• Title/Summary/Keyword: low frequency

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Efficacy of Low Frequency Stimulator in Patients with Frozen Shoulder (오십견 환자의 치료에 있어서 저주파자극기의 효과)

  • Lim, Yun Hee;Lee, Pyung Bok;Seo, Myung Sin;Park, Sang Hyun;Oh, Yong Seok;Park, Ji Hyun
    • The Korean Journal of Pain
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    • v.18 no.2
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    • pp.156-160
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    • 2005
  • Background: Frozen shoulder is not an uncommon disease, which is associated with chronic pain and joint movement limitation. However, there are numerous devices to assist in the treatment of shoulder pain, but their efficacy has not been proven and their use remains immensely controversial. Therefore, a randomized clinical study was conducted to determine the effectiveness of a low-frequency stimulator for the treatment of frozen shoulder. Methods: A randomized clinical trial was carried out on 40 patients with frozen shoulder, with 40 patients assigned to two groups; a control treatment group (group C, n = 20) and a low frequency stimulator application group (group T, n = 20). Both groups were given a routine treatment modality, such as trigger point injection, intramuscular stimulation or suprascapular nerve block etc. The level of the shoulder pain was evaluated using a 100mm VAS (visual analog scale) at each visit, with the limitation in the range of motion simultaneously evaluated. Results: All the subjects improved after treatment, with the VAS scores after termination of treatment showed a statistically significant reduction (P < 0.05). However, there was no significant difference between the two groups. One month after termination of 5 cycles of treatment, group T maintained their improved state, whereas the pain in some of those in group C reemerged, which also showed a statistically significant difference (P < 0.05). The limitation in the range of motion improved, with most subjects able to resume daily activity. Conclusions: Although the low frequency stimulation provided no more pain relief than routine treatment, the effect was significantly prolonged. From this result, low frequency stimulation can be considered to aide the therapeutic effect of classical frozen shoulder therapy.

Low frequency Instability in Hybrid Rocket Post-chamber Configuration (연소실 형상 변화에 의한 하이브리드 로켓의 저주파수 연소불안정)

  • Park, Kyungsu;Lee, Changjin
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.42 no.1
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    • pp.29-36
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    • 2014
  • Hybrid rocket displays many different low frequency pressure oscillations during combustion. Thermal lag between solid and gas phase is the primary mechanism to trigger low frequency pressure oscillations of around 10Hz, and Helmholtz or $L^*$ mode also produces other types of low frequency oscillations above 10 Hz which is associated with the change in combustion volume. Since the flow characteristics in hybrid rocket is very similar to those in solid rocket combustion, it is not surprising to observe similar pressure oscillation behaviors. Experimental test shows that combustion pressure suddenly turns into to a big amplitude oscillation around 10Hz then followed by returning to an original pressure level after a short period combustion. Further investigations show that this instability is independent of the change in O/F ratio at all. One of the possible candidates is the vortex shedding dynamics over the backward step in the post combustion chamber. It is required to investigate the low frequency oscillation mechanism in the future study.

Time Domain Prediction and Analysis of Low Frequency Noise from Wind Turbine using Hybrid Computational Aeroacoustics (CAA) Method (복합 전산 공력음향학(CAA) 방법을 이용한 시간영역 풍력터빈 저주파수 소음 예측과 분석)

  • Lee, Gwang-Se;Cheong, Cheolung;Kim, Hyung-Taek;Joo, Won-Ho
    • The Journal of the Acoustical Society of Korea
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    • v.32 no.5
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    • pp.369-376
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    • 2013
  • Using Lowson's acoustic analogy, low frequency noise of a wind turbine (WT) is predicted in time domain and the noise sources contributing to the low frequency noise is analyzed. To compute averaged pressure distribution on blades of the WT as noise source, XFOIL is utilized. The blade source domain is divided into several segments along the span direction to compute force exerted on air surrounding the blade segments, which is used as input for noise prediction. The noise sources are decomposed into three terms of force fluctuation, acceleration and velocity terms and are analyzed to investigate each spectral contribution. Finally, predicted spectra are compared with measured low frequency noise spectrum of a wind turbine in operation. It is found that the force fluctuation component contributes strongly in low frequency range with increasing wind speed.

Low Flow Frequency Analysis of Steamflows Simulated from the Stochastically Generated Daily Rainfal Series (일 강우량의 모의 발생을 통한 갈수유량 계열의 산정 및 빈도분석)

  • Kim, Byeong-Sik;Gang, Gyeong-Seok;Seo, Byeong-Ha
    • Journal of Korea Water Resources Association
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    • v.32 no.3
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    • pp.265-279
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    • 1999
  • In this study, one of the techniques on the extension of low flow series has been developed, in which the daily streamflows were simulated by the Tank model with the input of extended daily rainfall series which were stochastically generated by the Markov chain model. The annual lowest flow serried for each of the given durations were formulated form the simulated daily streamflow sequences. The frequency of the estimated annual lowest flow series was analyzed. The distribution types to be used for the frequency analysis were two-parameter and three-parameter log-normal distribution, two-parameter and three-parameter Gamma distribution, three-parameter log-Gamma distribution, Gumbel distribution, and Weibull distribution, of which parameters were estimated by the moment method and the maximum likelihood method. The goodness-of-fit test for probability distribution is evaluated by the Kolmogorov-Sminrov test. The fitted distribution function for each duration series is applied to frequency analysis for developing duration-low flow-frequency curves at Yongdam Dam station. It was shown that the purposed technique in this study is available to generate the daily streamflow series with fair accuracy and useful to determine the probabilistic low flow in the watersheds having the poor historic records of low flow series.

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Thin Film Multijunction Thermal Converter for Low Input Voltage with Low Frequency (저주파수 및 저입력전압용 박막형 다중접합 열전변환기)

  • Hwang, Chan-Soon;Lee, Hyung-Ju;Kim, Jin-Sup;Lee, Jung-Hee;Park, Se-Il;Kwon, Sung-Won
    • Journal of Sensor Science and Technology
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    • v.11 no.3
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    • pp.145-154
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    • 2002
  • NiCr-heaters with three different thicknesses ranging from 400 nm to 800 nm were fabricated and their characteristics were compared for the purpose of developing a chromel-alumel multijunction thermal converter for low input voltage with low frequency. The thermoelectric effect-induced AC-DC voltage transfer difference of the thermal converter with a built-in NiCr-heater of 400 nm-thickness was ${\pm}0.51{\sim}1.69\;ppm$ in the DC reversing frequency of $40\;Hz{\sim}10\;kHz$ with appling $0.5\;V_{rms}$ and the difference was increased to ${\pm}40{\sim}{\pm}115\;ppm$ in the frequency of $40\;Hz{\sim}1\;MHz$, when both thermoelectric effects and frequency effects were considered, showing the thermal converter would be suitable for the low input voltage application with low frequency.

A frequency Domain based High Resolution Positioning Method using Low Rate ADC in LR-WPAN (LR-WPAN에서 저속 ADC를 이용한 주파수 영역상의 고해상 무선 측위 기법)

  • Lee, Won-Cheol;Park, Woon-Yong;Hong, Yun-Gi;Choi, Sung-Soo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.34 no.2C
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    • pp.145-152
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    • 2009
  • Ultra-wideband communication systems for impulse radio have merits that are possible for either high resolution ranging system or radio determination. Conventionally, in order to accomplish these functions, the rapid analog to digital convertor (ADC) is necessary to apply radio determination system operating in time domain. However, considering that low rate - wireless personal area network (LR-WPAN) aims to low-cost hardware implementation, the expensive ADC converting GHz sampling per second is not appropriate. So, this paper introduces the high resolution ranging system operating in frequency domain with using low sampling rate ADC, and a new non-coherent ranging scheme utilizing analog Frequency Modulation (FM) mode for the frequency domain transformation. To verify the superiority of the proposed ranging algorithm working in frequency domain, the suggested IEEE 802.15.4a TG channel model is used to exploit affirmative features of the proposed algorithm with conducting the simulation results.

Low-Frequency Active Echo Reduction Using a Tile Projector (타일형 프로젝터를 이용한 저주파 능동 반향음 감소 기법)

  • Lee, Jae-Wan;Woo, Sangbeom;Jang, Hada;Lee, Keunsang;Kim, Wan-Gu;Kang, Hwi-Suk;Ohm, Won-Suk;Park, Youngcheol;Yoon, Suk Wang;Seo, Youngsoo
    • The Journal of the Acoustical Society of Korea
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    • v.33 no.6
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    • pp.366-374
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    • 2014
  • With the advent of submarine detection technology using low-frequency active sonar there is a call for a new submarine stealth device that can replace the existing passive anechoic tiles. Proposed in this study is a low-frequency echo reduction technique based on active impedance matching, which employs a tile projector designed to cover a wide area such as the surface of a ship. To judge the feasibility of the active impedance matching technique finite-element simulations of low-frequency echo reduction are performed. Based on the analysis, a tile projector is designed, fabricated, and tested in an acoustic tank for its low-frequency echo reduction performance.

An Experimental Study on Estimation of Size and Thickness of Cavitation(Void)s under Concrete Slabs and Tunnel Linings Using Law Frequency Type Radar(GPR) (저주파수 레이더(GPR)에 의한 콘크리트 상판 및 터널 라이닝 배면 공동의 크기 및 두께 추정에 관한 실험 연구)

  • Park, Seok-Kyun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.10 no.6
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    • pp.95-104
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    • 2006
  • The presence of cavitations under pavements or behind tunnel linings of concrete is likely to result in collapse. One method of detecting such voids by non-destructive means is low frequency type radar(GPR). By the way, the size and thickness of small cavitation can't be detected by the present radar technology with low frequency and low resolution when it apply to civil structures like that. To overcome these problems and limitations, this study aims to develope and propose a new analysis method for estimating the depth, cross-sectional size and thickness of cavitations using low frequency radar. A new proposed method is based on the experiments that are carried out for analyzing the correlation between the measurement values(the amplitudes of radar return) of low frequency radar and various type of cavitations. In this process, the threshold value for radar image processing which aims to represent only cavitations to be fitted size can be obtained. As the results, it is clarified that a proposed method has a possibility of estimating cavitation depth, size and thickness with good accuracy in laboratory scale.

Evaluation of Growth Inhibition for Microcystis aeruginosa with Different Frequency of Ultrasonic Devices (초음파 장치의 주파수 변화에 따른 Microcystis aeruginosa의 성장억제 평가)

  • Jang, So Ye;Joo, Jin Chul;Kang, Eun Byeol;Ahn, Chae Min;Park, Jeongsu;Jeong, Moo Il;Lee, Dong Ho
    • Ecology and Resilient Infrastructure
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    • v.8 no.3
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    • pp.143-153
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    • 2021
  • The growth inhibition effects of M. aeruginosa were verified using large volume (7.2 L) of algae samples and ultrasonication (high frequency of 1.6 MHz vs. low frequency of 23 kHz) in lab-scale experiment. The chlorophyll-a (chl-a) and cell number decreased gradually after 6 hr sonication with high frequency of 1.6 MHz whereas both decreased sharply after 6 hr sonication with low frequency of 23 kHz. Additionally, the first order degradation coefficient (k) values after sonication were greater than those during sonication. These results indicate that relatively low sonication energy per volume may affect the cell membrane and internal organs of M. aeruginosa in a slow and retarded manner and resulted in gradual decrease of cell numbers of M. aeruginosa. Based on the comparison of chl-a and cell number of M. aeruginosa after sonication, low frequency of 23 kHz is superior for growth inhibition of M. aeruginosa, since low frequency of 23 kHz easily penetrates the cell membrane and ruptures the internal organs including gas vesicles. As is evident in SEM and TEM images, ruptured cell membranes were clearly observed for low frequency of 23 kHz. Finally, the microcystin-LR in water is not detected and considered to be harmless in aquaculture systems.

Dynamic Characteristics of an Unsteady Flow Through a Vortex Tube

  • Kim, Chang-Soo;Sohn, Chang-Hyun
    • Journal of Mechanical Science and Technology
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    • v.20 no.12
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    • pp.2209-2217
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    • 2006
  • Dynamic flow characteristics of a counter-flow vortex tube is investigated using hot-wire and piezoelectric transducer (PZT) measurements. The experimental study is conducted over a range of cold air outlet ratios (Y=0.3, 0.5, 0.7, and 1.0) and inlet pressure 0.15 MPa. Temperatures are measured at the cold air outlet and along the vortex tube wall. Hot-wire is located at cold outlet and PZT is installed at inner vortex tube by mounting at throttle valve. The cold outlet temperature results show that the swirl flow of vortex tube is not axisymmetric. The hot-wire and PZT results show that there exist two distinct kinds of frequency, low frequency periodic fluctuations and high frequency periodic fluctuations. It is found that the low frequency fluctuation is consistent with the Helmholtz frequency and the high frequency fluctuation is strongly related with precession oscillation.