• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.12
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• pp.63-69
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• 1999

Center of photon mass, defined as the center of axial photon distribution in each half, is proposed as a unified design parameter in quarter wavelength shifted(QWS) DFB lasers. Shown is the way the parameter is related to the threshold pain difference and uniformity in axial photon density, which determine single-frequency stability of DFB lasers. Also, a general rule for single-frequency DFB laser design is presented. Using the design rule, we propose a sampled grating QWS-DFB laser that has a wider $_KL$ range 0f 100% single-frequency yield.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1258-1261
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• 2004

ACSR전력선의 송전용량 증가를 위해 개발된 증용량저이도 송전선인 STACBUAW(Super Thermal-resistant Aluminum alloy Conductors, aluminum-clad Invar-Reinforced)전선은 초내열 Al도체 및 인바강선의 사용으로 비교적 고온에서의 안정적 운전이 가능하다. 그러나 고온 환경에서 장시간 노출된 STACIR/AW전선의 안정적 관리를 위해서는, 열화 된 STACIR/AW 전선의 인장강도, 각 구성소재의 탄성 계수, 비틀림 계수 둥과 같은 기계적 물성이 장기 운전 모의를 위해 설정된 열화온도, 열화시간 등에 대해 종합적으로 평가될 필요가 있다. 또한 크립 등과 같이 고온응력 부하상태에서의 변형거동과 탄성계수 및 선 팽창계수의 온도의존성 등은 전선의 이도관리와 예측을 위해서도 명확히 규명되어야할 중요한 관리 인자이다. 그러나 현재까지는 이들에 대해 수행한 어떠한 연구결과들도 보고 되어 있지 않은 실정이다. 본 연구에서는 STACIR/AW $410mm^2$ 송전선을 장시간 운전의 모의를 위해 가속열화 시키고 가속열화에 따른 STACIR/AW전선 및 그 구성소재의 강도, 비틀림 특성의 변화를 조사하여 장시간 운전에 따른 STACIR/AW전선의 안정성을 평가하여 보고하고자 하였다.

• Journal of Korean Society of Steel Construction
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• v.22 no.4
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• pp.293-303
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• 2010

The purpose of this study was to evaluate the influence of the methods of application of the direct analysis method, using the load amplification factor suggested by the KBC 2009 design code, for the evaluation of frame stability. For this purpose, the direct analysis method was performed for three-story-one-bay and five-story-three-bay unbraced steel frames with various notional loads, bending stiffness reductions, and factor B2s. The results of the analyses were compared with the results of the second-order inelastic analysis to evaluate the influence of the applied methods. The scale of the frame, the axial load ratio, and the axial load distribution pattern were added to the main parameters to investigate the external effects. The research results showed that the influence of the methods of application of the direct analysis method is not significant in the case of the required axial strength and the application of the additional notional loads; and that the application of the factor B2 with the story stiffness concept to the direct analysis method is appropriate for the required flexural strength.

• Composites Research
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• v.31 no.6
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• pp.371-378
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• 2018

In this study, the thermoelastic properties of poly lactic acid (PLA) based nanocomposites are predicted by molecular dynamics (MD) simulation and a micromechanics model. The stereocomplex mixed with L-lactic acid (PLLA) and D-lactic acid (PDLA) is modeled as matrix phase and a single walled carbon nanotube is embedded as reinforcement. The glass transition temperature, elastic moduli and thermal expansion coefficients of pure matrix and nanocomposites unit cells are predicted though ensemble simulations according to the hydrolysis. In micromechanics model, the double inclusion (D-I) model with a perfect interface condition is adopted to predict the properties of nanocomposites at the same composition. It is found that the stereocomplex nanocomposites show prominent improvement in thermal stability and interfacial adsorption regardless of the hydrolysis. Moreover, it is confirmed from the comparison of MD simulation results with those from the D-I model that the interface between CNT and the stereocomplex matrix is slightly weak in nature.

• Journal of Energy Engineering
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• v.9 no.2
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• pp.146-155
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• 2000

연료분출을 수반하는 원통형 보염기 후류에 형성되는 확산화염에 대한 이온전류의 특성과 화염의 안정범위를 측정, 분석함으로써 연소특성을 고찰하였다. 난류강도가 큰 경우의 화염일수록 화염의 안정성은 악화되며, 화염내 중앙의 평균 이온전류값이 가장 높은 값을 갖는 영역은 블로오프 직전상태에 비해서 안정시의 경우 더욱 하류측에 존재한다. 난류의 정도가 강한 화염의 경우 국소적으로 반응이 활발한 화염 덩어리가 빠른 속도로 이동하며, 난류의 정도가 강한 화염의 경우에는 반응이 완만한 화염 덩어리가 저속으로 이동한다. 재순환영역에서 주류유동측으로 이동함에 따라 자기상관계수의 저하가 빨라지고 난류 시간스케일이 작아지며, 부염기 직후에서 하류로 이동함에 따라 자기상관계수의 저하가 늦어지고 난류시간스케일이 커진다. 주류공기에 강한 난류를 가하지 않은 경우에는 큰 난류시간스케일에 대응되는 저주파수 특성이외에도 작은 난류 시간스케일에 대응되는 고주파수 특성이 나타나며 , 주류공기에 강한 난류를 가한 경우에는 큰 난류 시간스케일에 대응되는 저주파수 특성이 나타난다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.382.2-382.2
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• 2016

현재 전 세계적으로 에너지 소비가 급격히 증가하고 있다. 하지만 급격한 에너지 소비에 따른 자원 및 에너지 공급의 불확실성은 점점 높아지고 있다. 특히, 우리나라는 공급 에너지의 96.4%를 해외 수입에 의존하고 있기 때문에 에너지 안보에 매우 취약한 구조를 갖고 있다. 그리고 열전달 시스템에서 임계 열유속은 열전달 시스템의 한계를 나타낸다. 따라서 임계 열유속의 향상은 열전달 시스템의 안전성의 향상을 위한 필수적인 요소이다. 이에 따라 다양한 산업에서 열전달 시스템을 통하여 막대한 양의 에너지가 소비됨에 따라 우수한 열전달 특성을 가진 나노유체를 사용하여 열전달 시스템의 효율 및 안정성을 높이고자 하는 많은 연구가 진행되고 있다. 따라서 본 연구에서는 유동 비등에서 그래핀 나노 유체 사용에 따른 열전달 특성을 분석하였다. 유동 비등에서 0.01 vol%의 산화 처리된 그래핀 나노유체를 사용하였을 경우 유속이 증가함에 따라 임계 열유속은 증가하였으며 유속이 증가함에 따라 비등 열전달 계수도 증가함을 확인하였다. 그리고 임계 열유속은 순수 물보다 최대 66.32% 증가하였으며, 비등 열전달 계수는 풀비등에서 보다 최대 28.14% 증가함을 확인하였다.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.9
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• pp.1075-1080
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• 2014

This study aims at dedicating to relevant technology fields by suggesting design methods of structures and estimating their safety in relation to substructure for offshore wind power requiring high safety to various environment conditions. Especially, with respect to 5MW Offshore Wind Power System, this study will provide information about major wind directions and duration in combination with the developing wave climate at the test field. Therefore, connections between wind fields and approaching wave trains will be estimated and their intensity, direction and time shift will be pointed out. Furthermore, the local pressure distribution of breaking waves will be investigated by physical and numerical modeling. The currently applied structural and fatigue assessment of support structures for offshore wind energy converters is based on common design rules. Normally, constructions in structural engineering are treated as limited, single structures. This means that varying aspects of manufacturing are considered by high safety factors.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.121-131
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• 2003

Tunneling in difficult geological conditions is often inevitable especially in urban areas. Ground improvement and reinforcement techniques are often required to guarantee safe tunnel excavations and/or to prevent damage to adjacent structures. The steel pipe-reinforced multistep grouting method has been recently applied to tunnel sites in Korea as an auxiliary technique. In this study, the face stability with steel pipe-reinforced multistep grouting was evaluated emphasizing the effect of seepage forces. The study revealed that the influence of the steel pipe-reinforced multistep grouting on the support pressure in dry condition is not significant while there is relatively a large amount of reduction in seepage forces by adopting the technique in saturated condition. The effect of the anisotropy of permeability on the seepage force acting on the tunnel face was also estimated by conducting the coupled analysis. It was found that a higher horizontal permeability compared with the vertical one causes reduction in the seepage farce acting on the tunnel face.

• Korean Journal of Optics and Photonics
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• v.8 no.1
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• pp.37-41
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• 1997

The optical property, the environmental stability and the crystallization of ZnS thin films prepared by ion-assisted deposition (IAD) were investigated and compared with those of conventional electron-beam deposited thin films. The humidity(R.H. 85%) test and the thermal(15$0^{\circ}C$) show that the IAD films have relatively higher refractive index, smaller extinction coefficient and environmentally more stable than the conventional films. It is believed to originate from the reduced adsorption of moisture which reflect the increased packing density and the improved microstructure by ion bombardment. XRD experiments also confirm that conventionally grown films have an amorphous in comparison with the crystalline structured IAD films.

• Journal of the Korean GEO-environmental Society
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• v.10 no.1
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• pp.49-54
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• 2009

The seismic slope stability is most often evaluated by the pseudo-static limit analysis, in which the earthquake loading is simplified as static inertial loads acting in horizontal and/or vertical directions. The transient loading is represented by constant acceleration via the pseudostatic coefficients. The result of a pseudostatic analysis is governed by the selection of the value of the pseudostatic coefficient. However, selection of the value is very difficult and often done in an ad hoc manner without a sound physical reasoning. In addition, the maximum acceleration is commonly estimated from the design guideline, which cannot accurately estimate the dynamic response of a slope. There is a need to perform a 2D dynamic analysis to properly define the dynamic response characteristics. This paper develops a new hybrid pseudostatic method that links the modified one-dimensional seismic site response analysis and the pseudostatic algorithm. The modified site response analysis adjusts the density of the layers to simulate the change in mass and weight of the layers of the slope with depth. Multiple analyses were performed at various locations within the slope to estimate the change in seismic response of the slope. The calculated peak acceleration profiles with depth from the developed procedure were compared to those by the two-dimensional analyses. Comparisons show that the two methods result in remarkable match. The calculated profiles are used to perform pseudostatic analysis. The results show that use of peak or a fraction of acceleration at the surface can seriously underestimate or overestimate the factor of safety, and that the proposed procedure significantly enhances the reliability of a standard procedure.