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Search Results: 1 - 10 of 17619 matches for " Eung-Bo Shim "
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Identification of Acceptable Restoration Strategies
Seung-Tae Cha,Nam-Ho Lee,Eung-Bo Shim,Jeong-Hoon Shin
Journal of Systemics, Cybernetics and Informatics , 2008,
Abstract: In recent years, we have seen several catastrophic and cascading failures of power systems throughout the world. Power system breakup and blackouts are rare events. However, when they occur, the effects on utilities and general population can be quite severe. To prevent or reduce cascading sequences of events caused by the various reasons, KEPRI is researching ways to revolutionize innovative strategies that will significantly reduce the vulnerability of the power system and will ensure successful restoration of service to customers. This paper describes a restoration guidelines / recommendations for the KEPS simulator, which allows power system operator and planner to simulate and plan restoration events in an interactive mode. The KEPS simulator provides a list of restoration events according to the priority based on some restoration rules and list of priority loads. Further, the paper will draw on research using information from a Jeju case study.
Stability Enhancement in HVDC System with STATCOM  [PDF]
Chan-Ki Kim, Jin-Young Kim, Sung-Doo Lee, Eung-Bo Sim
Engineering (ENG) , 2011, DOI: 10.4236/eng.2011.311133
Abstract: This paper deals with the stability problem at the inverter end of a HVDC link with STATCOM (Static Compensator), when connected to a weak AC system which has the stability enhancement for power instability and commutation failures. The HVDC stability problem is tackled with a STATCOM which not only provides a rapid recovery from power, harmonic stability and commutation failures but also offers a lower cost filter design for the HVDC system. PSCAD/EMTDC simulations are presented to demonstrate the robust performance and to validate the proposed topology.
String structures associated to indefinite Lie groups
Hisham Sati,Hyung-bo Shim
Mathematics , 2015,
Abstract: String structures have played an important role in algebraic topology, via elliptic genera and elliptic cohomology, in differential geometry, via the study of higher geometric structures, and in physics, via partition functions. We extend the description of String structures from connected covers of the definite-signature orthogonal group ${\rm O}(n)$ to the indefinite-signature orthogonal group O(p, q), i.e. from the Riemannian to the pseudo-Riemannian setting. This requires that we work at the unstable level, which makes the discussion more subtle than the stable case. Similar, but much simpler, constructions hold for other noncompact Lie groups such as the unitary group U(p, q) and the symplectic group Sp(p, q). This extension provides a starting point for an abundance of constructions in (higher) geometry and applications in physics.
Very High Cycle Fatigue Behaviors and Surface Crack Growth Mechanism of Hydrogen-Embrittled AISI 304 Stainless Steels  [PDF]
Seung-Hoon Nahm, Hyun-Bo Shim, Un-Bong Baek, Chang-Min Suh
Materials Sciences and Applications (MSA) , 2018, DOI: 10.4236/msa.2018.94027
Abstract: The influence of hydrogen embrittlement on the fatigue behaviors of AISI 304 stainless steel is investigated. The fatigue endurance limits of the untreated and hydrogen-embrittled materials were almost the same at 400 MPa, and hydrogen embrittlement had little influence even though the sample contained about 8.1 times more hydrogen. Thus, the sensitivity of hydrogen gas in this material is very low. A surface crack initiation, growth, coalescence, and micro ridge model is proposed in this study. Slip line formation? microcrack formation? increases in the crack width, and blunting of the crack tip as it grows? formation of many slip lines because of deformation in the shear direction? growth of the crack in the shear direction, forming micro ridges, coalescence with adjacent cracks ⇒?continuous initiation, growth, coalescence, and ridge formation of surface cracks and specimen breakage.
Rapid Hydrothermal Synthesis of Zinc Oxide Nanowires by Annealing Methods on Seed Layers
Jang Bo Shim,Hyuk Chang,Sung-O Kim
Journal of Nanomaterials , 2011, DOI: 10.1155/2011/582764
Abstract: Well-aligned zinc oxide (ZnO) nanowire arrays were successfully synthesized on a glass substrate using the rapid microwave heating process. The ZnO seed layers were produced by spinning the precursor solutions onto the substrate. Among coatings, the ZnO seed layers were annealed at 100°C for 5 minutes to ensure particle adhesion to the glass surface in air, nitrogen, and vacuum atmospheres. The annealing treatment of the ZnO seed layer was most important for achieving the high quality of ZnO nanowire arrays as ZnO seed nanoparticles of larger than 30 nm in diameter evolve into ZnO nanowire arrays. Transmission electron microscopy analysis revealed a single-crystalline lattice of the ZnO nanowires. Because of their low power (140 W), low operating temperatures (90°C), easy fabrication (variable microwave sintering system), and low cost (90% cost reduction compared with gas condensation methods), high quality ZnO nanowires created with the rapid microwave heating process show great promise for use in flexible solar cells and flexible display devices.
Computational Analysis of Cardiovascular Hemodynamics
Eun Bo Shim,Thomas Heldt,Akira Amano,Kyehan Rhee
Computational and Mathematical Methods in Medicine , 2012, DOI: 10.1155/2012/260396
Numerical Test of Born-Oppenheimer Approximation in Chaotic Systems
Jeong-Bo Shim,Mahir S. Hussein,Martina Hentschel
Physics , 2008, DOI: 10.1016/j.physleta.2009.07.080
Abstract: We study the validity of the Born-Oppenheimer approximation in chaotic dynamics. Using numerical solutions of autonomous Fermi accelerators, we show that the general adiabatic conditions can be interpreted as the narrowness of the chaotic region in phase space.
Nonlinear dynamical tunneling of optical whispering gallery modes in the presence of a Kerr nonlinearity
Jeong-Bo Shim,Peter Schlagheck,Martina Hentschel,Jan Wiersig
Physics , 2014,
Abstract: The effect of a Kerr nonlinearity on dynamical tunneling is studied, using coupled whispering gallery modes in an optical microcavity. The model system that we have chosen is the 'add-drop filter', which comprises an optical microcavity and two waveguide coupled to the cavity. Due to the evanescent field's scattering on the waveguide, the whispering gallery modes in the microcavity form doublets, which manifest themselves as splittings in the spectrum. As these doublets can be regarded as a spectral feature of dynamical tunneling between two different dynamical states with a spatial overlap, the effect of a Kerr nonlinearity on the doublets is numerically investigated in the more general context of the relationship between cubic nonlinearity and dynamical tunneling. Within the numerical realization of the model system, it is observed that the doublets shows a bistable transition in its transmission curve as the Kerr-nonlinearity in the cavity is increased. At the same time, one rotational mode gets dominant over the other one in the transmission, since the two states in the doublet have uneven linewidths. By using coupled mode theory, the underlying mode dynamics of the phenomena is theoretically modelled and clarified.
Analyzing the Dynamic Relationship between Tumor Growth and Angiogenesis in a Two Dimensional Finite Element Model
Eun Bo Shim,Yoo Seok Kim,Thomas S. Deisboeck
Quantitative Biology , 2007,
Abstract: Employing a novel two-dimensional computational model we have simulated the feedback between angiogenesis and tumor growth dynamics. Analyzing vessel formation and elongation towards the concentration gradient of the tumor-derived angiogenetic basic fibroblast growth factor, bFGF, we assumed that prior to the blood vessels reaching the tumor surface, the resulting pattern of tumor growth is symmetric, circular with a common center point. However, after the vessels reach the tumor surface, we assumed that the growth rate of that particular cancer region is accelerated compared to the tumor surface section that lacks neo-vascularization. Therefore, the resulting asymmetric tumor growth pattern is biased towards the site of the nourishing vessels. The simulation results show over time an increase in vessel density, a decrease in vessel branching length, and an increase in fracticality of the vascular branching architecture. Interestingly, over time the fractal dimension displayed a sigmoidal pattern with a reduced rate increase at earlier and later tumor growth stages due to distinct characteristics in vessel length and density. The finding that, at later stages, higher vascular fracticality resulted in a marked increase of tumor slice volume provides further in silico evidence for a functional impact of vascular patterns on cancer growth.
A Type 2C Protein Phosphatase FgPtc3 Is Involved in Cell Wall Integrity, Lipid Metabolism, and Virulence in Fusarium graminearum
Jinhua Jiang,Yingzi Yun,Qianqian Yang,Won-Bo Shim,Zhengyi Wang,Zhonghua Ma
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0025311
Abstract: Type 2C protein phosphatases (PP2Cs) play important roles in regulating many biological processes in eukaryotes. Currently, little is known about functions of PP2Cs in filamentous fungi. The causal agent of wheat head blight, Fusarium graminearum, contains seven putative PP2C genes, FgPTC1, -3, -5, -5R, -6, -7 and -7R. In order to investigate roles of these PP2Cs, we constructed deletion mutants for all seven PP2C genes in this study. The FgPTC3 deletion mutant (ΔFgPtc3-8) exhibited reduced aerial hyphae formation and deoxynivalenol (DON) production, but increased production of conidia. The mutant showed increased resistance to osmotic stress and cell wall-damaging agents on potato dextrose agar plates. Pathogencity assays showed that ΔFgPtc3-8 is unable to infect flowering wheat head. All of the defects were restored when ΔFgPtc3-8 was complemented with the wild-type FgPTC3 gene. Additionally, the FgPTC3 partially rescued growth defect of a yeast PTC1 deletion mutant under various stress conditions. Ultrastructural and histochemical analyses showed that conidia of ΔFgPtc3-8 contained an unusually high number of large lipid droplets. Furthermore, the mutant accumulated a higher basal level of glycerol than the wild-type progenitor. Quantitative real-time PCR assays showed that basal expression of FgOS2, FgSLT2 and FgMKK1 in the mutant was significantly higher than that in the wild-type strain. Serial analysis of gene expression in ΔFgPtc3-8 revealed that FgPTC3 is associated with various metabolic pathways. In contrast to the FgPTC3 mutant, the deletion mutants of FgPTC1, FgPTC5, FgPTC5R, FgPTC6, FgPTC7 or FgPTC7R did not show aberrant phenotypic features when grown on PDA medium or inoculated on wheat head. These results indicate FgPtc3 is the key PP2C that plays a critical role in a variety of cellular and biological functions, including cell wall integrity, lipid and secondary metabolisms, and virulence in F. graminearum.
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