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Shear deformable finite beam elements for composite box beams

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Acta Mechanica Sinica 2014年第2期30卷 223-240页

作者： nam-Il Kim Dong-ho Choi Department of Architectural Engineering Sejong University Department of Civil and Environmental Engineering Hanyang University

The shear deformable thin-walled composite beams with closed cross-sections have been developed for coupled flexural, torsional, and buckling analyses. A theoretical model applicable to the thin-walled laminated composite box beams is presented by taking into account all the structural couplings coming from the material anisotropy and the shear deformation effects. The current composite beam includes the transverse shear and the restrained warping induced shear deformation by using the first-order shear deformation beam theory. Seven governing equations are derived for the coupled axial-flexural-torsional-shearing buckling based on the principle of minimum total potential energy. Based on the present analytical model, three different types of finite composite beam elements, namely, linear, quadratic and cubic elements are developed to analyze the flexural, torsional, and buckling problems. In order to demonstrate the accuracy and superiority of the beam theory and the finite beam elements developed by this study,numerical solutions are presented and compared with the results obtained by other researchers and the detailed threedimensional analysis results using the shell elements of ABAQUS. Especially, the influences of the modulus ratio and the simplified assumptions in stress-strain relations on the deflection, twisting angle, and critical buckling loads of composite box beams are investigated.

关键词： Thin-walled Composite box beam Deflection Twisting angle Buckling load Shear deformation

Comparative Study of Transfer Learning Models for Retinal Disease Diagnosis from Fundus Images

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Computers, Materials & Continua 2022年第3期70卷 5821-5834页

作者： Kuntha Pin Jee ho chang Yunyoung nam Department of ICT Convergence Soonchunhyang UniversityAsan31538Korea Department of Ophthalmology Soonchunhyang University Bucheon HospitalSoonchunhyang University College of MedicineBucheon420-767Korea Department of Computer Science and Engineering Soonchunhyang UniversityAsan31538Korea

While the usage of digital ocular fundus image has been widespread in ophthalmology practice,the interpretation of the image has been still on the hands of the ophthalmologists which are quite *** explored a robust deep learning system that detects three major ocular diseases:diabetic retinopathy(DR),glaucoma(GLC),and age-related macular degeneration(AMD).The proposed method is composed of two ***,an initial quality evaluation in the classification system is proposed to filter out poorquality images to enhance its performance,a technique that has not been explored ***,the transfer learning technique is used with various convolutional neural networks(CNN)models that automatically learn a thousand features in the digital retinal image,and are based on those features for diagnosing eye *** performance of many models is conducted to find the optimal model which fits with fundus *** the different CNN models,DenseNet-201 outperforms others with an area under the receiver operating characteristic curve of ***,the corresponding specificities for healthy,DR,GLC,andAMDpatients are found to be 89.52%,96.69%,89.58%,and 100%,*** results demonstrate that the proposed method can reduce the time-consumption by automatically diagnosing multiple eye diseases using computer-aided assistance tools.

关键词： Multiclass classification deep neural networks glaucoma agerelated macular degeneration diabetic retinopathy transfer learning quality evaluation

Sorption enhanced catalytic CF4 hydrolysis with a three-stage catalyst-adsorbent reactor

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Frontiers of Chemical Science and Engineering 2017年第4期11卷 537-544页

作者： Han, Jae-Yun Kim, chang-Hyun Lee, Boreum nam, Sung-chan Jung, ho-Young Lim, Hankwon Lee, Kwan-Young Ryi, Shin-Kun Advanced Materials and Devices Laboratory Korea Institute of Energy Research (KIER) Daejeon Korea Department of Chemical and Biological Engineering Korea University Seoul Korea Department of Advanced Materials and Chemical Engineering Catholic University of Daegu Gyeongbuk Korea Department of Environment and Energy Engineering Chonnam National University Gwangju Korea

In this study, we developed a three-stage catalyst-adsorbent reactor for the catalytic hydrolysis of CF4. Each stage is composed of a catalyst bed followed by an adsorbent bed using Ca（OH）2 to remove HF. The three stages are connected in series to enhance the hydrolysis of CF4 and eliminate a scrubber to dissolve HF in water at the same time. With a 10 wt-% Ce/AlaO3 catalyst prepared by the incipient wetness method using boehmite and a granular calcium hydroxide as an adsorbent, the CF4 conversion in our proposed reactor was 7%-23% higher than that in a conventional single-bed catalytic reactor in the temperature range of 923-1023 K. In addition, experimental and numerical simulation （Aspen HYSYS） results showed a reasonable trend of increased CF4 conversion with the adsorbent added and these results can be used as a useful design guideline for our newly proposed multistage reactor system.

关键词： PFCs catalytic hydrolysis calcium hydro-xide sorption enhanced process simulation

Polygonal multi-polymorphed Li4Ti5Oi2@rutile TiO2 as anodes in lithium-ion batteries

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Nano Research 2019年第4期12卷 897-904页

作者： chang Hyun Hwang Hee-eun Kim Inho nam Jin ho Bang Department ofBionano Technology Hanyang University 55 Hanyangdaehak-ro Sangnok-gu Ansan Gyeonggi-do 15588 Republic of Korea School of Chemical Engineering & Materials Science Chung-Ang University 84 Heukseok-ro Dongjak-gu Seoul 06974 Republic of Korea Department of Chemical and Molecular Engineering Hanyang University 55 Hanyangdaehak-ro Sangnok-gu Ansan Gyeonggi-do 15588 Republic of Korea

Li4Ti50i2 (LTO) has attracted considerable attention in lithium-ion battery (LIB) applications because of its favorable characteristics as an anode material. Despite its promise, the widespread use of LTO is still limited primarily due to its intrinsically poor electric and ionic con ductivities and high surface reactivity. To address these issues, we desig ned polyg onal nano architectures composed of various Li-Ti oxide crystal polymorphs by a facile synthesis route. Depending on the pH condition, this synthesis approach yields multi-polymorphed Li-Ti oxides where the interior is dominantly composed of a Li-rich phase and the exterior is a Li-deficient (or Li-free) phase. As one of these variations, a polygonal LTO-rutile TiO2 structure is formed. The rutile TiO2 on the surface of this LTO composite significantly improves the kinetics of Li^+ insertion/extraction because the channel along the o-axis in TQ2 provides a Li^+ highway due to the significantly low energy barrier for Li^+ diffusion. Moreover, the presenee of rutile TiO2, which is less reactive with a carbonate-based electrolyte, ensures Iong-term stability by suppress)ng the undesirable interfacial reaction on LTO.

关键词： micro-polygon structure Li-Ti oxide multi-polymorphs Li4Ti5Oi2@ rutile TiO2 anode lithium-ion batteries

Etching characteristics of thin SiON films using a liquefied perfluorocarbon precursor of C_6F_(12)O with a low global warming potential

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Plasma Science and Technology 2020年第10期22卷 135-144页

作者： Junmyung LEE Yunho nam Jongchan LEE Hyun Woo LEE Kwang-ho KWON Department of Control and Instrumentation Engineering Korea UniversitySejong 30019Republic of Korea Department of Aeronautic Computer Engineering Hanseo UniversitySeosan 31962Republic of Korea

Perfluorocarbon gas is widely used in the semiconductor ***,perfluorocarbon has a negative effect on the global environment owing to its high global warming potential(GWP) *** alternative solution is ***,we evaluated the possibility of replacing conventional perfluorocarbon etching gases such as CHF_3 with C_6F_(12)O,which has a low GWP and is in a liquid state at room *** this study,silicon oxynitride(SiON) films were plasma-etched using inductively coupled CF4+C_6F_(12)O+O_2 mixed ***,the etching characteristics of the film,such as etching rate,etching profile,selectivity over Si,and photoresist,were investigated.A double Langmuir probe was used and optical emission spectroscopy was performed for plasma *** addition,a contact angle goniometer and x-ray photoelectron spectroscope were used to confirm the change in the surface properties of the etched SiON film ***,the etching characteristics of the C_6F_(12)O mixed plasma exhibited a lower etching rate,higher SiON/Si selectivity,lower plasma damage,and more vertical etched profiles than the conventional CHF_3 mixed *** addition,the C_6F_(12)O gas can be recovered in the liquid state,thereby decreasing global *** results confirmed that the C_6F_(12)O precursor can sufficiently replace the conventional etching gas.

关键词： global warming potential perfluorocarbon silicon oxynitride etching characteristics liquid-state perfluorocarbon

Extended X-ray absorption fine structure (EXAFS) of FAPbI_(3) for understanding local structure-stability relation in perovskite solar cells

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Journal of Energy Chemistry 2022年第4期31卷 549-554页

作者： Dong-ho Kang Yong-Jun Park Yun-Sung Jeon nam-Gyu Park School of Chemical Engineering and Center for Antibonding Regulated Crystals Sungkyunkwan UniversitySuwon 16419Korea

Perovskite solar cells (PSCs) employing formamidinium lead iodide (FAPbI_(3)) have shown high ***,operational stability has been issued due to phase instability of α phase FAPbI_(3) at ambient *** precursors in the perovskite precursor solution has been proposed to improve not only power conversion efficiency (PCE) but also device ***,there is a controversial issue on the beneficial effect on PCE and/or stability between excess FAI and excess PbI_(2).We report here extended X-ray absorption fine structure (EXAFS) of FAPbI_(3) to study local structural change and explain the effect of excess precursors on photovoltaic performance and *** films prepared from the precursor solution with excess PbI_(2)shows better stability than those from the one with excess FAI,despite similar PCE.A rapid phase transition from α phase to non-perovskite δ phase is observed from the perovskite film formed by excess ***,the (Pb-I) bond distance evaluated by the Pb L_(III)-edge EXAFS study is increased by excess FAI,which is responsible for the phase transition and poor device *** work can provide important insight into local structure-stability relation in the FAPbI_(3)-based PSCs.

关键词： Extended X-ray absorption fine structure EXAFS Excess precursor Local structure Stability Perovskite solar cells

Function-regeneration of non-porous hydrolyzed-MOF-derived materials

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Nano Research 2019年第8期12卷 1921-1930页

作者： Yo chan Jeong Jin Weon Seo Jae ho Kim Seunghoon nam Min chang Shin Young Shik Cho Jin Syul Byeon Chong Rae Park Seung Jae Yang Carbon Nanomaterials Design Laboratory Research Institute of Advanced Materials and Department of Materials Science and Engineering Seoul National UniversitySeoul 08826Republic of Korea Advanced Nanohybrids Lab. Department of Chemical Engineering Inha UniversityIncheon 22212Republic of Korea School of Advanced Materials Engineering College of Engineering Andong National University Andong Gyeongsangbuk-do 36729Republic of Korea

A facile synthetic strategy based on a water-based process is developed for the preparation of metal-organic framework (MOF)-derived materials by revisiting the hydrolyzed non-porous metal-organic frameworks (h-MOF). The poor water stability of MOF has been recognized as key limitations for its commercialization and large-scale applications because the hydrolysis resulted in the complete loss of their functionalities. however, we found that the negative effect of hydrolysis on MOF can be nullified during the heat treatment. As similar to the intact MOF, h-MOF can be used as a precursor for the preparation of MOF-derived materials from porous MOF-derived carbons (MDCs) to MDC@ZnO composites. The property of h-MOF-derived materials is almost equivalent to that of MOF-derived materials. In addition, h-MOF turned the weakness of water instability to the strength of facile water-based process for hybridization. With the demonstration of the hybrid composite between h-MDC@ZnO and reduced graphene oxide (rGO) as a prototype example, it exhibited superior electrochemical performance when evaluated as an electrode material for lithium-ion batteries.

关键词： nanomaterials metal-organic framework (MOF) porous materials MOF-derived carbon hydrolyzed MOF

Spatio-temporal variability in sea surface wind stress near and off the east coast of Korea

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Acta Oceanologica Sinica 2005年第1期24卷 107-114页

作者： nam SungHyun KIM Young ho PARK Kyung-Ae KIM Kuh Ocean Laboratory/RIO School of Earth and Environmental Sciences Seoul National University Seoul 151-742 KoreaOcean Laboratory/RIO School of Earth and Environmental Sciences Seoul National University Seoul 151-742 KoreaOcean Laboratory/RIO School of Earth and Environmental Sciences Seoul National University Seoul 151-742 KoreaOcean Laboratory/RIO School of Earth and Environmental Sciences Seoul National University Seoul 151-742 Korea

Sea surface wind stress variabilities near and off the east coast of Korea, are examined using 7 kinds of wind datasets from measurements at 2 coastal (land) stations and 2 ocean buoys,satellite scatterometer (QuikSCAT), and global reanalyzed products (ECMWF,NOGAPS,and NCEP/NCAR). Temporal variabilities are analyzed at 3 frequency bands; synoptic (2-20 d), intra-seasonal (20-90 d),and seasonal (>90 d).Synoptic and intra-seasonal variations are predominant near and off the Donghae City due to the passage of the mesoscale weather system. Seasonal variation is caused by southeastward wind stress during Asian winter monsoon. The sea surface wind stress from reanalyzed *** and KMA-B measurements off the coast show good agreement in the magnitude and direction,which are strongly aligned with the alongshore *** the land-based sites,wind stresses are much weaker by factors of 3-10 due to the mountainous landmass on the east parts of Korea *** first EOF modes(67%-70%) of wind stresses from reanalyzed and QuikSCAT data have similar structures of the strong southeastward wind stress in winter along the coast but show different curl structures at scales less than 200 km due to the orographic *** second EOF modes (23%-25%) show southwestward wind stress in every September along the east coast of the North Korea

关键词： sea surface wind stress spatio-temporal variability monsoon seasonal intra-seasonal synoptic band orographic effect

Mechanically reconfigurable architectured graphene for tunable plasmonic resonances

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Light(Science & Applications) 2018年第1期7卷 895-903页

作者： Pilgyu Kang Kyoung-ho Kim hong-Gyu Park SungWoo nam Department of Mechanical Science and Engineering University of Illinois at Urbana-ChampaignUrbanaIL 61801USA Department of Mechanical Engineering George Mason UniversityFairfaxVA 22030USA Department of Physics Korea UniversitySeoul 02841Republic of Korea KU-KIST Graduate School of Converging Science and Technology Korea UniversitySeoul 02841Republic of Korea

Graphene nanostructures with complex geometries have been widely explored for plasmonic applications,as their plasmonic resonances exhibit high spatial confinement and gate ***,edge effects in graphene and the narrow range over which plasmonic resonances can be tuned have limited the use of graphene in optical and optoelectronic *** we present a novel approach to achieve mechanically reconfigurable and strongly resonant plasmonic structures based on crumpled *** calculations show that mechanical reconfiguration of crumpled graphene structures enables broad spectral tunability for plasmonic resonances from mid-to nearinfrared,acting as a new tuning knob combined with conventional electrostatic ***,a continuous sheet of crumpled graphene shows strong confinement of plasmons,with a high near-field intensity enhancement of~1×10^(4).Finally,decay rates for a dipole emitter are significantly enhanced in the proximity of finite-area biaxially crumpled graphene *** findings indicate that crumpled graphene provides a platform to engineer graphenebased plasmonics through broadband manipulation of strong plasmonic resonances.

关键词： plasmon figuration proximity