Frequency Domain

This paper is devoted to a discussion of the Discrete Fourier Transform (DFT) representation of a chaotic finite-duration sequence. This representation has the advantage that is itself a finite-duration sequence corresponding to samples equally spaced in the frequency domain. The Fast Fourier Transform (FFT) algoritm allows us an effective computation, and it can be applied to a relatively short time series. DFT representation requirements were analized and applied for determining the order-chaos transition in a nonlinear system described by the equation $x[n+1]=rx[n](1-x[n])$. Its effectiveness was demonstrated by comparing the results with those obtained by calculating the largest Lyapounov exponent for the time series set, obtained from the logistic equation.

Wave propagation in a double negative (DNG) medium, i.e., a medium having negative permittivity and negative permeability, is studied both analytically and numerically. The choices of the square root that leads to the index of refraction and the wave impedance in a DNG medium are determined by imposing analyticity in the complex frequency domain, and the corresponding wave properties associated with each choice are presented. These monochromatic concepts are then tested critically via a one-dimensional finite difference time domain (FDTD) simulation of the propagation of a causal, pulsed plane wave in a matched, lossy Drude model DNG medium. The causal responses of different spectral regimes of the medium with positive or negative refractive indices are studied by varying the carrier frequency of narrowband pulse excitations. The smooth transition of the phenomena associated with a DNG medium from its early-time nondispersive behavior to its late-time monochromatic response is explo...

Fruit thinning has been practised for thousand of years, and serves a number of purposes. Too many fruits per tree can result in small fruit size and poor quality, breakage of limbs, exhaustion of tree reserves, and can also partially o completely inhibit bud initiation. Hand thinning of the peaches is the most common thinning practice adopted, but it is

This paper deals with the problem of noise cancellation of speech signals in an acoustic environment. In this regard, generally, different adaptive filter algorithms are employed, many of them may lack the flexibility of controlling the convergence rate, range of variation of filter coefficients, and consistency in error within tolerance limit. In order to achieve these desirable attributes as well as to cancel noise effectively, unlike conventional approaches, we formulate the task of noise cancellation as a coefficient optimization problem whereby we introduce and exploit the particle swarm optimization (PSO) algorithm. In this problem, the PSO is designed to perform the error minimization in frequency domain. The outcomes from extensive experimentations show that the proposed PSO based acoustic noise cancellation method provides high performance in terms of SNR improvements with a satisfactory convergence rate in comparison to that obtained by some of the state-of-the-art methods.

... Swarm intelligence is a member of artificial intelligence that study intelligence behaviour of groups rather than of individuals, such as social behaviour of insect like ants, bees, wasp, termites and fish. ... Figure 8: Pole-zero plot. REFERENCES Andries P. Engelbrecht. ...

Machine condition monitoring plays an important role in industry to ensure the continuity of the process. This work presents a simple and yet, fast approach to detect simultaneous machinery faults using sound mixture emitted by machines. We developed a microphone array as the sensor. By exploiting the independency of each individual signal, we estimated the mixture of the signals and compared time-domain independent component analysis (TDICA), frequency-domain independent component analysis (FDICA) and Multi-stage ICA. In this research, four fault conditions commonly occurred in industry were evaluated, namely normal (as baseline), unbalance, misalignment and bearing fault. The results showed that the best separation process by SNR criterion was time-domain ICA. At the final stage, the separated signal was analyzed using Instantaneous Frequency technique to determine the exact location of the frequency at the specific time better than spectrogram.

This paper presents a robust video watermarking scheme. It mainly contains three characteristics: 1) the sinusoidal signals pattern is embedded as watermark in the selected sub-bands of 3D dual-tree complex wavelet transform (3D-CWT), which is employed to preserve the image quality and improve the robustness of watermark; 2) at the detection end, the detected peaks response are used to achieve attacks estimation and rectification; and 3) the watermark is confirmed simply and objectively by detecting the prominent peaks in frequency domain. Experimental results conducted on several popular true color video sequences demonstrate that the proposed watermarking scheme has good performance in terms of common video operations as well as geometric distortions.

Purpose: In the present work was made the comparative analysis in time domain and frequency domain to the acoustical pressure generate by the electric arc to determinate which of the two analysis methods is better to evaluates the stability in GMAW process. Design/methodology/approach: Welds had been made with the parameters adjusted to get the highest stability. In these conditions, were

The dynamic characteristics of an edge-emitting laser under large-signal modulation are analyzed in the frequency domain using a harmonic balance method on device level. The simulations reveal the nonlinearities of the carrier dynamics in the quantum well region which strongly influence the optical power in the higher harmonics.

HRV and HRT are independent predictors of cardiovascular mortality. Aging reduces HRV, but results from the physical exercise trials are controversial. The primary aim was to study changes in heart rate variability (HRV) and heart rate turbulence (HRT) in a six-year controlled randomized trial at regular low to moderate intensity physical exercise. One hundred forty men aged 53--63 years were randomized in to an exercise or a control groups. The participants underwent a maximal bicycle ergometer exercise test with respiratory gas analyses annually for six years. At baseline and after intervention, 24-h ambulatory ECG registrations were performed to assess HRV (n=100). HRT was determined among subjects with single ventricular premature complexes (VPC) (n=73). In the exercise group, ventilatory aerobic threshold (VAT) increased by 16% indicating enhanced submaximal cardiorespiratory fitness. No significant differences were found in any of the HRV or HRT parameters between the groups. ...

Although electrical impedance tomography (EIT) for ventilation monitoring is on the verge of clinical trials, pulmonary perfusion imaging with EIT remains a challenge, especially in spontaneously breathing subjects. In anticipation of more research on this subject, we believe a thorough review is called for. In this paper, findings related to the physiological origins and electrical characteristics of this signal are