• Journal of electromagnetic engineering and science
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• 제6권1호
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• pp.76-81
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• 2006

Ultra wideband(UWB) technologies have been developed to exploit a new spectrum resource in substances and to realize ultra-high-speed communication, high precision geo-location, and other applications. The energy of UWB signal is extremely spread from near DC to a few GHz. This means that the interference between conventional narrowband systems and UWB systems is inevitable. However, the interference effects had not previously been studied from UWB wireless systems to conventional wireless systems sharing the frequency bands such as Broadcasting system. This paper experimentally evaluates the interference from two kinds of UWB sources, namely a orthogonal frequency division Multiplex UWB source and an impulse radio UWB source, to a Broadcasting transmission system. The receive power degradations of broadcasting system are presented. From these experimental results, we show that in all practical cases UWB system can coexist 35 m distance in-band broadcasting network.

• 소성∙가공
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• 제25권6호
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• pp.373-378
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• 2016

Recent researches have reported that the superposition of ultrasonic vibrations in metal forming provides beneficial effects such as the reduction of forming load, flow stress and interfacial friction which improves the surface quality of end products. This paper presents experimental investigations on the effects of ultrasonic vibrations in upsetting tests of aluminum. The ultrasonic exciting system consists of piezoelectric transducer and resonator was designed and constructed to superimpose high frequency oscillation on the forming tools. Ultrasonic vibration-assisted upsetting tests were performed for three vibration modes five amplitudes, and the results were compared with those of conventional upsetting tests. The results showed that the superimposition of ultrasonic vibration reduces the upsetting load, and the load reduction is only dependent on the amplitude of the applied vibration regardless of deformation histories and vibration modes.

• 한국군사과학기술학회지
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• 제22권2호
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• pp.233-240
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• 2019

High-altitude ElectroMagnetic Pulse(HEMP) is a high-power electromagnetic pulse caused by nuclear explosions at altitudes above 30 km. This pulse can cause serious damage to the electrical/electronic device. Therefore, there are a lot of studies on the effects of HEMP in the literature. When conducting studies on the effects of HEMP, it is essential to measure the simulated HEMP. Depending on the need for measurement, this paper focuses on the HEMP measurement method. This paper proposes a measurement method using frequency domain compensation to extract the correct waveform and solves the offset problem more efficiently than the conventional methods. The proposed method is verified by experiment using HEMP simulator and measurement system in ADD.

• The Journal of Korean Physical Therapy
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• 제13권2호
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• pp.335-346
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• 2001

This study was performed, using c-fos, to investigate the effect of TENS on pain model induced by capsaicin in spinal level. Twelve rats with 200-250g body weight were randomly divided into three groups: One group which induced by capsaicin, another group which applicated TENS with low frequency(4Hz. 200${\mu}$s, 20min) and the other group which applicated TENS with high frequency(100Hz, 50${\mu}$s, 20 min). The results of this study were as follows: 1. The number of c-fos immunoreactive neurons in superficial dorsal horn was increased markedly 2 hours after capsaicin injection, and decreased gradually from 4 hours to 16 hours after injection. 2. At 2hours after capsaicin injection, both low frequency and high frequency TENS decrease the number of c-fos immunoreactive neurons in superficial dorsal horn .3. In acute pain model, low frequency TENS greatly decrease c-fos expression than high frequency TENS. Therefore. decreasing the number of c-fos immunoreactive neurons which increased after capsaicin injection with application of TENS indicate that both of the TENS have inhibitory effect. In addition. low frequency TENS greatly decreased the number of neurons explains low frequency TENS is more effective than high frequency TENS in acute pain. This study also can become a part of scientific evidence on electrotherapy through measuring quantitively effects of TENS in pain model.

• 한국소음진동공학회논문집
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• 제21권5호
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• pp.447-454
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• 2011

This paper reports a filtered velocity feedback(FVF) controller, which is an alternative to direct velocity feedback(DVFB) controller. The instability problems due to high frequency response under DVFB can be alleviated by the suggested FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The FVF controller and the dynamics of clamped beams under forces and moments are first formulated. The effects of the design parameters(cut-off frequency, gain, and damping ratio) on the stability and the performance are then investigated. The cut-off frequency should be selected not to affect the system stability. The magnitude of the open loop transfer function(OLTF) at the cut-off frequency should be small. As increasing the gain of the FVF controller, the magnitude of the OLTF is increased, so that the closed loop response can be reduced more. The enhancement of the OLTF at the cut-off frequency is reduced but the phase behavior around the cut-off frequency is distorted, as the damping ratio is increased. The control performance is finally estimated for the clamped beam. More than 10 dB reductions in velocity response can be achieved at the modal frequencies from the first to eighth modes.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.264-270
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• 2011

This paper reports a filtered velocity feedback (FVF) controller, which is an alternative to direct velocity feedback (DVFB) controller. The instability problems due to high frequency response under DVFB can be alleviated by the suggested FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The FVF controller and the dynamics of clamped beams under forces and moments are first formulated The effects of the design parameters (cut-off frequency, gain, and damping ratio) on the stability and the performance are then investigated. The cut-off frequency should be selected not to affect the system stability. The magnitude of the open loop transfer function (OLTF) at the cut-off frequency should be small. As increasing the gain of the FVF controller, the magnitude of the OLTF is increased, so that the closed loop response can be reduced more. The enhancement of the OLTF at the cut-off frequency is reduced but the phase behavior around the cut-off frequency is distorted, as the damping ratio is increased The control performance is finally estimated for the clamped beam. More than 10dB reductions in velocity response can be achieved at the modal frequencies from the first to eighth modes.

• 한국정보과학회 언어공학연구회:학술대회논문집(한글 및 한국어 정보처리)
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• 한국정보과학회언어공학연구회 1999년도 제11회 한글 및 한국어 정보처리 학술대회
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• pp.351-358
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• 1999

범주화과제를 사용한 두 실험에서 단어 빈도가 단어의 의미를 처리하는데 영향을 주는지를 알아보았다. 두 실험에서 사용된 자극은 두 글자의 한글이었는데, 실험 1에서는 사례와 목표자극은 두 번째 글자의 종성에서만 달랐고(예, 범주: 관직: 사례: 시장; 목표자극: 시작), 실험 2에서는 첫 번째 글자의 종성에서만 달랐다(예, 범주: 관직: 사례: 시장; 목표자극: 심장). 실험 1에서는 통제자극보다 저빈도 목표자극의 오반응이 더 많았고, 고빈도 사례의 반응시간이 더 길었다. 실험 2에서는 고빈도 사례-저빈도 목표자극 조건이 통제조건보다 반응시간이 더 길었다. 이 결과는 이중경로모형(Jared & Seidenberg, 1991)을 지지한다고 볼 수 있다. 이 결과들은 음운 정보와 시각 정보의 사용은 단어의 빈도에 의존하며, 특히 음운정보의 활성화는 필연적인 과정이 아니라 선택적인 것을 시사한다.

• 소음진동
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• 제10권6호
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• pp.991-997
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• 2000

The objective of this study is to examine the onset condition and the frequency characteristics of the low-frequency combustion oscillation in a surface burner. For this purpose, extensive parametric studies have been performed experimentally and the effects of size of each section, the equivalence ratio, and the entrance velocity on oscillatory behavior explored. The experimental results were discussed in comparison with the other combustors associated tilth the low-frequency combustion oscillation. The combustion mode is driven at high combustion rate by the lift of unstable flame near the lower limit of the combustible equivalence ratio. The oscillation frequency is dependent not on the burner geometry but on the equivalence ratio and the combustion load. Low-frequency combustion mode was formed to be divided into two different modes, named C1 and C2 respectively. Two modes occurred individually, simultaneously or transitionally according to the equivalence ratio and combustion load. The characteristics of low-frequency oscillation is different from each other depending on the type of combustors. The surface burner has also its own characteristics of low -frequency oscillation.

• 대한기계학회논문집B
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• 제28권1호
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• pp.41-51
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• 2004

A direct numerical simulation is performed to analyze the effects of a localized time-periodic blowing on a turbulent boundary layer flow at R $e_{+}$=300. Main emphasis is placed on the blowing frequency effect on near-wall turbulent flow structures at downstream. Wall-normal velocity on a spanwise slot is varied periodically at different frequencies (0.004$\leq$ $f^{＋}$$\leq$0.080). The amplitude of periodic blowing is $A^{＋}$=0.5 in wall nit, which corresponds to the value of $v_{rms}$ at $y^{＋}$=15 without blowing. The frequency responses are scrutinized by examining the phase or time-averaged turbulent statistics. The optimal frequency ( $f^{＋}$=0.03) is observed, where maximum increase in Reynolds shear stress, streamwise vorticity fluctuations and energy redistribution occurs. The phase-averaged stretching and tilting term are investigated to analyze the increase of streamwise vorticity fluctuations which are closely related to turbulent coherent structures. It is found that the difference between PB and SB at a high blowing frequencies is negligible.e.e.

• 한국환경과학회지
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• 제33권5호
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• pp.333-343
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• 2024

This study aimed to investigate whether inhaling the aroma of essential oils could alleviate physiological stress responses and mimic the effects of forest therapy in urban settings. Briefly, 31 participants underwent stress index assessments for two days and inhaled the selected plant essential oils. The effects of this treatment on physiological responses were determined through electroencephalogram (EEG) and heart rate variability (HRV) measurements taken before and after inhaling the aroma of essential oils, extracting results for low frequency (LF) and high frequency (HF) components of HRV, as well as 𝜃 and 𝛼 brainwave activities. The results indicated that lavender oil did not yield significant differences, whereas pine, chamomile, and cypress oils exhibited significant differences in effects. Overall, stress relief was associated with enhanced 𝜃 and 𝛼 brainwave activities, a decrease in the LF component and an increase in the HF component of HRV. Among the essential oils studied, pine oil was the most effective. These findings underscore the potential of plant essential oils in replicating the therapeutic benefits of forest therapy, even in urban environments. Further investigations into their utilization are warranted to better understand and harness their therapeutic potential.