Search results for "harmonic"
showing 10 items of 984 documents
Spectral analysis of the Neumann-Poincaré operator and characterization of the stress concentration in anti-plane elasticity
2012
When holes or hard elastic inclusions are closely located, stress which is the gradient of the solution to the anti-plane elasticity equation can be arbitrarily large as the distance between two inclusions tends to zero. It is important to precisely characterize the blow-up of the gradient of such an equation. In this paper we show that the blow-up of the gradient can be characterized by a singular function defined by the single layer potential of an eigenfunction corresponding to the eigenvalue 1/2 of a Neumann–Poincare type operator defined on the boundaries of the inclusions. By comparing the singular function with the one corresponding to two disks osculating to the inclusions, we quant…
Graphical THD minimization procedure for single phase five-level converters
2017
This paper proposes two graphycal procedure to mitigate h harmonics and to minimize the total harmonic distortion (THD), respectively. The paper considers a five-level inverter and fundamental frequency modulation: it computes the two switching angles able to reduce low order harmonics and able to minimize the THD. Simulation results are obtained and, in order to validate the proposed procedure, an experimental prototype is built and experimental results are carried out. The comparison between simulation and experimental results confirms the accuracy of the proposed graphycal procedure. It is shown that the switching angles to mitigate the third-fifth and the third-fifth-seventh harmonics e…
Liver haemangiomas undetermined at grey-scale ultrasound: contrast-enhancement patterns with SonoVue and pulse-inversion US.
2005
The objective of this study was to describe the spectrum of contrast-enhancement patterns of hepatic haemangiomas undetermined at grey-scale ultrasound (US) on SonoVue-enhanced pulse-inversion (PI) US. Twenty patients (11 women, nine men) with 35 haemangiomas (size range: 1-7 cm; mean: 3.1 cm) undetermined at baseline US underwent PI at low M.I. (0.05-0.08) after i.v. injection of SonoVue. All haemangiomas were confirmed by typical helical computed tomography (CT) and/or magnetic resonance imaging (MRI) findings. US examinations were videotaped and then reviewed by two experienced radiologists blinded to the final diagnosis. Readers evaluated by consensus the baseline echogenicity and the d…
Harmonic sources detection in power systems via nonactive power measurements according to IEEE Std. 1459–2010: Theoretical approach and ex…
2010
In this paper an enhanced decision-making strategy is presented for the detection of harmonic sources in power systems able to detect also which is the prevailing nature of the disturbance (nonlinearity or unbalance). It makes use of some simple indices, which are evaluated by means of the measurements of some nonactive power quantities, proposed by the authors and derived from the approach of the IEEE Std. 1459–2010. The decision-making rules for the proposed strategy are presented and discussed by means of simulation and experimental tests. The results obtained are presented, showing the effectiveness of the proposed strategy for the detection of the dominant harmonic source upstream or d…
Finding Invariants of Group Actions on Function Spaces, a General Methodology from Non-Abelian Harmonic Analysis
2008
In this paper, we describe a general method using the abstract non-Abelian Fourier transform to construct “rich” invariants of group actions on functional spaces.
Measurement issues on harmonic analysis according to the IEC 61000-4-7
2022
The objective of this article is an analysis of measurement issues related to the implementation of digital signal processing techniques for harmonic analysis, by means of FFT algorithm with different interpolation algorithms (linear, quadratic and cubic) and different sampling rates. A comparative analysis is made on errors on harmonics measurement obtained in the various case study analyses. Such errors are compared with the IEC 61000-4-7 limits. The study is supported by both simulation and experimental tests; these last are performed with different acquisition boards for signals acquisition.
Fast Image Restoration Algorithms Based on PDE Models Using Modified Hopfield Neural Network
2010
Two image restoration algorithms based on modified Hop field neural network and variational partial differential equations (PDE) were proposed in our previous work [1, 2]. But the convergence rate of the proposed algorithms was slow. In this paper, we develop a fast update rule based on modified Hop field neural network (MHNN) of continuous state change and two fast image restoration algorithms. Experimental results show that, when compared with the previous algorithms, our proposed algorithms have better performance both in convergence rate and in image restoration quality.
Harmonic Analysis of Unstable Systems
2003
Periodic Discrete Splines
2014
Periodic discrete splines with different periods and spans were introduced in Sect. 3.4. In this chapter, we discuss families of periodic discrete splines, whose periods and spans are powers of 2. As in the polynomial splines case, the Zak transform is extensively employed. It results in the Discrete Spline Harmonic Analysis (DSHA). Utilization of the Fast Fourier transform (FFT) enables us to implement all the computations in a fast explicit way.
Hidden oscillations in nonlinear control systems
2011
Abstract The method of harmonic linearization, numerical methods, and the applied bifurcation theory together discover new opportunities for analysis of hidden oscillations of control systems. In the present paper new analytical-numerical algorithm for hidden oscillation localization is discussed. Counterexamples construction to Aizerman's conjecture and Kalman's conjecture on absolute stability of control systems are considered.