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cO_2 laser-micro plasma arc hybrid welding for galvanized steel sheets

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Transactions of Nonferrous Metals society of china 2011年第A01期21卷 47-53页

作者： c.H.kim Y.N.AHN J.H.kim Advance Welding & Joining Research Group Korea Institute of Industrial Technology Incheon 406-840 South Korea

A laser lap welding process for zinc-coated steel has a well-known unsolved problem-porosity formation. The boiling temperature of coated zinc is lower than the melting temperature of the base metal, which is steel. In the autogenous laser welding, the zinc vapor generates from the lapped surfaces expels the molten pool and the expulsion causes numerous weld defects, such as spatters and blow holes on the weld surface and porosity inside the welds. The laser-arc hybrid welding was suggested as an alternative method for the laser lap welding because the arc can preheat or post-beat the weldment according to the arrangement of the laser beam and the arc. cO2 laser-micro plasma hybrid welding was applied to the lap welding of zinc-coated steel with zero-gap. The relationships among the weld quality and process parameters of the laser-arc arrangement, and the laser-arc interspacing distance and arc current were investigated using a full-factorial experimental design. The effect of laser-arc arrangement is dominant because the leading plasma arc partially melts the upper steel sheets and vaporizes or oxidizes the coated zinc on the lapped surfaces. compared with the result from the laser-TIG hybrid welding, the heat input from arc can be reduced by 40%.

关键词： galvanized steel cO2 laser micro plasma hybrid welding

Plasma density measurement and downstream etching of silicon and silicon oxide in Ar/NF3 mixture remote plasma source

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Plasma science and Technology 2019年第6期21卷 52-57页

作者： H J YEOM D H cHOI Y s LEE J H kim D J sEONG s J YOU H c LEE Korea Research Institute of standards and science(KRIss) Daejeon 34113 Republic of Korea Department of Physics Chungnam National University Daejeon 34134 Republic of Korea

In this study,plasma density measurements were performed near the plume region of the remote plasma source (RPs) in Ar/NF3 gas mixtures using a microwave cutoff *** measured plasma density is in the range of 1010-1011 cm-3 in the discharge conditions with RPs powers of 2-4 kW and gas pressures of 0.87-4 *** plasma density decreased with increasing gas pressures and RPs powers under various Ar/NF3 mixing *** decrease in the plasma density measured at the fixed measurement position (plume region) can be understood by the reduction of the electron energy relaxation length with increases in the gas pressures and mixing ratio of NF3/(Ar/NF3).We also performed downstream etching of silicon and silicon oxide films in this *** etch rate of the silicon films significantly increases while the silicon oxide is slightly etched with the gas pressures and *** was also found that the etch rate strongly depends on the wafer position on the processing chamber electrode,and that the etch selectivity reached 96-131 in the discharge conditions of RF powers (3730-4180 W) and gas pressures (3.6-4 Torr).

关键词： remote plasma source electron density cutoff probe downstream etch

Efficient electron extraction of snO_(2) electron transport layer for lead halide perovskite solar cell

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npj computational Materials 2020年第1期6卷 836-843页

作者： Junu kim Kwang s.kim chang Woo Myung center for superfunctional Materials Department of PhysicsSchool of Natural ScienceUlsan National Institute of Science and Technology(UNIST)Ulsan 44919Korea center for superfunctional Materials Department of ChemistrySchool of Natural ScienceUlsan National Institute of Science and Technology(UNIST)Ulsan 44919Korea

snO_(2) electron transport layer(ETL)has been spotlighted with its excellent electron extraction and stability over TiO_(2) ETL for perovskite solar cells(Pscs),rapidly approaching the highest power conversion ***,how... 详细信息

关键词： ETL layer perovskite

sTUDY ON THE TENsILE FATIGUE DAMAGE OF QUAsI-IsOTROPIc cOMPOsITE LAMINATEs

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Acta Metallurgica sinica(English Letters) 2003年第1期16卷 1-7页

作者： I.G.kim I.s.kim O.s.kim YaragarraK.D.V.Prasad Department of Aerospace Engineering Chosun University 375 Seosuk-dong Dong-gu Gwangju 501-759Korea Department of Mechanical Engineering Mokpo National University 61 Dorimri Chunhke-myun Muan-gun Chonam 534-729 Korea Department of Mechanical Engineering Yosu National University San 96-1 Dunduck-dong Yosu Chon-nam 550-749 Korea school of Mech. & Med. Engineering Queensland University of Technology 2 George Street GPO Box 2434 Brisbane QLD 4001 Australia

Quasi-isotropic laminates have isotropic elastic properties in all in-plane directions. Therefore, this kind of laminate is widely used for structural elements. The simplest stacking sequence of quasi-isotropic laminates is [0/-60/60]s. When the direction of applied axial load to [0/-60/60]s laminate is inclined at a 30-degree angle, we have the other quasi-isotropic laminate [30/-30/90]s under axial load. The failure mechanisms of these two laminates are, however, entirely different from each other because these two laminates have different distribution of the interlaminar stresses. It was confirmed by tensile fatigue tests that the [0/-60/60]s laminate does not show any visible fatigue damage, but the [30/-30/90]s laminate develops edge-delamination during cyclic loading. The analytical results were in good agreement with the experimental results.

关键词： composite material delamination fatigue fracture mechanics interlaminar stress

Numerical analysis of thermal plasma scrubber for cF4 decomposition

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Plasma science and Technology 2019年第6期21卷 9-14页

作者： J KO T H kim s cHOI Department of Nuclear and Energy Engineering Jeju National University Jeju 63243 Republic of Korea Institute for Nuclear science and Technology Jeju National University Jeju 63243 Republic of Korea

cF4 gas emitted in the semiconductor and display manufacturing process is a very harmful greenhouse *** must be removed or converted safely due to its extreme *** a cF4 decomposition system using a thermal plasma scrubber was commercialized,its removal efficiency is *** this work,a numerical analysis of cF4 decomposition in the thermal plasma scrubber was carried out in order to propose an efficient decomposition *** decomposition and recombination temperatures of cF4 were analyzed using thermodynamic equilibrium *** chemical reaction of cF4 decomposition into carbon and fluorine gas was considered in this numerical *** injection position and angle of the cF4 were controlled in order to enhance the decomposition *** vertical injection of cF4 near the torch exit improved the mixing of the cF4 with the thermal plasma *** addition,it was confirmed that the high temperature region expanded due to a vortex generated by strong turbulence in the bottleneck-shaped *** a result,it is revealed that the cF4 injection location and the reactor configuration are the most important factors in improving the decomposition rate.

关键词： numerical simulation decomposition cF4 thermal plasma scrubber

clustering-based label estimation for network anomaly detection

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Digital communications and Networks 2021年第1期7卷 37-44页

作者： sunhee Baek Donghwoon Kwon sang c.suh Hyunjoo kim Ikkyun kim Jinoh kim computer science Department Texas A&M UniversityCommerceTX75429USA ETRI 218 Gajeong-roYuseong guDaejeon34129Republic of Korea

A substantial body of work has been done to identify network anomalies using supervised and unsupervised learning techniques with their unique strengths and *** this work,we propose a new approach that takes advantage of both worlds of unsupervised and supervised *** main objective of the proposed approach is to enable supervised anomaly detection without the provision of the associated labels by *** this end,we estimate the labels of each connection in the training phase using ***“estimated”labels are then utilized to establish a supervised learning model for the subsequent classification of connections in the testing *** set up a new property that defines anomalies in the context of network anomaly detection to improve the quality of estimated *** our extensive experiments with a public dataset(NsL-KDD),we will prove that the proposed method can achieve performance comparable to one with the “original”labels provided in the *** also introduce two heuristic functions that minimize the impact of the randomness of clustering to improve the overall quality of the estimated labels.

关键词： Label estimation Network anomaly detection clustering randomness

Flow imbalance in MHD flows in splitting ducts with locally different electric conductivities of the walls

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Journal of Hydrodynamics 2018年第5期30卷 920-927页

作者： Yang Luo Mengqi Zhu c.N.kim Department of Mechanical Engineering Graduate School Kyung Hee University Department of Mechanical Engineering College of Engineering Kyung Hee University

In this study, three-dimensional liquid-metal magnetohydrodynamic splitting flows in a duct with one inflow channel and two outflow channels with locally different wall electric conductivities（different conductance ratios） are computationally examined. The numerical calculation is achieved with the use of cFX code, with a structured grid system chosen after a series of mesh independence tests. The detailed features of the MHD flows are depicted in a case where the electric conductivities of the two outflow ducts are quite different. Also, the interdependency among the current, fluid velocity, pressure and electric potential is elucidated in order to describe the electromagnetic characteristics of the liquid-metal flows. The result shows that the imbalance of the mass flow rate in the two outflow channels strongly depends on the wall conductivity（i.e., conductance ratio） of each outflow channel.

关键词： Liquid metal flow splitting duct flow imbalance numerical examination conductance ratio

Mixing features in an electromagnetic rectangular micromixer for electrolyte solutions

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Journal of Hydrodynamics 2017年第4期29卷 668-678页

作者： M.M.Wen c.N.kim Department of Mechanical Engineering Graduate School Kyung Hee University Department of Mechanical Engineering College of Engineering Kyung Hee University

In this study, a new magnetohydrodynamic（MHD） mixer for electrolyte solutions with pumping function is reported, and the mixing performance of the device for two different electrolyte solutions is numerically examined in a uniform magnetic field. Application of different potentials to different electrodes allows the current to be induced. The combination of the induced current and magnetic field yields Lorentz force, resulting in the fluid motion. The numerical simulation for the flows in the device is carried out with commercial software cFX. The validity of cFX code for the present numerical model is presented. The mixing performance of the fluids is investigated in many different cases with different combinations of input voltage of the electrode. This study shows that the mixing performance can be enhanced by applying spatially alternating positive and negative voltages to the electrodes. The present simulation results show that with a magnetic field intensity lower than 0.5 T, a voltage difference smaller than 2.0 V, and an electric conductivity of electrolyte solution of 1.5 s/m the pumping capabilities ranging 1.6×10^（-7）-3.6×10^（-6） kg/s and the mixing indexes higher than 0.90 can be obtained with sophisticated designs of the micromixer.

关键词： Mixer electrolyte solution Lorentz force cFX

Numerical simulation and experimental study for rheo-forged component using direct and indirect die system

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Transactions of Nonferrous Metals society of china 2010年第9期20卷 1799-1804页

作者： H.H.kim c.G.KANG Precision Manufacturing systems Division Pusan National University school of Mechanical Engineering Pusan National University

sand casting and die casting processes have been used widely for complex automotive products such as knuckle, arm, ***, a part fabricated by casting has limited strength due to manufacturing defects such as the dendrite structure, segregation and *** an attempt to offer a solution to these problems, forging has been used as an alternative ***, the forging process provides limited formability for complex shape ***-forging of metal offers not only superior mechanical strength but also requires significantly lower machine loads than solid forming *** order to produce semi-solid materials of the desired microstructure, a stirring process is applied during solidification of molten *** results of an A356 aluminum alloy sample, which are obtained by experiment and by simulation using DEFORM 3D, are present.

关键词： rheo-forging A356 alloy formability forming defects