• Asian-Australasian Journal of Animal Sciences
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• 제19권9호
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• pp.1335-1341
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• 2006

We selected a Lactobacillus spp. from Korean healthy infant feces based upon their antioxidant activity. This strain was identified as Lactobacillus gasseri by 16S rDNA sequencing, and named Lactobacillus gasseri NLRI-312. In the present study, we investigate the protective effect of this strain on the $H_2O_2$ induced damage to cellular membrane lipid and DNA in Jurkat cells. To estimate the extent of cellular lipid peroxidation inhibition, MDA (malondialdehyde) was measured, and DNA damage was tested by the comet assay. We also examined probiotic properties including tolerance to acid and bile, antibiotic resistance. From the results obtained, the supplementation of Jurkat cells with NLRI-312 decreased in DNA damage, while no effect was shown on MDA decrease. In probiotic properties, this strain was resistance to both acid and bile, showed considerably higher survival when incubated in pH 2 or 1% bile salts (w/v). We concluded that the NLRI-312 could be used as potential probiotic bacteria, with the effect of reducing DNA damage induced by $H_2O_2$.

• International Journal of Fluid Machinery and Systems
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• 제3권4호
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• pp.301-308
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• 2010

Quest for reliability of hydraulic runners is a concern for all mature electricity producers. The fatigue damage caused by dynamics loads is frequently the root cause of runner failure. This paper presents the damage tolerance approach based on fracture mechanics as the method chosen by Alstom and Hydro-Qu$\acute{e}$bec to predict effects of damage on runner lifetime and consequently to be use as a design method. This is sustained by a research on fracture mechanics properties of runner materials and by recommendations on the strategy to define a safety margin for design. The acquired knowledge permits to identify potential improvement of the runner lifetime without significant cost increase, like being more specific on some chemical composition or heat treatment.

• 대한기계학회논문집A
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• 제29권6호
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• pp.876-888
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• 2005

Tensile properties and fracture toughness of monolithic aluminum, fiber reinforced plastics and glass fiber/aluminum hybrid laminates under tensile loads have been investigated using plain coupon and single-edge-notched specimens. Elastic modulus and ultimate tensile strength of GFMLs showed different characteristic behaviors according to the Al kind, fiber orientation and composition ratio. Fracture, toughness of A-GFML-UD which was determined by the evaluation of $K_{IC}$ and $G_{IC}$ based on critical load was similar to that of GFRP-UD and was much higher than monolithic Al. Therefore, A-GFML-UD presented superior fracture toughness as well as prominent damage tolerance in comparison to its constituent Al. By separating Al sheet from GFMLs after the test, optical microscope observation of fracture zone of GFRP layer in the vicinity of crack tip revealed that crack advance of GFMLs depended on the orientation of fiber layer as well as Al/fiber composition ratio.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.71-75
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• 2005

For the damage tolerance improvement of conventional laminated composites, stitching process have been utilized for providing through-thickness reinforcements. 2D preforms were stacked with S-2 glass plain weave and S-2 glass MWK (Multi-axial Warp Knit) L type. 3D preforms were fabricated using the stitching process. All composite samples were fabricated by RTM (Resin Transfer Molding) process. To examine the damage resistance performance the low speed drop weight impact test has been carried out. For the assessment of damage after the impact loading, specimens were examined by scanning image. CAI (Compressive After Impact) tests were also conducted to evaluate residual compressive strength. Compared with 2D composites, the damage area of 3D composites was reduced by 20-30% and the CAI strength showed 5-10% improvement.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.171-174
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• 2004

In order to improve the damage tolerance of the conventional laminated composites, three­dimensional fiber structures incorporated with stitching yams have been utilized in this study. From the newly developed process termed as TAPIS(TApe Placement Incorporated with Stitching), carbon/epoxy composites have been fabricated. Two-dimensional composites with the same stacking sequence as 3D counterparts have also been fabricated for the property comparison. To examine the damage resistance performance the low speed drop weight impact test has been adopted. For the assessment of damage after the impact loading, specimens were subjected to C-scan nondestructive inspection compression after impact(CAI) were also conducted to evaluate residual compressive strength. Although the damage area of 3D composites was greatly reduced$(30-40\%)$ compared with that of 2D composites, the CAI strength did not show drastic improvement.

• Structural Engineering and Mechanics
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• 제54권2호
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• pp.337-362
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• 2015

This paper presents a feasibility study on structural damage alarming and localization of long-span cable-supported bridges using multi-novelty indices formulated by monitoring-derived modal parameters. The proposed method which requires neither structural model nor damage model is applicable to structures of arbitrary complexity. With the intention to enhance the tolerance to measurement noise/uncertainty and the sensitivity to structural damage, an improved novelty index is formulated in terms of auto-associative neural networks (ANNs) where the output vector is designated to differ from the input vector while the training of the ANNs needs only the measured modal properties of the intact structure under in-service conditions. After validating the enhanced capability of the improved novelty index for structural damage alarming over the commonly configured novelty index, the performance of the improved novelty index for damage occurrence detection of large-scale bridges is examined through numerical simulation studies of the suspension Tsing Ma Bridge (TMB) and the cable-stayed Ting Kau Bridge (TKB) incurred with different types of structural damage. Then the improved novelty index is extended to formulate multi-novelty indices in terms of the measured modal frequencies and incomplete modeshape components for damage region identification. The capability of the formulated multi-novelty indices for damage region identification is also examined through numerical simulations of the TMB and TKB.

• Nuclear Engineering and Technology
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• 제47권3호
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• pp.323-331
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• 2015

Zirconium alloys are widely used in nuclear reactors as structural materials. During the operation, they are exposed to fast neutrons. Ion irradiation is used to simulate the damage introduced by neutron irradiation. In this article, we briefly review the neutron irradiation damage of zirconium alloys, then summarize the effect of ion irradiation on microstructural evolution, mechanical and corrosion properties, and their relationships. The microstructure components consist of dislocation loops, second phase precipitates, and gas bubbles. The microstructure parameters are also included such as domain size and microstrain determined by X-ray diffraction and the S-parameter determined by positron annihilation. Understanding the relationships of microstructure and properties is necessary for developing new advanced materials with higher irradiation tolerance.

• 한국항공우주학회지
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• 제47권1호
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• pp.35-40
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• 2019

본 연구의 목적은 항공기 구조개발에 널리 적용되고 있는 탄소섬유 복합재의 피로특성을 확인하고, 실기체 피로시험에 활용되고 있는 자료를 획득하는 것이다. 복합재 구조의 내구성 및 손상허용성의 평가는 주로 피로시험을 통하여 이루어지며, 실기체 피로시험에 적용되고 있는 파라미터에는 피로수명계수와 하중증대계수가 있다. 탄소섬유/에폭시 일방향 및 직물형 복합재로 시편을 제작하였으며, 응력비와 적층패턴을 달리하여 피로시험을 수행하였다. Sendeckyj 모델을 적용한 와이블 분포와 개별적인 피로수명에 대한 와이블 분포를 이용하여 형상 파라미터를 분석하였다. 또한 신뢰도를 고려한 피로수명계수와 하중증대계수를 평가하였다.

• Journal of the Korean Physical Society
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• 제73권10호
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• pp.1566-1570
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• 2018

We investigated the visible emission property of $SrTiO_3$ (STO) single crystals irradiated with gammy-ray (${\gamma}$-ray) at various total doses up to 900 kGy. The electric and optical absorption properties of the irradiated STO samples were hardly changed with the ${\gamma}$-ray irradiation, compared with those of un-irradiated STO. In contrast, the visible emission near 550 nm increased with the ${\gamma}$-ray dose increasing. While the development of the visible emission was indicative of the increase of oxygen vacancies inside STO by the ${\gamma}$-ray irradiation, the newly generated oxygen vacancies were not significantly harmful to the electric and optical properties of STO. We concluded that the STO single crystal should have a good tolerance against the damage by the ${\gamma}$-ray irradiation.

• 항공우주기술
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• 제8권1호
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• pp.42-48
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• 2009

복합재 항공기의 경우 인증 시 여러 가지 요소를 고려해야한다. 금속과는 달리 복합재구조물의 감항성은 운용 및 제작 중 발생하는 손상 등에 의해 큰 영향을 받는다. 그러므로 예상 가능한 여러 가지 손상에 대해 정적강도, 강성, 플러터 및 손상허용강도 등을 입증하여 야한다. 복합재료의 기계적물성은 환경조건에 영향을 받는다. 특히 압축강도는 수지의 영향이 지배적이고 수지가 온도와 습도의 영향을 많이 받으므로 설계/해석 시 고려하여야한다. 복합재 항공기의 경우 육안으로 탐지가 어려운 손상에 대한 정적강도를 입증하여야하고, 육안으로 보이는 큰 손상에 대해서는 발견 즉시 수리하도록 규정되어있다. 본 논문에서는 복합재 구조물의 설계/해석에 필요한 규정을 분석하고 해석방법 등에 대해 검토하려한다.