Fast Fourier Transform Results Research Articles

Fluctuations of DC atmospheric double arc argon plasma jet

An original DC double anode plasma torch has been devised and tested, which generates a long-time and highly stable argon plasma jet at atmospheric pressure. The arc unsteadiness and dynamic behaviour are investigated through the fluctuations of electrical signals combined with the classical tools, such as the statistic method, fast Fourier transform (FFT) and correlation analysis. The current–voltage characteristics of the argon plasma jet show an increasing tendency. The takeover mode is identified as the typical fluctuation behaviour of the double arc argon plasma jet in our experiment. The FFT and correlation calculation results of electrical signals exhibit the only characteristic frequency of 150 Hz, whereas the high frequency fluctuations are totally disappeared. Such low frequency fluctuation (150 Hz) can be attributed to the inherent characteristic of the torch power source and is independent of any change in the operating parameters. These results indicate that the nature of fluctuation in an argon plasma jet is mainly induced by the undulation of tri-phase rectified power supply. In addition, both arcs are characterized as the one and only system, and each arc root attachment is rather evenly diffused than located at a fixed position on the anode surface. The time shift derived from the cross correlation between the arc voltage and current intensity can be used as an independent parameter to reflect the fluctuating behaviour in the plasma jet.

Dynamic behaviour of dc double anode plasma torch at atmospheric pressure

An original dc double anode plasma torch which provides a long-time and highly stable atmospheric plasma jet has been devised for the purpose of hazardous waste treatment. The arc fluctuations and dynamic behaviour of the argon and argon–nitrogen plasma jets under different operating conditions have been investigated by means of classical tools, such as the statistic method, fast Fourier transform (FFT) and correlation analysis. In our experiments, the takeover mode is identified as the fluctuation characteristic of the argon plasma jet while the restrike mode is typical in the argon–nitrogen plasma dynamic behaviour. In the case of pure argon, the FFT and correlation calculation results of electrical signals exhibit the only characteristic frequency of 150 Hz, which originates from the torch power and is independent of any change in the operating conditions. It indicates that the nature of fluctuations in an argon plasma jet is mainly induced by the undulation of the tri-phase rectified power supply. In contrast, besides the same low frequency bulk fluctuation, the dynamic behaviour of the argon–nitrogen plasma jet at high frequency (4.1 kHz) is ascribed to the rapid motion of both arc roots on the anode surface. In addition, it is found that each arc root attachment is rather diffused than located at a fixed position on the anode wall in the argon plasma jet, while constricted arc roots occur when nitrogen is added into argon as the plasma working gas.

Chronic fatigue, unrefreshing sleep and nocturnal polysomnography

Background and purpose To investigate the complaint of unrefreshing sleep with study of sleep electroencephalogram (EEG) in patients with chronic fatigue. Patients and methods Fourteen successively seen patients (mean age: 41.1 9.8) who complained of chronic fatigue but denied sleepiness and agreed to participate were compared to 14 controls (33.6±10.2 years) who were monitored during sleep recorded in parallel. After performing conventional sleep scoring we applied Fast Fourier Transformation (FFT) for the delta 1, delta 2, theta, alpha, sigma 1, sigma 2, beta EEG frequency bands. The presence of non-rapid eye movement (NREM) sleep instability was studied with calculation of cyclic alternating pattern (CAP) rate. Two-way analysis of variance (ANOVA) was performed to analyze FFT results and Mann–Whitney U-test to compare CAP rate in both groups of subjects. Results Slow wave sleep (SWS) percentage and sleep efficiency were lower, but there was a significant increase in delta 1 (slow delta) relative power in the chronic fatigue group when compared to normals ( P<0.01). All the other frequency bands were proportionally and significantly decreased compared to controls. CAP rate was also significantly greater in subjects with chronic fatigue than in normals ( P=0.04). An increase in respiratory effort and nasal flow limitation were noted with chronic fatigue. Conclusions The complaints of chronic fatigue and unrefreshing sleep were associated with an abnormal CAP rate, with increase in slow delta power spectrum, affirming the presence of an abnormal sleep progression and NREM sleep instability. These specific patterns were related to subtle, undiagnosed sleep-disordered breathing.

190-m Heliox 해상 포화잠수에서의 수면패턴과 하루주기리듬

The purpose of this study is to examine sleep structure and circadian rhythmicity under the hyperbaric environment to obtain fundamental data so that a desirable sleep environment for divers may be organized using actigraphy. The total sleep time(TST), sleep period time(SPT), sleep efficiency(SE), sleep latency(SL), wake after sleep onset(WASO), number of awakenings(NA), length of daytime naps(LDN), and number of daytime naps(NDN) for 5 divers were measured over a period of 55 nights under a He O₂ open-sea hyperbaric saturation dive to 20 ATA with excursions to 21 ATA. The results of the one-way ANOVA, among the experimental days, showed significant effects in TST, SPT, SE, SL, LDN, and NDN. TST and SPT were significantly shortened in the bottom and decompression periods as opposed to the pre-dive period. SE showed the same tendency as TST. SL increased significantly from the bottom period through to the decompression period. WASO and NA with the LDN and NDN increased in the bottom and decompression periods. Individual time series were analyzed according to several statistical methods(autocorrelation function, Fast Fourier transform(FFT), and power spectrum analysis(PSA)) using wrist actigraphy, in order to estimate the prominent circadian period(tau = 24-h) and to evaluate each days differences. The autocorrelation function for the time series of each day showed significant circadian rhythmicity with circasemidian rhythmicity(tau = about 12-h) except the 1st day of the bottom period. The PSA for the time series of each day showed significant, about 25-h circadian rhythmicity with circasemidian rhythmicity, on the 1st, 2nd, and 5th days of the decompression period. The 2nd day of the bottom period showed a significant circadian rhythmicity with circasemidian rhythmicity, about 26-h. However, the remainder also showed significant circadian rhythmicity with circasemidian rhythmicity, about 24-h. The results of FFT showed similar changes to the autocorrelation function.

A sapphire fibre thermal probe based on fast Fourier transform and phase-lock loop

A sapphire fibre thermal probe with Cr3+ ion-doped end is developed by using the laser heated pedestal growth method. The fluorescence thermal probe offers advantages of compact structure, high performance and ability to withstand high temperature in a detection range from room temperature to 450°C. Based on the fast Fourier transform (FFT), the fluorescence lifetime is obtained from the tangent function of phase angle of the non-zeroth terms in the FFT result. This method has advantages such as quick calculation, high accuracy and immunity to the background noise. This FFT method is compared with other traditional fitting methods, indicating that the standard deviation of the FFT method is about half of that of the Prony method and about 1/6 of that of the log-fit method. And the FFT method is immune to the background noise involved in a signal. So, the FFT method is an excellent way of processing signals. In addition, a phase-lock amplifier can effectively suppress the noise.

Spectral analysis of heart rate variability: interchangeability between autoregressive analysis and fast Fourier transform

Interchangeability between fast Fourier transform (FFT) and autoregressive (AR) analysis was assessed on series of 256 R-R intervals recorded in 56 seated subjects and in 15 men performing an orthostatic test. Low- (LF) and high-frequency (HF) components were calculated and expressed both in absolute (square milliseconds) and normalized units (NU). During orthostatic stress, the same upward trend for LF square milliseconds and LF/HF ratio and downward trend for HF square milliseconds and HF NU were observed with FFT and AR analysis. However, the values for HF square milliseconds were significantly greater with FFT, as compared with AR analysis in standing position ( P < .05). Moreover, Bland & Altman method highlighted a large discrepancy between the results of FFT and AR analysis for all heart rate variability indices in the 3 conditions. Therefore, parametric and nonparametric spectral analyses could not be considered as interchangeable at rest in healthy subjects even if they give same qualitative results.

위상형 직선격자의 자체결상과 가시도 분석

위상형 직선격자에 가간섭 광원인 레이저 광을 조명하였을 때 이 격자가 렌즈없이 회절에 의하여 결상되는 자체결상 현상(또는 렌즈없는 결상)을 회절이론으로 해석하고 실험적으로 조사하였다. 위상형 격자의 위상분포가 강도분포로 바뀌면서 1:1 로 결상하는 자체결상거리( <TEX>$Z_{T,a}$</TEX>)를 진폭형 직선격자의 자체결상시 정의되는 자체결상거리 <TEX>$z_{T,a}$</TEX>를 이용하여(4n-3) <TEX>$z_{T,a}$</TEX>/4(n=양의 정수)와 같이 새로이 정의하였다. 실험적으로 <TEX>$z_{T,p}$</TEX>= <TEX>$z_{T,a}$</TEX>/4와 <TEX>$z_{T,p}$</TEX>=5 <TEX>$z_{T,a}$</TEX>/4에서 위상형 직선격자를 이용하여 자체결상거리에서 자체결상이 되는 것을 확인하였으며, <TEX>$z_{T,p}$</TEX>=3 <TEX>$z_{T,a}$</TEX>/4위치에서는 이 자체결상된 상의 위상이 반전되는 현상도 동시에 관찰하였다. 이러한 자체결상시 격자의 수에 따라 자체결상된 상의 가시도를 FFT(fast Fourier transform)로 처리하여 측정한 결과, 위상형 직선격자는 15 개 이상의 직선격자들로 구성되어야만 자체결상된 상의 가시도가 최대값 0.10 근처에서 일정하게 유지됨을 알 수 있었다.일정하게 유지됨을 알 수 있었다. The self-imaging effect or lensless imaging effect of a phase line grating is theoretically analyzed by using Fresnel diffraction theory, then experimentally investigated. The self-imaging distance <TEX>$z_{T,p}$</TEX>, that is the imaging distance being perfectly copied from the phase distribution of the phase grating to its intensity distribution with the magnification of 1X, can be uniquely defined as the (4n-3) <TEX>$z_{T,a}$</TEX>/4(n=positive integers), where rte is the well-known self-imaging distance of an amplitude grating. When the coherent laser beam is illuminated at the phase grating, the self-imaged images were obtained at <TEX>$z_{T,p}$</TEX>= <TEX>$z_{T,a}$</TEX>/4 and <TEX>$z_{T,p}$</TEX>=5 <TEX>$z_{T,a}$</TEX>/4 without any optics. On the other side, the phase-reversed self-imaging was obviously observed at <TEX>$z_{T,p}$</TEX> = 3 <TEX>$z_{T,a}$</TEX>/4. The visibility of self-imaged images of a phase line grating as a function of the number of slits of the input grating was measured by the FFT(Fast Fourier Transform) results of the self-imaging images. As a result a stationary maximum visibility of V = 0.10 can be obtained from a grating with more than 15 slit pairs.n 15 slit pairs.

Fast hydrogen elimination from the [Ru(PH3)3(CO)(H)2] complex in the first singlet excited states. A quantum dynamics study

Abstract The photodissociation dynamics of [Ru(PH 3 ) 3 (CO)(H) 2 ] complex in the lowest two singlet excited electronic states has been theoretically analyzed. Reduced two-dimensional potential energy surfaces (PES) are built up by combining a time-dependent method to calculate the excited states energy with DFT (B3LYP) electronic calculations of the ground state. By means of a Fast Fourier Transform (FFT) algorithm the time evolution of the wavefunction upon vertical transition from the minimum of the ground state to both diabatic states has been followed. The propagation in S 1 , the lowest in energy at the vertical transition point and the one with a larger transition probability from the ground state, discloses that the system is not evolving from the initial position at least in the time spanned by the calculations. Conversely the H 2 elimination is very fast (about 37 fs) in the S 2 state. In this state the vertical transition puts the system in a purely dissociative zone of the PES. In that state FFT results indicate that the lengthening of the Ru–H 2 distance and the shortening of the H–H one are taking place almost simultaneously.

Evaluation of deflections of the vertical on the sphere and the plane: a comparison of FFT techniques

This paper presents a set of efficient formulas to evaluate the deflections of the vertical on the sphere using gridded data. The Vening-Meinesz formula, the topographic indirect effect on the deflections of the vertical as well as the terrain corrections are expressed as both 2D and 1D convolutions on the sphere, and consequently can be evaluated by the 2D and the 1D fast Fourier transform (FFT). When compared with the results obtained from pointwise integration, the use of the 1D FFT gives identical results, and therefore these results were used as control values in this paper. The use of the spherical 2D FFT improves significantly the computational efficiency with little sacrifice of accuracy (0.6″ rms difference from the 1D FFT results). The planar 2D FFT, which is as efficient as the spherical 2D FFT, gives worse results (1.2″ rms difference from the 1D FFT results) because of the extra approximations.

Real-valued fast Fourier transform algorithms

This tutorial paper describes the methods for constructing fast algorithms for the computation of the discrete Fourier transform (DFT) of a real-valued series. The application of these ideas to all the major fast Fourier transform (FFT) algorithms is discussed, and the various algorithms are compared. We present a new implementation of the real-valued split-radix FFT, an algorithm that uses fewer operations than any other real-valued power-of-2-length FFT. We also compare the performance of inherently real-valued transform algorithms such as the fast Hartley transform (FHT) and the fast cosine transform (FCT) to real-valued FFT algorithms for the computation of power spectra and cyclic convolutions. Comparisons of these techniques reveal that the alternative techniques always require more additions than a method based on a real-valued FFT algorithm and result in computer code of equal or greater length and complexity.