• 비파괴검사학회지
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• 제21권4호
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• pp.391-397
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• 2001

비균질 적층 구조물에서의 유도초음파 전파는 이론적 분산성에 기초하여 실험적으로 규명된다. 이는 입사각도와 주파수의 적절한 선택은 적층 구조물에서의 유도초음파 발생에 중요하나는 깃을 드러낸다. 이론적 분산성은 접착층 두께와 층 두께, 물성치에 크게 의존한다. 실험적으로 분산성의 변화를 관찰하므로 비균질 적층 구조물의 접착층 두께를 측정하는 것이 가능하였다.

• 천문학회보
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• 제36권2호
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• pp.127.1-127.1
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• 2011

Over the past several years the millimeter wave VLBI(Veryl Long Baseline Interferometry) observations have been intensively carried out. However In millimeter and sub-millimeter waves observations for VLBI, it is crucial to calibrate correctly the phase variations of the electromagnetic waves propagation through the troposphere. To do this, KVN(Korean VLBI Network) has a unique multi-frequency bands receiver system which is able to perform the simultaneous observations in up to four bands such as 22, 43, 86, and 129GHz. The phase of a source at 22GHz can be used to calibrate the phase of the same source at higher frequency bands. The phase calibration using multi-frequency bands receiver system is possible because the phase fluctuations from a given amount of waver vapor increase linearly with frequency. That is to say that troposphere is non-dispersive property in terms of tropospheric delay fluctuations. In this talk, We present results of test observation for multi-frequency bands receiver system.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -1
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• pp.167-170
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• 2000

This paper describes a novel multi-operand radix-2 signed-digit(SD) adder. The novel multi-operand addition algorithm can eliminate carry propagation chain by dividing the input operands into even place part and odd place part, and adding them each. The multi-operand adder with this algorithm can add six operands in parallel, and is faster than the ordinary method of SD adder binary tree. A hardware model for proposed adder is shown which is implemented by the current-mode MOSFET circuit technology. Simulations have been made by SPICE in order to verify the function of the proposed circuit.

• Interaction and multiscale mechanics
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• 제6권2호
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• pp.83-105
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• 2013

In this paper, a multi-scale meshfree-enriched finite element formulation is presented for the analysis of acoustic wave propagation problem. The scale splitting in this formulation is based on the Variational Multi-scale (VMS) method. While the standard finite element polynomials are used to represent the coarse scales, the approximation of fine-scale solution is defined globally using the meshfree enrichments generated from the Generalized Meshfree (GMF) approximation. The resultant fine-scale approximations satisfy the homogenous Dirichlet boundary conditions and behave as the "global residual-free" bubbles for the enrichments in the oscillatory type of Helmholtz solutions. Numerical examples in one dimension and two dimensional cases are analyzed to demonstrate the accuracy of the present formulation and comparison is made to the analytical and two finite element solutions.

• 한국정밀공학회지
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• 제12권12호
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• pp.100-108
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• 1995

The In-process minitoring of the chatter vibration is necessarily required to an automatic manufacturing system. In this study, we constructed a multi-sensing system using tool dynamoneter, accelerometer and AE(Acoustic Emission) sensor for a more credible detection of chatter vibration. And a new approach using a multiple neural network to extract the features of multi-sensor for the recognition chatter vibration is proposed. With the Back-propagation training process, the neural network memorize and classify the features of multi-sensor signals. As a result, it is shown by multiple neural network that the chatter vibration can be monitored accurately, and it can be widely used in practical unmanned system.

• 전자공학회논문지
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• 제50권3호
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• pp.16-22
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• 2013

n 개의 균일한 결합선로를 해석하기 위하여 2n-port 어드미턴스 매트릭스의 추출에 기초한 일반적인 특성화 절차가 제시된다. 본 논문에서는 비대칭 다중 결합선로를 해석하기 위하여 시간영역의 유한차분법을 사용하여 정규화 모드 파라미터 접근법의 적용을 제안한다. 주파수 의존적인 정규화 모드 파라미터는 2n-port 어드미턴스 매트릭스로부터 얻어지고, 이로부터 주파수 의존적인 전파상수와 유효 유전율 및 결합선로의 특성임피던스를 계산할 수 있다. 이 기법을 설명하기 위해 몇몇의 실질적인 다중 유전체상의 결합선로 구조들이 모의 실험되었으며, 특히 전도체가 유전체 사이에 내재된 형태의 선로가 해석되었다. 시간영역 유한 차분법을 활용한 결과는 Spectral Domain Method의 모의실험 결과와 비교하였고, 잘 일치함을 보였다. 시간영역의 특성화 절차에 기인한 유한차분법은 얇거나 두꺼운 혼성 구조 뿐 아니라 다층 PCB상의 다중의 전도체 결합 선로 설계를 위한 훌륭한 광대역 모의실험 도구가 됨을 볼 수 있다.

• 대한전기학회논문지:전력기술부문A
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• 제49권3호
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• pp.95-106
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• 2000

The load frequency control of power system is one of important subjects in view of system operation and control. That is even though the rapid load disturbances were applied to the given power system, the stable and reliable power should be supplied to the users, converging unconditionally and rapidly the frequency deviations and the tie-line power flow one on each area into allowable boundary limits. Nonetheless of such needs, if the internal parameter perturbation and the sudden load variation were given, the unstable phenomenal of power system can be often brought out because of the large frequency deviation and the unsuppressible power line one. Therefore, it is desirable to design the robust neuro-fuzzy controller which can stabilize effectively the given power system as soon as possible. In this paper the robust neuro-fuzzy controller was proposed and applied to control of load frequency over multi-area power system. The architecture and algorithm of a designed NFC(Neuro-Fuzzy Controller) were consist of fuzzy controller and neural network for auto tuning of fuzzy controller. The adaptively learned antecedent and consequent parameters of membership functions in fuzzy controller were acquired from the steepest gradient method for error-back propagation algorithm. The performances of the resultant NFC, that is, the steady-state deviations of frequency and tie-line power flow and the related dynamics, were investigated and analyzed in detail by being applied to the load frequency control of multi-area power system, when the perturbations of predetermined internal parameters. Through the simulation results tried variously in this paper for disturbances of internal parameters and external stepwise load stepwise load changes, the superiorities of the proposed NFC in robustness and adaptive rapidity to the conventional controllers were proved.

• 컴퓨터교육학회논문지
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• 제5권4호
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• pp.79-89
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• 2002

기존의 고정 단발기 (PC)에서만 주로 행해지던 각종 다중 사용자 접속 온라인 응용이 최근 PC와 PDA, 휴대폰 등이 공동 작업을 수행하는 멀티 플랫폼 기반 온라인 응용으로 전환되고 있다. 그러나 지금까지 멀티 플랫폼 기반 온라인 응용은 다중 사용자의 공동 데이터의 동시 접근 및 각 클라이언트의 처리 능력과 통신 속도의 비대칭을 고려하지 않아 컨텐츠가 매우 단순한 실정이다. 이 논문에서는 멀티 플랫폼 기반 동시성 제어 기법, 다양한 클라이언트간의 변경 전파 프로토콜, 모바일 클라이언트의 특성을 고려한 객체 관리 기술을 제안하였다. 그리고 멀티 플랫폼 기반 채팅 프로그램을 제작하여 제안한 기법들이 적절히 동작함을 보였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권11호
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• pp.5394-5409
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• 2019

The paper investigates a novel detector receiver with Kalman channel information estimator and iterative channel response equalization for MIMO (multi-input multi-output) OFDM (orthogonal frequency division multiplexing) communication systems in fast multipath fading environments. The performances of the existing linear equalizers (LE) are not good enough over most fast fading multipath channels. The existing adaptive equalizer with decision feedback structure (ADFE) can improve the performance of LE. But error-propagation effect seriously degrades the system performance of the ADFE, especially when operated in fast multipath fading environments. By considering the Kalman channel impulse response estimation for the fast fading multipath channels based on CE-BEM (complex exponential basis expansion) model, the paper proposes the iterative receiver with soft decision feedback equalization (SDFE) structure in the fast multipath fading environments. The proposed SDFE detector receiver combats the error-propagation effect for fast multipath fading channels and outperform the existing LE and ADFE. We demonstrate several simulations to confirm the ability of the proposed iterative receiver over the existing receivers.

• ETRI Journal
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• 제17권1호
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• pp.11-22
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• 1995

This paper proposes a modified error function to improve the error back-propagation (EBP) algorithm for multi-Layer perceptrons (MLPs) which suffers from slow learning speed. It can also suppress over-specialization for training patterns that occurs in an algorithm based on a cross-entropy cost function which markedly reduces learning time. In the similar way as the cross-entropy function, our new function accelerates the learning speed of the EBP algorithm by allowing the output node of the MLP to generate a strong error signal when the output node is far from the desired value. Moreover, it prevents the overspecialization of learning for training patterns by letting the output node, whose value is close to the desired value, generate a weak error signal. In a simulation study to classify handwritten digits in the CEDAR [1] database, the proposed method attained 100% correct classification for the training patterns after only 50 sweeps of learning, while the original EBP attained only 98.8% after 500 sweeps. Also, our method shows mean-squared error of 0.627 for the test patterns, which is superior to the error 0.667 in the cross-entropy method. These results demonstrate that our new method excels others in learning speed as well as in generalization.