• Journal of Chest Surgery
• /
• 제24권11호
• /
• pp.1074-1080
• /
• 1991

A total and consecutive 62 patients between 13 and 58 years of age receiving biological prosthetic heart valves at the Korea University Hospital from January 1978 through October 1983 were analyzed. Out of 71 valves replaced, 64 were Carpentier-Edwards valves, 4 were Ionescu-Shiley valves, 2 were Angell-Shiley valves, 1 was Hancock valve. Early mortality within 30 days after operation was noted in 4 cases[6.4%]. There were no cases of valve-related early death. The 58 early survivors were followed-up for a total 387 patient-year over a period of 3 years to 12 years[Mean$\pm$S.D: 6.37$\pm$2.51 years] at the follow-up end of April 1991. During follow-up, seven patients died and late mortality rate was 12%. There were two major late complications: the one is thromboembolism[1.6% /patient-year], the other is primary tissue failure[2.76% /patient-year]. Ten patients underwent re-replacement of 13 tissue valves because of primary tissue failure[nine Carpentier-Edwards, two Ionescu-Shiley, two Angell-Shiley]. There was operative mortality. The probabilities of freedom from primary tissue failure were 95.4% and 75.3% at 5 and 10 years after operation respectively, The actuarial survival rates were 86.2% and 81.8% at 5 and 10 years after initial surgery respectively.

• 한국수소및신에너지학회논문집
• /
• 제26권2호
• /
• pp.192-198
• /
• 2015

Fault Tree Analysis to predict the lifetime in the design process of LNG compressor is considered. Fault Trees for P & ID of the compressor are created. Individual components that comprise the compressor are configured with the basic event. The failure rates in the PDS and OREDA are applied. As results, the system failure rate and the reliability over time are obtained. Further, the power transmission and the shaft seal system is confirmed to confidentially importantly contribute to the overall lifetime of the system. These techniques will help to improve the reliability of design of large scale machinery such as a plant.

• Geomechanics and Engineering
• /
• 제8권5호
• /
• pp.741-756
• /
• 2015

The prediction of impending collapse of deep tunnel is one of the most difficult problems. Collapse mechanism of deep tunnel in layered soils is derived using a new curved failure mechanism within the framework of upper bound theorem, and effects of seepage forces are considered. Nonlinear failure criterion is adopted in the present analysis, and the possible collapse shape of deep tunnel in the layered soils is discussed in this paper. In the layered soils, the internal energy dissipations along velocity discontinuity are calculated, and the external work rates are produced by weight, seepage forces and supporting pressure. With upper bound theorem of limit analysis, two different curve functions are proposed for the two different soil stratums. The specific shape of collapse surface is discussed, using the proposed curve functions. Effects of nonlinear coefficient, initial cohesion, pore water pressure and unit weight on potential collapse are analyzed. According to the numerical results, with the nonlinear coefficient increase, the shape of collapse block will increase. With initial cohesion of the upper soil increase, the shape of failure block will be flat, and with the lower soil improving, the size of collapsing will be large. Furthermore, the shape of collapsing will decrease with the unit weight decrease.

• Radiation Oncology Journal
• /
• 제11권2호
• /
• pp.285-294
• /
• 1993

A total of forty patients with resected N2 stage non-small cell lung cancer treated with postoperative adjuvant radiation therapy between Jan. 1975 and Dec. 1990 at the Department of Radiation Oncology, Yonsei University College of Medicine, Yonsei Cancer Center were retrospectively analysed to evaluate whether postoperative radiation therapy improves survival. Patterns of failure and prognostic factors affecting survival were also analysed. The 5 year overall and disease free survival rate were $26.3\%,\;27.3\%$ and median survival 23.5 months. The 5 year survival rates by T-stage were $T1\;66.7\%,\;T2\;25.6\%\;and\;T3\;12.5\%.$ Loco-regional failure rate was $14.3\%$ and distant metastasis rate was $42.9\%$ and both $2.9\%.$ Statistically significant factor affecting distant failure rate was number of postitive lymph nodes(>=4). This retrospective study suggests that postoperative radiation therapy in resected N2 stage non-small cell lung cancer can reduce loco-regional recurrence and may improve survival rate as compared with other studies which were treated by surgery alone. Further study of systemic control is also needed due to high rate of distant metastasis.

• International Journal of Reliability and Applications
• /
• 제3권1호
• /
• pp.1-16
• /
• 2002

In reliability engineering, the bathtub-shaped hazard rates play an important role in survival analysis and many other applications as well. For the bathtub-shaped, initially the hazard rate decreases from a relatively high value due to manufacturing defects or infant mortality to a relatively stable middle useful life value and then slowly increases with the onset of old age or wear out. In this paper, we present a new two-parameter lifetime distribution function, called the Loglog distribution, with Vtub-shaped hazard rate function. We illustrate the usefulness of the new Vtub-shaped hazard rate function by evaluating the reliability of several helicopter parts based on the data obtained in the maintenance malfunction information reporting system database collected from October 1995 to September 1999. We develop the S-Plus add-in software tool, called Reliability and Safety Assessment (RSA), to calculate reliability measures include mean time to failure, mean residual function, and confidence Intervals of the two helicopter critical parts. We use the mean squared error to compare relative goodness of fit test of the distribution models include normal, lognormal, and Weibull within the two data sets. This research indicates that the result of the new Vtub-shaped hazard rate function is worth the extra function-complexity for a better relative fit. More application in broader validation of this conclusion is needed using other data sets for reliability modeling in a general industrial setting.

• Korean Circulation Journal
• /
• 제53권1호
• /
• pp.34-46
• /
• 2023

Background and Objectives: Diabetes mellitus (DM)-associated heart failure (HF) causes high morbidity and mortality. In this study, we established a zebrafish larvae model for in vivo research on diabetic HF. Methods: DM-like phenotypes were induced by treating zebrafish larvae with a combination of D-glucose (GLU) and streptozotocin (STZ). HF was induced by treatment with terfenadine (TER), a potassium channel blocker. Additionally, myocardial contractility, motility, and viability were evaluated. Results: The zebrafish larvae treated with a combination of GLU and STZ showed significantly higher whole-body glucose concentrations, lower insulin levels, and higher phosphoenolpyruvate carboxykinase levels, which are markers of abnormal glucose homeostasis, than the group treated with only GLU, with no effect on viability. When treated with TER, DM zebrafish showed significantly less myocardial fractional shortening and more irregular contractions than the non-DM zebrafish. Furthermore, in DM-HF with reduced ejection fraction (rEF) zebrafish, a significant increase in the levels of natriuretic peptide B, a HF biomarker, markedly reduced motility, and reduced survival rates were observed. Conclusions: We established a DM-HFrEF zebrafish model by sequentially treating zebrafish larvae with GLU, STZ, and TER. Our findings indicate the potential utility of the developed zebrafish larvae model not only in screening studies of new drug candidates for DM-HFrEF but also in mechanistic studies to understand the pathophysiology of DM-HFrEF.

• Computers and Concrete
• /
• 제34권4호
• /
• pp.503-517
• /
• 2024

This study presents an analysis model to estimate the shear strength of a reinforced concrete (RC) member with corroded tensile reinforcements. The thick-walled cylinder theory was modified to fit the dual potential capacity model to reflect interdependent failure mechanisms, including the degradation effect of bonds in corroded tensile reinforcement. In the proposed model, it is considered that the shear failure of corroded RC members with no proper anchorage detail is primarily dominated by the flexural-bond mechanism, where insufficient bond strength is provided owing to corrosion damage. However, when tensile reinforcements are properly anchored in the end regions using end hooks or mechanical devices, it is assumed that the tied-arch action can be developed as a secondary shear transfer mechanism, even under severe corrosion damage. The proposed model was verified by comparison with shear test results of corroded RC members collected from the literature, and it appeared that the proposed model can estimate their shear strengths with a good level of accuracy, regardless of various anchorage details and corrosion rates in tensile reinforcements.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• 제27권2호
• /
• pp.178-183
• /
• 2001

Since the introduction of the concept of osseointegration, the success rate of dental implant has increased dramatically. So, the uses of dental implant in the treatment of partially or fully edentulous patients have played an important role in dental rehabilitation. Regardless of high success rate of dental implant, some amounts of fixtures cannot help failing. We can classify dental implant failure according to timing, causative factor, etc. This study is focused on dental implant fixture failure, occurring during preprosthetic stage. There are various reasons that cause implant failure on this periods, such as improper patient selection, poor bone quality, and periimplantitis, etc. We investigate the survival rate of 1058 fixtures, which installed in 306 patients in our clinic from January 1997 to December 1999, according to type, sex, location, fixture length and width, using Kaplan-Meier product-limit method and to compare each other with log-rank test. Overall survival rate was 96.80%, and 33 implants failed over the preprosthetic stage. Our survey data identified posterior location of mandible as being associated with implant failure(P<0.05).

• Journal of Chest Surgery
• /
• 제24권6호
• /
• pp.541-546
• /
• 1991

The Ionescu-Shiley bovine pericardial xenograft valve was the most common cardiac substitute valve at Seoul National University Hospital. Since the follow-up extended for longer than 10 years, a total of and consecutive 107 patients with double mitral and aortic valve replacement using this valve from May 1979 to June 1984 were studied for the long-term clinical results. Their ages were 34.0$\pm$11.9 years at surgery, and eight patients died within 30 days of surgery with operative mortality rate of 7.5%. Ninety-nine early survivors were followed up for a total of 488.1 patient-years[Mean$\pm$SD, 4.9$\pm$2.7 years], and nine died with the linearlized late mortality rate of 1.84% /patient-year[pt-yr]. They experienced major complications: thromboembolism, 0.615% /pt-yr bleeding, 0.205% /pt-yr; endocarditis, l. 639%/pt-yr; overall valve failure, 6.146% /pt-yr; and primary tissue failure, 1.639%/ pt-yr. The actuarial survival rates were 91.4$\pm$2.9% and 89.6$\pm$3.4% at postoperative 5 and 10 years, and the probability of freedom from thromboembolism was 95.8$\pm$2.5% at 10 years. The primary tissue failure began to occur from postoperative 6 years and the probabilities of freedom from structural valve failure were 80.2$\pm$7.9% and 62.3$\pm$12.7% at 8 and 10 years after surgery respectively. Although there was increasing number of patients with valve tissue failure after 6 years, the evidence of expected premature and accelerated valve degeneration among young population was not clear on the age-related analysis. And, no definite cumulative patient groups beyond the various age limits could be suggested for or against the use of this valve.

• 한국컴퓨터산업학회논문지
• /
• 제6권5호
• /
• pp.689-696
• /
• 2005

유한고장수를 가진 비동질적인 포아송 과정에 기초한 모형들에서 잔존 결함 1개당 고장 발생률은 일반적으로 상수, 혹은 단조증가 및 단조 감소 추세를 가지고 있다. 본 논문에서는 기존의 소프트웨어 신뢰성 모형인 Goel-Okumoto 모형과 Yamada-Ohba-Osaki 모형을 재조명하고 잔존 결함 1개당 고장 발생률이 단조 감소 추세를 가진 2모수 Kappa 분포를 이용한 Kappa모형을 제안하였다. 고장 간격시간으로 구성된 자료를 이용한 모수추정 방법은 최우추정법과 일반적인 수치해석 방법인 이분법을 사용하여 모수 추정을 실시하고 효율적인 모형 선택은 편차자승합과 콜모고로프 거리를 적용하여 모형들에 대한 효율성 입증방법을 설명하였다. 소프트웨어 고장 자료 분석에서는 고장수가 비교적 큰 실측 자료(고장수가 86)인 Allen P.Nikora 와 Michael R.Lyu가 인용한 SYS2 자료을 통하여 분석하였다. 이 자료들에서 카파 모형의 비교를 위하여 산술적 및 라플라스 검정, 편의 검정등을 이용하였다.