• Journal of Applied Reliability
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• 제18권1호
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• pp.1-7
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• 2018

Purpose: Maintaining appropriate operational availability (Ao) is a key element of combat victory, but estimates vary according to estimation methods. The purpose of this study is to improve the accuracy of estimating operational availability by tracing the changes of the weapon system's failure rate, repair rate, and the level of logistic support. Methods: In order to track the change in the operating availability, the MDT (mean down time) is modeled by adding the repair time and the ALDT (administration and logistic delay time) to the service time. Results: Using the field data of the weapon system A operated by the ROKAF, the failure rate follows a non-homogeneous Poisson process that changes with time, and it is modeled considering the changing repair rate and the logistic support time. Conclusion: The accuracy of the analytical results was verified by comparing the actual operating data with the estimated availability. The results of this study can be used to track and evaluate the availability in a realistic situation where the failure rate and maintenance rate continuously change in operating environment.

• The Transactions of the Korea Information Processing Society
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• 제4권6호
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• pp.1615-1624
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• 1997

In this paper, we propose and analyze various repair methods for a disk subsystem using mirroring. We also study the effects of the repair process that is invoked on disk faults on the mean response time of user disk requests. Finally, we analyze the effects of two different access patterns (uniform and non-uniform) on the repair process and performance. According to the results, average response times for non-uniform access pattern compared with uniform access pattern become shorter as the system load increases. Our simulation results show that the proposed repair algorithm with a short delay gives a better performance than the previous algorithms.

• Journal of Chest Surgery
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• 제28권10호
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• pp.906-911
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• 1995

From January 1991 to January 1995, 11 patients with aortic diseases underwent various surgical repairs. The age at operation ranged from 26 years to 63 years[ mean=50.9 years . The disease entities included 8 aortic dissections[ type I in 4, type II in 2 and type III in 2 cases , 2 Marfan`s syndrome with annuloaortic ectasia and 1 desecending thoracic aortic aneurysm The operative procedures we tried were 3 Bentall`s operation, 5 graft replacement of ascending aorta, and 3 graft interposition in descending thoracic aorta.Overall hospital mortality rate is 36.3%[4/11 . And causes of death are pump weaning failure in 2 cases and multiorgan failure in 2 cases. It was that 2 sternal dehiscence & mediastinitis, 1 acute renal failure, 2 hypoxic brain damages and 2 postoperative psychosis were complicated. Recently we tried surgical repair of aortic dissection five out of 6 cases using total circulatory arrest with deep hypothermia at 14$^{\circ}C$. Total circulatory arrest time ranged from 18 to 26 minutes[ mean 22.2 minutes , and mean aortic cross-clamping time was 48.2 minutes. One of 5 patient died on the 7th postoperative day due to multiorgan failure. Mortality of patients with TCA was 20%[1/5 , and it of remainders was 50%[3/6 . Our result for surgical repair using total circulatory arrest with deep hypothermia is satisfactory on the basis of our clinical data.

• Journal of the Korean Operations Research and Management Science Society
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• 제23권4호
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• pp.111-130
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• 1998

We propose an imperfect repair model which depends on external effects quantified by covariates. The model is based on the Brown-Proschan imperfect repair model wherefrom the probability of perfect repair is represented by a function of covariates. We are motivated by deficiency of the BP model whose stationarity prevents us from predicting dynamically the time to next failure according to external condition. Five types of function for the probability of perfect repair are proposed. This article also presents a procedure for estimating the parameter of the function for the probability of perfect repair, as well as the inherent lifetime distribution of the system, based on consecutive inter-failure times and the covariates. The estimation procedure is based on the expectation-maximization principle which is suitable to incomplete data problems. focusing on the maximization step, we derive some theorems which guarantee the existence of the solution. A Monte Carlo study is also performed to illustrate the prediction power of the model as well as to show reasonable properties of the estimates. The model reduces significantly the mean square error of the in-sample prediction. so it can be utilized in real fields for evaluating and maintaining repairable systems.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제10권2호
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• pp.41-47
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• 2006

The Renewal process and the Non-homogeneous Poisson process (NHPP) process are probably the most popular models for describing the failure pattern of repairable systems. But both these models are based on too restrictive assumptions on the effect of the repair action. For these reasons, several authors have recently proposed point process models which incorporate both renewal type behavior and time trend. One of these models is the Modulated Power Law Process (MPLP). The Modulated Power Law Process is a suitable model for describing the failure pattern of repairable systems when both renewal-type behavior and time trend are present. In this paper we propose Bayes estimation of the next failure time after the system has experienced some failures, that is, Mean Time Between Failure for the MPLP model. Numerical examples illustrate the estimation procedure.

• Advances in pediatric surgery
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• 제17권1호
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• pp.58-64
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• 2011

Minimally invasive techniques for pediatric inguinal hernia repair have been evolving in recent years. We applied the laparoscopic method to repair pediatric inguinal hernia using the techniques of sac transection and intra-corporeal ligation. Between November 2008 and August 2010, 67 pediatric patients (47 boys and 20 girls) with inguinal hernias were included in this study. Postoperative activities, pain, and complication were checked prospectively at regular follow-up. One patient presented with clinically bilateral hernia, and three patients had metachronous hernias. Thirty-two cases out of 63 patients with unilateral hernias had a patent processus vaginalis on the contralateral side. Mean operation time was $35{\pm}11.4$ minutes for unilateral hernias and $43{\pm}11$ minutes for bilateral hernias. There were no intra-operative complications. One patient had a small hematoma on the groin postoperatively, which subsided spontaneously in a week. Recurrence and metachronous hernia were not found at follow up. In summary, laparoscopic inguinal repair in children is safe, easy to perform and has an additional advantage of contralateral exploration. Further studies should include long term follow-up.

• Journal of Chest Surgery
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• 제55권1호
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• pp.55-60
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• 2022

Background: Robot-assisted repair of atrial septal defect (ASD) can be performed under either beating-heart or non-beating-heart conditions. However, the risk of cerebral air embolism (i.e., stroke) is a concern in the beating-heart approach. This study aimed to compare the outcomes of beating- and non-beating-heart approaches in robot-assisted ASD repair. Methods: From 2010 to 2019, a total of 45 patients (mean age, 43.4±14.6 years; range, 19-79 years) underwent ASD repair using the da Vinci robotic surgical system. Twenty-seven of these cases were performed on a beating heart (beating-heart group, n=27) and the other cases were performed on an arrested or fibrillating heart (non-beating-heart group, n=18). Cardiopulmonary bypass (CPB) was achieved via cannulation of the femoral vessels and the right internal jugular vein in all patients. Results: Complete ASD closure was verified using intraoperative transesophageal echocardiography in all patients. Conversion to open surgery was not performed in any cases, and there were no major complications. All patients recovered from anesthesia without any immediate postoperative neurologic symptoms. In a subgroup analysis of isolated ASD patch repair (beating-heart group: n=22 vs. non-beating-heart group: n=5), the operation time and CPB time were shorter in the beating-heart group (234±38 vs. 253±29 minutes, p=0.133 and 113±28 vs. 143±29 minutes, p=0.034, respectively). Conclusion: Robot-assisted ASD repair can be safely performed with the beating-heart approach. No additional risk in terms of cerebral embolism was found in the beating-heart group.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제42권2호
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• pp.345-348
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• 2017

MTTDL, a measure for reliability of distributed storage system, is analyzed for the case when double node repair is possible and compared with the single node repair cases.

• Journal of Chest Surgery
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• 제49권2호
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• pp.73-79
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• 2016

Background: The aim of this study was to report our early experiences with the endovascular repair of ruptured descending thoracic aortic aneurysms (rDTAAs), which are a rare and life-threatening condition. Methods: Among 42 patients who underwent thoracic endovascular aortic repair (TEVAR) between October 2010 and September 2015, five patients (11.9%) suffered an rDTAA. Results: The mean age was $72.4{\pm}5.1years$, and all patients were male. Hemoptysis and hemothorax were present in three (60%) and two (40%) patients, respectively. Hypovolemic shock was noted in three patients who underwent emergency operations. A hybrid operation was performed in three patients. The mean operative time was $269.8{\pm}72.3minutes$. The mean total length of aortic coverage was $186.0{\pm}49.2mm$. No 30-day mortality occurred. Stroke, delirium, and atrial fibrillation were observed in one patient each. Paraplegia did not occur. Endoleak was found in two patients (40%), one of whom underwent an early and successful reintervention. During the mean follow-up period of $16.8{\pm}14.8months$, two patients died; one cause of death was a persistent type 1 endoleak and the other cause was unknown. Conclusion: TEVAR for rDTAA was associated with favorable early mortality and morbidity outcomes. However, early reintervention should be considered if persistent endoleak occurs.

• Journal of the Korean Data and Information Science Society
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• 제18권2호
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• pp.535-541
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• 2007

The Non-homogeneous Poisson process is probably the most popular model since it can model systems that are deteriorating or improving. The renewal process is a model that is often used to describe the random occurrence of events in time. But both these models are based on too restrictive assumptions on the effect of the repair action. The Modulated Power Law Process is a suitable model for describing the failure pattern of repairable systems when both renewal-type behavior and time trend are present. In this paper we propose maximum likelihood estimation of the next failure time after the system has experienced some failures, that is, Mean Time Between Failure for the MPLP model.