• Journal of the Korea Institute of Building Construction
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• v.5 no.2 s.16
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• pp.107-113
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• 2005

This study analyzes remaining repair rate and applied repair rate with the presentation of profit model for the purpose of pursuing maximization of added value through remodeling of apartment house. Objects of remodeling and item applying the whole replacement of functionality evaluation items include exterior of building (3 items maintaining the current conditions, 8 items requiring the whole replacement), water supply/sanitary/gas/ventilation facilities (6 items maintaining the current conditions, 6 items requiring the whole replacement, electric/fire fighting/elevator facilities (8 items maintaining the current conditions, 20 items requiring the whole replacement) and heating/water heater facilities (2 items requiring the whole replacement).

• International Journal of Reliability and Applications
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• v.10 no.1
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• pp.33-42
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• 2009

In most of literatures of age replacement policy, the authors consider the case that a new item starts operating at time zero and is to be replaced by new one at time T. It is, however, often to purchase used items because of the limited budget. In this paper, we consider age replacement policy of a used item whose age is $t_0$. The mathematical formulas of the expected cost rate per unit time are derived for both infinite-horizon case and finite-horizon case. For each case, we show that the optimal replacement age exists and is finite and investigate the effect of the age of the used item.

• International Journal of Reliability and Applications
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• v.18 no.1
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• pp.1-8
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• 2017

In this paper, we study an extended warranty model under minimal repair-replacement warranty (MRRW) which is suggested by Park, Jung and Park (2013). Under MRRW policy, the manufacturer is responsible for providing the minimal repair-replacement services upon the system failures during the warranty period. And if the failure occurs during the extended warranty period, only the minimal repair is conducted. Following the expiration of extended warranty, the user is solely responsible for maintaining the system for a fixed length of time period and replaces the system at the end of such a maintenance period. During the maintenance period, only the minimally repair is given for each system failure. The main purpose of this article is to suggest the extended warranty and replacement model with MRRW. Given the cost structures incurred during the life cycle of the system, we formulate the expected cost and the expected length of life cycle to obtain the expected cost rate.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.175-176
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• 2014

Recently, in the apartment house of our country, office building, apartment, and etc, the lightweight composite panel is much used as the partition wall body. This is due to be very convenient when the execution and dismantling is convenient and it forms the space which the consumer in the space desires. Therefore, in this research, the thermal conductivity property of the lightweight composite panel core according to the replacement ratio variation of the pearlite tries to be analyze. As the density test result and replacement ratio of the pearlite increased, the density showed the tendency to rise. the replacement ratio of the pearlite increased, the absorption rate showed the tendency to fall. And this is determined that absorption rate is degraded due to the increase in the density. the thermal conductivity test result and pearlite replacement ratio increased, the tendency that the thermal conductivity increases was represented.

• Journal of Chest Surgery
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• v.19 no.1
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• pp.108-115
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• 1986

During 12 years period from 1974 to 1985, 76 valve replacement procedures were performed at Seoul National University Hospital in 67 pediatric patients aging up to 15 years [mean 12.3 years] and it was 7.3% of total valve replacement procedures in same period. Sixty seven patients were composed of 44 males and 23 females. Of the 67 patients, 43 patients had acquired valve lesions and 24 patients congenital valve lesions. Sixty cases received single valve replacement, 7 cases double or triple valve replacement and 9 cases redo-valve replacement. Sixty seven patients received 84 valves [65 bioprosthetic valves and 19 prosthetic valves by] 76 operations, Sixty three of 65 bioprosthetic valves had been replaced before 1983 and 15 of 19 prosthetic valves in recent 2 years. Eleven patients [14.6%] died within one month post-operatively and 8 patients [10.5%] during the follow-up period with the overall mortality rate of 25.1%. There were early post-operative complication of 23 cases [30.3%] and late post-operative complication of 27 cases [35.3%] with the total complication rate of 65.8%. In 58 patients received bioprosthetic valves, there were 14 cases of restenosis of replaced valves. Of the 14 cases of bioprosthetic valve restenosis, 8 cases received redo-valve replacement procedures without mortality in 1 5/12-5 years after initial operation but 4 cases died without reoperation and 2 cases lost during follow-up. The overall mortality and complication rate were still high but they markedly decreased during recent 2 years. So, in spite of its containing many problems, valve replacement in children is becoming safe and useful procedure in whom valve reconstructive procedures are impossible.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.107-114
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• 2003

Among soft ground treatment methods with granular soil used in domestic, the sand compaction pile method has been utilized greatly, but, as a result of exhaustion of sand and increase of unit cost, the necessity of an alternative method is suggested. In this study, the static load tests for crushed-stone compaction piles which were constructed on test field were performed. Based on test results, stress concentration ratios between the crushed-stone compaction pile and the soft ground were investigated and estimated. At loading pressure, settlement showed decreasing tendency as replacement rate increases. At replacement rate of 20%, yield pressure was smaller but, at replacement rates of 30% and 40%, settlement and yield pressure were similar. The stress concentration ratio was within the range of 1.7 to 3.0 and it was higher as replacement rate increased.

• Journal of Chest Surgery
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• v.16 no.4
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• pp.602-614
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• 1983

Six hundred fourteen consecutive cases of bioprosthetic cardiac valve replacement performed during the period from March 1976 through December 1982 were reviewed. A total of 748 tissue valves [534 Ionescu-Shiley valves, 144 Hancock valves, 46 Angell-Shiley, and 24 Carpentier-Edwards] were implanted in 610 patients. Of these, 477 had single valve replacements [403 mitral, 60 aortic, and 14 tricuspid] including three REDO MVR and one REDO AVR. The remaining 129 had double valve replacements [95 AVR and MVR and 34 MVR and TVR] and 8 had triple valve replacement.592 cases were evaluated. Overall early mortality rate [within 30 days of operation] was 7.1% [6.2% in single valve replacement, 10.2% in double valve replacement, and 16.7% in triple valve replacement]. Leading causes of mortality were low cardiac output or myocardial failure and ventricular arrhythmias. The follow-up period was from one month to 7 years with a cumulative follow-up of 906.6 patient-years [mean 1.53 years]. The late mortality was 1.6%, 3.9%, 0%, 2.6%, 6.6% and 2.0% per patient-year for MVR, AVR, TVR or triple valve replacement, AVR+MVR, MVR+TVR and total, respectively. Actuarial analysis of late results including early mortalities indicates an expected survival rate of 87.6+1.8% at 3 years and 85.92.4% at 7 years for all cases. We also analyzed actuarial survival rate between groups of each valve replacement [AVR, TVR, Double valve, and Triple valve] and the tissue valve groups in MVR. We experienced 7 cases [0.77% per patient-year] of confirmed endocarditis, two of which were fatal. Valve failure-free rates calculated according to the confirmed cases were 97.5% at 4 years, 87.5% at 7 years, and 88.3% at 6 years for Ionescu-Shiley, Hancock and Angell-Shiley valves, respectively. The occurrence rate of thromboembolism was 2.0% per patient-year in total cases, although almost all the patients were given anticoagulant therapy for one year. The occurring rate in MVR was 1.5% and 2.7% per patient-year for Ionescu-Shiley and Hancock valve groups, respectively. The difference in actuarial rate free from thromboemboli between Ionescu-Shiley and Hancock groups was statistically significant [P value less than 0.001]. Thromboembolic events beyond the period of anticoagulation therapy mainly occurred in patients with atrial fibrillation. The actuarial thromboemboli free survival was 95.71.4% at 3 years and 80.17.3% at 7 years. The incidence of hemorrhagic complications was 1.2% per patient-year [fatality 0.55% per patient-year] for anticoagulated patients. Although our clinical data favorably compares with results from other reports, our results suggest that anticoagulant therapy be given on a short-term basis or not at all to hemodynamically stable patients. Long-term therapy with antiplatelet drugs is probably inevitable with patients who have thromboembolic risk factors [such as atrial fibrillation].

• Journal of Korean Institute of Industrial Engineers
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• v.33 no.1
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• pp.70-75
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• 2007

This paper discusses condition based preventive replacement for deteriorating systems. The system continuouslydeteriorates in time and fails at any deterioration level which is always monitored, It is replaced at failure or atsome deteriorated level preventively before failure. The deterioration process is represented by a Weibulldistribution with a time-linear scale parameter. The cost rate function is formed considering replacement costand opportunity loss cost and deterioration dependent failure distribution, If the system has an increasingdeterioration dependent failure rate, the optimal deterioration level for preventive replacement can be determinedfrom minimizing the cost rate. An illustrative example is given for a Weibull deterioration dependent failuredistribution.

• International Journal of Reliability and Applications
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• v.18 no.1
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• pp.9-20
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• 2017

In this paper, we consider a renewable repair-replacement warranty strategy with age-dependent minimal repair service and propose an optimal maintenance model during post-warranty period. Such model implements the repair time limit under warranty and follows with a certain form of system maintenance strategy when the warranty expires. The expected cost rate is investigated per unit time during the life period of the system as for the standard for optimality. Based on the cost design defined for each failure of the system, the expected cost rate is derived during the life period of the system, considering that a renewable minimal repair-replacement warranty strategy with the repair time limit is provided to the customer under warranty. When the warranty is finished, the maintenance of the system is the customer's responsibility. The life period of the system is defined and the expected cost rate is developed from the viewpoint of the customer's perspective. We obtain the optimal maintenance strategy during the maintenance period by minimizing such a cost rate after a warranty expires. Numerical examples using field data are shown to exemplify the application of the methodologies proposed in this paper.

• Journal of Chest Surgery
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• v.27 no.2
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• pp.114-121
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• 1994

St. Jude Medical cardiac valve replacement was performed in 135 consecutive patients from Aug.1986 to Dec. 1991.72 had mitral, 28 had aortic, 1 had tricuspid and 34 had double valve replacement. The hospital mortality rate was 4.4% & the late mortality rate was 3.7 %. Follow-up was done on 115 surviving patients:mean follow-up period was 29.78 $\pm$ 18.32 months. Paravalvular leakage was observed in two patients, possible prosthetic valvular endocarditis wasobserved in one patient and other specific valve-related complications were none. The overall actuarial survival rate at 6 years were 91.6% in total, 96.4% in aortic, 95.5 % in mitral and 81.9 % in double valve replacement.We concluded, therefore that good clinical results and a low complication rate could be achieved with St. Jude Medical valve in short-term follow-up & long-term follow-up was also necessary.