• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.1
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• pp.37-44
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• 2001

This study is focused on the development of a new muffler. A control valve installed in the exhaust system is operated by torsion springs, and its open angle is controlled automatically corresponding to the engine operating conditions. The experiments were done using an exhaust system simulator having the same pulsation wave frequency and similar pulsation propagation characteristics of a real exhaust system. The purpose of this study is to develop a new muffler system which has improved noise reduction quality and less power loss than conventional mufflers and electronic-control mufflers.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.3
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• pp.167-176
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• 2003

This study is focused on the development of a new muffler. A control valve installed in the exhaust system is operated by torsion springs, and its open angle is controlled automatically corresponding to the engine operating conditions. A control valve and a control muffler sensing exhaust-gas pressure are made f3r developing a new muffler. The experiments were done using an exhaust system simulator having the same pulsation wave frequency and similar pulsation propagation characteristics of a real exhaust system. The purpose of this study is to develope a new muffler system which has improved noise reduction quality and less power loss than conventional mufflers and electronic-control mufflers. Finally the characteristic of noise compared with conventional muffler and muffler sensing exhuast-gas pressure.

• Journal of Biosystems Engineering
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• v.17 no.3
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• pp.223-228
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• 1992

This study was conducted to develop an electro-hydraulic three-point hitch control system using an electro-hydraulic servo valve and microcomputer and to investigate the performance of the three-point hitch control system through indoor and field experiments. 1. The results from indoor experiments coincided with those from computer simulation reported in the previous paper. However, the draft control with the value 4 of Kd showed a slight sustained oscillation after it reached the draft set. 2. From the field experiments, it appeared that the RMS errors increased with the ground speed of tractor. In position control, the three-point hitch control system with electro-hydraulic servo valve showed better performance than that with on-off electro-magnetic valve in the ground speed less than 1.6 m/s. In draft control, however, there was no significant differece in performance between those two systems. 3. In depth control, the both types of electro-hydraulic three-point hitch control system showed better performance than the conventional mechanical-hydraulic three-point hitch control system.

• Journal of Chest Surgery
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• v.30 no.11
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• pp.1139-1141
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• 1997

Recently, minimally invasive approach via limited incision becomes one of the rapidly developing strategy in cardiac surgery as it gives less surgical trauma and is more satisfactory to the patients in respect to operative scar although the surgical technique is more demanding. Here, we report two cases of aortic valve replacement via limited transsternal incision. The methodology is described with review of the relevant literature.

• Journal of Magnetics
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• v.7 no.2
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• pp.55-58
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• 2002

MR transfer behaviors of the permanent magnet biased spin valve MR sensors with SyAF (synthetic antiferromagnet) layers were studied by micromagnetics modeling. For narrow track MR heads, various height to width ratios were considered together with strength of permanent magnets which stabilities the free layed As the MR sensor width is reduced to $0.12 \mu{m}$, sensor height less than 0.09 ${\mu}{\textrm}{m}$ is needed to show good linearity and the Mr.t of permanent magnets smaller than 0.2 memu/$cm^2$ is sufficient for the domain stabilization. The conditions for single domain behavior of the free layer were also investigated through optimizing the biasing strength of permanent magneto the shield gap and the aspect ratio of MR sensor.

• Journal of Chest Surgery
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• v.40 no.10
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• pp.667-673
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• 2007

Background: Patients with severe aortic valve disease frequently display mitral valve regurgitation (MR). In such patients, the clinical course of MR after isolated aortic valve replacement (AVR) may be important for determining the treatment strategies. After isolated AVR, the change of the concomitant moderate degree or less of MR according to the type of aortic valve disease is not known well. The aim of this study was to analyze the post-operative changes of MR after performing AVR in those patients with severe AS (Group S) and those with severe AR (Group R). Material and Method: We retrospectively evaluated 43 patients with severe aortic disease and a moderate degree or less of mitral valve regurgitation, and these patients underwent isolated aortic valve replacement from January 1996 to June 2005. The patients were divided into two groups: the aortic valve stenosis group (n = 29) and the aortic valve regurgitation group (n = 14). The patients underwent transthoracic echocardiography preoperatively and at 7 days, $6{\sim}10$ months and more than 18 months (mean follow-up duration: 38 months) postoperatively. Result: The mean age was 60.9 years (Group S: 62 years, Group R: 52.5 years) and 60% (Group S=55%, Group R=71%) of the patients were male. The preoperative MR was mild in 29 (67.5%), mild to moderate in 11 (25.5%), and moderate in 3 (6.9%) patients. In the Group S patients, MR improved in 16 (55%) patients at the immediate postoperative days and in 17 (59%) patients at more than 18 months postoperatively. On the other hand, all the Group R patients exhibited earlier improvement. The decrease of LA size had a similar pattern to the MR change, but there were no significant differences in the change of the ejection fraction of the two groups. Conclusion: In the patients with severe aortic valve disease and concomitant low grade MR, the MR after AVR improved earlier and more effectively in the patients with AR than in those patients with AS.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.3
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• pp.239-248
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• 2017

According to the structure, solenoid valve can be categorized as spool valve or poppet valve. While various research on spool valve which has simple structure and fine susceptibility to contamination has been conducted, poppet valve which has less susceptibility to contamination and advantage in a long time operation still need much research because of its complicated structure. In order to design the poppet valve, various parameters such as the diameter of the poppet, the angle of the poppet, the diameter of the disk, the spring stiffness, the spring preload and flow path structure should be considered. Conventional studies on poppet valve usually take only one design parameters and did not much focused on the effect of the parameters on flow characteristics. In this paper, the change of the flow characteristics according to the design parameters of the poppet valve for 3/2Way solenoid valve is analyzed. The previous studies and the results of initial model analysis was referred for the selection of the design parameters. The effects of design parameters on maximum pressure, minimum pressure, and pressure drop was examined using analysis of means(ANOM).

• Journal of Chest Surgery
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• v.22 no.2
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• pp.246-255
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• 1989

A total and consecutive 291 patients of isolated single mitral valve replacement using the Ionescu-Shiley bovine pericardial xenograft valve operated on between October 1978 and June 1983 were retrospectively studied for the durability of the substitute valves based on the structural degeneration of primary tissue failure which had been proved on their re-replacement surgery. The mean age at the initial surgery was 32.4*12.5 years, and the operative mortality rate was 5.2 %. The early survivors of 276 patients were followed up for a total 1148.3 patient-years[mean\ulcornerD, 4.16*2.57 years]at the follow-up end of June 1988. They experienced 4 major late complications: 1.045 % thromboembolism/patient-year [pt-yr]; 0.871 % bleeding/pt-yr; 0.610% endocarditis/pt-yr; and 3.309% overall valve failure/pt-yr or 1.655% primary tissue failure/pt-yr. The actuarial survival rates were 89.4*2.2% and 87.7*2.5% at 5 and 10 years after initial surgery respectively. The probabilities of freedom from thromboembolism were 95.1*1.6% and 93.2*2.0% at 5 and 10 years after surgery. Nineteen patients underwent re-replacement of the Ionescu-Shiley valve because of primary tissue failure, and there was no operative mortality. The incidence of primary tissue failure was highest for the patients less than 15 years of age occurring in 9 out of 27 patients [33.3 %] or 8.68 %/pt-yr, while it was 4.0 % or 0.96 %/pt-yr for the rest of patients older than this age. The probabilities of freedom from primary tissue failure were 96.7*1.4 % and 84.2*3.8% at 5 and 9 years after surgery. The freedom from tissue failure increased as the age limits of cumulative younger patients were increased while it decreased as the age limits of cumulative older patients were decreased. Although it is clear that the Ionescu-Shiley valve would degenerate prematurely in young patients, the definite age limit could not be identified when the risk of early failure was significantly high.

• Journal of Chest Surgery
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• v.29 no.5
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• pp.504-509
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• 1996

When a valve prosthesis is to be implanted in the aortic position, simple interrupted suture, figure-of- eight suture, or horizontal mattress suture technique is used as a suture method. However, the suture techniques may be unacceptable for aortic valve replacement in patients with friable annulus caused by some lesions, such as endocarditis and degenerative change. We used an alternative technique for the aortic vlave replacement in 4 patients with valve endocarditis, ) patients with degenerative valvular lesion, and 1 with rheumatic valvular disease. Mattress sutures through the annulus were placed with pledgets on the ventricular side of the annulus, whi h resulted in implantation of the prosthesis at a supra-annular level. Mechanical valves of 21 mm or larger were implanted in the supra-annular position in all patients and there was no impeded motion of leaflets during the follow-up period of mean 13.3 mouths. The transvalvular pressure gradient was less than 6 mm Hg in 3 patients and 20 to 40 mm Hg in 5 patients. The supra-annular implantation of mechanical aortic valve using a vertical mattress suture technique may be a useful alternative method of aortic valve replacement for the selected patients with friable or destroyed aortic annulus.

• Journal of Chest Surgery
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• v.18 no.3
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• pp.371-382
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• 1985

Over the past 4 decades after World War II a great deal of data and clinical experiences have been accumulated relating to the diagnosis and surgical treatment of congenital and acquired cardiovascular diseases in Korea. Clinical data on cardiovascular surgical cases performed in all 22 hospitals for open heart surgery in Korea was collected from it`s starting up to December 1984. The first recorded open heart surgery for a young adult atrial septal defect was performed by Young Kyoon Lee, M.D. on August 7, 1959, Seoul National University Hospital, Korea. And, some scattered reports on cardiovascular surgical cases in it`s early period have changed recently the number of hospitals for open heart surgery and clinical cases enormously in total amount of 13, 100 cardiovascular operations performed on 12, 990 cases up to December 1984. Of the total 13, 100 cardiovascular operations, congenital cardiovascular anomaly occupied 70%. Of the congenital cases, 6, 580 operations for acyanotic group [operative mortality 4.5%], and 2, 489 operations for cyanotic group [operative mortality 20%]. The incidence of congenital cardiovascular anomaly in order of frequency was ventricular septal defect [29%], patent ductus arteriosus [26%], Tetralogy of Fallot [22%], atrial septal defect [8, 6%], pulmonary valve stenosis [3.0%], and endocardial cushion defect [1.1%]. Of the 3, 412 valvular heart disease cases, which occupied 85% of total 4, 031 acquired cardiovascular disease, individual incidence was in mitral 2, 565 [63.5%], double valve 451 [11.1%], and simple aortic valve 351 [8.7%]. Total number of valve replaced, mechanical and tissue, was 2, 795, and 1, 884 for mitral, 808 for aortic, and 103 for tricuspid in position. Operative mortality for prosthetic valve replacement in total was 9.8%. Remained acquired cardiovascular cases chronic constrictive pericarditis [7.9%], cardiac tumor [1.9%], coronary artery bypass [1.8%], cardiac trauma [1.2%] and less than 1% of thoracic aortic aneurysm. Overall operative mortality for open and non-open cardiovascular surgical operation was 7.7% [congenital acyanotic group 3.2%, congenital cyanotic group 19.4%, and acquired group 7.8%]. In conclusion, present status of cardiovascular surgery in Korea is stabilized with accumulation of clinical cases and experiences, and the future in the field of cardiovascular surgery is promising, especially in the infant cardiac surgery and aortocoronary bypass surgery, with abrupt increase of specialized cardiac centers, trained specialists, and expanding social health insurance.