• Journal of Communications and Networks
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• 제16권6호
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• pp.583-591
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• 2014

In wireless communications, knowledge of the signal-to-noise ratio is required in diverse communication applications. In this paper, we derive the variance of the maximum likelihood estimator in the data-aided and non-data-aided schemes for determining the optimal shrinkage factor. The shrinkage factor is usually the constant that is multiplied by the unbiased estimate and it increases the bias slightly while considerably decreasing the variance so that the overall mean squared error decreases. The closed-form biased estimators for binary-phase-shift-keying and quadrature phase-shift-keying systems are then obtained. Simulation results show that the mean squared error of the proposed method is lower than that of the maximum likelihood method for low and moderate signal-to-noise ratio conditions.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.277-280
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• 2001

This paper presents a speed sensorless implementation of digital speed control system of Surface Permanent-Magnet Synchronous Motor(SPMSM) drives with a direct torque control(DTC). The system presented are stator flux and torque observer of stator flux feedback control model that inputs are current and voltage sensing of motor terminal with estimated rotor angle for a low speed operating area, two hysteresis band controllers, an optimal switching look-up table, rotor speed estimator, and IGBT voltage source inverter by using fully integrated control software. The developed speed sensorless control system are shown a good motion control response characteristic results and high performance features using 1.0Kw purposed servo drive SPMSM.

• 산업경영시스템학회지
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• 제13권21호
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• pp.133-141
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• 1990

Human blood is a perishable product : it has a legal lifetime of 21 days from collection, during which it can be used for transfusion to a Patient of the same type, and after which it has to be discarded. Therefore, blood must be supplied safely and effectively because it is one of the medical resources which keep humanlife. In this study, the effects of blood issuing policies on average inventory levels and average age of blood at transfusion are determined by simulation applied the theory of absorbing Markov chains. And as a practical study, the daily demand distribution of blood is estimated by using the data of B General Hospital. The distribution estimated follows poisson distribution and the estimator of parameter estimated from the poisson distribution is 0.762. Simulation is done by using the parameter. The most important problem when control blood is the amount of outdata. So we compared random policy with Modified LIFO and Modified FIFO by using outdata. As a results it is shown that Modified LIFO and Modified FIFO by using outdata. As a results it Is shown that Modified LIFO and Modified FIFO present better issuing policy than Random Policy.

• 한국군사과학기술학회지
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• 제3권2호
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• pp.121-130
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• 2000

A practical method is proposed to improve hit probability of the digital gun fire control system, when the measured rate of the tracking sensor becomes biased under some operational situation. For ground moving target it is shown that the well-known Kalman filter which uses position measurement only can be optimally used to eliminate the rate bias error. On the other hand, for 3D moving aircraft we present a new algorithm which incorporate FIR-type filter, which uses position and rate measurement at the same time, and the fixed-lag smoother using position measurement only, and show that it has the optimal performance in terms of both estimation accuracy and response time.

• 대한산업공학회지
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• 제22권3호
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• pp.459-471
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• 1996

This paper considers ramp tests for exponential lifetime distribution when there are limitations on test stress and test time. The inverse power law and a cumulative exposure model are assumed. Maximum likelihood (ML) estimators of model parameters and their asymptotic covariance matrix are obtained. The optimum ramp test plans are also found which minimize the asymptotic variance of the ML estimator of the log mean life at design constant stress. For selected values of the design parameters, tables useful for finding optimal test plans are given. The effect of the pre-estimates of design parameters is studied.

• 산업경영시스템학회지
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• 제21권45호
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• pp.319-328
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• 1998

In this paper, the design of ALT(Accelerated Life Test) requires a sampling plan based on failure-censored(Type II censored) ALT with lognormal life distribution. Specially the environmental effect of products has been emphasized, so we considered the upper life limit as well as lower life limit in the ALT sampling plan. The optimal plan with a high stress and a low stress is used as test plan, and the total sample size for test and lot acceptability constant which minimize an asymptotic variance of maximum likelihood estimator of assumed model parameters and satisfy the given producer's risk and customer's risk are drawn out. These values can be acquired by means of the computer program that we coded for resolving the difficulty and complexity of calculation.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 전력전자학술대회 논문집
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• pp.397-400
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• 2001

This paper presents a implementation of digital sensorless position control system of surface permanent-magnet synchronous motor (SPMSM) drive with a direct torque control (DTC). The system are stator flux and torque observer of stator flux feedback control model that inputs are current and voltage sensing of motor terminal with estimated rotor angle for a low speed operating area, two hysteresis band controllers, an optimal switching look-up table, rotor speed estimator, and IGBT voltage source inverter by using fully integrated control software. The developed sensorless control system are shown a good motion control response characteristic results and high performance features using 1.0 (kW) purposed servo drive SPMSM.

• 한국해양공학회지
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• 제35권5호
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• pp.360-368
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• 2021

The need for energy harvesting in marine environments is gradually increasing owing to the energy limitation of marine robots. To address this problem, a catamaran-type sail drone (CSD), which can harvest marine energies such as wind and solar, was proposed in a previous study. However, it was designed and manufactured without considering the stability, optimal hull-form, and maintenance. To resolve these problems, a CSD with two keels, a performance estimator, V-shape hulls, and modularized components is proposed and its mechanism is developed in this study. To verify the performance of the CSD, the performance estimation using smoothed-particle hydrodynamics (SPH) and the heading control using fuzzy logic controller (FLC) are performed. Simulation results show the attitude stability of the CSD and the experimental results show the straight path of the CSD according to wind conditions. Therefore, the CSD has potential applications as an energy harvesting system.

• Journal of the Korean Data and Information Science Society
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• 제27권4호
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• pp.993-1000
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• 2016

반응 값이 없는 자료를 지도학습 (supervised learning)에 사용하는 준지도 학습 (semi-supervised learning)은 분류에 더 많은 관심을 갖는다. 본 연구는 준지도학습을 회귀분석에 적용하는 준지도 회귀함수 추정법을 제안한다. 제안된 방법은 기존의 방법과 형태는 같지만 반응 값이 있는 자료와 없는 자료의 주변분포를 다르게 가정하고, 서로 다른 평활계수를 사용하는 등 좀 더 일반화된 형태를 가진다. 제안된 추정법의 점근분포를 계산하고 점근평균제곱오차를 최소화하는 최적의 평활계수가 가지는 조건을 찾는다. 설명변수의 주변분포에 대한 추정이 잘 이루이지고, 반응 값이 있는 자료와 없는 자료의 크기에 대한 조건을 적절하게 통제할 수 있고, 그리고 평활계수가 적절하게 선택될 수 있다면 라벨없는 자료가 회귀분석에서도 도움을 줄 수 있음을 보인다. 그리고 준지도 분류에서 사용하는 것처럼 반응 값이 없는 자료의 초기추정은 작은 값을 가지는 평활계수를 사용하여 과적합 (overfitting)되도록 하는 것이 좋음을 증명한다.

• 정보처리학회논문지:소프트웨어 및 데이터공학
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• 제2권5호
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• pp.347-352
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• 2013

임펄스 잡음 제거 기법들에서 윈도우의 크기는 매우 중요한데, 보통 잡음의 밀도에 따라 적당한 크기의 윈도우를 사용한다. 이때 윈도우가 너무 작으면 잡음을 충분히 제거하지 못하며, 너무 크면 영상 내의 에지나 미세한 형태를 제대로 복원하지 못하고 흐릿하게 만들 수 있다. 또한 잡음이 있는 중앙 화소를 복원하기 위해 이러한 윈도우 내의 모든 화소들이 이용된다. 본 논문에서는 이러한 기존 방법과 달리 작은 크기의 윈도우를 사용하고 잡음이 없이 깨끗한 화소만을 사용하여 임펄스 잡음을 제거하는 새로운 반복적인 알고리즘을 제안한다. 제안된 방법은 모든 잡음 화소가 새로 계산된 추정치로 대체될 때까지 반복된다. 잡음 화소에 대해 최적의 값을 유추하기 위해 제안된 방법에서는 무잡음 화소를 이용한 유전자 프로그래밍 (GP) 기반의 추정자를 제안하는데, 이것은 윈도우 내의 무잡음 화소와, 산술 연산자 및 랜덤 상수들로 이루어진다. 실험을 통해 제안된 방법이 영상 내의 미세한 형태들을 잘 유지하면서 임펄스 잡음을 효과적으로 제거할 수 있음을 알 수 있었는데, 특히 심하게 잡음이 가해진 데이터의 복원에 매우 효과적임을 알 수 있었다.