Complex contact manifolds and S^{1} actions

We prove rigidity and vanishing theorems for several holomorphic Euler characteristics on complex contact manifolds admitting holomorphic circle actions preserving the contact structure. Such vanishings are reminiscent of those of LeBrun and Salamon on Fano contact manifolds but under a symmetry assumption instead of a curvature condition

A middleware for creating physical mashups of things

Indexación: Scopus.Nowadays, “things” deployed in cities are crucial to gather data to support decision making systems. Unfortunately, there is a low level of reuse of “things” between smart city applications of different organizations because “things” were unknown to developers or because it was harder to reuse them than use new ones due to technical details. In this ongoing work, we propose to convert “things” into active entities capable of discovering and organizing themselves driven by the applications goals’ satisfaction. Moreover, “things” are capable of collaborating between them in order to satisfy or maintain satisfied the published goals of applications. To validate the feasibility of our proposal, we are building mashThings, an Internet of Things (IoT) platform to build smart city applications as physical mashups, where the middleware layer is augmented by a multiagent layer of broker agents representing the available “things” in the city.http://ceur-ws.org/Vol-1950/paper11.pd

Relativistic gravitational collapse in comoving coordinates: The post-quasistatic approximation

A general iterative method proposed some years ago for the description of relativistic collapse, is presented here in comoving coordinates. For doing that we redefine the basic concepts required for the implementation of the method for comoving coordinates. In particular the definition of the post-quasistatic approximation in comoving coordinates is given. We write the field equations, the boundary conditions and a set of ordinary differential equations (the surface equations) which play a fundamental role in the algorithm. As an illustration of the method, we show how to build up a model inspired in the well known Schwarzschild interior solution. Both, the adiabatic and non adiabatic, cases are considered.Comment: 14 pages, 11 figures; updated version to appear in Int. J. Modern Phys.

Collapsing Spheres Satisfying An "Euclidean Condition"

We study the general properties of fluid spheres satisfying the heuristic assumption that their areas and proper radius are equal (the Euclidean condition). Dissipative and non-dissipative models are considered. In the latter case, all models are necessarily geodesic and a subclass of the Lemaitre-Tolman-Bondi solution is obtained. In the dissipative case solutions are non-geodesic and are characterized by the fact that all non-gravitational forces acting on any fluid element produces a radial three-acceleration independent on its inertial mass.Comment: 1o pages, Latex. Title changed and text shortened to fit the version to appear in Gen.Rel.Grav

Approximate gravitational field of a rotating deformed mass

A new approximate solution of vacuum and stationary Einstein field equations is obtained. This solution is constructed by means of a power series expansion of the Ernst potential in terms of two independent and dimensionless parameters representing the quadrupole and the angular momentum respectively. The main feature of the solution is a suitable description of small deviations from spherical symmetry through perturbations of the static configuration and the massive multipole structure by using those parameters. This quality of the solution might eventually provide relevant differences with respect to the description provided by the Kerr solution.Comment: 16 pages. Latex. To appear in General Relativity and Gravitatio

Oscillations of Thick Accretion Discs Around Black Holes

We present a numerical study of the response of a thick accretion disc to a localized, external perturbation with the aim of exciting internal modes of oscillation. We find that the perturbations efficiently excite global modes recently identified as acoustic p--modes, and closely related to the epicyclic oscillations of test particles. The two strongest modes occur at eigenfrequencies which are in a 3:2 ratio. We have assumed a constant specific angular momentum distribution within the disc. Our models are in principle scale--free and can be used to simulate accretion tori around stellar or super massive black holes.Comment: 4 pages, 4 figures, accepted for publication as a letter in the Monthly Notices of the Royal Astronomical Societ

Oscillations of Thick Accretion Discs Around Black Holes - II

We present a numerical study of the global modes of oscillation of thick accretion discs around black holes. We have previously studied the case of constant distributions of specific angular momentum. In this second paper, we investigate (i) how the size of the disc affects the oscillation eigenfrequencies, and (ii) the effect of power-law distributions of angular momentum on the oscillations. In particular, we compare the oscillations of the disc with the epicyclic eigenfrequencies of a test particle with different angular momentum distributions orbiting around the central object. We find that there is a frequency shift away from the epicyclic eigenfrequency of the test particle to lower values as the size of the tori is increased. We have also studied the response of a thick accretion disc to a localized external perturbation using non constant specific angular momentum distributions within the disc. We find that in this case it is also possible (as reported previously for constant angular momentum distributions) to efficiently excite internal modes of oscillation. In fact we show here that the local perturbations excite global oscillations (acoustic p modes) closely related to the epicyclic oscillations of test particles. Our results are particularly relevant in the context of low mass X-ray binaries and microquasars, and the high frequency Quasi-Periodic Oscillations (QPOs) observed in them. Our computations make use of a Smooth Particle Hydrodynamics (SPH) code in azimuthal symmetry, and use a gravitational potential that mimics the effects of strong gravity.Comment: 10 pages, 8 figures, accepted for publication as a paper in the Monthly Notices of the Royal Astronomical Societ