• Journal of Chest Surgery
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• v.30 no.9
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• pp.885-890
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• 1997

Patients with coronary artery disease and depressed ventricular function have better longterm benefits after coronary artery bypass grafting compared with medical therapy. But operative mortality remains high. This study was designed to identify the risk factors for coronary artery bypass grafting according to ventricular function. The records of 103 patients who underwent coronary artery bypass grafting from truly 1994 to June 1996 were analysed. The patients were divided into two groups based on preoperative ejection fraction: Low EF group(Ejection fraction < 40%, n=24) and Normal EF group(Ejection fraction $\geq$ 40%, n=79). The indication of operation was significantly different between the two groups (p=0.00003). Postinfarction angina was frequent in Low EF group but unstable angina was frequent in Normal EF group. The frequency of cardiomegaly(p=0.0012), serum creatinine abnormality(p=0.0473) and preoperative use of IABP(Intra Aortic Balloon Pump, p=0.0095) were higher in Low EP group. The left internal thoracic artery was used less frequently in Low EP group(p=0.00416). The operative mortality was 8.3% in Low EF group and 5.1% in Normal EF group, but without statistical difference(p=0.5492). In Normal EF group, age (p=0.041) was identified as a significant risk factor for operative mortality. In Low EF group, age(p=0.018), preopertive use of IABP(p=0.0036), hypercholesterolemia(p=0.0007), and emergency of operation(p=0.0037) were identified as significant risk factors. Postoperative morbidity was 50% in Low EF group and 33olo in Normal EP group, but without s atistical significance(p=0.1007). These results suggest that in patients with coronary artery disease and depressed ventricular function, more aggresive coronary artery bypass grafting is needed to improve the symptom and long-term benefit.

• International Journal of Vascular Biomedical Engineering
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• v.3 no.1
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• pp.1-5
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• 2005

Background: Coronary atherosclerosis artery disease is the leading cause of morbidity and mortality. Coronary artery bypass grafting (CABG) which utilizes the saphenous vein graft, has helped in alleviating the suffering of these patients. Newer techniques are being developed to improve upon the techniques. Still there is significant number of failures, leading to re-grafting or re-vascularization. Some studies have helped in identifying the high and low shear stress regions. Further studies based on their realistic models are required. Material, methods and results: we developed the realistic model of fully blocked right coronary with bypass graft placed at angle of $5^0$ with curvature similar to that of artery. Pulsatile flow of birefringent solution through this model by polarized light was visualized. The images of complete flow field in the model were recorded and analyzed. Regions of high flow disturbances which are prone to further changes are identified. Existence of recirculation in the blocked coronary may initiate new blood-tissue interactions deleterious to bypass graft. Conclusion: Our study shows that by selecting the procedure to place bypass graft at minimum angle with curvature similar to that of artery and smooth sutures may improve the life span of the graft. This study also identified that coronary blocked regions contributing by recirculation flow at the proximal and distal regions of bypass which may require further studies.

• Journal of Mechanical Science and Technology
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• v.15 no.9
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• pp.1302-1310
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• 2001

This paper introduces modeling and simulation results for pipeline inspection gauge (PIG) with bypass flow control in natural gas pipeline. The dynamic behaviour of the PIG depends on the different pressure across its body and the bypass flow through it. The system dynamics includes: dynamics of driving gas flow behind the PIG, dynamics of expelled gas in front of the PIG, dynamics of bypass flow, and dynamics of the PIG. The bypass flow across the PIG is treated as incompressible flow with the assumption of its Mach number smaller than 0.45. The governing nonlinear hyperbolic partial differential equations for unsteady gas flows are solved by method of characteristics (MOC) with the regular rectangular grid under appropriate initial and boundary conditions. The Runge-Kuta method is used for solving the steady flow equations to get initial flow values and the dynamic equation of the PIG. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. Simulation results show us that the derived mathematical model and the proposed computational scheme are effective for estimating the position and velocity of the PIG with bypass flow under given operational conditions of pipeline.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.693-696
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• 2003

Hermetic Compressor circulates refrigerant with constant flow rate regardless of operation condition. so, at the operating condition requiring low cooling capacity, too much refrigerant flow deteriorates seasonal energy efficiency ratio(SEER). In this reason, modulated compressor is needed to improve SEER. Among many types of modulated compressor, non-inverter type modulated compressor is required for its low cost and easy to development. In the modulated scroll compressor by bypass method, EER steeply decreases for many loss like re-compression, changes of volume ratio, decrease of motor efficiency by torque variation. So. the range of modulation ratio for optimized SEER must be selected accompany with air conditioner set development.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.241-246
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• 2001

This paper introduces modeling and solution for the dynamics of pipeline inspection gauge (PIG) flow in natural gas pipeline. Without of bypass flow, the dynamic behavior of the PIG depends on the different pressure between the rear and nose parts, which is generated by injected gas flow behind the tail of the PIG and expelled gas flow in front of its nose. With bypass flow, the PIG dynamics also depends on the amount of bypass flow across its body. The mathematical model are derived for unsteady compressible flow of the PIG driving and expelled gas, and for dynamics of the PIG. The bypass flow is assumed to be incompressible with the condition of its Mach number smaller than 0.45. The method of characteristic (MOC) and the Runge-Kutta method are used to solve the system governing equations. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. The simulation results show that the derived mathematical model and the proposed solution are effective for estimation the dynamics of the PIG with and without bypass flow under given operational condition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.3
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• pp.269-278
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• 2011

The details of engine manufacturer's engine simulations are generally kept secret and only those parameters that are used for control purposes are accessible to users. Hence, there is often only a limited amount of data accessible for creating a performance model of the engine. The performance modeling of a low bypass turbofan engine for supersonic aircraft is described herein. The Pratt and Whitney F100-PW-229 engine has been employed for low bypass turbofan engine performance modeling. Published data from the open literature are used as initial data for building the F100-PW-229 engine performance model. The unknown components' characteristics were estimated by optimization of parameters using by adaptive random search method and sensitivity analysis with respect to design variables. The engine performance model was evaluated to be properly constructed through the comparison of result of engine performance analysis and engine deck data.

• ETRI Journal
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• v.33 no.6
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• pp.880-886
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• 2011

With the introduction of high-current 8-inch solar cells, conventional Schottky bypass diodes, usually adopted in photovoltaic (PV) panels to prevent the hot spot phenomenon, are becoming ineffective as they cause relatively high voltage drops with associated undue power consumption. In this paper, we present the architecture of an active circuit that reduces the aforementioned power dissipation by profitably replacing the bypass diode through a power MOS switch with its embedded driving circuitry. Experimental prototypes were fabricated and tested, showing that the proposed solution allows a reduction of the power dissipation by more than 70% compared to conventional Schottky diodes. The whole circuit does not require a dedicated DC power and is fully compatible with standard CMOS technologies. This enables its integration, even directly on the panel, thereby opening new scenarios for next generation PV systems.

• Journal of computational fluids engineering
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• v.9 no.4
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• pp.34-40
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• 2004

It is known that the non-planar model of bypass is more profitable to suppress the development of intimal hyperplasia that tends to occur preferentially in regions of low time averaged shear stress and rapid temporal changes in wall shear stress. In this study it was numerically simulated the blood flow in an coronary artery grafted by artificial bypass to determine the flow characteristic variations due to the anastomosis angle changing. 5 different non-planar anastomosis angle models such as 45°, 60°, 90°, 120° and 135° were considered. When the anastomosis angle is higher, the backward flow region is spatially extended near the downstream region of the anastomosis because of the development of horseshoes vortex. For the case of the nan-planar 45° and 60° of anastomosis, the area of low-OSI zone was decreased by 26% and 13% respectively and the time averaged wall shear stress was increased by more than 55% as compared with 45° of planar model. However, both of the area of the low-OSI zone and the time averaged wall shear stress of 90°, 120° model were significantly increased.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.952-957
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• 2001

The objectives of this investigation were to obtain an excellent spray by cavitation under the low injection pressure. When cavitation occurs in the nozzle hole, the atomization of the liquid jet enhanced considerably. In this experiments, a acrylic nozzle made the gap and installed the bypass in the nozzle hole was used to enhance the atomization of the liquid jet at the low injection pressure. The liquid flow in the nozzle hole was photographed by a transmitted light using a micro flash. The spray angle was measured macroscope images of PMAS and the Sauter mean diameter was measured PDA system. To measure the pressure of the nozzle hole, pressure transducer was used. The results of this study indicated that enhanced atomization of the liquid jet at the low injection pressure was obtained by making the gap and installing the bypass at the single hole nozzle.

• Journal of Chest Surgery
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• v.38 no.5 s.250
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• pp.377-381
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• 2005

Background: Extra-anatomic bypass was performed in the patient who could not use anatomic bypass due to many causes. The purpose of this study is to evaluate the efficacy of extra-anatomic bypass surgery. Material and Method: We reviewed 31 patients who underwent extra-anatomic bypass surgery at Pusan national university hospital. We analysed the combined diseases, etiologic diseases, symptoms, patency rate and the factors affecting patency rate retrospectively. Result: There were 26 cases of femoro-femoral bypass and 5 cases of axillo-bifemoral bypass among 31 patients. The mean age was 70.23 years. Combined disease were hypertension, hyperlipidemia, and ischemic heart disease in order of frequency. The indications for surgery were disabled claudication, tissue necrosis, rest pain, and a cute ischemia. We analysed the ages, smoking history, hypertension, ischemic heart disease, severity of limb ischemia, and hyperlipidemia as factors affecting patency rate. We could not find any statistical differences between these factors. The primary graft patency rates were $73.65\%$ one year, $73.65\%$ two year, and $65.46\%$ three year respectively according to the Kaplan-Meier method. Conclusion: Nevertheless extra-anatomic bypass has a relatively low patency rate, it has good merits that is less dangerous, simple and easy re-do surgery compared to anatomic bypass. We think that extra-anatomic bypass is one of the good treatment modalities for the high risk vascular patients.