• 충청수학회지
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• 제17권2호
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• pp.163-167
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• 2004

In this paper, we obtain some coefficient estimates of harmonic, orientation-preserving, univalent mappings defined on ${\Delta}$ = {z : |z| > 1}.

• 전기학회논문지
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• 제56권2호
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• pp.311-316
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• 2007

This paper proposes the algorithm which estimates moment of the inertia and friction coefficient of friction for high performance speed control of electric motor. The proposed algorithm finds the moment of inertia and friction coefficient of friction by observing the speed error signal generated by the speed observer and using Recursive Least-Mean-Square method(RLS). By feedbacking the estimated inertia and estimated coefficient of friction to speed controller and full order speed observer, then the errors of the inertia and coefficient of friction and speed due to the inaccurate initial value are decreased. Inertia and coefficient of friction converge to the actual value within several times of speed changing. Simulation and actual experiment results are given to demonstrate the effectiveness of the proposed parameter estimator.

• 응용통계연구
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• 제24권1호
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• pp.207-216
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• 2011

본 논문에서는 일반화추정방정식(GEE)모형에 대한 부스트랩 방법의 적용에 대하여 살펴본다. 다양한 부스트랩 방법들 중 GEE모형에 적용이 가능한 잔차, 쌍 및 점수함수 부스트랩 방법을 가상 및 실제 자료들에 적용한 결과 회귀계수들에 대한 추정치와 표준오차가 점근값들과 차이를 보이는 것으로 나타났다. 따라서 표본수가 크지 않은 경우 부스트랩 방법을 통하여 GEE모형에서의 회귀계수에 대한 추정치화 표준편차를 구하는 것이 효과적임을 알 수 있다.

• Communications for Statistical Applications and Methods
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• 제27권5호
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• pp.523-533
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• 2020

This paper suggests three available methods for finding nonnegative estimates of variance components of the random effects in mixed models. The three proposed methods based on the concepts of projections are called projection method I, II, and III. Each method derives sums of squares uniquely based on its own method of projections. All the sums of squares in quadratic forms are calculated as the squared lengths of projections of an observation vector; therefore, there is discussion on the decomposition of the observation vector into the sum of orthogonal projections for establishing a projection model. The projection model in matrix form is constructed by ascertaining the orthogonal projections defined on vector subspaces. Nonnegative estimates are then obtained by the projection model where all the coefficient matrices of the effects in the model are orthogonal to each other. Each method provides its own system of linear equations in a different way for the estimation of variance components; however, the estimates are given as the same regardless of the methods, whichever is used. Hartley's synthesis is used as a method for finding the coefficients of variance components.

• 대한수학회보
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• 제60권5호
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• pp.1253-1263
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• 2023

Let 𝓤⁺ be the class of analytic functions f such that ${\frac{z}{f(z)}}$ has real and positive coefficients and f^-1 be its inverse. In this paper we give sharp estimates of the initial coefficients and initial logarithmic coefficients for f, as well as, sharp estimates of the second and the third Hankel determinant for f and f^-1. We also show that the Zalcman conjecture holds for functions f from 𝓤⁺.

• 한국유통학회지:유통연구
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• 제15권4호
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• pp.61-85
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• 2010

본 연구에서는 국내 대형할인점의 확산을 효과적으로 설명하기 위해 기업의 정보와 구매자의 구전으로 확산을 설명하는 Bass모형에 제3의 요소로 공간적 영향력을 고려하였다. 국내 대형할인점의 확산은 확산중심지인 서울경인지역에서 저차중심지인 4개 지역권역으로 확산되는 형태를 보임에 따라 공간적 영향이 중요하게 작용할 것으로 기대된다. 본 연구에서 공간적으로 구분된 시장 A(확산중심지)가 시장 B(저차중심지)에 미치는 영향이 완전히 통제되지 못하는 상황에서 시장 A가 시장 B에 미치는 공간적 영향을 다국가확산모형(multinational diffusion model)을 확장한 공간확산모형(spatial diffusion model)을 이용하여 정의하였다. Bass모형과 공간확산모형의 모수추정을 통해 두 가지 정보전달경로와 관련된 혁신계수와 모방계수로 확산을 설명하는 Bass모형보다 공간확산모형이 국내 대형할인점 확산을 더욱 효과적으로 설명하는 것으로 나타났다. 또한 혁신중심지인 서울경인과 4개 지역권역의 소매환경을 나타내는 개념적 거리에 따라 공간확산모형에서 공간적요인의 영향력이 달라질 것이 기대되어 공간확산계수와 소매환경변수간의 상관관계를 살펴보았고, 연구결과 확산중심지에서 저차중심지에 대한 공간적 영향력은 저차중심지의 소매환경이 확산중심지의 소매환경과 유사할수록 크다는 것을 밝혀내었다.

• Journal of Power Electronics
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• 제14권6호
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• pp.1243-1253
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• 2014

The phase inductance of a switch reluctance motor (SRM) is significantly nonlinear. With different saturation conditions, the phase inductance shape is clearly changed. This study focuses on the relationship between coefficient and current in an inductance model with ignored harmonics above the order of 3. A position estimation method based on the variable coefficient inductance model is proposed in this paper. A four-quadrant sensorless control system of the SRM drive is constructed based on the relationship between variable coefficient inductance and rotor position. The proposed algorithms are implemented in an experimental SRM test setup. Experimental results show that the proposed method estimates position accurately in operating two/four-quadrants. The entire system also has good static and dynamic performance.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 추계학술대회 초록집
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• pp.160.1-160.1
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• 2011

In this study, the influence of methodology of assessing water levels on the discharge coefficient of sluice for tidal power generation was investigated. A physical experiment was performed in a planar open channel by installing 1/70 scale model of the sluice caisson in the planar open channel. In front of and behind the sluice model, sloping bathymetry was made to reproduce corresponding field condition. By analyzing the experimental results, it was found that the location of measuring water levels significantly affects the estimates of the discharge coefficient, due to the variability of the parameter according to the head difference between the measuring locations. Therefore, it is necessary to be careful in estimating and utilizing the discharge coefficient in the relevant study of a tidal power generation.

• Journal of the Korean Data and Information Science Society
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• 제27권4호
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• pp.1059-1066
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• 2016

In this paper we propose a robust version of varying coefficient models, which is based on the regularized regression with L1 regularization. We use the iteratively reweighted least squares procedure to solve L1 regularized objective function of varying coefficient model in locally weighted regression form. It provides the efficient computation of coefficient function estimates and the variable selection for given value of smoothing variable. We present the generalized cross validation function and Akaike information type criterion for the model selection. Applications of the proposed model are illustrated through the artificial examples and the real example of predicting the effect of the input variables and the smoothing variable on the output.

• Korean Journal of Hydrosciences
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• 제6권
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• pp.13-22
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• 1995

The augmenting hydrologic data using a correlation procedure has been used to improve the estimates of the mean and variance at the site of interest with short record when one or more near by sites with longer records are available. The variance of the unbiased maximum likelihood estimator of $ derived by Moran based on the multivariate normal distribytion is modified into the form of Matalas and Jacobs for the biveriate normal distribution to get the critical minimum values of the multiple correlation coefficient which give the improvement for estimating the variance at the site of interest. Those values are tabulated for various lengths of short records and the number of sites.