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Cuff가 있는 End-to-Side 문합술시 혈류역학적 특성분석
유상신,김동익,서상호,노형운,이병붕 대한혈관외과학회 1999 Vascular Specialist International Vol.15 No.1
The hemodynamic characteristics of the cuff end-to-side anastomosis model are investigated using by the finite volume predictions. The flow rates and the impedance indices through of the cuff anastomosis model are compared with those of the anastomosis model without the cuff. Blood flow increased through the cuff anastomosis model than the standard anastomosis model. The impedance index decreased with the increase of flow rate. The impedance index at a given flow rate is reduced by the increase of anastomosis angle and further reduced by the addition of the cuff. The results suggest that the cuff anastomosis model should be applied for the low Reynolds number flow and/or the small artery anastomosis model.
유상신,김동익,서상호,노형운,이병붕 대한혈관외과학회 1999 Vascular Specialist International Vol.15 No.1
The objective of the present study is to obtain information on the hemodynamic characteristics in the anastomotic sites of femoral artery through the vascular implantation. Three dimensional steady and physiological blood flows in the femoral artery are simulated using the finite volume method. The eometrical shape of the anastomotic sites is made based on the vascular anatomy of a white rabbit. Wall shear stress distributions in the anastomotic sites for the physiological flow are compared with those or steady flow. Blood flow phenomena in the anastomotic sites of the femoral artery are discussed extensively.
유상신,김동익,서상호,노형운,이병붕 대한혈관외과학회 1999 Vascular Specialist International Vol.15 No.2
Purpose: Characteristics of pulsatile flow in 3-dimensional arterial geometry and elastic vessel wall should be investigated in order to understand the physiological blood flow in human body. In this study, the modelling of the physiological blood flow in the elastic blood vessel is proposed. Methods: The finite volume predictions are used to analyse the pulsatile flow characteristics in the elastic blood vessel. Results and Conclusion: Variations of the pressure and the velocity waveforms are obtained using the proposed modelling. The magnitudes of the pressure waveforms in the elastic blood vessel model are bigger than those of the rigid blood vessel model.
입자영상유속계(PIV)를 이용한 혈액대용유체의 맥동유동 가시화
유상신,김동익,서상호,노형운,이병붕 대한혈관외과학회 1999 Vascular Specialist International Vol.15 No.2
Purpose: The objective of the present study is to investigate the steady and pulsatile flow phenomena of the blood substitute fluids in the circular and bifurcated vessels numerically and experimentally. Methods: The particle image velocimetry (PIV) is adopted to visualize the flow fields in the circular and bifurcated vessels. In order to analyse the complex flow phenomena of the blood substitute fluids in the bifurcated vessel, the constitutive equations which are suitable to describe the rheological properties of the non-Newtonian fluids are determined and the steady and unsteady momentum equations are solved by the finite volume prediction. Results and Conclusion: Velocity vectors of the steady flow in the bifurcated tube obtained by the PIV system are in good agreement with those obtained by the numerical analysis. The experimental and numerical results show the recirculation zone in the outer wall distal to bifurcation.
유상신,김동익,서상호,이병붕 대한혈관외과학회 1998 Vascular Specialist International Vol.14 No.1
The objective of the current study is to investigate the effect of physical vibration on blood viscosity. The $quot;capillary tube viscometer concept$quot; is applied to measure blood viscosity. Blood viscosity can be measured at the minimum shear rate of 12 s^(-1) by the capillary tube viscometer. To examine the effect of physical vibration on blood viscosity, the vibrations are produced by contact with an electronic speaker. The frequencies of vibration are varied from 0 to 1000 Hz. The experimental results show that blood viscosity can be effectively reduced by applying vibration. Blood viscosity decreases as much as 10∼12 % by applying vibration.
Filter-Based Collision Resolution Mechanism of IEEE 802.11 DCF in Noisy Environments
유상신,Yoo, Sang-Shin The Korean Institute of Communications and Informa 2007 韓國通信學會論文誌 Vol.32 No.9a
본 논문은 IEEE 802.11 DCF가 잡음과 부하가 고려된 실제적인 환경에서 효과적으로 작동할 수 있도록 환경 변화에 따라 contention window를 동적으로 적응시키는 필터 기반의 메카니즘을 제안한다. 이는 이미지 프로세싱에서의 미디언 필터개념을 적용시킨 것으로 필터링의 결과에 따라 윈도우의 크기를 조정한다. 이를 통하여 잡음과 충돌에 의해 필연적으로 패킷 전달에 문제가 발생할 수밖에 없는 무선 환경에서 불필요한 윈도우의 조정을 제거하고, 성능을 최적화 할 수 있게 된다. 또한 제안하는 방법은 기존에 전송된 결과를 반영하는 히스토리 비트-패턴을 이용함으로써 기존 연구결과들을 거의 포함하는 일반적인 방법으로 쉽게 확장할 수 있는 장점을 가지고 있다. 제안된 방법은 시뮬레이션을 통해 성능과 지연 측면에서 기존의 연구결과보다 확실한 향상을 가져옴을 확인할 수 있었다. This paper proposes a filter-based algorithm to adaptively adjust the contention window in IEEE 802.11 DCF. The proposed mechanism is focused on the general and realistic environments that have various conditions regarding to noise, media types and network load. For this flexible adaptation, Filter-based DCF(FDCF) takes a more realistic policy such as median filter concept in the image processing technologies. We can handle these various environments by adjusting the contention window size according to the result of filtering based on history-buffer. We can ignore temporarily and randomly occurred transmission failures due to noise errors and collisions in noisy environments. In addition, by changing the reference number and history-buffer size, FDCF can be extended as a general solution including previous proposed mechanism. We have confirmed that the proposed mechanism can achieve the better performance than those of previous researches in aspects of the throughput and the delay in the realistic environments.