• 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.

• 에너지공학
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• 제11권1호
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• pp.26-33
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• 2002

본 연구에서는 butterfly valve주위의 비압축성 및 압축성유동 특성을 수치해석을 통하여 조사하였다. 밸브는 문제를 단순화시키기 위하여 평판 디스크로 간주하였으며, 다양한 디스크 각도 및 압력비 변화에 대한 계산을 수행하였다. 각도가 증가함에 따라 디스크 상류면의 정체점은 디스크의 중심으로 이동하는 것을 볼 수 있었고, 입구공기의 유입 속도는 감소함을 볼 수 있었다. 최고 유속은 디스크와 벽면사이에 형성되는 vena contracta 효과에 의해 생기는 목의 하류에서 형성됨을 볼 수 있었다. 압력비를 감소함에 따라 압축성 효과는 증대되며 유동이 초음속화 되면서 생성되는 강한 wall jet에 의해 shock cell structure가 형성되는 것을 볼 수 있었다. 입구유량은 디스크 각도와 압력비의 증가에 따라서 감소하며, 압력손실계수는 디스크 각도의 증가 및 압력비의 감소에 따라 증가하였다.

• 대한한방내과학회지
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• 제30권1호
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• pp.191-199
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• 2009

목 적 : 위 미주신경 활성 저하와 유문부 기능 장애를 동시에 가지고 있는 기능성 소화불량증 환자에서 전침 및 한약의 복합처치 치료가 이 두가지 면에서 각각 어떤 영향을 미치는지를 살펴보았다. 방 법 : 장음검사상 위 미주신경 활성 저하와 유문부 기능 장애를 동시에 가지고 있는 환자 10명을 대상으로 치료 전후의 장음 지표 변화를 비교하였다. 장음지표는 % of bowel sound (%BS)와 주 주파수(dominant frequency, DF)를 사용하였으며, %BS(6인 경우를 위 미주신경 활성저하 DF ratio(식후/식 전)<1를 유문부 기능장애로 평가하였다. 환자들에게 2주간 족삼리전 침과 체침이 매일 시술되었으며 평위산 전탕액이 하루 3회 투여되었다. 결 과 : 2주간의 치료 후 DF ratio는 $0.93\pm0.06$에서 $1.06\pm0.04$으로 유의성있게 증가했으며, 10명 중 9명의 환자가 DF ratio>1의 정상치로 회복되었다. %BS 역시 $2.97\pm1.17%$에서 4.27%로 증가했지만 통계적 유의성은 없었으며, 3명의 환자에서 %BS가 6이상으로 정상회복되었다. 결 론 : 위 미주신경 활성 저하와 유문부 기능 장애를 동시에 가지고 있는 기능성 소화불량증 환자에 대한 족삼리 전침과 일반 체침, 평위산의 치료는 미주신경 활성 저하보다는 유문부 기능 장애에 더 유의한 효과를 보였다.

• Journal of Mechanical Science and Technology
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• 제15권7호
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• pp.1061-1071
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• 2001

The present study investigated design parameters of shunt valves and anti-siphon device used to treat patients with hydrocephalus. The shunt valve controls drainage of cerebrospinal fluid (CSF) through passive deflection of a thin and small diaphragm. The anti-siphon device(ASD) is optionally connected to the valve to prevent overdrainage when the patients are in the standing position. The major design parameters influencing pressure-flow characteristics of the shunt valve were analyzed using ANSYS structural program. Experiments were performed on the commercially available valves and showed good agreements with the computer simulation. The results of the study indicated that predeflection of the shunt valve diaphragm is an important design parameter to determine the opening pressure of the valve. The predeflection was found to depend on the diaphragm tip height and could be adjusted by the diaphragm thickness and its elastic modulus. The major design parameters of the ASD were found to be the clearance (gap height) between the thin diaphragm and the flow orifice. Besides the gap height, the opening pressure of the ASD could be adjusted by the diaphragm thickness, its elastic modulus, area ratio of the diaphragm to the flow orifice. Based on the numerical simulation which considered the increased subcutaneous pressure introduced by the tissue capsule pressure on the implanted shunt valve system, optimum design parameters were proposed for the ASD.

• Advances in aircraft and spacecraft science
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• 제1권4호
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• pp.409-425
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• 2014

Converging flows of a gas and a liquid at a microchannel cross junction, under proper conditions, can result in the formation of periodic, dispersed microslugs. This microslug formation phenomenon has been proposed as the basis for a fuel injection system in a novel, 'discrete' monopropellant microthruster designed for use in next-generation miniaturized satellites. Previous experimental studies demonstrated the ability to generate fuel slugs with characteristics commensurate with the intended application during steady-state operation. In this work, numerical and experimental techniques are used to study the effect of valve actuation on slug characteristics, and the results are used to compare with equivalent steady-state slugs. Computational simulations of a valve with a 1 ms valve-actuation cycle show that as the ratio of the response time of the valve to the fully open time is increased, transient effects can increase slug length by up to 17%. The simulations also demonstrate that the effect of the valve is largely independent of surface tension coefficient, which is the thermophysical parameter most responsible for slug formation characteristics. Flow visualization experiments performed using a miniature valve with a 20 ms response time showed less than a 1% change in the length of slugs formed during the actuation cycle. The results of this study indicate that impulse bit and thrust calculations can discount transient effects for slower valves, but as valve technology improves transient effects may become more significant.

• 한국산학기술학회논문지
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• 제8권1호
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• pp.10-17
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• 2007

자동차 미끄럼방지 장치의 최적 제어를 위해서는 유압 모듈레이터 특히, 솔레노이드 밸브에 대한 정확한 동특성 해석이 필요하다. 그러나, 현재까지 진행된 대부분의 연구들은 솔레노이드 밸브 자체만을 고려하였기 때문에 실제 자동차 미끄럼방지 장치에 제한적으로 적용되었다. 본 연구에서는 유압 모듈레이터에 작용하는 압력을 고려한 솔레노이드 밸브의 동특성 해석을 위하여 실험과 이론 해석을 실시하였다. 작동 압력이 솔레노이드 밸브의 동특성에 끼치는 영향을 정량적으로 해석하였고 설계인자를 변화시키면서 성능향상 방안을 제안하였다. 따라서, 본 연구에서 수행한 솔레노이드 밸브 동특성 해석결과는 자동차 미끄럼방지 장치의 최적 제어 기준으로 활용할 수 있을 것이다.

• Journal of Chest Surgery
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• 제28권3호
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• pp.258-262
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• 1995

We have experienced 18 abdominal aortic aneurysms between March,1987 and June,1994.Unruptured patients were 11 cases and ruptured were 7.The fifth[33.4% ,sixth[27.7% and seventh[27.7% decades were most common age distributions.Sex ratio was 2.6:1[m:f .The most frequent symptoms were abdominal or back pain and palpable pulsating mass.Sixteen patients underwent resection and graft replacement.One patient refused operation.Atherosclerosis was the underlying pathology in 76%.Two ruptured patients died postoperative[28.5% .The frequency of postoperative complication was higher in the ruptured group.

• Journal of Chest Surgery
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• 제25권9호
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• pp.976-981
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• 1992

The results of the clinical observations on the 158 cases of the mitral valvular heart disease treated at the Department of Thoracic and Cardiovascular Surgery, Masan Koryo General Hospital from June, 1986 to December, 1991 were as follows; 1. There were 50 men and 108 women with sex ratio 1: 2.2. 2. The age of patient varied widely from 13 years to 65years. 3. The preoperative functional level accoridng to the NYHA classification were class II, III, IV in 18%, 67%, 15%. 4. All 158 patients were operated on under direct vision using extracorporeal circulation, mitral valve replacement in 118 cases, mitral and aortic valve replacement 40 cases. 5. The follow up period was between 2 months and 65 months postoperatively. [mean 30.1 months] 6. The early operative motality was 5.7%[9 cases], late motality was 4%[6 cases]. 7. The cardiothoracic ratio in the chest X-ray decreased at the 6th month postoperation. [pre-op: 0.60$\pm$0.07, post-op: 0.56$\pm$0.06 p<0.01]

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.107-111
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• 1997

Pressure control is possible by pulse width modulation signal driving a simple ON/OFF 2-way valve of hydraulic servo system. But it indices pressure fluctuation due to repeated on-off action and the pressure varies according to the duty ratio and carrier frequency. So mean pressure and ripple amplitude are arranged by experimental study as the driving signal change which decides the pressure characteristics. As the result selection criteria of the major design parameters may be established and the basic strategy to suppress the unnecessary flucturion may be provided for a hydraulic pressure control system.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.671-674
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• 2002

Pressure compensating temperature control valve(TCV) is one of the important control devices, which is used to maintain the constant temperature of working fluid in power and chemical plants. The ratio of cylinder hole diameters of inlet and outlet is the main design parameters of TCV. So this needs to be investigated to improve the function of control of temperature and void fraction. In this study, numerical analysis is carried out with various ratios of cylinder hole diameters of the inlet and outlet in the TCV. Especial1y, the distribution of the static pressure Is investigated to calculate the new coefficient($C_{\upsilon}$) and resistance coefficient(K). The governing equations are derived from making using of three-dimensional Naver-Stokes equations with standard $k-{\varepsilon}$ turbulence model and SIMPLE algorithm. Using a commercial code, PHOENICS, pressure and flow fields in TCV are calculated with different inlet and outlet diameters of the cylinder hole for cold and hot water passages.