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환원된 그래핀/단일벽 탄소나노튜브 복합체를 이용한 플렉시블 에너지 저장 매체의 개발
유영환,조재봉,김용렬,정현택 한국유화학회 2016 한국응용과학기술학회지 Vol.33 No.3
본 연구에서는 유연성을 갖는 전극 제조를 위해 환원된 그래핀 옥사이드/단일벽 탄소나노튜 브 복합체를 금이 코팅된 PET 기판 위에 스프레이 코팅하였다. 제조된 플렉시블한 전극의 전기 용량 값 은 1 M의 황산 전해질과 100 mV s-1 의 주사속도에서 82 F g-1 으로 측정 되었으며, 이 용량 값은 500 번의 굽힘 시험 후에 38 F g-1 로 감소되는 현상을 확인 하였다. 또한, 이러한 결과는 정전류 충 방전과 전기화학 임피던스법을 포함한 전기화학적 분석 결과와도 부합하는 결과를 나타내었다. 유연성을 갖는 환원된 그래핀 옥사이드/단일벽 탄소나노튜브 복합체 전극은 500회의 반복적인 굽힘 시험 후에도 대략 50%의 초기 전기 용량 값을 유지 할 수 있었으며, 이러한 여러 가지 전기화학적 특성을 고려하여 볼 때 미래 개발 가능한 플렉시블한 에너지 저장 매체로써의 적용이 가능 하다는 점을 확인 할 수 있었 다. We report on the preparation of reduced graphene oxide (rGO)/single-walled carbon nanotubes (SWNTs) electrodes deposited onto flexible polyethylene terephthalate (PET) via spray coating technique. The highest capacitance value of the unbent rGO/SWNTs electrode was 82 F g-1 in 1 M H2SO4 at 100 mV s-1, which decreased to 38 F g-1 after 500 bending cycle. Further characterization, including galvanostatic charge/discharge measurements and electrochemical impedance spectroscopy (EIS), showed that the rGO/SWNTs electrode retained a well-defined capacitive response after repetitive bending cycle.Overall, the rGO/SWNTs composite electrode showed reasonable electrochemical properties even prolonged bending cycle. Approximately 50% of the initial capacitance for the rGO/SWNTs composite electrode is remained after 500 bending cycle, making the electrode a potential option for flexible energy storage applications.
MB-OFDM UWB 시스템에서의 미세 주파수 동기화 기법
유영환 한국통신학회 2008 韓國通信學會論文誌 Vol.33 No.8
In this paper, a fine residual frequency offset estimation scheme is proposed for multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) systems. The basic idea of our approach is based on the fact that two adjacent OFDM symbols carry the identical information in the MB-OFDM UWB system, thus removing the need of pilot symbols. The mean square error of the synchronization scheme is evaluated and simulation results are used to verify the effectiveness of the proposed estimator. When compared to the pilot-aided conventional estimator, the proposed estimator has a lower estimation error.
수중음파 센서 네트워크에서 해파 모델링에기반한 센서 노드 전송파워 조절 기법
유영환,김성렬 에스케이텔레콤 (주) 2015 Telecommunications Review Vol.25 No.1
기존의 많은 연구들이 수중채널 모델링을 기반으로 최적의 전송파워와 주파수할당 방법을 제안하고 있으나 이들대부분은 반사손실을 고려하고 있지 않으며 동적으로 변하는 채널의 상태를 통신에 반영하지 못한다. 이에 본 연구에서는 10 kHz 이하 주파수를 사용하는 수중 통신네트워크에서 거리, 주파수, 파고 기반의 전송파워 소요 모델을 제시한다. 또한 이를 기반으로 채널의 상태를 예측하여 처리량을 보장하는 동시에 에너지 소모를 줄이는 전송파워 조절 기법을 제안한다. SNR(Signal-to-Noise Ratio)임계값을 보장하기 위한 전송파워를 정의할 때, 기존 연구에서 간과되었던 반사 계수를 Kirchhoff 근사법으로 유도하여 반사손실을 적용하였다. 또한 BELLHOP과 WAFO 시뮬레이터를 통해 각각 수중환경과 1 m 높이의 파도를 모델링하여 실제 수중환경에 근사한 시뮬레이션 환경에서 제안방법의 성능을평가하였다. 시뮬레이션 결과를 통해, 수표면에서 발생하는 반사가 송신 신호 및 전송 파워 조절에 미치는 영향을 파악할 수 있었고 제안 방법이 기존 방법에 비해 약 23.25%의 에너지 소비 절감을 보임을 확인할 수 있었다.
부정합된 최대 상관값을 이용한 초기 동기 임계치 결정 기법
유영환,김종헌,강성철,강창언 한국통신학회 1996 韓國通信學會論文誌 Vol.21 No.7
This paper describes an automatic threshold decision using a maximum mismatched correlation value in the direct sequence spread spectrum (DS-SS) system. For received PN codes with different single-to-noise ratio (SNR), this scheme is able to detect a desired threshold value in the search mode, i.e. a maximum mismstched correlation value, so that value is utilized as a threshold for the verification mode. Performance of the proposed scheme in both the additive white gaussian noise (AWGN) and frequency-selective Rayleigh fading channels is analyzed through the Monte Carlo simulation. And hardware implementation of this scheme using a DSP processor is demonstrated. The proposed acquisition shceme is compared to the conventional constant threshold (CT) scheme, and significant improvement of performance is shown. Analysis of system performance in the verification mode is presented, and key quantities such as the false alarm probability and the detection probability are derived in a AWGN channel.
소비자의 블록체인 기반 저작권 유통 플랫폼 수용의도와 이용행위에 관한 연구
유영환,박현숙,Yoo, Young-Hwan,Park, Hyeon-Suk 한국유통과학회 2019 The Journal of Industrial Distribution & Business( Vol.10 No.3
Purpose - Blockchain technology, which has the characteristics of credibility, security, integrity and decentralization, has brought innovation to internet platforms that mediate peer to peer transactions, as well as changes to the contents distribution services. Blockchain-based copyright distribution platforms can solve problems which have been articulated on prior internet social networks: increased market dominance of platform business because of centralization with no reward to creators who upload on platforms, and lack of fairness, such as unfair profit distribution between the copyright holder and businesses. With this background, the current research confirmed the factors that affect the intention of usage and behaviors, targeting potential users of blockchain-based copyright distribution platforms. Research design, data, and methodology - Centered around the UTAUT2 Model, the research model was designed with 'Perceived Security' added as Construct, and 'Age' and 'Knowledge Level' added as moderating variables. For data, 607 responses were collected by an online survey, and 601 responses were included in the final analysis. We analyzed the research model and sample by using SPSS 23.0 and AMOS 23.0 on the collected responses. Results - First, results of research on whether Constructs make positive effects on Intention of use is: social influence, facilitating conditions, habit, and perceived security had positive effects on intention of use, and performance expectancy, effort expectancy, hedonic motivation, and economic value did not. Second, results of the research on whether facilitating condition, habit, and intention of use made an impact on using behaviors, it was shown that only habit and intention of use made positive effects. Third, in two groups divided by age above or under 40, group effort expectancy, intention of use, habit, and intention of use had controlling effects, and facilitating condition, intention of use, perceived security, and intention of use had effects in both groups. Conclusions - The research shows that no matter how great a blockchain-based platform is, if advantages of blockchain are not proved in various industries and utilized in real life like the internet, blockchain-based distribution systems will develop slowly. Rather than a short-term inducement emphasizing technology, there is a need for a strategic approach that can foster the environment.