• Kyungpook Mathematical Journal
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• 제47권2호
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• pp.191-202
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• 2007

By using the weighted averaging techniques, we establish oscillation criteria for the second order damped quasilinear elliptic differential equation $$\sum_{i,j=1}^{N}D_i(a_{ij}(x){\parallel}Dy{\parallel}^{p-2}D_jy)+{\langle}b(x),\;{\parallel}Dy{\parallel}^{p-2}Dy{\rangle}+c(x)f(y)=0,\;p>1$$. The obtained theorems include and improve some existing ones for the undamped halflinear partial differential equation and the semilinear elliptic equation.

• 대한수학회지
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• 제47권6호
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• pp.1183-1196
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• 2010

Some annulus oscillation criteria are established for the second order damped elliptic differential equation $$\sum\limits_{i,j=1}^N D_i[a_{ij}(x)D_jy]+\sum\limits_{i=1}^Nb_i(x)D_iy+C(x,y)=0$$ under quite general assumption that they are based on the information only on a sequence of annuluses of $\Omega(r_0)$ rather than on the whole exterior domain $\Omega(r_0)$. Our results are extensions of those due to Kong for ordinary differential equations. In particular, the results obtained here can be applied to the extreme case such as ${\int}_{\Omega(r0)}c(x)dx=-\infty$.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2007년도 정기총회 및 학술발표대회
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• pp.441-444
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• 2007

Surge tank generally are used near the downstream end of tunnels of penstocks to reduce change in pressure caused by waterhammer resulting from load changes on the turbines. In this paper, the surge tank with chamber is selected to analyze water surface oscillation. the governing equation are derived using the law of conservation of mass and momentum. the water surface oscillation in the surge tank are computed using governing equation. In the case of upsurging, water surface oscillation is damped gradually and in the case of downsurging, it is damped rapidly.

• 대한수학회논문집
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• 제26권4호
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• pp.695-708
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• 2011

Based on the multiple-time-scale (MTS) method, a general formula has been presented for solving an n-th, n = 2, 3, ${\ldots}$, order ordinary differential equation with strong linear damping forces. Like the solution of the unified Krylov-Bogoliubov-Mitropolskii (KBM) method or the general Struble's method, the new solution covers the un-damped, under-damped and over-damped cases. The solutions are identical to those obtained by the unified KBM method and the general Struble's method. The technique is a new form of the classical MTS method. The formulation as well as the determination of the solution from the derived formula is very simple. The method is illustrated by several examples. The general MTS solution reduces to its classical form when the real parts of eigen-values of the unperturbed equation vanish.

• Kyungpook Mathematical Journal
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• 제46권2호
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• pp.219-229
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• 2006

Using the integral average method, we establish some oscillation criteria for the nonlinear differential equation with damped term $$a(t)|{x}^{\prime}(t)|^{\sigma-1}{x}^{\prime}(t)^{\prime}+p(t)|{x}^{\prime}(t)|^{\sigma-1}{x}^{\prime}(t)+q(t)f(x(t))=0,\;{\sigma}>1$$, where the functions $a,\;p$ and $q$ are real-valued continuous functions defined on $[t_o,{\infty})$ with $a(t)>0,\;f(x){\in}C^1(\mathbb{R})$ and $\frac{f^{\prime}(u)}{|f^{({\sigma}-1)/{\sigma}}(u)|}{\geq}k>0$ for $u{\neq}0$.

• Journal of applied mathematics & informatics
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• 제24권1_2호
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• pp.1-16
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• 2007

Some Kamenev-type oscillation criteria are obtained for a second order quasilinear damped differential equation with impulses. These criteria generalize and improve some well-known results for second order differential equations with land without impulses. In addition, new oscillation criteria are also obtained to generalize and improve known results. Two examples of applications are given to illustrate the theory.

• 한국자기학회지
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• 제18권4호
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• pp.127-130
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• 2008

본 논문에서는 수 백 나노미터 크기의 자성 소자에서 존재하는 강자기 소용돌이 구조의 운동에 대한 이론을 제시한다. LLG 방정식으로부터 유도된 운동방정식, 즉 Thiele 방정식에 그 이후 밝혀진 이론적 결과들을 도입하여 강자기 소용돌이의 감쇠 단조화 운동방정식을 도출하였다. 이러한 운동방정식으로부터 감쇠 단조화 운동의 고유 진동수와 감쇠 상수를 나타내는 수식을 유도하였으며, 유도된 수식을 micromagnetic 시늉 실험을 통하여 검증하였다.

• 한국광학회지
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• 제5권3호
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• pp.394-403
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• 1994

외부 광귀환이 있는 레이저 다이오드의 혼돈특성에 관해 고찰하였다. Fabry-Perot 공진기 형태의 레이저에 외부 거울에 의한 광귀환을 가정하였으며 파장 $1.3{\mu}m$의 "InGaAsP" buried-hetero structure 레이저에 $1.3J_{th}$의 전류가 인가되었을 때를 모의전산 하였다. 광귀환계수 K의 증가량에 따라 다음의 네단계로 진화현상을 보이고 있다. (1)광귀환계수 K가 아주 작을 때는 시간이 지남에 따라 이완발진은 감쇄되고, 정상 상태에 도달하여 안정된 동작특성을 보인다. (2)K가 조금 증가하면 이완발진은 감쇄되지 않고 주기적인 발진을 유지하기 시작한다. (3)K가 더욱 증가하면 발진의 폭은 증가하고 발진형태의 주기는 길어진다. (4)K가 매우 증가하면 발진형태는 안정을 잃고 coherence collapse 상태에 도달한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 C
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• pp.1035-1038
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• 1999

To improve the damping of all poorly damped oscillation modes, a control strategy of Static Synchronous Series Compensator (SSSC) based on energy method is presented in this Paper As a synchronous voltage-sourced inverter, SSSC is used to provide controllable series compensation. SSSC can provide controllable compensating voltage over an identical capacitive and inductive range. The damping effect of control strategy based on energy function is robustness with respect to loading condition, fault location and network configuration. Furthermore, the control inputs are based on local signals. In two area system, the effect of damping inter-area mode oscillation is demonstrated by the robust control strategy of SSSC.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 추계학술대회 논문집 학회본부
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• pp.120-124
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• 1995

TCSC can not only increase power flow but also damp low frequency oscillation by controlling firing angles of thyristors. But, a model considering voltage, current firing angles is not derived. This paper used a small signal model considirng these variables which was derived in paper [1]. TCSC model is combined with swing equation. Being related to rotor angles and firing angles of thyristors, current and synchronizing torque coefficient is reformulated. Because firing angles of thyristors can be controlled only twice within one period, swing equation is transformed to discrete time model. It is shown that low frequency oscillation can be damped by controlling firing angles in one machine infinite bus power system.