• 한국정밀공학회지
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• 제12권10호
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• pp.57-68
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• 1995

An upper bound elemental technique (UBET) program has been developed to predict forging load, die-cavity filling, preform in non-axisymmetric forging. To analyze the process easily, it is suggested that the deformation is divided into two different parts. Those are axisymmetric part in corner, plane-strain part in lateral. The plane-strain and axisymmetric parts are combined by building block method. And the total energy is computed through combination of three deformation parts. A dumbbell-type preform has been obtained from height and volumetric compensations of the billet based on the backward simulation. Experimetns have been carried out with pure plasticine at room temperature. Theoretical predictions are in good agreement with expereimental results.

• 대한기계학회논문집
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• 제18권11호
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• pp.3098-3107
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• 1994

The central burst defects, so-called chevroning, in wire drawing are analyzed by the rigid-plastic finite element method. The occurrence of central burst defects in wire drawing is estimated by the distribution of the hydrostatic pressure around the central part of the workpiece. It has been possible to obtain numerical boundaries which, in reduction in area vs. semicone angle plane, divide the safe and the danger zones, depending on friction factors and material properties. Based on the results of the analysis, it is suggested that the previous criterion derived from the upper bound analysis should be modified for better prediction of the defects. The back tension and the billet with a spherical hole on the central axis are also included in the analysis of the defects.

• Journal of applied mathematics & informatics
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• 제9권1호
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• pp.61-76
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• 2002

The robust non-fragile guaranteed cost control problem is studied in this paper for class of uncertain linear large-scale systems with time-varying delays in subsystem interconnections and given quadratic cost functions. The uncertainty in the system is assumed to be norm-hounded arid time-varying. Also, the state-feedback gains for subsystems of the large-scale system are assumed to have norm-bounded controller gain variations. The problem is to design state feedback control laws such that the closed-loop system is asymptotically stable and the closed-loop cost function value is not more than a specified upper bound far all admissible uncertainties. Sufficient conditions for the existence of such controllers are derived based on the linear matrix inequality (LMI) approach combined with the Lyapunov method. A parameterized characterization of the robust non-fragile guaranteed cost contrellers is 7iven in terms of the feasible solution to a certain LMI. Finally, in order to show the application of the proposed method, a numerical example is included.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제8권2호
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• pp.151-157
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• 2008

A non-fragile guaranteed cost control (GCC) problem is presented for a class of discrete time-delay nonlinear systems described by Takagi-Sugeno (T-S) fuzzy model. The systems are assumed to have norm-bounded time-varying uncertainties in the matrices of state, delayed state and control gains. Sufficient conditions are first obtained which guarantee that the closed-loop system is asymptotically stable and the closed-loop cost function value is not more than a specified upper bound. Then the design method of the non-fragile guaranteed cost controller is formulated in terms of the linear matrix inequality (LMI) approach. A numerical example is given to illustrate the effectiveness of the proposed design method.

• 전기학회논문지
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• 제57권8호
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• pp.1429-1433
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• 2008

In this paper, we consider the design method of robust guaranteed cost controller for discrete-time singular systems with norm-bounded time-varying parameter uncertainty. In order to get the optimum(minimum) value of guaranteed cost, an optimization problem is given by linear matrix inequality (LMI) approach. The sufficient condition for the existence of controller and the upper bound of guaranteed cost function are proposed in terms of strict LMIs without decompositions of system matrices. Numerical examples are provided to show the validity of the presented method.

• 전기학회논문지
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• 제56권8호
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• pp.1491-1497
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• 2007

This paper considers robust and non-fragile guaranteed cost controller design method for descriptor systems with parameter uncertainties and time delay, and static state feedback controller with gain variations. The existence condition of controller, the design method of controller, the upper bound to minimize guaranteed cost function, and the measure of non-fragility in controller are proposed using linear matrix inequality (LMI) technique, which can be solved efficiently by convex optimization. Therefore, the presented robust and non-fragile guaranteed cost controller guarantees the asymptotic stability and non-fragility of the closed loop systems in spite of parameter uncertainties, time delay, and controller fragility.

• Bulletin of the Korean Chemical Society
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• 제10권6호
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• pp.529-535
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• 1989

A general perturbation series solution of the Smoluchowski equation is applied to investigate the rate of recombination and the remaining probability of a pair of particles in liquids. The radiative boundary condition is employed and the convergence of the perturbation series is analyzed in terms of a convergene factor in time domain. The upper bound to the error introduced by the n-th order perturbation scheme is also evaluated. The long time behaviors of the rate of recombination and the remaining probability are found to be expressed in closed forms if the perturbation series is convergent. A new and efficient method of purely numerical integration of the Smoluchowski equation is proposed and its results are compared with those obtained by the perturbation method. For the two cases where the interaction between the particles is given by (i) the Coulomb potential and (ii) the shielded Coulomb potential, the agreement between the two results is found to be excellent.

• 정보보호학회논문지
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• 제7권2호
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• pp.3-10
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• 1997

상관면역 함수는 스트림 암호의 여과 함수, 비선형 결합 함수 뿐만 아니라 블럭 암호의 핵심 논리설계에 많이 이용된다. 본 논문에서는 새로운 방식으로 상관면역 함수를 설계하는 방법을 제시한다. 이 방법을 이용하여 상관면역 함수 개수의 하한값과 상한값을 구하였다. 이 값은 Mitchell(1990), Yang-Guo(1995)가 구한 하한값과 상한값을 크게 개선한다.

• 정보처리학회논문지B
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• 제14B권4호
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• pp.287-294
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• 2007

실세계의 문제에서 많은 기계학습의 알고리즘들은 데이터의 클래스 불균형 문제에 어려움을 겪는다. 이러한 클래스 불균형 문제를 해결하기 위하여 데이터의 비율을 변경하거나 좀 더 나은 샘플링 전략으로 극복하려는 연구들이 제안되었다. 그러나 데이터의 비율을 변경하는 연구에서는 전체 데이터 분포의 특성을 고려하지 못하고, 샘플링 전략을 제안하는 연구에서는 여러 가지 제한 조건을 고려해야만 한다. 본 논문에서는 위의 두가지 방법의 장점을 모두 포함하는 개선된 집중 샘플링 방법을 제안한다. 제안된 방법에서는 클래스 불균형 문제를 해결하기 위해 학습에 유용한 데이터들을 샘플링하는데 스코어링에 기반한 데이터 분할 방법을 이용한다. 즉, 입력 데이터들에 대해 SOM(Self Organizing Map)의 학습 결과로 얻은 BMU(Best Matching Unit)와의 거리를 계산하고, 이 거리론 스코어라 한다. 측정된 스코어는 오름차순으로 정렬되며, 이 과정에서 입력 데이터의 분포가 재 표현되고, 재 표현된 분포는 전체 데이터의 특성을 대표하게 된다. 그 결과로 얻은 데이터들 중에서 유용하지 못한 데이터들에 대해 제거하는 과정을 수행하여 새로운 학습 데이터 셋을 얻는다. 새로운 학습 데이터 생성 과정에서는 재 표현된 분포의 결과를 두 구간(upper, lower)으로 분할하는데, 두 추간 사이의 데이터들은 유용하지 못한 패턴들로 간주되어 학습에 이용되지 않는다. 본 논문에서 제안한 방법은 클래스 불균형의 비율 감수 훈련 데이터의 크기 감소, 과적합의 방지 등 몇 가지 장점을 보인다. 제안한 방법으로 샘플링된 데이터에 kNN 을 적용하여, 분류 실험한 결과 심한 불균형이 있는 ecoli 데이터의 분류 성능이 최대 2.27배 향상되었다.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 2000년도 춘계학술대회 학술발표 논문집
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• pp.249-255
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• 2000

HRIV(Hybrid Rule-Interval Variation) method is presented to stabilize a class of nonlinear systems, where SMC(Sliding Mode Control) and ADC (ADaptive Control) schemes are incorporated to overcome the unstable characteristics of a conventional FLC(Fuzzy Logic Control). HRIV method consists of two modes: I-mode (Integral Sliding Mode PLC) and R-mode(RIV method). In I-mode, SMC is used to compensate for MAE(Minimum Approximation Error) caused by the heuristic characteristics of FLC. In R-mode, RIV method reduces interval lengths of rules as states converge to an equilibrium point, which makes the defined Lyapunov function candidate negative semi-definite without considering MAE, and the new uncertain parameters generated in R-mode are compensated by SMC. In RIV method, the overcontraction problem that the states are out of a rule-table can happen by the excessive reduction of rule intervals, which is solved with a dynamic modification of rule-intervals and a transition to I-mode. Especially, HRIV method has advantages to use the analytic upper bound of MAE and to reduce Its effect in the control input, compared with the previous researches. Finally, the proposed method is applied to stabilize a simple nonlinear system and a modified inverted pendulum system in simulation experiments.