• Journal of Chest Surgery
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• v.44 no.6
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• pp.399-405
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• 2011

Background: Left ventricular (LV) hypertrophy caused by aortic valve stenosis (AS) leads to cardiovascular morbidity and mortality. We sought to determine whether aortic valve replacement (AVR) decreases LV mass and improves LV function. Materials and Methods: Retrospective review for 358 consecutive patients, who underwent aortic valve replacement for degenerative AS between January 1995 and December 2008, was performed. There were 230 men and 128 women, and their age at operation was $63.2{\pm}10$ years (30~85 years). Results: There was no in-hospital mortality, and mean follow-up duration after discharge was 48.9 months (2~167 months). Immediate postoperative echocardiography revealed that LV mass index and mean gradient across the aortic valve decreased significantly (p<0.001), and LV mass continued to decrease during the follow-up period (p<0.001). LV ejection fraction (EF) temporarily decreased postoperatively (p<0.001), but LV function recovered immediately and continued to improve with a significant difference between preoperative and postoperative EF (p<0.001). There were 15 late deaths during the follow-up period, and overall survival at 5 and 10 years were 94% and 90%, respectively. On multivariable analysis, age at operation (p=0.008), concomitant coronary bypass surgery (p<0.003), lower preoperative LVEF (<40%) (p=0.0018), and higher EUROScore (>7) (p=0.045) were risk factors for late death. Conclusion: After AVR for degenerative AS, reduction of left ventricular mass and improvement of left ventricular function continue late after operation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.6
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• pp.643-649
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• 2011

For the development of butterfly valves used in liquefied natural gas (LNG) vessels, the seat tightness is one of the important factors to be taken into account in the valve-design process. An O-ring-type metal seal with a retaining ring showing good seat tightness at cryogenic temperatures has been widely used, despite the high manufacturing costs involved. As an alternative, a flexible solid metal seal offers not only sufficient tightness of the butterfly valve, meeting specification requirements, but also relatively low manufacturing costs. In this study, a design criterion to ensure the seat tightness of the butterfly valve using the flexible solid metal seal is proposed. The contact pressure can be calculated by the simulation of the frictional contact behavior between the surface of the metal seal and the valve disc. The geometry of the flexible solid metal seal is determined so that it satisfies the design criterion for sufficient seat tightness, and is verified by experiments according to BS6755 and BS6364.

• Journal of the Korean Society of Radiology
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• v.84 no.6
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• pp.1324-1336
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• 2023

Purpose This study aimed to compare the diagnostic performance of cardiac CT and transthoracic echocardiogram (TTE) depending on the degree of valvular calcification and bicuspid aortic valve (BAV) subtype. Materials and Methods This retrospective study included 266 consecutive patients (106 with BAV and 160 with tricuspid aortic valve) who underwent cardiac CT and TTE before aortic valve replacement. Cardiac CT was used to evaluate the morphology of the aortic valve, and a calcium scoring scan was used to quantify valve calcium. The aortic valves were classified into fused and two-sinus types. The diagnostic accuracy of cardiac CT and TTE was calculated using a reference standard for intraoperative inspection. Results CT demonstrated significantly higher sensitivity, negative predictive value, and accuracy than TTE in detecting BAV (p < 0.001, p < 0.001, and p = 0.003, respectively). The TTE sensitivity tended to decrease as valvular calcification increased. The error rate of TTE for CT was 10.9% for the twosinus type of BAV and 28.3% for the fused type (p = 0.044). Conclusion Cardiac CT had a higher diagnostic performance in detecting BAV than TTE and may help diagnose BAV, particularly in patients with severe valvular calcification.

• Journal of the Korean Institute of Gas
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• v.21 no.5
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• pp.9-15
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• 2017

Natural gas fuel has known to be very promising in terms of abundancy and economic value. Therefore it is widely treated as research topics in a variety field of production, storage and utilization. Natural gas has become one of the major sources for the power generation by using internal combustion engines(ICE). Development of natural gas fuel injection device should be preceded to realize a reliable natural gas fuel supply system for a MW class power generation reciprocating ICE. In this research, an injection valve which consists of solenoid and body part with a moving plate was designed and its dynamic performance was experimented in the engine-like environment. Displacement length and diameter of an armature and diameter of a solenoid coil were tested at former study. In this research the effect of materials of solenoid core, size of main housing inlet and supply gas pressure are examined.

• Journal of the Korean Institute of Gas
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• v.28 no.2
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• pp.32-37
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• 2024

Recently, transportations using hydrogen energy is being researched for the alternative energy of fossil fuels. To use them, processes of producing, storing and transferring are required. When carrying them in liquid under 90 MPa pressure, it costs less than in a gas status. Thus, a hydrogen pump is necessary and in this research we predicted the flow in the chamber using finite element methods (FEM) program ANSYS. As a result, when the valve was opened by 3 mm, between the 1^st chamber and the 2^nd chamber, the maximum velocity was decreased to 8.111 m/s by 10.6% (without valve, 9.075 m/s). In addition, pressure was also increased to 0.63 MPa by 1.6% (without valve, 0.62 MPa). When using these results, more efficient processes would be possible in designing them in detail.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.12a
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• pp.72-72
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• 2003

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.144.1-144.1
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• 2007

• Journal of Magnetics
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• v.7 no.4
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• pp.147-150
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• 2002

The pinning direction, the spin flop behaviors and the magnetoresistive properties in top synthetic spin valve structure [NiFe/CoFe/Cu/CoFe (t$_{p2}$)/Ru/CoFe (t$_{p1}$)/IrMn] were investigated. The magnetoresistive and pinning characteristics of synthetic spin valves strongly depended on the differences in the two pinning layer thickness, ${\Delta}t(=t_{p2}-t_{p1})$. In contrast to the conventional spin valves, the pinning direction (P1) was canted off with respect to the growth field axis with ${\Delta}t$. We found that the canting angle ${\Phi}$ had different values according to the annealing field direction and ${\Delta}t$. When the samples were annealed at above the blocking temperature of IrMn with zero fields, the canted pinned layer could be set along the growth field axis. Because the easy axis which was induced by the growth field during deposition is still active in all ferromagnetic layers except the IrMn at $250{^{\circ}C}$, the pinning direction could be aligned along the growth field axis, even in 0 field annealing.

• Journal of Chest Surgery
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• v.44 no.2
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• pp.131-136
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• 2011

Background: We evaluated the surgical results and predictors of long-term survival in patients who underwent coronary artery bypass grafting (CABG) at the time of an aortic valve replacement (AVR) due to aortic stenosis. Materials and Methods: Between January 1990 and December 2009, 183 consecutive patients underwent CABG and concomitant aortic valve replacement for aortic stenosis. The mean follow-up period was $59.8{\pm}3.3$ months and follow-up was possible in 98.3% of cases. Predictors of mortality were determined by Cox regression analysis. Results: There were 5 (2.7%) in-hospital deaths. Follow-up of the in-hospital survivors documented late survival rates of 91.5%, 74.8%, and 59.6% at 1, 5, and 10 postoperative years, respectively. Age (p<0.001), a glomerular filtration rate (GFR) less than 60 mL/min (p=0.006), and left ventricular (LV) mass (p<0.001) were significant predictors of mortality in the multivariate analysis. Conclusion: The surgical results and long-term survival of aortic valve replacement with concomitant CABG in patients with aortic stenosis and coronary artery disease were acceptable. Age, a GFR less than 60 mL/min, and LV mass were significant predictors of mortality.

• Journal of Chest Surgery
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• v.31 no.8
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• pp.781-786
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• 1998

Materials and methods: Between 1984 to 1994, 136 patients underwent primary and isolated aortic valve replacement with 79 Carbomedics and 57 St. Jude prostheses. Results: Age ranged from 16 to 67 year(mean : 44.5${\pm}$12.7 years). Statistically significant differences in preoperative clinical characteristics between two groups were not found. There was one early death in the St. Jude group and none in the Carbomedics group. Early prosthetic valve-related complications including death were not significantly different between the two groups(p value= 0.572). One hundred thirty five early survivors were followed for a total of 354.2 patient-years(mean=31.5${\pm}$16 months). In the CarboMedics group, actuarial survial rate at 5 years was 97.1${\pm}$1.9%, and in the St. Jude group, it was 95.9${\pm}$2.8%. In the CarboMedics group, actuarial free rate from all valve-related events at 5 years was 92.1${\pm}$3.1%, and in St. Jude group, it was 89.8${\pm}$5.0%. Conclusion: We conclude that early and late results after performing isolated aortic valve replacement with CarboMedics and St. Jude valve are not significantlly different.