• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.4
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• pp.54-61
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• 1997

In this paper, a new holographic display system that can in real-time reconstruct the complex hologram without the bias and the conjugate image, which is obtained form the modified triangular interferometer, is presented. The proposed system is made of adding liquid crystal displays(LCDs), a $\lambda$/2 wave plate, and a polarizing beam splitter to the conventional mach-zehnder interferontric configuration. We demonstrate through theoretical analysis and experiment that real-time image reconstruction from the complex hologram is possible using the proposed system.

• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.4
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• pp.460-466
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• 1988

In this paper, the theory and experiments on the one-way optical image transmission through optical fiber by using degenerate four wave mixing in BSO single crystal are demonstrated. From the theoretical analysis, the diffraction efficiency of phase conjugate wave in BSO single crystal is greatly dependent on applied electric field intensity, diffraction grating period formed in the crystal and incident beam ratio, those are also in good agreement with the experimental results. Based on the experimental results, we have arranged the typical degenerate four wave mixing system in the optimal conditions (applied electric field, E. = 5kV/cm` diffraction grating period, 3\ulcorner` beam ratio of backward pump wave versus signal wave, 2.7) and realized one-way optical image transmission system through optical fiber using BSO single crystal.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.1
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• pp.54-58
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• 2008

Time reversal (TR) of body waves in fluids and isotropic solids has been used in many applications including ultrasonic NDE. However, the study of the TR method for anisotropic materials is not well established. In this paper, the full reconstruction of the input signal is investigated for anisotropic media using an analytical formulation, called a modular Gaussian beam (MGB) model. The time reversal operation of this model in the frequency domain is done by taking the complex conjugate of the Gaussian amplitude and phase received at the TR mirror position. A narrowband reference signal having a particular frequency and number of cycles is then multiplied and the whole signal is inverse Fourier transformed. The original input signal is seen to be fully restored by the TR process of MGB model and this model can be more generalized to simulate the spatial and temporal focusing effects due to TR process in anisotropic materials.

• ETRI Journal
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• v.20 no.2
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• pp.133-148
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• 1998

The objective of this paper is to present an adaptive algorithm for computing the weight vector which provides a beam pattern having its maximum gain along the direction of the mobile target signal source in the presence of interfering signals within a cell. The conjugate gradient method (CGM) is modified in such a way that the suboptimal weight vector is produced with the computational load of O(16N), which has been found to be small enough for the real-time processing of signals in most land mobile communications with the digital signal processor (DSP) off the shelf, where N denotes the number of antenna elements of the array. The adaptive procedure proposed in this paper is applied to code division multiple access (CDMA) mobile communication system to show its excellent performance in terms of signal to interference plus noise ratio (SINR), bit error rate (BER), and capacity, which are enhanced by about 7 dB, ${\frac{1}{100}}$ times, and 7 times, respectively, when the number of antenna elements is 6 and the processing gain is 20 dB.

• Steel and Composite Structures
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• v.26 no.6
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• pp.663-672
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• 2018

This paper contains a consistent couple-stress theory to capture size effects in Euler-Bernoulli nano-beams made of three-directional functionally graded materials (TDFGMs). These models can degenerate into the classical models if the material length scale parameter is taken to be zero. In this theory, the couple-stress tensor is skew-symmetric and energy conjugate to the skew-symmetric part of the rotation gradients as the curvature tensor. The material properties except Poisson's ratio are assumed to be graded in all three axial, thickness and width directions, which it can vary according to an arbitrary function. The governing equations are obtained using the concept of minimum potential energy. Generalized differential quadrature method (GDQM) is used to solve the governing equations for various boundary conditions to obtain the natural frequencies of TDFG nano-beam. At the end, some numerical results are performed to investigate some effective parameter on buckling load. In this theory the couple-stress tensor is skew-symmetric and energy conjugate to the skew-symmetric part of the rotation gradients as the curvature tensor.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.4
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• pp.639-647
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• 2002

A simplified analytical procedure is presented to estimate the reduction of elastic lateral stiffness of steel moment frames arising from the radius-cut dogbone weakening. With the original radius-cut dogbone shape, it is almost impossible or too complicated to integrate analytically the mathematical expressions encountered when applying the conjugate beam method to compute the beam deflection component. In this study, the problem is circumvented by replacing the original radius-cut dogbone with an equivalent dogbone of constant width. The equivalence between the two is established by imposing an equal dogbone elongation criterion. This approach is justified by using a calibrated finite clement analysis. Then, the elastic lateral deflection components from the column, panel zone, and beam are derived for a typical beam-column subassembly. The derived results can be used to evaluate the reduction of the frame lateral stiffness. Case studies conducted within some practical ranges of frame configurations show that the reduction in frame lateral stiffness due to the presence of dogbone cut is on the order of 1 to 2 percent and is reasonably negligible in practical sense.

• Computers and Concrete
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• v.18 no.5
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• pp.1019-1039
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• 2016

In this paper, a parallel algorithm of nonlinear dynamic analysis of three-dimensional (3D) reinforced concrete (RC) frame structures based on the platform of graphics processing unit (GPU) is proposed. Time integration is performed using Newmark method for nonlinear implicit dynamic analysis and parallelization strategies are presented. Correspondingly, a parallel Preconditioned Conjugate Gradients (PCG) solver on GPU is introduced for repeating solution of the equilibrium equations for each time step. The RC frames were simulated using fiber beam model to capture nonlinear behaviors of concrete and reinforcing bars. The parallel finite element program is developed utilizing Compute Unified Device Architecture (CUDA). The accuracy of the GPU-based parallel program including single precision and double precision was verified in comparison with ABAQUS. The numerical results demonstrated that the proposed algorithm can take full advantage of the parallel architecture of the GPU, and achieve the goal of speeding up the computation compared with CPU.

• Steel and Composite Structures
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• v.20 no.5
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• pp.1119-1131
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• 2016

As a first attempt, an inverse hybrid numerical method for small scale parameter estimation of functionally graded (FG) nanobeams using measured frequencies is presented. The governing equations are obtained with the Eringen's nonlocal elasticity assumptions and the first-order shear deformation theory (FSDT). The equations are discretized by using the differential quadrature method (DQM). The discretized equations are transferred from temporal domain to frequency domain and frequencies of the nanobeam are obtained. By applying random error to these frequencies, measured frequencies are generated. The measured frequencies are considered as input data and inversely, the small scale parameter of the beam is obtained by minimizing a defined functional. The functional is defined as root mean square error between the measured frequencies and calculated frequencies by the DQM. Then, the conjugate gradient (CG) optimization method is employed to minimize the functional and the small scale parameter is obtained. Efficiency, convergence and accuracy of the presented hybrid method for small scale parameter estimation of the beams for different applied random error, boundary conditions, length-to-thickness ratio and volume fraction coefficients are demonstrated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.3
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• pp.187-194
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• 2002

A seven-port impedance and admittance matrices of multilayered piezoelectric beam are derived for the analysis of piezoelectric AFM ( atomic force microscope) cantilever that is partially covered by the piezoelectric layer. The variational principle is used for deriving the extensional and flexural motional equations and the conjugate parameters. Overall impedance matrix of AFM cantilever can be obtained by combining two impedance matrices of the covered and the non-covered. she resonance and antiresonance frequencies and the effective electromechanical coupling factors are calculated using the derived matrices. The results and the three dimensional finite element solutions are compared with the experimental results in other publication.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.4
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• pp.523-533
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• 2000

In this paper, we present the hardware implementation of a smart antenna test-bed for a real -time performance analysis of the beam-forming algorithm operating in a wide-band CDMA environments of the WLL(Wireless Local Loop) standard. The test-bed introduced in this paper includes an external PC and signal generating module as well as the beam-forming module in order to perform, analyze, and evaluate the performance of the proposed smart antenna system. In the beam-forming module, the optimal weight vector is provided by the modified CGM algorithm. The computed weight vector is transferred back to the external PC for the performance analysis based on the off-line processing. From our analysis obtained in the hardware of the test-bed, it is concluded that the proposed smart antenna system for the WLL system is appropriate for enhancing the communication quality and capacity tremendously at the cell-site of the CDMA environment.