• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.103-110
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• 2021

Elastomeric bearings composed of flexible rubber materials and steel reinforcement plates are widely used for seismic retrofit of bridges due to their excellent vertical stiffness and flexible lateral stiffness. Especially, it has the advantages of simple construction and low cost. Chloroprene rubber, a type of rubber material, has greater resistance to aging than natural rubber, but its performance is also degraded due to various deterioration factors. Although these aging characteristics are not reflected in the seismic design standards and seismic performance evaluation guidelines, it is reasonable to reflect this when related studies are accumulated. For chloroprene rubber, accelerated heat aging test was performed with variables of heating temperatures and exposure time to analyze shear characteristics. As aging progresses the maximum shear stress and shear strain decrease. Also, the shear stiffness is greatly increased at the same shear strain.

• Journal of Korean society of Dental Hygiene
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• v.8 no.2
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• pp.77-92
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• 2008

This study was surveyed the knowledge and attitude toward the elderly in dental personnels, who play an important role in oral health of the elderly in the aging society, In order to arrange the basic data that is conducive to development in the mouth care of the elderly, the research was conducted from January 7 to February 14, 2008, targeting 270 dental personnels in Daejeon & Chungnam area, who are in charge of oral duties in the current clinic. As a result of analyzing so that questionnaire can be prepared with the self-administered questionnaire, the following results were obtained 1. The knowledge level on the elderly in dental hygienist was 13.47 marks out of 25-mark perfection. There was no difference in knowledge depending on job category and volunteer-work activity experience, And, there was no difference even depending on physical & physiological sphere, psychological sphere, and family & social sphere. 2. The attitude level toward the elderly in dental hygienist was 91.63 marks out of 150-mark perfection. Dental hygienist showed positive attitude in personality characteristic, emotional characteristic, and self-management ability by sphere, and showed statistically significant difference (p=0.011). 3. In case of having volunteer-work activity experience, the attitude level toward the elderly was 92.57 marks out of 150-mark perfection, A case of having volunteer-work activity experience showed positive tendency in emotional characteristic, self-management ability, and judgement-ability characteristic by sphere, And, the attitude toward family relation was indicated to be negative tendency, thus there was statistical significance(p=0.022). 4. As for the correlation between knowledge and attitude toward the elderly, dental hygienist was indicated to have high interest in the volunteer-work experience, the elderly education experience, and the elderly problem(r=0. 444). The knowledge and attitude toward the elderly had slightly positive correlation(r=0.155). Dental hygienists are being required gradually as the primary staff for the elderly people's dental care in the aging society. A continuous education is needed so that dental hygienists can have positive sight in understanding, knowledge, and attitude. And, the development in a mouth care program for the elderly in line with it is considered to be necessary.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1429_1430
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• 2009

본 연구에서는 7인치 샘플패널의 가속 Aging 실험을 통해 Aging time(24hr~529hr)변화에 따른 오방전 발생 Mechanism을 분석하고자 했다. 상온에서 Aging time변화에 따른 정마진, 휘도, Vt close curve를 측정 하였고 시간과 온도(고온: $70^{\circ}C$, 상온: $25^{\circ}C$, 저온: $-20^{\circ}C$)에 따른 Discharge time lag의 변화양상을 측정하였다. 그리고 Sustain pulse수의 조절을 통해 패널의 Priming 조건을 제어하면서 오방전 발생 확률을 수치적으로 측정하였다. 실험을 통해, 패널의 Aging time이 늘어남에 따라서 상판의 MgO층에서 Sputtering현상이 발생하여 MgO 잔재들이 하판의 형광체 표면을 덮는 등 방전 개시 전압의 변화가 오방전 발생에 주요한 원인임을 알 수 있었다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.10
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• pp.141-150
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• 2006

In this study we developed accelerated aging test cycle and equipment which can simulate domestic weather condition. And we proposed long term reliability assessment method for polymer housed distribution surge arresters. We carried out electrical and chemical analysis of the arresters which are used for accelerated aging test and outdoor exposure test. Through the analysis we verified the capability of the proposed method and we presented characteristic data for maintenance of domestic arresters.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.322-325
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• 2006

The nano/microstructure and mechanical properties of the eutectic regions in thixo and rheo cast A356 alloy parts were investigated using nano/micro-indentation and mechanical scratching, combined with optical microscopy and atomic force microscope (AFM).Most eutectic Si crystals in the A356 alloy showed a modified morphology as fine-fibers, however Si particles of network in eutectic region was formed quickly with aging time increase in thixo-cast. The aging responses of the eutectic regions in both the thixo and rheo cast A356 alloys aged at $150^{\circ}C$ for different times (0, 2, 4, 8, 10, 16, 24, 36, and 72 h) were investigated. Both Vickers hardness ($H_V$) and indentation ($H_{IT}$) test results showed almost the same trend of aging curves, the peak was obtained at the same aging time of 10 h.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.777-782
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• 2005

The importance of emergency diesel generator(EDG) has confirmed in the safety evaluation of PSA and the study on aging of EDG has been progressed actively as a part of the project of nuclear plant aging research in the U.S.A. As the result, the concept of performance evaluation is being transferred from statistical analysis of test results to performance monitoring and trending analysis for monitoring of aging and reliability. Recently, the study related aging characteristic and reliability for EDGS has begun in Korea. Consequently, the efficient performance monitoring based systematic and integrated monitoring and failure diagnostic technology is necessary. In the research, the knowledge basis of monitoring parameters for EDGS is constructed, and the prototype monitoring and diagnosis system applicable to Pielstick EDG is developed.

• Journal of Power System Engineering
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• v.20 no.5
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• pp.37-45
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• 2016

Exhaust gas recirculation has the advantage of being low-cost and easy to control of NOx emission. Therefore, it is most generally used to reduce NOx emission according to strengthen regulation. In the case of a non-road engine, such as the agricultural engine, since it mainly operate a middle or high-load state, NOx emission is decreased in accordance with the mapping range of the EGR rate, but results in an increase in the particulate matter which is caused to deposit and fouling problem of the EGR system. This problem has become an important issue for maintaining the performance of the engine, as well as emission performance. This study had examined the effects of cooler aging on the performance of heat transfer efficiency and NOx emission in non-road diesel engine. As a result of the EGR cooler aging during 200 hours engine operation, the cooling performance decreased about 25% compared with that of fresh cooler and the NOx emission increased about 14.6% on NRSC(non-road steady cycle) and 20% on NRTC(non-road transient cycle) compared with that of fresh cooler respectively.

• Nuclear Engineering and Technology
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• v.50 no.1
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• pp.88-96
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• 2018

Concerns over reliability assessments of the main components in nuclear power plants (NPPs) related to aging and continuous operation have increased. The conventional reliability assessment for main components uses experimental correlations under general conditions. Most NPPs have been operating in Korea for a long time, and it is predictable that NPPs operating for the same number of years would show varying extent of aging and degradation. The conventional reliability assessment does not adequately reflect the characteristics of an individual plant. Therefore, the reliability of individual components and an individual plant was estimated according to operating data and conditions. It is essential to reflect aging as a characteristic of individual NPPs, and this is performed through prognostics. To handle this difficulty, in this paper, the general path model/Bayes, a data-based prognostic method, was used to update the reliability estimated from the generic database. As a case study, the authors consider the aging for steam generator tubes in NPPs and demonstrate the suggested methodology with data obtained from the probabilistic algorithm for the steam generator tube assessment program.

• Proceedings of the Korean Reliability Society Conference
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• 2006.05a
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• pp.27-31
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• 2006

Rubber hoses for automobile radiators are apt to degraded and thus failed due to the influence of contacting stresses of air and coolant liquid under thermal and mechanical loadings. The aging behaviors of the skin part of the hoses due to thermo-oxidative and electro-chemical stresses were experimentally analyzed. Through the thermo-oxidative aging test, it was shown that the surface hardness IRHD(International Rubber Hardness Degrees) of the rubber increased with a considerable reduction of failure strain as the aging time and temperature were large. On account of the penetration of coolant liquid into the skin part the weight of rubber specimens influenced by electro-chemical degradation (ECD) test increased, whereas their failure strain and IRHD hardness decreased. The hardness decreased further as the test site on the hose skin approached to the negative pole.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2010.04a
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• pp.559-560
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• 2010