• 전기학회논문지
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• 제59권10호
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• pp.1832-1838
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• 2010

Aging of transformer insulating material in natural ester insulating oil is compared to that in conventional transformer oil. Aging of insulating paper and insulating oil have been studied by performing accelerated thermal aging test. Sealed aging test vessels containing cooper, laminated core, Kraft paper and insulating oil(natural oil or mineral oil) were aged at $140^{\circ}C$ for 500, 1000, 1500 and 2000 hours. Insulating oils after aging are investigated with total acid number, breakdown voltage and viscosity. Also, degradation of insulating paper after aging is determined using breakdown voltage and mechanical strength. Accelerated aging studies demonstrate a slower aging rate for natural ester insulating oil compared to the rate for conventional mineral oil.

• 대한토목학회논문집
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• 제33권3호
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• pp.855-864
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• 2013

지진격리장치로서 천연고무받침의 동적 특성은 주재료인 고무의 동적거동과 비선형 성질에 의존하고 있다. 역학적이나 환경적인 영향으로 인해 고무재료에 노화가 진행되고 결국에는 손상이 불가피하게 발생하게 된다. 고무재료의 노화에 주원인은 높은 온도에서 반응열로 인한 산화반응으로 알려져다. 이에 따라 천연고무받침에 대한 가속 열 노화실험을 수행하여 열 노화 전 후에 대해 받침의 특성값을 상호 비교하였다. 실험 결과 열 노화 현상은 전단강성과 에너지 감쇠 그리고 등가감소계수에 영향이 있음을 알 수 있었다. 또한 열 노화에 의한 동적특성의 저하를 실제 교량에 적용하여 천연고무받침의 열 노화가 교량의 내진성능에 미치는 영향을 수치해석을 통해 비교분석하였다. 그 결과 천연고무받침에 대하여 열 노화에 따른 기본 특성변화가 교량의 내진성능에 미치는 영향은 크지 않음을 알 수 있었다.

• 한국전기전자재료학회논문지
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• 제20권8호
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• pp.691-696
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• 2007

In this study accelerated aging test equipment was developed to simulate domestic weather condition for accelerated aging test of polymer housed distribution surge arresters. Polymer arresters were aged for 3,000 hours by this test equipment and chemical and electrical characteristics analysis of surge arresters were conducted after aging test. In addition, performance assessment of outdoor installed arresters for 3 years was conducted to compare aging effect between accelerated aging test and natural aging. Through this experiment it is verified that the capability of the proposed aging test for simulating natural aging and the housing material and disconnector of domestic polymer arresters can be deteriorated by the long time field operation.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.81-81
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• 2010

This paper presents results of experimental investigations on natural ester regarding the breakdown strength. Aging of insulating material in a pole transformer has been studied by performing accelerated thermal aging test. Sealed aging test vessels containing copper, laminated core, Krapt paper and insulating oil(Natural oil and Mineral oil) were aged at $140^{\circ}C$ for 30days. Compared to the conventional transformer oil, electric property of the natural ester fluid is excellent.

• Elastomers and Composites
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• 제21권3호
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• pp.205-212
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• 1986

The dielectric properties of natural rubber are very important to investigate the molecular structure. The charcteristics of the dielectric absorption in aging natural rubber were studied in the range of frequency from $1{\times}10^3Hz\;to\;3.2{\times}10^7Hz$ at the temperature of $23^{\circ}C$. As the results, it has been confirmed that in the case of aged NR vulcanized specimen with contained sulfur 2 phr above the specimens exhibit two kind of dielectic losses due to the the dipole polarization by impurities and sulfurs, and of raw rubber exhibit the kind of losses due the to dipole polarization. Particularly, it has been affirmed that the dielectric loss spectrum of the aging natural rubber is larger than that the natural rubber, and the dielectric strength of the aging natural rubber drop depreciate respctively.

• 한국발생생물학회지:발생과생식
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• 제25권4호
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• pp.213-223
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• 2021

Controlled ovarian hyperstimulation (COH) is routinely used in the in vitro fertilization and embryo transfer (IVF-ET) cycles to increase the number of retrieved mature oocytes. However, the relationship between repeated COH and ovarian function is still controversial. Therefore, we investigated whether repeated ovarian stimulation affects ovarian aging and function, including follicular development, autophagy, and apoptosis in follicles. Ovarian hyperstimulation in mice was induced by intraperitoneal injection with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG). Mice subjected to ovarian stimulation once were used as a control group and 10 times as an experimental group. Repeated injections with PMSG and hCG significantly reduced the number of primary follicles compared to a single injection. The number of secondary and antral follicles increased slightly, while the number of corpus luteum increased significantly with repeated injections. On the other hand, repeated injections did not affect apoptosis in follicles associated with follicular atresia. The expression of autophagy-related genes Atg5, Atg12, LC3B, and Beclin1, cell proliferation-related genes mTOR, apoptosis-related genes Fas, and FasL was not significantly different between the two groups. In addition, the expression of the aging-related genes Dnmt1, Dnmt3a, and AMH were also not significantly different. In this study, we demonstrated that repeated ovarian stimulation in mice affects follicular development, but not autophagy, apoptosis, aging in ovary. These results suggest that repetition of COH in the IVF-ET cycle may not result in ovarian aging, such as a decrease in ovarian reserve in adult women.

• 산업진흥연구
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• 제9권2호
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• pp.115-125
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• 2024

노인인구 증가와 피부미용에 관해 관심이 커지고 천연물에 대한 과학적 고찰의 전문화는 천연소재에 대한 활용 증가로 이어지고 있다. 본 논문은 천연원료를 피부노화 경감 소재로 활용한 문헌의 추출법 및 경감능을 기반으로 천연물의 종류, 추출물의 기능성 및 추출 기술을 조사하였다. 천연물 유래 기능성 소재의 피부노화 경감에 대한 직접적 영향을 평가하기 위해 콜라겐에 미치는 영향 중 Procollagen 합성능과 MMP-1 경감능을 기반으로 추출물의 기능성을 판단하였다. 각 천연물은 위의 평가법을 이용한 문헌 중 식물, 한약재 및 녹조류로 구분하여 각 원료로부터 기능성 소재의 확보를 위한 추출 기술과 주요 결과를 서술한다. 이에 따라 피부노화 완화를 위한 기능성 소재의 추출 기술과 연구 동향을 제공하여 천연물 활용 연구 분야에 신속한 접근을 제공한다.

• 한국자동차공학회논문집
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• 제15권3호
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• pp.147-152
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• 2007

This study investigates the aging characteristics of NOx storage and reduction(NSR) catalyst on the emission conditions of lean burn natural gas vehicles. We designed various NSR catalysts using by the double-layer washcoat technology to increase of a surface area and a thermal durability performance of the catalysts. The experiments were conducted with 3 kinds of the NSR catalysts, which were manufactured using by a honeycomb cordierite substrate. It was found that Ba is weak in the thermal aging because it has lower melting temperature than that of precious metals (PMs). The suitable loading amount of Ba in this study should be about 42 g/L from the results of the NOx adsorption and the NOx reduction efficiency. The major reason in deactivation of the NSR catalyst is the decrease of the adsorption site owing to the agglomeration and sintering of Ba rather than PM aging by hydrothermal aging. It was confirmed by results of BET, SEM and TEM.

• 한국추진공학회지
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• 제23권1호
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• pp.9-14
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• 2019

고체 추진기관의 HTPB 추진제는 저장소에서 저장소 환경에 따라 물리적, 화학적 노화가 진행된다. 추진기관 수명은 HTPB 추진제의 노화도에 의해 결정되며, 생산 초기에 점탄성 특성 및 노화 시험을 통해 예측된다. 본 논문에서는 생산 초기 물성 및 가속노화 시험을 통해 획득한 노화 물성과 장기 저장되어 자연 노화된 물성을 비교 분석하였다. 획득된 초기 및 노화물성 결과를 적용하여 중공형 그레인의 온도 하중에 의한 변형율을 분석하였다.

• Bulletin of the Korean Chemical Society
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• 제21권6호
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• pp.628-634
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• 2000

Crosslink is the most important chemistry in a rubber vulcanizate. Degree and type of crosslinks of the vulcanizate determine its physical properties. Change of crosslink density and deformation of a rubber vulcanizate by thermal aging were studied using natural rubber (NR) vulcanizates with various cure systems (conventional, semi-EV, and EV) and different cure times (under-, optimum-, and overture). All the NR vulcanizates were deformed by the thermal aging at 60-100 $^{\circ}C.$ The higher the aging temperature is, the more degree of the deformation is. The undercured NR vulcanizates after the thermal aging were deformed more than the optimumand overcured ones. The NR vulcanizates with the EV cure system were less deformed than those with the conventional and semi-EV cure systems. The deformation of the NR vulcanizates was found to be due to change of the crosslink density of the vulcanizates. The crosslink densities of all the vulcanizates after the extraction of organic materials were also changed by the thermal ging. The sources to change the crosslink densities of the vulcanizates by the thermal aging were found to be dissociation of the existing sulfur crosslink and the formation of new crosslinks by free sulfur, reaction products of curing agents, and pendent sulfide groups.