• The Journal of the Acoustical Society of Korea
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• v.29 no.3E
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• pp.131-139
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• 2010

This paper proposes a novel spectral hole substitution technique for low bit-rate audio coding. The spectral holes frequently occurring in relatively weak energy bands due to zero bit quantization result in severe quality degradation, especially for harmonic signals such as speech vowels. The enhanced aacPlus (EAAC) audio codec artificially adjusts the minimum signal-to-mask ratio (SMR) to reduce the number of spectral holes, but it still produces noisy sound. The proposed method selectively predicts the spectral shapes of hole bands using either intra-band correlation, i.e. harmonically related coefficients nearby or inter-band correlation, i.e. previous frames. For the bands that have low prediction gain, only the energy term is quantized and spectral shapes are replaced by pseudo random values in the decoding stage. To minimize perceptual distortion caused by spectral mismatching, the criterion of the just noticeable level difference (JNLD) and spectral similarity between original and predicted shapes are adopted for quantizing the energy term. Simulation results show that the proposed method implemented into the EAAC baseline coder significantly improves speech quality at low bit-rates while keeping equivalent quality for mixed and music contents.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.9
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• pp.72-79
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• 1997

The dominant physical process repsonsible for the nonlinear gain is from spectral-hole burning with the time constant fo about 50fs and the contribution to the nonlinea rgain form hot carriers effect is determined to be about 15% of the contribution due to spectral-hole burning. To prove the above results we fit the data of hall and found that hot carriers have a profound effect on their experimental data despite the fact that the magnitude of hot carriers effect is only 15% of spectral-hole burning. We suggest that the experimenta with a pump pulse width of 180 fs is very sensitive in detecting the effect of hot carriers, but is not sensitive in detecting much faster process associated with spectral-hole burning.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.223-225
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• 1996

We review current theoretical understanding of the spectral properties (low and high states, transition of states, quasi-periodic oscillations etc.) of the low mass as well as supermassive black hole candidates.

• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1311-1317
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• 2021

In this study, an airborne alpha detection system, which consists of a passivated implanted planar silicon (PIPS) detector and an air filter, was developed. A collimator applied to the alpha detection system showed an enhancement in resolution and a degradation in detection efficiency. The resolution and detection efficiency were compared and analyzed to evaluate the performance of the collimator. Thus, the resolution was found to be more important than the efficiency as a determining factor of the detection system performance, from the viewpoint of radionuclide identification. The performance was evaluated on three properties of the collimator: hole shape, hole length, and the ratio between the hole and frame pitches. From the hole shape performance evaluation, a hexagonal collimator showed the highest resolution. Further, the collimator with a hole pitch of 14 mm was found to have the highest resolution while that with a frame pitch of 4-6 mm (i.e., 1.2-1.4 times longer than the hole pitch) showed the highest resolution.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.54-58
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• 2001

The measurement method of the spectral emissivity by using hemispherical mirror which has an inclined observation hole is studied. This method is useful in measuring the spectral emissivity of the solid material both conductor and non-conductor. In this study, the effective reflectivity of the hemispherical mirror is also measured for calculating the spectral emissivity of materials. The effective reflectivity measured is 0.9.

• Journal of the Optical Society of Korea
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• v.9 no.4
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• pp.140-144
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• 2005

In this paper we have investigated the guiding properties of photonic crystal fibers (PCFs) with a square-lattice of air-holes in the cladding. We have shown numerical results of PCFs with various air hole sizes and hole-to-hole spacings over a wide wavelength range. The group velocity dispersion, effective area and effective refractive index of PCF have been calculated numerically. The waveguide dispersion has greatly affected the group velocity dispersion when hole-to-hole spacing is about $1{\mu}m$. The effective area is quite flat over the wide spectral range whether the hole-to-hole spacing is large or ratio of diameter to pitch is large. From the field distribution, we found that the field is tightly confined within the core region of PCF when the pitch is $3{\mu}m$ and the air-filling fraction is 0.9.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.789-795
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• 2003

It is studied that the measuring method of the spectral emissivity by using hemispherical mirror with an inclined observation hole. The in-service calibration method of mirror reflectivity is also dealed with. It is possible to apply this method on measuring emissivity of conductor or non-conductor.

• Journal of the Optical Society of Korea
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• v.12 no.3
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• pp.196-199
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• 2008

We have investigated spectral properties of the periodic arrays of aluminum rods and holes on papers using the terahertz time-domain spectroscopy. The size of a rod(hole) is $600{\mu}m{\times}100{\mu}m$ and the spacing is $300{\mu}m$. The samples were fabricated by a femtosecond laser micromachining system. The periodic arrays of aluminum rods exhibit high reflection around 0.25 THz when the polarization of the THz pulse is parallel to the long axis of the rod, whereas the periodic arrays of holes exhibit high transmission around 0.25 THz when the polarization of the THz pulse is perpendicular to the long axis of the hole.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.294-300
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• 1999

The density matrix is solved more rigorously, compared with the third-order pertubation method used in the conventional theory, for a semiconductor laser amplifier. Then the coupled wave equations are derived to explain the wavelength conversion due to the spectral hole burning in the semiconductor optical amplifier. It is shown that our results can explain the effect of saturation of the population density on the electric polarization, which affects the four-wave mixing and wavelength conversion, better than the conventional theroy where the third-order pertubation is used.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.04a
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• pp.19.1-19
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• 2003