Microwave Imaging from Limited-Angle Scattered Data using the Iterative Multi-Scaling Approach

In this paper, with reference to limited-angle data configurations, the performance of the nonlinear multi-scaling inversion approach (IMSA) is analyzed. Such an assessment is carried out by considering synthetically-generated as well as laboratory-controlled experimental data ('Marseille data') concerning two-dimensional dielectric scatterers. The obtained results demonstrate a satisfactory robustness and the reliability of the approach

Effect of potential fluctuations on shot noise suppression in mesoscopic cavities

We perform a numerical investigation of the effect of the disorder associated with randomly located impurities on shot noise in mesoscopic cavities. We show that such a disorder becomes dominant in determining the noise behavior when the amplitude of the potential fluctuations is comparable to the value of the Fermi energy and for a large enough density of impurities. In contrast to existing conjectures, random potential fluctuations are shown not to contribute to achieving the chaotic regime whose signature is a Fano factor of 1/4, but, rather, to the diffusive behavior typical of disordered conductors. In particular, the 1/4 suppression factor expected for a symmetric cavity can be achieved only in high-quality material, with a very low density of impurities. As the disorder strength is increased, a relatively rapid transition of the suppression factor from 1/4 to values typical of diffusive or quasi-diffusive transport is observed. Finally, on the basis of a comparison between a hard-wall and a realistic model of the cavity, we conclude that the specific details of the confinement potential have a minor influence on noise.Comment: 8 pages, 10 figures. This is the final version published in AIP Advances. With respect to the previous arXiv version, there are some changes in the text (mainly in the introduction and in the references); the numerical results are unchange

Magnetized birefringence and CMB polarization

The polarization plane of the cosmic microwave background radiation can be rotated either in a magnetized plasma or in the presence of a quintessential background with pseudoscalar coupling to electromagnetism. A unified treatment of these two phenomena is presented for cold and warm electron-ion plasmas at the pre-recombination epoch. The electron temperature is only relevant to the relativistic correction of the cold plasma results. The spectrum of plasma excitations is obtained from a generalized Appleton--Hartree equation, describing simultaneously the high-frequency propagation of electromagnetic waves in a magnetized plasma with a dynamical quintessence field. It is shown that these two effects are comparable for the plausible range of parameters allowed by present constraints. It is then argued that the generalized expressions derived in the present study may be relevant for direct searches of a possible rotation of the cosmic microwave background polarization.Comment: 9 pages; corrected typos, references adde

Semantic Ambiguity and Perceived Ambiguity

I explore some of the issues that arise when trying to establish a connection between the underspecification hypothesis pursued in the NLP literature and work on ambiguity in semantics and in the psychological literature. A theory of underspecification is developed `from the first principles', i.e., starting from a definition of what it means for a sentence to be semantically ambiguous and from what we know about the way humans deal with ambiguity. An underspecified language is specified as the translation language of a grammar covering sentences that display three classes of semantic ambiguity: lexical ambiguity, scopal ambiguity, and referential ambiguity. The expressions of this language denote sets of senses. A formalization of defeasible reasoning with underspecified representations is presented, based on Default Logic. Some issues to be confronted by such a formalization are discussed.Comment: Latex, 47 pages. Uses tree-dvips.sty, lingmacros.sty, fullname.st

Boosted Statistical Mechanics

Based on the fundamental principles of Relativistic Quantum Mechanics, we give a rigorous, but completely elementary, proof of the relation between fundamental observables of a statistical system when measured relatively to two inertial reference frames, connected by a Lorentz transformation.Comment: 8 page