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Mijin Choi,Hwee Kwon Jung,Stuart G. Taylor,Kevin M. Farinholt,Jung-Ryul Lee,Gyuhae Park 한국비파괴검사학회 2016 한국비파괴검사학회지 Vol.36 No.2
This paper presents the results obtained using time-series-based methods for structural damage assessment. The methods are applied to a wind turbine blade structure subjected to fatigue loads. A 9 m CX-100 (carbon experimental 100 kW) blade is harmonically excited at its first natural frequency to introduce a failure mode. Consequently, a through-thickness fatigue crack is visually identified at 8.5 million cycles. The time domain data from the piezoelectric active-sensing techniques are measured during the fatigue loadings and used to detect incipient damage. The damage-sensitive features, such as the first four moments and a normality indicator, are extracted from the time domain data. Time series autoregressive models with exogenous inputs are also implemented. These features could efficiently detect a fatigue crack and are less sensitive to operational variations than the other methods.
Choi, Kyoungjun,Nam, Sooji,Lee, Youngbin,Lee, Mijin,Jang, Jaeyoung,Kim, Sang Jin,Jeong, Yong Jin,Kim, Hyeongkeun,Bae, Sukang,Yoo, Ji-Beom,Cho, Sung M.,Choi, Jae-Boong,Chung, Ho Kyoon,Ahn, Jong-Hyun,Pa American Chemical Society 2015 ACS NANO Vol.9 No.6
<P>Preventing reactive gas species such as oxygen or water is important to ensure the stability and durability of organic electronics. Although inorganic materials have been predominantly employed as the protective layers, their poor mechanical property has hindered the practical application to flexible electronics. The densely packed hexagonal lattice of carbon atoms in graphene does not allow the transmission of small gas molecules. In addition, its outstanding mechanical flexibility and optical transmittance are expected to be useful to overcome the current mechanical limit of the inorganic materials. In this paper, we reported the measurement of the water vapor transmission rate (WVTR) through the 6-layer 10 × 10 cm<SUP>2</SUP> large-area graphene films synthesized by chemical vapor deposition (CVD). The WVTR was measured to be as low as 10<SUP>–4</SUP> g/m<SUP>2</SUP>·day initially, and stabilized at ∼0.48 g/m<SUP>2</SUP>·day, which corresponds to 7 times reduction in WVTR compared to bare polymer substrates. We also showed that the graphene-passivated organic field-effect transistors (OFETs) exhibited excellent environmental stability as well as a prolonged lifetime even after 500 bending cycles with strain of 2.3%. We expect that our results would be a good reference showing the graphene’s potential as gas barriers for organic electronics.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-6/acsnano.5b01161/production/images/medium/nn-2015-01161h_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b01161'>ACS Electronic Supporting Info</A></P>
Choi, Mijin,Jung, Hwee Kwon,Taylor, Stuart G.,Farinholt, Kevin M.,Lee, Jung-Ryul,Park, Gyuhae The Korean Society for Nondestructive Testing 2016 한국비파괴검사학회지 Vol.36 No.2
This paper presents the results obtained using time-series-based methods for structural damage assessment. The methods are applied to a wind turbine blade structure subjected to fatigue loads. A 9 m CX-100 (carbon experimental 100 kW) blade is harmonically excited at its first natural frequency to introduce a failure mode. Consequently, a through-thickness fatigue crack is visually identified at 8.5 million cycles. The time domain data from the piezoelectric active-sensing techniques are measured during the fatigue loadings and used to detect incipient damage. The damage-sensitive features, such as the first four moments and a normality indicator, are extracted from the time domain data. Time series autoregressive models with exogenous inputs are also implemented. These features could efficiently detect a fatigue crack and are less sensitive to operational variations than the other methods.
유무선 통신 환경에서 그룹 에이팅을 위한 사용자 관심도 기반 필터링 기법
최미진(MiJin Choi),조은영(EunYoung Cho),이동만(Dongman Lee),강경란(Kyungran Kang) 한국정보과학회 2002 한국정보과학회 학술발표논문집 Vol.29 No.2Ⅱ
현저한 대역폭의 차이를 보이는 유무선 통신 환경에서 협동작업, 예를 들면 그룹 에디팅을 하기 위해서는 데이터 전송 속도의 차를 극복하는 것이 중요하다. 이를 위해 선택적 전송, 압축, 프로토콜 차원에서 지원 등 다양한 필터링 방법이 제시되고 있다. 그러나 이런 방법은 효과적으로 메시지의 수를 줄였으나 사용자가 관심을 두지 않는 부분이라도 메시지가 발생 순서에 따라 전달되기 때문에 바로 알려줘야 하는 사용자에게 변경 메시지의 전송이 지연될 수 있다는 문제점이 있다. 본 논문에서는 사용자의 관심도에 따라 메시지간의 우선 순위를 부여하는 필터링 방법을 제안한다.