• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1527-1534
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• 2016

Online voltage stability monitoring using real-time measurements is one of the most important tasks in a smart grid system to maintain the grid stability. Loading margin is a good indicator for assessing the voltage stability level. This paper presents an Extreme Learning Machine (ELM) approach for estimation of voltage stability level under credible contingencies using real-time measurements from Phasor Measurement Units (PMUs). PMUs enable a much higher data sampling rate and provide synchronized measurements of real-time phasors of voltages and currents. Depth First (DF) algorithm is used for optimally placing the PMUs. To make the ELM approach applicable for a large scale power system problem, Mutual information (MI)-based feature selection is proposed to achieve the dimensionality reduction. MI-based feature selection reduces the number of network input features which reduces the network training time and improves the generalization capability. Voltage magnitudes and phase angles received from PMUs are fed as inputs to the ELM model. IEEE 30-bus test system is considered for demonstrating the effectiveness of the proposed methodology for estimating the voltage stability level under various loading conditions considering single line contingencies. Simulation results validate the suitability of the technique for fast and accurate online voltage stability assessment using PMU data.

• 전자공학회논문지B
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• 제31B권11호
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• pp.151-162
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• 1994

다차원 시스템(multidimensional system)에 대한 정확한 모델링을 위해 “자율 분산 신경망(Self-organized Distirbuted Networks, SODN)”을 제안하였다. 제안한 신경망은 자율 신경망(Self-organized Networks)과 다수의 소규모 다층 신경망(Multilayer Neural Networks)이 조합되어 지역적 병렬 학습을 수행하는 부분 학습망으로서 학습 속도가 빠르고 학습의 정밀도를 높일 수 있으며 타 부분망 학습에서 문제가 되는 과다한 학습 메모리 소요와 학습되니 않은 영역에 대한 낮은 일반화능력 등의 문제가 보완된 새로운 신경망이다. 학습 실험 결과, 제안한 신경망은 기존의 다층 신경망과 RBF(Radial Basis Function) 신경망에 비해서 우수한 성능을 보였다.

• 대한수학교육학회지:수학교육학연구
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• 제15권2호
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• pp.215-232
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• 2005

컴퓨터 대수 체계(CAS) 계산기는 점차 학교와 대학에서 보편화되어가고 있다 이 계산기는 교사와 학생들에게 꽤 정교한 수학적 기능을 제공하지만, 현재로서는 어떻게 잘 활용될 수 있는지에 대해서 명확하지 않다. 특히 학생들의 학습과 문제 해결의 통합은 문제로 남아있다. 본 논문에서 우리는 TI-89 CAS 계산기를 대학에 입학하려는 학생들에게 도입하는 연구에서 이러한 문제를 제기하고 학생들이 그들의 학습에서 CAS 계산기를 조작하면서 형성하는 협력 관계의 여러 측면을 기술하였다.

• 전자공학회논문지C
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• 제35C권2호
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• pp.56-64
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• 1998

Multi-layered perceptrons that are a nonlinear neural network model, have been widely used for various applications mainly thanks to good function approximation capability for nonlinear fuctions. However, for digital hardware implementation of the multi-layere perceptrons, the quantization scheme using "look-up tables (LUTs)" is commonly employed to handle nonlinear signmoid activation functions in the neworks, and thus requires large amount of storage to prevent unacceptable quantization errors. This paper is concerned with a new effective methodology for digital hardware implementation of multi-layered perceptrons, and proposes a "piecewise affine approximation" method in which input domain is divided into (small number of) sub-intervals and nonlinear sigmoid function is linearly approximated within each sub-interval. Using the proposed method, we develop an expression and an error backpropagation type learning algorithm for a multi-layered perceptron, and compare the performance with the quantization method through Monte Carlo simulations on XOR problems. Simulation results show that, in terms of learning convergece, the proposed method with a small number of sub-intervals significantly outperforms the quantization method with a very large storage requirement. We expect from these results that the proposed method can be utilized in digital system implementation to significantly reduce the storage requirement, quantization error, and learning time of the quantization method.quantization method.

• 한국정보통신학회논문지
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• 제13권5호
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• pp.1038-1043
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• 2009

최근 교육현장에서는 창의력과 문제해결력과 같은 고등사고능력을 신장시키기 위한 교육이 초 중등교육뿐만 아니라 대학교육에서도 요구되어지고 있다. 이에 본 연구에서는 대학생을 대상으로 컴퓨터 프로그래밍 교육을 실시함에 있어 학생들의 고등사고능력을 신장시키기 위한 컴퓨터 프로그래밍 교육에 대하여 논하고자 한다. 이를 위해 선행된 사례들과 문헌연구를 기반으로 프로젝트학습 기반의 컴퓨터 프로그래밍 교육을 제시하고자 한다. 본 연구가 컴퓨터 및 공학교육 전반에 걸쳐 컴퓨터 프로그래밍 교육을 실시하는데 있어 작은 밑거름이 되기를 기대한다.

• 정보처리학회논문지B
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• 제8B권5호
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• pp.477-484
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• 2001

본 논문에서는 회귀용 support vector machine의 성능 개선을 위한 모멘텀과 kernel-adatron 기법이 조합형 학습알고리즘을 제안하였다. 제안된 학습알고리즘은 supper vector machine의 학습기법인 기술기상승법에 발생하는 최적해로의 수렴에 따란 발진을 억제하여 그수렴속도를 좀 더 개선시키는 모멘텀의 장점과 비선형 특징공간에서의 동작과 구현의 용이성을 갖는 kernel-adatorn 알고리즘의 장점을 그대로 살린 것이다. 제안된 알고리즘의 support vector machine을 1차원과 2차원 비선형 함수 회귀에 적용하여 시뮬레이션한 결과, 학습속도에 있어서 2차 프로그래밍과 기존의 kernel-adaton 알고리즘보다 더 우수하고, 회귀성능면에서도 우수한 성능이 있음을 확인하였다.

• 한국학교수학회논문집
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• 제23권2호
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• pp.223-237
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• 2020

4차 산업혁명 시대를 대표하는 인공지능 기술은 이제 우리 삶에 깊숙이 관여되고 있고 미래 교육은 이러한 인공지능의 원리와 활용에 대한 학생들의 역량 함양을 중시하고 있다. 따라서 본 연구의 목적은 인공지능 역량과 가장 밀접한 교과인 수학에서 다루어야 하는 인공지능 관련 교육 내용을 고찰하는데 있다. 이를 위해 인공지능의 핵심 기술인 기계학습(machine learning)의 원리를 수학기반으로 학습할 수 있는 인공지능 교과를 수학과의 과목으로 신설할 것과, '인공지능과 데이터 과학을 위한 수학' 교과에서 다루어야 하는 주요 수학 내용들을 제안하였다.

• 한국CDE학회논문집
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• 제5권2호
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• pp.127-135
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• 2000

Emergent computing paradigms such as genetic algorithms have found increased use in problems in engineering design. These computational tools have been shown to be applicable in the solution of generically difficult design optimization problems characterized by nonconvexities in the design space and the presence of discrete and integer design variables. Another aspect of these computational paradigms that have been lumped under the bread subject category of soft computing, is the domain of artificial intelligence, knowledge-based expert system, and machine learning. The paper explores a machine learning paradigm referred to as teaming classifier systems to construct the high-quality global function approximations between the design variables and a response function for subsequent use in design optimization. A classifier system is a machine teaming system which learns syntactically simple string rules, called classifiers for guiding the system's performance in an arbitrary environment. The capability of a learning classifier system facilitates the adaptive selection of the optimal number of training data according to the noise and multimodality in the design space of interest. The present study used the polynomial based response surface as global function approximation tools and showed its effectiveness in the improvement on the approximation performance.

• Nuclear Engineering and Technology
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• 제52권2호
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• pp.287-295
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• 2020

Group method of data handling (GMDH) is considered one of the earliest deep learning methods. Deep learning gained additional interest in today's applications due to its capability to handle complex and high dimensional problems. In this study, multi-layer GMDH networks are used to perform uncertainty quantification (UQ) and sensitivity analysis (SA) of nuclear reactor simulations. GMDH is utilized as a surrogate/metamodel to replace high fidelity computer models with cheap-to-evaluate surrogate models, which facilitate UQ and SA tasks (e.g. variance decomposition, uncertainty propagation, etc.). GMDH performance is validated through two UQ applications in reactor simulations: (1) low dimensional input space (two-phase flow in a reactor channel), and (2) high dimensional space (8-group homogenized cross-sections). In both applications, GMDH networks show very good performance with small mean absolute and squared errors as well as high accuracy in capturing the target variance. GMDH is utilized afterward to perform UQ tasks such as variance decomposition through Sobol indices, and GMDH-based uncertainty propagation with large number of samples. GMDH performance is also compared to other surrogates including Gaussian processes and polynomial chaos expansions. The comparison shows that GMDH has competitive performance with the other methods for the low dimensional problem, and reliable performance for the high dimensional problem.

• 수산해양기술연구
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• 제33권4호
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• pp.290-297
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• 1997

Underwater robotic vehicles(URVs) are used for various work assignments such as pipe-lining, inspection, data collection, drill support, hydrography mapping, construction, maintenance and repairing of undersea equipment, etc. As the use of such vehicles increases the development of vehicles having greater autonomy becomes highly desirable. The vehicle control system is one of the most critic vehicle subsystems to increase autonomy of the vehicle. The vehicle dynamics is nonlinear and time-varying. Hydrodynamic coefficients are often difficult to accurately estimate. It was also observed by experiments that the effect of electrically powered thruster dynamics on the vehicle become significant at low speed or stationkeeping. The conventional linear controller with fixed gains based on the simplified vehicle dynamics, such as PID, may not be able to handle these properties and result in poor performance. Therefore, it is desirable to have a control system with the capability of learning and adapting to the changes in the vehicle dynamics and operating parameters and providing desired performance. This paper presents an adaptive and learning control system which estimates a new set of parameters defined as combinations of unknown bounded constants of system parameter matrices, rather than system parameters. The control system is described with the proof of stability and the effect of unmodeled thruster dynamics on a single thruster vehicle system is also investigated.