• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.95.1-95.1
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• 2010

Transparent conducting ZnO films were deposited to apply DSSC Substrate on glass substrates at $500^{\circ}C$ by ionbeam-assisted deposition. Crystallinity, microstructure, surface roughness, chemical composition, electrical and optical properties of the films were investigated as a function of deposition parameters such as ion energy, and substrate temperature. The microstructure of the polycrystalline ZnO films on the glass substrate were closely related to the oxygen ion energy, arrival ratio of oxygen to Zinc Ion bombarded on the growing surface. The main effect of energetic ion bombardment on the growing surface of the film may be divided into two categories; 1) the enhancement of adatom mobility at low energetic ion bombardment and 2) the surface damage by radiation damage at high energetic ion bombardment. The domain structure was obtained in the films deposited at 300 eV. With increasing the ion energy to 600 eV, the domain structure was changed into the grain structure. In case of the low energy ion bombardment of 300 eV, the microstructure of the film was changed from the grain structure to the domain structure with increasing arrival ratio. At the high energy ion bombardment of 600 eV, however, the only grain structure was observed. The electrical properties of the deposited films were significantly related to the change of microstructure. The films with the domain structure had larger carrier concentration and mobility than those with the grain structure, because the grain boundary scattering was reduced in the large size domains compared with the small size grains. The optical transmittance of ZnO films was dependent on a surface roughness. The ZnO films with small surface roughness, represented high transmittance in the visible range because of a decreased light surface scattering. By varying the ion energy and arrival ratio, the resistivity and optical transmittance of the films were varied from $1.1{\times}10^{-4}$ to $2.3{\times}10^{-2}{\Omega}cm$ and from 80 to 87%, respectively. The ZnO film deposited at 300 eV, and substrate temperature of $500^{\circ}C$ had the resistivity of $1.1{\times}10^{-4}{\Omega}cm$ and optical transmittance of 85% in visible range. As a result of experiments, we provides a suggestition that ZnO thin Films can be effectively used as the DSSC substrate Materials.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1172-1177
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• 2004

The evolution of incipient soot particles has been examined by high resolution electron microscopy (HRTEM) and elemental analyzer in ethylene-air inverse diffusion flames. Laser Induced Incandescence(LII) and laser scattering methods were introduced for examining the change of soot volume fraction and morphological properties in combustion generated soot qualitatively. Soot particles, collected by thermophoretic sampling were analyzed by using HRTEM to examine the nano structure of precursor particles. HRTEM micrographs apparently reveal a transformation of condensed phase of semitransparent tar-like material into precursor particles with relatively distinct boundary and crystalline which looks like regular layer structures. During this evolution histories C/H analysis was also performed to estimate the chemical evolution of precursor particles. The changes of C/H ratio of soot particles with respect to residence time can be divided into two parts: one is a very slowly increasing regime where tar-like materials are transformed into precursor particles (inception process) the other is an increasing region with constant rate where surface growth affects the increase of C/H ratio dominantly (surface growth region). These results provide a clear picture of a transition to mature soot from precursor materials.

• Journal of the Korean Society of Combustion
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• v.9 no.2
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• pp.38-44
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• 2004

The evolution of incipient soot particles has been examined by high resolution electron microscopy (HRTEM) and elemental analyzer in ethylene-air inverse diffusion flames. Laser Induced Incandescence(LII) and laser scattering methods were introduced for examining the soot volume fraction and morphological properties in combustion generated soot qualitatively. Soot particles, collected by thermophoretic sampling, were analyzed by using HRTEM to examine the nano structure of precursor particles. HRTEM micrographs apparently reveal a transformation of condensed phase of semitransparent tar-like material into precursor particles with relatively distinct boundary and crystalline which looks like regular layer structures. During this evolution histories, C/H analysis was also performed to estimate the chemical evolution of precursor particles. The changes of C/H ratio of soot particles with respect to residence time can be divided into two parts: one is a very slowly increasing regime where tar-like materials are transformed into precursor particles (inception process) the other is an increasing region with constant rate where surface growth affects the increase of C/H ratio dominantly (surface growth process). These results provide a clear picture of a transition to mature soot from precursor materials.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.6 no.1
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• pp.10-16
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• 1995

The E-polarized scattering problems by a perfect conductor strip grating are analyzed by the method of moments. For an E-polarization the induced surface current density is expected to blow up at the strip both edges. Then the induced surface current density on the strip is expanded in a series of multiplication of Ultraspherical ploynomials with zeroth order and functions with appropriate edge boundary condition. The numerical results for current density and reflection cofficient are compared with other functions, it is shown that numerical results better improves the convergence of the moment method soulutions with general incident angles than the existing several other functions. The sharp variation points in the magnitude of geometric-optical reflection coefficient can be moved by varying the incident angle, strip width, and strip spacing.

• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.174-186
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• 2009

When we apply a propagation model to the ocean with boundaries, we can calculate reflected wave using reflection coefficient suggested by Rayleigh assuming the boundaries are flat. But boundaries in ocean such as sea surface and sea bottom have an irregular rough surface. To calculate the reflection loss for an irregular boundary, it is needed to compute the coherent reflection coefficient based on an experimental formula or scattering theory. In this article, we derive the coherent reflection coefficients for a fluid-fluid interface using perturbation theory, Kirchhoff approximation and small-slope approximation respectively. Based on each formula, we can calculate coherent reflection coefficients for a rough sea surface or sea bottom, and then compare them to the Rayleigh reflection coefficient to analyze the reflection loss for a random rough surface. In general, the coherent reflection coefficient based on small-slope approximation has a wide valid region. Comparing it with the coherent reflection coefficients derived from the Kirchhoff approximation and perturbation theory, we discuss a valid region of them.

• The Journal of the Acoustical Society of Korea
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• v.32 no.2
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• pp.104-115
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• 2013

In a shallow water waveguide, reverberation signals and their Doppler effects form the primary limitation on sonar system performance. Therefore, in the reverberation-limited environment, it is necessary to estimate the reverberation level to be encountered under the conditions in which the sonar system is operated. In this paper, high-frequency reverberation model capable of simulating the reverberation signals received by a high-speed moving source in a range independent waveguide is suggested. In this model, eigenray information from the source to each boundary is calculated using the ray-based approach and the optimizing method for the launch angles. And the source receiving position changed by the moving source is found by a scattering path-finding algorithm, which considers the speed and direction of source and sound speed to find the path of source movement. The scattering effects from sea surface and bottom boundaries are considered by APL-UW scattering models. The model suggested in this paper is verified by a comparison to the measurements made in August 2010. Lastly, this model reflects well statistical properties of the reverberation signals.

• Journal of Environmental Science International
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• v.12 no.5
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• pp.521-527
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• 2003

To study the intruded phenomena of North Pacific Ocean around Boso peninsular, water property distribution in the adjacent seas to Japan is studied using the hydrographic data obtained by Japan Maritime Agency and Japan Fisheries Agency from 1973 to 1996, The scattering of water type in T-5 diagram is relatively small in the Kuroshio Region. Both the envelopes of saline side and of fresh side of the scattered data points shifts gradually from saline side to fresh side as the observation Line moves from southwest to northeast. In mixed water region, the scattering of water type increases rapidly as the observation line moves north; the envelope of fresh cold side moves towards fresh cold side much faster than that of saline side. This suggests that the water does not advect along the salinity minimum layer, but the salinity minimum layer can be understood as a boundary of two different waters aligned vertically, We defined the typical water masses as the Oyashio Water and the Kuroshio Water. The water mass below the salinity minimum layer may be created by isopycnal mixing of these two water masses with a fixed mixing rate. While the water mass above the salinity minimum cannot be created simply by isopycnal mixing. The salinity minimum layer may be eroded from upper side due to active minxing processes in the surface layer, while the water of the salinity minimum layer moves gradually southward. This appears to give an explanation why the thermosteric anomaly value at salinity minimun decereases towards south.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.321-327
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• 2006

In this paper, when a H-polarized plane wave is incident on the grating consisting of uniform resistive strips, electromagnetic scattering is analyzed using the moment of methods (MoM). The current density of each resistive strip on a grounded dielectric plane is fixed by zero at both edges. To satisfy the condition at both ends of each resistive strip, the induced surface current density is expanded in a series of cosine and sine functions. The scattered electromagnetic fields are expanded in a series of floquet mode functions. The boundary conditions are applied to obtain the unknown current coefficients. According to the variation of the involving parameters such as strip width and spacing and angle of the incident field, numerical simulations are performed by applying the Fourier-Galerkin moment method. The numerical results of the normalized reflected power for resistive strips case for zero and several resistivities are obtained.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.6 s.121
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• pp.656-663
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• 2007

In this paper, when a E-polarized plane wave is incident on the grating consisting of tapered resistive strips, electromagnetic scattering is analyzed using the method of moments(MoM). The induced current density of each resistive strip in a grounded double dielectric layer is expected to blow up at both edges. To satisfy this, the induced surface current density is expanded in a series of Chebyshev polynomials of the second kind. The scattered electromagnetic fields are expanded in a series of Floquet mode functions. The boundary conditions are applied to obtain the unknown current coefficients. According to the variation of the involving parameters such as strip width and spacing and angle of the incident field, numerical simulations are performed by applying the Fourier-Galerkin moment method. The numerical results of the normalized reflected power for resistive strips case for several resistivities are obtained.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.7
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• pp.819-827
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• 2007

A numerical algorithm for estimating precise backscattering coefficients of rice fields is proposed and its accuracy is verified in this paper. After a bunch of rice plants above water surface is modeled with a bunch of randomly oriented lossy dielectric bodies above an impedance surface and the equivalent volume currents of the lossy dielectrics are computed using the moment method. Then, the scattered fields of a rice field with many bunches are computed with a Monte Carlo method, and consequently the backscattering coefficient of the rice field is computed for various incidence angles and polarizations. Finally, the backscattering coefficient of a rice field is measured at 1.85 GHz using an R-band scatterometer system, and these experimental data are used to verify the numerical algorithm proposed in this paper. It is found that the numerical computation results agree well with the measurement data.