• Journal of the Korean Society for Marine Environment & Energy
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• v.5 no.1
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• pp.11-18
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• 2002

Directional breaking waves are generated by the component wave focusing both in direction and frequency based on constant wave steepness and constant wave amplitude spectrum models. The generated breaking waves are classified in the incipient, single and multi breaking waves. The characteristics of directional breaking waves are investigated in terms of surface profile parameters of wave crest steepness and asymmetry. The evolution of breaking wave characteristics is analyzed in a view of focusing efficiency. It shows that the front steepness and vertical asymmetry play an important role in breaking process, while the crest rear steepness and horizontal asymmetry are nearly constant during the process. The superposition of directional components greatly enhances the focusing efficiency and it suggests that characteristics of directional breaking waves may significantly different from uni-directional ones.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.10
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• pp.44-51
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• 2020

We studied the heating characteristics of a whirling spindle. This spindle is an important component of a whirling machine for turning a ball screw shaft. In the manufacturing process for a conventional ball screw shaft, a single tool is used to form a spiral in a lathe machine tool. Thereafter, a high-frequency heat treatment process is performed. Recently, a whirling-type cutting method has emerged. This method can perform hard turning in the rotating direction of the spiral portion of the ball screw shaft by rotating and mounting multiple tools. The whirling method can be applied to the heat-treated material. In this study, an experimental apparatus was constructed to analyze the whirling spindle. The experiment proceeded in four steps. The rotating speed of the whirling spindle was set to ISO random and sequential rising conditions. Cooling and non-cooling modes in the cooling jacket were tested. As a result of the above experiment, the heating characteristics of the whirling spindle were derived.

• Journal of Periodontal and Implant Science
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• v.31 no.3
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• pp.573-579
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• 2001

The purpose of this study was to investigate the characteristiss of korean multi-rooted teeth extracted by periodontal disease. A total of 182 extracted multi-rooted teeth were examined. The distance from the cementoenamel junction(CEJ) to the root groove and from the CEJ to the root division was measured. The frequency of the root grooves were calculated. The results are as follows : 1. Distances from CEJ to the root groove were $1.53{\cdot}1.60mm$ for maxillary first premolars mesial${\cdot}$distal sides, $1.26{\cdot}1.38{\cdot}1.75mm$ for maxillary first molars buccal${\cdot}$mesial${\cdot}$distal sides, $1.38{\cdot}1.71{\cdot}1.41mm$ for maxillary second molars buccal${\cdot}$mesial${\cdot}$distal sides, $0.98{\cdot}0.99mm$ for mandibular first molars buccal${\cdot}$lingual sides and $1.28{\cdot}1.35mm$ for mandibular second molars buccal${\cdot}$lingual sides. 2. The frequency of the root grooves were $17.4{\cdot}30.4%$ for maxillary first premolars mesial${\cdot}$distal sides, $44.4{\cdot}84.1{\cdot}67.5%$ for maxillary first molars buccal${\cdot}$mesial${\cdot}$distal sides, $100{\cdot}90.3{\cdot}90.3%$ for maxillary second molars buccal${\cdot}$mesial${\cdot}$distal sides, $42.9{\cdot}77.8%$ for mandibular first molars buccal${\cdot}$lingual sides and 90.6% for mandibular second molars buccal${\cdot}$lingual sides. 3. Distances from CEJ to the root division were $6.8{\cdot}7.2mm$ for maxillary first premolars mesial${\cdot}$distal sides, $3.3{\cdot}4.38{\cdot}4.34mm$ for maxillary first molars buccal${\cdot}$mesial${\cdot}$distal sides, $3.67{\cdot}4.8{\cdot}4.07mm$ for maxillary second molars buccal${\cdot}$mesial${\cdot}$distal sides, $3.1{\cdot}3.89mm$ for mandibular first molars buccal${\cdot}$lingual sides and $3.2{\cdot}4.06mm$ for mandibular second molars buccal${\cdot}$lingual sides.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.4
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• pp.46-53
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• 2008

In this study, we developed RBFN(Radial Basis Function Networks) based load modeling method with harmonic components. The developed method considers harmonic information as well as fundamental frequency and voltage considered as essential factors in conventional method. Thus, the reposed method makes it possible to effectively estimate load characteristics in power lines with harmonics. RBFN has some advantage such as simple structure and rapid computation ability compared with multi-layer perceptorn which is extensively applied for load modeling. To verify the effectiveness, the proposed method has been intensively tested with various dataset acquired under the different frequency and voltage and compared it with conventional methods such as polynomial method, MLPN and RBFN with no harmonic components.

• Progress in Superconductivity
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• v.5 no.1
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• pp.26-30
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• 2003

Magneto-cardiogram(MCG) signals may be highly distorted by the environmental noise, such as power-line interference, broadband white noise, surrounding magnetic noise, and baseline wondering. Several kinds of digital filters and noise cancellation methods have been designed and realized by many researchers, but these methods gave some problems that the original signal may be distorted by digital filter due to the wideband characteristics of background noise. To eliminate noise effectively without distortion of MCG signals, we performed multi-level frequency decomposition using wavelet packets and local adaptive noise cancellation in each local frequency range. In addition to the proposed wavelet filter to eliminate these various non-stationary noise elements, the local adaptive filter using the least mean square(LMS) algorithm and the soft threshold do-noising method are introduced in this paper. The signal to noise ratio(SNR) and the reconstruction square error(RSE) are calculated to evaluate the performance of the proposed method and compared with the results of the conventional wavelet filter and adaptive filter. The experimental results show that the proposed local adaptive filtering method is better than the conventional methods.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.3
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• pp.485-491
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• 2003

In this paper, We designed the multi-stage amplifier having high gain/low noise characteristics for terrestial repeater of direct digital satellite broadcasting system. In the design the amplifier, we optimized the parameters to have the stable operation between gain, noise figure and stability. The first stage of amplifier can be specified low noise impedance matching, 2nd stage to 5th stage show constant gain and stable operation and final stage of amplifier shows high gain impedance matching. As a result of experiment at the frequency of digital satellite terrestial, show 68dB gain under 2,4dB noise figure and 63dB dynamic range in the 11.7GHz-12.7GHz frequency range, it is a good agreement of communication channel amplifier requirements for satellite terrestial repeater.

• Journal of computational fluids engineering
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• v.12 no.2
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• pp.1-7
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• 2007

To develop an aerodynamic performance, two groups of studies have been achieved widely. One is about the geometric design of vehicles and the other is about aerodynamic devices. Geometric design is a credible and stable method. However, it is not flexible and each part is related interactively. Therefore, if one part of geometry is modified, the other part will be required to redesign. On the other hand, the flow control by aerodynamic devices is flexible and modulized method. Even though it needs some energy, a relatively small amount of input makes more advanced aerodynamic performance. Synthetic jet is one of the method in the second group. The device repeats suctions and blowing motions in constant frequency. According to the performance, the adjacent flow to flight surface are served momentum. This mechanism can reduce the aerodynamic loss of boundary layer and separated flow. A synthetic jet actuator has several parameters, which influences the flow control. This study focuses on the parameter effects of synthetic jet - orifice geometry, frequency, jet speed and etc.

• Journal of the Korean Society of Costume
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• v.57 no.6 s.115
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• pp.46-61
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• 2007

The analysis of exotic style in domestic fashion brand items aims to offer the ideas necessary for the style and item developments and to analyze exotic images and styles accepted in domestic fashion market. Therefore this study analyzed the domestic fashion brand items and categorized the main exotic factors and styles so that would catch on to its characters and appearance frequency. As for the research method of this study, the frequency and content multi-dimensional analysis were used in the investigation of the exotic images appearing in the domestic fashion brands. The styles of exotic image in domestic fashion brand items are 'natural' style, 'primitive' style, 'ethnic' style, and 'maximalism' style. Also, the main exotic factors in each exotic style were composed of a few exotic images such as 'natural', 'primitive', 'ethnic', 'romantic', 'elegance', 'splendid', 'seductive', 'retro', 'traditional', 'classical', 'bohemian', 'vintage', 'kidult', 'artistic', 'extreme compromise', and 'modern'.

• Journal of Sensor Science and Technology
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• v.8 no.2
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• pp.102-107
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• 1999

In this paper, to develop the fiber optic hydrophone for the use of low frequency applications, two channels TDM(Time Division Multiplexing) fiber-optic hydrophone array was fabricated and their acoustic charateristics were investigated in the acoustic water tank. A fiber length of the order of 150m is wounded at the hollow cylinder type aluminum mandrel and the fundamental natural frequency of the mandrel maintained above 10kHz. An unbalanced interferometer (discrete Mach-Zehnder type) was used. Sound detection performance is tested in the underwater tank with 3kHz continuous sound source. Finally, it is shown that two channels TDM fiber-optic hydrophone array can detect 3kHz sound stably. This results can also applicable for the development of multi-channel fiber optic hydrophone array.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.10C
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• pp.987-992
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• 2002

In this paper, a new clock and data recovery circuit is proposed for the application of data communication systems requiring ㎓-range clock signals. The circuit is suitable for recovering NRZ data which is widely used for high speed data transmission in ㎓ ranges. The high frequency jitter is one of major performance-limiting factors in PLL, particularly when NRZ data patterns are used. A novel phase detector is able to suppress this noise, and stable clock generation is achieved. Futhermore, the phase detector has an adaptive delay cell removing the dead zone problem and has the optimal characteristics for fast locking. The proposed circuit has a convenience structure that can be easily extended to multi-channels. The circuit is designed based on CMOS 0.25㎛ fabrication process and verified by measurement result.