• Journal of IKEEE
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• v.22 no.4
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• pp.1242-1245
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• 2018

In this paper, we have implemented a network that overcomes the over-blurring phenomenon that occurs when removing Gaussian noise. In the conventional filtering method, blurring of the original image is performed to remove noise, thereby eliminating high frequency components such as edges and corners. We propose a network that reducing over blurring while maintaining denoising performance by adding denoised high frequency components to denoisers based on CNN.

• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.3
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• pp.123-128
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• 2020

Analysis of the 2016 Gyeongju earthquake and the 2017 Pohang earthquake showed the characteristics of a typical high-frequency earthquake with many high-frequency components, short time strong motion duration, and large peak ground acceleration relative to the magnitude of the earthquake. Domestic nuclear power plants were designed and evaluated based on NRC's Regulatory Guide 1.60 design response spectrum, which had a great deal of energy in the low-frequency range. Therefore, nuclear power plants should carry out seismic verification and seismic performance evaluation of systems, structures, and components by reflecting the domestic characteristics of earthquakes. In this study, high-frequency amplification factors that can be used for seismic verification and seismic performance evaluation of nuclear power plant systems, structures, and equipment were analyzed. In order to analyze the high-frequency amplification factor, five sets of seismic time history were generated, which were matched with the uniform hazard response spectrum to reflect the characteristics of domestic earthquake motion. The nuclear power plant was subjected to seismic analysis for the construction of the Korean standard nuclear power plant, OPR1000, which is a reactor building, an auxiliary building assembly, a component cooling water heat exchanger building, and an essential service water building. Based on the results of the seismic analysis, a high-frequency amplification factor was derived upon the calculation of the floor response spectrum of the important locations of nuclear power plants. The high-frequency amplification factor can be effectively used for the seismic verification and seismic performance evaluation of electric equipment which are sensitive to high-frequency earthquakes.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.223-226
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• 1999

We study the propagation property of the transient signals along the microstrip using the wavelet transform. Wavelet transform can offer the time-frequency windows. It makes the resolution of time high in high frequency range and the resolution of frequency high in low frequency range. So It is useful to analyze the signals which have both low and high frequency components.

• Journal of Electrical Engineering and Technology
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• v.11 no.2
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• pp.383-392
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• 2016

This paper proposes the design considerations of resonant network and transformer magnetics for 500 kHz high switching frequency LLC resonant converter. The high power density can be effectively achieved by adopting high switching frequency which allows small size passive components in the converter. The design methodology of magnetizing inductance is derived for zero voltage switching (ZVS) condition, and the design methodology of the transformer and output capacitance is derived to achieve high power density at high operating frequency. Moreover, the structure of transformer is analyzed to obtain the proper inductance value for high switching operation. To verify the proposed design methodology, simulation and experimental results will be presented including temperature of passive and active components, and power conversion efficiency to evaluate dominant power loss. In addition, the validity of magnetics design will be evaluated with operating waveforms of the prototype converter.

• Science of Emotion and Sensibility
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• v.17 no.2
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• pp.101-110
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• 2014

High-frequency is sound produced in non-audible area, which couldn't be heard in daily life. The frequency range above 22Khz is called 'high-frequency' and its components are called 'HFC(High-Frequency Components)'. It is known that ocean wave sound is rich in HFC, because it brings serenity and causes ${\alpha}$-waves in human mind. When this natural sound is combined with high-frequency, it seems to give a pleasurable feeling, indicated by an ${\alpha}$-wave increase and a ${\beta}$-wave decrease. We call this phenomena "the hypersonic effects". In this experiment, subjects listened to the ocean wave sound simultaneously with corresponding frequencies similar to ocean wave frequency components created artificially in a electric circuit. Brain waves were measured by an EEG system with 8 channels using 8 electrodes on Fp1, Fp2, F3, F4, T3, T4, O1, and O2. The results showed that ${\alpha}$-wave increase and ${\beta}$-wave decrease were statistically significant while subjects were listening to the ocean wave sound along with the high frequency components, reflecting the hypersonic effect.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.27 no.1
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• pp.56-74
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• 2023

In order to obtain practical and high-quality satellite images containing high-frequency components, a large aperture optical system is required, which has a limitation in that it greatly increases the payload weight. As an attempt to overcome the problem, many multi-aperture optical systems have been proposed, but in many cases, these optical systems do not include high-frequency components in all directions, and making such an high-quality image is an ill-posed problem. In this paper, we use deep learning to overcome the limitation. A deep learning model receives low-quality images as input, estimates the Point Spread Function, PSF, and combines them to output a single high-quality image. We model images obtained from three rectangular apertures arranged in a regular polygon shape. We also propose the Modulation Transfer Function Loss, MTF Loss, which can capture the high-frequency components of the images. We present qualitative and quantitative results obtained through experiments.

• Journal of Power Electronics
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• v.16 no.3
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• pp.849-860
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• 2016

The high-switching-frequency operation of power converters can achieve high power density through size reduction of passive components, such as capacitors, inductors, and transformers. However, a small-output capacitor that has small capacitance and low effective series resistance changes the small-signal model of the converter power stage. Such a capacitor can make the converter unstable by increasing the crossover frequency in the transfer function of the small-signal model. In this paper, the design and implementation of a high-frequency LLC resonant converter are presented to verify the power density enhancement achieved by decreasing the size of passive components. The effect of small output capacitance is analyzed for stability by using a proper small-signal model of the LLC resonant converter. Finally, proper design methods of a feedback compensator are proposed to obtain a sufficient phase margin in the Bode plot of the loop gain of the converter for stable operation at 500 kHz switching frequency. A theoretical approach using MATLAB, a simulation approach using PSIM, and experimental results are presented to show the validity of the proposed analysis and design methods with 100 and 500 kHz prototype converters.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.4
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• pp.345-352
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• 2017

In this paper, a non-dissipative snubber for reducing the switching losses in the step down converter is proposed. The conventional step down converter, e.g., buck converter, suffers from serious switching losses and consequentially heat generation because of its hard switching. Thus, it is unsuitable for high switching frequency operation. Reduction of the reactive components' size, such as an output inductor and capacitor, is difficult. The proposed snubber can slow down the increasing current slopes and switch voltage at turn-on and turn-off transients, thereby significantly reducing the switching loses. Additionally, the slowly increasing current during switch turn-on transition, can effectively solve the output rectifier diode reverse recovery problem. Therefore, the proposed non-dissipative snubber not only leads to the efficiency of converter operation at high switching frequency but also reduces the reactive components size in proportion to the switching frequency. To confirm the validity of the proposed circuit, theoretical analysis and experimental results from a 150 W, 1 MHz prototype are presented.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2013.11a
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• pp.8-11
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• 2013

We implement the foveation and frequency sensitivity feature of human visual system in discrete cosine transform (DCT) domain. Resolution of human visual perception decays as distance from the eye-focused point, known as foveation property, and the middle frequency components give most pleasant image quality to human than the low and high frequency components, which is the frequency sensitivity property of human visual system. For satisfying the foveation property, we enhanced the local contrast at the focused regions and smoothed local contrast at the non-focused regions in the DCT domain without bringing the blocking and ringing artifacts. Moreover, the energies at each DCT frequency components is modified with various degree to fulfill the frequency sensitivity property. The proposed method is verified by the subjective and objective evaluations that it can the improve the human perceptual visual quality.

• Journal of the Korean Society for Railway
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• v.7 no.3
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• pp.232-238
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• 2004

The dynamic characteristics of the current collection process of the high-speed railway are investigated through signals acquired during a test run. The signals are obtained from accelerometers, load cells, and strain gauges attached to various positions of the pantograph, and they are processed in time-and frequency-domains to obtain the dynamic characteristics. The main natural frequency of the pantograph is found to be 8.5Hz. There also are components at low frequencies varying linearly with the train speed. The contact frequency components above 20Hz is attenuated as they pass through the secondary suspension. The main frequency component of the load cell signal is found to be related with the rolling motion of the panhead generated by the stagger in the catenary.