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Journal of Energy Chemistry 2018年第2期27卷 528-534页

作者： Parveen Sood ki.chul ki. Seung Soon Jang School of Materials Science and Engineering Georgia Institute of Technology Atlanta CA 30332-0245. USA Department of Chemical Engineering Konkuk University Seoul 05029 Republic of Korea Institute for Electronics and Nonotechnology Georgia Institute of Technology Atlanta GA 30332-0245 USA Parker H. Petit Institute for Bioengineering and Bioscience Georgia Institute of Technology Atlanta GA 30332-0245 USA

We have studied the redox potentials and electronic properties of C60 and C59N using density functional theory method. It is found that doping C60 with one nitrogen atom results in a slight increase in redox potential. Next, we have also studied C59N functionalized with various redox-active oxygen containing functional groups and strongly electron withdrawing functional groups. It is found that the intrinsic electronic structure of the molecule is the major determinant of the redox potential. Our DFT calculations show that the electron affinity to redox potential of functionalized C59N is correlated with the LUMO of the systems very well. This is the first systematic study on the redox properties and electronic structures of N-doped C60 systems.

关键词： DFT Redox potential C60 Doping Li-ion battery

Effect of drawing speed on microstructure distribution and drawability in twinning-induced plasticity steel during wire drawing

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Journal of Iron and Steel Research International 2020年第5期27卷 577-587页

作者： Joong-ki.Hwang School of Mechanical Engineering Tongmyong UniversityBusan 48520Republic of Korea

The effect of drawing speed on temperature rise and microstructure distribution in twinning-induced plasticity(TWIP)steel during wire drawing has been investigated to improve drawability for wire rod *** wire drawing process is performed at room temperature,heat is generated due to the plastic deformation and friction at the wire-die *** steel wires subjected to the low drawing speed(LD)of 0.5 m/min and the high drawing speed(HD)of 5.0 m/min were analyzed using the numerical simulation and electron backscatter diffraction ***,the specimens subjected to the HD had a higher drawability by about 18%compared to the LD,which is totally different from the general behavior of plain carbon pearlitic *** LD wire had uniform temperature distribution along the radial direction during wire *** contrast,the HD wire had a temperature gradient along the radial direction due to the higher frictional effect at surface:the minimum temperature of 58℃ at center area and the maximum temperature of 143 C at surface *** higher stacki.g fault energy of HD wire at the surface area due to the high temperature rise retarded twinning rate,resulting in the prevention of fast exhaustion in ductility in comparison with the LD wires since the earlier depletion of twins at surface area is known as the main reason for the fracture of TWIP steel during wire ***,HD process delayed the fracture strain of wire and increased the uniformity of microstructure and mechanical properties along the radial direction.

关键词： Twinning-induced plasticity steel Wire drawing Deformation twin Drawing speed Temperature rise

Strain hardening rate dependency of deformation shape,strain distribution,and contact pressure during wire flat rolling

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Journal of Iron and Steel Research International 2023年第3期30卷 475-486页

作者： Joong-ki.Hwang School of Mechatronics Engineering Korea University of Technology and EducationCheonan 31253Republic of Korea

The effect of the strain hardening exponent(n)of a material on the changes in shape,strain inhomogeneity,and contact pressure was investigated during wire flat rolling to understand its effect on the deformation behavior of a flat-rolled wire and to determine the optimal worki.g conditions with *** deformation behaviors of wires with various n values were systematically compared using finite element *** shape of the deformed wire was found to depend on the n value of the *** the contact width and lateral spreading of the wire decrease with increasing n,resulting in a large reduction in area with the n *** strain homogeneity of the wire increases with the n value of the *** improvement in the strain homogeneity with the n value is attributable to two factors:a lower strain concentration in the central region and a higher overall elongation as n *** addition,the average effective strain of the wire cross section decreases with the n value of a material during wire flat *** contact pressure distribution on the surface of the wire differs significantly depending on the n *** materials with a low n value,the contact pressure exhibits a higher value at the entry and edge zones of the contact *** contrast,materials with high n values exhibit a higher contact pressure at the exit *** behavior can be explained by the strain hardening behavior of the material during wire flat rolling.

关键词： Strain hardening exponent Wire flat rolling Shape change Strain inhomogeneity Contact pressure

Synergistic passivation of MAPbI_(3) perovski.e solar cells by compositional engineering using acetamidinium bromide additives

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Journal of Energy Chemistry 2021年第8期30卷 755-762,I0016页

作者： Kyungeun Jung Weon-Sik Chae Jae Won Choi ki.chul ki. Man-Jong Lee Department of Chemistry Konkuk University143-701 SeoulSouth Korea Department of Advanced Technology Fusion Konkuk University143-701 SeoulSouth Korea Analysis Research Division Daegu CenterKorea Basic Science Institute702-701 DaeguSouth Korea Division of Chemical Engineering Konkuk University05029 SeoulSouth Korea

For the global commercialization of highly efficient and stable perovski.e solar cells(PSCs),it is necessary to effectively suppress the formation of various defects acting as nonradiative recombination sources in perovski.e light-harvesting *** defects between the charge-selective layer and the perovski.e are easily formed in the solution process used to fabricate perovski.e *** addition,owing to the difference in thermal expansion coefficients between the substrate and the perovski.e film,internal residual tensile stress inevitably occurs,resulting in increased nonradiative ***,a simple compositional engineering scheme for realizing efficient and stable PSCs,which incorporates acetamidinium bromide(AABr)as an additive into the MAPbI_(3) lattice,is *** an additive,AABr has been found to provide synergistic multiple passivation for both internal and interfacial *** was found to effectively release the tensile strain of the MAPbI_(3) film by forming a structure stabilized by NH-I hydrogen bonds,as evidenced by calculations based on density functional theory(DFT).Furthermore,the incorporated AABr additives created a charge carrier recombination barrier to enhance charge collection capability by reducing interfacial ***,a power conversion efficiency(PCE)of 20.18%was achieved using a planar device employing AABr-incorporated MAPbI_(3).This was substantially higher than the 18.32% PCE of a pristine MAPbI_(3)-based ***,unencapsulated PSCs using AABr-incorporated MAPbI_(3) absorbers exhibited excellent long-term stability,maintaining>95% of initial PCE up to 1200 hours in ambient air.

关键词： Acetamidinium bromide Planar perovski.e solar cell Tensile stress Interface passivation Recombination barrier

Density functional theory study on the role of ternary alloying elements in TiFe-based hydrogen storage alloys

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Journal of Materials Science & Technology 2021年第33期92卷 148-158页

作者： Won-Seok Ko ki.Beom Park Hyung-ki.Park School of Materials Science and Engineering University of UlsanUlsan 44610Republic of Korea Functional Materials and Components R&D Group Korea Institute of Industrial TechnologyGangneung 25440Republic of Korea

The role of additional ternary alloying elements on the performance of stationary TiFe-based hydrogen storage alloys was investigated based on first-principles density functional theory *** a basic step for examinations,the site preference of each alloying element in the stoichiometric and nonstoichiometric B2TiFe compounds was clarified considering possible antisite *** on the revealed site preference,the effect of various possible ternary elements on the hydrogen storage was examined by focusing on the formation enthalpies of TiFeH and TiFeH_(2) hydrides,which were closely related to the change in the location of plateaus in the pressure-composition-temperature *** physical properties such as the volume expansion due to hydride formation were also examined to provide additional criteria for selecting optimum alloying conditions in future alloying design *** alloying elements that maximize the grain boundary embrittlement due to the solute segregation were proposed for the enhanced initial activation of TiFe-based hydrogen storage alloys.

关键词： Hydrogen storage alloy Titanium-iron Density functional theory calculation Metallic hydride

Development of practical postprocessor for 5-axis machine tool with non-orthogonal rotary axes

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Journal of Central South University 2011年第1期18卷 159-164页

作者： JUNG Hyoun-chul HWANG Jong-Dae PARK ki.Beom JUNG Yoon-Gyo School of Mechatronics Changwon National University

In order to develop a practical postprocessor for 5-axis machine tool,the general equations of numerically controlled(NC) data for 5-axis configurations with non-orthogonal rotary axes were exactly expressed by the inverse ki.ematics,and a windows-based postprocessor written with Visual Basic was developed according to the proposed *** developed postprocessor is a general system suitable for all ki.ds of 5-axis machines with orthogonal and non-orthogonal rotary *** implementation of the developed postprocessor and verification by a cutting simulation and machining experiment,the effectiveness of the proposed algorithm is *** is improved by allowing exchange of data formats such as rotational total center position(RTCP) controlled NC data,vector post NC data,and program object file(POF) cutter location(CL) data,and convenience is increased by adding the function of work-piece origin ***,a practical post-processor for 5-axis machining is developed.

关键词： post-processor 5-axis machining non-orthogonal rotary axes numerically controlled (NC) data CL data

Developing a geospatial web-GIS system for landscape and urban planning

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International Journal of Digital Earth 2013年第6期6卷 580-588页

作者： Junghoon ki Department of Public Administration Myongji UniversitySeoulKorea

This study discusses a geographical information system(GIS)for operating a local government’s landscape and urban planning activities via a *** this web-GIS system will help build a more realistic landscape and urban planning model that includes citizen participation and city *** approach is applicable to ubiquitous city(u-city)development based on geospatial web and its related *** approach presented is built on six selected elements of a u-city *** outcome of the study includes sustainable analysis,environmental planning,urban planning,and city market*** outcome is applicable to cities that are planning to adopt the u-city system or advanced telecommunication or planning tools into their urban frameworks.

关键词： geospatial data integration virtual reality 3D modeling ubiquitous city sustainable development

The IOSS Chaos Synchronization Method

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Chinese Physics Letters 2011年第1期28卷 32-35页

作者： Choon ki.Ahn Faculty of the Department of Automotive Engineering Seoul National University of Science&Technology172 Gongneung 2-dongNowon-guSeoul 139-743Korea

A new synchronization method, called the input/output-to-state stable synchronization (IOSSS) method, is proposed for a general class of chaotic systems with external disturbance. By introducing Lyapunov stability theory and linear matrix inequality (LMI) for the first time, the IOSSS controller is shown to not only guarantee the synchronization of the chaotic systems, but also reduce the effect of external disturbance. The proposed IOSSS controller can be obtained by solving the LMI, which can easily be done using standard numerical packages. A numerical example is given to demonstrate the availability of the proposed method.

关键词： method chaotic inequality

Unlocki.g power of neighboring vacancies in boosting hydrogen evolution reactions on two-dimensional NiPS3 monolayer

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eScience 2024年第3期4卷 104-115页

作者： Hyun Gu Han Jae Won Choi Minsu Son ki.chul ki. Computational Materials Design Laboratory Department of Chemical EngineeringKonkuk UniversitySeoul 05029The Republic of Korea Division of Chemical Engineering Konkuk UniversitySeoul 05029The Republic of Korea

This study investigates the effect of defect engineering on the catalytic activity of a NiPS3 monolayer catalyst for the hydrogen evolution reaction(HER).Three different types of vacancies on the basal plane of the monolayer are explored through a multi-step mechanism involving the dissociative adsorption of a water molecule and subsequent electrochemical adsorption of the dissociated ***-formation of vacancies in both Ni and S sites is found to be the most effective in enhancing the catalytic performance of the monolayer.A key resource for the reaction thermodynamics is the S-substitution-like physisorption of a water molecule on a vacant S site,followed by the dissociative occupation of OH and H into vacant sites of S and Ni elements,boosted by the NiS di-vacancy configuration with low activation energy *** reveals the highest contribution of bonding orbitals to the monolayer-H bond makes it the most desirable defect engineering approach for transition metal phosphorus chalcogenides with high HER ***,this study highlights the significance of controlled defect engineering in augmenting the catalytic performance of NiPS3 monolayer catalysts for HER.

关键词： Hydrogen evolution reaction Defect engineering Transition metal phosphorus trichalcogenide Density functional theory Reaction thermodynamics

Characteristics of turbulent flow distribution in branch piping system

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Journal of Central South University 2012年第11期19卷 3208-3214页

作者： YOO Geun-jong CHOI Hoon-ki.ki. chul-hwan School of Mechatronics Changwon National UniversityChangwon 641-773Korea

Flow distribution in branch piping system is affected by flow characteristics and different geometric variations. Most of the flow distribution studies are performed with one-dimensional analysis to yield overall information only. However, detailed analysis is required to find effects of design parameters on the flow distribution. For this aspect, three-dimensional turbulent flow analysis was performed to assess turbulence model performance and effects of upstream pressure and branch pipe geometry. Three different turbulence models of standard k-e model, realizable k-e model and standard k-co yield similar results, indicating small effects of turbulence models on flow characteristics analysis. Geometric variations include area ratio of main and branch pipes, branch pipe diameter, and connection shape of main and branch pipes. Among these parameters, area ratio and branch diameter and shape show strong effect on flow distribution due to high friction and minor loss. Uniform flow distribution is one of common requirements in the branch piping system and this can be achieved with rather high total loss design.

关键词： flow distribution pipe flow branch pipe turbulent flow