• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.717-722
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• 2016

In this paper, in order to support the peak current limiting function depending on the intensity of the fault current at the early stage of failure, a two magnetically coupled type superconducting fault current limiter (SFCL) is proposed, which includes high-Tc superconducting (HTSC) element 1, where the existing primary and secondary coils are connected to one iron core in parallel, and HTSC element 2, which is connected to the tertiary winding using an additional iron core. The results of the experiments in this study confirmed that the two magnetic coupling type SFCL having coil 1 and coil 2 connected in parallel using dual iron cores is capable of having only HTSC element 1 support the burden of the peak current when a failure occurs. The reason for this is that although HTSC element 1 was quenched and malfunctioned because the instantaneous factor of the initial fault current was large, the current flowing to coil 3 did not exceed the critical current, which would otherwise cause HTSC element 2 to be quenched and not function. In order to limit the peak current upon fault through the sequential HTSC elements, the design should allow it to have the same value as the low value of coil 1 while having coil 3 possess a higher self-inductance value than coil 2. In addition, a short-circuit simulation experiment was conducted to examine and validate the current limiting and recovery characteristics of the SFCL when the winding ratio between coil 1 and coil 2 was 0.25. Through the analysis of the short-circuit tests, the current limiting and recovery characteristics in the case of the additive polarity winding was confirmed to be superior to that of the subtractive polarity winding.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.1
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• pp.44-51
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• 2000

We have analyzed optical matched filters considering the third order signals in the optical code division multiple access (CDMA) system based on optical series coupler access encoder (SCAE) and series coupler access decoder (SCAD). In previous studies, the performance evaluation of the optical CDMA system using SCAE and SCAD was not sufficiently accurate because they analyzed system performance only considering the first order signals. Since optical SCAE and SCAD intrinsically have high order signals of various patterns as the number of coupler increases, they change auto- and cross-correlation intensities. Thus, it is necessary to investigate properties of the third order signals so that we may analyze the exact performance of system. In this paper, we mathematically interpret the optical signals up to the third order, and analyzed the effects of th third order signals on auto- and cross-correlation intensities. In result, as ${\alpha}$(coupling coefficient) value increases, the intensity of the third order signals increases. It is found that the peak to side-lobe ratio considering the third order signals is degraded by 3.75 dB at N(coupler number)=5 and ${\alpha}$=0.5. Also if threshold value in receiver is set by main-lobe peak of the first order signals, it is found that the number of users in an optical CDMA system is limited because the intensity peak of side-lobes is raised by the third order signals.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.8
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• pp.1165-1171
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• 2010

The OFDM system has better characteristics in transmission rate, power efficiency, bandwidth efficiency, impulse-noise immunity, and narrow band interference immunity etc. in comparison with other conventional systems. However, high PAPR of an OFDM signals causes some serious non-linear processing of RF amplifier. And performance of the communication system gets worse. Therefore, various methods reducing PAPR of an OFDM skills such as the clipping method, block coding method, and phase rotation method etc. have been researched. In this paper, we propose a high-speed adaptive PTS method which eliminates high PAPR. And we compare the proposed method with other conventional methods. The proposed method has decreased quantity of calculation compare with an adaptive PTS method. Of course, The more its calculation amount is decreased, the more its BER characteristic is not better than an adaptive PTS method. However, keeping up satisfactory BER performance, we highly improved calculation amount of a PTS method.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.808-815
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• 1995

The magnetic states of nonstoichiometric substituted ferrite Fe$_{}1.429$(Al$_{4-x}$ Ga$_{x}$)$_{0.286}$ Si$_{0.143}$ /O$_4$ system have been investigated using Mossbauer spectroscopy and SQUID. The Mossbauer spectra at room temperature show well-defined two Zeeman patterns for x=0.2, superpositions of two Zeeman patterns and a doublet for x=0.4. The doublet peak seems to be originated from the superparamagnetic clusters. The system shows significant departures from the Neel's collinear model and seems to be the diluted ferrites. The Mossbauer spectra below R.T show various and complicated patterns, which can be explained by freezing of the superparamagnetic clusters. On cooling, magnetic states of the system may be various and multicritical, Resulting from SQUID measurements, there was an unexpected dip in magnetization curves below 50K. It was interpreted as an effect of spin canting including spin freezing or collective spin behavior.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.5C
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• pp.706-715
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• 2004

In this paper, to decide the watermark embedding positions and embed the watermark we use the subband tee structure which is presented in the wavelet domain and the edge information in the spatial domain. The significant frequency region is estimated by the subband searching from the higher frequency subband to the lower frequency subband. LH1 subband which has the higher frequency in tree structure of the wavelet domain is divided into 4${\times}$4 submatrices, and the threshold which is used in the watermark embedding is obtained by the blockmatrix which is consists by the average of 4${\times}$4 submatrices. Also the watermark embedding position, Keymap is generated by the blockmatrix for the energy distribution in the frequency domain and the edge information in the spatial domain. The watermark is embedded into the wavelet coefficients using the Keymap and the random sequence generated by LFSR(Linear feedback shift register). Finally after the inverse wavelet transform the watermark embedded image is obtained. the proposed watermarking algorithm showed PSNR over 2㏈ and had the higher results from 2％ to 8％ in the comparison with the previous research for the attack such as the JPEG compression and the general image processing just like blurring, sharpening and gaussian noise.

• Korean Journal of Materials Research
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• v.3 no.3
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• pp.253-260
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• 1993

High strength and fracture toughness of Al-Li-Cu alloy(2090 Al alloy) have been achieved by the improvement of melting and casting, extrusion and heat treatment techniques. To establish the sucessful process for semi-industrial scale ingot(20Kg) the following areas have been investigated: (1) Improvement of melting and casting techniques for ingot by introducing atmospheric modifications, vacuum and rotary degassing, and deslagging. (2) The effect of heat treatment on mechanical properties (3) Mechanical characterization by tensile test, fracture toughness test and fatigue crack propagation test. High mechanical properties were found to be intimately related with ingot soundness. Tensile strength of final products varied from 534MPa to 566MPa in peak aged condition while elongation/ductility ranged from 9.0% to 11.9%. From the fracture toughness test with using compact tensile specimen, plane strain fracture toughness($K_{Ic}$) appeared to be 39MPa${\surd}$m in peak aged condition and 23MPa${\surd}$ m in underaged condition. When load ratios of 0.1, 0.3 and 0.5 were given ${\Delta}K_{th}$ was 6.0MPa${\surd}$ m, 5.3MPa${\surd}$ m and 4.3MPa${\surd}$ m respectively.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.5
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• pp.296-306
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• 2020

It has been reported that the wave heights measured by Wave and Tide gauges (WTG) have been underestimated, and thus it is important to improve its measuring accuracy for enhancing estimation of harbor tranquility. In this study, the significant wave heights from WTG were calibrated using measured data from AWAC and Waverider buoys moored at the same four locations with the WTG. It was observed that the product of significant wave height and peak wave period, HT, was not underestimated but linearly proportional between the measurements by two instruments. This linearity was applied to develop 3^rd order polynomial functions that best represented the relationship between HT and significant wave heights measured by WTG. These functions were then applied to calibrate the WTG significant wave heights that were lower than 0.7 m, the critical value established for the low waves in this study. The results showed that the linearity between the AWAC (or Waverider buoy) and calibrated wave heights were improved, and the magnitude of underestimated WTG wave heights were increased to be more realistic. The results of this study are expected to be effectively applied for other data sets obtained by WTG only, to increase the observation accuracy of WTG and to improve the estimation of harbor tranquility.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.3
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• pp.56-63
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• 2023

In this paper, we studied the effect of electron beam irradiation on sol-gel indium-gallium-zinc oxide (IGZO) thin films under air and nitrogen atmosphere and carried out the electrical characterization of the s ol-gel IGZO thin film transistors (TFTs). To investigate the optical properties, crystalline structure and chemical state of the sol-gel IGZO thin films after electron beam irradiation, UV-Visible spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were carried out. The sol-gel IGZO thin films exhibited over 80% transmittance in the visible range. The XRD analysis confirmed the amorphous nature of the sol-gel IGZO films regardless of electron beam irradiation. When electron beam irradiation was conducted in a nitrogen (N₂) atmosphere, we observed an increased proportion of peaks related to M-O bonding contributed to the improved quality of the thin films. Sol-gel IGZO TFTs subjected to electron beam exposure in a nitrogen atmosphere exhibited enhanced electrical characteristics in terms of on/off ratio and electron mobility. In addition, the electrical parameters of the transistor (on/off ratio, threshold voltage, electron mobility, subthreshold swing) remained relatively stable over time, indicating that the electron beam exposure process in a nitrogen atmosphere could enhance the reliability of IGZO-based thin-film transistors in the fabrication of sol-gel processed TFTs.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.4
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• pp.223-237
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• 2011

The intermittent freshwater discharge has an critical influence upon the biophysical environments and the ecosystems of the Yeongsan Estuary where the estuary dam altered the continuous mixing of saltwater and freshwater. Though freshwater discharge is controlled by human, the extreme events are mainly driven by the heavy rainfall in the river basin, and provide various impacts, depending on its magnitude and frequency. This research aims to evaluate the magnitude and frequency of extreme freshwater discharges, and to establish the magnitude-frequency relationships between basin-wide rainfall and freshwater inflow. Daily discharge and daily basin-averaged rainfall from Jan 1, 1997 to Aug 31, 2010 were used to determine the relations between discharge and rainfall. Consecutive daily discharges were grouped into independent events using well-defined event-separation algorithm. Partial duration series were extracted to obtain the proper probability distribution function for extreme discharges and corresponding rainfall events. Extreme discharge events over the threshold 133,656,000 $m^3$ count up to 46 for 13.7y years, following the Weibull distribution with k=1.4. The 3-day accumulated rain-falls which occurred one day before peak discharges (1day-before-3day -sum rainfall), are determined as a control variable for discharge, because their magnitude is best correlated with that of the extreme discharge events. The minimum value of the corresponding 1day-before-3day-sum rainfall, 50.98mm is initially set to a threshold for the selection of discharge-inducing rainfall cases. The number of 1day-before-3day-sum rainfall groups after selection, however, exceeds that of the extreme discharge events. The canonical discriminant analysis indicates that water level over target level (-1.35 m EL.) can be useful to divide the 1day-before-3day-sum rainfall groups into discharge-induced and non-discharge ones. It also shows that the newly-set threshold, 104mm, can just separate these two cases without errors. The magnitude-frequency relationships between rainfall and discharge are established with the newly-selected lday-before-3day-sum rainfalls: $D=1.111{\times}10^8+1.677{\times}10^6{\overline{r_{3day}}$, (${\overline{r_{3day}}{\geqq}104$, $R^2=0.459$), $T_d=1.326T^{0.683}_{r3}$, $T_d=0.117{\exp}[0.0155{\overline{r_{3day}}]$, where D is the quantity of discharge, ${\overline{r_{3day}}$ the 1day-before-3day-sum rainfall, $T_{r3}$ and $T_d$, are respectively return periods of 1day-before-3day-sum rainfall and freshwater discharge. These relations provide the framework to evaluate the effect of freshwater discharge on estuarine flow structure, water quality, responses of ecosystems from the perspective of magnitude and frequency.

• Korean Journal of Remote Sensing
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• v.40 no.4
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• pp.387-396
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• 2024

Most very high-resolution (VHR) satellite images provide rational polynomial coefficients (RPC) data to facilitate the transformation between ground coordinates and image coordinates. However, initial RPC often contains geometric errors, necessitating correction through matching with ground control points (GCPs). A GCP chip is a small image patch extracted from an orthorectified image together with height information of the center point, which can be directly used for geometric correction. Many studies have focused on area-based matching methods to accurately align GCP chips with VHR satellite images. In cases with seasonal differences or changed areas, edge-based algorithms are often used for matching due to the difficulty of relying solely on pixel values. However, traditional edge extraction algorithms,such as canny edge detectors, require appropriate threshold settings tailored to the spectral characteristics of satellite images. Therefore, this study utilizes deep learning-based edge information that is insensitive to the regional characteristics of satellite images for matching. Specifically,we use a pretrained pixel difference network (PiDiNet) to generate the edge maps for both satellite images and GCP chips. These edge maps are then used as input for normalized cross-correlation (NCC) and relative edge cross-correlation (RECC) to identify the peak points with the highest correlation between the two edge maps. To remove mismatched pairs and thus obtain the bias-compensated RPC, we iteratively apply the data snooping. Finally, we compare the results qualitatively and quantitatively with those obtained from traditional NCC and RECC methods. The PiDiNet network approach achieved high matching accuracy with root mean square error (RMSE) values ranging from 0.3 to 0.9 pixels. However, the PiDiNet-generated edges were thicker compared to those from the canny method, leading to slightly lower registration accuracy in some images. Nevertheless, PiDiNet consistently produced characteristic edge information, allowing for successful matching even in challenging regions. This study demonstrates that improving the robustness of edge-based registration methods can facilitate effective registration across diverse regions.