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Ko, Seunghwan,Lee, Junsu,Koo, Joonhoi,Joo, Beom Soo,Gu, Minseon,Lee, Ju Han IEEE 2016 Journal of Lightwave Technology Vol.34 No.16
<P>We propose a chemical wet etching technique that does not make use of toxic Hydrofluoric solution to produce cladding-etched optical fiber intended for use as a platform for a fiberized saturable absorber. The wet etching technique is based on the use of a mixed solution of NH4F and (NH4)(2)SO4, which is not toxic, and a small, specially-devised etching cradle to achieve precise control of the etched fiber length. A fiberized saturable absorber was implemented by depositing the graphene oxide particles on top of the residual cladding for our cladding-etched fiber by using the drop & dry method. The saturable absorber was incorporated into an erbium-doped fiber ring cavity to test its suitability as a mode-locker with a modulation depth larger than 4.3%. Femtosecond pulses with a temporal width of similar to 615 fs were readily obtained at a repetition rate of similar to 17.09 MHz. The saturable absorption and laser performance of our saturable absorber were compared to those of an absorber on a core-etched fiber platform prepared through the formation of microdroplets of HF and surface tension-driven flow, as in [57].</P>
지하공간개발에서 뮤오그래피 탐사기술의 적용성에 관한 연구
서승환 ( Seunghwan Seo ),임현성 ( Hyunsung Lim ),고영훈 ( Younghun Ko ),곽기석 ( Kiseok Kwak ),정문경 ( Moonkyung Chung ) 대한화약발파공학회 2021 화약발파 Vol.39 No.4
최근 도시지역의 지반침하가 빈번하게 발생하여 주민들의 불안이 증가하고 막대한 사회적 비용이 발생하고 있다. 지반침하의 원인 중 노후 상하수도관의 파열은 매설관의 가동을 정지시킬 뿐만 아니라 지반 및 수질오염 문제를 야기한다. 그러나 대부분의 파이프는 시공 후 매설되어 육안으로 볼 수 없기 때문에 다른 구조물에 비해 유지보수의 중요성이 저평가되고 있다. 최근 몇 년 동안 지하 파이프 및 구조물의 유지 보수에 통합 물리적 탐사가 적용되었다. 현재 지하 공간 내부와 지반취약점을 조사하기 위해 통합물리조사를 실시하고 있다. 통합물리조사는 여러 가지 물리조사를 이용하여 다양한 물성자료를 얻고 기존 자료를 추가하는 분석기법이다. 일반적으로 지반 공학에서는 전기 및 표면파 조사를 포함한 통합 물리 조사가 채택되지만, 이러한 조사를 이용하여 지하공간의 시간적 변화를 조사하는 것은 어렵다. 이에 반해 원자로 내부를 스캔하기 위한 투과기술로 우주선 뮤온을 이용한 탐사가 이루어지고 있다. 뮤온을 이용한 측량은 진동이나 전기의 영향 없이 실시간 관찰이 가능하다. 이러한 조사는 많은 노동력을 요구하지 않고 밀도 분포를 조사할 수 있기 때문에 활용 가능성 측면에서 큰 잠재력을 가지고 있다. 본 논문에서는 우주선 뮤온을 이용한 측량 기술을 소개하고, 이러한 기술을 지하 공간 및 지하구조물에 대한 새로운 물리 측량 기술로 적용할 가능성을 제시한다. Recently, the frequent occurrence of ground subsidence in urban areas has caused increasing anxiety in residents and incurred significant social costs. Among the causes of ground subsidence, the rupture of old water and sewer pipes not only halts the operation of the buried pipes, but also leads to ground and water pollution problems. However, because most pipes are buried after construction and cannot be seen with the naked eye, the importance of maintenance has underestimated compared to other structures. In recent years, integrated physical exploration has been applied to the maintenance of underground pipes and structures. Currently, to investigate the internal conditions and vulnerable portions of the ground, consolidated physical surveys are executed. Consolidated physical surveys are analysis techniques that obtain various material data and add existing data using multiple physical surveys. Generally, in geotechnical engineering, consolidated physical surveys including electrical and surface wave surveys are adopted. However, it is difficult to investigate time-based changes in under ground using these surveys. In contrast, surveys using cosmic-ray muons have been used to scan the inner parts of nuclear reactors with penetration technology. Surveys using muons enable real-time observation without the influence of vibration or electricity. Such surveys have great potential for available technology because of their ability to investigate density distributions without requiring as much labor. In this paper, survey technologies using cosmic ray muons are introduced, and the possibilities of applying such technologies as new physical survey technologies for underground structures are suggested.
조승환(Seunghwan Cho),이범호(Beomho Lee),이대엽(Daeyup Lee),고상철(Sangchul Ko) 한국자동차공학회 2008 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
In medium and heavy duty engines for vehicles heavier than 3.5 tons(GVW), an implementation of lean burn technology is very important to lower thermal load and enhance fuel economy. To meet EURO-5 emission regulations, the optimized emission characteristics are also important design factors. In this work, with lean burn technology, a swirl enhancing valve was used in the intake port to improve combustion. Also, the injection position was varied to see its effect on stratification of air fuel mixture, which thus may enhance lean burn characteristics. This work concluded that, with swirl enhancing valve, although torque was decreased, there exist conditions where NOx and THC emissions were reduced at the same level of torque compared with the baseline case. Whereas by varying injection positions with tumble port injection, the combustion characteristics was not satisfactory in terms of torque and emissions.
Bae, Seunghwan,Jo, Jea Woong,Lee, Phillip,Ko, Min Jae American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.19
<P>To realize a high-efficiency perovskite solar cell (PSC), it is critical to optimize the morphology of the perovskite film for a uniform and smooth finish with large grain size during film formation. Using a chemical compound as an additive to the precursor solution has recently been established as a promising method to control the morphology of the perovskite film. In this study, we propose a new method to achieve an improved morphology of the methylammonium lead iodide perovskite film by simultaneous addition of dimethyl sulfoxide (DMSO) and methoxyammonium salt (MeO) (dual additives). We demonstrated that an appropriate amount of the MeO additive helps the precursors form a stable intermediated PbI<SUB>2</SUB>-DMSO adduct during film formation and enlarges the perovskite grains by retarding the kinetics of conversion of the adduct to the perovskite. Furthermore, we experimentally observed that the optical band gaps and crystal structures of perovskite films are reasonably unaffected by the MeO additive because MeO is almost eliminated during annealing. By optimizing the amount of MeO, we achieved improved device performances of the PSCs with a high power conversion efficiency of 19.71% that is ∼15% higher than that obtained for the control device (17.15%).</P> [FIG OMISSION]</BR>
고성능 의료용 아날로그 프론트 엔드(AFE)를 이용한 12채널 심전도 획득 및 부정맥 판단 시스템 개발
고현철(Ko, Hyun-Chul),이승환(Lee, SeungHwan),허정현(Heo, JungHyun),이정직(Lee, Jeong-Jick),최우혁(Choi, Woo-Hyuk),최성환(Choi, Sung-Hwan),신태민(Shin, TaeMin),윤영로(Yoon, Young-Ro) 한국산학기술학회 2014 한국산학기술학회논문지 Vol.15 No.4
본 논문은 의료용 아날로그 프론트 앤드(analogfrontend;AFE)를 이용하여 12채널 심전도를 측정하고 신호 분석을 통해 부정맥을 판단할 수 있는 시스템 개발에 관한 논문이다.최근 국내 급성 심정지 발생이 증가하고 있으며 이에 원인이 되는 부정맥을 진단할 수 있는 시스템의 필요성이 증가하고 있다.기존의 12채널 심전도 시스템은 회로 구성이 복잡하고 큰 부피를 차지하는 단점이 있으며 이를 개선하기 위해 본 논문에서는 의료용 AFE와 부정맥을 판단 할 수 있는 알고리즘 및 신호 처리를 위한 DSP로 시스템을 구성하였다.추가적으로 12채널 심전도의 파형 관찰과 부정맥 판별 결과를 7인치 LCD 를 통해 출력하며 터치 패널을 통해 사용자 입력을 받는다.본 논문에서 구현된 시스템을 검증하기 위해 심전도 시뮬레이터 의 출력 신호(정상 신호/부정맥 신호)에 대한 판별 테스트와 부정맥 알고리즘을 임베디드 환경에 적용하기 위한 최적화 과정 의 성능 평가를 진행하였다. This paper deals with system development which measures 12 channel ECG using medical analog front end(AFE) and discriminates arrythmia through signal analysis. Recently, occurrences of cardiac arrest have been increased. So the need of system that diagnoses an arrythmia which results in cardiac arrest is increasing. There are some drawbacks of conventional 12 channel ECG system that it occupies bulk and consists of complicated circuit. To improve those, we made up the system composed of medical AFE, algorithm for discriminating arrythmia and DSP for signal processing. This system can be monitored 12 channel ECG waveforms and the discriminant analysis result of arrhythmia through 7" LCD and received the input through touch pannel. In this study, we conducted normal operation test about output signal of ECG simulator(normal/abnormal ECG signal) to verify the implemented system and performance evaluation of the optimization process for applying arrhythmia algorithm to an embedded environment.