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Abstract-Employing an attenuated oscillation method, the anisotropic interaction force between two vertically aligned dust particles located in the sheath of a complex plasma was measured experimentally based on a linear approximation to the interaction force. Experimental data show that, although both particles experience a repulsive interaction force, the upper particle experiences a stronger magnitude force than does the lower particle. This result can be explained by the ion wakefield since the lower particle resides within the ion wakefield generated by the streaming ions passing through the sheath and around the upper particle. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we consider the so-called p-system with linear damping, and we will prove an optimal decay estimates without any smallness conditions on the initial error. More precisely, if we restrict the initial data in the space , then we can derive faster decay estimates than those given in [P. Marcati, M. Mei, B. Rubino, Optimal convergence rates to diffusion waves for solutions of the hyperbolic conservation laws with damping, J. Math. Fluid Mech. 7 (2) (2005) 224–240; H. Zhao, Convergence to strong nonlinear diffusion waves for solutions of p-system with damping, J. Differential Equations 174 (1) (2001) 200–236] and [M. Jian, C. Zhu, Convergence to strong nonlinear diffusion waves for solutions to p-system with damping on quadrant, J. Differential Equations 246 (1) (2009) 50–77]. [Copyright &y& Elsevier]

Abstract: This paper considers the nonparametric deconvolution problem when the true density function is left (or right) truncated. We propose to remove the boundary effect of the conventional deconvolution density estimator by using a special class of kernels: the deconvolution boundary kernels. Methods for constructing such kernels are provided. The mean squared error properties, including the rates of convergence, are investigated for supersmooth and ordinary smooth errors. Numerical simulations show that the deconvolution boundary kernel estimator successfully removes the boundary effects of the conventional deconvolution density estimator. [Copyright &y& Elsevier]

The multiuser multiple-input-multiple-output (MU-MIMO) technique is an attractive candidate in improving spectrum efficiency. However, in the uplink, the difference in the transmit timing among the signals from multiple mobile terminals (MTs) becomes significant. If the arrival timing difference among MTs exceeds the cyclic prefix (CP) length, it is difficult to separate the signal of each MT, and the transmission quality is severely degraded due to the effect of interblock interference (IBI). In this paper, we propose a novel multiuser detection (MUD) technique that can separate the signals, regardless of the arrival timing differences between the MTs. The proposed MUD technique is performed in the frequency domain by overlapping the fast Fourier transform (FFT) blocks, and the technique can suppress the effect of the IBI while retaining a low complexity level. The achievable bit error rate (BER) performance is evaluated by computer simulation in a frequency-selective fading channel, and the results confirm the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

A new time-delay estimator is presented in this paper. It is evaluated based on the delay property of the fractional Fourier transform with less computation and is suitable for chirp signals. The statistical analysis in terms of signal-to-noise ratio (SNR) and estimation accuracy for this estimation is also studied. The proposed method for the time delay yields a variance which is theoretically equal to the Cramér-Rao lower bound. The validity of this estimation method is demonstrated via simulations. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a novel approach for simultaneous power generation and harmonic current mitigation using variable speed WECS with DFIG. A new control strategy is proposed to upgrade the DFIG control to achieve simultaneously a green active and reactive power source with active filtering capability. To ensure high filtering performance, we studied an improved harmonic isolator in the time-domain, based on a new high selectivity filter developed in our laboratory. We examined two solutions for harmonic current mitigation: first, by compensating the whole harmonic component of the grid currents or second, by selective isolation of the predominant harmonic currents to ensure active filtering of the 5th and 7th harmonics. Simulation results for a 3MW WECS with DFIG confirm the effectiveness and the performance of the two proposed approaches. [Copyright &y& Elsevier]

The results of experimental study of the weak localization phenomenon in 2D system with artificial inhomogeneity of potential relief are presented. It is shown that the shape of the magnetoconductivity curve is determined by the statistics of closed paths. The area distribution function of closed paths has been obtained using the Fourier transformation of the magnetoconductivity curves taken at different temperatures. The experimental results are found in a good agreement with the results of computer simulation. [ABSTRACT FROM AUTHOR]

This paper focuses on the amplitude estimation by a multipoint interpolated discrete Fourier transform (DFT) method. Accurate results are obtained using the weighted multipoint interpolated DFT (WMIpDFT) method with maximum sidelobe decay windows. In addition, using the WMIpDFT method with maximum sidelobe decay windows, it is mathematically proven that the systematic errors affecting the amplitude estimation decrease as the number of interpolation points and/or the window order increases. Computer simulations confirm the accuracy of the derived expressions. Moreover, the influence of white Gaussian noise on the amplitude estimations has been analyzed by means of computer simulations. [ABSTRACT FROM AUTHOR]

A theory is described for propagation of vortical waves across alternate rigid and compliant panels. The structure in the fluid side at the junction of panels is a highly vortical narrow viscous structure which is idealized as a wave driver. The wave driver is modelled as a 'half source cum half sink'. The incoming wave terminates into this structure and the outgoing wave emanates from it. The model is described by half Fourier-Laplace transforms respectively for the upstream and downstream sides of the junction. The cases below cutoff and above cutoff frequencies are studied. The theory completely reproduces the direct numerical simulation results of Davies & Carpenter (J. Fluid Mech., vol. 335, 1997, p. 361). Particularly, the jumps across the junction in the kinetic energy integral, the vorticity integral and other related quantities as obtained in the work of Davies & Carpenter are completely reproduced. Also, some important new concepts emerge, notable amongst which is the concept of the pseudo group velocity. [ABSTRACT FROM AUTHOR]

The relationship between thermal conductivity of porous material and fractal dimension is numerically simulated by using the finite element method. The solid matrix and pore space are generated randomly according to material porosity. Material parameters and element properties are changed by using ANSYS parameter design language. The effective thermal conductivity is derived according to thermal flux through some sections computed by FEM and Fourier heat transform law. The investigation shows that the effective thermal conductivity decreases with increasing porosity. The effective thermal conductivity will decrease exponentially with increasing fractal dimension of porosity space and increase exponentially with increasing fractal dimension of solid matrix. [ABSTRACT FROM AUTHOR]

Abstract: Grigoryan [Fourier transform representation by frequency-time wavelets, IEEE Trans. Signal Process. 53 (7) (2005) 2489–2497] has proposed an alternative representation of the Fourier transform, called A-wavelet transform. In that paper, the Cosine and Sine signals defined over one period have been used to develop the Cosine- and Sine-wavelet transforms and using those wavelet transforms the Fourier transform has been represented. For computing the Fourier transform at a given frequency, one does not require to compute the Cosine- and Sine-wavelet transforms at all time points in the time-frequency plane, but at specific time points that are separated out by 2π/ω, ω is the frequency variable. In this paper, we propose SC- and SS-wavelet transforms that help representing the Fourier transform of a signal in a better way. The SC- and SS-wavelet transforms use the Cosine and Sine signals defined over the smaller intervals (of length 2π/(mω), m⩾1) than that (of length 2π/ω) used in the A-wavelet transform. The SC- and SS-wavelet transforms not only give sharper time-frequency localization but also much more information in a better localized form than the A-wavelet transform. [Copyright &y& Elsevier]

The interpolated fast Fourier transform FFT (IpFFT) had been proposed to eliminate the picket fence effect of the fast Fourier transform. However, the modulus-based IpFFT (without windowing) is subjected to large bias in the condition of nearly coherent sampling condition. In addition, only the first and second highest spectral lines were used in most relevant references. The complex spectrum-based IpFFT is investigated. It is less sensitive to the interpolating direction error. Further, both directions of IpFFT can be averaged to decrease the estimation variance. The optimal weight required to minimise the estimation variance is established. The numerical simulation is carried out, and the results are compared with the Cramer–Rao bound. [ABSTRACT FROM AUTHOR]

The influence of systematic errors caused by the infleunce of the imaginary part in the spectrum of a sinusoidal signal on the estimator of its normalized frequency is analyzed by means of a discrete Fourier transformation with interpolation and a window with maximal rate of descent of the side lobes. An expression for the absolute error of the normalized frequency is presented and a condition for the minimal integral number of cycles of the sine curve is found; note that computation of the actual integral number of cycles enables us to assure that this error will be less than some specific value. The reliability of the expressions that are obtained is confirmed by a computer simulation. [ABSTRACT FROM AUTHOR]

We describe a video tracking application using the dual-tree PolarMatching Algorithm.We develop the dynamical and observation models in a probabilistic setting and study the empirical probability distribution of the Polar Matching output. We model the visible and occluded target statistics using Beta distributions. This is incorporated into a Track-Before-Detect (TBD) solution for the overall observation likelihood of each video frame and provides a principled derivation of the observation likelihood. Due to the nonlinear nature of the problem, we design a Rao-Blackwellised Particle Filter (RBPF) for the sequential inference. Computer simulations demonstrate the ability of the algorithm to track a simulated video moving target in an urban environment with complete and partial occlusions. [ABSTRACT FROM AUTHOR]

The single-pixel imaging (SPI) technique enables the tracking of moving targets at a high frame rate. However, when extended to the problem of multi-target tracking, there is no effective solution using SPI yet. Thus, a multi-target tracking method using windowed Fourier single-pixel imaging (WFSI) is proposed in this paper. The WFSI technique uses a series of windowed Fourier basis patterns to illuminate the target. This method can estimate the displacements of K independently moving targets by implementing 6 K measurements and calculating 2 K windowed Fourier coefficients, which is a measurement method with low redundancy. To enhance the capability of the proposed method, we propose a joint estimation approach for multi-target displacement, which solves the problem where different targets in close proximity cannot be distinguished. Using the independent and joint estimation approaches, multi-target tracking can be implemented with WFSI. The accuracy of the proposed multi-target tracking method is verified by numerical simulation to be less than 2 pixels. The tracking effectiveness is analyzed by a video experiment. This method provides, for the first time, an effective idea of multi-target tracking using SPI. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new method for calculating effective atomic radii within the generalized Born (GB) model of implicit solvation is proposed, for use in computer simulations of biomolecules. First, a new formulation for the GB radii is developed, in which smooth kernels are used to eliminate the divergence in volume integrals intrinsic in the model. Next, the fast Fourier transform (FFT) algorithm is applied to integrate smoothed functions, taking advantage of the rapid spectral decay provided by the smoothing. The total cost of the proposed algorithm scales as where M is the number of atoms comprised in a molecule and N is the number of FFT grid points in one dimension, which depends only on the geometry of the molecule and the spectral decay of the smooth kernel but not on M. To validate our algorithm, numerical tests are performed for three solute models: one spherical object for which exact solutions exist and two protein molecules of differing size. The tests show that our algorithm is able to reach the accuracy of other existing GB implementations, while offering much lower computational cost. [Copyright &y& Elsevier]

The distribution of water diffusion in biological tissues may be estimated by a 3-D Fourier transform (FT) of diffusion-weighted measurements in q-space. In this study, methods for estimating diffusion spectrum measures (the zero-displacement probability, the mean-squared displacement, and the orientation distribution function) directly from the q-space signals are described. These methods were evaluated using both computer simulations and hybrid diffusion imaging (HYDI) measurements on a human brain. The HYDI method obtains diffusion-weighted measurements on concentric spheres in q-space. Monte Carlo computer simulations were performed to investigate effects of noise, q-space truncation, and sampling interval on the measures. This new direct computation approach reduces HYDI data processing time and image artifacts arising from 3-D FT and regridding interpolation. In addition, it is less sensitive to the noise and q-space truncation effects than conventional approach. Although this study focused on data using the HYDI scheme, this computation approach may be applied to other diffusion sampling schemes including Cartesian diffusion spectrum imaging. [ABSTRACT FROM AUTHOR]

To simulate 3-D wave rapidly and effectively, a numerical simulation model of fully nonlinear waves was established using the high order spectral method. In this method, the velocity potential was expanded into a set of Fourier series, and the fast Fourier transform (FFT) algorithm was used to solve its spatial derivatives. It has high computational efficiency and precision; A numerical model was developed based on the high order spectral method to simulate nonlinear wave-wave interactions. Numerical results are compared with theoretical results and experimental results, and the sloshing wave in 3D tank is computed. The results show that the method is available and efficient for the simulation of high order nonlinear waves and focusing extreme waves. [ABSTRACT FROM AUTHOR]

Abstract: We propose a new method for image encryption using fractional Fourier transform and chaos theory. Random phase masks are generated using iterative chaos functions. The input image is combined with the first random phase mask at the object plane and is then transformed using the fractional Fourier transform. After the first fractional Fourier transform, the second random phase mask, again generated by using the chaos functions, is used at the fractional plane. The second fractional Fourier transform operation is then carried out to obtain the encrypted image. Three types of chaos functions have been used: the logistic map, the tent map and the Kaplan–Yorke map. The mean square error and the signal-to-noise ratio between the decrypted image and the input image for the correct order and the incorrect order of the fractional Fourier transform have been calculated. The computer simulations are presented to verify the validity of the proposed technique. [Copyright &y& Elsevier]

This paper presents a generalized analysis model for fringe pattern profilometry. We mathematically derived a new analysis model that gives a more general expression of the relationship between projected and deformed fringe patterns. Meanwhile, based on the proposed generalized model, a new algorithm is presented to retrieve 3-D surfaces from nonlinearly distorted fringes. Without any prior knowledge about the projection system, we still can obtain very accurate measurement results by using a generalized analysis model and a proposed algorithm. Computer simulation and experimental results show that the generalized model and the proposed algorithm can significantly improve the 3-D reconstruction precision, especially when the projected fringe pattern is nonlinearly distorted. [ABSTRACT FROM PUBLISHER]

The frequency-distance principle (FDP) is a well-known relationship that relates the distance between the object and the detector to the slope in the two-dimensional Fourier transform of the projection sinogram. This relationship has been previously applied to compensation of the distance dependent collimator blurring in SPECT (single photon emission computed tomography) in the literature. This paper makes an attempt to use the FDP to correct for uniform attenuation in SPECT. Computer simulations reveal that this technique works well for objects consisting of point sources but does not work well for distributed objects. [ABSTRACT FROM AUTHOR]

Abstract: A new method of optical image encryption with binary Fourier transform computer-generated hologram (CGH) and pixel-scrambling technology is presented. In this method, the orders of the pixel scrambling, as well as the encrypted image, are used as the keys to decrypt the original image. Therefore, higher security is achieved. Furthermore, the encrypted image is binary, so it is easy to be fabricated and robust against noise and distortion. Computer simulation results are given to verify the feasibility of this method and its robustness against occlusion and additional noise. [Copyright &y& Elsevier]

An exact calculation of the Voigt spectral line profile in spectroscopy has been derived using the Fourier transform method. The analytical formula we calculated is a real function, rather than a complex function as has been previously discussed, because the imaginary part will be zero in our calculation. The analytical formula is very convenient in practical applications. The relationship of the half width of the Voigt profile, the Gaussian profile and the Lorentzian profile is also discussed. Through analysis using a computer simulation, we find that the formula we calculated is in good agreement with the experimental result. [ABSTRACT FROM AUTHOR]

The article proposes a practical image hiding method using phase wrapping and real-valued decoding key. A zero-padded original image is Fourier transformed and its real-valued data denotes an encoded image in the embedding process. Computer simulation and an optical experiment are shown to support the proposed method.

An improved discrete Fourier transform (DFT)-based channel estimation for orthogonal frequency division multiplexing systems is proposed. Conventional DFT-based channel estimations improve the performance by suppressing time domain noise. However, they potentially require information on channel impulse responses and may also result in mean-square error (MSE) floor due to incorrect channel information such as channel delay spread. In contrast, our purposed channel estimation can improve the performance by deciding significant channel taps adaptively without requiring any channel statistical information. Significant channel taps are detected on the basis of a predetermined threshold. The optimal threshold to reduce the MSE of the estimation is also derived, and it is confirmed by computer simulation. Simulation results demonstrate that the proposed algorithm can improve the MSE performance ∼6.5 dB compared with the conventional DFT-based estimation, and the MSE floor is not observed in any channels. [ABSTRACT FROM AUTHOR]

Statistically optimized near field acoustic holography (SONAH) differs from conventional near field acoustic holography (NAH) by avoiding spatial Fourier transforms; the processing is done directly in the spatial domain. The main advantage of SONAH compared with NAH is that the usual requirement of a measurement aperture that extends well beyond the source can be relaxed. Both NAH and SONAH are based on the assumption that all sources are on one side of the measurement plane whereas the other side is source free. An extension of the SONAH procedure based on measurement with a double layer array of pressure microphones has been suggested. The double layer technique makes it possible to distinguish between sources on the two sides of the array and thus suppress the influence of extraneous noise coming from the “wrong” side. It has also recently been demonstrated that there are significant advantages in NAH based on an array of acoustic particle velocity transducers (in a single layer) compared with NAH based on an array of pressure microphones. This investigation combines the two ideas and examines SONAH based on an array of pressure-velocity intensity probes through computer simulations as well as experimentally. [ABSTRACT FROM AUTHOR]

We consider the influence of phase fluctuations on the operation characteristics of an OFDM radio-communication system. We present the results of studying the effect of additional nonorthogonality noise appearing after the fast Fourier transform due to the phase noise and frequency detuning between the receiver and transmitter oscillators. Approximate analytical expressions for the power of additional nonorthogonality noise are presented for the classical Lorentzian model of the phase noise. Degradation of the signal-to-noise ratio in the OFDM radio-communication system is studied and analytical expressions are given for calculation of this quantity as a function of the frequency detuning and half-width of the spectral line of an oscillator. We present the computer simulation results con.rming the analytical evidence. Based on the obtained results, recommendations for practical choice of the parameters of an OFDM radio-communication system can be given. [ABSTRACT FROM AUTHOR]

Abstract: This paper highlights the most recent progress in the quantitative study on the microstructure and the rheological properties of colloidal fat crystal networks. Several physical models describing the structural hierarchy of the colloidal fat crystal networks are reviewed here, with particular emphasis on fractal model, which can be used to explain the scaling behavior of fat crystal networks. The concept of the fractal dimension has been extensively used in the quantitative study of the microstructure of fat crystal networks and other colloidal networks; however, the relationship between the fractal dimension value and microstructural characteristics remains somewhat nebulous. Recent computer simulation work from our laboratory will be presented relating simulated microstructural features to values of particular measure of fractality including the box-counting, particle counting and Fourier-transform fractal dimensions. [Copyright &y& Elsevier]

A good deal is known by now on the so-called jellium model of the homogeneous electron liquid. However, much of the quantitative progress at experimentally realizable densities has come from quantal computer simulation. Therefore, we here consider a homogeneous Fermion liquid with ‘artificial’ repulsive interaction λ/(rij)2 between Fermions i and j at separation rij. We discuss first of all the way the static structure function S(q), essentially the Fourier transform of the pair correlation function, is changed because of non-zero λ from the ‘Fermi hole’ form due entirely to Pauli principle effects between parallel spin Fermions. Unlike jellium with e2/rij repulsive interactions, S(q) is proportional to q at long wavelengths, whereas the plasmon in jellium annulls the q term and S(q) is quadratic in q as q tends to zero. However for λ/(rij)2 interactions, the coefficient of q appearing in the Fermi hole structure factor, is renormalized by particle repulsions. Then some discussion is given of Fermion quasiparticle lifetimes τ as the Fermi surface is approached. Arguments are presented that τ-1 is proportional to |E - EF| as E tends to the Fermi energy. This is already interesting, in fact, in connection with the jellium model and therefore an approximate analytic form of τ is finally derived. [ABSTRACT FROM AUTHOR]

A new generation of multipurpose measurement equipment is transforming the role of computers in instrumentation. The new features involve mixed devices, such as analog-to-digital and digital-to-analog converters and digital signal processing techniques, that are able to substitute typical discrete instruments like multimeters and analyzers. Signal-processing applications frequently use least-squares (LS) sine-fitting algorithms. Periodic signals may be interpreted as a sum of sine waves with multiple frequencies: the Fourier series. This paper describes an algorithm that is able to fit a multiharmonic acquired signal, determining the amplitude and phase of all harmonics. Simulation and experimental results are presented. [ABSTRACT FROM AUTHOR]

In this paper, a new approach to constructing optimal nonlinear transforms of random vectors is proposed and justified. The proposed transform Tp, is presented in the form of a sum with p terms where each term is interpreted as a particular rank-reduced transform. Moreover, terms in Tp, are represented as a combination of three operations Fk Qk, and φk with k = 1,… , p. The prime idea is to determine Fk separately, for each k = 1,… , p, from an associated rank-constrained minimization problem similar to that used in the Karhunen—Loève transform (KLT). The operations Qk and φ are auxiliary for finding Fk. The contribution of each term in Tp improves the entire transform performance. A rigorous analysis of errors associated with the proposed transforms is given. It is shown that the proposed transform improves such characteristics of rank-reduced transforms as compression ratio and the accuracy of decompression and reduces required computational work. The Fourier series in Hilbert space, the Wiener filter, the KLT and the transforms presented in earlier author papers in the field are particular cases of the proposed method. Theoretical results are illustrated with numerical simulations. [ABSTRACT FROM AUTHOR]

In this letter, it is shown that a fast, prime-factor discrete Fourier transform (DFT) algorithm can be modified to compute Fourier-like transforms of long sequences of 2m - 1 points over GF(2m), where 8 ≤ m ≤ 10. Using these transforms, together with the Berlekamp-Massey algorithm, the complexity of the transform-domain decoder for correcting both errors and erasures of the Reed-Solomon codes of block length 2m - 1 over GF(2m) for 8 ≤ m ≤ 10 is reduced substantially from the previous time-domain decoder. A computer simulation verifies these new results. [ABSTRACT FROM AUTHOR]

Non-Cartesian sampling is widely used for fast magnetic resonance imaging (MRI). Accurate and fast image reconstruction from non-Cartesian k-space data becomes a challenge and gains a lot of attention. Images provided by conventional direct reconstruction methods usually bear ringing, streaking, and other leakage artifacts caused by discontinuous structures. In this paper, we tackle these problems by analyzing the principal point spread function (PSF) of non-Cartesian reconstruction and propose a leakage reduction reconstruction scheme based on discontinuity subtraction. Data fidelity in k-space is enforced during each iteration. Multidimensional nonuniform fast Fourier transform (NUFFT) algorithms are utilized to simulate the k-space samples as well as to reconstruct images. The proposed method is compared to the direct reconstruction method on computer-simulated phantoms and physical scans. Non-Cartesian sampling trajectories including 2D spiral, 2D and 3D radial trajectories are studied. The proposed method is found useful on reducing artifacts due to high image discontinuities. It also improves the quality of images reconstructed from undersampled data. [ABSTRACT FROM AUTHOR]

A serious disadvantage of orthogonal frequency-division multiplexing (OFDM) is its sensitivity to carrier frequency offset (CFO) and timing offset (TO). For many low-complexity algorithms, the estimation ambiguity exists when the CFO is greater than one or two subcarrier spacing, and the estimated TO is also prone to exceeding the ISI-free interval within the cyclic prefix (CP). This paper presents a method for joint CFO ambiguity resolution and accurate TO estimation in multipath fading. Maximum-likelihood (ML) principle is employed and only one pilot symbol is needed. Frequency ambiguity is resolved and accurate TO can be obtained simultaneously by using the fast Fourier transform (FFT) and one-dimensional (1D) search. Both known and unknown channel order cases are considered. Computer simulations show that the proposed algorithm outperforms some others in the multipath fading channels. [ABSTRACT FROM AUTHOR]

Two simple discrete-time methods for unbiased estimation of the phase-shift between two real sinusoidal signals in white noise are proposed. The first estimator removes the bias of the recently proposed quadrature delay estimator (QDE) by utilizing all in-phase and quadrature-phase components of the received signals. The phase estimate of the second method is given by the phase difference of the discrete-time Fourier transforms (DTFTs) of two complex sinusoids derived from the real signals. In particular, we have derived the mean square phase-shift error of the DTFT-based estimator as well as the minimum achievable variance for phase-shift estimation, which are identical. Computer simulations show that the two proposed estimators are superior to the biased QDE and can attain optimum performance, although the second estimator has a larger signal-to-noise ratio operation range. [ABSTRACT FROM AUTHOR]

Orthogonal frequency-division multiplexing (OFDM) is an attractive transmission technique for high-bit-rate communication systems. One major drawback of OFDM is the high peak-to-average power ratio (PAPR) of the transmitter's output signal. The selected mapping (SLM) approach provides good performance for PAPR reduction, but it requires a bank of inverse fast Fourier transforms (lFFTs) to generate a set of candidate transmission signals, and this requirement usually results in high computational complexity. In this paper, we propose a kind of low-complexity conversions to replace the IFFT blocks in the conventional. SLM method. Based on the proposed conversions, we develop two novel SLM schemes with much lower complexity than the conventional one; the first method uses only one IFFT block to generate the set of candidate signals, while the second one uses two IFFT blocks. Computer simulation results show that, as compared to the conventional SLM scheme, the first proposed approach has slightly worse PAPR reduction performance and the second proposed one reaches almost the same PAPR reduction performance. [ABSTRACT FROM AUTHOR]

A computer simulation (MD method) study is presented for a nanosystem composed of a limited number (n = 15, 25, 35) of hypoxanthine-3-N-oxide (H3NO) molecules surrounding a single fullerene molecule. The calculations were performed for several temperatures and densities (solid and fluid phases of hypoxanthine-3-N-oxide thin layers). The mean square displacement, diffusion coefficient, linear and angular velocity autocorrelation functions and their Fourier transforms have been obtained for H3NO. [ABSTRACT FROM AUTHOR]

Orthogonal frequency division multiplexing (OFDM) has been used in many communication systems. However, the major drawback of OFDM system is high pea k- to-average-power ratio (PAPR). In this paper, we introduce low complexity phase weighting method to reduce PAPR of OFDM signals. Proposed method is derived from property of discrete Fourier Transform (DFT) of periodical sequences. PAPR can be reduced efficiently by phase weighting method with low complexity. The simulation results show the same PAPR reduction efficiency of proposed method in comparison with Partial Transmit Sequence (PTS) or sub-block phase weighting (SPW). The proposed technique can reduce 2.15dB of PAPR with two phase-factors and 3.95dB of PAPR with four phase-factors. The analysis on complexity presents remarkable improvement of low complexity phase weighting method. Proposed method odd case can save 75% and 8 7.5% number of multiplications of PTS method and SPW method separately. The other case of proposed method, even case, can save near 60% number of additions of PTS and over 70% of SPW. [ABSTRACT FROM AUTHOR]

Harmonic distortion in power networks is continuously increasing owing to the increased use of nonlinear loads in power-distribution networks. Consequently, harmonic monitoring and control are becoming particularly important for both utilities and consumers to reduce their harmful effects. In some applications, such as real-time harmonic monitoring and active filters, techniques for fast extraction of individual harmonic components are required. The relatively long response time of conventional techniques make them less appealing when the speed of response is important. The paper deals with the problem of individual-harmonic extraction for the purpose of harmonic filtering and compensation. A common problem associated with existing individual-harmonic-extraction techniques is the speed of extracting a single harmonic component, which determines the response of the compensator. Standard harmonic-extraction techniques are investigated and a new fast-individual-harmonic-extraction (FIHE) technique is proposed. It is shown that the proposed FIHE is capable of performing harmonic extraction six times faster than the Fourier transform and provides better filtering characteristics than traditional filters such as Butterworth and FIR filters. Computer simulation and laboratory experimental results are provided to illustrate the characteristics and performance of the proposed technique. [ABSTRACT FROM AUTHOR]

We have proposed the multirate discrete Fourier transform (MR-DFT) as one of the DFT algorithms. The feature of the MR-DFT is that only one multiplication is used for each Fourier coefficient. Therefore, the number of multiplications can be decreased compared with the conventional DFT. In this paper, for applications of the MR-DFT, we consider how the noise affects the estimation performance of the MR-DFT. Then we propose two improved algorithms of the estimation performance, that is, a shifted multirate discrete Fourier transform (SMR-DFT) and a parallel shifted multirate discrete Fourier transform (PSMR-DFT). The SMR-DFT prevents an aliasing of the additive noise by a frequency modulation. The PSMR-DFT performs the parallel processing of the SMR-DFT with different sample points using the periodicity of an input signal. The estimation performances of the proposed algorithms are compared with MR-DFT by computer simulations. The SMR-DFT could prevent the degradation of the estimation performance of the MR-DFT in the lower components caused by the wide bandwidth noise. Hence its estimation variance could become 0.61 times that of the MR-DFT. Furthermore, the PSMR-DFT could improve the estimation variance of the SMR-DFT to 0.46 times. Comparing the number of operations of the proposed algorithms with the MR-DFT, the number of additions has increased, however, the number of multiplications has the same complexity. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 20–27, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20044 [ABSTRACT FROM AUTHOR]

Orientation tensors are widely used to describe fiber orientations in mold filling simulations of short-fiber-reinforced composite systems. In these flow calculations, a closure is employed that approximates the fourth-order orientation tensor as a function of the second-order orientation tensor. Sixth-order closures have also been proposed. This paper assesses the effect of using closure approximations in fiber orientation predictions by reconstructing the fiber orientation distribution function from successively higher order orientation tensors in a Fourier series representation. This approach recognizes that the orientation tensors are related to the series expansion coefficients of the distribution function. An error metric is introduced and applied that makes it possible to compare closures of varying order. Errors associated with several fourth-order closures and a sixth-order closure are investigated and compared with the truncation error that results from a reconstruction of the exact second-, fourth-, and sixth-order orientation tensors. Examples are provided over a range of interaction coefficients and flow fields typical of injection molded fiber-reinforced composites to illustrate the proposed closure assessment method. [ABSTRACT FROM AUTHOR]

There are many applications where it is necessary to estimate accurately the amplitude and phase of signals when the information regarding the frequencies is obtained in advance. This paper presents a new algorithm for estimating more accurately Fourier coefficients of a signal contaminated by additive noise where sinusoidal frequencies of interest are not distributed uniformly. In the proposed method, Fourier coefficients are adaptive parameters. It uses averaged gradient signals and has almost the same acquisition time as the conventional LMS algorithm with more accurate estimation. The performance analysis of the proposed method is presented and its validity and limits are verified under various conditions by computer simulations. It is shown that the proposed method has especially better performance than the LMS algorithm when both the number of frequencies and the step size parameter, µ, are large. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(1): 52–60, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10362 [ABSTRACT FROM AUTHOR]

Comparative outcomes of computer simulation of certain classes of images with application of discrete cosine transform, the Haar transform and wavelet transforms for JPEG image processing technique are presented on the basis of the main idea of substitute of the image of immediate object of coding for its discrete Fourier transform. In this way the image is subject to the unitary mathematical transform and as a result the obtained coefficients are quantized, encoded and transmitted by a communication channel or are stored in archive. [ABSTRACT FROM AUTHOR]

It is well known that orthogonal frequency-division multiplexing (01DM) is robust to frequency-selective fading in wireless channels due to the exploitation of a guard interval that is inserted at the beginning of each 01DM symbol. However, once delayed signals beyond the guard interval are introduced in a channel with a large delay spread, intersymbol interference causes a severe degradation in the transmission performance. In this paper, we propose a novel pit-fast Fourier transform (FFT) OFDM adaptive antenna array, which requires only one FFT processor at a receiver, for suppressing such delayed signals. We derive the optimum weight set for beamformers based on the maximum signal-to-noise-and-interference power ratio (Max-SNIR) and the minimum mean square error (mmse) criteria, respectively. In addition, we propose a novel mmse-criterion-based commutative optimization scheme, which is more robust to the estimation error of the channel state information. Furthermore, we show the equivalence between the Max-SNIR-criterion-based scheme and the proposed commutative optimization scheme. Computer simulation results show its good performance even in channels where directions of arrival of arriving waves are randomly determined. [ABSTRACT FROM AUTHOR]

A new method of measurement of distortion product otoacoustic emission (DPOAE) signal level based on a recently introduced nonlinear adaptive method of extraction of nonstationary sinusoids is presented. Essentially, three units of such an algorithm are employed to extract and measure the two stimuli and the DPOAE signal. Each unit has the capability of locking on a specified sinusoidal component of the input signal and tracking its variations over time. Performance of the proposed method is demonstrated with the aid of computer simulations and is verified in laboratory using recorded clinical data. Comparison is made between the proposed technique and existing methods. The proposed method features structural simplicity which renders it particularly attractive for implementation on both software and hardware platforms. It offers a high degree of immunity with regard to background noise and parameter variations. Compared to conventional methods, the proposed method offers a shorter measurement time which is of significant value in clinical examinations. [ABSTRACT FROM AUTHOR]

Some processes such as fractional order processes cannot be represented by state space equations. Large dimensional multi-input multi-output processes with time delays have approximated state space representations, but the number of state equations can be too large to handle. For such processes, fast Fourier transformation (FFT) methods can be used to simulate them. However, when the frequency responses and time responses have long tails, the FFT methods suffer from long computation time because they require a large number of frequency response data points. Both cases experience reduced efficiency for the FFT-based simulation methods. Here, a method based on series and/or parallel compensations is proposed to solve these problems. Simulation results for various processes including transcendental processes and large dimensional processes with time delays show that the proposed method is promising and can be used advantageously, complementing the state space method. [Copyright &y& Elsevier]

Iterative image reconstruction algorithums play an increasingly important role in modem tomographic systems, especially in emission tomography. With the fast increase of the sizes of the tomographic data, reduction of the computation demands of the reconstruction algorithms is of great importance. Fourier-based forward and back-projection methods have the potential to considerably reduce the computation time in iterative reconstruction. Additional substantial speed-up of those approaches can be obtained utilizing powerful and cheap off-the-shelf fast Fourier transform (FFT) processing hardware. The Fourier reconstruction approaches are based on the relationship between the Fourier transform of the image and Fourier transformation of the parallel-ray projections. The critical two steps are the estimations of the samples of the projection transform, on the central section through the origin of Fourier space, from the samples of the transform of the image, and vice versa for back-projection. Interpolation errors are a limitation of Fourier-based reconstruction methods. We have applied mm-max optimized Kaiser-Bessel interpolation within the nonuniform FFT (NUFFT) framework and devised ways of incorporation of resolution models into the Fourier-based iterative approaches. Numerical and computer simulation results show that the min-max NUFFT approach provides substantially lower approximation errors in tomographic forward and back-projection than conventional interpolation methods. Our studies have further confirmed that Fourier-based projectors using the NUFFT approach provide accurate approximations to their space-based counterparts but with about ten times faster computation, and that they are viable candidates for fast iterative image reconstruction. [ABSTRACT FROM AUTHOR]

Interleaved analog-digital converter (ADC) systems can be used to increase the sampling rate for a given ADC implementation technique. In theory, the maximum sampling rate that can be achieved is limited only by the bandwidth and the practical limits related to the power and space of integrated circuits. In this paper, a solution to increase the sampling rate of a digitizing system based on interleaved ADCs is presented. An error analysis, which takes into consideration offset and gain errors of the different ADC channels, is performed in order to quantify the effect of such errors in the system's performance. A software method based on the fast Fourier transform is presented for offset and gain error compensation of interleaved ADC associations. Numerical simulations and experimental results are used to validate the theory and the proposed compensation algorithm. [ABSTRACT FROM AUTHOR]

We propose a variant for the optical method of detection currently used in the scanning laser acoustic microscope. The proposed method consists in tilting the stage that contains the immersed object under test and coverslip with respect to the direction of the probe beam. We present a mathematical analysis of the optical process of detection. Additionally, we include computer simulations that show that the imaging resolution in the optical detection process can be improved by using our method. [Copyright &y& Elsevier]