• International Journal of Reliability and Applications
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• v.5 no.2
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• pp.81-103
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• 2004

Improvements of a bridge network system are studied in this paper. Then equivalence between different improved designs of the bridge network system is discussed. Three different methods are used to get different better designs of the network in the sense of having higher reliability and mean time to failure. Then two different types of reliability equivalence factors of the system are derived. It is assumed here that the failure rates of the system's components are identical and constant. The reliability functions and mean time to failure of the original and improved designs of the network are derived. Comparison between the mean time to failures of the original system and improved designs of the system are presented. Numerical studies and conclusion are presented in order to explain how one can apply the the theoretical results obtained.

• Nuclear Engineering and Technology
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• v.55 no.11
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• pp.4146-4158
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• 2023

This paper proposes a combined plastic and creep constitutive model of A533B1 pressure vessel steel to simulate progressive deformation of nuclear pressure vessels under severe accident conditions. To develop the model, recent tensile test data covering a wide range of temperatures (from RT to 1,100 ℃) and strain rates (from 0.001%/s to 1.0%/s) was used. Comparison with experimental data confirms that the proposed combined plastic and creep model can well reflect effects of temperature and strain rate on tensile behaviour up to failure. In the companion paper (Part II), the proposed model will be used to simulate OECD lower head failure (OLHF) test data.

• Journal of Korean Institute of Industrial Engineers
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• v.4 no.2
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• pp.83-90
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• 1978

Frequency and duration method is a well known model in the generation reserve reguirement planning area. In this paper, the model is used to measure the effect of increased failure rates of individual generating units on the capability of power system.

• Journal of Korean Institute of Industrial Engineers
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• v.21 no.4
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• pp.629-638
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• 1995

It is shown that the reliability function of an n-component parallel system is equivalent to that of n-component stand-by system if we increase the exponential failure rates of the parallel system's components in proportion to the increasing load per surviving component.

• The Korean Journal of Applied Statistics
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• v.17 no.2
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• pp.253-267
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• 2004

In some clinical trials, one may see that a significant fraction of patients are cured and their original disease does not recur even after termination of treatment and pro-longed follow-up. This situation occurs frequently in pediatric cancer trials where there are excellent therapeutic results. In such cases, interest concentrated on the difference of cure rates rather than other types of differences in failure distributions. Various authors have investigated the parametric and nonparametric methods for testing the difference of cure rates. In this study, we compare by simulation the power and size of a parametric test and five nonparametric tests in a various range of the alternatives, censoring rates and cure rates. Our objectives are to determine if any test was preferable on the basis of size and power in various situation, and to investigate the effect of the model misspecification.

• Clinical and Experimental Reproductive Medicine
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• v.21 no.1
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• pp.21-29
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• 1994

Subzonal insemination(SUZI) has been proposed for patients with severe male factor and previous fertilization failure. However, very low fertilization rates still persisted. The aims of this study were firstly, to examine the relationships between the fertilization rate and sperm parmeters, sperm incubation media and time, secondly, to evaluate the outcome of 119 cycles of SUZI applied the modified sperm preparation method. The fertilization rates were influenced more sensitively by sperm preincubation media and time than by sperm parameters. According to preincubation media and time, the fertilization rates were 43.3% in 50% follicular fluid (HFF), 36.6% in 10% fetal cord serum(FCS), and with the time, increased in FCS, but decreased in HFF. In regrd with sperm parameters, the fertilization rates were 42.9% in normal and 37.6% in subnormal group. The best results were obtained from SUZI by the spermatozoa incubated in 50% HFF for 6-8 hours. So we tried 119 cycles of SUZI(normal; 39 cycles, subnormal; 80 cycles) using the preparation method of 6-8 hour incubation in 50% HFF. There were no signigicant differences in the fertilization rates between normal(125/269, 46.4%) and subnormal sperm(264/635, 41.6%). Contrary to the fertilization rates, pregnancy outcomes were different between both groups. Better results obtained from the subnormal group than the normal in the number of transferred embryos, that of good embryos, and developmental rate of the fertilized eggs. The pregnancy rates per transfer were totally 13.3%(13/98),20.0%(13/65) in subnormal group. In the normal group, 2 patients showed ${\beta}$-hCG positive, but resulted in chemical pregnancy. Of 13 clinical pregnancies, two aborted, 6 on-going, and 5 delivered. In conclusion, SUZI is an effective technique to overcome fertilization failure for male factor and unexplained. The fertilization rate is influenced by sperm parameters, sperm incubation media and time. Also the quality of oocytes might be important for pregnancy as same as that of sperm.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.10 no.16
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• pp.89-100
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• 1987

In this paper, we present the effect of buffer storage capacity un two-stage transfer lines in such a way as to introduce the production rate to be reduced which is called a Slowed Down(SD) state. A Markov model is used to establish a formulation for the analysis of the delays associated with the stage to be starved or blocked. Operating policies are proposed by analyzing the effect of the decision variables such as the production rates, the failure rates, buffer capacities and SD rates through computer simulation experiments.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.1
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• pp.7-14
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• 2006

The finite failure NHPP models proposed in the literature exhibit either constant, monotonic increasing or monotonic decreasing failure occurrence rates per fault. In this paper, we propose the Erlang reliability model, which can capture the increasing nature of the failure occurrence rate per fault. Equations to estimate the parameters of the Erlang finite failure NHPP model based on failure data collected in the form of inter-failure times are developed. For the sake of proposing shape parameter of the Erlang distribution, we used to the goodness-of-fit test of distribution. Data set, where the underlying failure process could not be adequately described by the existing models, which motivated the development of the Erlang model. Analysis of the failure data set which led us to the Erlang model, using arithmetic and Laplace trend tests, goodness-of-fit test, bias tests is presented.

• 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 Korean Neurosurgical Society
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• v.62 no.2
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• pp.217-224
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• 2019

Objective : We attempted to discover that Ankylosing spondylitis (AS) has a comprehensive relationship with congestive heart failure and death. Methods : We used a nationwide database managed by the Korean National Health Insurance Service from 2010 to 2014. Twelve thousand nine hundred eighty-eight patients with a diagnosis of AS and 64940 age- and sex- stratified matching subjects without AS were enrolled in the AS and control groups. Incidence probabilities of 6 years congestive heart failure and death in each group were calculated. The Cox proportional hazard regression analysis was used to estimate the hazard ratio. We divided the AS and control groups into subgroups according to sex, age, income, and comorbidities. Results : During the follow-up period, 102 patients (0.79%) in the AS group and 201 patients (0.32%) in the control group developed congestive heart failure (p<0.0001). In addition, 211 (1.62%) subjects in the AS group died during the follow-up period compared to 639 (0.98%) subjects in the control group (p<0.0001). The adjusted hazard ratio of congestive heart failure and death in the AS group was 2.28 (95% confidence interval [CI], 1.80-2.89) and 1.66 (95% CI, 1.42-1.95), respectively. The hazard ratios of congestive heart failure and death were significantly increased in all of the subgroups. Conclusion : The incidence rates of congestive heart failure and death were increased in AS patients.