• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.12
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• pp.566-574
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• 2002

In this paper, the scattered field from a perfectly conducting fractal surface by the Monte-Carlo moment method was computed. An one-dimensional fractal surface was generated by using the fractional Brownian motion model. Back scattering coefficients are calculated with different values of the spectral parameter(S$\_$0/), and fractal dimension(D) which determine characteristics of the fractal surface. The number of surface realization for the computed field, the point number, and the width of surface realization are set to be 80, 2048, and 64L, respectively. In order to verify the computed results these results are compared with those of small perturbation methods, which show good agreement between them.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.581-586
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• 1998

We investigated the effect of mechanical back side damage in Czochralski grown silicon wafer. The intensity of mechanical damage was evaluated by minority carrier recombination lifetime by laser excitation/microwave reflection photoconductivity decay method, degree of X-ray diffuse scattering, X-ray section topography, and wet oxidation/preferential etching methods. The data indicate that the higher the mechanical damage intensity, the lower the minority carrier lifetime, and the magnitude of diffuse scattering and X-ray excess intensity increased proportionally, and it was at Grade 1:Grade 2:Grade 3=1:7:18.4 that the normalized relative quantization ratio of excess intensity in damaged wafer was calculated, which are normalized to the excess intensity from sample Grade 1.

• Economic and Environmental Geology
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• v.32 no.4
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• pp.379-384
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• 1999

In order to know the characteristics of attenuation of coda wave in the Kyungsang Sedimetary Basin, quality faclity factor for coda wave (coda Q) is estimated from the earthquake data recorded in the KIGAM local seismic network. Thesingle scattering model for coda wave generation is adopted is adopted in estimating coda Q. In the present study, coda Q(Qc)is estimated in the range of $\alpha$=1.5~3.0, where $\alpha$ denotes the normalized time to S-wave travel time and expressed in terms of frequency (f). The deduced function in the range of 1 to 25 Hz is Qc=36.8283$f^{1.15095}$ which represents the strong dependence of coda Q on frequency. It is found that the difference of Qc between U-D, N-S, and E-W components is negligible. This fact suports the back scattering therory that coda wave originates from scattered waves by randomly distributed heterogenities in the crust On the other hand, it is observed that the coda Q increases with increasing epicentral distence. This observation suggests that QC increases with depth.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.35-40
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• 1999

In order to know the characteristics of attenuation of coda wave in the Kyungsang Sedimentary Basin quality factor for coda wave or coda Q is estimated from the earthquake data recorded in the KIGAM microearthquake network. The single scattering model for coda wave generation is adopted in estimating coda Q. Coda Q appears to be largely dependent on the normalized time(a) which is the ratio of elapsed time to S-wave travel time. In the present study coda Q(Qc) is estimated in the range of a=1.5-3.Q and expressed in terms of frequency(f). The deduced function in the range of 1 to 25 Hz is Qc=36.8283 f1.15095 to represent the strong dependence of coda Q on frequency. It is found that the difference of Qc between U-D N-S and E-W components is negligible, This face supports the back-scattering theory that coda were originates from scattered waves by randomly distributed heterogeneities in the crust. On the other hand it is observed that the coda Q increases with depth.

• Proceedings of the National Institute of Ecology of the Republic of Korea
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• v.2 no.1
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• pp.21-25
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• 2021

We measured the sizes of microstructures and the reflectance of blue feathers in the Common Kingfisher (Alcedo atthis). The colors were mainly produced in the barbs, which were composed of keratin sponge layers with air spaces and melanin rods. The reflectance spectra of back and tail feathers of the Common Kingfisher showed a peak with a broad plateau in the visible wavelength, whereas those of the wing feathers showed peaks in ultraviolet and visible and short-wavelengths. Moreover, the reflectance of back and tail feathers was higher than that of wing feathers. The blue color of the feathers comes from the keratin sponge layer due to coherent scattering. The back and tail feathers are composed of the keratin sponge layer only, and the wing feathers are composed of the keratin sponge layer and the keratin honeycomb structure. Due to the difference in these structures, it supposed that the reflectance is different. Determining why the reflectance spectra of the back and tail feathers were flattened will require further study.

• Journal of Sensor Science and Technology
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• v.7 no.2
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• pp.131-139
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• 1998

$CdS_{0.67}Se_{0.33}$ single crystal was grown by vertical sublimation method of closed tube physical vapour deposition. The (0001) growth plane of oriented single crystals was confirmed from the back-ref1ection Laue patterns. From the Hall effects by van der Pauw method, the as-grown $CdS_{0.67}Se_{0.33}$ single crystals were found to be n-type semiconductors. The mobility appeared to be decreased by lattice scattering at temperature range from 150K to 293K and by impurity scattering at temperatures ranging from 30K to 150K In order to explore its applicability in photoconductive cells, we measured the ratio of photo-current to dark-current (pc/dc), maximum allowable power dissipation (MAPD), spectral response and response time respectively. The results indicated that for the samples annealed in Cu vapour the photoconductive characteristics are best. We obtained sensitivity of 0.99, the value of pc/de of $1.84{\times}10^{7}$, the MAPD of 323mW and the rise and decay time of 9.3 ms and 9.7 ms, respectively.

• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.1750-1753
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• 1997

This paper describes how the directivity pattern of the back-scattered sound pressure is distributed when a plane acoustic wave is incident on a righid spherical shell underwater. A coupled Finite Element-Boundary Element mehtod is developed as numerical technique. The result of the coupled FE-BE method is agreed with theoretical solution for algorithmic confirmation.

• Proceedings of the Korean Society of Crop Science Conference
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• 1995.05a
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• pp.44-45
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• 1995

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.1
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• pp.27-33
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• 1997

A neural network approach has been developed to determine the depth of a surface breaking crack in a steel plate from ultrasonic backscattering data. The network is trained by the use of feedforward three-layered network together with a back-scattering algorithm for error correction. The signal used for crack insonification is a mode converted 70$^{\circ}$transverse wave. A numerical analysis of back scattered field is carried out based on elastic wave theory, by the use of the boundary element method. The numerical data are calibrated by comparison with experimental data. The numerical analysis provides synthetic data for the training of the network. The training data have been calculated for cracks with specified increments of the crack depth. The performance of the network has been tested on other synthetic data and experimental data which are different from the training data.

• Journal of the Korean earth science society
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• v.23 no.8
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• pp.707-721
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• 2002

Seafloor acoustic image data using the side scan sonar system were gathered on the Sindu-ri offshore near the Taean peninsula, middle western Korea. The relationship between the back-scattering acoustic intensity and the sea-bottom sediment properties was studied. And these two data sets were compared and interpreted with the water depth, respectively. Most of sediment properties were correlated well to the acoustic intensity, however the distribution patterns of the sea-bottom sediment and the seafloor acoustic image were not similar to each other except the rocky bottom area. The water depth was not only influential on the distribution pattern of seafloor acoustic image but also showed a linear relation with the sediment properties distribution.