• Proceedings of the KSME Conference
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• 2005.11a
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• pp.63.1-63.1
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• 2005

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.386-386
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• 2015

담수가 해수에서 흘러드는 하구에서는 성층이 관측되며 이것은 난류의 미세구조를 변화시키는 주요 원인으로 작용한다. 이러한 성층화 현상은 하구 내 부유사의 군집인 하구 최대혼탁수(Estuarine Turbidity Maximum, ETM)의 형성에 영향을 주게 된다. 본 연구는 성층의 하구 최대 혼탁수 생성 메커니즘에 관심을 두고 수치모델링을 활용한 미세 난류의 부유사 거동 분석에 초점을 두었다. 성층과 전단응력 사이의 난류 혼합을 대표하는 유동인 켈빈-헬름홀츠 불안정성(Kelvin-Helmholtz Instability)을 도입하고 성층 경계면 근처에서 부유사의 이송을 높은 레이놀즈수(Reynolds number) 유동에서 RANS(Reynolds-averaged Navier-Stokes Simulation)보다 다양한 규모의 에너지 획득이 가능하여 미세 난류 구조 재현에 장점을 갖는 Large-eddy Simulation(LES)를 활용하여 모사하였다. 여기에서, 부유사는 주위 유동의 물리적 특성 변화에 영향을 미치지 않는 Passive scalar로 가정하였으며 $6^{th}$-order Lagrangian 다항식 보간법을 적용하여 입자의 이동 속도를 계산하고 이를 시간에 대해 적분함으로써 이동 궤적을 추적하였다. 수치 모델 결과 Lock-exchange 유동 내에서 켈빈-헬름홀츠 불안정성이 발생함에 따라 경계면 주위에 위치한 부유사가 billow 내에서 트랩핑(trapping)되는 것을 보여주어 KH-billow 혹은 braids 내의 미세 난류에 의한 영향이 확인되었다. 본 연구에서는 LES를 활용하여 성층류 및 성층류 내의 부유사 혼합을 모사하여 난류의 정도에 따른 이동 궤적의 차이에 대해서 분석함으로써 성층의 난류 강도 저하에 따른 부유사의 군집으로의 영향에 대해 서술한다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.8
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• pp.711-717
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• 2007

Shape optimization of a staggered herringbone groove micromixer using three-dimensional Navier-Stokes analysis has been carried using Kriging model. The analysis of the degree of mixing is performed by the calculation of spatial data statistics. The calculation of the variance of the mass fraction at various nodes on a plane in the channel is used to quantify mixing. A numerical optimization technique with Kriging model is applied to optimize the shape of the grooves on a single wall of the channel. Three design variables, namely, the ratio of groove width to groove pitch, the ratio of the groove depth to channel height ratio and the angle of the groove, are selected for optimization. A mixing index is used as the objective function. The results of the optimization show that the mixing is very sensitive to the shape of the groove which can be used in controlling mixing in microdevices.

• Journal of the Korean Magnetics Society
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• v.11 no.4
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• pp.157-162
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• 2001

Rheological characteristics of Sm-Co type plastic magnet compound for powder injection molding process were investigated with the variation of the magnetic powder size, their relative contents and volume fraction using the mixture of fine and coarse powder. Shear viscosity of Sm-Co type compound was decreased with increasing the size of coarse powder due to the increase of powder packing density. However, the smaller the average size of fine powder resulted in the higher viscosity of compound due to the increase of agglomeration force. In case of mechanically milled Sm-Co type powder, the viscosity of compound with the mixture of coarse powder of 125∼75 ㎛ and fine powder of average size of 4.9 ㎛ greatly depends on their relative contents and shows a minimum value at the 60 % coarse powder fraction. This means that the compound shows a maximum packing density at the 60% coarse powder fraction. Compound viscosities satisfied well the rheological model with the volume fraction of magnetic powder, and maximum volume fraction of magnetic powder in Sm-Co type compound for powder injection molding was about 66%.

• Journal of the Korean earth science society
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• v.41 no.1
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• pp.1-18
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• 2020

This study presented the effects of the assumed mass-size relationship for snow on the simulated surface precipitation by using cloud microphysics parameterizations in Weather Research and Forecasting (WRF) model. The selected cloud microphysics parameterizations are WRF Double-Moment 6-class (WDM6) and WRF Single-Moment 6-class (WSM6) in the WRF model. We replaced the mass-size relationship for snow in WDM6 and WSM6 with Thompson's mass-size relationship retrieved from measurement data. The sensitivity of the modified WDM6 and WSM6 was tested for the idealized 2-dimensional squall line and winter precipitation system over the Korean peninsula, respectively. The modified WDM6 and WSM6 resulted in the increase of graupel/rain mixing ratios and the decrease of snow mixing ratio in the low atmosphere. The changes of hydrometeor mixing ratio and surface precipitation could be due to the collision-coalescence process between raindrops and snow and the graupel melting process.

• Annual Conference on Human and Language Technology
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• 2022.10a
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• pp.531-534
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• 2022

신경망 기반 심층학습 기술은 대화처리 분야에서 대폭적인 성능 개선을 가져왔다. 특히 GPT-2와 같은 대규모 사전학습 언어모델을 백본 네트워크로 하고 특정 도메인 타스크 대화 데이터에 대해서 미세조정 방식으로 생성되는 종단형 대화모델의 경우, 해당 도메인 타스크에 대해서 높은 성능을 내고 있다. 하지만 이런 연구들은 대부분 하나의 도메인에 대해서만 초점을 맞출 뿐 싱글 모델로 두 개 이상의 도메인을 고려하고 있지는 않다. 특히 순차적인 미세 조정은 이전에 학습된 도메인에 대해서는 catastrophic forgetting 문제를 발생시킴으로써 해당 도메인 타스크에 대한 성능 하락이 불가피하다. 본 논문에서는 이러한 문제를 해결하기 위하여 MultiWoz 목적지향 대화 데이터에 오픈 도메인 칫챗 대화턴을 유사도에 기반하여 추가하는 데이터 증강 방식을 통해 사용자 입력 및 문맥에 따라 MultiWoz 목적지향 대화와 오픈 도메인 칫챗 대화를 함께 생성할 수 있도록 하였다. 또한 목적지향 대화와 오픈 도메인 칫챗 대화가 혼합된 대화에서의 시스템 응답 생성 성능을 평가하기 위하여 오픈 도메인 칫챗 대화턴을 수작업으로 추가한 확장된 MultiWoz 평가셋을 구축하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4A
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• pp.281-290
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• 2009

In this study, an analysis technique of hybrid girder considering nonlinearity of steel-concrete contact surface is presented. Steel-concrete hybrid girder shows partial-interaction behavior due to the deformation of shear connectors, slip and detachment at the interface, and cracks under the applied loads. Therefore, the partial-interaction approach becomes more reasonable. Contact surface is modeled by interface element and analyzed nonlinearly because of cost of time and effort to detailed model and analysis. Steel and Concrete are modeled considering non-linearity of materials. Material property of contact surface is obtained from push-out test and input to interface element. For the constitutive models, Drucker-Prager and smeared cracking model are used for concrete in compression and tension, respectively, and a von-Mises model is used for steel. This analysis technique is verified by comparing it with test results. Using verified analysis technique, various analyses are performed with different parameters such as nonlinear material property of interface element and prestress. The results are compared with linear analysis result and analysis result with the assumption of full-interaction.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1661-1668
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• 1990

In a turbulent premixed flame stabilized by the streamline step, and dominated by a coherent eddy, a flame micro-structure was investigated with analyzing the signals of temperature, the ion current, and schieren phtographs simultaneously. Generally the contours of large scale coherent eddies of schlieren photographs was considered as the flame front, however, the main reaction can be occurred within the eddy as a structure of fine flamelets scale. The surrounding burned gas of flamelets could not propagate to a unburned mixture, obstructing flamelets from propagating to a unburned mixture. Consequently, it could restrain flashback. The main reaction region was found to be located at higher temperature of the burned gas rather than at maximum rms of fluctuating temperature. The peak probability of higher temperature was 6 times greater than that of lower temperature. As it was difficult to infer a flame structure from PDF distribution of the fluctuating temperature in form of bimodal shape, it should be taken into consideration with other informations related to the sensitive flame front, for instance, ion current.

• Journal of KIISE:Computer Systems and Theory
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• v.34 no.8
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• pp.327-336
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• 2007

Lots of effort toward design optimizations have been paid for a cost-effective system design in various ways from a transistor level to RTL designs. In this paper, we propose a bit level optimization of an adder design for expanding its design space. For the bit-level optimization, a heterogeneous adder organization utilizing a mixture of carry propagation schemes is proposed to design a delay-area efficient adder which were not available in an ordinary design space. Then, we develop an optimization method based on Integer Linear Programming to search the expanded design space of the heterogeneous adder. The novelty of the Proposed architecture and optimization method is introducing a bit level reconstruction/recombination of IPs which have same functionality but different speed and area characteristics for producing more find-grained delay-area optimization.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2018.06a
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• pp.173-174
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• 2018

배경제거는 영상에서 움직이는 객체를 분리할 때 유용한 방법이며, 대표적인 예인 Mixture of Gaussian (MOG) 알고리즘은 픽셀 당 3-5 가우스 모델을 혼합해 배경과 움직이는 객체를 구분한다. 소형 표적을 추적하기 위해서는 화소 혹은 작은 블록 단위로 시/공간적 밝기 변화량을 이용하는 옵티컬 플로우 기법이 적절하다. 본 논문에서는 소형 표적의 강인한 객체 추적을 위해 MOG2와 옵티컬 플로우의 결합 방법을 소개한다. 제안된 방법은 MOG2를 사용하여 전경 영역을 획득하고 전경 영역에만 옵티컬 플로우를 적용한다. 실험 결과는 제안 방법이 잡음과 배경의 미세 변화가 있더라도 무인 비행체를 잘 추적할 수 있음을 보여준다.