• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.4
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• pp.550-563
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• 1999

A wavelet-Galerkin scheme based on the time-dependent Maxwell's equations is presented. Daubechies wavelet with two vanishing wavelet moments is expanded for basis function in spatial domain and Yee's leap-frog approach is applied. The shifted interpolation property of Daubechies wavelet family leads to the simplified formulations for inhomogeneous media without the additional matrices for the integral or material operator. The stability condition is formulated. The dispersion characteristics are analyzed and compared with those of finite difference time domain and multiresolution time domain methods. The analyses show the excellent trade-off between the regularity and the support width of the basis function. Although the basis function has only two vanishing wavelet moments, it is enough to provide negligible dispersive error in the numerical analysis and its compact support enables only several involved terms per nodes. The storage effectiveness, execution time reduction and accuracy of this scheme are demonstrated by calculating the resonant frequencies of the homogeneous and inhomogeneous cavities.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.12
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• pp.3277-3285
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• 1996

In this paper, w designed an opical power distribution device for application to an optical switching and an optical subscriber loop. We fabricated PSG thin film by LPCVD. Based on the measured index of fabricted thin film, rib-type waveguide was transformed to two-dimension by the effective index method and we simulated dispersion property to find asingle-mode condition. We found that the optimum design parameters of rib-type waveguide are:cladding layer of 3.mu.m, core layer of 3.mu.m, buffer layer of 10.mu.m, and core width of 4.mu.m. Each side of the guiding region was etched down to 4.mu.m to shape the core. We used these optimum parameters of the rib-type waveguide with branching angle of 0.5.deg. and simulted the Y-branch waveguide by the BPM simulation. Numerical loss in branching area was claculated to be 0.1581dB and equal to the total loss of the Y-branch. The loss of the fabricated Y-branch waveguide on PSG film ws 1.6dB at .lambda.=1.3.mu.m before annealing but was 1.2dB after annealing at 1000.deg. C for 10 minutes. Consequently, the loss of branching area from 3000.mu.m to 6000.mu.m in the z-direction was 0.8dB, and single-mode propagation was confirmed by measuring the near field pattern. For coupling the fabricated Y-branch waveguide with an optical fiber, we fabricated V-groove which was used as the upholder of optical fiber. An etching angle was 54.deg. and the width and depth of guiding groove was 150.mu.m, 70.mu.m, respectively. The optical fiber is inserted onto V-groove. Both the Y-branch and V-groove were connected through the index matching oil. Coupling loss after connecting Y-branch and the optical fiber on V-groove was 0.34dB and that after injecting index mateching oil was 0.14dB.

• Journal of Environmental Science International
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• v.26 no.5
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• pp.621-638
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• 2017

Meteorological characteristics related to variations in ozone ($O_3$) concentrations in the Korean peninsula before, during, and after Typhoon Talas (1112) were analyzed using both observation data and numerical modeling. This case study takes into account a high $O_3$ episode (e.g., a daily maximum of ${\geq}90ppb$) without rainfall. Before the typhoon period, high $O_3$ concentrations in the study areas (e.g., Daejeon, Daegu, and Busan) resulted from the combined effects of stable atmospheric conditions with high temperature under a migratory anticyclone (including subsiding air), and wind convergence due to a change in direction caused by the typhoon. The $O_3$ concentrations during the typhoon period decreased around the study area due to very weak photochemical activity under increased cloud cover and active vertical dispersion under a low pressure system. However, the maximum $O_3$ concentrations during this period were somewhat high (similar to those in the normal period extraneous to the typhoon), possibly because of the relatively slow photochemical loss of $O_3$ by a $H_2O+O(^1D)$ reaction resulting from the low air temperature and low relative humidity. The lowest $O_3$ concentrations during the typhoon period were relatively high compared to the period before and after the typhoon, mainly due to the transport effect resulting from the strong nocturnal winds caused by the typhoon. In addition, the $O_3$ increase observed at night in Daegu and Busan was primarily caused by local wind conditions (e.g., mountain winds) and atmospheric stagnation in the wind convergence zone around inland mountains and valleys.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.7
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• pp.665-670
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• 2010

The effect of a particle's spin is investigated numerically by taking into account the effect of lift forces originating due to difference between the rotations of a particle and of a fluid, such as the Saffman and Magnus lift forces. These lift forces have been ignored in many previous studies on particle-laden turbulence. The trajectory of the particles can be changed by the lift forces, resulting in a significant modification of the stochastic characteristics of heavy particles. Probability density functions and autocorrelations are evaluated from the velocity of solid particle, acceleration of solid particles, and acceleration of fluid at the position of solid particle. Changes in velocity statistics are negligible but statistics related with acceleration are affected by the rotation of particle. When a laden particle encounters coherent structures during its motion, the particle's rotation might significantly affects the motion due to intermittently large fluid acceleration near the coherent structures.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.11a
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• pp.19-26
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• 2003

The dispersion of recycled particulates in the complex coastal terrain containing Kangnung city, Korea was investigated using a three-dimensional non-hydrostatic numerical model and lagrangian particle model (or random walk model). The results show that particulates at the surface of the city that float to the top of thermal internal boundary layer (TIBL) are then transported along the eastern slope of the mountains with the passage of sea breeze and nearly reach the top of the mountains. Those particulates then disperse eastward at this upper level over the coastal sea and finally spread out over the open sea. Total suspended particulate (TSP) concentration near the surface of Kangnung city is very low. At night, synoptic scale westerly winds intensify due to the combined effect of the synoptic scale wind and land breeze descending the eastern slope of the mountains toward the coast and further seaward. This increase in speed causes development of internal gravity waves and a hydraulic jump up to a height of about 1km above the surface over the city. Particulate matter near the top of the mountains also descends the eastern slope of the mountains during the day, reaching the central city area and merges near the surface inside the nocturnal surface inversion layer (NSIL) with a maximum ground level concentration of TSP occurring at 0300 LST. Some particulates were dispersed following the propagation area of internal gravity waves and others in the NSIL are transported eastward to the coastal sea surface, aided by the land breeze. The following morning, particulates dispersed over the coastal sea from the previous night, tend to return to the coastal city of Kangnung with the sea breeze, developing a recycling process and combine with emitted surface particulates during the morning. These processes result in much higher TSP concentration. In the late morning, those particulates float to the top of the TIBL by the intrusion of the sea breeze and the ground level TSP concentration in the city subsequently decreases.

• Composites Research
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• v.26 no.1
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• pp.72-78
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• 2013

This study explores the resistive heating characteristics of discontinuous carbon fiber (CF)-epoxy composites. Test samples including 1, 3, and 5 wt.% CF were fabricated using sonication and cast molding processes. For heating performance characterization, DC currents were applied to the composite samples, and surface temperatures were evaluated visually and quantitatively using an infrared camera. To estimate the thermal performance of composites and verify the experimental results, finite element analyses were performed. The resistive heating mechanism was investigated in connection with CF loading and applied voltages. Resistive heating efficiency increased proportionately with CF concentration and applied voltage. To obtain homogeneous temperature distribution of the samples, high degree of CF dispersion is required.

• Earthquakes and Structures
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• v.15 no.4
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• pp.369-382
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• 2018

A free vibration analysis and wave propagation of functionally graded porous beams has been presented in this work using a high order hyperbolic shear deformation theory. Unlike other conventional shear deformation theories, a new displacement field that introduces indeterminate integral variables has been used to minimize the number of unknowns. The constituent materials of the beam are assumed gradually variable along the direction of height according to a simple power law distribution in terms of the volume fractions of the constituents. The variation of the pores in the direction of the thickness influences the mechanical properties. It is therefore necessary to predict the effect of porosity on vibratory behavior and wave velocity of FG beams in this study. A new function of the porosity factor has been developed. Hamilton's principle is used for the development of wave propagation equations in the functionally graded beam. The analytical dispersion relationship of the FG beam is obtained by solving an eigenvalue problem. Illustrative numerical examples are given to show the effects of volume fraction distributions, beam height, wave number, and porosity on free vibration and wave propagation in a functionally graded beam.

• Journal of Korean Society for Atmospheric Environment
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• v.10 no.E
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• pp.357-370
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• 1994

This paper introduces an Eulerian long- range transport model coupled with a mesoscale atmospheric model. The model has been applied to the simulation of tracer distribution during two cases of Cross Appalachian Tracer Experiment (CAPIEX). Meteorological fields are Predicted by CSU RAMS with four-dimensional assimilation and tracer transport is computed from an Eulerian dispersion model. The atmospheric model with a four-dimensional assimilation has produced meteorological fields that agree well with observation and has proved its high potential as a generator of meteorological data for a long-range transport model. The Present transport model Produces reasonable simulations of observed tracer transport although it was partially successful in the case with complicated structure in observed concentration. Model with Bott's 2nd-order scheme performs as well as that with Bott's 4th-order scheme and increased explicit horizontal diffusivity. Diagnosis of the model results indicates that the Present long-range transport model has a good potential as a framework for the acid deposition model with detailed cloud and chemical processes.

• Journal of Electrical Engineering and Technology
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• v.9 no.1
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• pp.301-306
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• 2014

We proposed a new PCB-type 'common-mode current($I_c$) and differential-mode current($I_d$) detector' working for fast detection of $I_c$ and $I_d$ from the differential-mode signaling, with miniaturization effect and possibility of cheaper fabrication. In order to realize this device, we suggest a branch-line-coupler balun having a composite right- and left-handed(CRLH) one-layer microstrip phase-shifting line as compact as roughly ${\lambda}_g/14$. The presented balun obviously is different from the conventional bent-&-folded delay lines or slits on the ground for coupling the lines on the top and bottom dielectrics. As we connect the suggested balun output ports of the differential-mode signal lines via the through-port named U and coupled-port named L, $I_c$ and $I_d$ will appear at port ${\Delta}$ and port ${\Sigma}$ of the present device, in order. The validity of the design scheme is verified by the circuit-and numerical electromagnetic analyses, and the dispersion curve proving the metamaterial characteristics of the geometry. Besides, the examples of the $I_c$ and $I_d$ indicator are observed as the even and odd modes in differential-mode signal feeding. Also, the proposed device is shown to be very compact, compared with the conventional structure.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1577-1583
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• 2012

Penetrator with enhanced lateral effect (PELE) is a novel projectile that does not require dynamite and a fuse. It comprises a high-density jacket that is closed at its rear end and filled with a low-density filling material. To study the explosion characteristics of PELE using AUTODYN-3D code, the calculation models of the projectile body and the bullet target were developed and the process of penetrating an aluminum-2024 alloy target using PELE was simulated. The scattering characteristics after PELE penetrated the aluminum-2024 alloy target were studied for different filling materials. The explicit finite element analysis of PELE fragmentation was implemented with the stochastic failure criterion in AUTODYN-3D code. As the filling expanded, the fragments gained velocity and dispersed laterally, increasing the damage area considerably. The number and shape of PELE fragments differed depending on the impact pressure of the filling that fragmented during the penetration and lateral dispersion processes.