• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.8-14
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• 2003

The particle dispersion in the turbulent mixing layer has been numerically investigated to clarify the effect of the velocity ratio in the large-scale vortical structures. In this study the LES with subgrid-scale model is employed. The Lagrangian method to predict the particle motion is applied. The particles of 10, 50, 150, 200${\mu}m$ in mean diameter were loaded into the origin of the mixing layer. It is shown that the characteristics of flow and growth rate are strongly dependent on the variation of the velocity ratio. It is also shown the relationship between the Stokes number and the particle dispersion. As a result, in the case of St~1 the particle dispersion is faster than the diffustion of the flow field while in the cases of both St<<1 and St>>1 it is shown that the particle dispersion in lower than the diffusion of the flow filed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.156-157
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• 2008

반도체 소자 회로의 집적도가 높아짐에 따라 선폭이 감소하였고 고온 공정이 필요하게 되었다. 기존의 반도체 회로 배선 재료인 Al을 사용할 경우 소자의 속도가 느려져서 소자의 신뢰도가 떨어지고 고온공정에서의 문제가 발생되어 이를 해결하기 위한 차세대 배선 물질로 비저항이 낮은 Cu의 사용이 요구되고 있다. 하지만 Cu는 Si와의 확산이 잘 일어나기 때문에 그 사이에서 확산을 막아주는 확산방지막에 대한 필요성이 제기되었고 연구가 활발히 진행되고 있다. 본 논문에서는 Cu와 Si사이의 확산을 방지하기 위한 W-C-N 확산방지막을 물리적 기상 증착법(PVD)중 하나인 RF Magnetron Sputtering 방식을 사용하여 증착하였다. 고온 공정에서의 안정성을 알아보기 위해 $600^{\circ}C$ 부터 $900^{\circ}C$ 까지 $100^{\circ}C$ 단위로 열처리를 하였고 4-point probe 장치를 사용하여 열처리 온도에 따른 비저항 측정을 통해 W-C-N 확산방지막의 특성을 분석하였다.

• Magazine of the Korea Concrete Institute
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• v.8 no.5
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• pp.145-154
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• 1996

Polymer-modified mortars have an excellent water proofness and water retentivity. Therefore, the study on the moisture diffusion behavior- is very important. The purpose of' this study is to investigate the effects of relative humidity and moisture content in mortars on the moisture diffusion, and the relationship between the shrinkage and moisture diffusion coefficient of polymer-modified mortars cured at $20{\circ}C$ 50% R.H and 80% R.H. The pore size distribution of the polymer-modified mortars was also measured. From the test results, the relative humidity and moisture content in mortars influenced on the moisture diffusion of polymer-modified mortars. The shrinkage and moisture diffusion coefficient of polymer-modified mortars cured at $20{\circ}C$ 50% R.H. was bigger than that cured at $20{\circ}C$ 80% R.H.. and decreased with increasing polymer-cement ratio regardless of polymer type.

• Journal of Korea Water Resources Association
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• v.32 no.4
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• pp.417-426
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• 1999

A series of numerical experiments is performed to compare the characteristics of outflow hydrograph using linear and nonlinear Muskingum-Cunge methods for two cases: (a) sinusoidal inflow hydrographs and (b) rainfall inputs. The nonlinear method shows the steepening of the rising limb, coupled with a corresponding flattening of the receding limb. The linear method conserves mass exactly. In contrast, the nonlinear method is subject to a gain and a loss of mass. The loss of mass and the subsidence of peak outflow increases with a mild slope, a small baseflow $q_b$ and a large peak inflow to baseflow ratio $q_p/q_b$. A shock wave and associated numerical instability results in the increase of mass for a steep slope and a large $q_p/q_b$ ratio. While the linear method depends on the reference flow per unit-width, the nonlinear method depends on a baseflow and the $q_p/q_b$ ratio. It is found that, unlike for the sinusoidal inflow, the outflow for the rainfall inputs conserves mass fairly exactly in the nonlinear method.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.113-120
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• 2011

A technique for measuring the thermal diffusivity of nanofluids is proposed in this study. In theory, it has been well known that the transient hot-wire method can be used to measure the thermal conductivity and diffusivity of fluids simultaneously. However, when traditional methods were employed, the accuracy of the calculated thermal conductivity was considerably higher than that of diffusivity. The proposed method has two advantages for practical use: it only needs a simple data-conversion process for calculating the diffusivity, and it can skip the tedious calibration process involved in the case of a wire sensor. A validation experiment for the new system has been performed with the basic fluids, and the comparison experiment to compare the change in diffusivity of the base oil and the change in diffusivity of the nano oil has been carried out. It is expected that the present system will provide numerous methods for investigating the variation in the thermal properties other than thermal conductivity.

• Journal of Korean Society of Forest Science
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• v.110 no.1
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• pp.35-42
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• 2021

In this study, the relationships between bamboo expansion and the nutrient characteristics of bamboo biomass, the forest floor, and mineral soil (at 30-cm depth) were determined in unfertilized expansion sites and fertilized plantations of Phyllostachys nigra var. henonis in Jinju, Gyeongsangnam-do. Nitrogen and phosphorus concentrations in bamboo components (culm, branches, and foliage) were significantly higher in the plantation site than those in the expansion site (P < 0.05). However, the nutrient concentration of the forest floor did not differ significantly between the plantation and expansion sites. Mean organic carbon concentration at 0-30-cm soil depth was significantly higher in the plantation site (30.80 g kg-1) than that in the expansion site (15.64 g kg-1). In addition, total nitrogen, phosphorus, and exchangeable K+ at 0-30-cm soil depth were significantly higher in the plantation site than those in the expansion site. These results indicate that bamboo can spread to areas with low-nutrient concentrations in adjacent forests.

• Asia Marketing Journal
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• v.11 no.1
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• pp.29-38
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• 2009

Estimating the Bass diffusion model often creates a time-interval bias, which leads the OLS approach to overestimate sales at early stages and underestimate sales after the peak. Further, a specification error from omitted variables might raise serial correlations among residuals when marketing actions are not incorporated into the diffusion model. Autocorrelated disturbances may yield unbiased but inefficient estimation, and therefore invalid inference results. This phenomenon warrants a modified approach to estimating the Bass diffusion model. In this paper, the authors propose a modified Bass diffusion model handling autocorrelated disturbances. To validate the new approach, authors applied the method on two different data-sets: CT Scanners in the U.S, and FPD TV sales in Korea. The results showed improved model fit and the validity of the proposed model.

• Journal of the Korean GEO-environmental Society
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• v.7 no.1
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• pp.41-53
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• 2006

In this study, estimation of nonlinear adsorption isotherms(Langmuir & Freundlich adsorption isotherm) and advection-dispersion model parameters was conducted using genetic algorithm(GA) for Zn and Cd adsorption. Estimated parameters of nonlinear adsorption isotherms, which were obtained from the optimization process using genetic algorithm(GA), are nearly same with the parameters obtained from a linearization process of the nonlinear isotherms. Estimated effective diffusion coefficients, which were obtained from a finite element analysis of the advection-dispersion model and an optimization procedure using the genetic algorithm, for the metals were approximately in the order of $10^{-7}cm^2/s$ which could be obtained based on the linear distribution coefficient. The effective diffusion coefficients based on the nonlinear retardation factors were in the range of $10^{-6}{\sim}10^{-5}cm^2/s$. As a result, the correlation coefficient obtained between the measured and calculated concentration was over 0.9 which means that the genetic algorithm should be successfully applied to estimate the unknown parameters of the nonlinear adsorption isotherms and advection-dispersion model.

• Proceedings of the Korea Water Resources Association Conference
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• 1994.02a
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• pp.199-204
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• 1994

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.127.2-127.2
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• 2016

연구된 Si위의 흡착원자들의 확산 메커니즘들에 비해 Ge 표면에서의 확산 메커니즘은 잘 알려져 있지 않다. 최근 연구에 따르면, 수소가 덮인 Ge(110) 표면에서 그래핀 결정 핵생성은 비등방적이며, 낟알 둘레없이 웨이퍼 크기로 성장시킬 수 있음을 보였다. 본 연구에서는 VASP(Vienna Ab-initio Simulation Package)의 NEB(Nudged Elastic Band) 방법을 이용하여 수소가 덮인 Ge(110) 표면과 청결한 표면에서 탄소원자의 확산 과정과 확산에 따른 에너지 장벽을 계산 하였다. 계산 결과 수소가 덮인 표면에서의 탄소원자 확산은 체인 방향으로 각각 3.29 eV, 2.67 eV의 에너지 장벽을 가지고 청결한 표면에서는 탄소원자가 게르마늄 연결을 치환하며 확산한다. 이때 에너지 장벽은 0.82 eV이고 치환된 게르마늄이 확산할 때는 각각 0.64 eV, 0.59 eV의 에너지 장벽을 넘어야 한다. 결과적으로 수소가 덮인 표면에서보다 청결한 표면에서 탄소 확산 에너지 장벽이 낮으며, 청결한 표면에서는 탄소가 게르마늄을 치환하고 치환된 게르마늄이 확산할 확률이 높음을 알 수 있었다.