• Journal of the Korean Statistical Society
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• 제28권4호
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• pp.515-522
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• 1999

A repair process of a system consisting of both perfect repairs and minimal repairs is introduced. The type of repair, when the system fails, is determined by an embedded two state Markov chain. We study several stochastic properties of the process including the preservation of ageing properties and the monotonicities of the time between successive repairs. After assigning repair costs to the process, we also show that an optimal repair policy uniquely exists, if the underlying life distribution of the system has DMRL.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1448-1450
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• 2003

The suspension insulators are subjected to harsh environment in service for a long time. Long term reliability of the insulators is required for both mechanical and electrical performances. We studied an analysing method to find out a deformation of brittle porcelain with a thermal expansion of simulation analysis and experimental results show that cement volume growths affect severely to be mechanical failure ageing.

• 한국표면공학회지
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• 제29권6호
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• pp.880-883
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• 1996

Plasma Source Ion Implantation (PSII) technique was used for the hydrophilization or hydrophobization of polymer surfaces. Polymers were modified with different plasma gases such as oxygen, nitrogen, argon, and tetrafluoromethane, and for varying lengths of treatment time. Plasma ion treatment of oxygen, nitrogen, argon and their mixtures increased significantly the hydrophilic properties of polymer surfaces. More hydrophobic surfaces of polymers were formed after the treatment with tetrafluoromethane. A study of plasma source ion implanted polymers was performed using contact angle measurements and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The TOF-SIMS spectra and depth profile were used to obtain the information about the treated surfaces of polymers. The permanence of this technique could be evaluated with respect to ageing time. The surfaces treated with PSII gave better stability than other surface modification methods.

• 공업화학
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• 제19권4호
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• pp.427-431
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• 2008

해수 하에서 경시변화에 따른 경질 폴리우레탄 폼의 물성변화를 알아보기 위해 이소시아네이트 인덱스를 변화시키며 경질 폴리우레탄 폼(PUF)을 합성하였다. 해수 하에서 이소시아네이트의 인덱스가 90, 100, 130, 150으로 증가함에 따라 PUF의 인장강도는 각각 10%, 3%, 7%, 4%씩 감소하였고, 압축강도는 각각 7%, 6%, 5%, 4%씩 감소하였다. PUF의 물성저하를 규명하기 위해 PUF의 기공을 확인한 결과 기공의 변화는 없었다. 해수 하에서 PUF의 유리전이온도($T_g$), 인장 모듈러스는 증가하였는데 적외선 스펙트럼 분석결과 우레아, 알로파네이트, 바이우렛이 증가하는 것을 알 수 있었다. 해수 하에서 PUF는 가교도 증가하고 이로 인해 폼이 brittle하게 형성되어 $T_g$의 증가에도 불구하고 기계적 물성이 저하된 것으로 사료된다. 해수 하에서 PUF의 물성변화를 고찰하기 위해 만능시험기, 시차 주사 열량계, 주사 전자 현미경, 적외선 분광계를 이용하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.435-438
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• 2002

In this paper, the effect of surface tension, wettability, flow rate of contaminants with varying surfactant content and frequency of applied voltage on the tracking breakdown of epoxy insulating materials were investigated. As the flow rate of contaminant is increased, the surface resistivity is decreased, and the leakage current is increased, the time to tracking breakdown is decreased. It is found that time to tracking breakdown depends on the surface tension of contaminant, that is difference of wettability And as the frequency of applied voltage is increased, time to tracking breakdown decreased.

• International Journal of Railway
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• 제6권1호
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• pp.13-25
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• 2013

Railpad prevents damage of the tie and ballast by reducing the impact and high frequency vibration, which occurs when a vehicle load transfers to a tie. But elasticity of the railpad can decrease under vehicle load and over usable period. If that happens, railpad will become stiffer. Increase in stiffness of the railpad also translates into a rise in track maintenance cost because it accelerates the damage of the track. In this study, accelerated heat ageing test was performed to predict an expectable lifetime of the railpad. As a result, it was predicted to be about sixteen years at $25^{\circ}C$ that life time of railpad using NR rubber from Arrhenius relationship. Also, it was predicted to be about thirty-two days at $100^{\circ}C$. At this time, a standard rate of thickness change is approximately within 12%.

• 재활치료과학
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• 제10권4호
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• pp.81-94
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• 2021

목적 : 반응시간은 인지 능력과 노화에 대한 연구에서 중요한 역할을 한다. 본 연구는 컴퓨터 프로그램을 이용한 인지반응시간(Cognitive response time: CRT) 검사를 실시하여 정보처리에 대한 인지 능력의 영향을 확인하는 것을 목적으로 한다. 연구방법 : 대구 및 경북 지역에 거주하고 있는 65~79세의 일반 노인(Normal elderly: NE) 30명과 기억성 경도인지장애(Amnestic mild cognitive impairment: aMCI) 노인 30명을 대상으로 하였다. 결과 분석은 통계 분석 프로그램 R 4.0.2(University of Auckland, Auckland, New Zealand)를 사용하였다. 결과 : CRT 검사의 세 개 하위 영역에서의 총 반응시간은 집단 및 연령에 따라 유의한 차이를 보였고, 오류율은 일부 하위 영역에서 연령 또는 집단에 따라 유의한 차이를 보였다. aMCI 집단의 CRT 검사 수행력은 전반적인 인지 및 기억 검사의 수행력과 유의한 상관성을 갖는 것으로 나타났다. 결론 : 인지반응시간을 측정하는 CRT 검사를 통해 노화 및 인지 능력에 따른 정보처리과정과 처리속도의 변별적 수행을 관찰할 수 있었다. 또한, 이 검사의 수행력이 전반적인 인지 및 기억 검사와 유의한 상관성을 갖고 있음을 확인하였다. 따라서 지역사회 일반 노인의 초기 인지장애를 예측하는 간편 도구로써 CRT 검사가 의미있게 사용될 수 있기를 기대한다.

• 지역사회간호학회지
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• 제28권1호
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• pp.13-22
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• 2017

Purpose: The aim of this study is to examine the reciprocal causal relationship between social activities and health with reference to the cognitive function level among community-dwelling older adults. Methods: We conducted a longitudinal data analysis using the $4^{th}$ (Time 1) and $5^{th}$ (Time 2) waves from the Korean Longitudinal Study of Ageing adopting cross-lagged panel analysis (CLPA). Results: A total of 3,473 community-dwelling older adults were included in the analysis: 2,053 in the normal cognitive function group, 912 in the mild cognitive impairment group, and 508 in the moderate to severe cognitive impairment group. The CLPA revealed that higher levels of social activities at Time 1 significantly influenced better subjective health perception at Time 2 in all three groups. In addition, better subjective health perception at Time 1 significantly influenced higher levels of social activities at time 2 only in the normal cognitive function group. Conclusion: This study demonstrates that participating in social activities has positive effects on health regardless of the cognitive function level in community-dwelling older adults. This finding suggests that there is a need to develop strategies that can be used to encourage older adults with cognitive decline to maintain participation in social activities.

• PNF and Movement
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• 제11권1호
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• pp.55-62
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• 2013

Purpose : This study was assessed muscle activity and onset time in trunk and upper extremity on functional reaching. Methods : The participant was 18 female(young 10, old 8). As functional reaching, we collection data by using EMG(MP150) on transverse abdominis, external oblique, erector spinae, deltoid middle and serratus anterior. Results : 1) In functional reaching, transverse abdominis, external oblique, erector spinae and deltoid middle muscle activity was augmented on old female(p>.05). Serratus anterior was augmented on young female(p>.05). 2) In functional reaching, transverse abdominis and erector spinae muscle onset time is significantly faster old female than young female(p<.05). External oblique and serratus anterior muscle onset time is faster old female than young female(p>.05). 3) As increase of age muscle activity of external oblique was more increased that we found .511 a coefficient correlation and onset time more faster on transverse abdominis and erector spinae were each -.492 and -.554 coefficient correlation. Conclusion : The muscle activity and onset time was difference in functional reaching according to ageing and task context. It is necessary concentration and attention to old female than young female. Therefore, these results suggest that importance of anticipatory postural control and selective strategy of postural control.

• 한국전기전자재료학회논문지
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• 제12권1호
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• pp.1-10
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• 1999

In this paper, we have investigated the effects of the environmental factors on Low Molecular Weight (LMW) silicone fluid contents existing in high temperature vulcanized (HTV) silicone rubber sample, using dipping method and contact angle, current measurement. Artificial treatments such as immersion in water, elevated temperature, UV irradiation and dry band arcing under salt-fog condition are selected as the environmental factors. This results will be helpful to investigate the degradation with time and to expect a life time, because the LMW silicone content, which is important to recovery the hydrophobicity of silicone rubber surface, show different results by each environmental factors.