• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3B
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• pp.325-335
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• 2010

The aim of this study is to survey the effects of laying drainage layer in sandy beach on beach stabilization. At first, the numerical model developed by Hur and Lee (2007), which is able to consider the flow through a porous medium with inertia, laminar and turbulent resistance terms, i.e. simulate directly WAve Structure Seabed/Sandy beach interaction and can determine the eddy viscosity with LES turbulent model in 3-D wave field (LES-WASS-3D), is validated by comparing with existing experimental data. And then, numerical simulation is carried out to examine the characteristics of wave-sandy beach interaction for a beach with/without drainage layer. From the numerical results, it is shown that mean ground-water level around a foreshore decreases and offshore-ward flow over a seabed reduces in case of a beach with drainage layer. Moreover, the effects of cross profile of drainage layer and incident wave condition on mean ground-water level around a foreshore are also discussed as well the distribution of wave setup around the foreshore.

• Proceedings of the Korean Printing Society Conference
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• 2001.06a
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• pp.45-45
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• 2001

자료의 보존에 있어서 종이의 열화로 인해 자료의 분석, 열화메커니즘의 해석, 종이의 보존이란 측면 하에서의 관심이 서서히 집중되고 있는 실정이며, 그 중요성도 크게 대두되고 있는 실정이다. 산성지를 중성화하는 화학적시스템, 즉, 탈산성화처리는 알카리계금속(Ca, Mg, Zn, Na)과 유기용매, 수용성용매를 이용하여 이들 약품을 종이내에 침투시켜 중성화(pH 6-8) 함으로써 종이의 주성분인 cellulose를 보다 안정화시키는 방법으로 산을 중화하여 보존성을 향상시킬 수 있는 것이다. 즉, 탈산처리란 화학적으로 종이속에 생기는 산 또는 산을 발생하는 물질을 알칼리물질로 중화하는 것이다. 또한 중화후 알칼리 물질이 종이에 잔류하면 장래에 내부적으로 발생하는 산이나 외부(대기중의 오염물질 등) 로부터 침입하는 산도 중화하여 보존성을 향상시킬 수가 있다. 따라서, 본 연구는 산성초지법에 의해 제조된 용지들의 열화특성과 알카리 토금속을 처리한 후에 알카리도를 상승시킨 용지의 열화특성을 물리·화학적 변화를 통하여 종이의 보존성을 비교 검토·규명함으로써 문(도)서의 보존체계를 마련하고자 하며, 보존과 관련된 기초자료를 얻고자 실시하였다.

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.19-24
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• 2002

Recent studies of a triple flame suggested that the presence of triple point (triple line in this planar configuration) could explain the mechanisms of stable fuel-lean premixed flames with equivalence ratio lower than the flammability limit. In the present study, for better understanding of the stability mechanisms of fuel rich-lean premixed flames, the fuel-rich flames were replaced with hot coils that will provide heat flux into the fuel-lean flames. It is found that the fuel-lean premixed flames could be stabilized without any triple point (triple line): however, the equivalence ratio limit for stable fuel-lean flame in this case is higher than that of the present work with the presence of fuel-rich flames. These results demonstrate that heat flux coming from fuel-rich flames should be considered in order to properly understand the roll of a triple flame for stable fuel rich-lean flames.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.91-98
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• 2015

Formamide의 중성가수분해 mechanism은 QM/MM (quantum mecahnics/molecular mechanics) molecular dynamics simulations 및 CPMD과 같은 방법으로 연구되어왔다. 본 연구에서는. Umbrella sampling을 이용한 QM/MM-MD simulation을 사용하여 4가지 반응의 free energy surface를 도출해냈다. 전체적으로, 가장 선호되는 메커니즘은 two step으로 구성된 water assisted stepwise mechanism이었으며 모든 mechanism은 ab-initio calculation과 QM/MM-MD simulation이 수행되었다. water assisted stepwise mechanism을 살펴보면, 첫 번째 step에서 formamide의 carbonyl group이 hydrate되면서 gem-diol intermediate를 형성한다. 다음 step에서, intermediate의 hydroxyl group으로부터 amino group으로 water-assisted proton transfer이 일어난다. 두 반응 모두에서 물이 proton transfer를 직접적으로 도와주는 것을 관찰할 수 있었다. 특히, ab-initio calculation과는 다르게 QM/MM-MD에서는 gem-diol intermediate가 안정화되는 것으로 solvent effect를 잘 보여준다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.3
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• pp.309-319
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• 2011

We experimentally investigated lifted propane jet flames diluted with nitrogen to obtain flame-stability maps based on heat-loss-induced self-excitation. We found that heat-loss-induced self-excitations are caused by conductive heat loss from premixed flame branches to trailing diffusion flames as well as soot radiation. The conductive-heat-loss-induced self-excitation at frequencies less than 0.1 Hz is explained well by a suggested mechanism, whereas the oscillation of the soot region induces a self-excitation of lift-off height of the order of 0.1 Hz. The suggested mechanism is also verified from additive experiments in a room at constant temperature and humidity. The heat-loss-induced self-excitation is explained by the Strouhal numbers as a function of the relevant parameters.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.6
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• pp.639-646
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• 2012

The characteristics of autoignited lifted flames in laminar jets of carbon monoxide/hydrogen fuels have been investigated experimentally in heated coflow air. In result, as the jet velocity increased, the blowoff was directly occurred from the nozzle-attached flame without experiencing a stabilized lifted flame, in the non-autoignited regime. In the autoignited regime, the autoignited lifted flame of carbon monoxide diluted by nitrogen was affected by the water vapor content in the compressed air oxidizer, as evidenced by the variation of the ignition delay time estimated by numerical calculation. In particular, in the autoignition regime at low temperatures with added hydrogen, the liftoff height of the autoignited lifted flames decreased and then increased as the jet velocity increased. Based on the mechanism in which the autoignited laminar lifted flame is stabilized by ignition delay time, the liftoff height can be influenced not only by the heat loss, but also by the preferential diffusion between momentum and mass diffusion in fuel jets during the autoignition process.

• KDI Journal of Economic Policy
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• v.19 no.1
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• pp.51-104
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• 1997

최근의 고금리논쟁과 자본시장개방에 대응한 정책방안을 둘러싼 많은 논의의 핵심은 우리나라의 제반 거시경제여건을 반영하는 장기적 의미에서의 균형금리수준이 어느 정도인가에 대한 것이다. 장기적인 관점에서 볼 때 한 나라의 금리수준은 그 나라의 거시경제여건을 반영하는 균형금리의 추세를 반영하기 마련이며, 이러한 균형금리수준을 왜곡하는 정책 및 규제는 경제의 불안정성을 야기할 뿐, 민간부문의 규제회피노력 등으로 결국은 무력화될 소지가 높기 때문이다. 본 연구의 목적은 우리나라 금리변동의 요인 및 특성에 대해 세밀히 살펴보고, 국내외 실질금리격차의 실증분석을 통하여 그 구조적 원인을 파악하여 보며, OECD 국제비교분석을 통하여 현재 우리나라의 균형금리수준을 가늠하여 봄으로써, 향후 본격적인 자본시장개방에 대응한 통화금융정책의 모색에 하나의 지표를 제시하여 보려는데 있다. 본고의 연구분석결과에 의하면 우리나라의 명목금리는 실질경제성장률 외에도 기대인플레이션 및 경상수지적자와 밀접한 관계가 있으며, 해외금리 및 예상환율절하율도 점차 주요한 금리의 설명변수로서 나타나고 있다. 엄밀한 의미에서의 피셔효과는 기각되나 기대인플레이션이 명목 및 실질금리의 가장 주요한 변동요인으로 나타나 물가안정을 통한 인플레이션 기대심리의 불식이 향후 금리안정의 관건으로 분석되었다. 특히 통화공급의 유동성효과는 단기적으로만 나타나며 장기적으로는 오히려 금리상승을 유발하는 것으로 나타나 금리안정을 위해서는 안정적인 통화관리가 중요한 것으로 분석되었다. OECD 국제비교분석을 통하여 추정해 본 결과 우리나라의 1997년 균형금리수준은 회사채수익률 기준 약 11%대로 나타나 소폭의 금리하락 가능성이 있으나 지속적인 경상수지의 불균형 등 금리하락여건은 여의치 않은 것으로 보인다. 이미 자본시장개방이 진전된 OECD 국가들의 실증분석에서도 나타나듯이 금리의 하향안정화는 거시경제의 안정과 금융의 효율성 제고가 동시에 이루어져야만 가능한 것이다. 그러므로 향후 금리정책은 금리의 가격기능을 조속히 회복시켜 자원배분의 효율성을 극대화할 수 있는 시장메커니즘을 활성화하는 방향으로 추진되어야 할 것이다.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.3
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• pp.233-239
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• 2013

This paper presents the analysis and control of the position of the COG (Center of Gravity) for a two-wheel balancing robot. The two-wheel balancing robot is required to maintain balance by driving two wheels only. Since the robot is not exactly symmetrical and its dynamics is changing with respect to moving parts, robust balancing control is difficult. Balancing performance becomes difficult when two arms hold a heavy object since the center of gravity is shifted out of the wheel axis. Novel design of a sliding waist mechanism allows the robot to react against the shift of the COG by moving the whole upper body to compensate for the imbalance of the mass as a counter balancer. To relocate the COG position accurately, the COG is analyzed by force data measured from two force sensors. Then the sliding COG mechanism is utilized to control the sliding waist position. Experimental studies are conducted to confirm the proposed design and method.

• Journal of Adhesion and Interface
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• v.21 no.2
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• pp.41-50
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• 2020

Organic-inorganic metal halide perovskite has shown a great promise in photovoltaic applications because of the skyrocketing power-conversion efficiencies up to 25.2% and their potentially low production cost. However, it also has critical issue of substantial material degradation during device operation to be overcome for successful commercialization. Understanding the nature of defects and their photochemistry related to material degradation is needed. Furthermore, strategy to passivate defects in perovskite should be adopted to improve the stability of perovskite. In this article, we present predominant defects formation in perovskite that contribute to material degradations in perovskite solar cells. We then discuss how material stability can be improved through reliable defect passivation engineering.

• Journal of KIISE
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• v.44 no.7
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• pp.726-732
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• 2017

In practical distributed sensing and prediction applications over wireless sensor networks (WSN), environmental sensing activities are highly dynamic because of noisy sensory information from moving source signals. The recent distributed online convex optimization frameworks have been developed as promising approaches for solving approximately stochastic learning problems over network of sensors in a distributed manner. Negligence of mobility consequence in the original distributed saddle point algorithm (DSPA) could strongly affect the convergence rate and stability of learning results. In this paper, we propose an integrated sliding windows mechanism in order to stabilize predictions and achieve better convergence rates in cooperative detection of a moving source signal scenario.