• 한국소음진동공학회논문집
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• 제17권8호
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• pp.736-740
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• 2007

A laboratory study on low frequency noise assessment has been carried out to evaluate the relevance of the weighting curve. Especially, the A-weighting curve which is used in most noise assessments has been evaluated using the acceptability limit in this study. The acceptability limit is one of the indicators in which the subjective responses were well-reflected. For the measurement of the acceptability limit, pure tone stimuli were used in the frequency range between 20 and 200 Hz. The measurement was proceeded in the anechoic chamber to minimize the background noise level. A total of 29 test subjects, who were aged between 19 to 33 years, participated in this study. They had been exposed to various stimuli for about 1 hour by supra-aural earphone. The measurement consisted of two listening sessions: hearing threshold and the acceptability limit session. The results showed that the tendency of the acceptability limit curve was approximately equal to C-weighting curve which had been found to be superior to A-weighting curve in assessment of low frequencies.

• Journal of Electrical Engineering and Technology
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• 제9권1호
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• pp.27-36
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• 2014

This paper presents an adaptive wide-area damping controller (WADC) based on generalized predictive control (GPC) and model identification for damping the inter-area low frequency oscillations in large-scale inter-connected power system. A recursive least-squares algorithm (RLSA) with a varying forgetting factor is applied to identify online the reduced-order linearlized model which contains dominant inter-area low frequency oscillations. Based on this linearlized model, the generalized predictive control scheme considering control output constraints is employed to obtain the optimal control signal in each sampling interval. Case studies are undertaken on a two-area four-machine power system and the New England 10-machine 39-bus power system, respectively. Simulation results show that the proposed adaptive WADC not only can damp the inter-area oscillations effectively under a wide range of operation conditions and different disturbances, but also has better robustness against to the time delay existing in the remote signals. The comparison studies with the conventional lead-lag WADC are also provided.

• International Journal of Oral Biology
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• 제35권4호
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• pp.137-144
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• 2010

To evaluate the biohazard properties of an extremely low frequency electromagnetic field (ELF-EMF), we explored the physical properties of the ELF-EMF that generates the electric current induction in the secondary coil from the chamber of a primary solenoid coil. We subsequently explored the biological effects of a strong alternating electromagnetic field (EMF), ranging from 730-960 Gauss, on the mouse testis. Mice were exposed to an alternating EMF field induced by a rectangular electric current at 1, 7, 20, 40, and 80 Hertz, for 1, 3, 5, and 7 hours. The mouse testes were examined for proliferative activity and apoptosis using the in situ terminal deoxynucleotidyl transferase (TdT) method and by immunostaining of proliferating cell nuclear antigen (PCNA), respectively. We found that the electric currentm induction increased in the 6-8 Hertz range, and that exposure to an ELF-EMF induced the apoptosis of mouse spermatocytes. In situ TdT staining was found to be most prominent in 7 Hertz group, and gradually reduced in the 20, 40, and 80 Hertz groups. These data suggest that a strong EMF can induce reproductive cell death within a short time, and the harmful effects of the EMF are maximal at low frequency alternating EMFs.

• 한국의류학회지
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• 제22권5호
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• pp.607-616
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• 1998

The purpose of this study was to develope a practical color range for the fashion industry in Korea. 3623 color sample used by 109 brands from'93 spring/summer to'96 spring/summer were collected. Also, the application frequency and consumer responses of each collected colorwere analyzed in this study. To clarify the characterstics of color range used in the fashion industry, density of color was etermined by color clustering based on A: and consumer responses. The resultsof this study were as follow; 1. The result analyzed based on the Munsell System revealed that the distributions of hue were concentrated in R, YR, Y, and PB. The chroma was concenturated mostly in the low range and the value, on the contrary, showed relatively even distribution. 2. 458 representative colors were selected by color clustering based on the toEless than 1. 0. In addition, the frequency of color applications and consumer responses were also considered when selecting the colors frequently used in the fashion industry and finals, 1163 colors wereobtained. The color range of the representative colors showed similar color characteristics with the 3623 colors supplied by the fashion industry. As a results, this approach was proven to appropriate to develope a color range for a practical use. 3. In conclusion, around 1200 colors were suggested to organize the color range to reflect the characteristics of the fashion industry with an acceptable color differance for color planning and management.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권11호
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• pp.5527-5545
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• 2019

Through-wall ultra-wide band (UWB) radar has been considered as one of the preferred and non-contact technologies for the targets detection owing to the better time resolution and stronger penetration. The high time resolution is a result of a larger of bandwidth of the employed UWB pulses from the radar system, which is a useful tool to separate multiple targets in complex environment. The article emphasised on human subject localization and detection. Human subject usually can be detected via extracting the weak respiratory signals of human subjects remotely. Meanwhile, the range between the detection object and radar is also acquired from the 2D range-frequency matrix. However, it is a challenging task to extract human respiratory signals owing to the low signal to clutter ratio. To improve the feasibility of human respiratory signals detection, a new method is developed via analysing the standard deviation based kurtosis of the collected pulses, which are modulated by human respiratory movements in slow time. The range between radar and the detection target is estimated using joint time-frequency analysis (JTFA) of the analysed characteristics, which provides a novel preliminary signature for life detection. The breathing rates are obtained using the proposed accumulation method in time and frequency domain, respectively. The proposed method is validated and proved numerically and experimentally.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.60-66
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• 2007

Separation control has been performed using synthetic jets on airfoil at high angle of attack. Computed results demonstrated that stall characteristics and control surface performance could be substantially improved by resizing separation vortices. It was observed that the actual flow control mechanism and flow structure is fundamentally different depending on the range of synthetic jet frequency. For low frequency range, small vortices due to synthetic jet penetrated to the large leading edge separation vortex, and as a result, the size of the leading edge vortex was remarkably reduced. For high frequency range, however, small vortex did not grow up enough to penetrate into the leading edge separation vortex. Instead, synthetic jet firmly attached the local flow and influenced the circulation of the virtual airfoil shape which is the combined shape of the main airfoil with the separation vortex. Theses results show the characteristic of unsteady flow of single synthetic jet. Beside, we researched on multi-array synthetic jet to obtain applicable synthetic jet velocity. Multi-location synthetic jet is proposed to eliminate small vortex on suction surface of airfoil. With the results, we concluded that the flow around airfoil is stable by high frequency synthetic jet with elimination of small vortex and confirmation of stable flow. Moreover, performance of multi-array/multi-location synthetic jet can be improved by changing phase angle of multi-location synthetic jet.

• 한국소음진동공학회논문집
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• 제16권7호
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• pp.690-696
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• 2006

Thickness of damping layer in sandwich plate needs to be optimized in order to make modal loss factor of the sandwich plate maximum. Since previous studies were interested in noise reductions over high frequency range, the modal properties were derived based on simply supported boundaries. This conventional formula is approximately applicable to other boundary conditions over high frequency range only. The purpose of this study is to propose a method to determine optimum damping layer thickness of sandwich plate for maximum modal damping in low frequency range when the boundary condition is not a simple support. The conventional RKU equation based on simply supported boundary is modified to reflect other boundary conditions and the modified RKU equation is subsequently applied to determine the optimum damping layer thickness for arbitrary conditions. In order to reflect frequency-dependent characteristics of elastic modulus of the damping layer, an iteration method is proposed in determining the modal properties. Test results on sandwich plates for optimum damping layer thickness are compared with predictions by the proposed method and conventional method.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.345-348
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• 1999

The monolayer behaviors at the air-water interface and the dielectric properties of MI-0 LB films for complex concentration were investigated by the surface pressure-area ($\pi$-A) isotherms and dielectric constant. The molecular area was expanded with increase of metal ions concentration. It is considered that the expansion of molecular area is due to electrostatic repulsion between the polymer chains andhydrophobic increase of ionic strength. In the frequency-dependent complex dielectric constant at room temperature, the real part of dielectric constant($\varepsilon'$) is about 6.0~10.0 in the low-frequency range and is decreasing slowly upto $1O^4$Hz. It decreased abruptly near $1O^5Hz$. It seems to be dielectric dispersion in this frequency range. Also, the imaginary part of dielectric constant ($\varepsilon"$) shows a peak in $1O^5$~$1O^6Hz$. It seems to be dielectric absorption in this frequency range.ange.

• 센서학회지
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• 제22권6호
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• pp.379-386
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• 2013

The influences of the load resistance $R_L$ on the magnetoelectric (ME) characteristics of $NiZnFe_2O_4+PZT$ composite were investigated in the non-resonance frequency range. The ME coefficient peak increases with increasing $R_L$, but the frequency indicating the ME coefficient peak decreases with increasing $R_L$. The maximum output power peak is approximately $9.3{\times}10^{-10}mW/Oe$ near $R_L=3.3M{\Omega}$ at f=280 Hz, and the ME coefficient seems to be saturated at $R_L>20M{\Omega}$. This frequency shift effect of $R_L$ shows that the frequency range for an ME sensor application can be modulated with the appropriate value of $R_L$. The ME output voltage has a good linear response to the ac field Hac and shows fair stability over a range of temperatures. The measured non-linearity of this sample is approximately 0.8%. This sample will allow for a low-strength magnetic ac-field sensor. The result from this sample will serve as basic data for a signal-processing circuit system.

• 한국콘텐츠학회논문지
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• 제12권6호
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• pp.361-370
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• 2012

이 연구의 목적은 경피신경전기자극을 저빈도-저강도, 저빈도-고강도, 고빈도-저강도, 고빈도-고강도 네 개의 치료조건으로 나누어 만성요통환자에게 적용하였을 때 각기 다른 주파수 빈도와 강도가 만성요통환자의 미치는 영향을 알아보는 것이다. 연구대상은 평균연령 39.19(${\pm}12.96$)세, 발병기간 8.57(${\pm}3.07$)개월인 요통환자 32명이었다. 치료기간은 2주 횟수는 총 10회로 1일 1회 15분간 시행하였으며 치료부위는 통증이 가장 심한 요추주변 부위에 시행하였다. 치료 전 후의 변화를 평가하기 위해 요통정도(요통장애지수)와 요추부 유연성을 측정하였다. 각 군간 윌콕슨, 맨-휘트니 검정을 하였고, 통계적 유의성은 p< .05로 하였다. 결과는 다음과 같다. 네 군 모두 실험 후 요통장애지수와 요추부 유연성에 유의한 결과가 나왔으며, 저빈도군에서는 고강도가, 고빈도군에서는 고강도가 보다 효과적이었다. 고빈도-고강도가 요통장애지수와 요추부 유연성에 유의한 차이는 없었지만 가장 효과적이었다.