An Improved Potential Energy Surface for the H2Cl System and Its Use for Calculations of Rate Coefficients and Kinetic Isotope Effects

We present a new potential energy surface (called G3) for the chemical reaction Cl + H2 → HCl + H. The new surface is based on a previous potential surface called GQQ, and it incorporates an improved bending potential that is fit to the results of ab initio electronic structure calculations. Calculations based on variational transition state theory with semiclassical transmission coefficients corresponding to an optimized multidimensional tunneling treatment (VTST/OMT, in particular improved canonical variational theory with least-action ground-state transmission coefficients) are carried out for nine different isotopomeric versions of the abstraction reaction and six different isotopomeric versions of the exchange reaction involving the H, D, and T isotopes of hydrogen, and the new surface is tested by comparing these calculations to available experimental data. The theoretical data are also used to investigate the equilibrium constant and the branching ratio for the reverse reaction, and calculations of these quantities are compared to the available experimental and theoretical data

Coordinated river infrastructure decisions improve net social-ecological benefits

We explore the social, ecological, economic, and technical dimensions of sustainable river infrastructure development and the potential benefits of coordinating decisions such as dam removal and stream crossing improvement. Dam removal is common practice for restoring river habitat connectivity and ecosystem health. However, stream crossings such as culverts are often 15 times more abundant than dams and may pose similar ecological impacts. Using multi-objective optimization for a model system of 6100 dams and culverts in Maine, USA, we demonstrate substantial benefit-cost improvements provided by coordinating habitat connectivity decisions. Benefit-cost efficiency improves by two orders of magnitude when coordinating more decisions across wider areas, but this approach may cause inequitable resource distribution. Culvert upgrades improve roadway safety and habitat connectivity, creating cost-effective opportunities for coordinating and cost-sharing projects between conservationists and safety managers. Benefit-cost trends indicate significant overlaps in habitat and safety goals, encouraging flexible stakeholder collaborations and cost-sharing strategies

SURVIVAL OF ESCHERICHIA COLI IN AGRICULTURAL SOILS AND STUDENT ENGAGEMENT IN ONLINE DISCUSSIONS

There is great interest in identifying manure management techniques to minimize the persistence of pathogenic Escherichia coli in agricultural fields and, thereby, decrease the risk of downstream contamination and human infection. The first two chapters of this dissertation seek to determine the how the agricultural environmental variable of manure application method shapes the genetic and phenotypic population structure of E. coli. First, we conducted a field and laboratory experiment that demonstrated the expression of extracellular fibers called curli, which are linked to environmental persistence of E. coli, was linked to surface-application of manure, as opposed to incorporation into the soil. Second, we applied whole genome sequencing technology to isolates collected from laboratory microcosms with differing manure application treatments. We found no systematic genomic differences (i.e. individual-level selection) that could be explained by week or manure application treatment. As higher education institutions offer online courses to growing audiences, there is increasing desire to understand how best to engage students. The third chapter of this dissertation examines the effects of assigning chat roles and facilitating self and group reflection on student-content and student-student interaction outcomes in synchronous online chats. Group reflections were the only intervention that had a significant effect on both outcomes

Student engagement with course content and peers in synchronous online courses discussions

As higher education institutions in United States offer online courses to growing audiences, there is increasing desire to understand how best to engage students with both course content and their peers. This case study examines the effects of assigning chat roles and facilitating self and group reflection on student-content and student-student interaction outcomes in four synchronous chats conducted in an online introductory-level sustainability course. We also considered what occurred within group reflections to inform how they are structured in the future. We found that assigning roles increased the proportion of critical student-student interactions. Self-reflections had no effect on either interaction type. Groups completing group reflections had a greater proportion of critical student-content interactions in the third chat and critical student-student interactions in the fourth chat than the groups that did not complete the group reflections. Based on our results, we plan to keep roles and group reflections going forward, and eliminate self-reflections. Furthermore, to increase the effectiveness of the group reflections, we propose some ideas to increase student ability to convert their ideas into change during subsequent chats

An Improved Potential Energy Surface for the H2Cl System and Its Use for Calculations of Rate Coefficients and Kinetic Isotope Effects

We present a new potential energy surface (called G3) for the chemical reaction Cl + H2 → HCl + H. The new surface is based on a previous potential surface called GQQ, and it incorporates an improved bending potential that is fit to the results of ab initio electronic structure calculations. Calculations based on variational transition state theory with semiclassical transmission coefficients corresponding to an optimized multidimensional tunneling treatment (VTST/OMT, in particular improved canonical variational theory with least-action ground-state transmission coefficients) are carried out for nine different isotopomeric versions of the abstraction reaction and six different isotopomeric versions of the exchange reaction involving the H, D, and T isotopes of hydrogen, and the new surface is tested by comparing these calculations to available experimental data. The theoretical data are also used to investigate the equilibrium constant and the branching ratio for the reverse reaction, and calculations of these quantities are compared to the available experimental and theoretical data.Reprinted (adapted) with permission from Journal of Physical Chemistry 100 (1996): 13575, doi:10.1021/jp960781j. Copyright 1996 American Chemical Society.</p