• Journal of Chest Surgery
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• v.13 no.1
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• pp.1-12
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• 1980

In 1979 during the period of about 10 months 320 cases of open heart surgery were done in Seoul National University Hospital. There were 220 Congenital anomaly cases consisting of 113 acyanotic and 107 cyanotic varieties, and 1 O0 acquired cardiac lesions. Out of 100 acquired lesions 96 were valvular cues. Among 97 valve replacement cases 3 were Ebstein anomaly treated with plication and tricuspid valve replacement. Operative mortality rate for congenital anomaly was 10.6%, with 2.7% for acyanotic and 22.4% for cyanotic group. For acquired lesions over all operative mortality was 7%. Tetralogy of Fallot, ventricular septal defect, and atrial septal defect were the 3 main congenital anomalies, with 88 cues, 69 cases, and 27 cues respectively. In 61 simple ventricular septal defect without other anomalies operative mortality rate was 1.6%, in 27 atrial septal defect no death and, in tetralogy of Fallot 12.2%. Among 69 ventricular septal defect cases 19[27.5%] type I VSDs, after Kirklin-Becu classification, were found, rather high relative incidence of type I compared with Caucasian patients. Among 97 valve replacement cases 20 double valves were replaced-11 mitral with aortic and 9 mitral with tricuspid valves. Over all operative mortality rate for valve replacement was 8.2% with 3.3% in 61 mitral valve replace-merit. The over all operative mortality rate for 320 open heart surgery cases was 10.6%. Bubble type oxygenator and xenograft bioprosthetic valves were utilized In almost all cases.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.89-96
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• 2011

In this study, increasing the range of replacement rate of FA with concrete properties were analyzed to provide basic data of FA replacement 0-40 % and curing temperature $5-35^{\circ}C$ range. As a result of the increased fluidity in proportion to the increase in FA, but decreased air. Setting time delayed at replacement rate increases and low temperature, simple insulation temperature history of the FA up to 40 % replacement rate increases the maximum temperature was low $8^{\circ}C$, the highest temperature reaching time delay of 13 hours. FA replacement up stream of the curing temperature, compressive strength compared to the higher plane, it was found that improved strength development. In carbonation tests with increasing the replacement ratio of FA carbonation depth was increased. Therefore, continued research on carbonation measures was to be necessary.

• Journal of Chest Surgery
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• v.14 no.4
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• pp.369-380
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• 1981

In this department 504 cases of valve replacement were done since 1968 to the end of October 1981. Since October 31, 1978 to the end of October 1981 ,333 Ionescu-Shiley bovine pericardial xenograft bioprosthetic cardiac valves were replaced in 265 patients. There were 149 males and 116 female. Ages ranged from 2 to 63 years with 25 cases under 15 years of age. Among 265 cases of Ionescu valve replacement there were 157 MVR, 36 VAR, 6 TVR, 45 MVR+ AVR, 16 MVR+TVR and 5 MVR+AVR+TVR cases with mortality of 5.7%, 8.3%, 16.7%, 8.9%, 18.8% and 20% for each group respectively. Over all mortality rate in 265 Ionescu valve replacement cases was 7.9% with 21 total deaths. Main causes of operative deaths were due to LCOS in 7, bleeding in 5, arrhythmia in 3, air embolism in 2,and heart block in 2 cases. There were 12 late complications with 6 deaths. Over all long-term survival rate was 89.8%. MVR showed the highest long-term survival rate with 92.4%, and MVR+AVR+TVR the lower with 80% lower with 80%.Average follow-up period was 14 month duration. Twenty five congenital anomaly cases were operated with Ionescu-valve replacement that consisted of 7 VSD+AI, and 5 Ebstein anomaly cases with over all operative mortality of 16% and late mortality of 14.3% among 21 operative survivors. There were 25 Ionescu valve replacement cases in pediatric patients under the age of 15 years, with 4 operative deaths. Fourteen MVR, 7 AVR, and 3 TVR cases were found. Even though long-term follow-up study was short in postoperative period with total of 33~.0 months among 244 operative survivors ranging one to 36 months, the late survivors showed beneficial long-term results two thromboembolic episodes in 244 patients were found. More cases and longer term follow-up study are warranted for valve replacement in pediatric and TVR cases with Ionescu-valves which have advantageous hemodynamic structures compared with other bio-prosthetic heart valves.

• Journal of the Korean GEO-environmental Society
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• v.12 no.8
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• pp.33-38
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• 2011

Presently, domestic SCP method with low replacement ratio is required as alternative in order to overcome the profitability of the sand resource because of the deficiency phenomenon of the sand resource by the actual condition design and construction is made by SCP method with low replacement ratio more than 70% for the port construction in the safe side. Sand compaction pile(SCP) method has been mainly used to improve the properties of soft clay or loose sandy ground. In design of SCP at soft clay ground, it is very important to determine the stress concentration ratio of composite ground relevant to the area replacement ratio. In this study, 2-dimensional FEM analyses were carried out to evaluate the stress concentration ratio of composite ground depending upon the area replacement ratio. When the interpretation result replacement ratio was 30%, the stress assigned rate showed and as the replacement ratio was high, the stress assigned rate according to the sinkage showed the low stress assigned rate.

• Proceedings of the Safety Management and Science Conference
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• 2004.11a
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• pp.115-123
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• 2004

Replacement problems can be classed as either deterministic of stochastic. Deterministic problems are those in which the timing and the outcome of the replacement action are assumed to be known with certainty. Before proceeding with development of replacement models it is important to note that preventive replacement actions, that is, ones taken before equipment reaches a failed state, require two necessary conditions: (1) The total cost of the replacement must be greater after failure than before. (2) The failure rate of the equipment must be increasing. Equipment is subject to failure. On failure, one of two possible actions can be taken : repair or complete replacement of the failed equipment. In this paper, we proposed optimal overhaul, repair, replacement maintenance model with two-state.

• Journal of Applied Reliability
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• v.17 no.4
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• pp.316-324
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• 2017

Purpose: The purpose of this study is to determine the replacement cycle applied age replacement policy by reliability analysis based on railway vehicle contactor's failure history data. Method: We performed reliability analysis based on railway vehicle contactor's failure history data. We found a suitable distribution by goodness of fit test and predicted the reliability through estimation of scale & shape parameter. Considering cost information we determined the replacement cycle that minimize the opportunity cost. Result: Suitable distribution was the Weibull and scale parameter & shape parameter are estimated by reliability analysis. The replacement cycle was predicted and MTTF, $B_6$ percentile life were suggested additionally. Conclusion: We confirmed that failure rate type of railway vehicle contactor is degradation model having a time dependent characteristic and examined the replacement cycle in our country's operating environment. We expect that this study result contribute to railway operation agency for maintenance policy decision.

• Journal of Chest Surgery
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• v.29 no.10
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• pp.1090-1094
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• 1996

From February 1980 to September 1995, 31 children between 2 months and 15 years of age with mitral valve disease have undergone mitral valve replacement(MVR) at Yonsei Cardiovascular Center and com- plete follow-up has been obtained on 28 patients. There were 10 males and 18 females whose weight ranged from 4.9kg to 56kg. Two patients died early postopeiatively and the overall hospital mortality rate was 7.1%. These two were infants but there were no statistically significant difference in overall mortality among the age groups(p=0.13). The valve related complication rate was 57.1% in children younger than 5 years of age, which showed higher complication rate compared to older patients(p< 0.05). The bioprosthetic valve have been applied in 7 patients, and its 5-year valve failure-free survival rate was 50% . No mechanical valve failu e had occurred in 21 patients. In considering high re-replacement rate of bioprosthetic valve, mechanical valve is recommended despite its possibility of bleeding and thromboembolic complications. However, the consequences of increasing body size and long-term interposition of a rigid prosthesis in a growing heart will require second valve replacement. En conclusion, mitral valve replacement can be performed tilth satisfactory long-term survival in children, although younger mean age of the children has an important influence on early mortality and com- plication rate. And therefore mitral valve replacement in children younger than 5 years of age needs special consideration.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.99-104
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• 2009

For recycling of waste foundry sands, researchers recently try to recycle them rather than depend on reclamation, and are studying on how to combine waste foundry sands with cement and use them for various kinds of construction material as the effective recycling method of waste foundry sand. In this research, The ways to find the proper replacement rate of waste foundry sands and to make use of them were suggested through the experiments on the range to apply waste foundry sands with two levels of 1:3 mixture rate of W/C 43% and 50%. The research result showed that in terms of liquidity as the characteristic of unhardened mortar, as the replacement rate of waste foundry sands increased, its flow tended to decrease. The amount of air also displayed a similar tendency to that of liquidity in that the higher the replacement rate of waste foundry sands became, the lower it became. With regard to the solidity trait of hardened mortar, it increased when the waste foundry sands were replaced more, and the replacement of waste foundry sands caused increased initial solidity. As for the amount of water permeated and that of water absorbed as the water tight proofing properties, the amount of permeated water was proved to decrease because of the gap recharge effect by the fine powder of waste foundry sands, and the replacement of waste foundry sands in the structures requiring watertightness is concluded to be very effective.

• International Journal of Reliability and Applications
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• v.12 no.1
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• pp.41-48
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• 2011

This paper considers the maintenance model suggested by Jung and Park (2010) to adopt the Bayesian approach and obtain an optimal replacement policy following the expiration of NFRRW. As the criteria to determine the optimal maintenance period, we use the expected cost during the life cycle of the system. When the failure times are assumed to follow a Weibull distribution with unknown parameters, we propose an optimal maintenance policy based on the Bayesian approach. Also, we describe the revision of uncertainty about parameters in the light of data observed. Some numerical examples are presented for illustrative purpose.

• Journal of the Korean Data and Information Science Society
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• v.14 no.4
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• pp.889-901
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• 2003

In this paper, we consider the optimal replacement policies following the expiration of the combination warranty. The combination warranty can be divided into the renewing combination warranty and the non-renewing combination warranty. The criterion used to determine the optimal replacement period is the overall value function based on the expected cost and the expected downtime. Thus, we obtain the expected cost rate per unit time and the expected downtime per unit time for our model. And then the overall value function suggested by Jiagn and Ji(2002) is applied to obtain the optimal replacement period. The numerical examples are presented for illustrative purpose.