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Kinetics of Perovskite Phase Formation via the Interfacial Diffusion
Sung, Yun-Mo,Hwang, Seung-Joon,Kwack, Woo-Chul 대진대학교 첨단소재연구소 2000 첨단소재연구소논문집 Vol.3 No.-
In this study, a kinetics equation for the perovskite (AIIBIVO3) phase formation was derived based upon a diffusion couple model. The diffusion of A2+ and O2- fluxes across the perovskite interlayer was considered in this derivation. From the parabolic kinetics between the thickness of the perovskite interlayer and time, the reaction rate constant (k) for the perovskite formation was determined to be a function of the average diffusion coefficient of slow A2+ ions (*****A2+) and the free energy for the formation of the perovskite phase (△GOABO3). By using experimental kinetics data, the diffusion constant (DO) and the activation energy for diffusion (Q) can be determined, and thus *****A2+ can be defined as a function of the temperature. Finally, by substituting *****A2+ and △GOABO3 into the kinetics equation, it can be completed and used for the estimation of perovskite phase formation reactions.
The role of second alkali or alkaline-earth ions in LAS glass-ceramics
Sung, Yun-Mo,Kwak, Woo-Chul,Jung, Se-Yan,Hwang, Seung-Joon 대진대학교 첨단소재연구소 2001 첨단소재연구소논문집 Vol.4 No.-
LAS glass-ceramics show very narrow compositional range with transparency and low thermal expansion. The relatively high melting temperature of parent glass limits wide range of applications. The addition of second alkali or alkaline-earth ions into the LAS glass composition was attempted and the effects on the melting, phase containing Ba²? showed transparency after crystallization as well as reduced melting temperature. The transparency of this glass-ceramic was discussed in terms of ionic field strength and ionic size.
Kinetic' analysis of spinel formation reaction via diffusion bonding
Sung, Yun-Mo,Kwak, Woo-Chul,Jung, Se-Yon,Hwang, Seung-Joon 대진대학교 첨단소재연구소 2001 첨단소재연구소논문집 Vol.4 No.-
Spinel(AB_2O_4)is one of the most important compound ceramic materials. The formation reactions have been extensively studied, however, the formation kinetics has not been completed. In this paper, a thorough derivation for the kinetics of MgAl_2O_4 spinel formation via diffusion bonding was performed using flux equations. Nernst-Planck type approach and a parabolic kinetics due to the interfacial diffusion were employed for this derivation. The final kinetic equation for spinel formation was determined a Δ§^2=2{(-8D ̄_(Al))·((ΔG^0_(MgAl_2O_4))/RT)}t=2kt s..
Hwang, Sung-Mi,Kang, Hye-Jin,Bae, Sang-Woo,Chang, Woo-Jin,Koo, Yoon-Mo 한국생물공학회 2010 Biotechnology and Bioprocess Engineering Vol.15 No.2
The effects of salt concentration in mobile phase, elution strategy, and hydrophobicity of stationary phase on lysozyme refolding in hydrophobic interaction chromatography (HIC) were investigated. Butyl Sepharose 4 Fast Flow, the least hydrophobic HIC resin among the tested adsorbent, showed the best refolding yield. The binding efficiency of unfolded lysozyme on the adsorbent was maximized when 1 and 0.4 M of initial and final concentration of ammonium sulfate was used in mobile phase, respectively. The optimum gradient strategy for refolding and elution of lysozyme was determined as linear increase of urea concentration to 4M. The optimized condition suggests the less hydrophobic environment than conventionally used salt solutions and HIC resins. Consequently, total refolding yield was improved 1.6 times comparing with optimized dilution-based batch refolding method.
Treatment of Supratentorial Primitive Neuroectodermal Tumors (PNETs) in Children
Hwang, Jun-Mo,Kim, Dong-Won,Lee, Sung-Yeal,Kim, Il-Man,Lee, Chang-Young,Yim, Man-Bin,Son, Eun-Ik The Korean Neurosurgical Society 2005 Journal of Korean neurosurgical society Vol.37 No.3
Objective: Strategies for managing supratentorial primitive neuroectodermal tumors(PNETs) in children include surgical resection, craniospinal irradiation and chemotherapy. This study is performed in order to compare the efficacy of various methods of treatment and to describe its optimal management. Methods: We have reviewed all medical records and pathology slides of six children(four males and two females) with supratentorial PNET from November, 1987 to May, 2003. The extent of resection was confirmed by computed tomography and magnetic resonance studies. Results: The patients were aged 1 to 13 years and treated postoperatively with/without adjuvant therapy. Tumor location included was four cortical, one gangliobasal, and one pineal region. The presenting symptoms and signs consisted of increased intracranial pressure and focal neurological deficits such as seizure and hemiparesis. The treatment consisted of surgical resection alone in one patient, postoperative radiotherapy in one patient, postoperative chemotherapy in one, and postoperative radiotherapy with chemotherapy in three. Five patients lived more than 12 months after diagnosis and one patient among them has been living more than 5 years after diagnosis. Conclusion: We can improve the survival and prognosis of supratentorial PNET patients by radical gross total resection of tumor followed by craniospinal irradiation and aggressive chemotherapy. First of all, gross total resection of tumor is the most important among many factors.
Gapped Nearly Free-Standing Graphene on an SiC(0001) Substrate Induced by Manganese Atoms
Hwang, Jinwoong,Lee, Ji-Eun,Kang, Minhee,Park, Byeong-Gyu,Denlinger, Jonathan,Mo, Sung-Kwan,Hwang, Choongyu The Korean Vacuum Society 2018 Applied Science and Convergence Technology Vol.27 No.5
The electron band structure of manganese-adsorbed graphene on an SiC(0001) substrate has been studied using angle-resolved photoemission spectroscopy. Upon introducing manganese atoms, the conduction band of graphene, that is observed in pristine graphene indicating intrinsic electron-doping by the substrate, completely disappears and the valence band maximum is observed at 0.4 eV below Fermi energy. At the same time, the slope of the valence band decreases by the presence of manganese atoms, approaching the electron band structure calculated using the local density approximation method. The former provides experimental evidence of the formation of nearly free-standing graphene on an SiC substrate, concomitant with a metal-to-insulator transition. The latter suggests that its electronic correlations are efficiently screened, suggesting that the dielectric property of the substrate is modified by manganese atoms and indicating that electronic correlations in grpahene can also be tuned by foreign atoms. These results pave the way for promising device application using graphene that is semiconducting and charge neutral.