• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.9-14
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• 2019

Hydroxy-terminated polybutadiene (HTPB) propellants of solid rocket motors age differently under different storage temperatures. The shelf life of a solid rocket motor depends on the aging ratio of the HTPB propellant; it can be estimated through the viscoelastic properties by an aging test. This study analyzed the initial and natural aging properties during long-term storage. The initial properties were obtained from characterization and accelerated test results. The test results were obtained by analyzing the strain on cylindrical grains when a thermal load was applied.

• Composites Research
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• v.20 no.2
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• pp.1-9
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• 2007

To evaluate and investigate the aging characteristics and the structural service lifetime of the CFV(carbon fiber pressure vessel), natural aging tests were carried out using the CFVs, which had been placed and aged at outdoor and indoor laboratories for 10 and 15 years, respectively. To obtain the probabilistic characteristics of ageing characteristics in aged CFVs, inner pressure loading test was conducted with ring specimens taken from aged CFVs. And, to observe the interface morphology of aged CFVs, the micro-photographs were taken by SEM microscope and the fractured interfaces between the carbon fiber and the matrix resin were scrutinized. Based on the Weibull parameters of the tensile failure strain of aged CFVs, the degradation of the 10 and the 15 year aged CFV occur by 19% and 23%, respectively, and the effect of the placement, whether being placed inside the laboratory or not, is not so significant. However, the outer layer protection, such as painting, is found very advantageous to prevent CFV from aging.

• Microbiology and Biotechnology Letters
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• v.35 no.4
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• pp.316-324
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• 2007

We studied the effects of genistein obtained from glycolysis of genistin, a kind of phytoestrogen present in soybeans, on cell proliferation and type I pN collagen synthesis in normal human dermal fibroblasts(NHDF). Cell proliferation was increased significantly with genistein treatment at 54-year aged NHDF. Genistein increased cell proliferation more strongly in cells form old doner than young doner. The senescence-associated ${\beta}$-galatosidase activity was decreased in NHDF from 77-year old doner with genistein treatment. Type I pN collagen synthesis was increased with genistein treatement in UVA treated and non-treated NHDF. The increasement of collagen synthesis was more effective in aged cells than young cells. Type I pN collagen synthesis was also increased with genistein treatment in collagen matrix culture with NHDF from sun-exposed and non-exposed skin from 54-year old doner. Genistein treatment inhibited MMP-1 synthesis in old NHDF but not in young NHDF. In conclusion, genistein may be a useful agent for preventing intrinsic aging as well as photoaging.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.29 no.1
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• pp.27-44
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• 2003

전반적인 피부세포의 생리적 지능 자하로 인한 자연노화와 더불어, 여러 피부 스트레스 요인들이 다양하게 작용하여 발생하는 외인성노화를 방지하거나, 개선할 수 있는 항노화소재로서의 개발 가능성을 알아보기 위해, 예로부터 항염활성이 있다고 알려진 oleanolic acid(OA)를 포함한 ursolic acid(UA), betulin, betulinic acid(BA) 등의 triterpenoids가 어떻게 피부에서의 항노화 활성을 나타내는지를 알아보았다. 시험 결과, OA는 자외선에 의한 각질형성세포에서의 PGE$_2$ 생성과 섬유아세포(NHF)에 의한 matrix metalloproteinase-1(MMP-1) 분비를 억제하였다. 그리고, NHF의 procollagen 생성을 촉진하였으며, 이런 procollagen 생성촉진활성이 in vivo에서도 발현되는 것을 무모생쥐의 실험을 통해서 확인하였다. 또한 OA는 각질세포의 증식과 분화를 촉진하여 표피세포로 하여금 세라마이므와 필라그린 생성을 증가시키도록 하는 작용도 있음을 보여주었다. 더불어 실험한 UA, betulin, BA 들은 비록, betulin, BA의 경우 세포 독성이 다른 물질 들에 비해 높았고, UA가 각질세포의 분화를 오히려 억제하는 양상을 보이기는 했지만, 대부분의 기능은 OA와 유사하였다. 피부세포보호작용과 진피 기질물질에 대한 작용, 그리고, 표피의 장벽기능과 보습기능에 대해 시험한 본 연구는, 식물성분인 triterpenoids가 피부를 위한 항노화소재로서의 개발 가능성이 있음을 확인하는 계기가 되었고, 그 중에서도 OA가 보다 우수한 항노화 소재가 될 수 있음을 시사하고 있다.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.3
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• pp.84-90
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• 2017

Explosive bolt is coupled in a variety of guided weapons and space projectiles, to perform the separation function. Thus, the role of the explosive bolt in guided weapons systems is very important, as it can cause failure of the entire system in the case of mission failure. For this reason, the design life prediction for explosive bolt is highly and frequently required recently, but its accurate prediction method has not been presented. In order to apply the existing accelerated aging process, we should know the activation energy and the acceleration factor of the explosive bolt. Since the information required for accelerated aging is not presently secured, it is difficult to predict the design life of explosive. Thus, in the present study, we have evaluated the performance of actual explosive bolts in the condition of natural aging over 10 years in order to present a minimum design life.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.148-153
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• 2017

During natural ageing of HTPB propellant undergoes a series of slow physico-chemical degradation reactions. By using accelerated ageing conditions it is possible to simulate the material behaviour at different time-temperature conditions especially focused on the in-service conditions. Ageing behaviour of HTPB propellant were investigated using HFC(Micro-Heat Flow Calorimeter) is universal technique for measuring the rate of slow chemical and physical processes in long-term storage.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.5
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• pp.59-65
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• 2018

During natural aging, hydroxyl-terminated polybutadiene(HTPB) propellant undergoes a series of slow physico-chemical degradation reactions. By using accelerated ageing conditions it is possible to simulate the material behavior at different time-temperatures focusing on in-service conditions. Aging behaviors of HTPB propellant are investigated using HFC(heat flow calorimeter), a universal technique for measuring the rate of slow chemical and physical processes in long-term storage.

• Composites Research
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• v.21 no.6
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• pp.23-30
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• 2008

In this paper, the effect of the natural aging on the strength distribution and structural service life of a Filament Wound (FW) composite pressure vessel was studied. The fiber failure strain, which is varied significantly, was considered as the design random variable and the strength analysis was carried out by probabilistic numerical approach. The progressive failure analysis technique and the First Order Reliability Method (FORM) were embedded in this numerical model. As the calculation results, the probability of failure was obtained for each aging time steps and it is found that the strength degradation in FW composite pressure vessel, due to the natural aging, appears within 10 year-aging-time. As an example of the life prediction under natural aging using arbitrary laminated model, the service lifetime of 13 years was predicted based on the probability of failure of 2.5% and the design pressure of 3,250 psi.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.4
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• pp.49-57
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• 1992

This study was conducted to evaluate physical property change of asphalt cement chromatograms (by HP-GPC) were experimentally obtained from 3 types of AC-20 virgin ACs, 5 and 24-hour artificially aged ACs, and naturally aged 4 ACs that were recovered from 4 different roads. Absolute viscosity, kinematic visoosity and penetration were the physical properties tested. THF was used for mobil phase and RI detector was used as a detector for Hp-GPC testing. Correlation between each physical property change and the chromatogram variation was evaluated. Each chromatogram was divided into ten-equal-time slices. The percentage areas of 10 slices and each physical property were used for statistical correlation evaluation. Statistical analysis results showed that eaoh physical property had a strong correlation with the chromatogram characteristics. Aging was identified as a mechanism of change of molecular size distribution - increasing large size molecules and reducing coresponding samll size molecules.

• Journal of the Korean Wood Science and Technology
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• v.33 no.4 s.132
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• pp.53-59
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• 2005

This study was performed to understand the changes in wood extractives, mainly acetone extracts, in pine woods (Pinus densiflora and Pinus rigida) treated by three blue stain fungi (BSF) such as native BSF in Korea, Leptographium sp., screened Albino strain (BSFcs-1) and commercial Cartapip. BSF treatment has significantly reduced acetone extracts, 25.1~30.4% decreasing in red pine and 22.9~28.1% in pitch pine. The decreasing rates of fatty acids and sterols in woods were 10.6~11.2% by 3 week aging and 36~41.1% by BSF treatments, respectively. Triglycerides were also decreased to 5.68~9.4% by 3 week aging and 38.5~40.0% by BSF treatments, respectively. Resin acids were 6.1~11.3% by 3 week aging and 36~41.5% by BSF treatments, respectively. There were not so significant differences in extracts among native BSF and Albino-type strains (Albino strain, BSFcs-1, and commercial Cartapip). It was known that the Albino strain (BSFcs-1) screened for the biocontrol of wood discoloration has effectively decreased acetone extractives in pine woods.