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Advances in Atmospheric Sciences 2005年第2期22卷 230-237页

作者： jae-jin kim Jong-jin BAIK Climate Environment System Research Center Seoul National University Seoul 151-742 KoreaSchool of Earth and Environmental Sciences Seoul National University Seoul 151-742 Korea

The effects of street bottom heating and inflow turbulence on urbanstreet-canyon flow are experimentally investigated using a circulating water channel. Threeexperiments are carried out for a street canyon with a street aspect ratio of 1. Results from eachexperiment with bottom heating or inflow turbulence are compared with those without bottom heatingand appreciable inflow turbulence. It is demonstrated that street bottom heating or inflowturbulence increases the intensity of the canyon vortex. A possible explanation on how street bottomheating or inflow turbulence intensifies the canyon vortex is given from a fluid dynamicalviewpoint.

关键词： urban street-canyon flow street bottom heating inflow turbulence circulating water channel

Effects of a Building’s Density on Flow in Urban Areas

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Advances in Atmospheric Sciences 2009年第1期26卷 45-56页

作者： jae-jin kim Do-Yong kim Department of Environmental Atmospheric Sciences Pukyong National University Busan Korea Center for Atmosphere Science and Earthquake Research Korea Meteorological Administration Busan Korea

The effects of a building＇s density on urban flows are investigated using a CFD model with the RNG k - ε turbulence closure scheme. Twenty-seven cases with different building＇s density parameters （e.g., building and street-canyon aspect ratios） are numerically simulated. As the building＇s density parameters vary, different flow regimes appear. When the street canyon is relatively narrow and high, two counterrotating vortices in the vertical direction are generated. The wind speed along streets is mainly affected by the building＇s length. However, it is very difficult to find or generalize the characteristics of the street-canyon flows in terms of a single building＇s density parameter. This is because the complicated flow patterns appear due to the variation of the vortex structure and vortex number. Volume-averaged vorticity magnitude is a very good indicator to reflect the flow characteristics despite the strong dependency of flows on the variation of the building＇s density parameters. Multi-linear regression shows that the volume-averaged vorticity magnitude is a strong function of the building＇s length and the street-canyon width. The increase in the building＇s length decreases the vorticity of the street-canyon flow, while, the increase in the street- canyon width increases the vorticity.

关键词： urban flow characteristics building's density parameter volume-averaged vorticity CFD model

Effects of Street-Bottom and Building-Roof Heating on Flow in Three-Dimensional Street Canyons

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Advances in Atmospheric Sciences 2010年第3期27卷 513-527页

作者： jae-jin kim Jong-jin BAIK Department of Environmental Atmospheric Sciences Pukyong National University School of Earth and Environmental Sciences Seoul National University

Using a computational fluid dynamics （CFD） model, the effects of street-bottom and building-roof heating on flow in three-dimensional street canyons are investigated. The building and street-canyon aspect ratios are one. In the presence of street-bottom heating, as the street-bottom heating intensity increases, the mean kinetic energy increases in the spanwise street canyon formed by the upwind and downwind buildings but decreases in the lower region of the streamwise street canyon. The increase in momentum due to buoyancy force intensifies mechanically induced flow in the spanwise street canyon. The vorticity in the spanwise street canyon strengthens. The temperature increase is not large because relatively cold above-roof-level air comes into the spanwise street canyon. In the presence of both street-bottom and building-roof heating, the mean kinetic energy rather decreases in the spanwise street canyon. This is caused by the decrease in horizontal flow speed at the roof level, which results in the weakening of the mean flow circulation in the spanwise street canyon. It is found that the vorticity in the spanwise street canyon weakens. The temperature increase is relatively large compared with that in the street-bottom heating case, because relatively warm above-roof-level air comes into the spanwise street canyon.

关键词： street canyon flow CFD model street-bottom heating building-roof heating mean kineticenergy vorticity

Effects of Wind Fences on the Wind Environment around Jang Bogo Antarctic Research Station

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Advances in Atmospheric Sciences 2017年第12期34卷 1404-1414页

作者： Jang-Woon WANG jae-jin kim Wonsik CHOI Da-Som MUN Jung-Eun KANG Hataek KWON jin-Soo kim Kyung-Soo HAN Department of Environmental Atmospheric Sciences Pukyong National University 45Yongso-ro Korea Polar Research Institute 26 Songdomirae-ro Yeonsu-gu Department of Spatial Information Engineering Pukyong National University 45Yongso-ro

This study investigated the flow characteristics altered by Jang Bogo Antarctic Research Station using computational fluid dynamics(CFD) modeling. The topography and buildings around Jang Bogo Station were constructed with computeraided-design data in the CFD model domain. We simulated 16 cases with different inflow directions, and compared the flow characteristics with and without Jang Bogo Station for each inflow direction. The wind data recorded by the site’s automatic weather station(AWS) were used for comparison. Wind rose analysis showed that the wind speed and direction after the construction of Jang Bogo Station were quite different from those before construction. We also investigated how virtual wind fences would modify the flow patterns, changing the distance of the fence from the station as well as the porosity of the fence. For westerly inflows, when the AWS was downwind of Jang Bogo Station, the decrease in wind speed was maximized(-81% for west-northwesterly). The wind speed reduction was also greater as the distance of the fence was closer to Jang Bogo Station. With the same distance, the fence with medium porosity(25%–33%) maximized the wind speed *** results suggest that the location and material of the wind fence should be selected carefully, or AWS data should be interpreted cautiously, for particular prevailing wind directions.

关键词： Jang Bogo Antarctic Research Station CFD model observation environment wind fence porosity

Electrochemically Deposited CZTSSe Thin Films for Monolithic Perovskite Tandem Solar Cells with Efficiencies Over 17%

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Energy & Environmental Materials 2024年第1期7卷 147-152页

作者： Sun Kyung Hwang Ik jae Park Se Won Seo jae Hyun Park So Jeong Park jin Young kim Department of Materials Science and Engineering Seoul National UniversitySeoul 08826Korea Department of Applied Physics Sookmyung Women's UniversitySeoul 04310Korea Research Institute of Advanced Materials and Systems Sookmyung Women's UniversitySeoul 04310Korea Research Institute of Advanced Materials(RIAM) Seoul National UniversitySeoul 08826Korea

In spite of the high potential economic feasibility of the tandem solar cells consisting of the halide perovskite and the kesterite Cu2ZnSn(S,Se)4(CZTSSe),they have rarely been demonstrated due to the difficulty in implementing solution-processed perovskite top cell on the rough surface of the bottom ***,we firstly demonstrate an efficient monolithic two-terminal perovskite/CZTSSe tandem solar cell by significantly reducing the surface roughness of the electrochemically deposited CZTSSe bottom *** surface roughness(R_(rms))of the CZTSSe thin film could be reduced from 424 to 86 nm by using the potentiostatic mode rather than using the conventional galvanostatic mode,which can be further reduced to 22 nm after the subsequent ion-milling *** perovskite top cell with a bandgap of 1.65 eV could be prepared using a solution process on the flattened CZTSSe bottom cell,resulting in the efficient perovskite/CZTSSe tandem solar *** the current matching between two subcells involving the thickness control of the perovskite layer,the best performing tandem device exhibited a high conversion efficiency of 17.5%without the hysteresis effect.

关键词： CZTSSe monolithic tandem solar cells perovskite solution process surface roughness control

Boosted Lithium-Ion Transport Kinetics in n-Type Siloxene Anodes Enabled by Selective Nucleophilic Substitution of Phosphorus

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Nano-Micro Letters 2024年第10期16卷 618-637页

作者： Se In kim Woong-Ju kim jin Gu Kang Dong-Wan kim School of Civil Environmental and Architectural EngineeringKorea University02841 SeoulSouth Korea Nanophotonics Research Center Korea Institute of Science and Technology02792 SeoulSouth Korea

Doped two-dimensional(2D)materials hold significant promise for advancing many technologies,such as microelectronics,optoelectronics,and energy ***,n-type 2D oxidized Si nanosheets,namely n-type siloxene(n-SX),are employed as Li-ion battery *** thermal evaporation of sodium hypophosphite at 275℃,P atoms are effectively incorporated into siloxene(SX)without compromising its 2D layered morphology and unique Kautsky-type crystal ***,selective nucleophilic substitution occurs,with only Si atoms being replaced by P atoms in the O_(3)≡Si-H *** resulting n-SX possesses two delocalized electrons arising from the presence of two electron donor types:(i)P atoms residing in Si sites and(ii)H *** doping concentrations are varied by controlling the amount of precursors or their mean free *** at 2000 mA g^(-1),the n-SX electrode with the optimized doping concentration(6.7×10^(19) atoms cm^(-3))delivers a capacity of 594 mAh g^(-1) with a 73%capacity retention after 500 *** improvements originate from the enhanced kinetics of charge transport processes,including electronic conduction,charge transfer,and solid-state *** approach proposed herein offers an unprecedented route for engineering SX anodes to boost Li-ion storage.

关键词： Li-ion battery Two-dimensional N-type siloxene Doping mechanism Kinetics

Random pinhole attenuator for high-power laser beams

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High Power Laser Science and Engineering 2024年第3期12卷 116-121页

作者： Seong Cheol Park Hyeok Yun jin Woo Yoon Seong Ku Lee jae Hee Sung Il Woo Choi Chang Hee Nam Kyung Taec kim Department of Physics and Photon Science Gwangju Institute of Science and TechnologyGwangjuRepublic of Korea Center for Relativistic Laser Science Institute for Basic ScienceGwangjuRepublic of Korea Advanced Photonics Research Institute Gwangju Institute of Science and TechnologyGwangjuRepublic of Korea

The intensity attenuation of a high-power laser is a frequent task in the measurements of optical *** intensity can be attenuated by inserting an optical element,such as a partial reflector,polarizer or absorption *** devices are,however,not always easily applicable,especially in the case of ultra-high-power lasers,because they can alter the characteristics of a laser beam or become easily *** this study,we demonstrated that the intensity of a laser beam could be effectively attenuated using a random pinhole attenuator(RPA),a device with randomly distributed pinholes,without changing the beam *** this device,a multi-PW laser beam was successfully attenuated and the focused beam profile was measured without any alterations of its *** addition,it was confirmed that the temporal profile of a laser pulse,including the spectral phase,was ***,the RPA possesses significant potential for a wide range of applications.

关键词： high-power laser intensity attenuation laser diagnostics

Driving inward growth of lithium metal in hollow microcapsule hosts by heteroatom‐controlled nucleation

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Carbon Energy 2024年第8期6卷 262-272页

作者： Siwon kim Hong Rim Shin Ki jae kim Min‐Sik Park Jong‐Won Lee Division of Materials Science and Engineering Hanyang UniversitySeoulRepublic of Korea Department of Energy Science and Engineering Daegu Gyeongbuk Institute of Science and Technology(DGIST)DaeguRepublic of Korea Department of Energy Science Sungkyunkwan UniversitySuwonRepublic of Korea Department of Advanced Materials Engineering for Information and Electronics Integrated Education for Frontier Science and Technology(BK21 Four)Kyung Hee UniversityYonginRepublic of Korea

The application of Li metal anodes in rechargeable batteries is impeded by safety issues arising from the severe volume changes and formation of dendritic Li ***‐dimensional hollow carbon is receiving increasing attention as a host material capable of accommodating Li metal inside its cavity;however,uncontrollable and nonuniform deposition of Li remains a *** this study,we synthesize metal–organic framework‐derived carbon microcapsules with heteroatom clusters(Zn and Ag)on the capsule walls and it is demonstrated that Ag‐assisted nucleation of Li metal alters the outward‐to‐inward growth in the microcapsule ***‐incorporated microcapsules are prepared via chemical etching of zeolitic imidazole framework‐8 polyhedra and are subsequently decorated with Ag by a galvanic displacement reaction between Ag^(+)and metallic *** introduced Ag significantly reduces the energy barrier and increases the reaction rate for Li nucleation in the microcapsule host upon Li *** combined electrochemical,microstructural,and computational studies,we verify the beneficial role of Ag‐assisted Li nucleation in facilitating inward growth inside the cavity of the microcapsule host and,in turn,enhancing electrochemical *** study provides new insights into the design of reversible host materials for practical Li metal batteries.

关键词： hollow carbon hosts lithium metal batteries lithium plating metal-organic frameworks nucleation

Modification strategies improving the electrochemical and structural stability of high-Ni cathode materials

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Journal of Energy Chemistry 2024年第9期96卷 185-205页

作者： Yoon Bo Sim Hami Lee Junyoung Mun Ki jae kim Department of Energy Science Sungkyunkwan UniversitySuwon 16419Republic of Korea School of Advanced Materials Science and Engineering Sungkyunkwan UniversitySuwon 16419Republic of Korea SKKU Institute of Energy Science and Technology(SIEST) Sungkyunkwan UniversitySuwon 16419Republic of Korea

With the increasing spotlight in electric vehicles,there is a growing demand for high-energy-density batteries to enhance driving ***,several studies have been conducted on high-energy-density LiNi_(x)Co_(y)Mn_(z)O_(2)***,there is a limit to permanent performance deterioration because of side reactions caused by moisture in the atmosphere and continuous microcracks during cycling as the Ni content to express high energy increases and the content of Mn and Co that maintain structural and electrochemical stabilization *** direct modification of the surface and bulk regions aims to enhance the capacity and long-term performance of high-Ni cathode ***,an efficient modification requires a study based on a thorough understanding of the degradation mechanisms in the surface and bulk *** this review,a comprehensive analysis of various modifications,including doping,coating,concentration gradient,and single crystals,is conducted to solve degradation issues along with an analysis of the overall degradation mechanism occurring in high-Ni cathode *** also summarizes recent research developments related to the following modifications,aims to provide notable points and directions for post-studies,and provides valuable references for the commercialization of stable high-energy-density cathode materials.

关键词： High energy density High-Ni cathode materials Degradation Structural stability Lithium-ion battery

Tribological behavior of TiN,AlTiN,and AlTiCrN coatings in atmospheric and vacuum environments

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Friction 2024年第11期12卷 2611-2626页

作者： Youn-Hoo HWANG Kuk-jin SEO Tae-Hyeong kim You jin MIN Yuzhen LIU Dae-Eun kim Department of Mechanical Engineering Yonsei UniversitySeoul 03722Republic of Korea Department of Mechatronics and Energy Engineering Ningbo Tech UniversityNingbo 315211China

In this study,the tribological characteristics of TiN,AlTiN,and AlTiCrN coatings sliding against a SUS420J1 stainless steel pin were investigated in atmospheric and vacuum *** coatings were deposited on SUS440C substrates using the arc-physical vapor deposition *** friction and wear behavior of the coatings were evaluated based on the systematic analyses of the friction coefficient data as well as the physical and chemical state of the wear *** results revealed that the friction coefficients of the SUS440C specimen and AlTiCrN coatings increased,whereas those of the TiN and AlTiN coatings decreased when the environment was changed from atmospheric to *** was confirmed that the formation of an oxide layer and adsorption of oxides on the surface were dominant factors that influenced the tribological behavior in the atmospheric *** the other hand,the compatibility,oxidation inhibition,and droplets of the surface mainly affected the frictional characteristics in the vacuum *** results of this work are expected to aid in the selection of proper coating materials for tribological systems operating in a vacuum.

关键词： friction wear coating vacuum TiN