• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.725-728
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• 2005

The scattering problem of the randomly rough surface is examined by the method of moments(MoM), small perturbation method (SPM), integral equation method (IEM) and the semi-empirical polarimetic model. To apply the numerical technique of the MoM to microwave scattering from a rough surface, at first, many independent randomly rough surfaces with a rms height and a correlation length are generated with Gaussian random deviate. Then, an efficient Monte Carlo simulation technique is applied to estimate the scattering coefficients of the surfaces.

• Korean Journal of Mathematics
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• v.6 no.2
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• pp.195-203
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• 1998

In [3], we showed that overintegration may be needed to obtain the optimal $H^1$ error rate for the $p$ version. In this paper, we examine the convergence of the $p$ version in practice, and comment on the implementation of the $p$ version in commercial codes. Also, we give an example of a problem with extremely rough coefficients, for which overintegration is necessary to obtain the optimal $H^1$ convergence rate.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.28.5-28
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• 2001

This paper investigates a classification method of the electrocardiogram (ECG) into different disease categories. The features for the classification of the ECG are the coefficients of the discrete wavelet transform (DWT) of ECG signals. The coefficients are calculated with Haar wavelet, and after DWT we can get 64 coefficients. Each coefficient has morphological information and they may be good features when conventional time-domain features are not available. Since all of them are not meaningful, it is needed to reduce the size of meaningful coefficients set. The distributions of each coefficient can be the rules to classify ECG signal. The optimally reduced feature set is obtained by fuzzy c-means algorithm and rough set theory. First, the each coefficient is clustered by fuzzy c-means algorithm and the clustered ...

• Korean Journal of Remote Sensing
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• v.16 no.1
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• pp.65-72
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• 2000

Scattering coefficients of randomly rough lossy dielectric surfaces were computed by using the FDTD(Finite-Difference Time-Domain) method and the Monte Carlo method in this paper. The FDTD method was applied to compute electromagnetic wave scattering characteristics at any incident angles, any linear polarizations by dividing the computation region into the total-field region and the scattered-field region. The radar cross sections(RCS) of conducting cylinders have been computed and compared with theoretical results, measurement data and the results from the method of moment(MoM) to verify the FDTD algorithm. Then, to apply the algorithm to compute scattering coefficients of distributed targets, a two-dimensionally rough surface was generated numerically for given roughness characteristics. The far-zone scattered fields of 50 statistically independent dielectric rough surfaces were computed and the scattering coefficient of the surface was calculated from the scattered fields by using the Monte Carlo method. It was found that these scattering coefficients agree well with the SPM(Small Pertubation Method) model in its validity region.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.1
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• pp.45-52
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• 1995

A new Kirchhoff approximation(KA) method was proposed for microwave scttering from randomly rough surfaces. Using the spectral representation of delta function and its sifting theorem, a new KA was formulated directly without any further approximation, and this formulated was used to compute exact backscttering coefficients. The validity of the KA was verified by a numerical method, and this new KA technique was used to evaluate the existing approximated KkA methods; i.t., the zeroth-order and the first-order approximated physical optics(PO) models. It was shown that the first-order approximated PO model has small error than the zeroth-order approximated PO model at low incidence angles and the opposite happens at higher incidence angles. This new KA model can be used to compute exact scattering coefficients in the validity regions of KA and to evaluate other theoretical and numerical models for scattering from randomly rough surfaces.

• Journal of electromagnetic engineering and science
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• v.18 no.2
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• pp.136-140
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• 2018

We propose an improved semi-empirical scattering model for X-band radar backscattering from rough sea surfaces. This new model has a wider validity range of wind speeds than does the existing semi-empirical sea spectrum (SESS) model. First, we retrieved the small-roughness parameters from the sea surfaces, which were numerically generated using the Pierson-Moskowitz spectrum and measurement datasets for various wind speeds. Then, we computed the backscattering coefficients of the small-roughness surfaces for various wind speeds using the integral equation method model. Finally, the large-roughness characteristics were taken into account by integrating the small-roughness backscattering coefficients multiplying them with the surface slope probability density function for all possible surface slopes. The new model includes a wind speed range below 3.46 m/s, which was not covered by the existing SESS model. The accuracy of the new model was verified with two measurement datasets for various wind speeds from 0.5 m/s to 14 m/s.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.10a
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• pp.191-192
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• 2005

• 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 Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.4 s.107
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• pp.393-399
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• 2006

In this paper we applied a ray tracing method to estimate the scattering characteristics from large scale random rough surfaces. For the electromagnetic field evaluation, we have used the diffracted coefficient of the knife edge diffraction for the diffracted rays and Fresnel's reflection coefficients in connection with reflected rays. In addition, we examine to search for the traced rays using the imaging method which can be obtained all rays to arrived at receivers accurately and the diffracted field from rough surfaces is considered. Numerical examples have been carried out for the scattering characteristics of an ocean wave-like rough surface and delay spread characteristics of a building-like surface. In the present work we have demonstrated that the ray tracing method is effective to numerical analysis of a rough surface scattering.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.438-444
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• 1993

The circuit board of an electronic equipment were simulated with a vertical channel which had thermal blocks protruded from one of the channel walls. A rought front plate was made of a circuit board attached with short wires to simulate the back side of a printed circuit board. Natural convection experiments were carried out to study the effects of channel space and rough front plate and to find the suitable characteristic value after the fourth row. The effect of a rough front plate was negligble. There were negligible effects of the channel space on the first and second heaters. Heat transfer coefficients after the third row decreased as the channel space decreased. Heat transfer coefficients were almost constant for larger than 20 mm channel space. A characteristic length was suggested to non-dimensionalize Nu and Ra numbers in a vertical channel with protruded heaters. A correlation was obtained using the new characteristic lengths.