• International Journal of Reliability and Applications
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• 제16권1호
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• pp.1-13
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• 2015

In this paper, we investigate reliability and availability of repairable systems with two types of failure. The first one is to one unit and the second one is to M units in parallel structure. Let failure rate and repair rate of [type1, type2] components are assumed to be exponentially distributed. The expressions of availability and reliability characteristics such as the system reliability and the mean time to failure are derived for two systems. We used several cases to analyze graphically the effect of various system parameters on the reliability system and availability system.

• 기술혁신학회지
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• 제15권1호
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• pp.203-223
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• 2012

본 연구는 사업타당성이 있다고 평가되었지만 기술사업화가 중지된 사례의 실패원인을 규명하는데 목적이 있다. 이를 위해 여러 경로로 신기술사업화 타당성 평가 보고서 92건을 수집하고, 확실하게 사업화가 실패한 것으로 판단되는 4건에 대하여 추적조사 하였다. 추적조사는 기술사업화 성공과 실패에 관한 여러 이론적 갈래, 즉 기술사업화 성공실패론, 벤처기업 성공실패론 및 기술가치평가론 등의 선행 연구에서 지적된 결과를 중심으로 작성한 분석 틀에 기초하였다. 연구결과 표면적인 신기술사업화 실패원인들은 자금부족과 불가항력적인 요인, 관리력, 대량생산기술 부재 등으로 본 연구의 분석 틀로 제시된 선행연구 결과와 별반 다르지 않다. 하지만, 이면에 숨겨진 핵심 실패 원인은 광의의 기술이해 부족으로 분석되었다. 특히 기술구성 및 기술제품 단계별 소요기술이 존재한다는 점과 기술개발 성공이 기술사업화 성공과 다르다는 것을 이해하지 못한 것이 주요 원인으로 나타났다. 이러한 결과의 배경은 경영자의 전공과 경력이 평가기술과 연관성이 낮거나, 보유경험의 부족으로 분석되었다. 본 연구는 4개의 사례만 조사했다는 점에서 모든 요인을 일반화시키기 어렵지만 다음과 같은 시사점을 도출할 수 있다. 먼저, 표면상의 기술사업화 실패요인들이 선행연구 결과로 설명되었지만, 기술이해 부족이 이면에 숨겨진 핵심 실패요인임을 규명하였다. 둘째, 실패원인들을 분석함으로써 성공적인 기술사업화를 위한 패턴이 제시되었으며, 마지막으로 향후 기술사업화 주체인 경영자와 기업의 역량에 대한 깊은 분석과 기술사업화 평가 모형에 대한 적합성 검토가 필요하다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제16권1호
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• pp.56-63
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• 2016

Purpose: The purpose of this study is to point out that the Kaplan-Meier method is not valid to calculate the survival probability or failure probability (risk) in the presence of competing risks and to introduce more valid method of cumulative incidence function. Methods: Survival analysis methods have been widely used in biostatistics division. However the same methods have not been utilized in reliability division. Especially competing risks cases, where several causes of failure occur and the occurrence of one event precludes the occurrence of the other events, are scattered in reliability field. But they are not noticed in the realm of reliability expertism or they are analysed in the wrong way. Specifically Kaplan-Meier method which assumes that the censoring times and failure times are independent is used to calculate the probability of failure in the presence of competing risks, thereby overestimating the real probability of failure. Hence, cumulative incidence function is introduced and sample competing risks data are analysed using cumulative incidence function and some graphs. Finally comparison of cumulative incidence functions and regression type analysis are mentioned briefly. Results: Cumulative incidence function is used to calculate the survival probability or failure probability (risk) in the presence of competing risks and some useful graphs depicting the failure trend over the lifetime are introduced. Conclusion: This paper shows that Kaplan-Meier method is not appropriate for the evaluation of survival or failure over the course of lifetime. In stead, cumulative incidence function is shown to be useful. Some graphs using the cumulative incidence functions are also shown to be informative.

• Journal of Chest Surgery
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• 제13권1호
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• pp.34-40
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• 1980

Total 193 patients over 16 years of age who have underwent a surgical correction of congenital heart diseases during the period 1964 to September of 1979 were reviewed. 106 patients were male and 87 patients were female. 85 patients were in the ages of 16 years through 20 years. The oldest patient was 54 years old male who had atrial septal defect. The commonest defects were atrial septal defect that accounted for 66 cases [34.2%]. Ventricular septal defect was next one that accounted for 66 cases [34.2%]. Patients with tetralogy of Fallot defects were 34 cases [17.6%]. 25 cases had patent ductus arteriosus [13.0%]. Patients with pulmonary stenosis were 17 cases [8.8%] and transposition of the great arteries cases were 2 cases [1%]. There were 14 cases of operative death in this series. So operative mortality rate was 7.3%. The commonest cause of death was low output syndrome and next was renal failure. This reviewed series reveals the incidence of operable congenital heart defects appearing in adult cardiac surgical patients and an aggressive surgical approach can be justified with low operative mortality like as pediatric age group.

• Journal of Chest Surgery
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• 제21권1호
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• pp.62-69
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• 1988

In the department of chest surgery of WonKwang university hospital, mechanical valve replacement was performed in 51 cases from June 1985 to September 1987. Among these, 32 cases were mitral valve replacement, 4 cases were aortic valve replacement, and 15 cases were double valve replacement. 26 cases were male and 25 cases were female and age distribution ranged from 16 years old to 63 years old. Early death within 30 days after operation was 2 cases [3.9%] and causes of death were right heart failure [1] and right ventricular wall rupture [1]. Among 49 early survivors, 2 cases of late death were developed and the causes of death were cardiomyopathy [1] and ventricular arrhythmia [1] Anticoagulant therapy was done with warfarin sodium to the level of 1.5-2 times of normal prothrombin time [20-40%] in 47 survivors. Symptomatically, 93.6% of preoperative NYHA functional class III or IV were converted to the NYHA functional class I or II during follow up.

• Journal of Chest Surgery
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• 제22권5호
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• pp.834-838
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• 1989

Tracheal stenosis is being encountered more frequently as ventilatory support and cuffed tubes are increasingly used for treatment of respiratory failure. We experienced 13 cases of tracheal stenosis treated surgically at department of Thoracic and Cardiovascular Surgery, school of medicine, Kyung Hee university during the 4 years. The causes of tracheal stenosis were prolonged endotracheal intubation 5 cases, tracheostomy 3 cases, tracheal tumor 2 cases, thyroid tumor 1 case and congenital double aortic arch 1 case. The methods used to manage the tracheal stenosis were tracheal resection % end to end anastomosis 8 cases, 2 cases of subglottic stenosis were underwent primary laryngotracheal anastomosis, Lt. aortic arch division 1 case, and stent insertion 2 cases. In two cases, who had 6 cm in length of tracheal stenosis, we were underwent tracheal resection k end to end anastomosis with supralaryngeal release procedure. Postoperative courses were uneventful except one case with tracheal tumor.

• 대한임상독성학회지
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• 제16권2호
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• pp.86-92
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• 2018

Purpose: Cardiovascular or respiratory complications of acute intoxication are the most common causes of mortality. Advanced cardiac life support (ACLS) or specific antidotes help manage these cardiac or respiratory complications in acute intoxication. On the other hand, some cases do not respond to ACLS or antidotes and they require some special treatment, such as extracorporeal life support (ECLS). ECLS will provide the chance of recovery from acute intoxication. This study examined the optimal timing of ECLS in acute intoxication cases. Methods: This paper is a brief report of a case series about ECLS in acute poisoning. The cases of ECLS were reviewed and the effects of ECLS on the blood pressure and serum lactate level of the patients were analyzed. Results: A total of four cases were reviewed; three of them were antihypertensive agent-induced shock, and one was respiratory failure after the inhalation of acid. The time range of ECLS application was 4.8-23.5 hours after toxic exposure. The causes of ECLS implementation were one for recurrent cardiac arrest, two for shock that did not respond to ACLS, and one for respiratory failure that did not respond to mechanical ventilator support. Three patients showed an improvement in blood pressure and serum lactate level and were discharged alive. In case 1, ECLS was stared at 23.5 hours post toxic exposure; the patient died due to refractory shock and multiple organ failure. Conclusion: The specific management of ECLS should be considered when a patient with acute intoxication does not recovery from shock or respiratory failure despite ACLS, antidote therapies, or mechanical ventilator support. ECLS improved the hemodynamic and ventilator condition in complicated poisoned patients. The early application of ECLS may improve the tissue perfusion state and outcomes of these patients before the toxic damage becomes irreversible.

• Journal of Chest Surgery
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• 제15권2호
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• pp.204-212
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• 1982

The presence of left atrial thrombus in mitral stenosis has been reported to be associated with several factors. These are age, sex, presence of atrial fibrillation, episodes of congestave heart failure, calcification of mitral valve, embolic episode, etc. Since none of these single factor has been always related to the presence of left atrial thrombus, related risk factors to left atrial thrombosis were studied in patients with mitral stenosis using chi square test. We had operated on 191 cases of mitral valvular heart disease from Jan. 1978 to June 1981 at Severance Hospital, Yunsei University College of Medicine. The left atrial thrombi were present in 41 cases among 191 cases of mitral valvular heart disease and it was present in 31 cases among 89 cases of pure mitral stenosis. Only 10 cases among 74 cases of mitral stenoregurgitation had left atrlal thrombi, whereas no left atrlal thrombus was found in patients with pure mitral regurgitation. Related risk factors studied herein were sex, episodes of congestive heart failure, atrial fibrillation, pulmonary capillary wedge pressure, mitral valve area calculated by Gorlin and Gorlin`s formula cardiac output and left atrial dimension by echocardiogram. In this study presence of atrial fibrillation was deemed to be one of the most potential risk factors and other factors of age, duration of symptoms, episode of embolization, calclfication of mitral valve, associated aortic and tricuspid valve disease, ejection fraction of left ventricle by cineangiocardiogram and echocardiogram were not significantly related to the presence of left atrlal thrombi in a statistical viewpoint.

• Journal of Chest Surgery
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• 제23권2호
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• pp.299-308
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• 1990

A review of 50 patients with primary mediastinal tumors or cysts has been done to evaluate clinical and pathological behavior of this heterogeneous group of tumors proved by either excision or biopsy from January 1980 to August 1989 at the cardiovascular department of surgery in Kyungpook National University Hospital. There were 30 males and 20 females in this series. The ages of patients ranged from 4 months to 64 years. The mean age of subjects was 30.4 years. Neurogenic tumors [14 cases, 28%] and teratoma [14 cases, 28%] were most frequently encountered and followed by thymoma [10 cases, 20%] and benign cysts [4 cases, 8%]. The anatomic location of the primary mediastinal tumors or cysts was classified as anterior mediastinum and middle or visceral mediastinum and paravertebral or costovertebral mediastinum on the basis of the Shields’ proposition. In 32 patients[64%], the tumors or cysts were located in anterior mediastinum and in 13 patients[26%], the tumors or cysts were located in paravertebral or costovertebral mediastinum. And the rest 5 patients[10%] had middle or visceral mediastinal tumors or cysts. One of the characteristic features of primary mediastinal tumors or cysts is that some mediastinal tumors or cysts have their own preferred location in the mediastinum. In our series, all of the 14 patients with teratoma and 10 patients with thymoma had the anterior mediastinal location, while 13 of the 14 patients with neurogenic tumors had the paravertebral mediastinal location. 14 patients[28%] were asymptomatic and they all were discovered via so-called “Routine” chest x-ray examination. 39 of 50 patients[78%] were benign. 11 patients[22%] were malignant and they were all symptomatic. 40 patients[80%] were treated with complete resection. 5 patients[10%] were treated with partial resection : 2 of malignant thymoma, 3 of lipoma, neuroblastoma, primary squamous cell carcinoma. The rest 5 patients[10%] were only biopsied: 2 of undetermined malignancy and 3 of hemangioma, lymphoma, primary squamous cell carcinoma. 4 of the 10 patients were treated with combination of irradiation and chemotherapy. Postoperative complications were as followings: Horner’s syndrome [4cases, ado], respiratory failure [3 cases, 6%], pleural effusion[3 cases, 6%], Wound infection[2 cases, 4%] and bleeding, pneumothorax, empyema. There were 5 postoperative deaths [10%]. One patient with neuroblastoma died from intraoperative massive bleeding, 3 patients died early postoperatively from respiratory failure with undetermined malignancy died late postoperatively from congestive heart failure due to direct invasion of the tumor to the heart.

• Journal of Chest Surgery
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• 제15권3호
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• pp.278-284
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• 1982

As of today, the frequency of primary lung cancer is one of the improved problems in modern medicine and is increasing rapidly year by year. This study dealed with 138 cases of primary lung cancer proved by histopathologic examination in Thoracic & Card iovascular Surgery Dept. of N.M.C. from Sept. 1966 through June 1981. The majority of patients belong to 5th and 6th decade. Ratio between male and female was 3.7: 1. Initial symptoms were cough, blood tinged sputum, hemoptysis, chest pain, dyspnea and duration of symptoms before admission was within 6 months [60%] and 12 months [78%]. Histopathologically, 64 cases [61%] of them were the squamous cell carcinoma, 21 cases [15%] were the adenocarcinoma, 20 cases [14.8%] were the anaplastic carcinoma. Fifty-six cases were resectable: 43 cases were subjected to pneumonectomy and 13 cases were to lobectomy. The remaining 82 cases were nonresectable, but exploratory thoracotomy was performed in 22 cases of them. Among 56 resected cases, 33 cases were radically operated and 17 cases were subjected to palliative operation and 6 cases were subjected to extended operation. [Concomitant pericardium resection in 1 case and concomitant chest wall resection in 5 cases]. Surgical mortality was 10.7% and causes of death were aspiration of contralateral lung, respiratory insufficiency, postop. empyema with B.P.F, cardiogenic failure. This study analysed the cancer stage between preop clinical T.N.M. stage and postop. T.N.M. stage in 78 cases; resectable 56 cases and non-resectable 22 cases.