• 전기전자학회논문지
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• 제5권1호
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• pp.1-7
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• 2001

본 논문에서 역 방향 링크 채널에 대해 비 선형 등화기를 이용하여 CDMA 셀룰라 시스템을 연구하였다. 일반적으로 무선 통신에서 불확실한 채널 특성 때문에 Observable 들의 확률분포는 유한 세트의 파라미터로 규정될 수 없다. 대신에 training 샘플에 기반을 둔 Quantile과 Vector Quantizer를 사용함으로서 유한 수의 disjoint된 영역으로 m차 샘플 공간으로 분할하였다. 제안된 알고리듬은 RMSA 알고리즘에 의해 예측된 Quantile와 조건부 분할 모멘트에 따른 regression function의 부분적인 근사에 근간을 두고 있다. 본 논문의 등화기와 검출기는 잡음 분포의 Variation에 민감하지 않다는 관점에서 상당히 강한 특성을 보여 준다. 주요 아이디어는 Robust equalizer와 Robust partition detector가 어떤 환경의 무선 채널 하에서도 partition되지 않은 Observation space의 일반적인 등화기 보다 Observation의 등 확률로 분할된 부 공간에서 더 낳은 성능을 보여 준다. 또한 이런 개념을 CDMA 시스템에 적용하여 BER 성능을 분석하였다.

• 한국정보통신학회논문지
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• 제22권1호
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• pp.33-39
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• 2018

질량 스펙트럼 분석 시스템을 위한 부가 잡음제거 알고리즘을 제안하였다. 측정된 이온 신호로부터 먼저 백색 가우시안 특성을 갖는 바닥 잡음의 제거를 위해 측정된 신호의 최빈값으로부터 추정된 임계값을 사용하였다. 또한 각각의 질량 지수에 해당하는 신호 블록을 구성하여 이 신호 블록에 대한 2차 커브 피팅 및 선형 근사를 수행한다. 이 과정에서 임펄스성 잡음과 정상적인 이온 신호로 보기에 불충분한 샘플 신호들을 제거함으로써 이온 신호만으로 구성된 유효 신호 블록을 재 구성할 수 있다. 이 유효 신호 블록에 대한 커브 피팅 곡선으로부터 잡음이 제거된 질량 스펙트럼을 얻을 수 있다. 제안한 방법의 성능평가를 위해 개발장비로부터 취득된 신호를 이용한 시뮬레이션을 수행하였다. 시뮬레이션 결과를 통해 최빈값으로부터 추정된 임계값 설정의 타당함과 제안한 커브 피팅 및 선형 근사기반 잡음제거 알고리즘의 우수성을 보였다.

• Steel and Composite Structures
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• 제37권6호
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• pp.663-678
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• 2020

This paper proposes a novel topology optimization method generating multiple materials for external linear plane crack structures based on the combination of IsoGeometric Analysis (IGA) and eXtended Finite Element Method (X-FEM). A so-called eXtended IsoGeometric Analysis (X-IGA) is derived for a mechanical description of a strong discontinuity state's continuous boundaries through the inherited special properties of X-FEM. In X-IGA, control points and patches play the same role with nodes and sub-domains in the finite element method. While being similar to X-FEM, enrichment functions are added to finite element approximation without any mesh generation. The geometry of structures based on basic functions of Non-Uniform Rational B-Splines (NURBS) provides accurate and reliable results. Moreover, the basis function to define the geometry becomes a systematic p-refinement to control the field approximation order without altering the geometry or its parameterization. The accuracy of analytical solutions of X-IGA for the crack problem, which is superior to a conventional X-FEM, guarantees the reliability of the optimal multi-material retrofitting against external cracks through using topology optimization. Topology optimization is applied to the minimal compliance design of two-dimensional plane linear cracked structures retrofitted by multiple distinct materials to prevent the propagation of the present crack pattern. The alternating active-phase algorithm with optimality criteria-based algorithms is employed to update design variables of element densities. Numerical results under different lengths, positions, and angles of given cracks verify the proposed method's efficiency and feasibility in using X-IGA compared to a conventional X-FEM.

• ETRI Journal
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• 제42권4호
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• pp.619-632
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• 2020

Highly dispersive S-boxes are desirable in cryptosystems as nonlinear confusion sublayers for resisting modern attacks. For a near optimal cryptosystem resistant to modern cryptanalysis, a highly nonlinear and low differential probability (DP) value is required. We propose a method based on a piecewise linear chaotic map (PWLCM) with optimization conditions. Thus, the linear propagation of information in a cryptosystem appearing as a high DP during differential cryptanalysis of an S-box is minimized. While mapping from the chaotic trajectory to integer domain, a randomness test is performed that justifies the nonlinear behavior of the highly dispersive and nonlinear chaotic S-box. The proposed scheme is vetted using well-established cryptographic performance criteria. The proposed S-box meets the cryptographic performance criteria and further minimizes the differential propagation justified by the low DP value. The suitability of the proposed S-box is also tested using an image encryption algorithm. Results show that the proposed S-box as a confusion component entails a high level of security and improves resistance against all known attacks.

• 한국멀티미디어학회논문지
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• 제20권8호
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• pp.1406-1420
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• 2017

Artificial neural networks (ANNs) play an important role in the fields of function approximation, prediction, and classification. ANN performance is critically dependent on the input parameters, including the number of neurons in each layer, and the optimal values of weights and biases assigned to each neuron. In this study, we apply the particle swarm optimization method, a popular optimization algorithm for determining the optimal values of weights and biases for every neuron in different layers of the ANN. Several regression models, including general linear regression, Fourier regression, smoothing spline, and polynomial regression, are conducted to evaluate the proposed method's prediction power compared to multiple linear regression (MLR) methods. In addition, residual analysis is conducted to evaluate the optimized ANN accuracy for both training and test datasets. The experimental results demonstrate that the proposed method can effectively determine optimal values for neuron weights and biases, and high accuracy results are obtained for prediction applications. Evaluations of the proposed method reveal that it can be used for prediction and estimation purposes, with a high accuracy ratio, and the designed model provides a reliable technique for optimization. The simulation results show that the optimized ANN exhibits superior performance to MLR for prediction purposes.

• 한국전산응용수학회:학술대회논문집
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• 한국전산응용수학회 2003년도 KSCAM 학술발표회 프로그램 및 초록집
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• pp.6-6
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• 2003

In this work we consider the mathematical formulation and numerical resolution of the linear feedback control problem for Boussinesq equations. The controlled Boussinesq equations is given by $$\frac{{\partial}u}{{\partial}t}-{\nu}{\Delta}u+(u{\cdot}{\nabla}u+{\nabla}p={\beta}{\theta}g+f+F\;\;in\;(0,\;T){\times}\;{\Omega}$$, $${\nabla}{\cdot}u=0\;\;in\;(0,\;T){\times}{\Omega}$$, $$u|_{{\partial}{\Omega}=0,\;u(0,x)=\;u_0(x)$$ $$\frac{{\partial}{\theta}}{{\partial}t}-k{\Delta}{\theta}+(u{\cdot}){\theta}={\tau}+T,\;\;in(0,\;T){\times}{\Omega}$$ $${\theta}|_{{\partial}{\Omega}=0,\;\;{\theta}(0,X)={\theta}_0(X)$$, where $\Omega$ is a bounded open set in $R^{n}$, n=2 or 3 with a $C^{\infty}$ boundary ${\partial}{\Omega}$. The control is achieved by means of a linear feedback law relating the body forces to the velocity and temperature field, i.e., $$f=-{\gamma}_1(u-U),\;\;{\tau}=-{\gamma}_2({\theta}-{\Theta}}$$ where (U,$\Theta$) are target velocity and temperature. We show that the unsteady solutions to Boussinesq equations are stabilizable by internal controllers with exponential decaying property. In order to compute (approximations to) solution, semi discrete-in-time and full space-time discrete approximations are also studied. We prove that the difference between the solution of the discrete problem and the target solution decay to zero exponentially for sufficiently small time step.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2148-2158
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• 1996

Uncoupled, quasi-static and linear thermoviscoelastic problems are analyzed in time domain by the finite element approximation which is developed using the principle of virtual work and viscoelasticity matrices instead of shear and bulk relaxation functions as in usual formulations. The material is assumed to be isotropic, homegeneous and thermorheologically simple, which means that the temperature-time equivalence postulate is effective. The stress-strain laws are expressed by relaxation-type hereditary integrals. In spatial and time discritizations, isoparametric quadratic quadrilateral finite elements and linear time variations are adopted. For explicit derivations, the viscoelastic material is assumed to behave standard linear solid in shear and elastically in dilatation. Two-dimensional examples are solved under general temperature distributions T = T(x, t), and compared with other opproximate solutions to show the versatility of the presented analysis.

• 한국인터넷방송통신학회논문지
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• 제16권3호
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• pp.73-80
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• 2016

"제주 정낭 Code I, II, III"에서는 배경과 역사 그리고 물리적 의미에 대해 알아보았다. "제주 정낭 Code II" 논문에서는 디지털휴먼 이진 코드인 한국의 제주도 전통에서 나무문으로 쓰인 정낭 정보통신의 뿌리를 소개하면서 AWGN 모델과 비슷한 정낭 결정 채널 모델을 조사하고, 채널 용량 분석에 접근하는 결정적 모델을 발견을 목표로 했다. 정낭 정보통신은 가족의 행방을 전달 위해 세 구멍으로 두 수직 돌에 3개의 서까래를 놓은 것으로 결정적인 신호였다. 본 논문에서는 선형 결정적 (linear deterministic) 신호에 대해 근사적(approximately)으로 결정적 신호처리의 채널 용량을 구한다.

• 응용통계연구
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• 제30권6호
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• pp.957-981
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• 2017

관측되지 않는 효과 또는 고정효과로 설명할 수 없는 분산 구조가 포함되어 정확한 모수 추정이 어려운 경우 체계적인 분석을 위해 일반화 선형 모형은 임의효과가 포함된 일반화 선형 혼합 모형으로 확장되었다. 본 연구에서는 일반화 선형 모형 중에서도 이분적인 반응변수를 다루는 로지스틱 회귀모형에 임의효과를 포함한 최대 우도 추정 방법을 설명한다. 그중에서도 라플라스 근사법, 가우스-에르미트 구적법, 적응 가우스-에르미트 구적법 그리고 유사가능도 우도에 대한 최대우도 추정법을 자세히 알아본다. 또한 제안한 방법을 사용하여 한국 복지 패널 데이터에서 정신건강과 생활만족도가 자원봉사활동에 미치는 영향에 대해 분석한다.

• 설비공학논문집
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• 제9권1호
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• pp.43-54
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• 1997

This paper presents an approximate analytical solution to a two-region one-dimensional model for the charging process of stratified thermal storage tanks with variable inlet temperature in the presence of momentum-induced mixing. Based on the superposition principle, an arbitrary-varying inlet temperature is decomposed into inherent discontinuous steps and continuous intervals approximated as a finite number of piecewise linear functions. This approximation allows the temperature of the upper perfectly-mixed layer to be expressed in terms of constant, linear and exponential functions with respect to time. Applying the Laplace transform technique to the model equation for the lower thermocline layer subject to each of three representative interfacial conditions yields compact-form solutions, a linear combination of which constitutes the final temperature profile. A systematic method for deriving solutions to the plug-flow problem having polynomial-type boundary conditions is also established. The effect of adiabatic exit boundary on solution behaviors proves to be negligible under the actual working conditions, which justifies the assumption of semi-infinite domain introduced in the solution procedure. Finally, the approximate solution is validated by comparing it with an exact solution obtained for a specific variation of inlet temperature. Excellent agreements between them suffice to show the necessity and utility of this work.