• 전자공학회논문지A
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• 제33A권3호
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• pp.65-81
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• 1996

In this study forty-five X-bnd rectangular microstrip patch antennas fed by microstrip line using ${\lambda}$/4 transformer were fabricated on teflon substrates with low high permittivities and varous thickness (substrate thickness : 0.6 ~ 2.4 mm, permittivities : 2.15 ~ 10.0), and effects of permittivity and electrical thickness on antenna characteristics were studied with measured return loss (1/S$_{11}$) and resonant frequencies. When substrate electrical thickness was greater than 0.060 ${\lambda}_{0}$return loss was very good and genrally more than 20 dB, but resonance characteristics was somewhat unstable. The more than 0.088 ${\lambda}_{0}$ the thickness was, the more unstable it was. As a result, in the rest range except 12, 13 GHz we had very good mesured return loss iwth greater than 20 dB, and in the range 7 to 9 GHz resonant frequencies were within $\pm$2 % error, on ${\epsilon}_{r}$=5.0, height = 2.4 mm substrate.

• Kyungpook Mathematical Journal
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• 제60권3호
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• pp.647-671
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• 2020

In this paper, we consider the Cauchy-type problem for a nonlinear differential equation involving a Ψ-Hilfer fractional derivative and prove the existence and uniqueness of solutions in the weighted space of functions. The Ulam-Hyers and Ulam-Hyers-Rassias stabilities of the Cauchy-type problem is investigated via the successive approximation method. Further, we investigate the dependence of solutions on the initial conditions and their uniqueness using 𝜖-approximated solutions. Finally, we present examples to illustrate our main results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 A
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• pp.406-408
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• 1999

캐패시터(capacitor)의 고주파(수십MHz) 전기장에서 유전손실(dielectric loss)에 의한 유리의 용융 및 합성에 관한 이론적 고찰이 수학적 모델에 의하여 이루어졌다. 유전 가열법에 있어서 캐패시터에 놓여진 유전체가 흡수하는 에너지는 용융인자(전압, 주파수)와 피시물(유리)의 전기, 물리적 성질[유전율(${\epsilon}$). power factor($tan{\delta}$)]에 의존한다. 본 연구에서는 이러한 물성들의 온도 의존성뿐만 아니라 외부로의 열손실 등이 조사되었으며, 특성 분석을 통해 최적의 용융 모델을 설계하였다.

• 대한인간공학회지
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• 제16권2호
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• pp.15-27
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• 1997

Brain potential is described using the mesocolumnar activity defined by averaged firings of excitatory and inhibitory neuron of neocortex. Lagrangian is constructed based on SMNI(Statistical Mechanics of Neocortical Interaction) and then Euler Lagrange equation is obtained. Excitatory neuron firing is assumed to be amplitude- modulated dominantly by the sum of two modes of frequency .omega. and 2 .omega. . Time series of this neuron firing is calculated numerically by Euler Lagrangian equation. I .omega. L related to low frequency distribution of power spectrum, I .omega. H hight frequency, and Sd(standard deviation) were introduced for the effective extraction of the dynamic property in the simulated brain potential. The relative behavior of I .omega. L, I .omega. H, and Sd was found by parameters .epsilon. and .gamma. related to nonlinearity and harmonics respectively. Experimental I .omega L, I .omega. H, and Sd were obtained from EEG of human in rest state and of canine in deep sleep state and were compared with theoretical ones.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.128-133
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• 2002

The heat transfer characteristics of a turbulent flow in a ribbed two-dimensional channel have been investigated numerically. The fully elliptic governing equations, coupled with a four-equation turbulence model, $\kappa-\omega-\bar{t^2}-\epsilon_t$, are solved by a finite volume method of SIMPLE type. Calculations have been carried out for three rib cross-sections : square, triangular, and semicircular, with various rib pitches and Reynolds numbers. The procedure appears to be satisfactory as the results for the square rib compare favorably with available experimental data and earlier calculation. The optimal rib pitch that yields the maximum heat transfer has been identified. It is also found that the square rib is most effective in enhancing the heat transfer. The semicircular rib, on the other hand, incurs the least amount of pressure drop but the improvement in heat transfer is substantially lower.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 추계 학술대회논문집
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• pp.41-46
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• 2002

A numerical simulation was made to determine the motion of particles in the fluid. The simulation is based on the Eulerian-Lagrangian method. The fluid motion was solved using a PISO-based finite-element method and a $\kappa-\epsilon$ model of turbulence. In the Lagrangian method for the solid phase, the trajectories of particles are calculated by integrating the equations of motion of a single Particle, and the collision between particles are taken into account. The influence of particles on the fluid phase is taken into account by introducing source terms in the Eulerian equations govering the fluid flow. It is known as the particle-source-in-cell (PSIC) method. Also, the turbulent effect in the particles and fluid notion is considered. The numerical results were compared with the experiment for a two-phase flow in a vertical pipe.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.17-22
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• 2002

This paper describes numerical research on transverse jet behind rearward-facing step in turbulent supersonic flowfields without chemical reaction. The purpose of transverse jet behind rearward-facing step is to improve mixing of the fuel in the combustor. Two-dimensional unsteady flowfields generated by slot injection into supersonic flow are numerically simulated by integration of Navier-Stokes equation. Final-scale turbulence effects are modeled with two-equation $\kappa-\epsilon$ model. Numerical methods are modeled high-order upwind TVDschemes. A total of 4 cases are computed, comprising slot momentum flux ratios at four step heights downstream of the step. These numerical results are represented periodic phenomenon in unsteady flowfields.

• 대한기계학회논문집
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• 제18권1호
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• pp.184-192
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• 1994

The parameters such as Richardson numbers or stability parameters are widely used to account for the extra straining effects due to three-dimensionality, curvature, rotation, swirl and others arising in paractical complex flows. Existing expressions for the extra strain in turbulence models such as $k-{\epsilon}$ models, however, do not satisfy the tensor invariant condition representing the coordinate indifference. In the present paper, considering the characteristics of both the mean strain rate and the mean vorticity, a new parameter to deal with the extra straining effects is proposed. The new parameter has a simple form and satisfies the tensor invariant condition. A semi-quantitative analysis between the present and previous parameters for several typical complex flows suggests that the newly proposed parameter is more general and adequate in representing the extra straining effects than the previous ad-hoc parameters.

• 대한기계학회논문집
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• 제15권3호
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• pp.954-962
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• 1991

본 연구에서는 횡 방향으로 속도구배를 타내는 a=.part.W/.part.z에 대한 방정식을 3차원 운동량 방정식으로 부터 유도한 준 3차원 수학적 모델을 성정하여 해석하였다. 또한 수치 해석을 위하여 Chen에 의하여 고안된 유한 해석법과 2-방정식 저 레이놀즈 K-.epsilon. 난류모델, 그리고 Maeng에 의해 제시된 경계 공정 좌표계를 사용하였다. 그리 고 프로그램의 검증을 위하여 G.Ber geles가 수행한 실험치와 비교하여 그 타당성을 입증하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2777-2781
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• 2008

Gas atomization of liquid metal using nozzle technology has more advantages over other methods. Previous study shows that high-velocity gas is important for effective liquid metal atomization. An important first step towards understanding the gas atomization using nozzle is complete evaluation of the flow fields. This will provide a basis for understanding how well high velocity gas is brought to bear on the liquid metal. Present work is a fundamental study of liquid metal atomization for various pressure ratio, different gas and temperature. A two-dimension, axisymmetry compressible Navier-Stokes equations are considered. Two-equation k-epsilon turbulence model is selected.