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서용성,양정희 대한설비관리학회 1999 대한설비관리학회지 Vol.4 No.3
Replacement policies under minimal repair are useful in maintaining large, complex systems. In this paper, practical application of replacement polities under minimal repair are taken into consideration to provide maintenance managers with some guidelines. Three well-known policies, which called time-based model, failure numbers based model and hybrid type generalized model, are compared with respect to economics and real implementation. Moreover, sensitivity analyses are undertaken since there may exist estimation of parameters in real situations.
Impact of Statin Treatment on Strut Coverage after Drug-Eluting Stent Implantation
서용성,홍명기,김병극,신동호,김중선,고영국,최동훈,장양수 연세대학교의과대학 2015 Yonsei medical journal Vol.56 No.1
Purpose: To evaluate the effect of statin treatment on strut coverage after drug-eluting stent (DES) implantation. Materials and Methods: In this study, 60 patientswere randomly assigned to undergo sirolimus-eluting stent (SES) or biolimus-eluting stent (BES) implantation, after which patients were randomly treated with pitavastatin 2 mg or pravastatin 20 mg for 6 months. The degree of strut coveragewas assessed by 6-month follow-up optical coherence tomography, which was performed in 52 DES-implanted patients. Results: The percentages of uncovered struts were 19.4±14.7% in pitavastatin-treated patients (n=25) and 19.1±15.2% in pravastatin-treated patients (n=27; p=0.927). A lower percentage of uncovered struts was significantly correlated with a lower follow-up low-density lipoprotein (LDL) cholesterol level (r=0.486; p=0.009) and a greater decline of the LDL cholesterollevel (r=-0.456; p=0.015) in SES-implanted patients, but not in BES-implantedpatients. In SES-implanted patients, the percentage of uncovered struts was significantly lower among those with LDL cholesterol levels of less than 70 mg/dL after 6 months of follow-up (p=0.025), but no significant difference in this variable according to the follow-up LDL cholesterol level was noted among BES-implanted patients (p=0.971). Conclusion: Lower follow-up LDL cholesterol levels,especially those less than 70 mg/dL, might have a protective effect against delayedstrut coverage after DES implantation. This vascular healing effect of lower LDL cholesterol levels could differ according to the DES type.
A Newly Developed Stent Thrombus Related to Optical Coherence Tomography
서용성,김진선,이정명,손지영,김광준,김웅,김중선,고영국,최동훈,장양수 대한심장학회 2008 Korean Circulation Journal Vol.38 No.12
Optical coherence tomography (OCT) is a useful coronary imaging tool for atherosclerotic plaque characterization and stent evaluation. However, proximal balloon inflation is required in order to reduce signal changes caused by red blood cells and to acquire a clear image. One rare acute complication related to proximal balloon occlusion is micro-thrombus formation. We report a case of multiple, acute micro-thrombi forming after an OCT procedure, despite the use of appropriate prevention for intracoronary thrombus formation Optical coherence tomography (OCT) is a useful coronary imaging tool for atherosclerotic plaque characterization and stent evaluation. However, proximal balloon inflation is required in order to reduce signal changes caused by red blood cells and to acquire a clear image. One rare acute complication related to proximal balloon occlusion is micro-thrombus formation. We report a case of multiple, acute micro-thrombi forming after an OCT procedure, despite the use of appropriate prevention for intracoronary thrombus formation
서용성,박영택 成均館大學校 科學技術硏究所 1992 論文集 Vol.43 No.2
A replacement policy under two types of failures, repairable or irrepairable, is considered. In the policy, the system is replaced at the n-th failure if all the previous (n-1) failures are repairable; Otherwise it is replaced at the first irrepairable failure. Assuming that the j-th failure is repairable with probability a_j and minimal repairs are performed for repairable failures between replacements, we derive the expected cost rate through the application of NHPP in order to determine the optimal number n*. The policy includes some previous studies as special cases.
서용성 永同大學校 2001 硏究論叢 Vol.7 No.1
최근 들어 많은 기업에서는 고객확보를 위하여 보증기간을 연장하는 등 보증정책을 강화하고 있다. 그러나 소비자들은 보증기간 동안에 사용 가능한 제품일지라도 매력적인 신제품이 출현하게 된다면 기존 제품을 신제품으로 대체하게 될 것이다. 즉, 기존 제품에 비하여 신제품이 보다 고기능, 고품질이고 가격도 낮다면 사용 가능한 기존제품의 대체가 발생하게 된다. 본 연구에서는 무료 보증정책 하에서 대체현상을 고려한 기대 보증비용을 추정하고자 하였다. 수리 불가능한 제품의 고장에 대해서는 동일 제품으로의 교체를, 수리 가능한 고장에 대해서는 최소수리를 고려하였다. Recently, many companies have increased the warranty period for their products to capture more customers. But customers may dispose of them, even if they are usable, during the warranty period when an attractive new product appears. If the challenger product has better function and lower price in comparison with the defender, the disposal of usable products is likely to occur. Under the free warranty policy, expected warranty cost for an item with disposal is estimated in this paper. We assumed the minimal repair for repairable failures, and replacement with new one for irrepairable failures.
서용성,박영택 成均館大學校 科學技術硏究所 1995 論文集 Vol.46 No.2
Some systems such as early warning system should be inspected occasionally in order to detect failures. If the system is inspected too frequently, the inspection cost increases. On the other hand, if the number of inspections is reduced too much, the undetected system downtime cost increases. Thus, it is of interest to find effective inspection schedule, which minimizes the sum of inspection and downtime costs. Periodic inspection policies under imperfect inspection for the case are considered.
서용성 永同大學校 1997 硏究論叢 Vol.3 No.1
시스템의 고장이 검사에 의해서만 탐지되는 경우에는 검사를 하면서 사용하게 된다. 고장탐지를 위하여 검사를 너무 자주 한다면 검사에 소요되는 비용이 증가하고, 반대로 검사회수를 줄이면 고장방치에 의한 비용이 늘어난다. 그러므로 시스템을 경제적으로 운용하기 위해서는 일련의 검사일정을 구하는 것이 필요하다 본 연구에서는 첫 번째 검사시점 이후부터 정기적인 검사간격을 적용하는 수정된 정기 검사정책의 근사적인 비용함수를 도출하고, 검사일정을 보다 간단히 결정할 수 있는 방법을 제시하였다. 수치예를 통하여 본 연구에서 구하는 검사일정은 경제적이면서 현장 적용이 용이함을 보였다. Some systems such as early warning system should be inspected occasionally in order to detect failures. If a system is inspected too frequently, the inspection cost increases. On the other hand, if the number of inspections is reduced too much, the undetected system downtime cost increases. Thus it is of interest to find effective inspection schedule, which minimizes the sum of inspection and downtime costs. In this paper, an approximated cost function is dreived for the modified periodic inspection policy which peforms inspection periodically except the first inspection. And a simple method to determine the inspection schedule is presented. Numerical examples showed that the inspection schedule is easily applicable and cost-effective.