1,721,239 research outputs found
Inversion of bremsstrahlung spectra emitted by solar plasma
No full textBremsstrahlung radiation coming from the solar atmosphere is linked to the distribution function of electrons in the solar plasma through a Volterra equation of the first kind. We have assumed the Bethe-Heitler approximation for the bremsstrahlung cross section and we have applied the SVD method to the integral equation with discrete data. Using Tikhonov's regularisation technique, reconstructions of the electronic distribution functions have been obtained, both for simulated and real data
A simple regularization method for solving acoustical inverse scattering problems
No full textThe problem of determining the shape of an object from far-field data is considered. We present a method, originally formulated in Ref. 1 and furtherly modified in Ref. 3, for the solution of this ill-posed nonlinear inverse problem whose main features are:
• the method is exact, that is no low- or high-frequency approximation is considered;
• it is not necessary to know the number of scatterers and whether or not the scatterers are penetrable by the waves;
• if the medium is not penetrable, it is not necessary to know whether the obstacle is sound-hard or sound-soft;
• in the case of an inhomogeneous scatterer, the method provides the shape of the inhomogeneity.
The method is particularly simple since it requires only the solution of a linear Fredholm integral equation of the first kind whose integral kernel is the far-field pattern. The numerical instability due to ill-conditioning can be reduced by using regularization algorithms such as Tikhonov method where the regularization parameter is chosen by using Morozov's discrepancy principle generalized to the case where the noise affects the kernel of the integral operator
On uniqueness for anisotropic inhomogeneous inverse scattering problems
No full textThe problem of determining the shape of a two-dimensional inhomogeneous orthotropic scatterer from far-field data is considered. In particular, by using integral equation techniques we prove that the support of the scatterer is uniquely determined if the far-field pattern is known for all incident directions. We point out that this uniqueness result may be useful also for practical applications, since in previously treated cases (isotropic inhomogeneous objects in the case of transverse magnetic incident waves and homogeneous orthotropic objects in the case of transverse electric incident waves) the theorems proving uniqueness have been quite straightforwardly extended to formulate a simple method for solving the inverse scattering problem
Computational validation of a particle filtering approach to the solution of the meg inverse problem
No full textComputational validation of a particle filtering approach to the solution of the meg inverse problem
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