nutrition knowledge, attitudes, dietary self-efficacy. Four domains of acculturation were assessed among Chinese in the US. Using these data, we compared the four sub-groups and tested the prediction model of dietary intake and BMI. Results: Our results showed that American-born Chinese participants consumed significantly higher energy and fat than the other three groups. Participants in the US had higher nutrition knowledge, attitude and self- efficacy than participants in China. Chinese-born immigrant men in the US had the highest nutrition knowledge and attitude and the lowest prevalence of overweight among the four study groups of men. The study results suggested that preferring Chinese food and Chinese leisure activity are predictors of lower energy and fat intake in Chinese-born immigrants. Conclusions: The Chinese-born immigrants showed significant advantages in nutrition knowledge, attitude, and dietary self-efficacy and had the lowest prevalence of overweight in men. American-born Chinese consumed the highest energy and fat among the four study groups even though their nutrition knowledge, attitude and self-efficacy were high. Future nutrition promotion programs should make use of these cultural and environmental differences when designing theses programs. The web-based survey method can be utilized in future nutrition research

An initial biochemical and cell biological characterization of the mammalian homologue of a central plant developmental switch, COP1

BACKGROUND: Constitutive photomorphogenic 1 (COP1) has been defined as a central regulator of photomorphogenic development in plants, which targets key transcription factors for proteasome-dependent degradation. Although COP1 mammalian homologue has been previously reported, its function and distribution in animal kingdom are not known. RESULTS: Here we report the characterization of full-length human and mouse COP1 cDNAs and the genomic structures of the COP1 genes from several different species. Mammalian COP1 protein binds to ubiquitinated proteins in vivo and is itself ubiquitinated. Furthermore, mammalian COP1 is predominately nuclear localized and exists primarily as a complex of over 700 kDa. Through mutagenesis studies, we have defined a leucine-rich nuclear export signal (NES) within the coiled-coil domain of mammalian COP1 and a nuclear localization signal (NLS), which is composed of two clusters of positive-charged amino acids, bridged by the RING finger. Disruption of the RING finger structure abolishes the nuclear import, while deletion of the entire RING finger restores the nuclear import. CONCLUSIONS: Our data suggest that mammalian COP1, similar to its plant homologue, may play a role in ubiquitination. Mammalian COP1 contains a classic leucine-rich NES and a novel bipartite NLS bridged by a RING finger domain. We propose a working model in which the COP1 RING finger functions as a structural scaffold to bring two clusters of positive-charged residues within spatial proximity to mimic a bipartite NLS. Therefore, in addition to its well-characterized role in ubiquitination, the RING finger domain may also play a structural role in nuclear import