Duality between k-essence and Rastall gravity

The k-essence theory with a power-law function of $(\partial\phi)^2$ and Rastall's non-conservative theory of gravity with a scalar field are shown to have the same solutions for the metric under the assumption that both the metric and the scalar fields depend on a single coordinate. This equivalence (called k-R duality) holds for static configurations with various symmetries (spherical, plane, cylindrical, etc.) and all homogeneous cosmologies. In the presence of matter, Rastall's theory requires additional assumptions on how the stress-energy tensor non-conservation is distributed between different contributions. Two versions of such non-conservation are considered in the case of isotropic spatially flat cosmological models with a perfect fluid: one (R1) in which there is no coupling between the scalar field and the fluid, and another (R2) in which the fluid separately obeys the usual conservation law. In version R1 it is shown that k-R duality holds not only for the cosmological models themselves but also for their adiabatic perturbations. In version R2, among other results, a particular model is singled out that reproduces the same cosmological expansion history as the standard $\Lambda$CDM model but predicts different behaviors of small fluctuations in the k-essence and Rastall frameworks.Comment: 10 pages, no figures. Two references adde

Energy impact analysis on DTN routing protocols

In this paper, a mechanism designed and implemented on a simulator module is used to study the energy consumption of a network node in a DTN. The mechanism accounts energy consumption in transmission and reception of a message and also in neighboring nodes discovery. These are routine operations performed by nodes as cell phones or PDAs that traditionally integrate the Delay Tolerant Networks. This module includes a battery recharging option, which makes the simulation environment more realistic. The energy module enables the study of the energy consumption impact on the routing protocols used by Delay Tolerant Networks. The experimental results show that, when energy consumption is considered, the optimal operating parameters of the protocols change substantially. As the search for neighboring nodes is mainly responsible for the energy consumption of the nodes, the design of new protocols whose strategy is based only on the reduction of messages exchanged may have little impact in terms of actual network performance.FC

Ghost free dual vector theories in 2+1 dimensions

We explore here the issue of duality versus spectrum equivalence in abelian vector theories in 2+1 dimensions. Specifically we examine a generalized self-dual (GSD) model where a Maxwell term is added to the self-dual model. A gauge embedding procedure applied to the GSD model leads to a Maxwell-Chern-Simons (MCS) theory with higher derivatives. We show that the latter contains a ghost mode contrary to the original GSD model. On the other hand, the same embedding procedure can be applied to $N_f$ fermions minimally coupled to the self-dual model. The dual theory corresponds to $N_f$ fermions with an extra Thirring term coupled to the gauge field via a Pauli-like term. By integrating over the fermions at $N_f\to\infty$ in both matter coupled theories we obtain effective quadratic theories for the corresponding vector fields. On one hand, we have a nonlocal type of the GSD model. On the other hand, we have a nonlocal form of the MCS theory. It turns out that both theories have the same spectrum and are ghost free. By figuring out why we do not have ghosts in this case we are able to suggest a new master action which takes us from the local GSD to a nonlocal MCS model with the same spectrum of the original GSD model and ghost free. Furthermore, there is a dual map between both theories at classical level which survives quantum correlation functions up to contact terms. The remarks made here may be relevant for other applications of the master action approach.Comment: 15 pages, 1 figur

Black-bounce solution in kk-essence theories

In the present work, we construct black-bounce configurations in the context of $k$-essence theory. The solutions have a regular metric function at the origin. The area metric function is linked to the black-bounce area initially considered by Simpson-Visser, $\Sigma^2=x^2+a^2$. Subsequently, the expressions for the scalar field and scalar potential corresponding to the found solutions are determined, exhibiting phantom behavior everywhere due to violation of Null Energy Condition $(NEC^\phi)$. The Kretschmann scalar is regular throughout spacetime, and the geodesics are complete. The energy conditions are analyzed, verifying that the null $(NEC^\phi_1)$ and dominant energy conditions $(DEC^\phi_1)$ are violated inside and outside the event horizon. Finally, the extrinsic curvature method was applied to determine the sign of the mass on the junction surface.Comment: 13 pages, 15 figure

ANÁLISE DO NÍVEL DE ABERTURA DE DADOS GOVERNAMENTAIS DA ÁREA DO TRÂNSITO NO BRASIL

The study aimed to identify the level of data openness of the state transit departments in Brazil (DETRANs). Two assessment instruments were used: Berners-Lee’s (2010) Five Star Scheme and the 15 Open Data Principles proposed by Opengovdata (2007). Based on them, a methodology for structured analysis was built, and used to analyze three sets of data: related to the National Driver's License (CNH), to vehicles, and to traffic violations. Results indicate a low level of openness, a lack of standardization, and the absence of specific regulations to stimulate or oblige the publication of traffic data in open formats.O artigo teve como objetivo identificar o nível de abertura de dados governamentais dos departamentos de trânsito dos governos estaduais (DETRANs) no Brasil. Foram usados dois instrumentos de avaliação: o Esquema de Cinco Estrelas de Berners-Lee (2010) e os 15 Princípios de Dados Abertos do Opengovdata (2007). A partir deles, construiu-se uma metodologia para análise estruturada, aplicada a três conjuntos de dados: os da Carteira Nacional de Habilitação (CNH), os de veículos, e os de infrações de trânsito (multas). Os resultados da análise indicam: baixo nível de abertura de dados e de qualidade das iniciativas de abertura; ausência de padronização de abertura dos dados de trânsito; e ausência de regulamentação específica para estimular e/ou tornar obrigatória a publicação dos dados de trânsito em formato aberto