Theses and Dissertations from UMD
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Item SYSTEMATIC INVESTIGATION OF QUORUM SENSING IN Escherichia coli(2007-04-17) Li, Jun; Bentley, William E; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High throughput techniques and advanced mathematical tools have enabled systematic investigations of biological systems with unparalleled precision. Not only molecular interactions between components but mechanisms and the dynamic behaviors associated with these systems are revealed, suggesting that comprehensive systems biology can be realized in the near future. Quorum sensing, especially the auto-inducer2 (AI-2) system, has been extensively studied due to its commonality among bacteria and connections to pathogenic phenotypes. In this study, the E. coli quorum sensing AI-2 system was studied combing system-based mathematical modeling and high throughput genomic profiling. First, a Stochastic Petri Network (SPN) model was constructed based on available regulatory information. Simulations together with experimental data demonstrated that the apparent stimulation of AI-2 in the presence of glucose is not from the increased transcriptional or translational expression of AI-2 synthases luxS and pfs, nor from the increased metabolic flux associated with LuxS-related pathways but from an alternative AI-2 synthesis pathway. The conversion of adenosine with cellular extracts from both luxS and pfs mutants validated our prediction about the existence of an alternative non-LuxS related AI-2 synthesis pathway. Second, AI-2 uptake regulatory network was investigated in detail: lsrR-lacZ, lsrK-lacZ fusion reporters were constructed and the analysis found that lsrR is subject to its own repression and is induced by both lsrK and luxS. Further transcriptome analysis demonstrated that lsrR and lsrK, together with quorum signal AI-2, coregulate lsrRK regulon, which influences phenotypes (biofilm, small RNAs). Importantly, this regulation is in a distinctly different manner than that mediating the lsr operon. We hypothesize that lsrR acts together with AI-2 to mediate cellular processes and that the phosphorylation of AI-2 molecule through lsrK triggers different response pathways. These investigations demonstrated that lsrR, lsrK are indispensable for AI-2 uptake. These newly elucidated regulatory mechanisms and associations undoubtedly broaden the scope of the AI-2 quorum sensing system, and provide a solid foundation for further mathematical modeling of the dynamics and system behaviors in E. coli . Finally, a tight coupling of experimental manipulation with mathematical analysis, as demonstrated in this study, provides a good example for systematically investigating biological systems.Item Analysis of the Implementation of Teacher Education Policy in China since the 1990s: A Case Study(2006-11-30) Li, Jun; Lin, Jing; Education Policy, and Leadership; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)China has at present the largest system of basic education and the largest teacher work force in the world. The teacher education system plays a critical role in preparing an enormous army of qualified teachers for the basic education system. Since the 1990s, China's teacher education has been undergoing radical transformations: The vision and mission of teacher education have changed significantly; teachers' roles are redefined in order for them to respond to the new demands of the dramatically changing society; the "market" for preparing teachers is shared by various competitors; new degrees, programs as well as curricula are designed for prospective teachers. The implementation process of the national policy of reform, however, has not been paid enough attention. This study looks into the complicated implementation process of China's teacher education reform policy since the 1990s from the rational and critical frameworks. It has been designed with a case study approach to investigate and understand how a higher teacher education institution has responded to the national policy of teacher education reform. The study focuses on changes in institutional goals, strategies the case university adopted, and examines communication channels of policy, conflicts among stakeholders, and barriers arising from internal and external factors for the implementation of the national policy of teacher education reform. The study serves as an explanatory instrument to understand what the national policy of teacher education reform in China is about, to explore how the teacher education policy was implemented in a higher teacher education institution, and to reveal the unique policy implications derived from the Chinese experience. The findings of this study reveal that the implementation of the national policy was a linearly developed process to resolve the substantial problems of the teacher education system by unitary policy players, viewed from the rational framework. The policy action was advanced and developed to meet the need of the rapidly changing society. The critical framework suggested that the stakeholders of the national policy were diverse conflicting groups who worked together to implement the national policy while at the same time they conflicted with each other on many fronts for their own legitimacy and benefits. The implementation process became a heatedly contested process for redistribution of political and economic benefits among the interest groups. In addition, this study identifies that there were severe institutional barriers accounting for the success or failure of the implementation of the national policy. These barriers include stakeholders' adverse attitudes, authoritarian traditional culture, and overlapping implementation of other national policies. Theoretical reflections are rendered from the findings for implementation studies. Specifically, the role of the cultural dimension in the implementation process is discussed. Finally, recommendations are proposed for implementation practices and for future research.