• 대한수학회보
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• 제49권6호
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• pp.1223-1240
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• 2012

The system $$\dot{x}=(A+{\varepsilon}Q(t,{\varepsilon}))x+{\varepsilon}g(t,{\varepsilon})+h(x,t,{\varepsilon}),$$ where A is elliptic whose eigenvalues are not necessarily simple and $h$ is $\mathcal{O}(x^2)$. It is proved that, under suitable hypothesis of analyticity, for most values of the frequencies, the system is reducible.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 26-27 Oct. 1990
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• pp.1139-1144
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• 1990

In this paper, we consider linear periodic discrete-time control systems under periodic compensation. Such a closed-loop system generally represents a periodic time-varying system. We examine the problem of finding a compensator such that the closed-loop system is realized as LTI model (if possible) with the closed-loop stability being satisfied. We present a necessary and sufficient condition for solving such problem and also give the characterization of realizable LTI models.

• Journal of applied mathematics & informatics
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• 제22권1_2호
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• pp.263-271
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• 2006

In this paper, a quasilinear second-order system with periodic boundary conditions is studied. By the least action principle and classical theorems of variational calculus, existence results of periodic solutions are obtained.

• 한국정보전자통신기술학회논문지
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• 제3권2호
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• pp.31-38
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• 2010

PBG 구조의 메타물질 설계시 패턴 형태와 배열 구조에 따른 금지대역(bandgap)을 정확하게 설계하기 어려운 문제가 있다. 본 논문에서는 2차원 배열구조로 어떤 모양의 패턴에 대해서도 빠르고 정확하게 원하는 금지대역을 설계할 수 있는 방법을 제안한다. 2차원 평면상의 메타물질 구조는 주기배열로 이루어져 있기 때문에 FDTD 수치해석 방법에 주기경계조건을 부여함으로서 계산영역을 줄였다. 또한 각 패턴이 갖는 L, C 값을 2차원적으로 고려하여 계산하였기 때문에 보다 정확한 설계가 가능하였다. 5GHz 대역에서 정사각형 패턴을 갖는 메타물질을 설계하여 기존의 마이크로스트립 선로를 이용한 1차원 메타물질 해석 값과 비교하였을 때 정확도가 평균적으로 14.7% 향상됨을 확인할 수 있었다.

• Interaction and multiscale mechanics
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• 제2권2호
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• pp.129-151
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• 2009

This paper presents a meshfree procedure using a convex generalized meshfree (GMF) approximation for the large deformation analysis of particle-reinforced rubber compounds on microscopic level. The convex GMF approximation possesses the weak-Kronecker-delta property that guarantees the continuity of displacement across the material interface in the rubber compounds. The convex approximation also ensures the positive mass in the discrete system and is less sensitive to the meshfree nodal support size and integration order effects. In this study, the convex approximation is generated in the GMF method by choosing the positive and monotonic increasing basis function. In order to impose the periodic boundary condition in the unit cell method for the microscopic analysis, a singular kernel is introduced on the periodic boundary nodes in the construction of GMF approximation. The periodic boundary condition is solved by the transformation method in both explicit and implicit analyses. To simulate the interface de-bonding phenomena in the rubber compound, the cohesive interface element method is employed in corporation with meshfree method in this study. Several numerical examples are presented to demonstrate the effectiveness of the proposed numerical procedure in the large deformation analysis.

• 한국안광학회지
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• 제12권3호
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• pp.117-120
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• 2007

대학생 304명을 대상으로 정기적 시력검진의 실태를 조사, 분석하여 안보건교육 프로그램의 개발 및 교육의 실시를 위한 자료를 얻고자 하였다. 연구대상의 59.21%가 정기적 시력검진을 받지 않는 것으로 나타났으며 여학생의 정기적 시력검진률이 남학생보다 높게 나타났다. 도시출신의 정기적 시력검진률이 43.07%, 농 어촌출신이 24.32%로 유의한 차이를 보여주었으며(p<0.05) 4년제 대학생의 정기적 시력검진률이 65.71%, 2-3년제 대학생이 27.64%로 유의한 차이를 보여주었다(p<0.001). 시력을 교정한 대학생의 정기적 시력검진률이 50.25%, 시력을 교정하지 않는 대학생이 23.36%로 유의한 차이를 보여주었다(p<0.001).

• 한국수학교육학회지시리즈B:순수및응용수학
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• 제9권1호
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• pp.19-30
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• 2002

We consider one class of bursting oscillation models, that is square-wave burster. One of the interesting features of these models is that periodic bursting solution need not to be unique or stable for arbitrarily small values of a singular perturbation parameter $\epsilon$. Recent results show that the bursting solution is uniquely determined and stable for most of the ranges of the small parameter $\epsilon$. In this paper, we present a condition of uniqueness and stability of periodic bursting solutions for all sufficiently small values of $\epsilon$ > 0.

• Korean Journal of Mathematics
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• 제21권1호
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• pp.81-90
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• 2013

We investigate the bounded weak solutions for the Hamiltonian system with bounded nonlinearity decaying at the origin and periodic condition. We get a theorem which shows the existence of the bounded weak periodic solution for this system. We obtain this result by using variational method, critical point theory for indefinite functional.

• 대한수학회논문집
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• 제32권2호
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• pp.457-466
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• 2017

We study the existence and uniqueness of S-asymptotically ${\omega}-periodic$ mild solutions for some partial functional integrodifferential equations with infinite delay and nonlocal conditions.

• Korean Journal of Mathematics
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• 제16권2호
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• pp.243-257
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• 2008

We seek the sign changing periodic solutions of the nonlinear wave equation $u_{tt}-u_{xx}=a(x,t)g(u)$ under Dirichlet boundary and periodic conditions. We show that the problem has at least one solution or two solutions whether $\frac{1}{2}g(u)u-G(u)$ is bounded or not.