• Transactions of the Korean hydrogen and new energy society
• /
• v.20 no.6
• /
• pp.464-470
• /
• 2009

In order to analysis the possibility of high expansion and performance without backfire in a hydrogenfueled engine using external mixture injection, combustion characteristics and performance enhancement were analyzed in terms of retarding valve timing and increasing the boosting pressure. As the results, it was found that thermal efficiency increased by retarding intake valve timing with the same level of supplied energy is over 6.6% by the effect of high expansion including effect of combustion enhancement due to supercharging. It was also shown that the achievement of high power (equal to that of a gasoline engine), low brake specific fuel consumption and low emission (NOx of less than 16 ppm) without backfire in a hydrogen-fueled engine is possible around a boosting pressure of 1.5 bar, intake valve opening time of TDC and $\Phi$=0.35 in fuel-air equivalence ratio.

• Journal of Chest Surgery
• /
• v.54 no.3
• /
• pp.165-171
• /
• 2021

As a percutaneous technique for the reduction of mitral regurgitation, the MitraClip system (Abbott Vascular, Abbott Park, IL, USA) for transcatheter edge-to-edge repair of the mitral valve was developed in 1998 and first used in 2003. Its main advantage is being less invasive than surgery, because it can be performed through a transcatheter approach without any hemodynamic compromise. Recent studies have shown that this procedure reduces symptoms and improves functional capacity with low complication rates. Two randomized clinical trials have investigated the use of this technique for functional mitral regurgitation. The Korean Ministry of Food and Drug Safety approved its use for degenerative mitral regurgitation in 2019, and this procedure started to be performed in Korea in January 2020. Its use for functional mitral regurgitation was also approved in Korea in 2020. In this article, recent evidence on transcatheter edge-to-edge repair of the mitral valve and our initial experiences in Korea will be reviewed.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.24 no.5
• /
• pp.77-83
• /
• 2020

The operating characteristics of a main oxidizer shut-off valve have been examined by life-cycle tests in which the valve operates as many times as is required at room and cryogenic temperatures. It is shown that there is no significant change of the operating characteristics in the course of the life-cycle tests. The critical pressures and principal forces, which represent the operating characteristics, differ at each operating time by less than about 3%. These qualified operating characteristics of the valve are expected to play an indispensible role in the stable startup and shutdown of a liquid rocket engine.

• Journal of the Korean Society of Industry Convergence
• /
• v.25 no.4_2
• /
• pp.541-547
• /
• 2022

Before making a prototype, we predicted the inlet/outlet differential pressure and flow coefficient, which are the most basic design data for the valve through the design and numerical analysis of the trim, which is the most important in the localization development of the 1500Ib high differential pressure control valve used for boiler feed water. As a result, the design value and the analysis value were found to be about 98% similar. The flow field within the fluid velocity of 23m/s to prevent cavitation was also found. The result of the numerical analysis on thermal stress due to the characteristics of valves exposed to high temperatures showed that it was found to be about 18% less than the allowable stress of the bolt fixing the trim. When all loads such as pressure, self-weight, and vibration are applied, however, it is judged to go beyond the currently calculated thermal stress, exceeding the allowable stress.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.23 no.2
• /
• pp.86-94
• /
• 1987

In order to examine the flow motion in a combustion chamber of a motored diesel engine, the variation of instantaneous are velocity at a fixed point in combustion chamber was measured by the constant temperature hot wire anemometer, varing engine speed, shroud shape and shroud position. The results are summerized as follows: 1. The variation of air velocity in a combustion chamber is closely related with the valve timing and piston velocity. 2. The air velocity in the cylinder at suction stroke is being increased and maximized at 60$^{\circ}$ ABDC in compression stroke and then decreased at the e.v.o. in expansion stroke. 3. The mean velocity using shroud valve was less than no shroud valve. However the turbulent intensity using shroud valve was larger than no shroud valve. 4. The turbulent intensity with 90$^{\circ}$shroud valve was larger than that of 120$^{\circ}$shroud valve, and 90$^{\circ}$shroud valve at 180$^{\circ}$shroud position had the largest turbulent intensity.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.23 no.2
• /
• pp.40-40
• /
• 1987

In order to examine the flow motion in a combustion chamber of a motored diesel engine, the variation of instantaneous are velocity at a fixed point in combustion chamber was measured by the constant temperature hot wire anemometer, varing engine speed, shroud shape and shroud position. The results are summerized as follows: 1. The variation of air velocity in a combustion chamber is closely related with the valve timing and piston velocity. 2. The air velocity in the cylinder at suction stroke is being increased and maximized at 60° ABDC in compression stroke and then decreased at the e.v.o. in expansion stroke. 3. The mean velocity using shroud valve was less than no shroud valve. However the turbulent intensity using shroud valve was larger than no shroud valve. 4. The turbulent intensity with 90°shroud valve was larger than that of 120°shroud valve, and 90°shroud valve at 180°shroud position had the largest turbulent intensity.

• Journal of Chest Surgery
• /
• v.20 no.4
• /
• pp.673-682
• /
• 1987

The principal feature of bioprosthetic valve which remains to be completely defined is long-term durability, especially, with regard to the impact of patient age. This report provides extended data regarding valve durability derived from a data base of 515 patients who received lonescu-Shiley bioprosthetic valve between 1978 and 1985; cumulative duration of follow-up was 1562.3 patient-years, with a maximum follow-up duration of 8.7 years. The results of this survey showed as follows: 1] The actuarial freedom from valve failure at 6 years were 43*7% for 0-19 year-old group, 70*1% for 20-39 year-old group and 75*1% for over 40 year-old group separately. 2] Of the causes of valve failure, only the primary tissue failure was markedly influenced by patient`s age [p<0.001], but the prosthetic valve endocarditis was not [p>0.1]. 3] The linealized incidences of primary tissue failure were 7.31% per patient-year in 0-19 year-old group and 0.12% in 20-39 year-old group. 4] The primary tissue failure rate in 0-19 year-old group was 6.36% during first 4 years, but then increased upto 10.95% at postoperative 5 year. Thus we find that in bioprosthetic valve the primary tissue failure is apt to occur when patient is young [especially less than 20 years old] and the postreplacement time passes [especially over 5 years]. The rate of bioprosthesis failure among children and adolescents is clearly higher than that observed in adult patients; however, conclusive quantification of time-related risk for young patient is not yet possible on the basis of existing data. Therefore, the advisability of bioprosthesis implantation in children remains to be determined.

• Journal of Chest Surgery
• /
• v.46 no.2
• /
• pp.124-129
• /
• 2013

Background: Mitral valve repair for posterior mitral leaflet (PML) prolapse has been considered to be a standard treatment because of its high success rate and high level of patient satisfaction. The aim of this study was to evaluate the clinical results of two different techniques of PML prolapse, quadrangular resection (QR) and chordal replacement (CR). Materials and Methods: The subjects consisted of 56 patients who had undergone mitral valve repair for PML prolapse between November 1997 and December 2010. The patients were divided into two groups according to surgical technique. Among them, 31 patients underwent QR (group QR) and 25 patients had CR (group CR). We reviewed the medical records of the patients retrospectively to compare the clinical outcomes of both groups. Results: After mitral valve repair, the degree of mitral regurgitation (MR) in both groups decreased to the to a mild degree or less and the amount of remnant MR was slightly higher in the CR group but it was not statistically different. Three patients received mitral valve-related reoperation (2 in the QR group and 1 in the CR group). Freedom from mitral valve-related reoperation at 7 years was 93% for the QR group and 96% for the CR group and was not significantly different between the two groups. Conclusion: Both QR and CR showed excellent long-term results and were considered equally effective methods for PML prolapse.

• Journal of Chest Surgery
• /
• v.16 no.4
• /
• pp.602-614
• /
• 1983

Six hundred fourteen consecutive cases of bioprosthetic cardiac valve replacement performed during the period from March 1976 through December 1982 were reviewed. A total of 748 tissue valves [534 Ionescu-Shiley valves, 144 Hancock valves, 46 Angell-Shiley, and 24 Carpentier-Edwards] were implanted in 610 patients. Of these, 477 had single valve replacements [403 mitral, 60 aortic, and 14 tricuspid] including three REDO MVR and one REDO AVR. The remaining 129 had double valve replacements [95 AVR and MVR and 34 MVR and TVR] and 8 had triple valve replacement.592 cases were evaluated. Overall early mortality rate [within 30 days of operation] was 7.1% [6.2% in single valve replacement, 10.2% in double valve replacement, and 16.7% in triple valve replacement]. Leading causes of mortality were low cardiac output or myocardial failure and ventricular arrhythmias. The follow-up period was from one month to 7 years with a cumulative follow-up of 906.6 patient-years [mean 1.53 years]. The late mortality was 1.6%, 3.9%, 0%, 2.6%, 6.6% and 2.0% per patient-year for MVR, AVR, TVR or triple valve replacement, AVR+MVR, MVR+TVR and total, respectively. Actuarial analysis of late results including early mortalities indicates an expected survival rate of 87.6+1.8% at 3 years and 85.92.4% at 7 years for all cases. We also analyzed actuarial survival rate between groups of each valve replacement [AVR, TVR, Double valve, and Triple valve] and the tissue valve groups in MVR. We experienced 7 cases [0.77% per patient-year] of confirmed endocarditis, two of which were fatal. Valve failure-free rates calculated according to the confirmed cases were 97.5% at 4 years, 87.5% at 7 years, and 88.3% at 6 years for Ionescu-Shiley, Hancock and Angell-Shiley valves, respectively. The occurrence rate of thromboembolism was 2.0% per patient-year in total cases, although almost all the patients were given anticoagulant therapy for one year. The occurring rate in MVR was 1.5% and 2.7% per patient-year for Ionescu-Shiley and Hancock valve groups, respectively. The difference in actuarial rate free from thromboemboli between Ionescu-Shiley and Hancock groups was statistically significant [P value less than 0.001]. Thromboembolic events beyond the period of anticoagulation therapy mainly occurred in patients with atrial fibrillation. The actuarial thromboemboli free survival was 95.71.4% at 3 years and 80.17.3% at 7 years. The incidence of hemorrhagic complications was 1.2% per patient-year [fatality 0.55% per patient-year] for anticoagulated patients. Although our clinical data favorably compares with results from other reports, our results suggest that anticoagulant therapy be given on a short-term basis or not at all to hemodynamically stable patients. Long-term therapy with antiplatelet drugs is probably inevitable with patients who have thromboembolic risk factors [such as atrial fibrillation].

• Journal of Chest Surgery
• /
• v.29 no.10
• /
• pp.1090-1094
• /
• 1996

From February 1980 to September 1995, 31 children between 2 months and 15 years of age with mitral valve disease have undergone mitral valve replacement(MVR) at Yonsei Cardiovascular Center and com- plete follow-up has been obtained on 28 patients. There were 10 males and 18 females whose weight ranged from 4.9kg to 56kg. Two patients died early postopeiatively and the overall hospital mortality rate was 7.1%. These two were infants but there were no statistically significant difference in overall mortality among the age groups(p=0.13). The valve related complication rate was 57.1% in children younger than 5 years of age, which showed higher complication rate compared to older patients(p< 0.05). The bioprosthetic valve have been applied in 7 patients, and its 5-year valve failure-free survival rate was 50% . No mechanical valve failu e had occurred in 21 patients. In considering high re-replacement rate of bioprosthetic valve, mechanical valve is recommended despite its possibility of bleeding and thromboembolic complications. However, the consequences of increasing body size and long-term interposition of a rigid prosthesis in a growing heart will require second valve replacement. En conclusion, mitral valve replacement can be performed tilth satisfactory long-term survival in children, although younger mean age of the children has an important influence on early mortality and com- plication rate. And therefore mitral valve replacement in children younger than 5 years of age needs special consideration.