Search results for "Signal Processing"

Correlation spectroscopy in molten and supercooled antimony trichloride.

1990

Correlation spectroscopy measurements performed on molten and supercooled antimony trichloride with the homodyne technique show correlation functions that have a nonexponential behavior. Two well-defined distributions of correlation times can be observed in different temporal regions. This behavior is discussed in terms of a structural relaxation of clusters dynamically formed by intermolecular and interchain bonds. The Arrhenius plot of these correlation times shows a linear behavior with the same activation energy for both. In contrast, the activation energy of shear viscosity has a different value, showing that the processes determining the temperature behavior of \ensuremath{\tau} and $…

Sampling methods for low-frequency electromagnetic imaging

2007

For the detection of hidden objects by low-frequency electromagnetic imaging the linear sampling method works remarkably well despite the fact that the rigorous mathematical justification is still incomplete. In this work, we give an explanation for this good performance by showing that in the low-frequency limit the measurement operator fulfils the assumptions for the fully justified variant of the linear sampling method, the so-called factorization method. We also show how the method has to be modified in the physically relevant case of electromagnetic imaging with divergence-free currents. We present numerical results to illustrate our findings, and to show that similar performance can b…

Recent progress in electrical impedance tomography

2003

We consider the inverse problem of finding cavities within some body from electrostatic measurements on the boundary. By a cavity we understand any object with a different electrical conductivity from the background material of the body. We survey two algorithms for solving this inverse problem, namely the factorization method and a MUSIC-type algorithm. In particular, we present a number of numerical results to highlight the potential and the limitations of these two methods.

Energy dissipative characteristic schemes for the diffusive Oldroyd-B viscoelastic fluid

2015

A regularized Newton method for locating thin tubular conductivity inhomogeneities

2011

We consider the inverse problem of determining the position and shape of a thin tubular object, such as for instance a wire, a thin channel or a curve-like crack, embedded in some three-dimensional homogeneous body from a single measurement of electrostatic currents and potentials on the boundary of the body. Using an asymptotic model describing perturbations of electrostatic potentials caused by such thin objects, we reformulate the inverse problem as a nonlinear operator equation. We establish Frechet differentiability of the corresponding operator, compute its Frechet derivative and set up a regularized Newton scheme to solve the inverse problem numerically. We discuss our implementation…

Jacobian of solutions to the conductivity equation in limited view

2022

Abstract The aim of hybrid inverse problems such as Acousto-Electric Tomography or Current Density Imaging is the reconstruction of the electrical conductivity in a domain that can only be accessed from its exterior. In the inversion procedure, the solutions to the conductivity equation play a central role. In particular, it is important that the Jacobian of the solutions is non-vanishing. In the present paper we address a two-dimensional limited view setting, where only a part of the boundary of the domain can be controlled by a non-zero Dirichlet condition, while on the remaining boundary there is a zero Dirichlet condition. For this setting, we propose sufficient conditions on the bounda…

Influence of Active Device Nonlinearities on the Determination of Adler's Injection.Locking Q-Factor

2011

The problem of the correct evaluation of Q-factor appearing in Adler's equation for injection-locking is addressed. Investigation has shown that recent results presented in the literature, while extending applicability of the original method, do not completely account for nonlinear effects occurring when two-port active devices are involved. To overcome such limitation, use can be made of a newly developed theory in the dynamical complex envelope domain, capable of providing first-approximation exact dynamical models of driven quasi-sinusoidal oscillators. Some preliminary results are presented here concerning a class of injection-locked oscillators with single-loop feedback type configurat…

Finite element approximation of parabolic hemivariational inequalities

1998

In this paper we introduce a finite element approximation for a parabolic hemivariational initial boundary value problem. We prove that the approximate problem is solvable and its solutions converge on subsequences to the solutions of the continuous problem

Reliable polygonal approximations of imaged real objects through dominant point detection

1998

Abstract The problem of dominant point detection is posed, taking into account what usually happens in practice. The algorithms found in the literature often prove their performance with laboratory contours, but the shapes in real images present noise, quantization, and high inter and intra-shape variability. These effects are analyzed and solutions to them are proposed. We will also focus on the conditions for an efficient (few points) and precise (low error) dominant point extraction that preserves the original shape. A measurement of the committed error (optimization error, E 0 ) that takes into account both aspects is defined for studying this feature.

Energy savings for indoor lighting in a shopping mall: A case of study

2018

The paper presents an application of energy saving in the final users. In particular, the case of study evaluates the energy consumptions of a big shopping mall, located in the middle part of Italy, illuminated by fluorescent lamps. In order to reduce the energy demand, the case of study shows a first solution based on LED lamps; a second step considers the adding of a building automation system, maximizing the energy saving, thanks lighting sensors that module the luminous flux taking in count of natural lighting through skylights.