• Journal of Welding and Joining
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• v.15 no.5
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• pp.25-35
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• 1997

현재, 표면개질에 주로 많이 사용되는 레이저는 세 종류로서, C $O_{2}$$laser(파장길이:10.6.\mum),$ Nd:YAG(neodymium-doped yettrium aluminum garnet) $laser(파장길이:1.06.\mum)$ 및 excimer laser(157~350nm) 등이다. 이 외에도 초기에는 ruby레이저빔이 사용되기도 하였으나, 현재는 많이 사용되고 있지 않다. 레이저 빔에 의한 표면개질에는 몇가지 장점이 있는데, 이러한 장점은 주로 급속가열과 급속냉각 효과에 기인하는 것이다. 즉, 1) 급냉효과에 의한 미세한 결정입자 형성, 2) 불안정상 (metastable phase) 또는 비정질 상 생성, 3) 열역학적 용해도 보다 높은 용해도. 4) 편석이 없는 균질한 미세조직, 5) 극히 낮은 기공도, 6) 좁은 열영향 부위, 7) 표면층과 모재 사이의 높은 결합력 등이다. 이 외에도 공정상의 장.단점들이 Ref.5, 6에 잘 요약 정리되어 있다. 지금까지 국내에서 레이저 표면개질에 대한 조사가 몇몇 있었으나, 본 조사에서는 보통 많이 다루어지지 않은 부분, 즉 충격경화 및 표면제어에 비중을 두었으며, 비용융 부분(I)과 용융부분(II)을 분리하여 정리하였다.

• Transactions of The Korea Fluid Power Systems Society
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• v.3 no.1
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• pp.1-6
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• 2006

A servo actuator with a valve using MR (Magneto-Rheological) fluid is proposed for fluid control systems. The MR fluid is well known as a functional fluid whose apparent viscosity is controlled by the applied magnetic field strength. The pressure in the MR cylinder can be controlled by the applied magnetic field strength. Good points of the MR cylinder are more simple, compact and reliable structure than a conventional oil hydraulic cylinder. The experimental results show that the MR cylinder could be used as a servo actuator.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2002.11a
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• pp.161-161
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• 2002

수도권 지역에서 3차원 바람장 및 농도장의 공간 특징을 모의하기 위해 AWS 자료동화 기법을 호주 CSIRO에서 개발된 비정역학 TAPM(The Air Pollution Model, V.2) 에 적용하여 2002년 7월 2일부터 7월 11일까지 10일 동안 1km$\times$1km격자에서 바람장 및 농도장을 도출하였다. (중략)

• Proceedings of the Korean Information Science Society Conference
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• 2002.04b
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• pp.709-711
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• 2002

웹 기반의 교육의 활성화로 이를 학습에 응용하기 위한 노력으로 GVA(Global Virtual Academy) 등과 같은 학습 보조 도구가 많이 발표하고 있는 설정이다. 대부분의 학습 보조 도구들은 각각의 특성들만 제시할 뿐 통합된 표준호가 되어 있지 않다. 최근 가상교육에서 학습기술이 상호운용성에 기반한 표준화의 일반적인 필요성을 인식하게 됨에 다라 가상교육의 국제표준을 소개하고 체계적으로 AICC(Aviation Industry CBT Committee), IMS Global Learning Consortium, ADL(Advanced Distributed Learning)을 중심으로 진행되어 오고 있다. 웹 기반의 교육을 통한 질의 응답의 학습방법을 고려한 도구가 없으므로 질의 응답 학습 도구(QALT)지원을 위한 표준화된 LTSA(Learning Technology Standard Architecture) 기반 시스템을 학습 객체에 대한 질의 응답과 개방형 단순 질의 응답 측면으로 구현한다. 그러므로 개방형 단순 질의 응답 측면을 구현하기 위해 학습 기술의 표준화로 제시되어 있는 LOM(Learning Object Metadata)을 통해 설계 자체를 체계화하고 전체적으로 명세 작업을 가능하게 하여 일관성을 유지하는 정련화된 문서로 질의 응답할 수 있도록 한다. 또한, Web 상에서의 Network delivery와 DTD(Document Type Definition)와 Stylesheet를 사용자가 쉽게 수정 가능하며 다양한 Linking Type을 제공하므로 단순 질의 응답 문서의 형식을 XML로 한다

• YAKHAK HOEJI
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• v.37 no.2
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• pp.193-197
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• 1993

For the investigation of medicinal resources in Crataegus species, a study was carried out to clarify the constituents in the leaves of Crataegus Pinnatifida var. pubescens (Rosaceae), of which fruits have been used to stomachic, digestive, astringent, analgesic, and cardiotonic, etc. as a folk medicine in Korea. From the n-BuOH fraction of MeOH extract two flavone glycosides, vitexin(apigenin-8-C-$\beta$-D-glucopyranoside) and 2"-O-rhamnosyl vitexin(apigenin-8-C-$\alpha$-L-rhamnosyl-(1$\rightarrow$2)-$\beta$-D-glucopyrano side) were isolated and identified on the basis of their physico-chemical properties and spectroscopic evidences(UV, IR, NMR, FAB-Mass etc.) in comparision with authentic samples.amples.

• Journal of the Korean Society for Railway
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• v.9 no.1 s.32
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• pp.18-22
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• 2006

The dynamic characteristics of the current collection system are investigated by conducting a test run in which signals from accelerometers and load cells attached to the various parts of the pantograph are analyzed in both the time and frequency domains. The dynamic characteristics of the current collection system are found to be strongly influenced by the train speed; the fluctuation in the pantograph motion increases in direct proportion to the train speed. There exist two major fequency components in the pantograph motion related to the current collection, a speed-dependent component arising from the train traversing a span of the catenary, and a speed-independent component related to the pantograph resonant frequency. The train acceleration is also found to exert strong influence on the current collection system characteristics. The effect of the train motion is found to be stronger on the speed-dependent frequency component than on the speed-independent one.

• Proceedings of the KSR Conference
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• 1998.05a
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• pp.525-532
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• 1998

In this study, dynamic characteristics of catenary that supplies electrical power to high-speed trains is investigated. A particular emphasis is placed on the effect of droppers on the dynamic response of the contact wire, a dropper is an element that connects the contact wire with the messenger wire so as to maintain near uniform compliance, Finite element model compressing 3 spans is constructed. For the linear model, droppers are modeled as linear springs with various stiffness values. Modal analysis is performed to obtain the natural frequencies and modes and the variation in the modal density distribution for changing stiffness values are noted. Impulse response is also obtained through computer simulation. In practice, dropper is a nonlinear element with low stiffness in compression and high stiffness in tension. Hence, dropper can be modeled as a nonlinear spring with hi-directional stiffness values. Impulse and harmonic responses are obtained for the nonlinear model through simulation. The responses aye also compared with the linear cases.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.6
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• pp.397-402
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• 2016

This paper proposes a robust tracking control for constrained uncertain linear systems by combining a disturbance observer (DOB) and linear matrix inequality (LMI) based state feedback control. To this end, the state feedback control is designed for the nominal system and then a DOB based feed-forward control is added to reject uncertainties. In doing so, the DOB and state feedback controller are joined in a way that the combined control satisfies the input constraints and closed loop stability is guaranteed. Simulation results are provided to show that the proposed control scheme successfully stabilizes uncertain systems.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.5
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• pp.9-17
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• 2013

In this paper we introduce modular symmetric designs and use them to study the existence of Hadamard-Jacket matrices modulo 3/5. We prove that there exist 5-modular Hadamard-Jacket matrices of order n if and only if n≢3.7 (mod 10) and n≢6,11. In particular, this solves the 5-modular version of the Hadamard conjecture.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.313-316
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• 2005

In the recent design of high ductile fiber-reinforced cementitious composite ECC, which exhibits tensile strain-hardening behavior in the hardened state, optimizing both processing mechanical properties for specific applications is critical. This study introduced a method to develop useful ECCs in field, which possess the different fluid properties to facilitate diverse types of processing (i.e., self-consolidating or spray processing). Control of rheological modulation was regarded as a key factor to allow the performance of the desired processing, while retaining the ductile material properties. To control the rheological properties of the composite, we first determined basic ECC compositon, which is based on micromechanics and steady-state cracking theory. The stability and consequent viscosity of suspensions were, then, mediated by optimizing dosages of chemical and mineral admixtures. The rheological properties altered by this approach were revealed to be effective in obtaining ECC hardened properties, allowing us to readily achieve the desired function of the fresh ECC.