Acceleration and Cyclotron Radiation, Induced by Gravitational Waves

The equations which determine the response of a charged particle moving in a magnetic field to an incident gravitational wave(GW) are derived in the linearized approximation to general relativity. We briefly discuss several astrophysical applications of the derived formulae taking into account the resonance between the wave and the particle's motion which occurs at $\omega_g=2\Omega$, whenever the GW is parallel to the constant magnetic field. In the case where the GW is perpendicular to the constant magnetic field, magnetic resonances appear at $\omega_g=\Omega$ and $\omega_g=2\Omega$. Such resonant mechanism may be useful to build models of GW driven cyclotron emitters.Comment: 16 pages, 1 figure, accepted for publication in Astronomy & Astrophysic

Eigenvalue gaps for the Laplacian on hypersurfaces of the sphere

We provide lower estimates for the eigenvalues of the laplacian for hypersurfaces of the round sphere.Comment: We repair crucial typos and constant

Corporate Governance as an instrument of change state owned Corporate Governance as an instrument of change state owned companies: The case of the Hellenic Telecommunications Organization

This paper analyses the evolution of Corporate Governance (CG) mechanisms and organizational changes of the Hellenic Telecommunication Organization (HTO) and has two objectives: to enrich the debate and to contribute to the increasing body of literature by examining and analyzing the organizational and institutional changes taken place in the HTO; and to place the HTO’s case within the international debate regarding the privatization of state-owned companies and the importance of CG mechanisms as instruments of change. It is argued that the privatization of state-owned companies, when is accompanied with appropriate reform measures, can produce multiple positive effects. CG reforms were the main instruments that used in order to prepare the telecommunications incumbent to face the open and competitive markets.Corporate Governance Hellenic Telecommunications Organization (HTO), state-owned companies, privatization, change

The instability of naked singularities in the gravitational collapse of a scalar field

One of the fundamental unanswered questions in the general theory of relativity is whether ``naked'' singularities, that is singular events which are visible from infinity, may form with positive probability in the process of gravitational collapse. The conjecture that the answer to this question is in the negative has been called ``cosmic censorship.'' The present paper, which is a continuation previous work, addresses this question in the context of the spherical gravitational collapse of a scalar field.Comment: 35 pages, published version, abstract added in migratio

The route to chaos for the Kuramoto-Sivashinsky equation

The results of extensive numerical experiments of the spatially periodic initial value problem for the Kuramoto-Sivashinsky equation. This paper is concerned with the asymptotic nonlinear dynamics at the dissipation parameter decreases and spatio-temporal chaos sets in. To this end the initial condition is taken to be the same for all numerical experiments (a single sine wave is used) and the large time evolution of the system is followed numerically. Numerous computations were performed to establish the existence of windows, in parameter space, in which the solution has the following characteristics as the viscosity is decreased: a steady fully modal attractor to a steady bimodal attractor to another steady fully modal attractor to a steady trimodal attractor to a periodic attractor, to another steady fully modal attractor, to another periodic attractor, to a steady tetramodal attractor, to another periodic attractor having a full sequence of period-doublings (in parameter space) to chaos. Numerous solutions are presented which provide conclusive evidence of the period-doubling cascades which precede chaos for this infinite-dimensional dynamical system. These results permit a computation of the length of subwindows which in turn provide an estimate for their successive ratios as the cascade develops. A calculation based on the numerical results is also presented to show that the period doubling sequences found here for the Kuramoto-Sivashinsky equation, are in complete agreement with Feigenbaum's universal constant of 4,669201609... . Some preliminary work shows several other windows following the first chaotic one including periodic, chaotic, and a steady octamodal window; however, the windows shrink significantly in size to enable concrete quantitative conclusions to be made