1,721,137 research outputs found
Asymmetric generalized Gaussian function: a new HOS-based model for generic noise pdfs
No full textThe work is addressed to provide realistic modelling of generic noise probability density functions (pdfs), in order to optimize signal detection in non-Gaussian environments. The target is to obtain a model depending on few parameters (quick and easy to estimate), and so general to be able to describe many kinds of noise (e.g., symmetric or asymmetric, with variable sharpness). To this end, a new HOS-based model is introduced, which derives from the generalized Gaussian function and depends on three parameters: kurtosis (fourth order), for representing variable sharpness, and left and right variances (whose combination provides the same information of skewness - third order) for describing deviation from symmetry. The model is applied in the design of a LOD test for detecting signals corrupted by real underwater acoustic noise in a low-frequency range
Density evaluation and tracking of multiple objects from image sequences
No full textThe architecture of a distributed vision system (DVS) based on a combination of multiple modules of standard and extended Kalman filters is presented. It exploits a representation of static and dynamic knowledge for estimation purposes. Spatial constraints describe how observed image features lead to estimate parameters (i.e., in the present application, the density and position of monitored people in the monitored scene); time constraints are used to describe knowledge on dynamic evolution of the mentioned estimated variables. Using dynamic knowledge allows the system to track groups of people, dynamically interacting each others, on the image plane over time. Experimental results, deriving from an extensive test phase carried out on real-life images of an underground station, confirm that integration of different spatial and temporal constraints is an efficient approach for optimizing parameter estimation in DVSs
Application to locally optimum detection of a new noise model
No full textThe authors discuss the need to provide a realistic model of a generic noise probability density function (PDF), in order to optimize the signal detection in non-Gaussian environments. The target is to obtain a model depending on a few parameters (that are quick and easy to estimate), and is so general that it is able to describe many kinds of noise (e.g., symmetric or asymmetric, with variable sharpness). To this end, a new HOS-based model is introduced, which is derived from the generalized Gaussian function, and depends on three parameters: kurtosis, for representing variable sharpness, and left and right variances (whose combination provides the same information of skewness) for describing the deviation from symmetry. This model is applied to the design of a locally optimum detection (LOD) test. Promising experimental results are presented which are derived from the application of the test to detecting signals corrupted by real underwater acoustic noise
BLOW-UP ON METRIC GRAPHS AND RIEMANNIAN MANIFOLDS
No full textWe study blow-up versus global existence of solutions to a model semilinear parabolic equation in metric measure spaces. Applications to metric graphs and Riemannian manifolds are considered, pointing out the occurrence of the Fujita phenomenon
On a class of perturbed conservation laws
No full textNatalini, R.; Tesei, A.. (1991). On a class of perturbed conservation laws. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/1679
On a pseudoparabolic regularization of a forward-backward-forward equation
No full textWe consider an initial-boundary value problem for a degenerate pseudoparabolic regularization of a nonlinear forward-backward-forward parabolic equation, with a bounded nonlinearity which is increasing at infinity. We prove existence of suitably defined nonnegative solutions of the problem in a space of Radon measures. Solutions satisfy several monotonicity and regularization properties; in particular, their singular part is nonincreasing and may disappear in finite time. The problem is of intrinsic mathematical interest, but also arises naturally when studying, by time reversal, the spontaneous appearance of singularities in a specific application. © 2015 Elsevier Ltd. All rights reserved
Nonuniqueness of solutions for a class of forward-backward parabolic equations
No full textWe study the initial–boundary value problem with measure-valued initial data. Here Ω is a bounded open interval, φ(0)=φ(∞)=0, φ is increasing in (0,α) and decreasing in (α,∞), and the regularising term ψ is increasing but bounded. It is natural to study measure-valued solutions since singularities may appear spontaneously in finite time. Nonnegative Radon measure-valued solutions are known to exist and their construction is based on an approximation procedure. Until now nothing was known about their uniqueness.
In this note we construct some nontrivial examples of solutions which do not satisfy all properties of the constructed solutions, whence uniqueness fails. In addition, we classify the steady state solutions
Pseudo-parabolic regularization of forward- backward parabolic equations: Power-type nonlinearities
No full textWe study a quasilinear parabolic equation of forward-backward type, under
assumptions on the nonlinearity which hold for a wide class of mathematical models, using
a pseudo-parabolic regularization of power type.We prove existence and uniqueness of positive
solutions of the regularized problem in a space of Radon measures. It is shown that these
solutions satisfy suitable entropy inequalities. We also study their qualitative properties, in
particular proving that the singular part of the solution with respect to the Lebesgue measure is
constant in time
HOS-based noise models for signal-detection optimization in non-Gaussian environments
No full textTwo pdf models suitable for describing nonGaussian iid noise are introduced. The models are used in the design of a LOD test for detecting weak signals in real
non Gaussian noise. Results obtained in tlie context of an
underwater acoustic application are encouraging
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