• 한국철도학회:학술대회논문집
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• 한국철도학회 2000년도 추계학술대회 논문집
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• pp.514-520
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• 2000

Numerical simulation is conducted to clarify the heat transfer and fluid flow characteristics of HVAC(Heating, Ventilating and Air-Conditioning) for Mugunghwa passenger car. The HVAC system is installed under the floor of carbody. This new HVAC system has a lot of merits in respect of the center of gravity of carbody, flow induced noise and reduction of condensation water etc. The standard k-epsilon turbulent model and SIMPLEC algorithm based on finite volume method are used to solve the physical HVAC model. To assure convergence, QUICK scheme for momentum equation and the first order upwind scheme for turbulent equations are used. From the results of simulation, the temperature and velocity magnitude are also distributed uniformly in the interior of car.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제15권2호
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• pp.143-150
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• 2011

We consider the global existence of strong solutions of the 3D incompressible Navier-Stokes equations in a thin periodic domain. We present a simple proof that a strong solution exists globally in time when the initial velocity in $H^1$ and the forcing function in $L^p$(0,${\infty}$;$L^2$), $2{\leq}p{\leq}{\infty}$ satisfy certain condition. This condition is basically similar to that by Iftimie and Raugel[7], which covers larger and larger initial data and forcing functions as the thickness of the domain ${\epsilon}$ tends to zero.

• 한국정밀공학회지
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• 제10권2호
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• pp.146-153
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• 1993

Thd specimens were melited in high frequency induction furnace. The samples for measurements were prepared by machining cylinder of 9.5mm diameter and 15mm height. These samples were then hot-pressed according to strain rate ( .epsilon. ). These samples were decanned and cut out, and subsequently heat treated at 1000 .deg. C for 4hours. These were investigated for the change of microstructure, domain pattern, X-ray diffraction and magnetic properties. The stress distributions in the specimens during compressing process were calculated by a finite element method program(SPID). The calculated stresses were effective stress( .sigma. $_{eff}$), compressive direction stress( .sigma. $_{z}$), and shear stress( .tau. $_{rz}$ ). These stresses were compared with the experimental data.a.a.

• 한국정밀공학회지
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• 제7권1호
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• pp.28-36
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• 1990

In this paper, the flow field with steady, axisymmetric flow characteristics in cylinder has been numerically investigated. The prediction of flow in cylinder was compared to experimental result. The turbulence closure being applied was K-${\epsilon}$ model and numerical scheme was Hybrid and Power-law scheme. The results of numerical computation showed some deviation from exper- imental data in the in cial region of cylinder, where streamline curvature is significant. However, the computational results agree qualitatively well with Mores's experimental results and the difference between Hybrid and Power-law schows similar results

• Journal of the Korean Statistical Society
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• 제26권3호
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• pp.299-308
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• 1997

In the simple linear regression model Y = .alpha.$_{0}$ + .beta.$_{0}$Z + .epsilon. under the right censorship of the response variables, the estimation of the mean lifetime E(Y) is an interesting problem. In this paper we propose a method of estimating E(Y) based on the observations modified by the arguments of Buckley and James (1979). It is shown that the proposed estimator is consistent and our proposed procedure in the simple linear regression case can be naturally extended to the multiple linear regression. Finally, we perform simulation studies to compare the proposed estimator with the estimator introduced by Gill (1983).83).

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2003년도 기술심포지움 논문집
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• pp.165-168
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• 2003

본 연구에서는 마이크로파응용을 위한 이동통신기기용 안테나 모듈용 유전체재료 개발을 위해 $20\~80$의 중유전율을 가지는 글래스-세라믹스 복합체를 제조하고자 하였다. $BaO-Nd_2O_3-TiO_2$계 세라믹스를 기본조성으로 하고, $Na_2O-BaO-B_2O_3-P_2O_5$계 글래스 프릿의 첨가를 통해 제조된 글래스-세라믹스 복합체의 소결특성 및 유전특성을 조사하였다. 글래스 프릿을 5, 10, $15wt\%$ 첨가하였으며, $800\~950^{\circ}C$에서 각각 1시간동안 소결을 진행하였다. 그 결과로서 글래스 프릿의 한량이 증가하고, 소결온도가 높을수록 유전율$(\epsilon_r)$은 증가하였으며, 복합체의 결정특성은 감소함을 나타내었다.

• 한국해양공학회지
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• 제11권4호
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• pp.141-151
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• 1997

This paper deals with a numerical study of flow-guider applied to controlling current in a bay. Two dimensional numerical model for tidal currents based on the depth averaged equation is developed and standard k-.epsilon. model is adopted to determine the turbulence diffusion. Equations are described in a generalized coordinate system to be implemented by non-staggered grid system and discretized by using finite volume method. Unsteady flow is simulated by fully implicit scheme. Hybrid scheme and central differencing are used to compute the convective terms and source terms, respectively. The tidal current in a rectangular bay is simulated and it gives satisfactory results. The realistic and distinct models of a large structure placed in bay are also exemplified with or without flow-guiders. The simulation results show that the flow-guider gives the residual tidal current in the bay by the different flux with respect to the direction of tidal current.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2003년도 종합학술발표회 논문집 Vol.13 No.1
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• pp.437-441
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• 2003

The major drawback of the classical microstrip patch antennas Is their narrow band characteristic from 1% to 5%. In this paper, to improve this drawback, we designed the antenna with stacked structure having one drive patch connected with feed line and four identical radiation patches. Resonance is achieved by adjust ing coupling area between one drive patch and four identical radiation patches and changing the size of drive patch or radial ion patches. Used substrate is FR4(${\epsilon}_r$=4.6 and t=1.6mm) and designed center frequency is 2.45GHz. The designed antenna has a wide bandwidth of 380Mhz form 2.333GHz to 2.713GHz(about 15.5%) including ISM band from 2.4GHz to 2.4835GHz.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2003년도 종합학술발표회 논문집 Vol.13 No.1
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• pp.630-637
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• 2003

In this paper, a DBM(double balanced mixer) of 2 GHz is implemented on FR4(h=1.6mm, ${\epsilon}_r=4.6$) substrate. The structure of double balanced mixer requires, in general, two talons and a quad diode. For balun, a novel planar balun using microstrip to CPS(Coplanar Strip) is suggested and designed. The suggested balun shows the phase imbalance of $180^{\circ}{\pm}1.5^{\circ}$ and the amplitude imbalance of ${\pm}0.2 dB$ for 1.5 to 2.5 GHz. Using the balun, DBM is successfully implemented, and the measured conversion loss of up/down converter show about 6 dB over the bandwidth. The balun may be applicable for MMIC(Monolithic Microwave Integrated Circuit) DBM with the process supporting backside via though more study.

• 한국전기전자재료학회논문지
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• 제29권10호
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• pp.613-619
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• 2016

The aim of this study is to improve of dielectric properties using epoxy/nano alumina composites with adding glycerol diglycidyl ether (GDE:1,2 g). This paper deals with the effects of dielectric properties(${\epsilon}^{\prime}_r$ and $tan{\delta}$) for epoxy/nano alumina contents (1,3 phr) and GDE addition (1,2 g)composites. 5 kinds specimen were prepared with containing epoxy resins, epoxy nano alumina composites. Average particle size of nano used were 30 nm. The nano alumina used were gamma phase particles of spherical shape. The suppression of epoxy chain motion by addition of nano alumina+GDE decreased dielectric loss and relative permittivity magnitude.