Coalescing binaries as possible standard candles

Gravitational waves detected from well-localized inspiraling binaries would allow to determine, directly and independently, both binary luminosity and redshift. In this case, such systems could behave as "standard candles" providing an excellent probe of cosmic distances up to $z <0.1$ and thus complementing other indicators of cosmological distance ladder.Comment: 6 pages, 5 figures. accepted in Astroparticle Physic

Epistemic Logic Programs: A Study of Some Properties

Epistemic logic programs (ELPs), extend answer set programming (ASP) with epistemic operators. The semantics of such programs is provided in terms of world views, which are sets of belief sets, that is, syntactically, sets of sets of atoms. Different semantic approaches propose different characterizations of world views. Recent work has introduced semantic properties that should be met by any semantics for ELPs, like the Epistemic Splitting Property, that, if satisfied, allows to modularly compute world views in a bottom-up fashion, analogously to "traditional"ASP. We analyze the possibility of changing the perspective, shifting from a bottom-up to a top-down approach to splitting. We propose a basic top-down approach, which we prove to be equivalent to the bottom-up one. We then propose an extended approach, where our new definition: (i) is provably applicable to many of the existing semantics; (ii) operates similarly to "traditional"ASP; (iii) provably coincides under any semantics with the bottom-up notion of splitting at least on the class of Epistemically Stratified Programs (which are, intuitively, those where the use of epistemic operators is stratified); (iv) better adheres to common ASP programming methodology

Epistemic Logic Programs: a Novel Perspective and Some Extensions

Epistemic Logic Programs (ELPs), which propose an extension to Answer Set Programming (ASP) with epistemic operators, have their semantic defined, in various ways, in terms of world views, which are sets of belief sets. Several semantic approaches have in fact been proposed over time to characterize world views, and, recently, to also characterize semantic properties that should be met by any semantics for ELPs. We propose a new semantics, easy also from the computational point of view, but effective, also in order to compare the different semantic approaches. We also propose a significant extension to the ELP approach, by allowing epistemic atoms in rule heads

Gravitational and electromagnetic emission by magnetized coalescing binary systems

We discuss the possibility to obtain an electromagnetic emission accompanying the gravitational waves emitted in the coalescence of a compact binary system. Motivated by the existence of black hole configurations with open magnetic field lines along the rotation axis, we consider a magnetic dipole in the system, the evolution of which leads to (i) electromagnetic radiation, and (ii) a contribution to the gravitational radiation, the luminosity of both being evaluated. Starting from the observations on magnetars, we impose upper limits for both the electromagnetic emission and the contribution of the magnetic dipole to the gravitational wave emission. Adopting this model for the evolution of neutron star binaries leading to short gamma ray bursts, we compare the correction originated by the electromagnetic field to the gravitational waves emission, finding that they are comparable for particular values of the magnetic field and of the orbital radius of the binary system. Finally we calculate the electromagnetic and gravitational wave energy outputs which result comparable for some values of magnetic field and radius.Comment: 9 pages, 3 figures, to appear in Astroph. Sp.Scienc

Fast Prototyping of a Solver for Reduct-based ELP Semantics

Several semantic approaches have been proposed over time for Epistemic Logic Programs (ELPs), which is an extension to Answer Set Programming (ASP) with epistemic operators. ELP semantics has been defined, in various ways, in terms of world views, which are sets whose elements are sets of atoms. Several semantic approaches are Reduct-based, i.e., extend to ELPs what done for ASP, in the sense that in order to find the world views of a given program they propose to: start with a candidate world view; build the reduct of the program with respect to this candidate world view, according to some specific definition of such reduct; compute the set of stable models of the reduct; check whether the candidate world view is indeed a world view, which is the case if it coincides with the set of stable models of the reduct. Solvers have been developed for some of these approaches, but new semantics/variations have been introduced, and are likely to be introduced in the future, as there is no consensus yet on the “right” semantics. We propose a fast-prototyping approach to obtain a solver for any reduct-based semantics, with the advantage to be able to experiment the approach on small/medium programs, and not only on very small programs as done so far, prior to undertaking the costly process of developing a dedicated solver

Epistemic Logic Programs: an Approach to Semantic Comparison

Epistemic Logic Programs (ELPs) extend Answer Set Programming (ASP) with epistemic operators. The semantics of such programs is provided in terms of world views, which are sets of belief sets. Several semantic approaches have been proposed over time to characterize world views. Recent work has introduced semantic properties that should be met by any semantics for ELPs. We propose a new method, easy but, we believe, effective, to compare the different semantic approaches

Temporalizing Epistemic Logic L-DINF

Agents and Multi-Agent Systems (MAS) are a technology that has many fields of application, which extend also to human sciences and where Computational Logic has been widely applied. In this paper, we join together two of our long-lasting lines of work in this field. In particular, we introduce time and time intervals into the epistemic logic L-DINF, that copes with group dynamics in MAS

A Timed Epistemic Logic for Formalizing Cooperation among Groups of Agents

In the multi-agent setting, it is relevant to model group dynamics of agents, and logic has proved to be an excellent tool. We have proposed in previous work an epistemic logic that allows one to formalize the new beliefs formed or removed by a group of agents, where several groups can co-exist and where an agent can pass from one group to another. A novelty introduced in this paper is that an agent can be lent by a (willing) group to another one in case of need. Another distinguished feature we introduce in this paper is time and temporal instants/intervals to express the time periods in which agents’ beliefs hold

The structure of the plasma sheet-lobe boundary in the Earth's magnetotail

The structure of the magnetotail plasma sheet-plasma lobe boundary was studied by observing the properties of tailward flowing O+ ion beams, detected by the ISEE 2 plasma experiment inside the boundary during three time periods. The computed value of the north-south electric field component as well as the O+ parameters are shown to change at the boundary. The results are related to other observations made in this region. The O+ parameters and the Ez component behavior are shown to be consistent with that expected from the topology of the electric field lines in the tail as mapped from the ionosphere