• 대한의용생체공학회:의공학회지
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• 제20권1호
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• pp.29-36
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• 1999

본 연구는 목적은 PIV 시스템을 이용하여 분기관내 유동현상을 가시화하여 분기부 영역의 유동특성을 분석하는데 있다. PIV 시스템으로 유동장을 가시화하기 위해서 분기관 모델은 투명 아크릴판으로 제작하였고 작동유체와 추적입자는 각각 물과 송화가루를 사용하였다. 유동장에서 획득된 영상으로부터 속도벡터를 얻기 위해서 입자추적방법의 1-프레임 법과 2-프레임 법, 상호상관 PIV법인 2-프레임법을 사용하였다. PIV 시스템으로 측정된 실험결과의 신뢰성을 확보하기 위해서 표면구동 캐비티 유동의 속도분포를 4-프레임법으로 얻어진 기준 실험 데이터와 비교하였다. 분기관에서 뉴턴유체의 유동현상을 효과적으로 가시화하는데 필요한 상호상관 PIV방법의 2-프레임법을 적용하는 알고리즘을 개발하였고, sub-pixel과 면적보간을 사용하여 오벡터를 제거후 최종속도벡터를 얻었다. PIV를 이용한 분기관내 유동가시와 실험결과를 신뢰할 수 있는 수치해석 결과를 이용하여 검증한 결과 PIV 실험으로 얻어진 속도벡터는 수치해석의 결과와 잘 일치하였다. PIV 실험과 수치해석 결과로부터 분기관모델의 분기점 원위부에 재순환영역이 형성됨이 확인되었고 두 다른 방법을 이용한 재순환영역의 길이와 높이는 거의 동일하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.542-546
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• 2008

In this study, we developed a whole cardiovascular system model combined with a Laplace heart based on the numerical cardiac cell model and a detailed arterial network structure. The present model incorporates the Laplace heart model and pulmonary model using the lumped parameter model with the distributed arterial system model. The Laplace heart plays a role of the pump consisted of the atrium and ventricle. We applied a cellular contraction model modulated by calcium concentration and action potential in the single cell. The numerical arterial model is based upon a numerical solution of the one-dimensional momentum equations and continuity equation of flow and vessel wall motion in a geometrically accurate branching network of the arterial system including energy losses at bifurcations. For validation of the present method, the computed pressure waves are compared with the existing experimental observations. Using the cell-system-arterial network combined model, the pathophysiological events from cells to arterial network are delineated.

• International Journal of Vascular Biomedical Engineering
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• 제2권2호
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• pp.27-32
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• 2004

The objective of the present study is to visualize the steady and pulsatile flow fields in a branching model by using a high-resolution PIV system. A bifurcated flow system was built for the experiments in the steady and pulsatile flows. Harvard pulsatile pump was used to generate the pulsatile velocity waveforms. Conifer powder as the tracing particles was added to water to visualize the flow fields. CCD cameras($1K{\times}1K$(high resolution camera) and $640{\times}480$(low resolution camera)) captured two consecutive particle images at once for the image processing of several cross sections on the flow system. The range validation method and the area interpolation method were used to obtain the final velocity vectors with high accuracy. The results of the image processing clearly showed the recirculation zones and the formation of the paired secondary flows from the distal to the apex of the branch flow in the bifurcated model. The results also indicated that the particle velocities at the inner wall moved faster than the velocities at the outer wall due to the inertial force effects and the helical motions generated in the branch flows as the flow proceeded toward the outer wall. Even though the PIV images from the high resolution camera were closer to the simulation results than the images from the low resolution camera at some locations, both results of the PIV experiments from the two cameras generally agreed quite well with the results from the computer simulations. Therefore, instead of using the expensive stereoscopic PIV or 3D PIV system, the three-dimensional flow fields in a bifurcated model could be easily and exactly investigated by this study.

• Korean Journal of Hydrosciences
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• 제7권
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• pp.61-75
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• 1996

The purpose of this study is to develop an efficient model for the least cost design of multi-site detention systems. The IDP (Incremental Dynamic Programming) model for optimal design is composed of two sub-models : hydrologic-hydraulic model and optimization model. The objective function of IDP is the sum of costs ; acquisition cost of the land, construction cost of detention basin and pumping system. Model inputs include channel characteristics, hydrologic parameters, design storm, and cost function. The model is applied to the Jung-Rang Cheon basin in Seoul, a watershed with cetention basins in multiple branching channels. The application results show that the detention system can be designed reasonably for various conditions and the model can be applied to multi-site detention system design.

• Journal of the Korean Statistical Society
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• 제35권4호
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• pp.397-407
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• 2006

A new stochastic process is introduced for describing a mechanism of viruses. The process generalizes the $Bartoszy\'{n}ski's$ process ($Bartoszy\'{n}ski$, 1975a, 1975b, 1976) by allowing the stochastic perturbation between consecutive jumps to take into account the persistent infection (the infection without breaking infected cells). It is shown that the new process can be obtained by a weak limit of a sequence of Markov branching processes. Along with the construction of the new process, we study how the stochastic perturbation influences the risk of a symptom in an infected host. For this purpose, the quantal response model and the threshold model are investigated and compared through their induced survival functions.

• 한국해양학회지
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• 제28권4호
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• pp.281-291
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• 1993

대한 해협 및 황해의 해수수송량 변화와 수입자의 라그랑지안(Lagrangian) 이동경 로의 추적을 통하여 실제의 해저지형을 고려한 시간의존적 간략화된 2차원적 수치모델 의 계산을 수행하였다. 이 일련의 수치실험에서 에디에 의한 쿠로시오 해류의 지류들 은 대륙붕의 해류순환을 조율할 수 있을 정도의 충분한 강도를 지니고 있음을 보여준 다. 대륙붕 지역에서의 이러한 해수유입은 바람, 조류 및 부력 등과 같이 해수운동에 영향을 미치는 중요한 영향력들 중의 하나로 사료된다. 대륙붕사면의 해수수송량 변화 는 쿠로시오 지류, 특히 큐슈섬의 남서지역에서의 수송량 변화가 대한해협 및 황해 남부지역의 수송량과 밀접한 관련이 있음을 보여준다. 모델에 의한 수입자의 궤적은 WOCE/TOGA 계획의 일환으로 얻어진 인공위성추적 표류부의(drifter) 의 궤적과 잘 일 치하고 있으나 그 이동 시간이 현재의 모델에서는 다소 더 걸리고 있는 점이 다르다.

• Macromolecular Research
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• 제17권5호
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• pp.289-295
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• 2009

Low viscosity aromatic hyperbranched polyester epoxy resin (HTBE) was synthesized by the reaction between epichlorohydrin (ECH) and carboxyl-end hyperbranched polyester (HTB) which was prepared from inexpensive materials $A_2$ (1,4-butanediol glycol, BEG) and $B_3$ (trimellitic anhydride, TMA) by pseudo one-step method. The molar mass of the HTB was calculated from its acid value by "Recursive Probability Approach". The degree of branching (DB) of the HTB was characterized by model compounds and $^1H$ NMR-minus spectrum technology, and the DB of the HTB was about $0.47{\sim}0.63$. The viscosity and epoxy equivalent weight of the HTBE were $3,600{\sim}5,000\;cp$ and lower than 540 g/mol respectively. The reaction mechanism and structure of the $AB_2$ monomer, HTB and HTBE were investigated by MS, $^1H$ NMR and FTIR spectra technology. The molecular size of HTBE is under 8.65 nm and its shape is ellipsoid-like as determined by molecular simulation.

• 대한기계학회논문집B
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• 제21권11호
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• pp.1527-1537
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• 1997

Extinction characteristics and acoustic response of hydrogen-air diffusion flames at various pressures are numerically studied by employing counterflow diffusion flame as a model flamelet in turbulent flames in combustion chambers. The numerical results show that extinction strain rate increases linearly with pressure and then decreases, and increases again at high pressures. Thus, flames are classified into three pressure regimes. Such nonmonotonic behavior is caused by the change in chemical kinetic behavior as pressure rises. The investigation of acoustic-pressure response in each regime, for better understanding of combustion instability, shows different characteristics depending on pressure. At low pressures, pressure-rise causes the increase in flame temperature and chain branching/recombination reaction rates, resulting in increased heat release. Therefore, amplification in pressure oscillation is predicted. Similar phenomena are predicted at high pressures. At moderate pressures, weak amplification is predicted since flame temperature and chain branching reaction rate decreases as pressure rises. This acoustic response can be predicted properly only with detailed chemistry or proper reduced chemistry.

• 한국정밀공학회지
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• 제10권4호
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• pp.81-93
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• 1993

The three dimensional(3D) shape reconstruction from two dimensional(2D) cross-sections can be completed through three main phases : the input compilation, the triangular grid formation, and the smooth surface construction. In the input compilation phase, the cross-sections are analyzed to exctract the input data required for the shape reconstruction. This data includes the number of polygonized contours per cross-section and the vertices defining each polygonized contour. In the triangular grid formation phase, a triangular grid, leading to a polyhedral approximations, is constructed by extracting all the information concerning contour links between two adjacent cross- sections and then performing the appropriate triangulation procedure for each contour link. In the smooth surface construction phase, a smooth composite surface interpolating all vertices on the triangular grid is constructed. Both the smooth surface and the polyhedral approximation can be used as reconstructed models of the object. This paper proposes a new method for reconstructing the geometric model of a 3D objdect from a sequence of planar contours representing 2D cross-sections of the objdect. The method includes the triangular grid formation algorithms for contour closing, one-to-one branching, and one-to-many braanching, and many-to-many branching. The shape reconstruction method has been implemented on a SUN workstation in C.

• 한국관개배수논문집
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• 제3권2호
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• pp.44-52
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• 1996

To make a real hydraulic simulation model, Hazen-Williams' coefficient must be calibrated using the measured discharges and hydraulic head loss. In this paper, calibrating method of Hazen-Williams' coefficient was proposed for pipeline system. The calibra