• Journal of Welding and Joining
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• 제29권5호
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• pp.82-89
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• 2011

The effect of welding condition on tensile properties of KS5J32 Al Alloy was investigated under various welding conditions. The 1.6 mm thick KS5J32 alloy sheets were joined by friction stir welding (FSW) technique with butt joint. The tool rotation speeds were 1000, 1250 and 1500 rpm, and the welding speeds were varied within the range from 100 to 600 mm/min. Voids mainly occurred at the advancing side of the tool probe, when the tool rotation speed was low, due to insufficient materials flow. When the weld pitch exceeded 0.4 mm/rev, voids were observed under all welding conditions and the area of voids increased with increasing weld pitch. For void-free specimens, fracture always occurred at base materials. However voids affected the location of fractures, base metal or welded zone, when the voids existed within the welds.

• Journal of Welding and Joining
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• 제30권6호
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• pp.98-105
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• 2012

The focus of this investigation is to evaluate the effect of joining parameter on the microstructure and mechanical properties of welds produced by friction stir lap welding. The dissimilar Al alloys, KS5J32 and AA6K31, were joined by friction stir lap welding technique under several welding conditions, and KS5J32 alloy was placed on the top of AA6K31 alloy. The tool rotation speeds were 1000, 1250, and 1500rpm, and the welding speeds were 100, 300, 500, 700mm/min, respectively. The results showed that two shapes of nugget, such as onion ring and irregular vortex type, were observed with various revolutionary pitch. In all welding conditions, fracture occurred at the soften region of bottom sheet(AA6K31) and the strengths were 64~78% of those of base metal. Fractured positions were classified into three types : HAZ, triple point, void depending on the revolutionary pitch. The actual thickness of specimen at the fractured location was decreased with decreasing heat input. A linear relationship exists between the effective thickness of fractured position and peak load.

• 천문학논총
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• 제32권1호
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• pp.73-75
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• 2017

Debris disks are important observational clues to understanding on-going planetary system formation. They are usually identified by significant mid-infrared excess on top of the photospheric emission of a central star on the basis of prediction from J-, H-, and Ks-band fluxes and the stellar model spectra. For bright stars, 2MASS near-infrared fluxes suffer large uncertainties due to the near-infrared camera saturation. Therefore we have performed follow-up observations with the IRSF 1.4 m near-infrared telescope located in South Africa to obtain accurate J-, H-, and Ks-band fluxes of the central stars. Among 754 main-sequence stars which are detected in the AKARI $18{\mu}m$ band, we have performed photometry for 325 stars with IRSF. As a result, we have successfully improved the flux accuracy of the central stars from 9.2 % to 0.5 % on average. Using this dataset, we have detected $18{\mu}m$ excess emission from 57 stars in our samples with a $3{\sigma}$ level. We find that some of them have high ratios of the excess to the photospheric emission even around very old stars, which cannot be explained by the current planet-formation theories.

• 생명과학회지
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• 제32권12호
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• pp.938-946
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• 2022

본 연구는 대풍자 에탄올 추출물에 대한 항산화 활성 및 주름생성 억제 활성을 확인하고자 하였다. 대풍자 에탄올 추출물의 항산화 활성을 확인하기 위하여 DPPH와 ABTS⁺ radical 소거능을 측정하였고 그 결과 추출물 1,000 ㎍/ml 농도에서 각각 73.5%와 74.4%의 높은 소거능을 나타냈다. 주름생성 억제 활성을 확인하기 위하여 collagenase 저해 활성을 실험하였으며, 그 결과 추출물 1,000 ㎍/ml 농도에서 78.8%의 유의할만한 우수한 결과를 보였다. 또한 추출물에 대한 세포의 독성을 확인하기 위해 MTT assay를 수행하였으며, 50 ㎍/ml 이하의 농도에서 약 91.7%의 생존율을 보여, 이후의 세포 실험은 50 ㎍/ml 이하의 농도에서 진행하였다. 섬유아세포인 CCD-986sk에 UVB (20 mJ/cm²)의 자극을 주고 대풍자 에탄올 추출물을 농도별로 처치한 후 procollagen type I과 MMP-1의 발현에 대한 영향을 확인하고자 ELISA 및 RT-PCR 분석을 하였다. 그 결과 대풍자 에탄올 추출물은 PIP의 생합성과 mRNA 발현은 농도의존적으로 증가하였으며, 특히 UVB만 자극한 Cont (각각의 생합성율은 50.3%와 45.8%)과 비교하였을 때 50 ㎍/ml의 농도에서 각각 약 64.2%와 83.4%의 생합성을 보였다. MMP-1의 protein과 mRNA 발현에 대한 결과는 농도의존적으로 감소했음을 확인하였으며, 50 ㎍/ml의 농도에서 각각 약 48.7%와 35.9%의 낮은 발현율을 보였다. 이와 같은 결과를 바탕으로 본 연구는 대풍자 에탄올 추출물이 주름억제 기능성 소재로써의 활용 가능성을 제시해 줄 것으로 사료된다.