Kinetics and Mechanism of Oxygen Delignification

Considerable research has been conducted into the kinetics and selectivity of the oxygen delignification process to overcome limitation in its use. However most studies were performed in a batch reactor whereby the hydroxide and dissolved oxygen concentrations are changing during the reaction time in an effort to simulate tower performance in pulp mills. This makes it difficult to determine the reaction order of the different reactants in the rate expressions. Also the lignin content and cellulose degradation of the pulp are only established at the end of the experiment when the sample is removed from the batch reactor. To overcome these deficiencies, we have adopted a differential reactor system used frequently for fluid-solid rate studies (so-called Berty reactor) for measurement of oxygen delignification kinetics. In this reactor, the dissolved oxygen concentration and the alkali concentration in the feed are kept constant, and the rate of lignin removal is determined from the dissolved lignin content in the outflow stream measured by UV absorption. The mass of lignin removed is verified by analyzing the pulp at several time intervals. Experiments were performed at different temperatures, oxygen pressures and caustic concentrations. The delignification rate was found to be first order in HexA-free residual lignin content. The delignification rate reaction order in caustic concentration and oxygen pressure were determined to be 0.42 and 0.44 respectively. The activation energy was found to be 53kJ/mol. The carbohydrate degradation during oxygen delignification can be described by two contributions: one due to radicals produced by phenolic delignification, and a much smaller contribution due to alkaline hydrolysis. From the first order of the reaction and the pKa of the active lignin site, a new oxygen delignification mechanism is proposed. The number 3 carbon atom in the aromatic ring with the attached methoxyl group forms the lignin active site for oxygen adsorption and subsequent electrophic reaction to form a hydroperoxide with a pKa value similar to that of the present delignification kinetics. The uniform presence of the aromatic methoxyl groups in residual lignin further support the first order in lignin kinetics

Molecular and functional analysis of Drosophila Hillarin and its leech homolog

This thesis describes the molecular and functional analysis of the leech Hillarin and its Drosophila homolog D-hil. Leech Hillarin was identified by screening a leech expression library with the mAb Lan3-15, which specifically labels the axon hillock region of leech neurons. Database searches revealed that leech Hillarin has a number of potential homologs in a variety of organisms such as yeast, cyanobacterium, fly, nematode, mouse and human and that these proteins share two novel protein domains, the W180 domain and the H domain. The W180 domain is enriched with tryptophans whereas the H domain shares high number of invariant residues among family members and was named since it was first described in Hillarin. Drosophila member of this protein family, D-hil, is localized to the neuropil of central nervous system neurons, the cortex of metaphase S2 cells, and the cleavage furrow of dividing S2 cells. The protein level of D-hil starts to increase 12 hours after egg laying and the expression persists into adult stage, indicating the expression of D-hil is developmentally regulated. Pnut, a Drosophila septin member, was identified as an interactor of D-hil. The interaction is supported by the co-immunoprecipitation and co-localization results. Furthermore, GFP-D-hil in transfected S2 cells co-localizes with Pnut and F-actin. Genetic interaction studies between a mutant Pnut allele and a mutant D-hil allele suggest that they function in the same genetic pathway since D-hilPnut double mutants show double amount of polyploid cells in the third instar larval brains compared to that of the Pnut single mutants. This genetic interaction between D-hil and Pnut further supports their interaction in vivo

Help-seeking intention among college students: Cross-cultural study between East Asian international students and domestic students in the Unites States

The purpose of this study is to understand East Asian international student’s underutilization of counseling services (versus U.S. domestic students) by applying Theory of Reasoned Action/Planned Behavior (TRA/PB) and Ludwikowski, Vogel, and Armstrong (2009)’s stigma model to help-seeking. Participants were 146 East Asian international students and 210 domestic college students at Purdue University. AMOS 23.0 for Structural Equation Modeling was used to conduct a Latent Mean Analysis (LMA) and a multigroup analysis. The multigroup analysis results found that help-seeking intention was explained by the same hypothesized model in both groups, which was based on the TRA/PB (Ajzen, 2012) and the stigma model (Ludwikowski et al., 2009). However, no significant group differences were found for most of the hypothesized paths, except a path from personal stigma to self-stigma. The LMA results revealed that East Asian international students reported significantly higher help-seeking intention and lower self-stigma and perceived behavior control. Historically, Asian students are known to have more stigma and negative attitudes (Sue & Sue, 2008), so this finding draws our attention to the further cross-cultural studies about the reason for this discrepancy. Implications for theory, research, and practice are addressed

Private tutoring and its impact on students' academic achievement, formal schooling, and educational inequality in Korea

Over the last two decades, private tutoring has emerged as an important issue in education as its demand has been growing around the world. However, the evidence of the effectiveness of private tutoring is still mixed. Using the Korean Educational Longitudinal Survey, this dissertation explores the causal impact of private tutoring in Korea on three outcomes: students' academic achievement, the quality of the learning environment in formal schooling, and educational inequality. The first set of empirical analyses explores how private tutoring in secondary schools affects students' academic achievement in both short-term and long-term aspects using Ordinary Least Squares, Instrumental Variable, and Propensity Score Matching methods. The results suggest that private tutoring in middle school, on average, has positive short-term effects on students' academic achievement in middle school, but minimal long-term effects on the university entrance examination scores. By subject area, English and math tutoring are effective in improving academic achievement in middle school, whereas verbal tutoring is not. Moreover, private tutoring in grade 7 is most beneficial for students in middle school. In terms of private tutoring in high school, only math tutoring is beneficial for high school students in improving scores on the university entrance examination. The second set of the analyses employs Ordered Logit, Propensity Score Matching, and Difference-in-Differences methods to estimate the impact of private tutoring on the quality of formal schooling. The quality of the learning environment in formal schooling is measured by students' attention to lessons in class. On average, private tutoring shows a positive influence on students' attention to lessons in grade 8, but the magnitude of its influence is not substantial. However, when differentiating the results by ability group, positive effects are detected mostly in the low-ability group, which means that low achievers pay more attention to lessons in schools if they participate in private tutoring. These results imply that private tutoring improves the overall learning environment in formal schooling, which in turn increases the overall quality of schooling. The third set of the analyses uses Quantile Regression, Two-Stage Least Absolute Deviation estimator, and Propensity Score Subclassification to estimate the heterogeneous effects of private tutoring between ability groups, which provides implications on educational inequality based on academic achievement. The overall results suggest that private tutoring in middle school exacerbates educational inequality between high and low achievers, which implies a widening of the achievement gap. In addition, enrolling in tutoring at an earlier grade level results in greater heterogeneity between high and low achievers in academic performance than enrolling in tutoring during later grade levels. However, private tutoring in high school contributes to reducing the achievement gap; low achievers benefit more from private tutoring in high school compared to high achievers. Moreover, three years of cumulative math tutoring and receiving a single year of math tutoring in grade 12 contribute to narrowing the achievement gap between low and high achievers in the university entrance examination scores

Water Quality in Uganda

Drinking water quality monitoring is critical in the effort to improve health outcomes in developing countries. Poor waste management, rapid industrialization, agricultural activity, and soil erosion are examples of anthropogenic and natural processes that affect the concentrations of heavy metals, anions, nutrients, and bacterial concentrations in water. The purpose of this study was to investigate the concentrations of these contaminants in water from shallow wells, boreholes, rivers, and lakes in the southwestern region of Uganda. The water samples were analyzed in the field and in the laboratory at USD and at the U.S. Geological Survey in Boulder, Colorado to determine the concentrations of various anions and cations that may have long-term health impacts. Data presented here depict single sampling events at the various locations and provide a snapshot of the various water quality issues facing a developing country like Uganda