• Title/Summary/Keyword: 500 kHz

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Flame Interaction with Shear Layer Flow in the Post Chamber of Hybrid Rocket (하이브리드 로켓 후연소실 전단유동과 연소반응의 상호 간섭)

  • Moon, Young Joo;Lee, Changjin
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.44 no.7
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    • pp.585-592
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    • 2016
  • Visualization was done by using $CH^*$ chemiluminescence images and PMT measurements in order to understand the origin of fluctuating pressure and chemical luminosity at about 500 Hz frequency even in stable combustion, which was observed in recent experimental tests, and to find the physical correlation leading to Low Frequency Instability(LFI) in terms of phase angle. In stable combustion, chemical reactions are distributed along the shear layer flow showing a negative coupling(about 180 degree in phase angle) with combustion pressure. However, phase difference is shifted to a positive coupling showing less than 90 degree in unstable case. Also a periodic change in the distribution of chemical reactions is observed along with local flame extinction and the appearance of big scale vortex flow. In the transition to LFI, local flame extinction and small vortex flow start to appear in a row. As seen in the bluff body wake in reactive flow, the periodic appearance of vortex flow seems to share the same physical process of BVK(Bernard Von Karman) instability generation. Thus, the appearance of local extinction in 500 Hz fluctuations is gradually amplified to complete extinctions of about 20 Hz, and it leads into LFI.

Effect of Sintering Conditions on the Electromagnetic Properties of Mn-Zn Ferrites (소결조건이 Mn-Zn Ferrites의 전자기적 물성에 미치는 효과)

  • 최윤호;신명승;한승기;한영호
    • Journal of the Korean Ceramic Society
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    • v.34 no.6
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    • pp.561-568
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    • 1997
  • The effects of sintering temperature and oxygen partial pressure on the electromagnetic properties of Mn-Zn ferrites were investigated. The grain increased with increasing temperature. The power loss at 100 kHz was decreased, while the power loss at 500 kHz was increased as the grain size increased with sintering temperature. Sintering with low oxygen partial pressure at 115$0^{\circ}C$ resulted in high density and initial permeability, and decreased the power loss at 100 kHz and 500 kHz. The oxygen partial pressure lower than 10-2 atm. during heating, significantly suppressed the hysteresis loss. However, the oxygen activity did not affect the grain size of sintered cores.

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A Basic Study on Acoustic Conditioning of Fish Suitable for a Marine Ranch -1. The Sound Sensitivity of Japanese Parrot Fish Oplegnathus fasciatus- (해양목장 대상 어류의 음향순치에 관한 기초적 연구 -1. 돌돔의 청각 특성-)

  • Kim Seong Ho;Lee Chang Heon;Seo Du Ok;Kim Yong Ju
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.35 no.6
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    • pp.563-567
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    • 2002
  • Developing base data on luring fish schools into netting position by the use of underwater audible sound on japanese parrot fish Oplegnathus fasciatus found in the coastal waters of Jeju Island, S. Korea. Auditory threshold was determined by the heartbeat condition technique using pure tones coupled with a delayed electric shock. The audible range of japanese parrot fish extended from 80 Hz to 500 Hz with a peak sensitivity at 200 Hz. The mean auditory thresholds at the frequencies of 80 Hz, 100 Hz, 200 Hz,300 Hz and 500 Hz were 104 dB, 95 dB, 91 dB, 99 dB and 113 dB, respectively. As the frequency became higher than 200 Hz, the auditory threshold increased almost linearly with increasing frequency. Critical ratios of fishes measured in the presence of masking noise in the spectrum level range of 69$\~$78 dB (0 dB re 1$\mu$Pa/$\sqrt{Hz}$) ranged from 21 dB to 40 dB at test frequencies. The noise spectrum level at the start of masking was about 70 dB within the test frequency range. The sound pressure level of 100$\~$200 Hz recognized by japanese parrot fish under the ambient noise is above 91 dB and the critical ratio for them is above 21 dB.

Influence of stress and pure tone audiometry on noise-exposed dental laboratory technicians by dental instrument (치과기공 소음 노출이 치기공과 학생의 스트레스와 순음청력에 미치는 영향)

  • Yon, Jung-Min;Lee, Ju-Hee;Kim, Dae-Hyun;Lee, Og-Kyoung
    • Journal of Digital Convergence
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    • v.14 no.4
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    • pp.363-370
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    • 2016
  • Noise is unwanted sound that is the reason of the stress and hearing loss. The current study attempted to estimate whether the noise of dental laboratory affected stress and pure tone audiometry (PTA) of dental laboratory technicians (DLTs) using heart rate variability, air and bone conduction audiometry. The age, heights, and weights of DLTs were resembled control. Standard deviation of normal to normal interval such as stress resistance and normalized HF of DLTs were significantly decreased, but heart rates, normalized LF, and LF/HF ratio of DLTs were significantly increased compared with control. In air conduction audiometry of DLTs, significant increments of thresholds encountered in 125, 250, 500, 1000, 2000, 3000, 4000, and 6000 Hz in the right ears and 125, 250, 500, 1000, and 2000 Hz in the left ears. Thresholds of bone conduction audiometry in both ears were significantly increased in 250, 500, 1000, 2000, and 4000 Hz. The findings in this study provide that stress and hearing loss observed in noise-exposed DLTs at dental laboratory. Therefore, proper safety precautions should be carried out at dental laboratory.

Vibration Source Identification of Agricultural Machinery Using Coherence Function (기여도함수를 이용한 농업기계의 소음원 규명)

  • 김우택;오재응
    • Journal of Biosystems Engineering
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    • v.26 no.6
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    • pp.503-508
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    • 2001
  • In this paper, time-fiequency analysis and multi-dimensional spectral analysis methods are applied for source identification and diagnosis of non-stationary sound/vibration signals. Sound or vibration problems of general vehicle and agricultural machinary are under 500 Hz. So We used linearly increased chirp signals under 500 Hz. By checking the coherences on concerned time, fur time-variant non-stationary signals, this simulation it very well coincident to expected results.

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Co-Fe-B 자왜변환기를 이용한 간섭계형 광섬유 자계센서의 동작특성

  • 이경식
    • Korean Journal of Optics and Photonics
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    • v.4 no.4
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    • pp.474-479
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    • 1993
  • An interferometric fiber-optic magnetic field sensor is constructed by bonding a Co-Fe-B metallic glass transducer developed here by the melt-spun method to a single mode fiber arm in the fiber Mach-Zehnder interferometer and is tested. The bias field for the peak ac-sensitivity was observed near 0.97 Oe and the minimum detectable magnetic field was 3.9${\times}10^{-5}$ Oe(rms)/${\sqrt{Hz}}$ a 3 kHz. The output of the ac field sensor becomes saturated near the input signal level of 1 Oe(rms). The Co- Fe-B transducer exhibits peak response near 500 Hz.

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Application of AMDF for Improvement of algorithm in estimation sytem of speech source (음원위치 추정 시스템에서 속도향상을 위한 AMDF의 적용)

  • 송도훈
    • Proceedings of the Acoustical Society of Korea Conference
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    • 1998.06d
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    • pp.64-67
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    • 1998
  • 원격지간 화상회의 시스템에서 화자의 위치에 따른 카메라 제어를 위해서는 마이크로폰 배렬(Microphone Array)로 수음한 음성신호에 대해 각 마이크로폰간의 빠른 지연시간 추정이 요구된다. 본 연구에서는 음원위치 추정을 위한 지연시간(Time delay) 계산을 위해 AMDF(Average Magnitude Difference Function)를 적용하여 연산시간을 단축시키는데 목적을 두고 있다. 기본의 상호상관함수 (Cross-correlation )알고리즘 과 본 연구에서 적용한 AMDF 알고리즘을 비교하기 위해 SNR 10dB 와 20dB 인 200Hz, 500Hz, 1kHz, 2kHz의 정현파 합성신호와 단음절 음성신호에 대해 시뮬레이션을 행하였다. 시뮬레이션 결과 AMDF 알고리즘의 정확한 지연시간 추정을 확인하였다.

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Bioelectrical Impedance Analysis at Popliteal Regions of Human Body using BIMS

  • Kim, J.H.;Kim, S.S.;Kim, S.H.;Baik, S.W.;Jeon, G.R.
    • Journal of Sensor Science and Technology
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    • v.25 no.1
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    • pp.1-7
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    • 2016
  • Bioelectrical impedance (BI) at popliteal regions was measured using a bioelectrical impedance measurement system (BIMS), which employs the multi-frequency and the two-electrode method. Experiments were performed as follows. First, a constant AC current of $800{\mu}A$ was applied to the popliteal regions (left and right) and the BI was measured at eight different frequencies from 10 to 500 kHz. When the applied frequency greater than 50 kHz was applied to human's popliteal regions, the BI was decreased significantly. Logarithmic plot of impedance vs. frequency indicated two different mechanisms in the impedance phenomena before and after 50 kHz. Second, the relationship between resistance and reactance was obtained with respect to the applied frequency using BI (resistance and reactance) acquired from the popliteal regions. The phase angle (PA) was found to be strongly dependent on frequency. At 50 kHz, the PA at the right popliteal region was $7.8^{\circ}$ slightly larger than $7.6^{\circ}$ at the left popliteal region. Third, BI values of extracellular fluid (ECF) and intracellular fluid (ICF) were calculated using BIMS. At 10 kHz, the BI values of ECF at the left and right popliteal regions were $1664.14{\Omega}$ and $1614.08{\Omega}$, respectively. The BI values of ECF and ICF decreased sharply in the frequency range of 10 to 50 kHz, and gradually decreased up to 500 kHz. Logarithmic plot of BI vs. frequency shows that the BI of ICF decreased noticeably at high frequency above 300 kHz because of a large decrease in the capacitance of the cell membrane.

Study for Dynamic Characteristics of the Accelerometer Mounting Fixtures (가속도계 고정기구의 동특성에 대한 연구)

  • Lee, Jong-Kyu;Kim, Sung-Boo;Lee, Doo-Hee;Bae, Dong-Myung;Shin, Chang-Hyuk;Cho, Seung-Il
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.17 no.4 s.121
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    • pp.350-355
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    • 2007
  • Accelerometer mounting fixtures were prepared with the different materials(Ti and SUS). The dynamic characteristics of the mounting fixture were analyzed by finite element method(FEM), and the mode shape of each order and the displacement response for modelling the mounting fixture were analyzed by ANSYS, then resonant frequencies of the mounting fixtures with Ti and SUS were 22.700 and 23.390 kHz, respectively. The dynamic characteristics of the mounting fixture with the different positions were obtained by using laser interferometer. The response of the accelerometer was nearly a constant from 40 Hz to 500 Hz, but the change of the acceleration was increased with an increase of the frequency above 500 Hz.

Dielectric Characteristics of EVA and LLDPE Films (에틸렌비닐아세테이트와 선형저밀도폴리에틸렌 박막의 유전특성)

  • 성민우;고시현;신종열;이충호;조경순;홍진웅
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2000.07a
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    • pp.783-786
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    • 2000
  • In this paper, physical properties and dielectric characteristics of LLDPE and EVA which are used as a blending material to improve PE's performance are studied. LLDPE of 0.92[g/cm3] and EVA with the EVA contents of 12.5[%1 were selected as specimens, and X-ray diffraction(XRD) are used to analysis physical properties. We measured dielectric constant with the frequency range from 20[Hz] to 1 [MHz], applied voltage 6[V] and the temperature from 25[$^{\circ}C$] to 110[$^{\circ}C$]. From XRD, LLDPE has a crystallinity of 53[%] and, 46[%] for EVA. LLDPE has as low tan$\delta$ as of 10$^{-3}$ ~10$^{-4}$ and inflection point near 500[Hz]. At frequency region lower than 500[Hz], tan$\delta$ decreases with frequency and increases with temperature and it is considered to be caused by conductive carriers within specimen. Over 500[Hz], it is the reverse and we thought that it was caused by decrease of relaxation time due to Debye theory, EVA has tan$\delta$with the values of 10$^{-2}$ ~10$^{-3}$ , which is higher than that of LLDPE, and it has inflection point at 60[Hz]. It is shown that Dielectric characteristics of EVA are similar to LLDPE's.

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