• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.249-252
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• 2003

Acoustic behavior in combustion chamber with acoustic cavity is numerically investigated by adopting linear acoustic analysis. Helmholtz-type resonator is employed as a cavity model to suppress acoustic instability. The tuning frequency of acoustic cavity is adjusted by varying the sound speed in acoustic cavity. Acoustic pressure responses of chamber to acoustic oscillating excitation are shown md acoustic damping effect of acoustic cavity is quantified by damping factor. As the tuning frequency approaches the target frequency of the resonant mode, mode split from the original resonant mode to lower and upper modes appears and thereby damping effect is degraded. Considering mode split and damping effect as a function of tuning frequency, it is desirable to make acoustic cavity tuned to maximum frequency of those of the possible splitted upper modes.

• Journal of Biomedical Engineering Research
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• v.24 no.4
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• pp.347-354
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• 2003

In this paper, a computational method of an action potential including the effect of extremely low frequency and mobile phone (external) electromagnetic fields is Proposed. The method is based on the Hodgkin and Huxley model, applies the effect of the electromagnetic fields on the action Potential in terms of a binding factor into the injection current of the model, and calculates the Strength-Duration curve from numerical experiments for a frequency range of electromagnetic fields. In the numerical experiments, the coupled ordinary differential equations of the action potential and the state variables are solved solf-consistently by using Runge-Kutta Fehlberg method. The range of the frequency considered is from 1Hz through 100Hz and of 900MHz, which is specific for a mobile Phone. The Strength-Duration curves resulted showed good agreements with the equation suggested by Hodgkin and Huxley.

• KEPCO Journal on Electric Power and Energy
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• v.8 no.1
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• pp.31-36
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• 2022

This paper presents the measuring process of dynamic properties of offshore wind power foundation and provides consideration of each step. This Guideline enables to maintain consistent measuring procedure and therefore increase the reliability of test results. Small scaled suction bucket foundation was fabricated to represent the commercial support structure installation mechanism and two cases(free-free, free-fixed) of dynamic tests were performed at workshop. From the tests, the importance of dynamic properties of connection part between suction bucket and tower was figured out. More over, types and configuration of measuring devices are recommended which can help find the natural frequency of wind turbine foundation correctly. In field test, it was found that the natural frequency of suction bucket foundation was increased linearly with the penetration depth due to the confining effect of ambient soil. Meanwhile, it was not easy to get an enough excitation force with normal impact hammer because the N.F of suction bucket model was in the lower range of 0 Hz ~ 5 Hz. Therefore, new excitation method which has enough force and can excite lower frequency range was devised. This study will help develop safety check procedure of suction bucket foundation in field at each installation stage using the N.F measurement.

• Journal of Nutrition and Health
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• v.27 no.3
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• pp.253-262
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• 1994

This study was intended to investigate the anticarcinogenic effect of ginseng previously elucidated by other researches in animal studies. The sister chromatid exchange(SCE) method of human lymphocytes was used as a biomarker. Based on the literature search and the results of our laboratory, smoking was used as a parameter elevating the SCE frequency of general human population. To evaluate the smoking and ginseng effect on SCE frequency, 98 male healthy factory workers aged 23 to 58 years were divided into 4 groups : smoker with ginseng (SG), smoker control(SC), non-smoker with ginseng(NSG), and non-smoker control(NSC) groups, according to their smoking habits and ginseng intake. The mean sponteneous SCE per cell for the SG(10.8$\pm$0.3) and SC(10.4$\pm$0.3) groups were significantly higher than the NSG(9.1$\pm$0.2) and NSC(9.3$\pm$0.3) groups(p<0.05). High frequency cells (HFCs, cells with 15 SCEs) in SG and SC groups were also greater than those in NSG and NSC groups. However, the SCE levels of the SG and SC groups were not associated with the personal smoking history and the number of cigaretts smoked per day. Ginseng intake did not show any effect on the increased SCE caused by smoking. There were no correlations of the elevated SCE among smoking and ginseng types, history of ginseng intake, and consumption frequencies of ginseng intake. These results does not support the findings of other researchers that ginseng could be a protective agent to DNA damage.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.603-609
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• 1999

The effect of an external acoustic excitation on the wake structure behind a circular cylinder was experimentally investigated. The sound wave was excited in the frequency range of the shear layer instability and two sound pressure levels of 114 and 120dB were used in this study. As a result, the acoustic excitation modified the wake structure by increasing the velocity fluctuation energy without changing the vortex shedding frequency. The acoustic excitation enhanced the vortex shedding process and promoted the shear layer instability. Consequently, the acoustic excitation reduced the length of the vortex formation region and decreased the base pressure. In addition, the vortex strength of vortices was increased and the width of the wake was spread out due to the acoustic excitation. When the excitation frequency was identical to the shear layer instability frequency, the effect of the external flow control on the cylinder wake was maximized. In addition, with increasing the sound pressure level, the effect of the external acoustic excitation on the wake structure increased.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.2
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• pp.105-111
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• 2012

High speed machining is the core technology that influences the performance of machine tools, and the high speed motor spindle is widely used for the high speed machine tools. The important problem in high speed spindle is to minimize the thermal effect by motor and bearing and frequency effect. This paper presents the thermal characteristic analysis and frequency experiment for a high speed spindle considering the flow rate of cooling oil. A high speed spindle is composed of angular contact ceramic ball bearings, high speed built-in motor, oil cooling jacket and so on. The thermal analyses of high speed spindle need to minimize the thermal effect and maximize the cooling effect and they are carried out under the various cooling conditions. Heat generations of the bearing and the high speed motor are estimated from the theoretical and experimental data. To find out the characteristic of vibration, the high speed spindle is excited in operational range. This result can be applied to the design and manufacture of a high speed tapping spindle.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.8
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• pp.1861-1868
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• 2014

In wireless communication systems, a frequency offset exist at the received signal due to the transmitter-receiver oscillator mismatch and Doppler effect in mobile environments. Those offsets rotate the received signal's phase and degrade the receiver performance. Hence, estimation and compensation of the frequency offset is crucial at the receiver. This paper proposes a new frequency offset estimation technique based on partial correlation. The proposed method requires less computational complexity than that of the conventional method. In addition, since the proposed one can estimate a wide range of frequency offset without estimation accuracy loss, the application of the method is desirable for the communication environments that have a large frequency offset. In order to verify the performance of our proposed scheme, a series of computer simulations have been carried out and compared against those of the conventional method.

• Speech Sciences
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• v.12 no.4
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• pp.17-29
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• 2005

Time-frequency representation reveals some useful information about instantaneous frequency, instantaneous bandwidth and boundary of each AM-FM component of a speech signal. In many cases, the instantaneous frequency of each component is not constant. The variability of instantaneous frequency causes degradation of resolution in time-frequency representation. This paper presents a method of adaptively adjusting the transform kernel for preventing degradation of resolution due to time-varying instantaneous frequency. The transform kernel is the form of frequency modulated function. The modulation function in the transform kernel is determined by the estimate of instantaneous frequency which is approximated by first order polynomial at each time instance. Also, the window function is modulated by the estimated instantaneous. frequency for mitigation of fringing. effect. In the proposed method, not only the transform kernel but also the shape and the length of. the window function are adaptively adjusted by the instantaneous frequency of a speech signal.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.10
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• pp.1137-1146
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• 2008

OFDM is very effective for the high speed communication system. However, OFDM has the problems of high PAPR and serious ICI, which is different from the single carrier system. Especially, ICI problem caused by phase noise, Doppler effect and frequency offset is main reason for poor performance since it breaks down the orthogonality between subcarriers in OFDM communication system. Therefore, WFMT modulation scheme is studied and the effect of the carrier frequency offset and phase noise is analyzed. WFMT modulation scheme is based on the wavelet theory and complex filter banks for synthesis and analysis of multichannel signal. WFHT modulation scheme keeps on the advantage of filter banks system and can be easily possible for the implementation of filter banks. In this paper, we compare ISI and ICI distortions of the WFMT and OFDM system due to the carrier frequency offset and phase noise. Also, we analyze the PAPR and BER performances in the HPA and ICI situation caused by the Doppler frequency shift and the frequency offset.

• Journal of the Korean Society of Clothing and Textiles
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• v.18 no.2
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• pp.180-188
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• 1994

The purpose of this study was to evaluate the effect of basic needs and demographic variables of adult woman on the modesty and aethetics In the selection of clothes. The results of the study were as follows: 1. There are factors which have effect on variables of need. School careers have effect on physical need. Age, marriage status and household type have effect on safty need. Native community and household type have effect on self-esteem. School career, native community, household type and frequency of contact with mass media have effects on need of self-actualizing and native community has effect on the aesthetic need. 2. Physical bleed, self-esteem, self-actualization, safety need, fiequency of contact with mass media, age, native community and income have direct effect on the modesty of clothing. 3. Aethetic and self-actualization need, frequency of contact with mass media and income have direct effect on the aethetics of clothing.