• 전기학회논문지
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• 제59권2호
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• pp.471-475
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• 2010

This paper presents a frequency synthesizer using low voltage active inductor VCO(Voltage Controlled Oscillator). The low voltage active inductor VCO with feedback resistor increases its equivalent inductance and the quality-factor(Q). Under certain conditions, the low voltage active inductor with feedback resistor generates a negative resistance at the input. In this paper, the conditions for negative resistance are obtained by small signal analysis. The designed low voltage active inductor VCO covers a frequency band between 1059MHz and 1223MHz. The measured phase noise at 1.178GHz is -81.8dBc/Hz at 1MHz offset.

• Corrosion Science and Technology
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• 제2권2호
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• pp.93-97
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• 2003

Fatigue crack growth test or low alloy steel was performed in high temperature water. Test parameters were dissolved oxygen content. loading frequency and R-ratio ($P_{min}/P_{max}$). Since the sulfur content or the steel was low, there were no environmentally assisted cracks (EAC) in low dissolved oxygen(DO) water. At high DO, the crack growth rate at R = 0.5 tests was much increased due to environmental effects and the crack growth rate depended on loading frequency and maximized at a critical frequency. On the other hand, R = 0.7 test results showed an anomalous decrease of the crack growth rate as much different behavior from the R = 0.5. The main reason of the decrease may be related to the crack tip closure effect. All the data could be qualitatively understood by effects of oxide rupture and anion activity at crack tip.

• 전기학회논문지
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• 제58권6호
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• pp.1078-1086
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• 2009

This paper presents a Fourier based algorithm for estimating the parameters of the low frequency oscillating modes. The proposed methods estimates various parameters(frequency, damping factor, mode magnitude, phase) by fitting Fourier spectrum and phase with a damped exponential cosine function. Dominant frequency is selected by taking frequency corresponding to the peak spectrum, and damping factor is estimated using the left/right spectra of Fourier spectrum. In addition, mode magnitude is calculated by the normalized peak spectrum, and phase is estimated from spectrum phase. Also, we introduce an accuracy index in order to determine the accuracy of the estimated parameters, and the index is calculated using the deviations of the peak spectrum and the left/right spectra. The parameter estimation methods proposed in this paper include very simple arithmetical processes, so the algorithms are simple and the calculation speed is very fast. The proposed methods are applied to test functions with two dominant modes. The results show that the proposed methods are highly applicable to low frequency parameter estimation.

• International Journal of Aeronautical and Space Sciences
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• 제16권3호
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• pp.339-346
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• 2015

Aerodynamic flow control phenomena were investigated with a low-current DC surface discharge plasma actuator. The plasma actuator was found to operate in three different discharge modes with similar discharge currents of about 1 mA or less. Stable continuous DC discharge without audible noise was obtained at higher ballast resistances and lower discharge currents. However, even with continuous DC power input, a low-frequency self-pulsed discharge was obtained at lower ballast resistances, and a high-frequency self-pulsed discharge was obtained at higher set-point currents and higher ballast resistances, both with audible noise. The Schlieren image reveals that the low-frequency self-pulsed mode produces a synthetic jet-like flow implying that a gas heating effect plays a role, even though the discharge current is small. The high-frequency self-pulsed mode produces pulsed jets in a tangent direction, and the continuous DC mode produces a steady straight pressure wave. Particle image velocimetry (PIV) images reveal that the induced flow field by the low-frequency self-pulsed mode has flow propagating in the radial direction and centered between the electrodes. The high-frequency self-pulsed mode and continuous DC mode produce flow from the anode to the cathode. The perturbed region downstream of the cathode is larger in the high-frequency self-pulsed mode with similar maximum speeds.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.875-880
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• 2018

This paper proposes a novel combined compensation structure in the infrared receiver chip. For the infrared communication chip, the current-voltage (I-V) convert circuit is crucial and important. The circuit is composed by the transimpedance amplifier (TIA) and the combined compensation structures. The TIA converts the incited photons into photocurrent. In order to amplify the photocurrent and avoid the saturation, the TIA uses the combined compensation circuit. This novel compensation structure has the low frequency compensation and high frequency compensation circuit. The low frequency compensation circuit rejects the low frequency photocurrent in the ambient light preventing the saturation. The high frequency compensation circuit raises the high frequency input impedance preserving the sensitivity to the signal of interest. This circuit was implemented in a $0.6{\mu}m$ BiCMOS process. Simulation of the proposed circuit is carried out in the Cadence software, with the 3V power supply, it achieves a low frequency photocurrent rejection and the gain keeps 109dB ranging from 10nA to $300{\mu}A$. The test result fits the simulation and all the results exploit the validity of the circuit.

• Smart Structures and Systems
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• 제6권5_6호
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• pp.661-673
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• 2010

This paper presents recent developments in an extremely compact, wireless impedance sensor node (the WID3, $\underline{W}$ireless $\underline{I}$mpedance $\underline{D}$evice) for use in high-frequency impedance-based structural health monitoring (SHM), sensor diagnostics and validation, and low-frequency (< ~1 kHz) vibration data acquisition. The WID3 is equipped with an impedance chip that can resolve measurements up to 100 kHz, a frequency range ideal for many SHM applications. An integrated set of multiplexers allows the end user to monitor seven piezoelectric sensors from a single sensor node. The WID3 combines on-board processing using a microcontroller, data storage using flash memory, wireless communications capabilities, and a series of internal and external triggering options into a single package to realize a truly comprehensive, self-contained wireless active-sensor node for SHM applications. Furthermore, we recently extended the capability of this device by implementing low-frequency analog-to-digital and digital-to-analog converters so that the same device can measure structural vibration data. The compact sensor node collects relatively low-frequency acceleration measurements to estimate natural frequencies and operational deflection shapes, as well as relatively high-frequency impedance measurements to detect structural damage. Experimental results with application to SHM, sensor diagnostics and low-frequency vibration data acquisition are presented.

• The Korean Journal of Pain
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• 제2권2호
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• pp.145-154
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• 1989

Pain is a common and important clinical symptom, and treatments aimed at relieving pain have a central position in medical practice. Recently Transcutaneous Electrical Nerve Stimulation (TENS) has been effectively used to control acute and chronic conditions that produce pain. But the mechanism of analgesia resulting from TENS remains obscure. In order to investigate the analgesic effect of TENS and it's action mechanism, TENS was applied in 40 rabbits with different frequencies, low frequency (2Hz) and high frequency (100Hz), for 20 minutes. And the pain threshold was measured by the temperature before and after stimulation, and an attempt was made to antagonize the stimulation effect with naloxone pretreatment (0.4 mg/kg) The results are as follows: 1) Both low frequency and high frequency TENS resulted in increasing the pain threshold significantly (Both p<0.01). 2) Naloxone pretreatment could antagonize the effect of increasing the pain threshold with low frequency TENS significantly (p<0.01), but not with high frequency TENS. Plasma beta-endorphin was measured by radioimmunoassay using an Beta-Endorphin Kit (Immunonuclear Corporation, Stillwater, Minnesota, USA) and Automatic Gamma Scintillation Counter (Micromedic System 4/2000) before and after stimulation. An attempt was made to reverse the stimulation effect with naloxone pretreatment (0.4 mg/kg). The results are as follows: 1) Low frequency TENS resulted in increasing the level of plasma beta.endorphin significantly (p<0.01), but high frequency TENS did not. 2) Naloxone pretreatment could reverse the effect of increasing the plasma beta-endorphin level with low frequency TENS significantly (p<0.01).

• 한국군사과학기술학회지
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• 제20권5호
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• pp.673-680
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• 2017

In the proposed paper, we designed low noise frequency synthesizer with compact size for Multi-Band. The proposed frequency synthesizer consists of fundamental frequency band(2 GHz) and harmonic frequency band(4 GHz). To improve the phase noise and spurious level of frequency synthesizer, we analyze how the configuration of frequency synthesizer affect the phase noise and design the multi-band's structure. The implemented frequency synthesizer reduce both the phase noise and spurious level. The phase noise is -92.17 dBc/Hz at 1 kHz frequency offset in 2 GHz and -90.50 dBc/Hz at 1 kHz frequency offset in 4 GHz. All spurious signals including fundamental frequency are suppressed at least 20 dBc than the second harmonic frequency.

• 한국의류학회지
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• 제25권6호
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• pp.1025-1036
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• 2001

This paper explores the effects of price discount frequency on consumer evaluation of clothing brand equity as well as the impact on consumers who exhibit different consumer characteristics. Following a preliminary investigation, two clothing brand groups were identified according to the frequency of their price discounts, one with a high frequency of price discounts, the other with a low frequency. Each brand group consisted of three women's clothing brands. A questionnaire was developed and administered to 351 females between the ages of nineteen and thirty-four in October 2000. The questionnaire included questions on evaluations on clothing brand equity (i.e., perceived quality, brand image, perceived value, reliability and brand knowledge), on consumer characteristics (i.e., clothing knowledge, clothing evaluative criteria, price perception and demographic characteristics), as well as on price discount frequency. Statistical tests, such as factor analysis. t-test and pearson's correlation, were used to analyze the data. Results of this research showed that price discount frequency negatively impacted consumer perception of clothing brand equity. The negative influence was particularly strong on the perceived quality and brand image dimensions of brand equity. The findings also suggested the effect of price discount frequency on consumer assessment of clothing brand equity was related to consumer characteristics as well. The equity of the clothing brand group with a low frequency of price discounts was positively related to clothing knowledge, price-quality inference, price-prestige inference, sale prone-ness. price mavenism, valuing the fashionable and symbolic uses of clothing and family income. On the other hand, it was negatively related to low price consciousness. The equity of the clothing brand group with a high frequency of price discounts was positively related to utilitarian economic aspects of clothing values as well as to low price consciousness. To establish and maintain high brand equity, marketers must pay attention to the frequency of price discount as it may have a negative impact on clothing brand equity.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.185-190
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• 2006

The correct estimation of the ionospheric delays is very important for the precise kinematic positioning especially in case of the long baseline. In case of triple frequency system, the ionospheric delays can be estimated from the measurements, but, in case of dual frequency system, the situation is not so simple. The precision of those supplied by the external information source such as IONEX is not sufficient. The high frequency component is neglected, and the precision of the low frequency component is not sufficient for the long baseline positioning. On the other hand, the high frequency component can be estimated from the phase range measurements. If the low frequency components are estimated by using the external information source or pseudo range measurements, a more reasonable estimation of the ionospheric delays may be possible. It has already been discussed by the author that the estimation of the low frequency components by using the external information source is not sufficient but fairly effective. The estimation using the pseudo range measurements is discussed in the present paper. The accuracy is not sufficient at present because of the errors in the pseudo range measurements. It is clarified that the bias errors in the pseudo range measurements are responsible for the poor accuracy of the ionospheric delays. However, if the accuracy of the pseudo range measurements is improved in future, the method would become very promising.