A Study on the Surface State of Catalytic Chemistry Using First-Principles calculation

Department of ChemistryA catalyst refers to that accelerates a chemical reaction without being consumed during the chemical reactions. This property is usually referred to as the catalytic activity. For a multi-step chemical reaction with multiple possible products, a catalyst can promote the production of a specific chemical compound, which is related to the rate-determining step of the reaction. Heterogeneous catalytic reactions mainly occur on the surface of solid catalysts with accompanying elementary surface chemical processes such as adsorption of reactants from a reaction mixture, surface diffusion and reaction of adsorbed species, and desorption of reaction products. The promotion of a chemical reaction is originated from the high reactivity of surface atoms that facilitates bond breaking and bond rearrangement of adsorbed molecules. In order to increase the yield of a desired reaction, the demand for catalysts showing high activity is growing throughout modern industries. Beyond simple chemical reactions, the complex and multi-step reactions have been important in various fields that require effective catalyst. However, research is needed in many cases to understand the detailed bond rearrangement of the reaction on the catalyst surface or the diffusion or dissolution process of the interface. As the demand for catalyst design or material synthesis increases, the first-principles calculations are required to understand a detailed catalysis. One area where catalyst is highly required is hydrogen production. As the use of fossil fuels increases, the world faces a climate crisis due to carbon dioxide emissions, and as a promising substitute for fossil fuels, hydrogen has emerged as a clean and renewable energy. In particular, green hydrogen production without CO2 emission can be achieved through electrocatalytic water splitting. In water splitting reactions, the commercial electrocatalysts composed of rare metals such as Ir, Pt and Ru has a problem with their price. Besides, sluggish multi-step oxygen evolution reaction (OER) is another hindrance for efficient water splitting. To overcome these problems, development of cheap electrocatalysts with high performance is necessary. First-principles calculations using density functional theory (DFT) has been used to describe and predict the intrinsic activity of catalysts. The adsorption energies of intermediates determine the activity of the catalyst. The surface electronic structure is highly correlated with intermediate species adsorption energies which determine the catalytic activity. In Chapter 2, we investigated the influence of cation mixing on the oxygen evolution reaction (OER) activity of LaxSr1-xCoyFe1-yO3 (LSCF) double perovskite in the perspective of surface electronic structure. Based on projected density of states and wavefunction analysis, the minority spin dxy electrons of surface layer metal atoms are significant due to their stability, where the antibonding states between dxy and the lattice oxygen p become occupied when Co atoms with one d electron more than Fe are present. Thus, by additionally considering the dxy band center, surface electronic descriptor (E2p ??? 0.4 Edxy) excellently describes the binding energy of the OER intermediates and the stability against oxygen vacancy formation, which also explains the enhanced OER stability and efficient Fe???Co mixing. Based on the computational analysis, several efficient perovskite electrocatalysts were presented, and it was confirmed that the electronic structure analysis could provide guidance for electrocatalysts design. Another area in which catalysts play an important role, is the synthesis and etching of low-dimensional carbon materials through the 3d transition metal surface. Graphene is produced from amorphous sp3 carbon through Ni junction, and the surface of diamond is etched under high-temperature conditions. In order to control these interfacial reactions, accurate understanding and mechanism analysis are required, and detailed bond dissociation and forming processes can be identified through first-principles DFT simulations. In Chapter 3, we analyze the kinetics of dissolution of single crystal diamond (100) and (110), ???D(100)??? and ???D(110)???, into thin films of nickel (Ni) and cobalt (Co). This dissolution occurs at the metal-D(100) or metal-D(110) interface and was studied in the presence and also absence of water vapor at temperatures near 1000 ???. Based on the first-principles calculation, the mechanism of why the diamond surface carbon can diffuse through Ni or Co despite the low activation energy of the reverse reaction were unveiled.ope

Effects of physical activity type and sedentary time on metabolically healthy obesity and metabolically unhealthy normal weight Korean men

Obesity has become a global health challenge linked to morbidity and mortality associated with cardiovascular diseases. This study aimed to compare metabolic health indicators according to obesity phenotypes and examine prevalence according to physical activity (PA) and sedentary time in metabolically healthy obesity (MHO) and metabolically unhealthy normal weight (MUNW). Data were obtained from 3242 men participating in the 7th and 8th Korean National Health and Nutrition Examination Surveys. Participants were divided into four groups based on body phenotype and metabolic health status using obesity. Metabolic health was defined as metabolic syndrome. Representative statistical analyzes were one-way analysis of variance (ANOVA) and multiple logistic regression analysis. Compared with MUNW, the MHO had higher obesity, but systolic blood pressure (SBP), diastolic blood pressure (DBP), fasting glucose (FG), hemoglobin A1c (HbA1c), triglycerides (TG), low density lipoprotein cholesterol (LDLC), and total cholesterol (TC) were significantly lower. In comparison between MHO and metabolically healthy normal weight (MHNW), the same health group, there were no significant differences in SBP, FG, HbA1c, and LDLC. The odds ratio of MUNW in the normal weight group was 1.8 times higher than that of the high group in the low leisure PA group. The group with high sedentary time increased the MUNW odds ratio by 1.5 times compared to the low group. Meanwhile, in the obesity group, the high leisure PA group showed a 1.4-fold increase in the MHO odds ratio compared to the low group. In addition, the low sedentary group showed a 1.6-fold increase in the MHO odds ratio compared to the high sedentary group. In conclusion, MHO had higher adiposity than MUNW, but the metabolic health index was better. Low PA and high sedentary time increased the risk of MUNW even in normal weight. Conversely, high PA and low sedentary time increased the likelihood of MHO in the obesity group

Development of Web GIS-Based VFSMOD System with Three Modules for Effective Vegetative Filter Strip Design

In recent years, Non-Point Source Pollution has been rising as a significant environmental issue. The sediment-laden water problem is causing serious impacts on river ecosystems not only in South Korea but also in most countries. The vegetative filter strip (VFS) has been thought to be one of the most effective methods to reduce the transport of sediment to down-gradient area. However, the effective width of the VFS first needs to be determined before VFS installation in the field. To provide an easy-to-use interface with a scientific VFS modeling engine, the Web GIS-based VFSMOD system was developed in this study. The Web GIS-based VFSMOD uses the UH and VFSM executable programs from the VFSMOD-w model as core engines to simulate rainfall-runoff and sediment trapping. To provide soil information for a point of interest, the Google Map interface to the MapServer soil database system was developed using the Google Map API, Javascript, Perl/CGI, and Oracle DB programming. Three modules of the Web GIS-based VFSMOD system were developed for various VFS designs under single storm, multiple storm, and long-term period scenarios. These modules in the Web GIS-based VFSMOD system were applied to the study watershed in South Korea and these were proven as efficient tools for the VFS design for various purposes

Development of Web GIS-Based VFSMOD System with Three Modules for Effective Vegetative Filter Strip Design

In recent years, Non-Point Source Pollution has been rising as a significant environmental issue. The sediment-laden water problem is causing serious impacts on river ecosystems not only in South Korea but also in most countries. The vegetative filter strip (VFS) has been thought to be one of the most effective methods to reduce the transport of sediment to down-gradient area. However, the effective width of the VFS first needs to be determined before VFS installation in the field. To provide an easy-to-use interface with a scientific VFS modeling engine, the Web GIS-based VFSMOD system was developed in this study. The Web GIS-based VFSMOD uses the UH and VFSM executable programs from the VFSMOD-w model as core engines to simulate rainfall-runoff and sediment trapping. To provide soil information for a point of interest, the Google Map interface to the MapServer soil database system was developed using the Google Map API, Javascript, Perl/CGI, and Oracle DB programming. Three modules of the Web GIS-based VFSMOD system were developed for various VFS designs under single storm, multiple storm, and long-term period scenarios. These modules in the Web GIS-based VFSMOD system were applied to the study watershed in South Korea and these were proven as efficient tools for the VFS design for various purposes

Development of a Web-Based L-THIA 2012 Direct Runoff and Pollutant Auto-Calibration Module Using a Genetic Algorithm

The Long-Term Hydrology Impact Assessment (L-THIA) model has been used as a screening evaluation tool in assessing not only urbanization, but also land-use changes on hydrology in many countries. However, L-THIA has limitations due to the number of available land-use data that can represent a watershed and the land surface complexity causing uncertainties in manually calibrating various input parameters of L-THIA. Thus, we modified the L-THIA model so that could use various (twenty three) land-use categories by considering various hydrologic responses and nonpoint source (NPS) pollutant loads. Then, we developed a web-based auto-calibration module by integrating a Genetic-Algorithm (GA) into the L-THIA 2012 that can automatically calibrate Curve Numbers (CNs) for direct runoff estimations. Based on the optimized CNs and Even Mean Concentrations (EMCs), our approach calibrated surface runoff and nonpoint source (NPS) pollution loads by minimizing the differences between the observed and simulated data. Here, we used default EMCs of biochemical oxygen demand (BOD), total nitrogen (TN), and total phosphorus-TP (as the default values to L-THIA) collected at various local regions in South Korea corresponding to the classifications of different rainfall intensities and land use for improving predicted NPS pollutions. For assessing the model performance, the Yeoju-Gun and Icheon-Si sites in South Korea were selected. The calibrated runoff and NPS (BOD, TN, and TP) pollutions matched the observations with the correlation (R2: 0.908 for runoff and R2: 0.882–0.981 for NPS) and Nash-Sutcliffe Efficiency (NSE: 0.794 for runoff and NSE: 0.882–0.981 for NPS) for the sites. We also compared the NPS pollution differences between the calibrated and averaged (default) EMCs. The calibrated TN and TP (only for Yeoju-Gun) EMCs-based pollution loads identified well with the measured data at the study sites, but the BOD loads with the averaged EMCs were slightly better than those of the calibrated EMCs. The TP loads for the Yeoju-Gun site were usually comparable to the measured data, but the TP loads of the Icheon-Si site had uncertainties. These findings indicate that the web-based auto-calibration module integrated with L-THIA 2012 could calibrate not only the surface runoff and NPS pollutions well, but also provide easy access to users across the world. Thus, our approach could be useful in providing a tool for Best Management Practices (BMPs) for policy/decision-makers

NGL-1/LRRC4C Deletion Moderately Suppresses Hippocampal Excitatory Synapse Development and Function in an Input-Independent Manner

Netrin-G ligand-1 (NGL-1), also known as LRRC4C, is a postsynaptic densities (PSDs)-95-interacting postsynaptic adhesion molecule that interacts trans-synaptically with presynaptic netrin-G1. NGL-1 and its family member protein NGL-2 are thought to promote excitatory synapse development through largely non-overlapping neuronal pathways. While NGL-2 is critical for excitatory synapse development in specific dendritic segments of neurons in an input-specific manner, whether NGL-1 has similar functions is unclear. Here, we show that Lrrc4c deletion in male mice moderately suppresses excitatory synapse development and function, but surprisingly, does so in an input-independent manner. While NGL-1 is mainly detected in the stratum lacunosum moleculare (SLM) layer of the hippocampus relative to the stratum radiatum (SR) layer, NGL-1 deletion leads to decreases in the number of PSDs in both SLM and SR layers in the ventral hippocampus. In addition, both SLM and SR excitatory synapses display suppressed short-term synaptic plasticity in the ventral hippocampus. These morphological and functional changes are either absent or modest in the dorsal hippocampus. The input-independent synaptic changes induced by Lrrc4c deletion involve abnormal translocation of NGL-2 from the SR to SLM layer. These results suggest that Lrrc4c deletion moderately suppresses hippocampal excitatory synapse development and function in an input-independent manner

A Numerical Investigation of Delamination Response of CNT/Epoxy Film Interleaved Composite

In this study, numerical modeling through the cohesive zone theory was performed to simulate the end notch flexure (ENF) test with same conditions of the experimental results of previous study that investigated the effect of a carbon nanotube (CNT)/epoxy film in carbon fiber reinforced polymer (CFRP) composite through the mode II interlaminar fracture toughness of a non-interleaved, epoxy film interleaved, CNT/epoxy film interleaved CFRP laminate specimen. The effect of the presence of CNT/epoxy film interleave on a composite laminate was modeled. The influence of the interleave cohesive parameters was studied to link the parameters to the material strength and energy release rate. Cohesive parameter identification was performed by matching the initial loading and the damage evolution phase by dividing the cohesive zones into cohesive front and remaining cohesive zones. This is because, when modeling with a single cohesive zone, the critical load point that causes delamination or the curve after load drop do not match the experimental values. Results showed that the divided cohesive zone model is in good agreement with the experimental results and that there is a clear relationship between the cohesive energy of the interface and CNT/epoxy film parameters