• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.402.2-402.2
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• 2016

In photoelectrochemical (PEC) water splitting, Cu2ZnSnS4 (CZTS) compound has attracted intense attention as a photocathode due to not only large optical absorption coefficient, but also earth-abundance of constituent elements and suitable band alignment. With rapid development of nanotechnology, one-dimensional nanostructures of CZTS have been investigated as a potential form to achieve high efficiency because the nanostructures are expected to be capable of capturing more light and enhancing charge separation and transport. Here, we report a well-controlled fabrication route for vertically-aligned CZTS nanorod arrays on anodic aluminium oxide (AAO) template via simple sol-gel process followed by deposition of ZnS or CdS buffer layers on the CZTS nanorod to enhance charge separation. The structure, morphology, composition, optical absorption, and PEC properties of the resulting CZTS nanorod samples were characterized using X-ray diffraction, Raman spectroscopy, transmission electron microscopy, energy dispersive X-ray spectrometry, scanning electron microscopy, and UV-vis spectroscopy.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.401-401
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• 2016

Although vertically aligned one-dimensional (1D) structure has been considered as efficient forms for photoelectrode, development of efficient 1D nanostructured photocathode are still required. In this sense, we recently demonstrated a simple fabrication route for CuInS2 (CIS) nanorod arrays from aqueous solution by template-assisted growth-and-transfer method and their feasibility as a photoelectrode for water splitting. In this study, we further evaluated the photoelectrochemical properties surface-modified CIS nanorod arrays. Surface modification with CdS and ZnS was performed by successive ion layer adsorption and reaction (SILAR) method, which is well known as suitable technique for conformal coating throughout nanoporous structure. With surface modification of CdS and ZnS, both photoelectrochemical performance and stability of CuInS2 nanorod arrays were improved by shifting of the flat-band potential, which was analyzed both onset potential and Mott-schottky plot.

• 대한기계학회논문집
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• 제17권12호
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• pp.2995-3006
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• 1993

An automatic mesh generation scheme has been developed for finite element analysis with two-dimensional, quadrilateral elements. The basic strategies of the method are to transform the analysis domain into loops with key nodes and the loops are recursively subdivided into subloops with the use of best split lines. Finally by using the basic loop operators, the meshes are completed. In this algorithm an eight-node loop operator is proposed, which is useful in the area where the change of element size is large and the splitting criteria for subdividing the loops have also been modified to the existing algorithms. Lines, arcs, and cubic spline curves are used to define the boundaries of analysis domain. Sample meshes for several geometries are presented to demonstrate the robustness of the algorithm.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.99-105
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• 1997

A finite-difference method based on conservative supra characteristic method type upwind flux difference splitting has been developed to study the nonequilibrium chemically reacting inviscid flow. For nonequilibrium air, NS-1 species equations were strongly coupled with flowfield equations through convection and species production terms. Inviscid nonequilibrium chemically reacting air mixture flows over Blunt-body were solved to demonstrate the capability of the current method. At low altitude flight conditions the nonequilibrium air models predicted almost the same temperature, density and pressure behind the shock as equilibrium flow: however, at high altitudes they showed substantial differences due to nonequilibrium chemistry effect. The new nonequilibrium chemically reacting upwind flux difference splitting mettled can be extended to viscous flow and multi-dimensional flow conditions.

• ETRI Journal
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• 제27권4호
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• pp.446-448
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• 2005

Using tightly focused femtosecond laser pulses, we produce an optical waveguide and devices in transparent materials. This technique has the potential to generate not only channel waveguides, but also three-dimensional optical devices. In this paper, an optical splitter and U-grooves, which are used for fiber alignment, are simultaneously fabricated in a fused silica glass using near-IR femtosecond laser pulses. The fiber- aligned optical splitter has a low insertion loss, less than 4 dB, including an intrinsic splitting loss of 3 dB and excess loss due to the passive alignment of a single-mode fiber. Finally, we present an output field pattern, demonstrating that the splitting ratio of the optical splitter becomes approximately 1:1.

• Coupled systems mechanics
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• 제8권2호
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• pp.147-168
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• 2019

This work aims to simulate three-dimensional heavy oil flow in a reservoir with heater-wells. Mass, momentum and energy balances, as well as correlations for rock and fluid properties, are used to obtain non-linear partial differential equations for the fluid pressure and temperature, and for the rock temperature. Heat transfer is simulated using a two-equation model that is more appropriate when fluid and rock have very different thermal properties, and we also perform comparisons between one- and two-equation models. The governing equations are discretized using the Finite Volume Method. For the numerical solution, we apply a linearization and an operator splitting. As a consequence, three algebraic subsystems of linearized equations are solved using the Conjugate Gradient Method. The results obtained show the suitability of the numerical method and the technical feasibility of heating the reservoir with static equipment.

• Journal of the Korean Wood Science and Technology
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• 제51권6호
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• pp.447-447
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• 2023

This study aimed to convert underutilized moso bamboo into high-value added products such as fences, interior materials, lighting fixtures, and accessories. Green moso bamboo poles with a diameter of approximately 10 cm and a length of approximately 3.7 m were heat treated at 140℃ using a large-scale kiln. The processing time was meticulously adjusted through various stages, including pretreatment (6-8 hours at 60℃), cooking (8-10 hours at 100℃), steaming (26-30 hours at 120℃), heating (4-6 hours at 140℃), and finally, cooling (below 80℃). A meticulously designed heat treatment process has enabled efficient mass production of moso bamboo poles with improved qualities, including minimal splitting, moisture levels below 3%, and a specific gravity of 1.05. The focus of this study was to present the physical and drying properties, such as color, dimensional change, specific gravity, moisture content, and splitting, observed during the heat treatment process.

• 대한수학회보
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• 제61권3호
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• pp.637-669
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• 2024

The goal of this paper is to study decay properties of weak solutions to Cauchy problem of the non-stationary fractional Navier-Stokes equations. By using the Fourier splitting method, we give the time L²-decay rate of weak solutions, which reveals that L²-decay is generally determined by its linear generalized Stokes flow. In second part, we establish various decay results and the uniqueness of the two dimensional fractional Navier-Stokes flows. In the end of this article, as an appendix, the existence of global weak solutions is given by making use of Galerkin' method, weak and strong compact convergence theorems.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 춘계 학술대회논문집
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• pp.51-59
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• 2001

An evaluation of one zero-equation and two one-equation eddy viscosity-transport turbulence closure models as implemented CFDS(Characteristic Flux Difference Splitting ) code is presented herein. Comparisons of Baldwin-Lomax model as zero-equation and Baldwin-Barth and Spalart-Allmaras model as one-equation are presented for three test cases, first inlvolving the 3 dimensional supersonic flow at M=1.98 over tangent ogive cylinder, second involving the 2 dimensional transonic flow at M=0.79 over RAE 2822 airfoil, third involving the 3 dimensional transonic flow at M=0.84 over ONERA M6 wing. The numerical results of CFDS code will also examined through direct comparison with experimental data.

• Communications for Statistical Applications and Methods
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• 제29권5호
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• pp.561-589
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• 2022

When multiple classifications and regression trees are combined, tree-based ensemble models, such as random forest (RF) and Bayesian additive regression trees (BART), are produced. We compare the model structures and performances of various ensemble models for regression settings in this study. RF learns bootstrapped samples and selects a splitting variable from predictors gathered at each node. The BART model is specified as the sum of trees and is calculated using the Bayesian backfitting algorithm. Throughout the extensive simulation studies, the strengths and drawbacks of the two methods in the presence of missing data, high-dimensional data, or highly correlated data are investigated. In the presence of missing data, BART performs well in general, whereas RF provides adequate coverage. The BART outperforms in high dimensional, highly correlated data. However, in all of the scenarios considered, the RF has a shorter computation time. The performance of the two methods is also compared using two real data sets that represent the aforementioned situations, and the same conclusion is reached.