• Journal of the Korean Chemical Society
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• v.39 no.9
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• pp.685-691
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• 1995

EHMACC and EHPC programs written in VAX version to calculate the tight-binding extended Huckel method is converted into the micro-soft fortran available to PC. The band calculation of LaNiO3 unit cell and extended ($2{\times}2{\times}1$) cell with perovskite structure is made by the PC/386 and PC/486. The calculation is also made for the DOS and the COOP. It is supposed that the electronic property of $LaNiO_3$ is semiconductor along to the ${\Gamma}{\rightarrow}H,\;H{\rightarrow}N,\;and\;N{\rightarrow}{\Gamma}(2D)$ direction with band gap about 0u.35 eV, while metal property in ${\Gamma}{\rightarrow}P\;and\;P{\rightarrow}N(3D)$ direction. The oxygen atom property in $LaNiO_3$ is more effectively affected by oxygen atom position than defect of nickel atom.

• Journal of the Korean Geotechnical Society
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• v.40 no.2
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• pp.41-53
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• 2024

Micropiles are small, cast-in-place piles with a diameter of 300 mm or less, primarily used to reinforce existing structures and support new constructions. As the application of these piles has expanded, extensive research has been conducted on their bearing characteristics, particularly in micropiled rafts. These studies have consistently demonstrated the positive impact of micropiles on foundation reinforcement. However, previous research often overlooked the potential variations in behavior between micropiled and conventional piled rafts based on different pile conditions. Furthermore, the influence of the cohesive characteristics of the soil layer beneath the foundation on the reinforcing effect of the micropiles has not been adequately addressed. This study, therefore, undertook 3D numerical analysis to assess the reinforcing effect of micropiles, considering both pile conditions and the cohesive characteristics of the soil layer beneath the foundation. The findings revealed that micropiles are significantly more effective in non-cohesive soil layers compared to cohesive ones, with the potential to increase the bearing capacity of the raft by up to 3.7 times.

• Journal of the Korean Geotechnical Society
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• v.37 no.2
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• pp.19-31
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• 2021

Micropiles are cast-in-place piles with small diameters. The advantage of micropile is low construction expense and simple procedures, so it is widely applied to existing buildings and structures for the reinforcement of foundation and seismic performances. The base expansion structure has been developed following the original mechanism of horizontal expansion steps under compressive loading. This kind of structure can be installed at the pile end to improve the bearing capacity by tip area enlargement and horizontal force increment to the pile surface area. However, 'Micropile with base expansion structure' cannot be put into practical use, because detailed verification for the developed technique has not been conducted so far. In this research, 3-D numerical analysis was conducted to figure out the bearing mechanism of base expansion micropile and to verify the bearing capacity improvement compared to the general micropiles. 3-D modelling of micropile with base expansion structure was carried out and input parameter was determined. Bearing mechanism induced by base expansion structure was analyzed by lab-scale modelling, and bearing capacity improvement was verified by field-scale analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.514-517
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• 2005

Microstereolithography(MSL) has evolved from the stereolithography technique, and is also based on a light-induced layer-stacking fabrication. Although integral MSL allows the manufacture of a complete layer by one irradiation only, there is a problem related with shape precision due to the light-intensity distribution of focused image. In this study, we developed the integral MSL apparatus using Digital Micromirror Device ($DMD^{TM})$, Texas Instruments) as dynamic pattern generator. It is composed of Xenon-Mecury lamp, optical devices, pattern generator, precision stage, controllers and the control program. Also, we have studied curing depth and width of photocurable resin according to the change of exposure energy.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.157-158
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• 2006

A novel nanofabrication process has been developed using two-photon crosslinking (TPC) for the fabrication of three-dimensional (3D) SiCN ceramic microstructures applicable to high functional 3D devices, which can be used in harsh working environments requiring a high temperature, a resistance to chemical corrosion, as well as tribological properties. After sequential processes: TPC and pyrolysis, 3D ceramic microstructures are obtained. However, large shrinkage due to low-ceramic yield during the pyrolysis is a serious problem to be solved in the precise fabrication of 3D ceramic microstructures. In this work, silica nanoparticles were employed as a filler to reduce the amount of shrinkage. In particular, the ceramic microstructures containing 40 wt% silica nanoparticles exhibited relatively isotropic shrinkage owing to its sliding free from the substrate during pyrolysis.

• Composites Research
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• v.34 no.4
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• pp.264-268
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• 2021

In this study, we propose a method for fabricating hydrophobic coatings/films with three-dimensional (3D) hierarchical nanostructured organic/inorganic composite surfaces. An epoxy-based, large-area 3D ordered nanoporous template is first prepared through an advanced photolithography technique called Proximity-field nanoPatterning (PnP). Then, a hierarchically structured surface is generated by densely impregnating the template with silica nanoparticles with an average diameter of 22 nm through dip coating. Due to the coexisting micro- and nano-scale roughness on the surface, the fabricated composite film exhibits a higher contact angle (>137 degrees) for water droplets compared to the reference samples. Therefore, it is expected that the materials and processes developed through this study can be used in various ways in the traditional coating/film field.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.3
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• pp.109-114
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• 2016

Monodispersed $ZnGa_2O_4$ microspheres were synthesized by a facile two-step process consisting of a solvothermal method and calcination process. The prepared monodispersed $ZnGa_2O_4$ microspheres were aggregated into 3D microstructures by self-assembly with a large number of small $ZnGa_2O_4$ particles generated in nucleation. This nucleation and self-assembly making hierarchical microstructures were depended on the concentration of PEG (polyethylene glycol) due to CAC (critical aggregation concentration) theory. And also we controlled the amount of zinc acetate to make pure $ZnGa_2O_4$ phase. Additionally, to fix the optimized calcination condition, sample was characterized by TG-DTA to prove the thermal property in the calcination process and by FT-IR to identify the changes of functional group bonding between each element of the $ZnGa_2O_4$ precursor and oxide calcined at $900^{\circ}C$ for 1 h.

• Journal of the Korean Geotechnical Society
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• v.38 no.9
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• pp.53-67
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• 2022

Micropiles are cast-in-place-type piles with small diameters. They are widely used for the foundation reinforcement of existing buildings and structures because this technique is easy to construct and economic. A base expansion structure is developed following the mechanism of radial expansion at the pile tip under compression. Numerical analysis, durability tests, and centrifuge tests have been conducted using the base expansion structure. In this study, three-dimensional numerical modeling was performed to describe the behavioral mechanism of the base expansion structure using steel bar penetration under compressive loading, and numerical analyses using centrifuge test conditions were performed for the comparative studies. Additionally, the base structure was modified based on the results of lab-scale analyses, and the bearing capacities of micropiles were compared using field-scale numerical analyses under various ground conditions.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.3
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• pp.111-118
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• 2023

MXene, a two-dimensional transition metal carbide or nitride, has recently attracted much attention as a lightweight and flexible electromagnetic shielding material due to its high electrical conductivity, good mechanical strength and thermal stability. In particular, the Ti-based MXene, Ti₃C₂T_x and Ti₂CT_x are reported to have the best electrical conductivity and electromagnetic shielding properties in the vast MXene family. Therefore, in this study, Ti₃C₂T_x and Ti₂CT_x films were prepared by vacuum filtration using Ti₃C₂T_x and Ti₂CT_x dispersions synthesized by interlayer metal etching and centrifugation of Ti₃AlC₂ and Ti₂AlC. The electrical conductivity and electromagnetic shielding efficiency of the films were measured after heat treatment at high temperature. Then, X-ray diffraction and photoelectron spectroscopy were performed to analyze the structural changes of Ti₃C₂T_x and Ti₂CT_x films after heat treatment and their effects on electromagnetic shielding. Based on the results of this study, we propose an optimal structure for an ultra-thin, lightweight, and high performance MXene-based electromagnetic shielding film for future applications in small and wearable electronics.

• Membrane Journal
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• v.29 no.2
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• pp.105-110
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• 2019

Porous membranes are widely used in industry for removing particulate matter. Unlike conventional porous membrane fabrication methods, the solution spreading phase separation method can form pores very simply. The first step is to wet the mesh with the support layer, then to let the polysulfone solution flow into a solvent without water. The solvent is readily vaporized and the polysulfone is made into a thin film. When the polysulfone solution is mixed with water to form pores, the pore size can be adjusted according to the concentration ratio of the polysulfone solution. The thickness of the membrane is easily controlled by the concentration of the solution. The porous separator has the formation of meshes intact and is very useful for forming a three-dimensional structure. The solution spreading phase separation method proposed in this study is characterized by its high cost competitiveness compared with conventional membranes due to its low production cost and easy process control.