1,353 research outputs found
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
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 invesÂtigates 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
Galaxy formation and cosmic-ray acceleration in a magnetized universe
We study the linear magneto-hydrodynamical behaviour of a Newtonian cosmology
with a viscous magnetized fluid of finite conductivity and generalise the Jeans
instability criterion. The presence of the field favors the anisotropic
collapse of the fluid, which in turn leads to further magnetic amplification
and to an enhanced current-sheet formation in the plane normal to the ambient
magnetic field. When the currents exceed a certain threshold, the resulting
electrostatic turbulence can dramatically amplify the resistivity of the medium
(anomalous resistivity). This could trigger strong electric fields and
subsequently the acceleration of ultra-high energy cosmic rays (UHECRs) during
the formation of protogalactic structures.Comment: 10 pages, ApJL in pres
Gravito-magnetic instabilities in anisotropically expanding fluids
Gravitational instabilities in a magnetized Friedman - Robertson - Walker
(FRW) Universe, in which the magnetic field was assumed to be too weak to
destroy the isotropy of the model, are known and have been studied in the past.
Accordingly, it became evident that the external magnetic field disfavors the
perturbations' growth, suppressing the corresponding rate by an amount
proportional to its strength. However, the spatial isotropy of the FRW Universe
is not compatible with the presence of large-scale magnetic fields. Therefore,
in this article we use the general-relativistic (GR) version of the
(linearized) perturbed magnetohydrodynamic equations with and without
resistivity, to discuss a generalized Jeans criterion and the potential
formation of density condensations within a class of homogeneous and
anisotropically expanding, self-gravitating, magnetized fluids in curved
space-time. We find that, for a wide variety of anisotropic cosmological
models, gravito-magnetic instabilities can lead to sub-horizonal, magnetized
condensations. In the non-resistive case, the power spectrum of the unstable
cosmological perturbations suggests that most of the power is concentrated on
large scales (small k), very close to the horizon. On the other hand, in a
resistive medium, the critical wave-numbers so obtained, exhibit a delicate
dependence on resistivity, resulting in the reduction of the corresponding
Jeans lengths to smaller scales (well bellow the horizon) than the
non-resistive ones, while increasing the range of cosmological models which
admit such an instability.Comment: 10 pages RevTex, 4 figures, accepted for publication in the
International Journal of Modern Physics
Magnetohydrodynamics and Plasma Cosmology
We study the linear magnetohydrodynamic (MHD) equations, both in the
Newtonian and the general-relativistic limit, as regards a viscous magnetized
fluid of finite conductivity and discuss instability criteria. In addition, we
explore the excitation of cosmological perturbations in anisotropic spacetimes,
in the presence of an ambient magnetic field. Acoustic, electromagnetic (e/m)
and fast-magnetosonic modes, propagating normal to the magnetic field, can be
excited, resulting in several implications of cosmological significance.Comment: 9 pages, RevTeX, To appear in the Proceedings of the Peyresq X
Meeting, IJTP Conference Serie
Graviton production in the scaling of a long-cosmic-string network
In a previous paper [1] we considered the possibility that (within the
early-radiation epoch) there has been (also) a short period of a significant
presence of cosmic strings. During this radiation-plus-strings stage the
Universe matter-energy content can be modelled by a two-component fluid,
consisting of radiation (dominant) and a cosmic-string fluid (subdominant). It
was found that, during this stage, the cosmological gravitational waves (CGWs)
- that had been produced in an earlier (inflationary) epoch - with comoving
wave-numbers below a critical value (which depends on the physics of the
cosmic-string network) were filtered, leading to a distorsion in the expected
(scale-invariant) CGW power spectrum. In any case, the cosmological evolution
gradually results in the scaling of any long-cosmic-string network and, hence,
after a short time-interval, the Universe enters into the late-radiation era.
However, along the transition from an early-radiation epoch to the
late-radiation era through the radiation-plus-strings stage, the
time-dependence of the cosmological scale factor is modified, something that
leads to a discontinuous change of the corresponding scalar curvature, which,
in turn, triggers the quantum-mechanical creation of gravitons. In this paper
we discuss several aspects of such a process, and, in particular, the
observational consequences on the expected gravitational-wave (GW) power
spectrum.Comment: 12 pages, 2 figures, accepted for publication in Physical Review
Nonperturbative semiclassical stability of de Sitter spacetime for small metric deviations
We consider the linearized semiclassical Einstein equations for small deviations around de Sitter spacetime including the vacuum polarization effects of conformal fields. Employing the method of order reduction, we find the exact solutions for general metric perturbations (of scalar, vector and tensor type). Our exact (nonperturbative) solutions show clearly that in this case de Sitter is stable with respect to small metric deviations and a late-time attractor. Furthermore, they also reveal a breakdown of perturbative solutions for a sufficiently long evolution inside the horizon. Our results are valid for any conformal theory, even self-interacting ones with arbitrarily strong coupling
Energy Resolution Performance of the CMS Electromagnetic Calorimeter
The energy resolution performance of the CMS lead tungstate crystal electromagnetic calorimeter is presented. Measurements were made with an electron beam using a fully equipped supermodule of the calorimeter barrel. Results are given both for electrons incident on the centre of crystals and for electrons distributed uniformly over the calorimeter surface. The electron energy is reconstructed in matrices of 3 times 3 or 5 times 5 crystals centred on the crystal containing the maximum energy. Corrections for variations in the shower containment are applied in the case of uniform incidence. The resolution measured is consistent with the design goals
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