• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.22-27
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• 2006

This paper describes the development of the stream-tube based dispersion model for modeling contaminant transport in open channels. The operator-splitting technique is employed to separate the 2D contaminant transport equation into the pure advection and pure dispersion equations. Then the total variation diminishing (TVD) schemes are combined with the second-order Lax-Wendroff and third-order QUICKEST explicit finite difference schemes respectively to solve the pure advection equation in order to prevent the occurrence of numerical oscillations. Due to various limiters owning different features, the numerical tests for 1D pure advection and 2D dispersion are conducted to evaluate the performance of different TVD schemes firstly, then the TVD schemes are applied to experimental data for simulating the 2D mixing in a straight trapezoidal channel to test the model capability. Both the numerical tests and model application show that the TVD schemes are very competent for solving the advection-dominated transport problems.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.165-169
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• 2007

액체로켓엔진의 시스템 시험에서는 엔진의 개발 최종 단계로서 각 구성품의 성능과 조합된 상태에서의 시스템 성능을 확인하고 인증한다. 엔진의 성능 분산, 비행시 발생하는 입구 조건 변화에 따른 변동, 인증을 위한 추가 성능을 고려하여 시스템의 시험 영역을 결정하였다. 또한 터보펌프의 양정 곡선에 의해 변화되는 시험영역과 구성품의 작동점의 변화폭을 비교하였다. 그 결과 터보펌프 양정곡선의 기울기가 완만할수록 엔진 보정에서 발생하는 구성품 성능영역 변동이 감소되고 엔진 입구조건이나 내부 구성품 오차에 의한 변동은 증가 한다.

• KSBB Journal
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• 제31권4호
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• pp.219-227
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• 2016

Valsartan, a drug for the treatment of cardiovascular disease, exhibited low bioavailability which was caused by, at least in part, limited solubility at low pH. Present investigation deals with the preparation and characterization of gastro-retentive drug delivery system (GRDDS) using valsartan solid dispersion. We prepared solid dispersion using surfactants (Poloxamer 407) and alkalizer ($Na_2CO_3$) which may to be useful for improving solubility of valsartan at low pH and evaluated by saturated solubility of valsartan in distilled water. Valsartan gastro-retentive (GR) tablets containing solid dispersion prepared and evaluated by weight variation, floating time and dissolution rate. Compression at lower pressures resulted in the tablets floating over simulated gastric fluid (pH 1.2) for more than 17 h. In vitro release of valsartan from GR tablet was dependent on the amount of poloxamer 407 and hydroxypropyl methylcellulose. On the basis of evaluation parameter, formulation E-3 was selected as a final formulation. Therefore, it can be concluded that the GR tablets containing solid dispersion may be exploited successfully for the delivery of poorly drug such as valsartan.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2018년도 학술발표회
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• pp.325-325
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• 2018

The main purpose of this study is to suggest the more reliable flow direction methods within the framework of DEM by investigating the existing methodologies. To this end SFD(single flow direction method), MFD(multiple flow direction method) and IFD(Infinite flow direction method) are applied to determination of flow direction for water particles in Jeonjeokbigyo basin, and then assessed with respect to the variation of flow accumulation. As the main results the different patterns of flow accumulation are found out from each application of flow direction methods. As the flow dispersion increases on DEM contributing areas to outlet grow in sequence of SFD, IFD, MFD but contribution of individual pixels into outlet decreases. Especially MFD and IFD tend to make additional hydrologic abstraction from rainfall excess due to the flow dispersion within flow paths on DEM. Based on parameter estimation for power law distribution by maximum likelihood flow accumulation can be thought of as scale invariance factor. Combination of several flow direction methods could give rise to the more realistic water flow on DEM through separate treatment of flow direction methods for dispersion and aggregation effects of water flow within different topographies.

• 대한전기학회논문지
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• 제37권1호
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• pp.55-62
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• 1988

The variation of electrical resistivity of silver particle-filled polymers with the volume percent of silver particles was investigated. Also, the relationships between the surface tension of polymer and dispersion effect of silver particles were studied to find the steep drop of electrical resisivity, in view of agglomerate morphology. The critical volume precent of silver particles varied depending on the polymer species and increased with the increasing surface tension of polymer. The steep variation of resistivity with the increasing temperature was explained with the expansion of polymer at the melting temperature of polymer. The conductive break down current increased with the increasing volume percent of silver particles in the Ag/LDPE system and that was attributed to heat of Joule taken througn the contact area between the silver particle.

• 한국통신학회논문지
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• 제31권8A호
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• pp.735-744
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• 2006

In this paper, the optimum pump light powers of optical phase conjugator(OPC) are numerically investigated as a function of amplifier spacing in 1,200 km $8{\times}40$ Gbps WDM systems with 0.1, 0.4, 0.8, or 1.6 ps/nm/km dispersion coefficient. It is confirmed that the variation of optimal pump light power dependence on amplifier spacing for NRZ transmission system is smaller than that for RZ transmission system through the evaluations and analysis of eye opening penalty(EOP) characteristics. And, in both cases of NRZ and RZ transmission, the variation of optimal pump light power is more increased as amplifier spacing becomes longer. Additionally, it is confirmed that the best amplifier spacing in NRZ and RZ transmission system is 50 km.

• 한국군사과학기술학회지
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• 제13권1호
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• pp.126-132
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• 2010

A Lamb wave guided by a plate structure has dispersive characteristics because phase and group velocity change with the variation of frequency and thickness. The Lamb wave has two modes, symmetric and anti-symmetric mode, which propagates symmetrically and non-symmetrically with respect to centerline. In this paper, the derivation of Lamb wave equation with anisotropic material property is investigated. The phase velocity and group velocity dispersion curves are shown using the stiffness matrix of composite materials with the variation of angle.

• 한국수자원학회논문집
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• 제36권4호
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• pp.575-586
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• 2003

하천에 오염물질이 순간적으로 유입된 경우에는 연속적인 유입의 경우와 다르게 분산계수의 변화에 따라 오염물질의 거동 특성이 민감하게 변한다. 하천에 순간적으로 유입된 오염물질의 거동특성을 분석하기 위하여 한강하류부에서 수리인자 및 수질인자를 실측하였다. 분산계수 추정에 사용되는 경험식에 실측된 수리인자를 적용하여 갈수시 한강하류부의 분산계수의 규모를 분석하고, 적용 가능성이 큰 경험식을 제시하였다 또한, 실측된 수질인자를 RMA-4 모형의 계산치와 비교하여 만족할 만한 결과를 얻었다. 한강하류부에 순간적으로 유입된 오염물질의 분산계수, 하류단 수위 등의 변화에 따라 오염물질의 분산범위, 분산경로, 최초 및 최대농도 도달시간 등을 파악하였다.

• 한국대기환경학회지
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• 제16권2호
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• pp.141-150
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• 2000

In order to genralize the vertical dispersion of plume at long distances on mesoscale over complex terrain dispersion coefficients data have been obtained systematically according to lapsed time after release by using a composite turbulence water tank that simulates convective boundary layer. Dispersion experiments have been carried out for various combined conditions of thermal turbulence intensity mechanical turbulence intensity and plume release height at slightly to moderately unstable conditions. Results of tracer dispersion experiments conducted using water tank camera and image processing system have been converted into atmospheric dispersion data through the application of similarity law. The equation $\sigma$z/Zi=aX/(b+c X2)0.5 where $\sigma$2; vertical dispersion coefficient zi : mixing height X : dimen-sionaless downwind distance was confirmed to be an appropriate and general equation for expressing $\sigma$2 variation with turbulence intensity and plume release height, The value of "a" was found to be principally affected by mechanical turbulence intensity and that of "b" by mechanical turbulence intensity and release height. It was confirmed that the magnitude of "c" varies with release height. Results of water tank experiments on the relationship of $\sigma$2 vs downwind distance x have been compared with actual atmospheric dispersion data such as CONDORS data and Bowne's nomogram Operating conditions of a composite turbulence water tank for simulating the field turbulence situations of CONDORS experiments and Bowne's $\sigma$2(x) nomogram for suburban area have also been investigated in terms of water temperature difference between convection water tank and bottom plate heating tank grid plate stroke mixing water depth length scale and velocity scale. Moreover the effect of mechanical turbulence intensity on vertical dispersion has been discussed in the light of release height and downwind distance. height and downwind distance.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2002년도 학술발표회 논문집(I)
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• pp.389-393
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• 2002