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Department of Urban and Environmental Engineering (Environmental Science and Engineering)This dissertation investigated the synergistic inhibition effect of gas hydrate inhibitors, newly designed gas hydrate inhibitors, and gas hydrate remediation method development for the field of production chemistry of flow assurance. In order to perform above research topics, fundamental experimental studies of thermodynamic stability, structural analysis, gas uptakes, cage-filling molecular behaviors in the presence inhibitors were examined with computational methods and tried to synthesize eco-friendly and innovative gas hydrate inhibitors. The sigma (??) profiles of inhibitor molecules obtained from the Conductor-Like Screening Model for Real Solvents (COSMO-RS) software were used to estimate inhibitor???water interactions for the pre-screening of potential inhibitors. From the ?? profile results, candidates for thermodynamic hydrate inhibitor (THI) and kinetic hydrate inhibitor (KHI) were selected. In addition, the stability conditions in the presence of various inhibitors show that thermodynamic inhibition effect is related to molecular interaction between water and inhibitor. As is well known, intrinsic properties and the number of inhibitors are the biggest factors influencing the thermodynamic inhibition effect. Thus, even if two or more inhibitors mixed, it is hard to observe thermodynamic synergistic inhibition effect. Moreover, inhibitors hard to enclathrated in the gas hydrate structure because their sizes are too large (van der Waals radius values), so they reside on the outside of the cages or are partly involved in cages to disrupt the water-water networks. Furthermore, kinetic analyses were conducted to observe kinetic inhibition effect regarding onset temperature, growth rates and conversion of water into gas hydrates. It was confirmed that different results of onset temperature, growth rates and conversion of water into gas hydrates are shown according to types of inhibitor and inhibitor mixtures. Therefore, density functional theory (DFT) calculation, quantum theory of atoms in molecules (QTAIM) calculation, fourier-transform infrared (FT-IR) spectroscopy, and in-situ Raman spectroscopy were used to demonstrate inhibition mechanisms of each inhibitor. The DFT and QTAIM calculations indicated that each inhibitor has different interaction energy with cage, and the smaller negative interaction energy means that inhibitor significantly retards gas hydrate formation. The FT-IR was used to investigate the interaction sites of inhibitors toward water and find the peak shifts to observe the hydrogen bonding sites. In particular, in-situ Raman analysis verified inhibition mechanisms of inhibitors during nucleation and formation process, thus delaying behaviors of cages could be observed directly. The overall experimental and computational results in this dissertation provide invaluable information of THI and KHI, thus can contribute to the opening up a new field for flow assurance in oil and gas industries and CO2 storage process.ope

Flow Dynamics and Condensation of Film Flows in Small Modular Reactors

There is renewed interest in the reliability and safety of nuclear power plants following the Fukushima Daiichi nuclear accident followed by 8.9 magnitude earthquake and Tsunami with the height of 15 m on March 11, 2011. Small Modular Reactors (SMRs) have been developed to improve safety systems by utilizing passive and natural circulation forces under normal operations and accident conditions. One key feature of the safety systems in SMRs is the use of containment condensation to prevent core melt down. For further development of the SMR for design certifications, the condensation model at relatively high pressures compared with current operating power plants should be verified and validated. For this process, at Oregon State University, the MASLWR (Multi Application Small Light Water Reactor) test facility, which has 1:3 length scale, can perform integrated tests on containment condensation of SMRs. Using the MASLWR test facility experimental data, this study investigated three major subjects: heat flux estimation on the containment wall, flow transition of condensation film flow dynamics and assessing the scaling effects of the MASLWR test facility. An inverse heat conduction algorithm was developed to estimate the heat fluxes of film condensation at the containment wall in the MASLWR test facility during transients. Through a fundamental one-dimensional approach for condensation film flow, the governing equations were derived and numerically solved. A linear perturbation stability analysis using steady-state results of condensation film flow at the containment wall found that Re ~1600 is the transition point between laminar and turbulent film flow regimes. This finding agreed with the experimental results of Ishigai et al. (1974) and Morioka et al. (1993). Based on scaling analysis using the diffusion layer model and experimental correlations, the length distortion factor was examined. In this study, it was found that the 1:3 length scale test facility underestimated the heat transfer rate more than the prototype. The results presented in this dissertation cover the film flow dynamics of condensation film flows as well as an inverse heat transfer calculation to advance the knowledge of containment condensation in SMRs

Analytical and numerical analysis of natural circulation for reactor cavity cooling system in gas cooled reactor

Among the Generation IV reactors, the Very High Temperature Reactor (VHTR) is being considered as the ideal design for a Next Generation Nuclear Plant (NGNP). The VHTR system is designed for a gas cooled reactor and originates from modifying and further developing the 600MW Gas Turbine-Module Helium Reactor (GTMHR). The GT-MHR system has inherent safety features that make events leading to a severe accident significantly unlikely. The Reactor Cavity Cooling System (RCCS) is a crucial component in passive decay heat removal using air natural convection. The PIRT (Phenomena Identification and Ranking Table) for the RCCS was developed through evaluations of physical phenomena which might arise during a LBLOCA. In addition, this study presents the basic performance for the RCCS using analytical and numerical analysis

Implication of Mitochondrial Cytoprotection in Human Islet Isolation and Transplantation

Islet transplantation is a promising therapy for type 1 diabetes mellitus; however, success rates in achieving both short- and long-term insulin independence are not consistent, due in part to inconsistent islet quality and quantity caused by the complex nature and multistep process of islet isolation and transplantation. Since the introduction of the Edmonton Protocol in 2000, more attention has been placed on preserving mitochondrial function as increasing evidences suggest that impaired mitochondrial integrity can adversely affect clinical outcomes. Some recent studies have demonstrated that it is possible to achieve islet cytoprotection by maintaining mitochondrial function and subsequently to improve islet transplantation outcomes. However, the benefits of mitoprotection in many cases are controversial and the underlying mechanisms are unclear. This article summarizes the recent progress associated with mitochondrial cytoprotection in each step of the islet isolation and transplantation process, as well as islet potency and viability assays based on the measurement of mitochondrial integrity. In addition, we briefly discuss immunosuppression side effects on islet graft function and how transplant site selection affects islet engraftment and clinical outcomes

Trophic structure of fish assemblages in two offshore islands (Ulleungdo and Dokdo) of Korea revealed using stable isotope analysis

The objective of this study was to characterize the trophic structure of fish assemblages on the coasts of offshore islands and the eastern mainland of the Korean Peninsula. We compared the seasonal variability in the trophic structure of fish assemblages between the coasts of two island sites (Ulleungdo and Dokdo) and one mainland site (Hupo), which are on a similar latitude. We analyzed the stable carbon and nitrogen isotope ratios (δ13C and δ15N) of fish assemblages during spring (April) and summer (August) 2021. No temporal differences in the isotope values of fish and basal resources (i.e., suspended particulate organic matter (SPOM)) were found over the sampling period at the Hupo site. In contrast, at the Ulleungdo and Dokdo sites, the fishes and SPOM showed seasonal differences in the δ13C and δ15N values between the two seasons. In particular, the fish δ15N values at the island sites were relatively higher in summer compared to those in spring, suggesting the seasonal variation in the food chains and/or trophic status between consumers and their dietary sources. These regional isotopic variations also result in differences in the seasonal tendencies of the isotopic niche parameters of fish assemblages between the mainland and island coasts. Such differences in the seasonal isotopic patterns of fish assemblages suggest a relatively substantial shift in the dietary resources available to fish consumers on island coasts compared to those on the mainland coast. Overall, our results suggest that fish assemblages in offshore island coasts have distinct seasonal variability in trophic characteristics in response to changing environmental conditions, including basal resources, compared with fish food webs on the mainland coast at similar latitudes

Implication of Mitochondrial Cytoprotection in Human Islet Isolation and Transplantation

Islet transplantation is a promising therapy for type 1 diabetes mellitus; however, success rates in achieving both short-and longterm insulin independence are not consistent, due in part to inconsistent islet quality and quantity caused by the complex nature and multistep process of islet isolation and transplantation. Since the introduction of the Edmonton Protocol in 2000, more attention has been placed on preserving mitochondrial function as increasing evidences suggest that impaired mitochondrial integrity can adversely affect clinical outcomes. Some recent studies have demonstrated that it is possible to achieve islet cytoprotection by maintaining mitochondrial function and subsequently to improve islet transplantation outcomes. However, the benefits of mitoprotection in many cases are controversial and the underlying mechanisms are unclear. This article summarizes the recent progress associated with mitochondrial cytoprotection in each step of the islet isolation and transplantation process, as well as islet potency and viability assays based on the measurement of mitochondrial integrity. In addition, we briefly discuss immunosuppression side effects on islet graft function and how transplant site selection affects islet engraftment and clinical outcomes