• Journal of Chest Surgery
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• 제46권4호
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• pp.256-264
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• 2013

Background: Surgical treatment of infective endocarditis (IE) remains a challenge, especially in cases of multiple valve surgery. We evaluated the clinical outcomes of native valve IE and compared the outcomes of single valve surgery with those of multiple valve surgery. Materials and Methods: From 1997 to 2011, 90 patients underwent surgery for native valve IE; 67 patients with single valve surgery (single valve group) and 23 patients with multiple valve surgery (multiple valve group). The mean follow-up duration was $73.1{\pm}47.4$ months. Results: The surgical mortality in the total cohort was 4.4%. The overall survival (p=0.913) and valve-related event-free survival (p=0.204) did not differ between the two groups. The independent predictor of postoperative complications was New York Heart Association class (p=0.001). Multiple valve surgery was not a significant predictor of surgical mortality (p=0.225) or late mortality (p=0.936). Uncontrolled infection, urgent or emergency surgery, and postoperative complications were identified as independent predictors of valve-related morbidity, excluding multiple valve surgery (p=0.072). Conclusion: In native valve IE, multiple valve surgery as a factor was not an independent predictor of mortality and morbidity. The number of surgically corrected valves in native IE seems to be unrelated to perioperative and long-term outcomes.

• 한국분말재료학회지
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• 제26권2호
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• pp.112-118
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• 2019

Infiltration is a popular technique used to produce valve seat rings and guides to create dense parts. In order to develop valve seat material with a good thermal conductivity and thermal expansion coefficient, Cu-infiltrated properties of sintered Fe-Co-M(M=Mo,Cr) alloy systems are studied. It is shown that the copper network that forms inside the steel alloy skeleton during infiltration enhances the thermal conductivity and thermal expansion coefficient of the steel alloy composite. The hard phase of the CoMoCr and the network precipitated FeCrC phase are distributed homogeneously as the infiltrated Cu phase increases. The increase in hardness of the alloy composite due to the increase of the Co, Ni, Cr, and Cu contents in Fe matrix by the infiltrated Cu amount increases. Using infiltration, the thermal conductivity and thermal expansion coefficient were increased to 29.5 W/mK and $15.9um/m^{\circ}C$, respectively, for tempered alloy composite.

• 대한기계학회논문집A
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• 제35권10호
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• pp.1193-1198
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• 2011

연료전지 내의 작동유체는 폭발성을 가지고 있기 때문에 솔레노이드 밸브의 실링특성은 일반적인 시스템에 비해 매우 중요하다 할 수 있다. 하지만, 이 시스템의 경우 작동 온도가 일반적인 경우에 비해 비교적 높으며, 작동 유체의 화학적 특성 때문에 실링에 사용되는 재질은 내화학성이 뛰어나면서도 연료전지 시스템에서 요구하는 수명을 보장해야 하는 어려움이 있다. 본 연구에서는 연료전지 내에서 사용가능한 솔레노이드 밸브의 실링 특성을 확인하기 위하여, 내화학성이 뛰어난 실링용 링의 재질인 불소고무에 대한 수명을 아레니우스(Arrhenius) 관계식을 이용하여 예측하였다. 또한, 수상치환법을 이용하여 실제 제작된 연료전지용 솔레노이드 밸브가 제품으로써 충분히 사용가능함을 확인하였다.

• 한국정밀공학회지
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• 제25권6호
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• pp.108-115
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• 2008

The wear on engine valve and seat insert is one of the most important factors affecting engine performance. The engine valve and seat insert must be able to withstand the severe environment that is created by: high temperature exhaust gases generated while the engine is running, rapid movement of the valve spring, high pressure generated in the explosive process. In order to study such problems, a simulator has been developed to generate and control high temperatures and various speeds during motion. The wear simulator is considered to be a valid simulation of the engine valve and seat insert wear process with various speeds during engine activity. This work focused on the test of various degrees of wear on four different exhaust valve materials such as HRV40, HRV40-FNV (face nitrided valve), STL #32, STL #6,. Throughout all tests performed in this study, the outer surface temperature of the seat insert was controlled at $350^{\circ}C$, the cycle number was $4.0{\times}10^6$, the test load was 6860 N, the fuel was LPG the test speed was 20 Hz (2400 RPM) and the seat insert material was HVS1-2. The mean (standard deviation) maximum roughness of the exhaust valve and seat insert was $25.44\;(3.16)\;{\mu}m$ and $27.53\;(3.60)\;{\mu}m$ at the HRV40, $21.58\;(2.38)\;{\mu}m$ and $25.94\;(3.07)\;{\mu}m$ at the HRV40-FNV, $36.73\;(8.98)\;{\mu}m$ and $61.38\;(7.84)\;{\mu}m$ at the STL #32, $73.64\;(23.80)\;{\mu}m$ and $60.80\;(13.49)\;{\mu}m$ at the STL #6, respectively. It was discovered that the maximum roughness of exhaust valve was lower as the high temperature hardness of the valve material was higher under the same test conditions such as temperature, test speed, cycle number, test load and seat insert material. The set of the HRV40-FNV exhaust valve and the HVS1-2 seat insert showed the best wear resistance.

• Tribology and Lubricants
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• 제20권5호
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• pp.231-236
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• 2004

Sulfur Hexafluoride, S $F_{6}$ is widely used for leak detection and as a gaseous dielectric in transformers, condensers and circuit breakers. S $F_{6}$ gas is also effective as a cleanser in the semiconductor industry. This paper presents a numerical study of the sealing force of disk type seal in S $F_{6}$ gas safety valve. The sealing force on the disk seal is analyzed by the FEM method based on the Taguch's experimental design technique. Disk seals in S $F_{6}$ gas safety valve are designed with 9 design models based on 3 different contact length, compressive ratio and gas pressure. The calculated results of Cauchy stress and strain showed that the sealing characteristics of Teflon $^{ }$PTFE is more effective compared to that of FKM(Viton), which is related to the stiffness of the materials. And also, the contact length of the disk seal is important design parameter for sealing the S $F_{6}$ gas leakage in the safety valve.afety valve.

• 동력기계공학회지
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• 제19권5호
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• pp.93-98
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• 2015

Nuclear power plants has a number of valves, which are operating at a high temperature-high pressure and radiation environment conditions. Nevertheless, it is important to maintain the reliability of the valves to ensure safe operation of the nuclear power plant. However, the aging of the valves by increasing of years of plant operation and the system transients due to the sudden load change are working the failures of the reliability of the valve. In this paper, we evaluate experimentally the performance change according to the thermal aging of the valve. Results show that the valve stem and the actuator leakages were enlarged by the thermal aging.

• Journal of Chest Surgery
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• 제45권3호
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• pp.141-147
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• 2012

Background: Although the aortic valve-sparing procedure has gained popularity in recent years, it still remains challenging in patients with advanced aortic regurgitation (AR). We compared the long-term outcomes of the aortic valve-sparing procedure with the Bentall operation in patients with advanced aortic regurgitation secondary to aortic root dilatation. Materials and Methods: A retrospective review of 120 patients who underwent surgery for aortic root dilatation with moderate to severe AR between January 1999 and June 2009 was performed. Forty-eight patients underwent valve-sparing procedures (valve-sparing group), and 72 patients underwent the Bentall procedure (Bentall group). The two groups' overall survival, valve-related complications, and aortic valve function were compared. Results: The mean follow-up duration was $4.9{\pm}3.1$ years. After adjustment, the valve-sparing group had similar risks of death (hazard ratio [HR], 0.61; p=0.45), and valve related complications (HR, 1.27; p=0.66). However, a significant number of patients developed moderate to severe AR in the valve-sparing group at a mean of $4.4{\pm}2.5$ years of echocardiographic follow-up (p<0.001). Conclusion: Both the Bentall operation and aortic valve-sparing procedure showed comparable long-term clinical results in patients with advanced aortic regurgitation with aortic root dilatation. However, recurrent advanced aortic regurgitation was more frequently observed following valve-sparing procedures.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2961-2966
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• 2007

When the pressure at the weak spot established at a certain part of a high pressure vessel or piping system exceeds a design pressure, this weak spot is burst, and the pressurized gas emitted through the weak spot will cause a compression wave system. In this connection, in the present study, an experimental study by using a conventional shock tube facility is performed to estimate the effects of the material of diaphragm, curvature radius and thickness of materials on the valve opening time in diaphragm. Pressure sensor having 500kHz in natural frequency is installed at 35mm downstream of the rupture diaphragm to measure the static pressure history of propagating and being accumulated compression wave. 4 kinds of materials are used as diaphragm that is aluminium, copper, stainless steel and zinc. The diaphragm radii of curvature R are ${\infty}$, 120mm and 60, respectively. And the depth for $90^{\circ}$ groove is 0.04mm. It is found that the smaller the tensile strength and elongation of the rupture diaphragm is, the smaller the radius of curvature of the rupture diaphragm is, and for the same conditions the thinner the thickness of the rupture diaphragm is, the shorter the valve opening time becomes. Also, the tensile strength, elongation and the radius of curvature of the rupture diaphragm for the same conditions are smaller, the maximum pressure rise caused by the coalescences of the compression wave is smaller. Finally the pressure ratio is higher, the valve opening time is shortened and gradient of pressure increment is more steepen.

• Journal of Advanced Marine Engineering and Technology
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• 제31권6호
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• pp.744-752
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• 2007

Recently a fuel oil of the diesel engine in the ship is being changed with low quality as the oil price is higher more and more. Therefore the wear and corrosion in all parts of the engine like cylinder liner ring groove of piston crown, spindle and seat ring of exhaust valve are increased with using of heavy oil of low quality In particular the degree of wear and corrosion in between valve spindle and seat ring are more serious compared to the other parts of the engine due to operating in severe environment such as the high temperature of exhaust gas and repeating impact. Thus the repair weld to the valve spindle and seat ring is a unique method to prolong the life of the exhaust valve in an economical point of view In this study. corrosion property of both weld metal zone and base metal was investigated with some electrochemical methods such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram and polarization resistance etc. in 5% $H_2SO_4$ solution. in the case of being welded with some welding methods and welding materials to the exhaust valve specimen as the base metal. In all cases. the values of hardness of the weld metal zone were more high than that of the base metal. And their corrosion resistance were also superior to the base metal. The weld metal of A2F(AC SMAW: 2 pass welding with foreign electrode) showed a relatively good results to the corrosion resistance as well as the hardness compared to the ether welding methods and welding materials. Moreover it indicated that hardness of the weld metal by the domestic electrode was considerably high compared to that of the foreign electrode.

• 대한기계학회논문집B
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• 제39권1호
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• pp.21-27
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• 2015

현행 배기가스규제인 유로6을 대응하기 위해선 질소산화물과 메탄의 배출량을 크게 저감시켜야 하는 실정이다. 본 연구에서는 부분부하운전조건에서 밸브오버랩 감소가 수소-천연가스엔진의 연소 및 배기특성에 미치는 영향을 살펴보았다. 각 연료와 기존캠 및 밸브오버랩이 감소된 변경캠에 대하여 연소 및 배기특성을 분석하였다. 실험결과 변경캠을 사용하였을 때 열효율이 감소하고 연료유량이 증가하였다. 열효율 감소로 인하여 메탄과 이산화탄소의 배출량은 증가하였다. 희박한 운전조건에서 질소산화물 배출량은 기존캠 대비 감소하였다. 동일한 연료 및 운전조건에서는 효율과 배기특성에 악영향을 미치는 것을 알 수 있었다.