Siloxanes are widely used in personal care and industrial products due to their low surface tension, thermal stability, antimicrobial and hydrophobic properties, among other characteristics. Volatile methyl siloxanes (VMS) have been detected both in landfill gas and biogas from anaerobic digesters at wastewater treatment plants. As a result, they are released to gas phase during waste decomposition and wastewater treatment. During transformation processes of digester or landfill gas to energy, siloxanes are converted to silicon oxides, leaving abrasive deposits on engine components. These deposits cause increased maintenance costs and in some cases complete engine overhauls become necessary. The objectives of this study were to compare the VMS types and levels present in biogas generated in the anaerobic digesters and landfills and evaluate the energetics of siloxane transformations under anaerobic conditions. Siloxane emissions, resulting from disposal of silicone-based materials, are expected to increase by 29% within the next 10 years. Estimated concentrations and the risk factors of exposure to siloxanes were evaluated based on the initial concentrations, partitioning characteristics and persistence. It was determined that D4 has the highest risk factor associated to bioaccumulation in liquid and solid phase, whereas D5 was highest in gas phase. Additionally, as siloxanes are combusted, the particle size range causes them to be potentially hazardous to human health. When inhaled, they may affix onto the alveoli of the lungs and may lead to development of silicosis. Siloxane-based COD-loading was evaluated and determined to be an insignificant factor concerning COD limits in wastewater. Removal of siloxane compounds is recommended prior to land application of biosolids or combustion of biogas. A comparison of estimated costs was made between maintenance practices for removal of siloxane deposits and installation/operation of fixed-bed carbon absorption systems. In the majority of cases, the installation of fixed-bed adsorption systems would not be a feasible option for the sole purpose of siloxane removal. However they may be utilized to remove additional compounds simultaneously.

The original goal of this project was to build a peer e-mentoring program for parents and measure the effect of the program on persistence. In spite of strong mentor participation, two terms of focused recruiting did not attract mentees. This sparked the question of why those who had successfully navigated the higher education system thought a peer e-mentoring program was needed but those in the process did not. A focused ethnography was designed to try to understand why students with children were resistant to peer e-mentoring. Students with children used technology to integrate the various roles of life. They used smart phones to organize, schedule, and research. They used them to schedule rides or childcare for children, communicated with professors and classmates, reviewed course resources, and whatever else they needed to communicate about. They solved problems by taking them one at time and planning for emergencies with contingencies. These students considered planning their best defense against failing to reach to graduation. They realized establishing and keeping communication lines open was critical. The turned most often to family for help but would reach out to professors and even staff if needed. They looked for professors who were known to go above and beyond for their students just in case they needed to reschedule exams or assignments. The overwhelming consensus about participation was that they just can’t see how it is possible make another commitment. Two mentor participants agreed to be interviewed and shared thoughts about privacy concerns but were willing to take the chance to help ease the way for another student parent. The students with children interviewed expressed the need to find solutions to constantly changing requirements but were not comfortable sharing their problems in a one to one mentoring program. Previous studies have suggested that implementing solutions for non-traditional students required a focused needs assessment. Many programs designed to increase retention for non-traditional students have resulted in exactly the results this one originally faced, a lack of participants or low results. Ultimately these students need just in time solutions for a changing myriad of road blocks to graduation.

We study diffusion-reaction-advection models describing population dynamics of aquatic organisms subject to a constant drift, with reflecting upstream and outflow downstream boundary conditions. We consider three different models: single logistically growing species, two and three competing species. In the case of a single population, we determine conditions for existence, uniqueness and stability of non-trivial steady-state solutions. We analyze the dependence of such solutions on advection speed, growth rate and length of the habitat. Such analysis offers a possible explanation of the "drift paradox" in our context. We also introduce a spatially implicit ODE (nonspatial approximation) model which captures the essential behavior of the original PDE model. In the case of two competing species, we use a diffusion-advection version of the Lotka-Volterra competition model. Combining numerical and analytical techniques, in both the spatial and nonspatial approximation settings, we describe the effect of advection on competitive outcomes. Finally, in the case of three species, we use the nonspatial approximation approach to analyze and classify the possible scenarios as we change the flow speed in the habitat.

The purpose of this qualitative, exploratory study was to develop a deeper understanding of educational and other social experiences and relationships of post-secondary students who were clinically diagnosed with primary obsessive-compulsive disorder (OCD). The researcher also investigated their strengths, weaknesses, coping strategies, and quality of life through mental and physical health. The majority of people with OCD have obsessions and compulsions that last greater than an hour each day or severely impact daily life. Obsessions are irritating feelings or mental pictures that individuals try to block or mitigate with irrational physical or mental compulsions, often appearing as excessive hand washing in reaction to a contamination obsession. Participants comprised seven university students who completed three self-report questionnaires and two semi-structured interviews with the researcher. Five participants submitted self-report journals. These data were examined using interpretative phenomenological analysis (IPA).The present study advanced previous research as it documented extensive lifelong characteristics, experiences, and relationships from these students. It yielded salient findings related to their OCD functional impairment and quality of life. Further, it showed that as students, their intellectual integration seemed to play a greater role in academic persistence than did their social integration. In addition, participants’ university policy and practice recommendations were congruent with a similar study from about a decade ago indicating that perhaps few or none of the past recommendations were implemented for the benefit of such students. Present recommendations should be implemented accordingly.

Attrition in online learning is a problem that faces many institutions of higher education that are turning to online programs as cost-effective means by which to bring about fiscal viability. There is a strong demand for online learning options by students due to the flexibility they afford to be able to work and study while also caring for a family, as well as economic benefits such as a quick and affordable degree. However, many of the reasons that students choose online learning end up being a catalyst for lack of completion, especially among underserved populations. While there is much research currently available on persistence in higher education and much available regarding online learning, there is a dearth of research on the lack of persistence of African-American students in online learning programs. This research was originally designed to take a grounded theory approach to investigating the factors affecting college completion among African Americans with a specific focus on online learning. Due to a small participant response rate, a phenomenological data analysis methodology was employed instead. This study examined participants' recollections of their experience as students in an online undergraduate program, focusing on their reasons for leaving. Forty-nine African-American students who had left their undergraduate online program at New England College were invited to participate in this study. Ten responded and six semi-structured interviews were completed focusing on the question, "Why did you choose to leave the program?" Four themes emerged: (a) lack of integration; (b) personal issues; (c) discomfort with technology; and (d) age. The findings were congruent with current research in online learning attrition and not culturally specific. Recommendations resulted from the data analysis in three major areas: (a) inclusive course development; (b) faculty training; and (c) student support. These recommendations should be considered by faculty and administrators in order to develop more inclusive online learning programs that maximize the success of all students.

This quantitative study investigated relationships among and between university early and late admitted freshmen and academic performance and persistence. The participants in this study consisted of 3,197 early freshmen applicants and 309 late freshmen applicants admitted at a large southwestern student centered public research university over the course of the year prior to the fall 2008 academic year. Significant results, using a statistical significance level of p < .05, were reported for the majority of variables examined: chi-square analysis revealed a significant relationship between application date and ethnicity; independent-samples t-tests revealed significant differences in SAT scores; 78.06% of late applicants were male compared to 40.83% of early applicants; mean GPA of early applicants was 2.62 compared to 2.18 among those who applied late; and lastly, 76.62% of early applicants returned the following year in comparison to 57.42% of late applicants. The results of this study provide preliminary support for the examination of admission policies and procedures in relation to late application. Recommendations are made for advising, counseling, and other interventions that may ease the transition of freshmen late applicants while enhancing retention and persistence.

Les comportements politiques et sociaux tels que la participation politique, la confiance en autrui, l'engagement collectif, la prévention en santé, ou les attitudes vis à vis de la contraception, peuvent persister pendant de très nombreuses années. Cette thèse présente des travaux qui explorent et quantifient rigoureusement des instances de persistance dans ces comportements, en utilisant de nouvelles sources de données historiques et contemporaines. Les travaux présentés dans cette thèse contribuent à la littérature de trois manières différentes. En premier lieu, ils présentent une nouvelle base de données sur la présence des missionnaires chrétiens en Afrique et leurs investissements. Cette base de données est unique en ce qu'elle est entièrement géocodée et présente des données à un niveau de désagrégation très fin. En deuxième lieu, ces travaux mettent en avant de manière originale des canaux de persistance dans le développement qui ne sont pas attribuables aux différences institutionnelles. En troisième lieu, en analysant la marge intensive de la diversité, ces travaux proposent aussi une nouvelle manière d'aborder la question de l'endogénéité dans l'étude du rôle économique de la diversité des origines dans une société. La première partie de cette thèse est un travail sur l'effet persistant sur le développement de l'activité missionnaire en Afrique subsaharienne. 
La deuxième partie de cette thèse étudie les conditions sociales qui font que les différences d'origine peuvent devenir une barrière à la réussite économique aux États-Unis. / Individual and social behaviors, such as voting patterns, the ability to trust others, participation in the community, health-seeking behaviors, or attitudes towards contraception, can persist over many years. Relying on new historical and contemporary data sources, the works compiled in this thesis aim at explaining and quantifying rigorously instances of persistence in behaviors and preferences. This work presents three contributions to the literature. Firstly, it compiles a new micro-level geocoded historical datasource on missionary activity in sub-Saharan Africa. Secondly, it has elucidated, in original ways, channels of persistence in development, which are not attributable to formal institutions. Thirdly, it has analyzed the intensive margin of diversity, providing a new way to address the endogeneity issue in the study of the role of diversity on income. 
The first part of the thesis is a work on the long-lasting influence of missionary activity in sub-Saharan Africa. I present there the research I have conducted with Julia Cagé. It relies a new database that we constructed and geocoded based on the Geography and Atlas of Protestant missions. This research is developed in the two first chapters of the thesis. The second part of this thesis studies the social conditions under which ancestry differences act as a persistent barrier for individual earnings in the United States. The United States is a natural choice to study the persistent effect of ancestry on income, as this is a country that was populated by subsequent waves of migration from different origins during a relatively short period of time. Moreover, the American Census Bureau has recorded data about ancestries since the 1850s.

The purpose of this study was to integrate traditional student success models with theories which focus on nontraditional students to create a model of early community college student success. The researcher sought to understand the pre-college behaviors, attitudes, and attributes, from both cognitive and noncognitive domains, which influence the success of first-time community college students enrolled in a developmental mathematics course. First-time community college students enrolled in Elementary Algebra (N=385) were surveyed on their educational goals, prior academic achievement, anticipated interactions during the first semester, and items from the Noncognitive Questionnaire (NCQ) (Sedlacek, 2004). Institutional data supplemented the survey variables as well as provided all dependent variables. Factor analyses were conducted to reduce the number of anticipatory variables. Descriptive statistics were reported for all dependent and independent variables. Both linear regression and logistic regression were utilized to examine the six research questions. Variables were entered into the regression equations in five blocks: demographics, college plans, prior mathematics achievement, anticipated experiences and interactions, and noncognitive variables. The model proved to be statistically significant in explaining each of the six dependent measures of student success. Moreover after controlling for the first four blocks of independent variables, six of the eight noncognitive variables reached statistical significance in its relationship to at least one dependent variable, with at least one significant finding regarding the effects of noncognitive variables on each of the six outcome measures. The findings of the study suggest noncognitive variables are useful in predicting student success and persistence at least early in the community college experience. Future researchers, policymakers, and administrators will gain insights into the application of noncognitive variables with a population of community college students.

The thesis shows the relationship between the persistence in the financial markets returns and their efficiency. It interprets the efficient markets hypothesis and provides various time series models for the analysis of financial markets. The concept of long memory is broadly presented and two main types of methods to estimate long memory are analysed - time domain and frequency domain methods. A Monte Carlo study is used to compare these methods and selected estimators are then used on real world data - exchange rate and stock market series. There is no evidence of long memory in the returns but the stock market volatilities show clear signs of persistence.

We propose a model that generates a family network based on real-world family network data. We use this model to study the extent to which distances to union and the number of children characterize family networks. To determine how accurate our model is we use persistent homology to identify and compare the structure of our modeled family networks to real-world family networks. To accomplish this, we introduce the notion of a network's persistence curve, which encodes the network's set of persistence intervals. Using the bottleneck distance allows us to measure the difference in the homological structure between any pair of networks. We also study how the distribution of distance to union and the distribution of children build family networks. What we find is that these two features of distance to union and number of children allow us to fairly accurately recreate family networks at least at the level of their persistent homology.