• 한국입자에어로졸학회지
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• 제10권1호
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• pp.27-31
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• 2014

A simple bimodal model has been developed to analyze charged particle coagulation by modifying previously suggested bimdal model for evolution of particle generation and growth. In the present model, two monodisperse modes are used and 40 charge nodes are assigned to each mode to account both change of the particle size and charge distribution. In addition, we also implemented the effect of electrostatic dispersion loss in the present model. Based on the developed model, we analyzed coagulation of asymmetric bipolar charged particles by computing evolutions of particle number concentration, geometric mean diameter of particles, charge asymmetric ratio and geometric standard deviation of particle size distribution for various initial charge asymmetric ratios. The number concentration of asymmetric bipolar charged particles decreases faster than that of neutral particles but that does not give faster growth of particles since the electrostatic dispersion loss overwhelms particle growth by coagulation.

• 한국환경보건학회지
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• 제35권6호
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• pp.478-485
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• 2009

This study was performed to assess airborne fungi concentrations during fall in eight subway stations in Seoul, Korea. The purpose of this study was to investigate appropriate culture media and evaluate factors affecting airborne fungi concentrations. Results indicated that airborne fungi concentrations showed log-normal distribution. Thus, geometric mean (GM) and geometric standard deviation (GSD) were calculated. The GM of airborne fungi concentrations cultured on malt extract agar (MEA) media was 466 $cfu/m^3$ (GSD 3.12; Range 113~4,172 $cfu/m^3$) and the GM of concentrations cultured on DG18 media was 242 $cfu/m^3$ (GSD 4.75; Range 49~6,093 $cfu/m^3$). Both of GM values exceeded 150 $cfu/m^3$, the guideline of World Health Organization (WHO). There was no significant difference between two fungi concentrations cultured on MEA and DG18 media, respectively. Two factors, such as relative humidity and depths of subway stations were significantly related to airborne fungi concentrations. It is recommended that special consideration should be given to deeper subway stations for improvement of indoor air quality.

• 한국입자에어로졸학회지
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• 제6권1호
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• pp.21-27
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• 2010

New process consisting of electrospray and epitaxial crystal growth processes was applied to the preparation of c-plane oriented barium ferrite ($BaFe_{12}O_{19}$) thin film for high density magnetic recording media. Sodium citrate aided process was proper to preparation of amorphous $BaFe_{12}O_{19}$ nanoparticles with geometric mean diameter of 3 nm and geometric standard deviation of 1.1. The electrospray was applicable to the prepare of amorphous $BaFe_{12}O_{19}$ thin film on a substrate, and the film thickness could be controlled by adjusting the electrospray deposition time. The c-plane oriented $BaFe_{12}O_{19}$ thin film was successfully prepared by 3 step annealing process of the $BaFe_{12}O_{19}$ amorphous film on a sapphire($Al_2O_3$) substrate; annealing at $350^{\circ}C$ for 30 min, annealing at $500^{\circ}C$ for 30 min, and annealing at $700^{\circ}C$ for 60 min.

• 아동학회지
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• 제24권5호
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• pp.43-58
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• 2003

This research was conducted to comprehend the effects of computer games on the development children's visual perception. First, the effects of experience of computer games on children's visual perception abilities was analyzed. Second, the effects of different types of computer games on children's visual perception abilities were examined. And third, the interaction effects of sex and computer game types were examined. The subjects of this study were 78 5-year-olds engaging public kindergarten located in Cheung-Ju. To analyse data, percent, mean, standard deviation, and ANCOVA were used. The results showed that children's visual perception abilities were improved significantly with the experience of computer games. And the improvement of children's visual perception varied significantly according to the type of computer game. No interaction effects were found between a child's sex and the types of computer games.

• 물과 미래
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• 제26권4호
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• pp.107-115
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• 1993

본 연구는 3가지 교각형상에 대하여 국부적 정지상세굴에 대한 수리실험결과를 분석한 것이다. 실험결과에 의하면 국부적 상대세굴심은 교각형사, 하상입경의 기하표준편차, 유속비, 교각 푸르드수와 관계가 있는 것으로 나타났다. 교각의 상대세굴심은 반원사각형교각에서 가장 작고 하상재료가 균일할 때 보다 불균일할 때 현저하게 작게 나타났다. 입도의 불균일성으로 인한 세굴감소효과는 Raudkivi와 Ettema의 연구결과와 비교 검토하였다.

• International Journal of CAD/CAM
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• 제12권1호
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• pp.9-19
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• 2012

Generation of optimum planar B-spline curve in terms of minimum deviation and required fairness to approximate a target shape defined by a strip-shaped unorganized 2D point cloud is studied. It is proposed to use the location of control points as variables within the geometric optimization framework of point distance minimization. An adaptive simulated annealing heuristic optimization algorithm is developed to iteratively update an initial approximate curve towards the target shape. The new implementation comprises an adaptive cooling procedure in which the temperature change is adaptively dependent on the objective function evolution. It is shown that the proposed method results in an improved convergence speed when compared to the standard simulated annealing method. A couple of examples are included to show the applicability of the proposed method in the surface model reconstruction directly from point cloud data.

• 반도체디스플레이기술학회지
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• 제10권4호
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• pp.21-23
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• 2011

Uniformity of plasma etching processes critically depends on the wafer temperature and its distribution. The wafer temperature is affected by plasma, chucking force, He back side pressure and the surface temperature of ESC(electrostatic chuck). In this work, 3D mathematical modeling is used to investigate the influence of the geometry of coolant path and the temperature distribution of the ESC surface. The model that has the coolant path with less change of the cross-sectional area and the curvature shows low standard deviation of the ESC surface temperature distribution than the model with the coolant path of the larger surface area and more geometric change.

• 한국대기환경학회지
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• 제5권1호
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• pp.88-95
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• 1989

The aspects of the occurence frequency of $SO_2$ concentration were studied with the observed data in Seoul and the scheme that is capable of estimating not only highest concentration for a variety of averaging times but also concentrations for arbitary occurrence frequency with long term arithmatic mean and geometric standard deviation data, was evaluated. The results of the statistical analysis show that the occurrence frequency is almost log normal except a few cases, and 3rd highest values of daily mean concentration were about 4.2 $\sim$ 5.2 times higher than annual arithmatic mean. The evaluation with the observed hourly concentration shows that the scheme fairly well estimate the short concentration of arbitary occurrence frequence and it can be used for air quality management and environmental impact assessment.

• 한국전기전자재료학회논문지
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• 제35권3호
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• pp.255-263
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• 2022

The subthreshold swing (SS) of an asymmetric junctionless double gate (AJLDG) MOSFET is analyzed by the use of Gaussian function. In the asymmetric structure, the thickness of the top/bottom oxide film and the flat-band voltages of top gate (V_fbf) and bottom gate (V_fbb) could be made differently, so the change in the SS for these factors is analyzed with the projected range and standard projected deviation which are parameters for the Gaussian function. An analytical subthreshold swing model is presented from the Poisson's equation, and it is shown that this model is in a good agreement with the numerical model. As a result, the SS changes linearly according to the geometric mean of the top and bottom oxide film thicknesses, and if the projected range is less than half of the silicon thickness, the SS decreases as the top gate oxide film is smaller. Conversely, if the projected range is bigger than a half of the silicon thickness, the SS decreases as the bottom gate oxide film is smaller. In addition, the SS decreases as V_fbb-V_fbf increases when the projected range is near the top gate, and the SS decreases as V_fbb-V_fbf decreases when the projected range is near the bottom gate. It is necessary that one should pay attention to the selection of the top/bottom oxide thickness and the gate metal in order to reduce the SS when designing an AJLDG MOSFET.

• 한국산업보건학회지
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• 제5권2호
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• pp.172-183
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• 1995

The airborne concentrations of the welding fumes produced during $CO_2$ arcwelding process at shipbuilding, shiprepairing, container manufacturing and car accessary manufacturing industry were investigated. The effects how much reduced the welding fume were checked when the portable fan was used. The results were as follows; 1.The geometric mean of welding fume concentration in shipbuilding factory was $10.05mg/m^3$. This exposure concentration was higher than other 3 manufacturing industries at 95% confidence level. 2. The sampling filters for welding fume could be digested with acid within 1 hour by microwave oven. The recoveries for investigated metal elements were all over 95%. 3. The optimal wavelength could be selected for the simultaneous analysis of 8 metal elements by ICP(Inductively Coupled Plasma). 4. Noxious gases($O_1,NO_2$) produced during $CO_1$ gas arc welding process were detected that the concentration of ozone($O_1$) was less than 0.01 ppm and that of nitrogen dioxide($NO_2$) was 0.01-0.03 ppm. 5. The geometric mean of welding fume particle diameter was $1.26{\mu}m$ and geometric standard deviation was 1.51 for the counts when particle an analyzer(ELZONE) had been used. 6. When the portable fan had been used,the reduced percent of total welding fume for workers was about 47.8% when portable fan was applied to blow and 71.7% when to exhaust.