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

THE CAPITAL STRUCTURE OF COMPANIES LISTED IN THE GREEK STOCK EXCHANGE

The paper’s aim is to review the capital structure theories, and especially signalling theory. It investigates whether the capital structure signalling theory is reliable in cases of companies listed at the Athens Stock Exchange. The companies used in the sample, raised new equity from 2004 until 2006, and the paper examines their stock price reaction to the announcement.Capital structure, signalling theory

Use of unbalanced laminates as a screening method for microcracking

State-of-the-art, high temperature polyimide matrix composites, reinforced with continuous graphite fibers are known to be susceptible to intraply cracking when thermally cycled over their useful service temperature range. It is believed that the transply cracking, in part, results from residual stresses caused by differences in coefficients of thermal expansion (CTE) between the polymer matrix and the reinforcement. Thermal cycling tests to investigate this phenomenon involve expensive time and energy consuming programs which are not economically feasible for use as a part of a materials screening process. As an alternative to thermal cycling studies, a study of unbalanced crossply graphite fiber reinforcement composites was conducted to assess the effect of the composite ply layup and surface condition on the residual stresses that remain after the processing of these materials. The residual stresses were assessed by measuring the radii of curvature of the types of laminates that were studied. The temperature at which stress-free conditions existed were determined and a dye penetrant method was used to observe surface damage resulting from excessive residual stress buildup. These results are compared with some published results of thermal cycling tests that were previously conducted on balanced polyimide composites

Pre-Inflation in the Presence of Conformal Coupling

We consider a massless scalar field, conformally coupled to the Ricci scalar curvature, in the pre-inflation era of a closed FLRW Universe. The scalar field potential can be of the form of the Coleman-Weinberg one-loop potential, which is flat at the origin and drives the inflationary evolution. For positive values of the conformal parameter \xi, less than the critical value xi_c=(1/6), the model admits exact solutions with non-zero scale factor and zero initial Hubble parameter. Thus these solutions can be matched smoothly to the so called Pre-Big-Bang models. At the end of this pre-inflation era one can match inflationary solutions by specifying the form of the potential and the whole solution is of the class C^(1).Comment: 11 pages, 5 figures, LaTeX, Accepted for publication in MPL

The effect of contact stresses in four-point bend testing of graphite/epoxy and graphite/PMR-15 composite beams

The results of in-plane four-point bend experiments on unidirectionally reinforced composite beams are presented for graphite/epoxy (T300/934) and graphite/polyimide (G30-500/PMR-15) composites. The maximum load and the location of cracks formed during failure were measured for testpieces with fibers oriented at various angles to the beam axis. Since most of the beams failed near one or more of the load points, the strength of the beams was evaluated in terms of a proposed model, for the local stress distribution. In this model, an exact solution to the problem of a localized contact force acting on a unidirectionally reinforced half plane is used to describe the local stress field. The stress singularity at the load points is treated in a manner similar to the stress singularity at a crack tip in fracture mechanisms problems. Using this approach, the effect of fiber angle and elastic material properties on the strength of the beam is described in terms of a load intensity factor. For fiber angles less than 45 deg from the beam axis, a single crack is initiated near one of the load points at a critical value of the load intensity factor. The critical load intensity factor decreases with the increasing fiber angle. For larger fiber angles, multiple cracks occur at locations both near and away from the load points, and the load intensity factor at failure increases sharply with increasing fiber angle

The capital structure of companies listed in the greek stock exchange

The paper’s aim is to review the capital structure theories, and especially signalling theory. It investigates whether the capital structure signalling theory is reliable in cases of companies listed at the Athens Stock Exchange. The companies used in the sample, raised new equity from 2004 until 2006, and the paper examines their stock price reaction to the announcement

Capital structure signaling theory : evidence from the greek stock exchange

The paper's aim is to review the capital structure theories, and especially signaling theory. It inves­tigates whether the capital structure signaling theory is reliable in cases of companies listed at the Athens Stock Exchange. The companies used in the sample, raised new equity from 2004 until 2006, and the paper examines their stock price reaction to the announcement