Light-cone fluctuations and the renormalized stress tensor of a massless scalar field

We investigate the effects of light-cone fluctuations over the renormalized vacuum expectation value of the stress-energy tensor of a real massless minimally coupled scalar field defined in a ($d+1$)-dimensional flat space-time with topology ${\cal R}\times {\cal S}^d$. For modeling the influence of light-cone fluctuations over the quantum field, we consider a random Klein-Gordon equation. We study the case of centered Gaussian processes. After taking into account all the realizations of the random processes, we present the correction caused by random fluctuations. The averaged renormalized vacuum expectation value of the stress-energy associated with the scalar field is presented

Reference Frames and the Physical Gravito-Electromagnetic Analogy

The similarities between linearized gravity and electromagnetism are known since the early days of General Relativity. Using an exact approach based on tidal tensors, we show that such analogy holds only on very special conditions and depends crucially on the reference frame. This places restrictions on the validity of the "gravito-electromagnetic" equations commonly found in the literature.Comment: 9 Pages, 1 figure. To appear in the Proceedings of the IAU Symposium 261 "Relativity in Fundamental Astronomy: Dynamics, Reference Frames, and Data Analysis", Virginia Beach, USA, 27 April - 1 May 200

Einstein-Cartan theory as a theory of defects in space-time

The Einstein-Cartan theory of gravitation and the classical theory of defects in an elastic medium are presented and compared. The former is an extension of general relativity and refers to four-dimensional space-time, while we introduce the latter as a description of the equilibrium state of a three-dimensional continuum. Despite these important differences, an analogy is built on their common geometrical foundations, and it is shown that a space-time with curvature and torsion can be considered as a state of a four-dimensional continuum containing defects. This formal analogy is useful for illustrating the geometrical concept of torsion by applying it to concrete physical problems. Moreover, the presentation of these theories using a common geometrical basis allows a deeper understanding of their foundations.Comment: 18 pages, 7 EPS figures, RevTeX4, to appear in the American Journal of Physics, revised version with typos correcte

Guidance, Flight Mechanics and Trajectory Optimization. Volume 5 - State Determination And/or Estimation

Guidance, flight mechanics, and trajectory optimizatio

The definition of corporate corruption prevention during the last decade: Bibliometrics and content data for the future research agenda

The purpose of this research is to provide a valuable study about the development of literature on corruption prevention during the last decade suggesting the way for the future agenda. We collected documents with the aims to develop a structured literature review (SLR). We collected 113 documents adopting a not grey analysis. Our results shows two main research areas: (i) the corruption prevention understanding its features and using accounting and ethical activities in the business and government procurement and (ii) anticorruption measures, disclosure and behaviours as renewed tools to increase corporate governance sustainability and corporate social responsibility. This is the first time for proposing the SLR on corporate corruption preventions and renewed models directed to build an updated background and emerging issues. This paper is original because proposes for the first time the literature collection of corporate corruption prevention's models providing valuable insights, critique and definition for the future research

Gravitomagnetic Resonance Shift due to a Slowly Rotating Compact Star

The effect of a slowly rotating mass on a forced harmonic oscillator with two degrees of freedom is studied in the weak field approximation. It is found that according to the general theory of relativity there is a shift in the resonat frequency of the oscillator which depends on the density and rotational frequency of the gravitational source. The proposed shift is quite small under normal physical situations however it is estimated that for compact x-ray sources such as white dwarfs, pulsars, and neutron stars the shift is quite appreciable.Comment: 8 pages, 2 figures, Accepted for Publication in Inter. Journal of Modern Physics

Media devices in pre-school children: the recommendations of the Italian pediatric society

BACKGROUND: Young children are too often exposed to mobile devices (MD) and most of them had their own device. The adverse effects of a early and prolonged exposure to digital technology on pre-school children has been described by several studies. Aim of the study is to analyze the consequences of MD exposure in pre-school children. METHODS: We analyzed the documented effects of media exposure on children's mental and physical health. RESULTS: According to recent studies, MD may interfere with learning, children development, well being, sleep, sight, listening, caregiver-child relationship. DISCUSSION: Pediatricians should be aware of both the beneficial and side effects of MD and give advice to the families, according to children's age. CONCLUSION: In according to literature, the Italian Pediatric Society suggest that the media device exposure in childhood should be modulated by supervisors

Chaotic Accretion in a Non-Stationary Electromagnetic Field of a Slowly Rotating Compact Star

We investigate charge accretion in vicinity of a slowly rotating compact star with a non-stationary electromagnetic field. Exact solutions to the general relativistic Maxwell equations are obtained for a star formed of a highly degenerate plasma with a gravitational field given by the linearized Kerr metric. These solutions are used to formulate and then to study numerically the equations of motion for a charged particle in star's vicinity using the gravitoelectromagnetic force law. The analysis shows that close to the star charge accretion does not always remain ordered. It is found that the magnetic field plays the dominant role in the onset of chaos near the star's surface.Comment: 9 pages, 4 figure

Doppler Effects from Bending of Light Rays in Curved Space-Times

We study Doppler effects in curved space-time, i.e. the frequency shifts induced on electromagnetic signals propagating in the gravitational field. In particular, we focus on the frequency shift due to the bending of light rays in weak gravitational fields. We consider, using the PPN formalism, the gravitational field of an axially symmetric distribution of mass. The zeroth order, i.e. the sphere, is studied then passing to the contribution of the quadrupole moment, and finally to the case of a rotating source. We give numerical estimates for situations of physical interest, and by a very preliminary analysis, we argue that analyzing the Doppler effect could lead, in principle, in the foreseeable future, to the measurement of the quadrupole moment of the giant planets of the Solar System.Comment: 16 pages, 2 EPS figures; to appear in the International Journal of Modern Physics