Adolescence is a period of dynamic behavioural and emotional development that can increase young people's vulnerability to mental health problems. With 70% of mental disorders having their onset during childhood or adolescence, identifying modifiable factors of these disorders among adolescents can help inform future interventions aiming to improve mental health. One of these factors is electronic technology which has become pervasive in our modern society, occupying an important portion of young people's days and changing their lifestyle. This has created serious concerns regarding the impact of heavy recreational screen use on adolescents' health, especially with the vast majority exceeding the sedentary recreational screen time recommendations of 2 hours or less per day. Evidence suggests that screen time can be associated with adolescent mental health problems. However, little is known about how the extent, nature, and types of recreational screen engagement among adolescents are associated with mental health problems as the body of evidence is very mixed, and many questions remain unanswered. Accordingly, the aims of this dissertation were: i) to summarize the evidence regarding correlates of sedentary screen pursuits among youth, ii) to examine how different types of screens, incorporating their newer forms, are associated with adolescents' mental health cross-sectionally and longitudinally, iii) to examine the nature of screen use and its association with suicidal behaviours; and iv) to explore the moderating role of sex, age, and parental support in the association between screen time and different mental health problems. To achieve these objectives, we completed four manuscripts, all prepared for submission to peer-reviewed scientific journals: 1. A narrative review on the psychological correlates of sedentary screen time behaviour among children and adolescents. 2. Heavy social media use and psychological distress among adolescents: the moderating role of sex, age, and parental support. 3. Problematic technology use, suicidal ideation, and suicide attempt among adolescents: the moderating role of sex. 4. Longitudinal associations between different types of screen use and depression and anxiety symptoms in adolescents. Collectively, our results identified that high levels of sedentary screen behaviour are associated with more severe anxiety, depressive symptoms, and suicidality among adolescents. However, the strength of associations varied between some screen types. Additionally, the findings of this dissertation indicate that a further increase in screen time is associated with increased mental health problems. Lastly, an important role of sex and age in this association was identified. These results can be used to inform future research in this field and guide future interventions designed to manage screen use among adolescents and improve their mental health.

Indiana University-Purdue University Indianapolis (IUPUI) / Time-to-event outcomes are widely utilized in medical research. Assessing the cumulative effects of time-varying exposures on time-to-event outcomes poses challenges in statistical modeling. First, exposure status, intensity, or duration may vary over time. Second, exposure effects may be delayed over a latent period, a situation that is not considered in traditional survival models. Third, exposures that occur within a time window may cumulatively in uence an outcome. Fourth, such cumulative exposure effects may be non-linear over exposure latent period. Lastly, exposure-outcome dynamics may differ among groups defined by individuals' characteristics. These challenges have not been adequately addressed in current statistical models. The objective of this dissertation is to provide a novel approach to modeling group-specific dynamics between cumulative timevarying exposures and a time-to-event outcome. A framework of group-specific dynamic models is introduced utilizing functional time-dependent cumulative exposures within an etiologically relevant time window. Penalizedspline time-dependent Cox models are proposed to evaluate group-specific outcome-exposure dynamics through the associations of a time-to-event outcome with functional cumulative exposures and group-by-exposure interactions. Model parameter estimation is achieved by penalized partial likelihood. Hypothesis testing for comparison of group-specific exposure effects is performed by Wald type tests. These models are extended to group-specific non-linear exposure intensity-latency-outcome relationship and group-specific interaction effect from multiple exposures. Extensive simulation studies are conducted and demonstrate satisfactory model performances. The proposed methods are applied to the analyses of group-specific associations between antidepressant use and time to coronary artery disease in a depression-screening cohort using data extracted from electronic medical records.

A unified optimization framework for traffic signal priority scheduling based on the phasetime network models is presented in this research work with two mathematical programming formulations: (i) Mixed Integer Linear Programming (MILP) formulation and resilient MILP formulation (R-MILP). A heuristic algorithm is developed using the delay generated by the cumulative arrival and departure curves for searching optimum solution in phase-time network. An acceptance and rejection policy is also developed based on the proposed R-MILP. A set of numerical experiment with the proposed policy is conducted for fully adapted and coordinated phase-time network. The third set of numerical experiment is destined for the comparison of the performance of proposed phase-time network with the signal timing given by traditional traffic engineering method and Multi-Modal Intelligent Traffic Signal System (MMITSS) (1). The results show that in each case, the proposed formulation gives shorter delay and arterial travel time than the other two methods.

Cotton is a very important economical crop in the U.S. and throughout the world. The developments in molecular biology offer new and innovative approaches toward evaluating and understanding genetic mechanisms of important agronomical traits. Bacterial artificial chromosome (BAC) libraries have rapidly become the preferred choice for physical mapping. BAC-derived microsatellite or simple sequence repeats (SSRs) markers facilitate the integration of physical and genetic recombination maps. The first objective in this research was to identify chromosome locations of a set of BAC-derived SSR markers in tetraploid cotton. A total of 192 SSR primer pairs were derived from BAC clones of an Upland cotton (Gossypium hirsutum L.) genetic standard line TM-1. Using deletion analysis method, we assigned 39 markers out of the 192 primer pairs to 18 different chromosomes or chromosome arms. Chromosomal assignment of these markers will help to improve the current cotton genetic linkage maps and facilitate positional candidate gene cloning, comparative genome analysis, and the coordination of chromosome-based genome sequencing projects. Wild race stocks (Gossypium spp.) represent valuable resources for genetic improvement. Most primitive accessions are photoperiod sensitive; they do not flower under the long days of the U.S. cotton belt. Molecular markers were used to locate quantitative trait loci (QTLs) for node of first fruiting branch (NFB), node of first open boll (NOB), and fruiting score (FS). An F2 population consisted of 251 plants from the cross of a day neutral cultivar Deltapine 61, and a photoperiod sensitive accession Texas 701, were used in this study. For each trait, three major QTLs were mapped to chromosome 16, 21, and 25. QTL analysis was also conducted in two F2 populations generated from the cross between Deltapine 61 and two photoperiod sensitive accessions (T1107, PI 607174; T1354, PI 530082) of Upland cotton (G. hirsutum L.). QTL analysis indicated that NFB differed between the two F2 populations. Two major QTLs (q-NFB-c21-1 and q-NFB-c25-1) were found in population 1107; whereas, only one (q-NFB-c25-1) was important in population 1354. Discovering QTLs associated with flowering time may have the potential to facilitate day neutral conversion of wild photoperiod sensitive accessions.

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