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Han, Jihoon,Sohn, Dongwoo,Woo, Wanchuck,Kim, Dong-Kyu Elsevier 2017 Computational materials science Vol.129 No.-
<P><B>Abstract</B></P> <P>We investigate the deformation and fracture behaviors of pristine and bi-crystalline graphenes by molecular dynamics simulations. For pristine graphene with a pre-crack, fracture toughness is strongly dependent on the crack morphology and atomic configuration at the crack tip. For bi-crystalline graphene, fracture toughness becomes comparable to that of pristine graphene with increase in density of topological 5–7 defects arranged uniformly along grain boundary due to cancellation of the dipole stress field. In addition, we find that trans-intergranular transition can occur during the rupture process with increase in the slant angle of grain boundary with respect to the external loading direction. Our findings provide a fundamental understanding of failure mechanisms and fracture behaviors in graphene and other two-dimensional materials.</P> <P><B>Graphical abstract</B></P> <P>Both intergranular and transgranular fractures are observed. With an increase in GB slant angle, trans- to intergranular transition in the rupture process takes place over the slant angle of 50°. For slant angles of 80°, it shows that a transgranular fracture occurs initially; then intergranular fracture becomes the predominant fracture mechanism because the GBs are weakened when the direction of external stress is close to perpendicular to the GB.</P> <P>[DISPLAY OMISSION]</P>
Jihoon HAN,Mi-ran KI,Eui-Kyung JANG,Ryeo Gang SON,Seung Pil PACK,Sungwook CHUNG 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.10
Combining nanoparticle-based drug delivery system (NDDS) with photodynamic therapy is one of strategies for effective cancer therapy. We successfully synthesized poly(acrylic acid)-calcium phosphate passivated TiO₂. TiO₂@PAA-CaP NPs exhibited higher loading capacity higher than unfunctionalized TiO₂ NPs, and DOX-loaded TiO₂@PAA-CaP NPs released more DOX in acidic conditions than in neutral conditions. In-vitro cell viability tests revealed that DOX loaded TiO₂@PAA-CaP NPs exhibited efficient toxicity and cellular uptake towards MCF-7 cancer cells, likely due to pH-triggered efficient DOX release characteristics at acidic (pH ~ 5) cellular environments. PDT tests revealed TiO₂@PAA-CaP NPs under UV irradiation generated similar intracellular ROS, and exhibited cytotoxicity towards MCF-7 cancer cells comparable to un-functionalized TiO₂ NPs; however, in the case of BEAS-2B normal cells, passivated TiO₂ under UV irradiation produced lower ROS and showed lower cytotoxicity than the raw TiO₂ NPs. DOX loaded TiO₂@PAA-CaP NPs under UV irradiation exhibited overall higher cytotoxicity likely due to synergistic effects of efficient NDDS and enhanced PDT characteristics of TiO₂@PAA-CaP NPs.
Han, Jihoon,Ryu, Seunghwa,Kim, Dong-Kyu,Woo, Wanchuck,Sohn, Dongwoo IOP Publishing - Europhysics Letters 2016 Europhysics letters Vol.114 No.6
<P>Nanoindentation experiments and simulations are carried out to estimate the elastic modulus of freely-suspended-multilayer graphene. However, due to the difficulty of clamping all layers of multilayer graphene in experiments, and to the ambiguity of imposing the clamped boundary conditions in numerical simulations, the estimated values of elastic modulus exhibit large variation. In particular, interlayer sliding can affect the estimation of elastic modulus. From a series of molecular dynamics simulations, we demonstrate that the estimated elastic modulus of multilayer graphene depends on the level of interlayer sliding involved in boundary conditions. Under fully clamped boundary conditions that prevent interlayer sliding, the elastic modulus is constant regardless of the number of layers. In contrast, under weakly clamped boundary conditions that involve interlayer sliding, the elastic modulus decreases with increasing number of layers. In the case of weakly clamped conditions, a few wrinkles form in the interlayer and then coalesce into a single large wrinkle due to interlayer sliding. Our findings provide an understanding of the variation of elastic modulus observed in other experimental and numerical studies. Copyright (C) EPLA, 2016</P>
Temperature Dependence of Screw Dislocation Mobility on Shuffle-Set of Silicon
Jihoon Han,Mingyu Park,Arim Lee,손동우,Jaeshin Park,임세영 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.5
Large-scale atomistic simulations are performed in order to observe local behaviors of screw dislocationslocated on the shuffle set of (111) in single crystal silicon, focusing on the propagation process of the screwdislocations. A quadrupolar arrangement of screw dislocations is utilized to impose the periodic boundaryconditions along each of the three spatial directions. With the aid of molecular dynamics simulations, thedislocation mobility is investigated in terms of the critical resolved shear stress. Based on the results fromthe simulations, we discuss effects of the model size and temperature on the critical resolved shear stress. After choosing the proper model size to reduce undesirable interference between the dislocations, we furtherestimate the Peierls stress by fitting from a set of the critical resolved shear stresses at various temperatures. Meanwhile, we observe a double kink mechanism in the dislocation propagation which is the most energeticallyfavorable dislocation movement in silicon. We investigate the formation and migration of kinkpairs on an undissociated screw dislocation in silicon.
JiHoon Han 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2
Currently, Korea is planning to use various equipments and technologies for cutting, decontamination, compression, solidification, and packaging at decommissioning site of Kori unit 1 and Wolsung unit 1. In particular, Korea is considering to apply new technologies like inorganic acid decontamination, spent resion treatment technology not only to localize various decommissioning technology, but to meet the limit of 14,500 drums of the decommissioning waste per unit. However, before the techniques applied to decommissioning, it is necessary to demonstrate the effectiveness and the safety of the techniques. Because unlike the industrial fields, the failure of the decommissioning technique in nuclear power plants can cause the spread or leakage of radioactive materials. In the「Regulation on Technical Standards for Nuclear Reactor Facilities, Etc.」is stated that the licensee shall apply proven technology to decommissioning and if the licensee apply new technology, he must provide resonable evidence and prove its safety. In accordance with this approach, Nuclear Safety and Security Commission (NSSC) Notice No. 2021-24 can be applied to the decommissioning technology as one of a technical standard related with the demonstration of it. And it states 9 kinds of elements related to the radioactive waste management facilites and components like the management of radioactive effluents, prevention of contamination and overflow by radioactive materials, etc. But, they are mixed with the radioactive material considerations and industrial considerations, and these considerations are usually for the facilities, not equipments or techniques. On the other hand, in the IAEA Safety Standards Series No. WS-G-2.1 Section 6.15 to 6.20, it recommended to evaluate 12 considerations for the decontamination technique and 7 considerations for the dismantling techniques. The Decommissioning Guide in Germany recommends to consider 3 conditions for radiation protection of decontamination techniques and 4 conditions for dismantling techniques. Therefore, it is necessary to compare the safety requirements or recommendations related to the demonstration of decommissioning technology with the other countries to check there is something to learn from it.
OpenFOAM을 이용한 Supplementary 버너 난류 연소해석과 배기가스 예측 및 검증
장지훈(Jihoon Jang),이영재(Youngjae Lee),한가람(Karam Han),한우주(Woojoo Han),허강열(Kang Y. Huh) 한국연소학회 2014 KOSCOSYMPOSIUM논문집 Vol.2014 No.5
In this study, simulations of supplementary burner combustion were performed to analyze turbulent combustion and emissions. In order to simulate detailed chemical reaction mechanism, The steady laminal flamelet model(SLFM) and lagrangian conditional moment closure(CMC) model are implemented in open source code, OpenFOAM. Validatation is performed against measured Temperatures, CO and NOx emissions at different fuels and load conditions