• 한국결정학회지
• /
• 제11권4호
• /
• pp.200-206
• /
• 2000

In a 200 mm Cz-Si crystal, a macroscopic fluctuation in pulling rate was intentionally introduced then the variations of the pulling rate and the formation behaviors of grow-in defects were compared. The diameters of the OSF-ring and the FPD area were affected by the fluctuation in the region above 1100℃. The COP density depended on the diameter of the OSF-ring. ΔOi and BMD were affected by the fluctuation in the region near 1000Δ. As the result, when a macroscopic fluctuation in pulling rate is introduced, the quality of crystal in the region of 150 mm from the growth interface should be reviewed carefully because it can be affected by the fluctuation.

• International Journal of Fluid Machinery and Systems
• /
• 제9권3호
• /
• pp.237-244
• /
• 2016

An unsteady three-dimensional simulation based on Reynolds time-averaged governing equation and RNG $k-{\varepsilon}$ turbulence model, was presented for pump-as-turbine, the pressure fluctuation characteristic of hydraulic turbine with guide vane was obtained. The results show that the time domains of pressure fluctuation in volute change periodically and have identical cycles. In volute tongue and inlet pressure fluctuations are light, while in dynamic and static coupling interface pressure fluctuations are serious; In impeller blade region the pressure fluctuation of pressure surface are lighter than that of suction surface. The dominant frequencies of pressure fluctuation concentrate in low frequency region, and concentrate within 2 times of the blade passing frequency.

• International Journal of Fluid Machinery and Systems
• /
• 제10권3호
• /
• pp.307-317
• /
• 2017

In liquid-propellant rockets, POGO instability can occur, in which a fluctuation of propellant supply to the engine, a thrust fluctuation, and a structural vibration are coupled. For the prediction of this instability, it is required to provide dynamic characteristics of the pump represented as the transfer matrix correlating the upstream and downstream pressure and flow rate fluctuations. In the present study, the flow rate fluctuation is evaluated from the fluctuation of pressure difference at the different locations assuming that the fluctuation is caused by the inertia of the flow rate fluctuation. The experiments were performed in some flow conditions, and it was shown that the tendencies of dynamic characteristics are related to excitation frequencies, cavitation numbers and flow rate coefficients.

• 감성과학
• /
• 제18권3호
• /
• pp.63-70
• /
• 2015

본 연구는 1/f fluctuation의 ${\alpha}$기울기 따라 구성된 사운드를 들었을 때 감정 스트레스 업무에 종사하고 있는 피험자들의 심박 변화를 확인하고자 하였다. 기존의 연구에서는 주로 사용자의 심리상태 안정시키는 효과 또는 생리적 안정성에 1/f fluctuation의 ${\alpha}$기울기가 관계가 있는 것으로 보고되었다. 본 연구에서는 1/f fluctuation 수준을 총 3가지 나누어 제작한 사운드를 독립변수로 사용하였다. 독립변수는 감정노동 종사자에게 제시하여 그에 따른 심장반응을 측정하였다. 종속변수는 네 가지로 BPM(Beat Per Minute), VLF(Very Low Frequency), SDNN(Standard Deviation of NN intervals), 그리고 HF(High Frequency) 파워(Power)값을 확인하였다. 분석결과 기울기가 3인 1/fluctuation 사운드는 각성효과를 보였다. 기울기 1, 2인 사운드는 이완효과가 있는 것을 통계적으로 검증하였다. 이러한 1/f fluctuation 사운드의 특성을 활용해 감정 노동자들의 스트레스를 완화시키기 위한 서비스에 응용될 수 있을 것으로 사료된다.

• 상하수도학회지
• /
• 제21권4호
• /
• pp.485-491
• /
• 2007

The fluctuation of inlet flow to a water treatment plant makes a serious problem that it can change the filtration rate abruptly, and ultimately occur the breakthrough of the detained particles inside filter media. Also, since it takes very short time (about 10 minutes) for the surface wave occurred from the fluctuation of inlet flow to reach the filtration process, it is impossible to control the filtration rate stably. Therefore, this study was conducted to evaluate the effect of daily flow-rate fluctuation on the performance of sand filtration process, and to suggest the dual media composition for coping with that effect. Comparative column tests have been carried out for various dual media (sand and anthracite) compositions. From the results of column tests, dual media, especially in the case of sand 45cm/anthracite 30cm, is more effective to cope with the effect of flow-rate fluctuation on the performance of filtration than single media (only sand). In addition, irrespective of dual media composition, managing ability to cope with that fluctuation tends to be weak at the end of allowable filtration duration time,

• 설비공학논문집
• /
• 제24권5호
• /
• pp.433-442
• /
• 2012

The influence of outdoor sky conditions on photosensor signals were examined to determine an appropriate index that is effectively used for optimum illuminance fluctuation when a daylight dimming system is used for a small office. Field measurements were conducted under various sky conditions. Results indicate that the outdoor global and vertical illuminance fluctuated within narrow ranges under clear and overcast sky conditions. The fluctuation of sky ratio under partly-cloudy sky caused wide ranges of illumnance fluctuation. A partially-shielded photosensor at backwall produced 56% of light output from fixtures controlled by a photosensor at ceiling. This implies that the photosensor at backwall does not always guarantee target illuminance due to the less output. The fluctuation of light output from fixtures were insignificant under clear and overcast sky. The fluctuation range of photosensor illuminance under partly-cloudy sky caused wide fluctuation ranges of light output. Regression result implies that the outdoor vertical illuminance was recommended for an effective index that is used for control of light output.

• 한국광학회:학술대회논문집
• /
• 한국광학회 1990년도 제5회 파동 및 레이저 학술발표회 5th Conference on Waves and lasers 논문집 - 한국광학회
• /
• pp.242-247
• /
• 1990

By self-homodyne method we measured the relative phase fluctuation of a light wave. Balanced detection system can eliminate local oscillator excess noise and multiport detection makes it possible ot measure the phase change of the signal beam. Deriving the SB(Signal Beam) and the LO(Local Oscillator) from the same laser source, we find the SB maintain constant phase relative to that of the LO. We have introduced a phase fluctuation in the SB by modulating the beam path of the SB. The measured phase fluctuation agreed well with the predicted one, thereby we confirmed the reliability of our system.

• 대한전자공학회논문지TC
• /
• 제48권1호
• /
• pp.1-8
• /
• 2011

본 논문에서는 수조 실험을 통해 수중 다중경로 채널의 수면변동과 지연확산이 텍스트 전송성능에 미치는 영향 확인하였다. 수면변동과 지연확산은 채널의 코히어런스 대역폭을 제한하는 요인으로 수중음향 통신의 전송성능을 제한한다. 잔잔한 수면과 교란하는 수면에 따른 응답특성 실험결과에서 수면 반사파의 진폭변동과 지연확산 특성을 확인하였다. 각각의 지연확산 유효치는 각각 5ms, 4ms로 그에 대응하는 코히어런스 대역폭은 200Hz, 250Hz였다. BFSK (Binary Frequency Shift Keying) 방식을 이용한 수중 텍스트 전송성능에서 지연확산에 따른 채널의 코히어런스 대역폭 제한으로 인해 잔잔한 수면인 경우 200bps이하에서 $10^{-4}$, 교란하는 수면인 경우 250bps 이하에서 $10^{-4}$으로 오류율이 나타났다. 따라서 본 실험을 통해 수중 다중경로 채널에서 수면변동에 의한 코히어런스 대역폭 제한용 수중음향 통신의 전송성능을 결정하는 중요한 요인임을 확인하였다.

• 생물정신의학
• /
• 제16권2호
• /
• pp.69-75
• /
• 2009

Objectives : The detrended fluctuation analysis is one of the nonlinear methods for the investigation of biological time series. It quantifies the fractal scaling properties and is known to be useful in the evaluation of long-range correlations in time series. The heart rate variability(HRV) of obstructive sleep apnea syndrome (OSAS) patients during nighttime was analyzed by detrended fluctuation analysis to assess its relationship with the severity of the symptoms. Methods : Fifty nine untreated male OSAS patients with moderate to severe symptoms(mean age=45.4${\pm}$11.7 years, apnea-hypopnea index, AHI${\geq}$15) underwent nocturnal polysomnography. Moderate(AHI=15-30, N=22) and severe(AHI>30, N=37) OSAS patients were compared for the indices derived from detrended fluctuation analysis and frequency domain analysis of HRV. Results : In the detrended fluctuation analysis, the alpha values were 0.75${\pm}$0.11 and 0.82${\pm}$0.07 for the severe and the moderate OSAS groups respectively. The difference was significant(p<.01). The alpha value had negative correlation with AHI(r=-.425, p=.001). Negative correlation coefficients were also found in the relationships between the alpha values and very low frequency(VLF)(r=-.425, p=.001), low frequency(LF)(r=-.633, p= <.001) and the LF/HF ratio(r=-.305, p=.019) respectively. LF/HF ratio(p=.005) was higher in the severe OSAS group compared to that of the moderate OSAS group. Conclusion : In this study, the detrended fluctuation analysis showed the significant difference between the two OSAS groups classified according to their severity of symptoms. The scaling exponent showed the negative correlation with AHI and indicies of frequency domain analysis. This result suggests that detrended fluctuation analysis can be helpful to estimate the severity of OSAS.

• International Journal of Fluid Machinery and Systems
• /
• 제7권2호
• /
• pp.42-53
• /
• 2014

Phase resonance in Francis type hydraulic turbine is studied. The phase resonance is a phenomenon that the pressure fluctuation in the penstock of hydraulic turbine installation can become very large when the pressure waves from each guide vane caused by the interaction with the runner vane reach the penstock with the same phase. Experimental and numerical studies have been carried out using a centrifugal fan. In the present study, comparisons between the pump mode and the turbine mode operations are made. The experimental and numerical results show that the rotational direction of the rotor does not affect characteristics of the pressure fluctuation but the propagation direction of the rotorstator interaction mode plays an important role. Flow rate fluctuations through the stator are examined numerically. It has been found that the blade passing flow rate fluctuation component can be evaluated by the difference of the fluctuating pressure at the inlet and the outlet of the stator. The amplitude of the blade passage component of the pressure fluctuation is greater at the stator inlet than the one at the stator outlet. The rotor-stator interaction mode component is almost identical at the inlet and the outlet of the stator. It was demonstrated that the pressure fluctuation in the volute and connecting pipe normalized by the flow rate fluctuation becomes the same for pump and turbine mode operations, and depends on the rotational direction on the interaction mode.