• 대한수학회지
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• 제44권3호
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• pp.511-523
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• 2007

We consider a two parametric family of the planar systems with the form $\dot{x}=P(x,\;y)+{\in}_1p_1(x,\;y)+{\in}_2p_2(x,\;y)$, $\dot{y}=Q(x,\;y)+{\in}_1p_1(x,\;y)+{\in}_2p_2(x,\;y)$, where the unperturbed equation(${\in}_1={\in}_2=0$) is assumed to have at least one periodic solution or limit cycle. Our aim here is to study the behavior of the system under two parametric perturbations; in fact, using the Poincare-Andronov technique, we impose conditions on the system which guarantee persistence of the periodic trajectories. At the end, we apply the result on the Van der Pol equation ; where, we consider the effect of nonlinear damping on the equation. Also the Hopf bifurcation for the Van der Pol equation will be investigated.

• 대한수학회지
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• 제51권4호
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• pp.679-702
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• 2014

Investigation of the numerical solution of singularly perturbed turning point problems dates back to late 1970s. However, due to the presence of layers, not many high order schemes could be developed to solve such problems. On the other hand, one could think of applying the convergence acceleration technique to improve the performance of existing numerical methods. However, that itself posed some challenges. To this end, we design and analyze a novel fitted operator finite difference method (FOFDM) to solve this type of problems. Then we develop a fitted mesh finite difference method (FMFDM). Our detailed convergence analysis shows that this FMFDM is robust with respect to the singular perturbation parameter. Then we investigate the effect of Richardson extrapolation on both of these methods. We observe that, the accuracy is improved in both cases whereas the rate of convergence depends on the particular scheme being used.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2002년도 International Meeting on Information Display
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• pp.137-140
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• 2002

The frequency response analysis of complex impedance spectra using small perturbation ac impedance spectroscopy is an informative method of OLED performance characterization and lifetime analysis. Using simple RC equivalent circuit mode,l macroscopic nonliniear transport properties of semiconductive emission/transport layers can be analyzed and parameterized. We present the bias voltage dependence and aging effect in impedance spectra measured from an ITO/CuPC/TPD/$Alq_3$/LiF/Al OLED device, and discuss possible failure mechanism based on impedance model parameters.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.803-809
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• 2005

This paper presents the theoretical model to investigate the effect of Coulomb damping in the sub-structure of a foil bearing. Foil deflection is restricted by friction of bumps. Equivalent viscous damping of the bump foils is derived from the Coulomb friction. Dynamic equation of the bumps is constituted by stiffness and damping terms. This point give the difference from Heshmat's frictionless and simple compliance bump model. The fluid is modeled with the compressible Reynolds equation. A perturbation approach is used to determine the static and dynamic performance of the bearing from the coupled fluid-structural model. The analysis result shows that the static and dynamic performance is enhanced by bump friction. This analysis technique would be extended to development of a high performance bearing.

• Journal of Astronomy and Space Sciences
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• 제3권1호
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• pp.15-27
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• 1986

인공위성이 원궤도를 유지하도록 초기궤도 요소를 주고, 섭동요소들에 의한 동경 반경의 변화를 계산하였다. 위성의 궤도에 영향을 미치는 섭동 요소로는 지구의 비대칭 potential, 달과 태양 의 인력을 고려하였다. 계산결과로부터 다음과 같은 결론을 얻었다. 1) 위성의 례도 청사각이 $0^{\circ}$ 일 때, $J_2$ 항은 전혀 섭동을 일으키지 않는다. 2) 이 경우에는 tesseral harmonics 만이 큰 섭동을 냐타내며 영년 변화가 나타난다. 3) 기타의 다른 섭동은 비교적 작지만 주기성을 갖는다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.153-159
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• 2002

This paper deals with the measurement of the fluid viscosity by using the torsional vibration of a circular red excited by a torsional vibrator at one end. The effect of an adjacent viscous fluid on the torsional vibration of the rod has been studied theoretically and expressed in terms of the mechanical impedance. The theoretically-obtained trend that the mechanical impedance is proportional to the square root of the viscosity times the density of the fluid has been confirmed by the impedance measurement. The paper demonstrates that a torsionally-vibrating rod can be used as a sensor to measure the viscosity of a fluid.

• 응용통계연구
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• 제7권2호
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• pp.21-34
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• 1994

본 논문에서 대기체계 M/M/1에서 평균 도착시간간격 $\theta$에 대한, 평형상태에서 평균시스템시간 (Steady State Mean System Time) W의 민감도 $dW/d\theta$를 표본통로(Sample Path)를 관찰하므로서 얻을 수 있는 방안을 제시하였으며, 평형상태에서 시스템 내에 고객이 k명 있을 확률, 즉 극한 확률(Limiting Probability) $P_k$의 민감도 $dP_k/d\theta$에 대해서도 유사한 결과를 얻었다. 또한 두 경우 모두 민감도의 추정값이 IPA(Infinitesimal Perturbation Analysis) 추정값과 그 이외의 요인에 의한 값의 합으로 명확히 표시됨을 보임으로서 IPA 추정값이 일반적으로 적용될 수 없음을 확인하였다.

• Tribology and Lubricants
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• 제23권5호
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• pp.240-247
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• 2007

The design process of the dental handpiece is described. The parameters of the high speed air turbine are estimated. The effect of supply hole on the stiffuess and damping of the air bearing for handpiece is studied numerically. The Reynolds equation is solved by using the divergence formulation and the perturbation method. The test rig is built and the test procedure is developed for the turbine rotational speed measurement by using Fourier transform of noise generated by the turbine during steady operation.

• 자원환경지질
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• 제21권2호
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• pp.165-169
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• 1988

2차원 구조에 대한 음수의 분도분극 반응을 차분법을 이용한 2차원 모델링 기술로 검토하였다. 유도분극 변수로서는 섭동방법으로 효율적으로 계산이 가능한 주파수 효과를 사용하였다. 전도성이면서 분극성인 얇은 표토층은 가상단면도상에서 뚜렷한 음수의 유도분극 반응을 일으킨다. 이는 분극성 표토층하에 존재하는 저항성인 부극체에 의한 반응이 단지 비저항분포의 함수만으로 음폐되는 것을 뜻한다. 그러나, 분극성 표토층하의 저항성인 비 분극체는 음수의 반응으로 발견될 수 있다.

• 한국통신학회논문지
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• 제21권2호
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• pp.340-346
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• 1996

In this paper, we propose a ne weighted backward covariance matrix method to enhance the resolution for direction-of-arrival(DOA) estimation. The proposed method (MEVM:modified eigenvector method) is an enhanced covariance matrix method which is an extended form of the conventional covariance matrix. We analyze the effect of using the weighted forward-baskward covariance matrix on the performance of the eigenvector method(EVM). By comparing the perturbation angle of the noise-subspace, we show that the spectral estimate obtained using the proposed method is less distorted than the spectral estimate obtained using the conventional EVM. The simulation results show that the new method is more accurate and has better resolution than the conventional EVM under the same noise conditions.