• Journal of Applied Reliability
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• v.18 no.2
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• pp.130-142
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• 2018

Purpose: The purpose of this study is to introduce regression method in the presence of competing risks and to show how you can use the method with hypothetical data. Methods: Survival analysis has been widely used in biostatistics division. But the same method has not been utilized in reliability division. Especially competing risks, where more than a couple of 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 utilized in the area of reliability or they are analysed in the wrong way. Specifically Kaplan-Meier method 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. In addition, sample competing risks data are analysed using cumulative incidence function along with some graphs. Lastly we compare cumulative incidence functions with regression type analysis briefly. Results: We used cumulative incidence function to calculate the survival probability or failure probability in the presence of competing risks. We also drew some useful graphs depicting the failure trend over the lifetime. Conclusion: This research shows that Kaplan-Meier method is not appropriate for the evaluation of survival or failure over the course of lifetime in the presence of competing risks. Cumulative incidence function is shown to be useful in stead. Some graphs using the cumulative incidence functions are also shown to be informative.

• Journal of the Korean Society of Safety
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• v.34 no.1
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• pp.14-20
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• 2019

This paper presents a safety assessment based approach for the safe operation for PCS(Power Conditioning System) of photovoltaic and energy storage systems, applying FTA. The approach established top events as power outage and a failure likely to cause the largest damage among the potential risks of PCS. Then the Minimal Cut Set (MCS) and the importance of basic events were analyzed for implementing risk assessment. To cope with the objects, the components and their functions of PCS were categorized. To calculate the MCS frequency based on IEEE J Photovolt 2013, IEEE Std. 493-2007 and RAC (EPRD, NPRD), the failure rate and failure mode were produced regarding the basic events. In order to analyze the top event of failure and power outage, it was assumed that failures occurred in DC breaker, AC breaker, SMPS, DC filter, Inverter, CT, PT, DSP board, HMI, AC reactor, MC and EMI filter and Fault Tree was drawn. It is expected that the MCS and the importance of basic event resulting from this study will help find and remove the causes of failure and power outage in PCS for efficient safety management.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.45 no.3
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• pp.78-89
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• 2022

The purpose of this study was to propose useful suggestion by analyzing preventive replacement policy under which there are minor and major failure. Here, major failure is defined as the failure of system which causes the system to stop working, however, the minor failure is defined as the situation in which the system is working but there exists inconvenience for the user to experience the degradation of performance. For this purpose, we formulated an expected cost rate as a function of periodic replacement time and the number of system update cycles. Then, using the probability and differentiation theory, we analyzed the cost rate function to find the optimal points for periodic replacement time and the number of system update cycles. Also, we present a numerical example to show how to apply our model to the real and practical situation in which even under the minor failure, the user of system is not willing to replace or repair the system immediately, instead he/she is willing to defer the repair or replacement until the periodic or preventive replacement time. Optimal preventive replacement timing using two variables, which are periodic replacement time and the number of system update cycles, is provided and the effects of those variables on the cost are analyzed.

• Geomechanics and Engineering
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• v.34 no.3
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• pp.285-301
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• 2023

During the construction of E75 highway through Grdelica gorge in Serbia, a major failure occurred in the zone of reinforced rock slope. Excavation was performed in highly anisotropic Paleozoic schist rock formation. The reinforcement consisted of the two rows of micropile wall with pre-stressed anchors. Forces in anchors were monitored with load cells while benchmarks were installed for superficial displacement measurements. The aim of the study is to investigate possible causes of instability considering different probability distributions of the strength of discontinuities and anchor bond strength by applying different optimization techniques for finding the critical failure surface. Even though the deterministic safety factor value is close to unity, the probability of failure is governed by variability of shear strength of anisotropic planes and optimization method used for locating the critical sliding surface. The Cuckoo search technique produces higher failure probabilities compared to the others. Depending on the assigned statistical distribution of input parameters, various performance functions of the factor of safety are obtained. The probability of failure is insensitive to the variation of bond strength. Different sampling techniques should yield similar results considering that the sufficient number of safety factor evaluations is chosen to achieve converged solution.

• Korean Journal of Construction Engineering and Management
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• v.13 no.3
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• pp.78-88
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• 2012

Previous construction failure researches were focused on the utilization plan based on failure information and development of failure classification. However, it has limitation to set up the plan for prevention of construction failure due to the lack of the number of on-site staffs. In order to prevent effectively construction failure, a prevention plan should be established through quantitative evaluation of failure causes. The purpose of this study is to suggest the assessment method for selection Critical Management Factor(CMF) and to analyze the CMF on the apartment structural framework using FMEA(Failure Mode and Effective Analysis) which is one of the methods of quantitative evaluation. The element of risk evaluation separated degree of failure risk and prevention respectively. The assessment method for selection of CMF can be utilized for planning proactive solutions on the failure, and it can be also selected critical factors about each project phases, type of facility and construction work.

• Journal of Chest Surgery
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• v.23 no.1
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• pp.95-106
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• 1990

Between May 1979 and April 1989, 213 patients with esophageal injuries visited the Department of the Thoracic and cardiovascular surgery Department, Yonsei University College of Medicine. There were 159 non perforated esophageal injuries accompanied by hematemesis, and 54 perforated esophageal injuries. The causes of non perforated esophageal injuries were Mallory-Weise Syndrome [%], corrosive esophagitis [54], esophageal carcinoma [4], foreign bodies [2], sclerotherapy due to esophageal varices [3]. The causes of perforated esophageal injuries were esophageal anastomosis[13], malignancies[17], esophagoscopy or bougienage[5], chest trauma[5], foreign bodies[5], paraesophageal surgery[3], others[6] In esophageal perforation due to foreign bodies, esophagoscopy or bougienage, there were 6 cervical esophageal perforations and 9 thoracic esophageal perforations. There were no mortalities in the treatment of the cervical esophageal perforations and 5 deaths resulted in the treatment of 9 thoracic esophageal perforations. And four of six patients with thoracic esophageal perforations died in the initiation of treatment over 24 hours, after trauma. There were another 12 deaths in the patients with chest trauma, malignancies or chronic inflammation except esophageal injuries due to foreign bodies or instruments during the hospital stay or less than 30 days after esophageal injuries. One patient with esophageal carcinoma died due to bleeding and respiratory failure after irradiation. Another patient with esophago gastrostomy due to esophageal carcinoma died of sepsis due to EG site leakage. One patient with a mastectomy due to breast cancer followed by irradiation died of sepsis due to an esophagopleural fistula. Two patients with Mallory-Weiss syndrome died; of hemorrhagic shock in one and of respiratory failure due to massive transfusion in the other. One patient with TEF died of respiratory failure and another died of pneumonia and respiratory failure. One patient with esophageal perforation due to blunt chest trauma died of brain damage accompanied with chest trauma.

• Korean Journal of Materials Research
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• v.26 no.10
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• pp.528-534
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• 2016

The aim of this paper is to consider the effect of the manufacturing processes on corrosion and centerline cracking of ancient bronze spoons. The ancient bronze spoons in question were made by several steps of forging, in reheated condition with cast ingots. The manufacturing method is similar to that of the modern spoons. The investigations include observations from light and scanning electron microscopes of the microstructure in terms of the crack propagation. Cracks in the centerline are caused by solute segregation in the center-line region; this solute is solidified in the final stage of bronze spoon manufacture. Centerline cracking is also caused by ${\alpha}$ phase segregation, accompanied by forged overlapping along the longitudinal direction of the spoons. A vertical stripe with cracks along the centerline of the spoon's width is formed by folding in the wrought process. The overlapping area causes crack propagation with severe corrosion on the spoon surfaces over a period of a thousand years. The failure mechanisms of ancient bronze spoons may be similar to that of modern spoons, and the estimation of the failure mechanisms of ancient spoons can be appropriate to determine failure causes for such modern spoons.

• Journal of Chest Surgery
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• v.25 no.1
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• pp.49-56
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• 1992

Total 20 cases of reoperation for mitral vavular disease, which had been performed during the period from May 1983 till October 1991, were reviewed. This study contained 1 case of previous balloon valvuloplasty and 1 case of death with bleeding from right ventricle during sternal reenrty. The average time intervals between reoperation and previous operation was 19 years in closed mitral commissurotomy[n=4], 7 years and 2 months in mitral valve replacement[n=10], 1 year and 8 months in mitral valvuloplasty[n=4], 3 years and 10 months in open mitral commissurotomy [n=2]. The cause of reoperation in closed mitral commissurotomy was progression of the disease, and residual stenosis with progression was the cause in open mitral commissurotomy cases. Technical failure might be the cause in the cases of valvuloplasty. In prosthetic valve replacement group the causes of reoperation were primary failure. Also two cases of suggested valve thrombosis and one case of failure of tricuspid annuloplasty was noted in prosthetic valve replacement group. The used valves for reoperation were Ionescue-Shiley in 3 cases, Bjork-Shiley in 6 cases, St. Jude Medical in 2 cases and CarboMedics in 8 cases. The mortality rate was 20%[n=4] and the causes of death were low output syndrome in 1 case, multiple organ failure in 2 cases and bleeding in 1 case during sternal reentry. During follow up 1 case of sudden death was observed.

• Journal of Convergence for Information Technology
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• v.7 no.6
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• pp.201-207
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• 2017

Failure of the power apparatus causes many inconveniences and problems due to power outage in all places using power such as industry and home. The main causes of faults in the Power Apparatus are aging, natural disasters such as typhoons and earthquakes, and animals. At present, the long high temperature status is monitored only by the assumption that a fault occurs when the temperature of the power apparatus becomes higher. Therefore, it is difficult to cope with the failure of the power apparatus at the right time. In this paper, we propose a power apparatus monitoring system as an efficient countermeasure against general faults except for faults caused by sudden natural disasters. The proposed monitoring system monitors the power apparatus in real time by attaching a thermal sensor, collects the monitored data, and predicts the failure using the accumulated information through learning using the artificial neural network. Through the learning and experimentation of artificial neural network, it is shown that the proposed method is efficient.

• Journal of the Korean Society of Safety
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• v.27 no.4
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• pp.90-95
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• 2012

To prevent similar accidents with the basis of industrial accidents already occurred in industrial plants, it would be possible only after true causes are grasped. Unfortunately, however, most accident investigation carried out with the basis of legal regulation failed to grasp them so that similar accidents have been repeated without cease. This research aimed to find out differences between results from conventional accident investigation and those from human error analysis, and to draw out effective and practical counter-plans against industrial accidents occurred repeatedly in an autoglass manufacturing company. As for analysis, about 110 accident cases that occurred for last 7 years were collected, and by adopting the Comprehensive Human Error Analysis Technique developed by the previous researchers, not direct causes but basic fundamental causes that might induce workers to human errors were sought. In consequence, the result showed that facility factors or environmental factors such as improper layout, mistakes in engineering design, and malfunction of interlock system were authentic major accident causes as opposed to managerial factors such as personal carelessness or failure to wearing personal protective equipments, and/or improper work methods.