• Steel and Composite Structures
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• v.27 no.5
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• pp.599-611
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• 2018

In this article a four unknown quasi-3D shear deformation theory for the bending analysis of functionally graded (FG) plates is developed. The advantage of this theory is that, in addition to introducing the thickness stretching impact (${\varepsilon}_z{\neq}0$), the displacement field is modeled with only four variables, which is even less than the first order shear deformation theory (FSDT). The principle of virtual work is utilized to determine the governing equations. The obtained numerical results from the proposed theory are compared with the CPT, FSDT, and other quasi-3D HSDTs.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.8
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• pp.307-317
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• 2003

We analyze the performance of MC-CDMA and MC-DS/CDMA system on quasi-synchronized moble satellite return link. Quasi-synchronization is considered that chip offset between terminals is within a few chips. In 10-3 BER, performance of MC-DS/CDMA system with walsh code is 0.3dB better than that of MC-CDMA system when the number of user is 5 from -0.5 $T_{c}$ to 0.5 $T_{c}$ quasi-synchronization of MC-DS/CDMA system and from -5/64 $T_{c}$ $^{MC}$ to 5/64 $T_{c}$ $^{MC}$ quasi-synchronization of MC-CDMA system. MC-DS/CDMA system with walsh code is over 0.2dB better than that of MC-DS/CDMA system with extended m code and gold code. MC-CDMA system with walsh code is over 1.2dB better than that of MC-CDMA system with gold code when the number of user is 5 and lower than from -5/32 $T_{c}$ $^{MC}$ to 5/32 $T_{c}$ $^{MC}$ quasi-synchronization.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.941-942
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• 2008

• Bulletin of the Korean Mathematical Society
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• v.55 no.3
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• pp.967-970
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• 2018

The aim of this paper is to show that there exists a weakly quasisymmetric homeomorphism $f:(X,d){\rightarrow}(Y,d^{\prime})$ between two locally compact non-complete metric spaces such that $f:(X,d_h){\rightarrow}(Y,d^{\prime}_h)$ is not quasi-isometric, where dh denotes the Gromov hyperbolic metric with respect to the metric d introduced by Ibragimov in 2011. This result shows that the answer to the related question asked by Ibragimov in 2013 is negative.

• Journal of Korean Society for Atmospheric Environment
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• v.19 no.E2
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• pp.75-81
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• 2003

Variational data assimilation, which is recently introduced to the air quality modeling, is a promising tool for obtaining optimal estimates of initial conditions and other important parameters such as emission and deposition rates. In this paper. two advanced techniques for variational data assimilation, based on the adjoint and quasi-inverse methods, are tested for a simple air quality problem. The four-dimensional variational assimilation (4D-Var) requires to run an adjoint model to provide the gradient information in an iterative minimization process, whereas the inverse 3D-Var (I3D-Var) seeks for optimal initial conditions directly by running a quasi -inverse model. For a process with small dissipation, I3D-Vu outperforms 4D-Var in both computing time and accuracy. Hybrid application which combines I3D-Var and standard 4D-Var is also suggested for efficient data assimilation in air quality problems.

• Journal of Advanced Navigation Technology
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• v.16 no.5
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• pp.760-765
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• 2012

In this paper, we studied a design method for a quasi-Yagi antenna (QYA) with broadband characteristics of an impedance bandwidth ratio greater than 2 : 1 and a gain > 4 dBi. The QYA is fed by a microstrip line fabricated on a coplanar strip line and it consists of 3 elements; a planar dipole, a nearby director close to the dipole, and a ground plane reflector. By placing a wide rectangular patch-type director near to the dipole driver, broadband characteristics are achieved. An optimized 3-element QYA for operation over 1.6-3.5 GHz (bandwidth ratio 2.2 : 1) is fabricated on an FR4 substrate with a size of 90 mm by 90 mm and tested experimentally. The results show an impedance bandwidth of 1.56-3.74 GHz (bandwidth ratio 2.4 : 1) for VSWR < 2, a peak gain of 4.2-6.3 dBi, and a front-to-back ratio (FBR) > 13.6 dB within the bandwidth.

• Earthquakes and Structures
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• v.22 no.5
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• pp.447-460
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• 2022

In this article, wave propagation in functional gradation plates (FG) resting on an elastic foundation with two parameters is studied using a new quasi-three-dimensional (3D) higher shear deformation theory (HSDT). The new qausi-3D HSOT has only five variables in fields displacement, which means has few numbers of unknowns compared with others quasi-3D. This higher shear deformation theory (HSDT) includes shear deformation and effect stretching with satisfying the boundary conditions of zero traction on the surfaces of the FG plate without the need for shear correction factors. The FG plates are considered to rest on the Winkler layer, which is interconnected with a Pasternak shear layer. The properties of the material graded for the plates are supposed to vary smoothly, with the power and the exponential law, in the z-direction. By based on Hamilton's principle, we derive the governing equations of FG plates resting on an elastic foundation, which are then solved analytically to obtain the dispersion relations. Numerical results are presented in the form of graphs and tables to demonstrate the effectiveness of the current quasi-3D theory and to analyze the effect of the elastic foundation on wave propagation in FG plates.

• Geomechanics and Engineering
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• v.22 no.5
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• pp.415-431
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• 2020

In this study, dynamics responses of advanced composite plates resting variable elastic foundations via a quasi-3D theory are developed using an analytical approach. This higher shear deformation theory (HSDT) is included the shear deformation theory and effect stretching that has five unknowns, which is even inferior to normal deformation theories found literature and other theories. The quasi-three-dimensional (quasi-3D) theory accounts for a parabolic distribution of the transverse shear deformation and satisfies the zero traction boundary conditions on the surfaces of the advanced composite plate without needing shear correction factors. The plates assumed to be rest on two-parameter elastic foundations, the Winkler parameter is supposed to be constant but the Pasternak parameter varies along the long side of the plate with three distributions (linear, parabolic and sinusoidal). The material properties of the advanced composite plates gradually vary through the thickness according to two distribution models (power law and Mori-Tanaka). Governing differential equations and associated boundary conditions for dynamics responses of the advanced composite plates are derived using the Hamilton principle and are solved by using an analytical solution of Navier's technique. The present results and validations of our modal with literature are presented that permitted to demonstrate the accuracy of the present quasi-3D theory to predict the effect of variables elastic foundation on dynamics responses of advanced composite plates.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.05a
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• pp.70-73
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• 2012

In this paper, we introduce a design method for a quasi-Yagi antenna (QYA) with broadband characteristics of an impedance bandwidth ratio of > 2 : 1 and a gain of > 4 dBi. The QYA is fed by a microstrip line fabricated on a coplanar strip line and it consists of 3 elements; a planar dipole, a nearby director close to the dipole, and a ground plane reflector. By placing a rectangular patch-type director with large width near to the dipole driver, broadband characteristics are achieved. An optimized 3-element QYA for operation over 1.6-3.5 GHz (bandwidth ratio 2.2 : 1) is fabricated on an FR4 substrate with a size of $90mm{\times}90mm$ and tested experimentally. The results show an impedance bandwidth of 1.56-3.74 GHz (bandwidth ratio 2.4 : 1) for VSWR < 2, a peak gain of 4.41-6.53 dBi, and a front-to-back ratio (FBR) > 13.6 dB within the bandwidth.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.6
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• pp.1-10
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• 1997

By using the boundary element method, the cahracterization and the circuit modelling of the coplanar waveguide (CPW) discontinuities are performed bvia quasi-static approximation. The capacitive equivalent circuits are obtained by developing the 3-D boundary element method with collocation method. On the triangular patch, the numerical scheme employed the linear basis functions and the analytic solutions of the integrals on the singular points. The capacitive discontinuities of gaps, end-gaps, and open-ends are characterized and the results compared with the conductor backed coplanar waveguides.