• 한국항만학회지
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• 제12권2호
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• pp.303-312
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• 1998

It is necessary to quantitatively asses the influence of tidal currents to analysis the coastal current patterns before or after constructing offshore structures like as breakwaters. This assesment can be made through the use of simulation models designed to reproduce the water movements of the area. And it is very important to predict a phenomenon of pollutant dispersion in the area. In this study, in order to predict the changes of sea water quality for the port development plan, Ilgwang harbour, located at the east coast of Pusan, the numerical computations were carried out. The flow patterns were investigated before and after the development of the harbour bay and coastal area connected on it. The computational models are an extension of earlier work on the flow which used the ADI Method (Alternating Direction Implicit Method) in appling to Osaka Bay by KANEKO et al. The transport of pollutant constituents depends upon the currental characteristics of the water-transporting medium. In the currental flow model, water velocities and water levels are computed throughout the regions of it. These value are then used in the mass-balance equation to obtain the pollutant-constituent transport. As a result of this research, the present water quality of Ilgwang harbour and the coastal areas connected on it was proved out some good condition. The changes of sea water quality due to the port development plan of the Ilgwang habour bay and the coastal area were not large compared with the present condition, but it will be likely able to get worse by increasing the semi-enclosed areas in the harbour bay. In order to improve the water quality of the area after development, the method to activate tidal exchange in the area can be needed, as a mitigation technique.

• 한국자동차공학회논문집
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• 제21권4호
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• pp.62-69
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• 2013

Visual demands associated with in-vehicle display usage and text messaging distract a driver's visual attention from the roadway. To minimize eyes-off-the-road demands, voice interaction systems are widely introduced. Under cognitively distracted condition, however, awareness of the operating environment will be degraded although the driver remains oriented to the roadway. It is also know that the risk of inattentive driving varies with age, thus systematic analysis of driving risks is required for the older drivers. This paper aims to understand the age-related driving performance degradation and visual attention changes under auditory cognitive demand which consists of three graded levels of cognitive complexity. In this study, two groups, aged 25-35 and 60-69, engaged in a delayed auditory recall task, so called N-back task, while driving a simulated highway. Comparisons of younger and older drivers' driving performance including mean speed, speed variability and standard deviation of lane position, and gaze dispersion changes, which consist of x-axis and y-axis of visual attention, were conducted. As a result, it was observed that gaze dispersion decreased with each level of demand, demonstrating that these indices can correctly rank order cognitive workload. Moreover, gaze dispersion change patterns were quite consistent in younger and older age groups. Effects were also observed on driving performance measures, but they were subtle, nonlinear, and did not effectively differentiate the levels of cognitive workload.

• 대한기계학회논문집B
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• 제23권11호
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• pp.1434-1443
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• 1999

The turbulent fluctuations of temperature and two components of velocity have been measured with hot- and cold-wires in the Thermally Stratified Wind Tunnel(TSWT). Using the fin-tube heat exchanger type heaters and the neural network control algorithm, both stable ($dT/dz=109.4^{\circ}C$) and unstable ($dT/dz=-49.1^{\circ}C$) stratifications were realized. An ambient air jet was issued normally into the cross flow($U_{\infty}=1.0 m/s$) from a round nozzle(d = 6 mm) flushed at the bottom waII of the wind tunnel with the velocity ratio of $5.8(U_{jet}/U_{\infty})$. The characteristics of turbulent dispersion in the cross flow jet are found to change drastically depending on the thermal stratification. Especially, in the unstable condition, the vertical velocity fluctuation increases very rapidly at downstream of jet. The fluctuation velocity spectra and velocity-temperature cospectra along the jet centerline were obtained and compared. In the case of stable stratification, the heat flux cospectra changes Its sign from a certain point at the far field because of the restratification phenomenon. It is inferred that the main reason in the difference between the vertical heat fluxes is caused by the different length scales of the large eddy motions. The turbulent kinetic energy and scalar dissipation rates were estimated using partially non-isotropic and isotropic turbulent approximation. In the unstable case, the turbulent energy dissipation decreases more rapidly with the downstream distance than in the stable case.

• Journal of Pharmaceutical Investigation
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• 제25권1호
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• pp.31-36
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• 1995

Solid dispersions and inclusion complex were prepared for the enhancement of solubility and dissolution rate of poorly water-soluble ibuprofen(IPF) as a model drug. Polyethylene glycol 4000(PEG4000) and polyvinylpyrrolidone(PVP) were used for the preparation of solid dispersion. $2-Hydroxypropyl-{\beta}-cyclodextrin(2-HP{\beta}CD)$ was also used for the preparation of inclusion complex. The solubility of IPF increased as the concentration of PEG4000, PVP and $2-HP{\beta}CD$ increased. Solubilization capacity of $2-HP{\beta}CD$ was increased about 10 times when compared to PEG 4000 and PVP. The dissolution rate of drug from solid dispersions and inclusion complex in the simulated gastric fluid was enhanced when compared to pure IPF and commercial $BR4^{\circledR}$ tablet as a result of improvement of solubility. In case of solid dispersions, dissolution rate of drug was proportional to polymer concentration in the formulation. The marked enhancement of dissolution rate of drug by inclusion complexation with $2-HP{\beta}CD$ was noted. However, dissolution rate of drug from solid dispersions and inclusion complex in the simulated intestinal fluid was not significant because IPF was readily soluble in that condition. From these findings, water-soluble polymers and cyclodextrin were useful to improve solubility and dissolution rate of poorly water-soluble drugs. However, easiness and reliability of preparation method, scale-up and cost of raw materials must be considered for the practical application of solid dispersion and inclusion complex in pharmaceutical industry.

• Asian Journal of Atmospheric Environment
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• 제12권1호
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• pp.47-58
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• 2018

The aim of this work is to investigate the effect of atmospheric stability on near-field pollutant dispersion from rooftop emissions of a single cubic building using computational fluid dynamics (CFD). This paper used the shear stress transport (here after SST) k-${\omega}$ model for predicting the flow and pollutant dispersion around an isolated cubic building. CFD simulations were performed with two emission rates and six atmospheric stability conditions. The results of the simulations were compared with the data from wind tunnel experiments and the result of simulations obtained by previous studies in neutral atmospheric condition. The results indicate that the reattachment length on the roof ($X_R$) obtained by computations show good agreement with the experimental results. However, the reattachment length of the rooftop of the building ($X_F$) is greatly overestimated compared to the findings of wind tunnel test. The result also shows that the general distribution of dimensionless concentration given by SST k-${\omega}$ at the side and leeward wall surfaces is similar to that of the experiment. In unstable conditions, the length of the rooftop cavity was decreased. In stable conditions, the horizontal velocity in the lower part around the building was increased and the vertical velocity around the building was decreased. Stratification increased the horizontal cavity length and width near surface and unstable stratification decreased the horizontal cavity length and width near surface. Maintained stability increases the lateral spread of the plume on the leeward surface. The concentration levels close to the ground's surface under stable conditions were higher than under unstable and neutral conditions.

• 한국수자원학회논문집
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• 제34권5호
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• pp.499-509
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• 2001

자연하천에서의 이송-확산 과정의 모의를 위하여 입자위치의 이산확률분포에 기초한 2차원 수송 모형을 개발하였다. 제안된 모형에서는 단위 시간간격동안 격자간의 질량이송을 예측하기 위하여 평균과 분산의 함수로 나타내어진 확률분포를 사용하였다. 개발된 모형은 유속, 확산계수, 단면적이 일정한 단순영역에 대하여 수치확산이 없는 해를 구하였고, 양의 확률을 만족시키는 안정조건이 성립한다면, 해석해와 다른 유한차분법과 비교하였을 때, 좋은 결과를 나타내었다. 본 모형의 현장적용성을 검토하기 위하여 캐나다에 위치한 Grand River를 대상을 얻은 수치실험 결과를 정상상태의 색소실험 결과와 비교하였다. 그 결과로서 본 모형은 자연하천에서의 2차원 이송-확산을 잘 모의할 수 있는 것으로 나타났다.

• Composites Research
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• 제33권1호
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• pp.1-6
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• 2020

탄소나노튜브의 함량에 따라 폴리우레탄 타입 탑코트의 분산도 및 전기저항의 평가를 통해 탄소나노튜브의 최적함량을 찾기 위한 연구를 진행하였다. 초음파 분산을 통하여 탄소나노튜브를 폴리우레탄 탑코트 내에 분산하였고, 중력식 스프레이건을 이용하여 탄소섬유/에폭시 복합재 표면에 탄소나노튜브/폴리우레탄 탑코트의 코팅을 진행하였다. 4가지 용매를 이용하여 탄소섬유복합재와 탄소나노튜브/폴리우레탄 탑코트의 정적접촉각을 측정하였고, 이를 이용하여 접착일을 계산하였다. 탄소나노튜브/폴리우레탄 탑코트의 표면저항을 측정하였고 이를 통하여 탄소나노튜브의 최적 함량조건을 파악하였다. ASTM D3359를 기반으로 크로스 컷 시험을 진행하였고 이를 통하여 탄소나노튜브/폴리우레탄 탑코트의 부착특성을 평가하였다. 실험결과를 통해 탄소나노튜브의 최적 조건을 파악하였다.

• Elastomers and Composites
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• 제46권1호
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• pp.60-69
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• 2011

[ $2.1\;{\mu}m$ ]입자경의 단분산 PBA seed를 이용한 2단계 분산중합을 seeded batch process 와 seeded semi-continuous process를 이용하여 다양한 형태의 PBA/PMMA composite 미립자를 제조하였다. Batch process의 경우 PBA/PMMA composite 입자의 모폴로지는 중합 분산매인 methanol/water 비와 중합 2단계에서의 PBA seed/MMA단량체의 비에 따라 크게 영향을 받으며, methanol/water 중합분산매중 물의 량이 증가함에 따라, 그리고 중합 2단계에서 MMA단량체량이 증가함에 따라 PBA와 PMMA간의 상분리현상이 심화되어 구형의 입자로부터 egg, snowman, confetti, peanut와 같은 비구형의 PBA/PMMA composite 입자들이 제조되었다. Semi-continuous process의 경우 단량체 부가시간을 조절함으로서 PBA/PMMA composite 입자의 모폴로지가 변함을 발견하였고 특히, 단량체의 결핍된 조건하에서 구형의 PBA(코어)/PMMA(쉘) composite 라텍스가 제조되었다.

• 지구물리
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• 제3권4호
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• pp.251-260
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• 2000

수중 SASW 실험에서 얻은 표면파의 실험분산곡선으로부터 지반의 강성을 추정하기 위한 역해석 과정에서 적용할 수 있는 파동해석기법인 로드해석법(2차원 해석법)과 변위해석법(3차원 해석법)의 적용성을 평가하였다. 그 결과 지반의 강성이 깊이에 따라 점진적으로 증가하고 지반 강성이 비교적 낮아 그 압축파 속도가 물의 압축파 속도보다 느린 경우에 대해서는 고유치 해석법을 적용할 수 있었다. 그러나 지반의 강성이 크거나 깊이에 따른 지반강설의 변화가 역전되는 경우에는 고차모트의 영향이나 고유치가 복소수가 되는 등의 문제가 발생하게 되므로 고유치 해석법으로 적절한 이론분산곡선을 얻을 수 없는 경우가 많고, 이 경우에는 변위해석법을 적용하여야 한다는 결론을 얻었다. 한편 수중 SASW 현장실험으로부터 얻은 결과를 제안된 변위해석법을 이용하여 분석한 결과 지반의 강성주상을 적절하게 추정한 수 있어 수중 SASW 실험의 현장 적용성을 확인할 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 센서 박막재료 반도체 세라믹
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• pp.166-169
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• 2003

In this study, we evaluated the characteristics by the addition of 3 different kinds of nonionic surfactant to improve the dispersion stability of slurries. Slurry stability is an issue in any industry in which settling of particles can result in poor performance. So we observed the variation of particle size and settling rate when the concentration and addition time of surfactant are changed. When the surfactant is added after milling process, the particle size and pH became low. It is supposed that the particle agglomeration was disturbed by adsorption of surfactant on alumina abrasive. The settling rate was relatively stable when nonionic surfactant is added about 0.1~1.0 wt%. When molecular weight(MW) is too small like Brij 35, it was appeared low effect on dispersion stability. Because it can't prevent coagulation and subsequent settling with too small MW. The proper quality of MW for slurry stability was presented about 500,000. Consequently, the addition of nonionic surfactant to alumina slurry has been shown to have very good effect on slurry stabilization. If we apply this results to copper CMP process, it is thought that we will be able to obtain better yield.