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Search Results: 1 - 10 of 21697 matches for " Hyung-Il Kim "
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Hardening and overaging Mechanisms in an Au-Ag-Cu-Pd alloy with In additions
Geon-Hoo Jeon,Yong Hoon Kwon,Hyo-Joung Seol,Hyung-Il Kim
Gold Bulletin , 2008, DOI: 10.1007/BF03214879
Abstract: Hardening and overaging mechanisms were examined in a semi-precious Au Ag Cu Pd dental alloy with small amounts of In, Zn and Ir. The alloy showed maximum age-hardenability at the aging temperature of 400°C. The hardness value increased to reach the maximum value, and then decreased continuously with aging time. In the early stage of aging process, the matrix of the single α0 phase separated into the α1 and AuCu I phases, and the fine InPd-based precipitates containing Zn and Cu formed at the grain boundaries. During further aging, the grain boundary precipitates grew toward the grain interior. In overaged specimens, the original matrix was replaced by the coarse lamellar structure composed of the AuCu I phase containing Pd and Zn and the Ag Au-based α1 phase of Cu-, Pdand Zn-depleted. The hardness increase in the early stage of aging process was caused by the nucleation of the InPd-based phase and the AuCu I phase in the ga0 matrix; this introduced significant lattice strains into the interface with the matrix. The hardness decrease in the latter stage of aging process was caused by the formation and coarsening of the lamellar structure composed of the α1 phase and the AuCu I phase. The minor constituent, In formed InPd-based grain boundary precipitates prior to the lamellar structure formation of α1 and AuCu I.
Right trisegmentectomy with thoracoabdominal approach after transarterial embolization for giant hepatic hemangioma
Hyung-Il Seo, Hong Jae Jo, Mun Sup Sim, Suk Kim
World Journal of Gastroenterology , 2009,
Abstract: Hepatic hemangiomas need to be treated surgically in cases where they are accompanied with symptoms, have a risk of rupture, or are hardly distinguishable from malignancy. The present authors conducted embolization of the right hepatic artery one day before an operation for a huge hemangioma accompanied with symptoms and confirmed a decrease in its size. The authors performed a right trisegmentectomy through a J-shape incision, using a thoracoabdominal approach, and safely removed a giant hemangioma of 32.0 cm × 26.5 cm × 8.0 cm in size and 2300 g in weight. Even for inexperienced surgeons, a J-shape incision with a thoracoabdominal approach is considered a safe and useful method when right-side hepatectomy is required for a large mass in the right liver.
Polysplenia syndrome with preduodenal portal vein detected in adults
Hyung-Il Seo, Tae Yong Jeon, Mun Sup Sim, Suk Kim
World Journal of Gastroenterology , 2008,
Abstract: Polysplenia syndrome, defined as the presence of multiple spleens of almost equal volume, is a rare condition involving congenital anomalies in multiple organ systems. We report this anomaly in a 41-year-old female who underwent a left lateral sectionectomy due to recurrent cholangitis and impacted left lateral duct stones. Polysplenia syndrome with preduodenal vein was diagnosed preoperatively by computed tomography (CT) and surgery was done safely. Although the polysplenia syndrome with preduodenal portal vein (PDPV) in adult is rarely encountered, surgeons need to understand the course of the portal vein and exercise caution in approaching the biliary tract.
Age-hardenability and related microstructural changes during and after phase transformation in an Au-Ag-Cu-based dental alloy
Kim, Hyung-Il;Kim, Tae-Wan;Kim, Young-Oh;Cho, Su-Yeon;Lee, Gwang-Young;Kwon, Yong Hoon;Seol, Hyo-Joung;
Materials Research , 2013, DOI: 10.1590/S1516-14392012005000169
Abstract: the aim of this study was to clarify how the microstructural changes during and after phase transformation determine the age-hardenability of an au-ag-cu-based dental alloy. the rapid increase in hardness in the initial stage was the result of rapid atomic diffusion by spinodal decomposition into metastable ag-rich' and cu-rich' phases. the constant hardening after apparent initial hardening was the result of a subsequent transformation of the metastable ag-rich' and cu-rich' phases to the stable ag-rich α1phase and aucu i phase through the metastable aucu i' phase. during the increase in hardness, fine block-like structure with high coherency formed in the grain interior, which changed to a fine cross-hatched structure. a relatively coarse lamellar structure composed of ag-rich α1and aucu i phases grew from the grain boundaries, initiating softening before the grain interior reached its maximum hardness. as a result, the spinodal decomposition attributed to rapid hardening by forming the fine block-like structure, and the subsequent ordering into aucu i, which is a famous hardening mechanism, weakened its hardening effect by accelerating the lamellar-forming grain boundary reaction.
Age-hardening and overaging mechanisms related to the metastable phase formation by the decomposition of Ag and Cu in a dental Au–Ag–Cu–Pd–Zn alloy
Sang-Hwa Lee,In-Sook Lim,Mi-Hyang Cho,Ae-Ri Pyo,Yong Hoon Kwon,Hyo-Joung Seol,Hyung-Il Kim
Gold Bulletin , 2011, DOI: 10.1007/s13404-011-0021-x
Abstract: The age-hardening and overaging mechanisms related to the metastable phase formation by the decomposition of Ag and Cu in a dental casting gold alloy composed of 56Au–25Ag–11.8Cu–5Pd–1.7Zn–0.4Pt–0.1Ir (wt.%) were elucidated by characterizing the age-hardening behaviour, phase transformations, changes in microstructure and changes in element distribution. The fast and apparent increase in hardness at the initial stage of the aging process at 400°C was caused by the nucleation and growth of the metastable Ag–Au-rich phase and the Cu–Au-rich phase by the miscibility limit of Ag and Cu. The transformation of the metastable Ag–Au-rich phase into the stable Ag–Au-rich phase progressed concurrently with the ordering of the Cu–Au-rich phase into the AuCu I phase through the metastable state, which resulted in the subsequent increase in hardness. The further increase in hardness was restrained before complete decomposition of the parent α0 phase due to the initiation of the lamellar-forming grain boundary reaction. The progress of the lamellar-forming grain boundary reaction was not directly connected with the phase transformation of the metastable phases into the final product phases. The heterogeneous expansion of the lamellar structure from the grain boundary caused greater softening than the subsequent further coarsening of the lamellar structure. The lamellar structure was composed of the Ag–Au-rich layer which was Cu-, Pd- and Zn-depleted and the AuCu I layer containing Pd and Zn.
Age-hardening by grain interior and grain boundary precipitation in an Au-Ag-Pt-Zn-In alloy for multipurpose dental use
Joo-Hee Park,Mi-Hyang Cho,Mi-Gyoung Park,Yong Hoon Kwon,Hyung-Il Kim,Hyo-Joung Seol
Gold Bulletin , 2010, DOI: 10.1007/BF03215001
Abstract: The complex precipitation mechanisms related to the age-hardening of Cu-free Au-Ag-Pt-Zn-In alloy for multipurpose dental use was studied by means of hardness test, X-ray diffraction (XRD) studies, field emission scanning electron microscopic (FE-SEM) observations, energy dispersive spectrometer (EDS) analysis, and electron probe microanalysis (EPMA). The early diffusion and then clustering of the In-concentrated phase in the grain interior, together with the early diffusion and then ordering of the PtZn phase in the grain boundary, introduced the internal strains in the Au-Ag-rich α1 matrix, resulting in the hardening process. As the Au-Ag-rich α 1 ’ and PtZn β lamellarforming grain boundary reaction progressed, the phase boundaries between the solute-depleted face-centered cubic (FCC) α 1 ’ matrix and the face-centered tetragonal (FCT) PtZn β precipitate reduced, resulting in softening. In the particlelike structures composed of the major Pt-Au-rich α2 phase and the minor Pt-Zn-rich α3 phase, the separation of In and Zn progressed producing the In-increased Pt-Au-rich α 2 ’ phase and the Zn-increased PtZn α3′ phase with aging time without restraining the softening. The miscibility limit by complex systems of Au-Pt, Ag-Pt, Au-In and In-Zn resulted in the phase transformation and related microstructural changes.
Age-hardening by miscibility limit in a multi-purpose dental gold alloy containing platinum
Hyo-Joung Seol,Joo-Hee Park,Ri-Mo Ku,Mi-Gyoung Park,Yong Hoon Kwon,Hyung-Il Kim
Gold Bulletin , 2010, DOI: 10.1007/BF03214965
Abstract: This study examined the age-hardening by miscibility limit in a multi-purpose dental gold alloy containing platinum. The hardness increased rapidly in the initial stage of the aging process, reached the maximum value, then decreased continuously with aging time. The significant hardness increase resulted from the heterogeneous precipitation of the Pt-rich β phase from the grain boundary of the Au-rich α1 matrix due to the miscibility limit of Au-Pt system. With increasing aging time, the fine Pt-rich β precipitates covered almost the whole matrix, and by further aging, the precipitates grew coarse. The microstructural coarsening reduced the interface between the Au-rich α1 matrix and the Pt-rich β precipitates, which released the lattice strains between the two phases, resulting in a softening effect. In the later stage of aging process, the Au-containing Pt3In particle-like structure was transformed into the Au-depleted particle-like structure containing relatively large amounts of Cu resulting from the overlapping miscibility limit of both Au-Pt and Ag-Cu systems, which was responsible for the slow decreasing rate in hardness in the later stage of aging.
Age-hardening characteristics of a dental low-carat gold alloy with dual hardener system of In and Cu
Hyo-Joung Seol,Seong-Woo Kweon,Su-Yeon Cho,Gwang-Young Lee,Yong Hoon Kwon,Hyung-Il Kim
Gold Bulletin , 2011, DOI: 10.1007/s13404-011-0034-5
Abstract: The age-hardening characteristics of a dental low carat gold alloy with a dual hardener system of indium (In) and Cu (33.9 Au–26.2 Ag–20.28 Cu–9.8 Pd–7.8 In–2 Zn (at%)) were examined by observing the age hardenability and related phase transformation, microstructural changes and elemental distribution during the aging process at 400°C. The dual hardener system by the use of both In and Cu provided more powerful hardening effect compared to a single-hardener system of In or Cu, without the formation of a AuCu type ordered phase. The alloy showed apparent initial hardening, which was attributed to the pre-precipitation or zone formation by the help of quenched in excess vacancies. During the constant increase in hardness, the single parent phase separated into three phases, Au–Ag-based phase, Au–Cu-based phase containing Pd and In, and InPd-based phase, through a metastable state. Indium which was added as one of the hardeners induced initial grain boundary precipitation, followed by an expansion of the lamellar structure, which was responsible for softening. The alternative lamellar structure was composed of a Cu-rich layer (Au–Cu-based phase containing Pd and In) and an Ag-rich layer (Au–Ag-based phase) replaced partly by the InPd-based phase. Separation of the Ag-rich layer from the Cu-rich layer is based on the miscibility limit of Ag and Cu due to their eutectic property.
Pseudo-Newtonian Models for the Equilibrium Structures of Rotating Relativistic Stars
Jinho Kim,Hee Il Kim,Hyung Mok Lee
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.15228.x
Abstract: We obtain equilibrium solutions for rotating compact stars including the special relativistic effects. The gravity is assumed to be Newtonian, but we used the active mass density, which takes into account all the energies such as motions of the fluids, internal energy, pressure energy in addition to the rest mass energy, in computing the gravitational potential using Poisson's equation. Such a treatment could be applicable to the neutron stars with relativistic motions or relativistic equation of state. We applied the Hachisu's self-consistent field (SCF) method to find spheroidal as well as toroidal sequences of equilibrium solutions. Our solutions show better agreement than Newtonian relativistic hydrodynamic approach that does not take into account the active mass, with general relativistic solutions. The physical quantities such as the peak density, equatorial radii of our solutions agree with general relativistic ones within 5%.Therefore our approach can be a simple alternative to the fully relativistic one when large number of model calculations are necessary as it requires much less computational resources.
Axially symmetric pseudo-Newtonian hydrodynamics code
Jinho Kim,Hee Il Kim,Matthew William Choptuik,Hyung Mok Lee
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21203.x
Abstract: We develop a numerical hydrodynamics code using a pseudo-Newtonian formulation that uses the weak field approximation for the geometry, and a generalized source term for the Poisson equation that takes into account relativistic effects. The code was designed to treat moderately relativistic systems such as rapidly rotating neutron stars. The hydrodynamic equations are solved using a finite volume method with High Resolution Shock Capturing (HRSC) techniques. We implement several different slope limiters for second order reconstruction schemes and also investigate higher order reconstructions. We use the method of lines (MoL) to convert the mixed spatial-time partial differential equations into ordinary differential equations (ODEs) that depend only on time. These ODEs are solved using 2nd and 3rd order Runge-Kutta methods. The Poisson equation for the gravitational potential is solved with a multigrid method. In order to confirm the validity of our code, we carry out four different tests including one and two dimensional shock tube tests, stationary star tests of both non-rotating and rotating models and radial oscillation mode tests for spherical stars. In the shock tube tests, the code shows good agreement with analytic solutions which include shocks, rarefaction waves and contact discontinuities. The code is found to be stable and accurate: for example, when solving a stationary stellar model the fractional changes in the maximum density, total mass, and total angular momentum per dynamical time are found to be $3 \times 10^{-6}$, $5 \times 10^{-7}$ and $2 \times 10^{-6}$, respectively. We also find that the frequencies of the radial modes obtained by the numerical simulation of the steady state star agree very well with those obtained by linear analysis.
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