• Journal of the Korean earth science society
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• v.28 no.2
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• pp.179-186
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• 2007

The response spectrum is one of the important basic materials for the aseismic design. Numerous strong ground motions based on the seismic source characteristics for the earthquakes occurring in the Korean Peninsula were simulated to obtain the response spectra by using the computer program, SMSIM, developed by Boore (2005). Through the extensive review of other study outcomes, the input data for the simulation such as seismic source and attenuation characteristics were selected. The spectra obtained from the simulated ground motions were normalized to 1.0 g of zero period acceleration and compared with the standard response spectrum proposed by the U.S. Atomic Energy Commission (AEC, 1973). In this study, we found that the spectral values for the response spectra appeared to be larger than those of the standard spectrum in the frequency band above roughly 10 Hz. The variation of resulting response spectra was evaluated with the variable stress drops. It was shown that the spectral amplitude of the spectrum for the larger stress drop denotes higher value in the low frequency range.

• Explosives and Blasting
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• v.38 no.1
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• pp.14-22
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• 2020

Bit damage is one of the primary causes of decreasing drilling efficacy. Nevertheless the management of bit ware and failure are often left for field engineers' experience. Thus it is imperative to establish a proper system to predict and manage the bit damage during the rock drilling process. In this study, the drilling sound signal has been recorded and analyzed using wavelet transform analysis to identify the exact moment of bit failure. Through the analysis wavelet time-frequency spectrums have been constructed and an abnormal point has been identified with 0.9 of wavelet transform value at the 652.8s on a frequency band around 500Hz. Furthermore it is also observed that the penetration rate of the damaged bit has been decreased to 23mm/s which is 9mm/sec lower than the average of undamaged bit. The study verifies that wavelet transform analysis can be used to build a system to diagnose the bit damage while drilling.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.1072-1086
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• 1998

Transform, subband, and wavelet transform decompositions are powerful linear transformation tools in image coding because of their decorrelating effects on image pixels, the concentration of energy in a few coefficients, their multirat/multiresolution framework, and their frequency splitting, which allows for efficient coding matched to the statistics of each frequency band and to the characteristics of the human visulal system. Thus, a growingbody of research has bee performed to extend these tools in various kinds of modified formations. Hence, in this paper, an overall survey to achieve a general view on these transformation tools have been attempted. Starting from basic tools such as orthogonal transforms, lapped transforms, QMF(quadrature mirror filter) subband filter banks, and wavelet transforms, their hierarchical extensions, vector extensions, and linear time-varying extensions are investugated in detail.

• Journal of the Korean Electrochemical Society
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• v.2 no.1
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• pp.23-26
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• 1999

The Langmuir adsorption isotherm at the $(Pt)/0.1M\;H_2SO_4$ electrolyte interface has been qualitatively analyzed using the ac impedance measurement and phase-shift method. The phase shift $(\phi)$ depends on both the cathode potential (E<0) and frequency (f) and is inversely proportional to the factional surface coverage $(\theta)$. At an intermediate frequency band (ca. $1\~100$ Hz), the phase-shift profile $(\phi\;vs.\;E)$ can be related to the fractional surface coverage $(\theta\;vs.\;E)$. The phase-shift profile $(\phi\;vs.\;E)$ can be used as an experimental method to estimate and analyze the Langmuir adsorption isotherm $(\theta\;vs.\;E)$. The equilibrium constant (K) and the standard free energy $({\Delta}G_{ads})$ of the adsorbed hydrogen atom $(H_{ads})\;and\;3\times10^{-4}$ and 20.1 kJ/mol, respectively.

• Korean Journal of Materials Research
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• v.8 no.6
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• pp.526-531
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• 1998

A hydride vapor phase epitaxy (HVPE) method was performed to grow the $10~240\mu{m}$ thick GaN films on (111) spinel $MgAl_2O_4$ substrate. The GaN films on $MgAl_2O_4$ substrate revealed a photoluminescence (PL) characteristics of the impurity doped GaN by the out-diffusion and auto-doping of Mg from $MgAl_2O_4$ substrate during GaN growth. The PL spectrum measured at 10K consists of free and bound excitons related recombination transitions and impurity-related donor-acceptor pair recombination and its phonon replicas. However, the deep-level related yellow band emission was not observed. The peak energy of neutral donor bound excitonic emission and the frequency of Raman $E_2$ mode were exponentially decreased with increasing the GaN thicknesses. and the frequency of E, Raman mode was shifted with the relation of $\Delta$$\omega$=3.93$\sigma$($cm^{-1}$/GPa), where l1 (GPa) is the residual strain in the GaN epilayers.

• Economic and Environmental Geology
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• v.21 no.3
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• pp.277-285
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• 1988

The ELF-MT survey has been conducted at 9 points along the national road between the Sindangri and Dojonri area to study on the boundary between the Okchon and Choson systems, and subsurface geological structure of these two systems. Natural electromagnetic fields of 7.8, 14, and 20 Hz in the Schumann resonant frequency band were used for ELF-MT measurement. Apparent resistivity values were calculated from the measured magnetic and electric fields at each frequency, and resistivity sections were obtained by means of a trial and error method for one-dimensional analysis and finite element method for two-dimensioal analysis. The results of this study show that the resistivities of the Okchon and Choson systems are 700-3500 ohm-m and 40-5000 ohm-m, respectively. The boundary between these two systems is a fault with the width of 1 km fault zone and resistivity value of 200 ohm-m, and is located around Koburangjae. Another fault is appeared in Sindangri, and its resistivity value is 130 ohm-m. Intrusion of biotite granite is distributed in Jungchijae, and its resistivity value is 750 ohm-m. The area between Susanri and Koburangjae shows the highest resistivity value of 3500 ohm-m because metabasite and amphibolite are distributed in that area. Extremely low resistivity value of 40 ohm-m around Yongamsan is due to the Yongam formation, which is composed of graphitic black slate and overlying Choson Great Limestone group.

• Journal of Broadcast Engineering
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• v.28 no.1
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• pp.100-108
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• 2023

In hybrid block-based video coding, transform coding converts spatial domain residual signals into frequency domain data and concentrates energy in a low frequency band to achieve a high compression efficiency in entropy coding. The state-of-the-art video coding standard, VVC(Versatile Video Coding), uses DCT-2(Discrete Cosine Transform type 2), DST-7(Discrete Sine Transform type 7), and DCT-8(Discrete Cosine Transform type 8) for primary transform. In this paper, considering that DCT-2, DST-7, and DCT-8 are all linear transformations, we propose an inverse transform that reduces the number of multiplications in the inverse transform by using the linearity of the linear transform. The proposed inverse transform method reduced encoding time and decoding time by an average 26%, 15% in AI and 4%, 10% in RA without the increase of bitrate compared to VTM-8.2.

• Journal of the Korea Society of Computer and Information
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• v.14 no.7
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• pp.57-64
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• 2009

Based on this article, I have analyzed the OFDM system which applies three types of equalizer forms in the two-path channel of the microwave baseband. The Two-path channel of microwave baseband had been simulated through the Rummler channel. In the Two-path channel, the OFDM system which has three forms of equalizer has been analyzed and the result is, equalizer 1-tab has great improvement in efficiency compared with Pre-FFT 11-tab which has noise power ratio less than 18dB. On the contrary, if the symbol energy to the noise ratio is more than 18dB, the equalizer which applies Pre-FFT 11-tab has greater efficiency compared to the equalizer which applies 1-tab frequency. Last but not least, the OFDM system which applies Dual equalizer has better efficiency compared to the system which has 1-tab frequency and equalizer which applies Pre-FFT 11-tab.

• Korean Journal of Materials Research
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• v.33 no.10
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• pp.400-405
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• 2023

Tb³⁺-doped CaNb₂O₆ (CaNb₂O₆:Tb³⁺) thin films were deposited on quartz substrates at a growth temperature of 300 ℃ using radio-frequency magnetron sputtering. The deposited thin films were annealed at several annealing temperatures for 20 min and characterized for their structural, morphological, and luminescent properties. The experimental results showed that the annealing temperature had a significant effect on the properties of the CaNb₂O₆:Tb³⁺ thin films. The crystalline structure of the as-grown CaNb₂O₆:Tb³⁺ thin films transformed from amorphous to crystalline after annealing at temperatures greater than or equal to 700 ℃. The emission spectra of the thin films under excitation at 251 nm exhibited a dominant emission band at 546 nm arising from the ⁵D₄→⁷F₅ magnetic dipole transition of Tb³⁺ and three weak emission bands at 489, 586, and 620 nm, respectively. The intensity of the ⁵D₄→⁷F₅ (546 nm) magnetic dipole transition was greater than that of the ⁵D₄→⁷F₆ (489 nm) electrical dipole transition, indicating that the Tb³⁺ ions in the host crystal were located at sites with inversion symmetry. The average transmittance at wavelengths of 370~1,100 nm decreased from 86.8 % at 700 ℃ to 80.5 % at an annealing temperature of 1,000 ℃, and a red shift was observed in the bandgap energy with increasing annealing temperature. These results suggest that the annealing temperature plays a crucial role in developing green light-emitting CaNb₂O₆:Tb³⁺ thin films for application in electroluminescent displays.

• Korean Journal of Optics and Photonics
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• v.9 no.4
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• pp.221-226
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• 1998

Ternary heavy metal oxide glasses in the $PbO-Bi_2O_3-Ga_2O_3$ system doped with $Er_2O_3$ were prepared and their spectroscopic properties, such as radiative transition probability, calculated and measured radiative lifetimes and cross-sections of 1.5 $\mu\textrm{m}$ and 2.7 $\mu\textrm{m}$ emissions were analyzed. Enhanced quantum efficiencies of some electronic transitions were evident mainly because of the low vibrational phonon energy ($~500cm^{-1}$) inherent in the host glasses. This seems to be the main reason for obtaining the 2.7 $\mu\textrm{m}$ luminescence which is normally quenched in the conventional oxide glasses. In addition, green and red fluorescence emissions were observed through the frequency upconversion processes of the 798 nm excitation. Non-radiative transition due to the multiphonon relaxation is a dominant lifetime-shortening mechanism in the 4f-4f transitions in $Er^{3+}$ ion except for the $^4S_{3/2}{\rightarrow}^4I_{15/2}$ transition where a non-radiative transfer to band-gap excitation of the host glasses is dominant. Melting of glasses under an inert gas atmosphere and (or) addition of the typical glass-network former into glasses is necessary in order to enhance the quantum efficiency of the transition.