1,219 research outputs found
A relativistic positioning system exploiting pulsating sources for navigation across the Solar System and beyond
No full textWe introduce an operational approach to the use of pulsating sources, located at spatial infinity, for defining a relativistic positioning and navigation system, based on the use of null four-vectors in a flatMinkowskian spacetime. We describe our approach and discuss the validity of it and of the other approximations we have considered in actual physical situations. As a prototypical case, we show how pulsars can be used to define such a positioning system: the reception of the pulses for a set of different sources whose positions in the sky and periods are assumed to be known allows the determination of the user's coordinates and spacetime trajectory, in the reference frame where the sources are at rest. In order to confirm the viability of the method, we consider an application example reconstructing the world-line of an idealized Earth in the reference frame of distant pulsars: in particular we have simulated the arrival times of the signals fromfour pulsars at the location of the Parkes radiotelescope in Australia. After pointing out the simplifications we have made, we discuss the accuracy of the method. Eventually, we suggest that the method could actually be used for navigation across the Solar System and be based on artificial sources, rather than pulsar
Rotation Effects in Relativity
No full textRotation has always been a central thread in physics and has influenced its development [...
Solar System tests in f(T) gravity
No full textWe investigate the four solar system tests of gravity - perihelion precession, light bending, Shapiro time delay, gravitational redshift - in gravity. In particular, we investigate the solution derived by Ruggiero and Radicella, Phys. Rev. D 91, 104014 (2015), for a nondiagonal vierbein field for a polynomial , where is a constant and . In this paper, we derive the solutions for each test, in which Weinberg's, Bodenner and Will's, Cattani et al. and Rindler and Ishak's methods are applied, Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity (Wiley, New York, 1972); Am. J. Phys. 71 (2003); Phys. Rev. D 87, 047503 (2013); Phys. Rev. D 76, 043006 (2007). We set a constraint on alpha for = 2, 3 by using data available from literatur
A Note on the Gravitoelectromagnetic Analogy
No full textWe discuss the linear gravitoelectromagnetic approach used to solve Einstein’s equations in the weak-field and slow-motion approximation, which is a powerful tool to explain, by analogy with electromagnetism, several gravitational effects in the solar system, where the approximation holds true. In particular, we discuss the analogy, according to which Einstein’s equations can be written as Maxwell-like equations, and focus on the definition of the gravitoelectromagnetic fields in non-stationary conditions. Furthermore, we examine to what extent, starting from a given solution of Einstein’s equations, gravitoelectromagnetic fields can be used to describe the motion of test particles using a Lorentz-like force equation
Understanding political violence: a criminological analysis
No full textUnderstanding Political Violence introduces political violence in the context of sociological and criminological debates. The author distinguishes between political violence from below, for example collective violence, insurgency, armed struggle and terrorism; and political violence from above, which includes indiscriminate repression, institutional and state violence, torture and war. Vincenzo Ruggiero discusses and critiques the contribution of criminological theory to understanding political violence. He draws on stimulating case studies to illustrate the theory, including interviews with former members of the Red Army Faction in Germany and the Brigate Rosse in Italy.The concluding chapter examines the recent development of a criminology of war and calls for a general ceasefire and the criminalisation of war, the most extreme form of institutional violence.This is essential reading for students and researchers in criminology, political studies, sociology, and war and conflict studies.
This book, published in 2006, is now available in Italian and a Spanish and a Russian edition will soon be available
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