• Journal of Chest Surgery
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• v.31 no.2
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• pp.118-124
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• 1998

Minimally invasive coronary artery bypass grafting without using cardiopulmonary bypass (CPB) is a recently accepted modality of myocardial revascularization prcedures which is particularly suitable to the patients with lesions in the left anterior descending(LAD) and the right coronary arteries. Of the consecutive 35 patients of coronary artery bypass grafting performed at Sejong General Hospital from March to August 1996, six patients underwent minimally invasive coronary artery bypass grafting without CPB. All had stenotic lesions of the LAD more than 90%. Bypass grafting of the LAD was approached through midline sternotomy in one, through ministernotomy in two, and through limited left anterior thoracotomy in three patients, respectively. The internal mammary arteries were prepared without the use of thoracoscope. The mobilized mammary arteries were connected directly to the LAD in 5 patients, and the anastomosis required interposition of a segment of the radial artery in the remaining one. The diagonal branch was revascularized with the saphenous vein graft at the same time in one patient. No blood transfusion was necessary in 2 patients, and average blood required during surgery was 800ml in 4 patients. All patients were extubated from 4 to 14 hours(mean 9 hours) after operation. Early postoperative coronary angiography in 5 patients between 7 and 10 days after surgery has proved full patency of the grafts. With these limited clinical experiences, the clinical results demonstrated that minimally invasive coronary artery bypass grafting without CPB is an useful procedure especially in patients with isolated lesion in the proximal LAD.

• Journal of the Korean Society for Nondestructive Testing
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• v.6 no.2
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• pp.17-36
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• 1987

In this experimental research, fracture mechanisms of spheroidal graphite cast iron (As Cast, annealed and normalized) were investigated by using Acoustic Emission (AE) technique. In this study, the data (AE signal) are digitized and processed with the 8 bits micro-computer (APPLE II) connected to the AE measuring device without data processing unit. The source of AE signal was estimated by fractography analysis. The results obtained in this experimental study are summarized as follows : For the heterogeneous materials (spheroidal graphite cast iron) with inclusions which may considered as cracks, it is found that low and high AE amplitude appear simultaneously and the load is found to be fluctuated in the final stage of deformation. But the lad is not fluctuated in tension test with low AE amplitude only. AE is measured within elastic region and it is confirmed that 0.2% offset yield load agrees approximately with the load point where AE counts decrease steeply after the point of maximum AE counts.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.40 no.6
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• pp.574-581
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• 1991

Damage in film capacitors has been investigated, using FTIR and ESCA, aiming to elucidate the nature of electrode removal and the possibility of base films to be damaged. Also, tests were conducted to investigate the effect of a long-term thermal aging at elevated temperatures. Unsuccessful clearing or grape-clustering processes can induce a long-term degradation which involves the chemical and morphological changes. Major changes are the oxidation and the decrease in surface crystallinity possibly arising from the corona discharge. An immediate deterioration of BOPP film may occur when the air entrapped between the film layers induces an extensive autocatalytic oxidative degradation. This type of immediate damage may result in a premature failure at an early stage of qualification test. As far as the nature of electrode removal is concerned, a permanent removal of electrode materials was observed in the main erosion area.

• Journal of the Korean Statistical Society
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• v.26 no.1
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• pp.31-46
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• 1997

Let $X_{t}$ = .beta. $X_{{t-1}}$ + .epsilon.$_{t}$ be an autoregressive process where $\mid$.beta.$\mid$ < 1 and {.epsilon.$_{t}$} is independent and identically distriubted with regularly varying tail probabilities. This process is called the asymptotically stationary first-order autoregressive process (AR(1)) with infinite variance. In this paper, we obtain a host of weak convergences of some point processes based on bootstrapping of { $X_{t}$}. These kinds of results can be generalized under the infinite variance assumption to ensure the asymptotic validity of the bootstrap method for various functionals of { $X_{t}$} such as partial sums, sample covariance and sample correlation functions, etc.ions, etc.

• Journal of Chest Surgery
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• v.23 no.2
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• pp.245-252
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• 1990

To see the change of pulmonary arterial pressure after mitral valve replacement, postoperative cardiac catheterization and echocardiographies were performed in 12 patients of mitral valvular disease with pulmonary hypertension[systolic pulmonary arterial pressure>50 mm Hg]. The mean follow-up duration was 35.4[range: 15-47] months per patient. The following results were obtained. 1] Preoperative systolic pulmonary arterial pressure value of 66.17\ulcorner10.73mmHg decreased significantly to 29.17\ulcorner6.86mmHg postoperatively[p<0.01]. 2] Preoperative Pp/Ps value of 0.67\ulcorner0.13 decreased significantly to 0.28\ulcorner0.06 postoperatively[p<0.01]. 3] Preoperative PAWP value of 29.00\ulcorner4.02mmHg decreased significantly to 9.92\ulcorner4.27 mmHg postoperatively[p<0.01]. 4] Preoperative LAD value of 5.58\ulcorner1.20cm decreased significantly to 4.37\ulcorner0.67cm postoperatively [p<0.01]. In conclusion, pulmonary arterial hypertension secondary to mitral valvular disease could be reduced to normal range after successful mitral valve replacement.

• Journal of Chest Surgery
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• v.20 no.2
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• pp.384-392
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• 1987

The occlusive coronary artery disease presents a potential threat to a significant population in the United State. According to many case reports, the increasing incidence of coronary artery disease due to atherosclerosis is noted in Korean, recently. We experienced one case of coronary artery disease. He was a 68 year old male who had been suffered from hypertension since 1 5 years ago, and had intermittent conservative treatment at local clinic. He had been afflicted with severe chest pain on exertion, but this symptom was relieved on rest. Pre-operative EKG finding revealed no any other ischemic sign. Significant S-T segment depression was noted at lead II, aVF, V3, V4, and V5, and inverted T wave in V5 and V6 after Master`s test. Simple chest X-ray finding showed emphysematous field, bilaterally. Final pre-operative diagnosis was made by coronary angiogram, which showed almost 90% degree of occlusive lesion in the proximal part of left main coronary artery above the origin LAD artery. He was treated successfully by aorta-coronary saphenous vein graft under extra-corporeal circulation in May, 1987. He has been followed up with uneventful course.

• Journal of the Korean Data and Information Science Society
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• v.11 no.1
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• pp.1-18
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• 2000

In this paper, we study several parameter estimation methods used for autoregressive processes and compare them in view of forecasting. The least square estimation, least absolute deviation estimation, robust estimation are compared through Monte Carlo simulations.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.3
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• pp.335-343
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• 1983

Modified-Shrink-Fit(MSF) method of compound cylinder is studied to increase elastic load carrying capacity (ELCC) of pressure vessel. The autofrettage and the shrink-fit processes are used to study the MSF process. Theoretical analyses based on the Tresca yield criterion, Hencky's total strain theory and elastic linearly strain-hardening material are carried out to derive closed form solutions. Experimental results are compared with theoretical results with various diameter ratios between outer (SM45C) and inner (SM20C) bloc cylinder. For various diameter ratios, increments of ELCC have errors in strains vs. internal loading pressures between experimental and theoretical results. But experimental results show good agreements with theoretical results in reyield pressurizing state. The increments of ELCC of compound cylinder manufactured by the MSF process is proved by measuring the residual stresses.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.723-724
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• 2002

Computational modeling is presented to investigate the hemodynamics of coronary circulation for the cardiac arrest model during the operation of an ECLS called T-PLS. A lumped parameter model is utilized to delineate the hemodynamics of coronary circulation. For verification of the present method, we compute the coronary circulation for normal case and compare those results with the existing data. Numerical results on the cardiac arrest model show that T-PLS can increase LAD flow significantly.

• International Journal of Precision Engineering and Manufacturing
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• v.1 no.2
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• pp.61-66
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• 2000

In this paper, we discuss the machining characteristics of HDD glass. Glass is now being used globally as a data storage device, Such glasses are usually machined by lapping by this technique requires a long machining time, resulting in low productivity, For this reason, we examine the possibility of EILD grinding in HDD glass workpieces, A move to ELID grinding may result in substantial cost reduction. Our purpose is to investigate the grinding characteristics of HDD glass in ELID grinding. The bonding materials for fixing the abrasives of cast iron, cobalt and bronze are applied, and grinding conditions such as rotation speed and feeding are varied. Results show that with the use of ELID, mirror surfaces can be achieved with high efficiency.