No description available.

No description available.

Introduction: Executive functions (EFs) are a set of inter-related neurocognitive abilities, recruited for top-down, conscious control of thoughts, actions and emotions. EFs develop rapidly during the preschool period (age 3 to 6 years), which is the same time, during which the symptoms of Attention Deficit/Hyperactivity Disorder (ADHD), namely hyperactivity, impulsivity, and inattention, become evident. Furthermore, hyperactivity, inattention, and the EFs contribute to academic performance once children begin formal schooling. To clarify the interplay of these processes, this dissertation conducted 3 studies that used a longitudinal design (4 time-points) to investigate the development of EFs from age 3 to 6 years, the relations between EFs and hyperactivity across this same period of time, and their relative contributions to inattention and academic performance at 6 years of age. Study One: Children’s performance on EF tasks was examined across 4 time points, beginning at 36-48 months of age. Results indicated significant between-child variability for all EF component processes at 3 years of age, significant growth over time, and preliminary support for the theory that, among EFs, working memory may develop first. Furthermore, EF performance at 3 years of age made significant contributions to performance on complex tasks of problem solving and planning at 6 years of age. Study Two: The aim of study two was to evaluate the relations between EF, hyperactivity, and inattention. Results indicated significant between-child variability in EF task performance, with a decrease in variability from age 3 to 4.5 years. Hyperactivity at age 3 years reliably predicted hyperactivity at 6 years of age for females, who also had lower hyperactivity scores. In contrast, for males, child EF performance and parent-report of EF at age 3 years were the best predictors of hyperactivity at 6 years of age. Study Three: The aim of study three was to expand upon the relations between EF, hyperactivity, and inattention by evaluating their relative contributions to academic performance. There were limited relations between academic performance, hyperactivity, and inattention. However, EF performance at 3 years of age predicted age 6 reading and math, whereas parent-report EF only predicted reading. Furthermore, hyperactivity at 4.5 years of age moderated the relation between age 3 performance EF and age 6 academic performance, with this relation becoming stronger as hyperactivity increased. Conclusion: Together, these studies make several notable contributions to the field: (a) that initial EF abilities at 3 years of age are highly variable between children, but improve consistently over time, (b) that the relations between hyperactivity and EF appear to be different for males and females (or higher/lower levels of hyperactivity), and (c) that even in a community sample, hyperactivity moderates the EF-academic performance relation. These findings contribute to the early identification of hyperactivity and interindividual differences in EF abilities, in very young pre-schoolers, who may go on to have more difficulty in a formal schooling setting. / Graduate / 2023-08-09

Mechanical stress exerted on long bones stimulate ossification and it has been shown that the mechanical variable frequency promotes osteogenesis. This ex-vivo study aimed to investigate how compressive and cyclic loading frequency impacts longitudinal growth of long bones. Three separate experiments were performed utilizing fetal Sprague-Dawley rat bones as experimental model. In the first two trials metatarsals where used while tibias were tested in the third trial. The bones were loaded once with a material testing system, cultured in an incubator and had their length measured on several occasions throughout their growth period. Loading protocol and days of length measurement differed between the trials. The first trial failed, since all of the control bones decreased in length in relation to the day of loading, while they should at least have grown 30% on the fifth day after loading. The results obtained from the second trial indicate that the frequency 0.4 Hz has a great impact on longitudinal growth, with a length increase of 50%-60% in relation to the day of loading. A conclusion regarding the other frequencies studied could not be made due to high spread of length alteration data. The tibias from the last trial did not show any significant results. Moreover, it was concluded that compressive and cyclic loading do promote longitudinal growth, despite the great variation in length alteration for most of the bones, including the control bones. The findings of this study could serve as a foundation for a research study further investigating the relation between frequency and longitudinal growth.

University education across history and contexts aimed for a myriad of purposes, from the advancement of knowledge to educating citizens and contributing to the social good. With the rise of universities functioning in a market economy, and navigating higher education institutions' public role, some of the university purposes are constantly debated, and often without accounting for the students' perspectives. The purpose of this qualitative multi-case study is to explore the students' perspectives on the purpose of enrolling in a higher education institution and obtaining an engineering higher education degree. Each case is focused on a higher education institution, for a total of four institutions across the U.S. and England. The embedded units of analysis focus on twenty (20) undergraduate chemical engineering students' narratives from the time they enroll in those institutions to the time they graduate to answer the following two main research questions: RQ 1: What are the perspectives of undergraduate engineering students towards the purpose of higher education? RQ 2: How, if at all, do undergraduate engineering students' perspectives of the purpose of higher education change throughout their degree? The Capabilities Approach is used as the main theoretical framing. The framework is concerned with the question of what a person is able to do and be. It also provides a perspective on thinking about the purposes of education in terms of instrumental, intrinsic, and social values. Results show a variety of perspectives and reasons why students pursue an engineering degree, mainly expressed in terms of career-driven purposes and personal-driven purposes. Fulfilling being good at math and science, seeking a job for purposes beyond individualistic reasons, and personal growth were some of the common purposes mentioned by the students. In addition, more students than not maintained a fixed perspective throughout their undergraduate years. This research is set to address the problem of the neglect of the students' voices in the literature and to address the lack of research on longitudinal studies, higher education, and capabilities approach within the engineering education space. / Doctor of Philosophy / University education across history and contexts aimed for a myriad of purposes, from the advancement of knowledge to educating citizens and contributing to the social good. With the rise of universities functioning in a market economy, and navigating the institutions' public role, some of the university purposes are constantly debated, and often without accounting for the students' perspectives. The purpose of this dissertation is to explore the students' perspectives on the purpose of enrolling in a higher education institution and obtaining an engineering higher education degree. I focused my study on four institutions across the U.S. and England. Within each institution, I interviewed undergraduate chemical engineering students from the time they started their degree till the time they graduated to answer the following main research question: RQ: What are the perspectives of undergraduate engineering students towards the purpose of higher education? To help position the study, I used the Capabilities Approach framework. The framework is concerned with the question of what a person is able to do and be. It also provides a perspective on thinking about the purposes of education in terms of different values including seeking knowledge for the sake of knowledge and helping in the community. Results show a variety of perspectives and reasons why students pursue an engineering degree. Fulfilling being good at math and science, seeking a job for purposes beyond individual reasons, and personal growth were some of the common purposes. In addition, more students than not maintained a fixed perspective on why they chose to enroll in university throughout their undergraduate years. This research is set to amplify students' voices and add to longitudinal research studies in the engineering education literature space.

At California State University, Los Angeles and California Polytechnic University, San Luis Obispo, a longitudinal survey was created in response to the COVID-19 pandemic for students within their respective engineering departments. A combination of nonparametric and longitudinal analysis is performed to evaluate the impacts of the transition to a virtual educational environment and the stressors brought on by the global pandemic. Additional qualitative evaluation is performed to gain insight and make program recommendations to enhance the resilience of individuals in the academic systems. Results demonstrate a large shift in circumstances immediately at the start of the pandemic, with a variety of significant trends across the survey cycles and topics. A comparison of the two institutions both qualitatively and quantitatively demonstrate how different institutional responses and student bodies impacted the overall student experience.

No

<p> There is a great need for sensors that can infer the properties of polymer latices. Measuring ultrasonic wave travel parameters through a latex and calibrating these against polymer properties is one potential technique for measuring the polymer properties of a latex without separating the polymer particles from water. Ultrasonic longitudinal waves can be characterized by three travel parameters: the velocity, the attenuation and the frequency. For colloidal systems the attenuation will depend on molecular properties of the system inside a frequency window where diffraction and scattering are negligible.</p> <p> In this thesis the equipment for measuring ultrasonic waves is discussed and a measurement cell for measuring waves in liquids is designed and built. This equipment is used to measure the velocity and attenuation as functions of frequency for two sets of copolymer latices. These latices were measured separately using a combination of standard quality control analyses and polymer characterization techniques. It was discovered that the velocity of sound through latices does not differ significantly from the velocity for pure water while the ultrasonic attenuation of latices at solids concentrations of greater than 10 percent is much greater than the value for pure water.</p> <p> For the copolymer latices produced from styrene and methyl-methacrylate the attenuation measurements were all too similar to distinguish between changes in the properties of the latex. For the copolymer latices produced from styrene and butadiene, the attenuation and composition were related by an approximately linear relationship between 30 and 80 mole percent styrene. In this region, the attenuation spectra were regressed onto the property space using a linear multivariate algorithm called projection to latent structures. It was found that the attenuation is only useful for predicting latex properties that are related to composition in this range. Future work should focus on the use of a non-linear regression technique to model the behaviour of attenuation over the entire composition range and the use of independent analyses to better characterize some of the polymer properties such as crosslinking.</p> / Thesis / Master of Engineering (MEngr)

A mixture model approach for clustering longitudinal data is introduced. The approach, which is based on mixtures of multivariate power exponential distributions, allows for varying tail-weight and peakedness in data. In the longitudinal setting, this corresponds to more or less concentration around the most central time course in a component. The models utilize a modified Cholesky decomposition of the component scale matrices and the associated maximum likelihood estimators are derived via a generalized expectation-maximization algorithm. / Thesis / Master of Science (MSc)

The majority of current smokers in the United States want to quit smoking; however, long-term abstinence rates do not improve beyond 30%, despite the availability of effective pharmaco-behavioral treatments and increased outreach of awareness programs on quitting benefits. One of the reasons is non-adherence to pharmacological treatment. Pharmacological treatments are developed to alleviate withdrawal symptoms experienced during a quit attempt. However, without continued treatment adherence, especially in the first few weeks of a quit attempt (when withdrawal symptoms fluctuate the most), the chances of relapse peak. Thus, adherence to pharmacological treatments must be improved to sustain long-term smoking abstinence. Moreover, smoking cessation is a complex and time-varying process. Therefore, the time-varying causal structure of adherence and smoking cessation must be studied carefully.The time-varying mechanisms underlying the smoking cessation process can be captured efficiently through intensive longitudinal data and quantified through appropriate methods. Mediation analysis is an efficient tool for studying such mechanisms. However, despite the time-varying nature of the data, existing approaches for assessing mediation provide overall average (in)direct effects over time and omit describing the temporal characteristic of the dynamic effect. This dissertation research aims to develop a new approach to estimating time-varying causal (in)direct effects of pharmacological treatments on daily smoking cessation outcome(s) mediated via daily treatment adherence. Additionally, it is hypothesized that adherence is influenced by daily stress events related to social contextual factors, not treatment-induced. The purpose of this research is to derive time-varying causal (in)direct effects. A local polynomial regression-based approach integrated with the mediational g-formula was proposed as a possible solution. Furthermore, since no other studies have studied time-specific mediation effects using a potential outcomes framework-based method, the performance of the proposed method was tested using two simulation studies. Finally, the optimum analytical approach (based on the findings from the simulation studies) was applied to answer the substantive research questions on smoking cessation using empirical data from a smoking cessation clinical trial. This dissertation is divided into six chapters. A brief overview of the chapters is as follows: Chapter 1 provides a comprehensive background and rationale for the methodological and substantive research that motivated this work. The chapter concludes with the three specific aims addressed in this research and a summary of the next steps. In Chapter 2, the longitudinal causal frameworks and the assumptions required to interpret the estimated time-varying (in)direct effects as causal are described in detail. These frameworks were further used in Chapters 3 and 4 for the two simulation studies that evaluated the performance of the proposed new approach. The simulation study in Chapter 3 evaluates the time-varying (in)direct effects in a longitudinal study in the absence of exposure-induced time-varying confounding of a mediator-outcome pathway. Four outcome scenarios with a binary exposure, a binary mediator, and a time-varying binary confounder of the mediator-outcome pathway were examined: 1) continuous outcome, 2) rare binary outcome, 3) common binary outcome, and 4) count outcome that is not zero-inflated. Two types of path-specific causal estimands are identifiable for these scenarios. The findings suggest good performance of the proposed analytical approach in producing accurate effect estimates (reduced bias and reasonable coverage) of these estimands for all the outcome scenarios. The simulation study in Chapter 4 evaluates the time-varying (in)direct effects in a longitudinal study in the presence of exposure-induced time-varying confounding of a mediator-outcome pathway. A zero-inflated count outcome scenario with a binary exposure, a binary mediator, and a time-varying binary confounder of the mediator-outcome pathway was examined. Four types of path-specific causal estimands are identifiable for this scenario, and the findings suggest good performance of the proposed analytical approach in producing accurate effect estimates. Chapter 5 uses the Wisconsin Smokers Health Study II data to assess the mechanisms via which pharmacological smoking cessation treatments affect the cessation-related outcome(s) in the presence of time-varying confounding that is not exposure induced. We found that individuals randomized to Nicotine Patch only group have better smoking cessation outcome(s) compared to individuals on Varenicline or combination Nicotine Replacement Therapy. This is due to better adherence among Nicotine Patch-only users. Finally, Chapter 6 presents the concluding remarks, including key findings from the three studies, limitations, and recommendations for future research. / Epidemiology