Cryptanalysis of a computer cryptography scheme based on a filter bank

This paper analyzes the security of a recently-proposed signal encryption scheme based on a filter bank. A very critical weakness of this new signal encryption procedure is exploited in order to successfully recover the associated secret key.Comment: 6 pages, 1 figur

Beyond the String Genus

In an earlier work we used a path integral analysis to propose a higher genus generalization of the elliptic genus. We found a cobordism invariant parametrized by Teichmuller space. Here we simplify the formula and study the behavior of our invariant under the action of the mapping class group of the Riemann surface. We find that our invariant is a modular function with multiplier just as in genus one.Comment: 40 pages, 1 figur

Invertibility of spectral x-ray data with pileup--two dimension-two spectrum case

In the Alvarez-Macovski method, the line integrals of the x-ray basis set coefficients are computed from measurements with multiple spectra. An important question is whether the transformation from measurements to line integrals is invertible. This paper presents a proof that for a system with two spectra and a photon counting detector, pileup does not affect the invertibility of the system. If the system is invertible with no pileup, it will remain invertible with pileup although the reduced Jacobian may lead to increased noise

A Fatou theorem for FF-harmonic functions

In this paper we study a class of functions that appear naturally in some equidistribution problems and that we call $F$-harmonic. These are functions of the universal cover of a closed and negatively curved which possess an integral representation analogous to the Poisson representation of harmonic functions, where the role of the Poisson kernel is played by a H\"older continuous kernel. More precisely we prove a theorem \`a la Fatou about the nontangential convergence of quotients of such functions, from which we deduce some basic properties such as the uniqueness of the $F$-harmonic function on a compact manifold and of the integral representation of $F$-harmonic functions.Comment: 26 pages, final version, to appear in Mathematische Zeitschrif

Aharonov-Bohm scattering on a cone

The Aharonov-Bohm scattering amplitude is calculated in the context of planar gravity with localized sources which also carry a magnetic flux. These sources cause space-time to develop conical singularities at their location, thus introducing novel effects in the scattering of electrically charged particles. The behaviour of the wave function in the proximity of the classical scattering directions is analyzed by means of an asymptotic expansion previously introduced by the author. It is found that, in contrast with the Aharonov-Bohm effect in flat space, integer values of the numerical flux can produce observable effects.Comment: 6 pages, 1 figur