Collapse Transition of Two-Dimensional Flexible and Semiflexible Polymers

The nature of the globule-coil transition of surface-confined polymers has been an issue of debate. Here this 2D collapse transition is studied through a partially directed lattice model. In the general case of polymers with positive bending stiffness ($\Delta>0$), the collapse transition is {\em first-order}; it becomes {\em second-order} only in the limiting case of zero bending stiffness ($\Delta\equiv 0$). These analytical results are confirmed by Monte Carlo simulations. We also suggest some possible future experiments.Comment: 4 pages, 3 figure

The Effect of the HOPE Scholarship Program on Interstate Migration

The HOPE scholarship program, created by the state of Georgia in 1993, is the first large scale, merit-based higher educational scholarship program in the United States. In this research, I use border analysis and difference-in-differences estimates to test the hypothesis that the HOPE scholarship program attracts interstate education migration from Georgia’s neighboring states. My results support my hypothesis. I find that border areas in Georgia attract high school seniors from the adjacent areas in border states that do not have the HOPE scholarship program. In addition, I use the IPUMS dataset to provide further analysis to the effect of the HOPE scholarship program on interstate migration for entire states rather than for border areas. I find that for a family with high school children, Georgia is the most popular destination state in the inter-state migration within the southeastern area in the period of 1995-2000, because the HOPE scholarship reduces tuition in Georgia significantly

Solid Oxide Electrochemical Cells for High Temperature Hydrogen Production: Theory, Fabrication and Characterization

In this dissertation, the concept of water splitting using solid oxide photoelectrochemical cells (SOPCs) at high temperature was introduced and experimentally investigated. High temperature photoelectrochemical water splitting physically broadens the selection of potential applicable semiconductor materials and enables more visible sunlight absorption. This newly conceived concept provides a unique pathway for solar hydrogen production, as compared to conventional photoelectrochemical cells (PECs) that use wide band gap semiconductors in aqueous environments. The theoretical framework of SOPC was elaborated, followed by the experimental investigation to search for appropriate high temperature materials. Selected high temperature Schottky and p-n junction diodes, which were expected to be applicable to the photocatalytic/oxygen electrodes of SOPCs, were fabricated and evaluated. Their rectifying characteristics were characterized at elevated temperatures. Among those diodes, only LSM/TiO2 demonstrated acceptable rectifying properties up to 450 °C, indicating that such configuration may be applicable to the proposed SOPC. The further investigation was carried out on fabrication of the electrodes of SOPC and solid oxide fuel cell (SOFC) using fused deposition modeling (FDM), a technique of 3D printing. The goal was to directly print out ceramic substrates and eventually make porous electrodes. Ceramic filaments that consist of ceramic electrode materials and thermoplastics were fabricated in house. After experimenting many thermoplastics, Nylon 12 was identified as an ideal thermoplastic polymer to make composite ceramic filaments. The printouts were sintered in the furnace to burn out all the organics, leaving behind porous electrodes made of pure ceramics. The 3D printed cathodes on half SOFCs were evaluated and demonstrated comparable performance to conventional SOFCs using dip-coating method. Therefore, FDM provides a viable and low cost means to fabricate the porous electrodes of SOPC/SOFC