Time filter

Source Type

De Melo V.V.,Federal University of São Paulo | Carosio G.L.C.,Brazilian Technological Institute of Aeronautics
Expert Systems with Applications | Year: 2013

Several constrained and unconstrained optimization problems have been adequately solved over the years thanks to advances in the metaheuristics area. In the last decades, different metaheuristics have been proposed employing new ideas, and hybrid algorithms that improve the original metaheuristics have been developed. One of the most successfully employed metaheuristics is the Differential Evolution. In this paper it is proposed a Multi-View Differential Evolution algorithm (MVDE) in which several mutation strategies are applied to the current population to generate different views at each iteration. The views are then merged according to the winner-takes-all paradigm, resulting in automatic exploration/exploitation balance. MVDE was tested to solve a set of well-known constrained engineering design problems and the obtained results were compared to those from many state-of-The-art metaheuristics. Results show that MVDE was very competitive in the considered problems, largely outperforming several of the compared algorithms. © 2012 Elsevier Ltd. All rights reserved.

Dias S.S.,Embraer SA | Bruno M.G.S.,Brazilian Technological Institute of Aeronautics
IEEE Transactions on Signal Processing | Year: 2013

This paper introduces new cooperative particle filter algorithms for tracking emitters using received-signal strength (RSS) measurements. In the studied scenario, multiple RSS sensors passively observe different attenuated and noisy versions of the same signal originating from a moving emitter and cooperate to estimate the emitter state. Assuming unknown sensor noise variances, we derive an exact decentralized implementation of the centralized particle filter solution for this problem in a fully connected network. Next, assuming only local internode communication, we introduce two fully distributed consensus-based solutions to the cooperative tracking problem using respectively average consensus iterations and a novel ordered minimum consensus approach. In the latter case, we are able to reproduce the exact centralized solution in a finite number of consensus iterations. To further reduce the communication cost, we derive in the sequel a new suboptimal algorithm which employs suitable parametric approximations to summarize messages that are broadcast over the network. Numerical simulations with small-scale networks show that the proposed approximation leads to a modest degradation in performance, but with much lower communication overhead. Finally, we introduce a second alternative low communication cost algorithm based on random information dissemination. © 1991-2012 IEEE.

de Assis S.C.,Brazilian Technological Institute of Aeronautics | Terra M.O.,Brazilian Technological Institute of Aeronautics
Celestial Mechanics and Dynamical Astronomy | Year: 2014

The escape of trajectories of a spacecraft, or comet or asteroid in the presence of the Earth–Moon system is investigated in detail in the context of the planar circular restricted three-body problem, in a scattering region around the Moon. The escape through the necks around the collinear points L1 and L2 as well as the leaking produced by considering collisions with the Moon surface, taking the lunar mean radius into account, were considered. Given that different transport channels are available as a function of the Jacobi constant, four distinct escape regimes are analyzed. Besides the calculation of exit basins and of the spatial distribution of escape time, the qualitative dynamical investigation through Poincaré sections is performed in order to elucidate the escape process. Our analyses reveal the dependence of the properties of the considered escape basins with the energy, with a remarkable presence of fractal basin boundaries along all the escape regimes. Finally, we observe the plentiful presence of stickiness motion near stability islands which plays a remarkable role in the longest escape time behavior. The application of this analysis is important both in space mission design and study of natural systems, given that fractal boundaries are related with high sensitivity to initial conditions, implying in uncertainty between safe and unsafe solutions, as well as between escaping solutions that evolve to different phase space regions. © 2014, Springer Science+Business Media Dordrecht.

Frederico T.,Brazilian Technological Institute of Aeronautics
Few-Body Systems | Year: 2014

The theoretical few-body aspects associated with universal properties of weakly-bound neutron-rich light nuclei close to the drip line will be reviewed briefly, considering recent theoretical and experimental works. We will address low-energy properties of the one- and two-neutron halo of light exotic nuclei, which are dominated by s-wave short-range two-body interactions. In view of recent experiments with light neutron-rich nuclei, we will discuss properties of exotic nuclei as 11Li, 14Be, 20C and 22C, within a three-bodyneutron-neutron-core model. Particular emphasis will be given to model independent properties associated to halo neutrons, which obey universal scaling laws. We discuss how the scaling laws for the s-wave observables of two-neutron halo will be identified with limit-cycles and Thomas-Efimov effect in a zero-range three-body model. © 2014 Springer-Verlag Wien.

de Paula W.,Brazilian Technological Institute of Aeronautics | Frederico T.,Brazilian Technological Institute of Aeronautics
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2010

We show that the infrared dynamics of string modes dual to qq̄ states within a Dynamical AdS/QCD model of coupled dilaton-gravity background gives the Regge-like spectrum of f0's scalars and higher spin mesons consistent with experimental data. The pion mass and its trajectory were also described with a scale deformation of the metric and a rescaled string mass. The available experimental decay widths of the S→PP decays provided a complementary check of the proposed classification scheme for f0(980), f0(1370), f0(1500) and f0(1710) as radial excitations of f0(600). For f0(980) we estimated a mixing angle of ±20o with other structures. © 2010 Elsevier B.V.

de Lemos M.J.S.,Brazilian Technological Institute of Aeronautics
International Communications in Heat and Mass Transfer | Year: 2010

The objective of this paper is to present an extension of a simplified reaction kinetics model that, combined with a thermo-mechanical closure, entails a full-generalized turbulent combustion model for flow in porous media. In this model, one explicitly considers the intra-pore levels of turbulent kinetic energy. Transport equations are written in their time-and-volume-averaged form and a volume-based statistical turbulence model is applied to simulate turbulence generation due to the porous matrix. The rate of fuel consumption is described by an Arrhenius expression involving the product of the fuel and oxidant mass fractions. These mass fractions are double decomposed in time and space and, after applying simultaneous time-and-volume integration operations to them, distinct terms arise, which are here associated with the mechanisms of dispersion and turbulence. Modeling of these extra terms remains an open question and the derivations herein might motivate further development of models for turbulent combustion in porous media. © 2010 Elsevier Ltd. All rights reserved.

Moraes P.H.R.S.,Brazilian Technological Institute of Aeronautics
International Journal of Theoretical Physics | Year: 2016

In this work I present a generalization of f(R, T) gravity, by allowing the speed of light to vary. Cosmological solutions are presented for matter and radiation-dominated universes, the former allowing the universe expansion to accelerate while the latter contemplating a possible alternative to inflationary scenario. Remarkably, standard gravity is always retrieved for a special case of f(R, T). © 2015, Springer Science+Business Media New York.

de Melo J.P.B.C.,Southern Cross University of Brazil | Frederico T.,Brazilian Technological Institute of Aeronautics
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

The issue of the contribution of zero-modes to the light-front projection of the electromagnetic current of phenomenological models of vector particles vertices is addressed in the Drell-Yan frame. Our analytical model of the Bethe-Salpeter amplitude of a spin-1 fermion-antifermion composite state gives a physically motivated light-front wave function symmetric by the exchange of the fermion and antifermion, as in the ρ-meson case. We found that among the four independent matrix elements of the plus component in the light-front helicity basis only the 0 → 0 one carries zero-mode contributions. Our derivation generalizes to symmetric models, important for applications, the above conclusion found for a simplified non-symmetrical form of the spin-1 Bethe-Salpeter amplitude with photon-fermion point-like coupling and also for a smeared fermion-photon vertex model. © 2012 Elsevier B.V.

Brazilian Technological Institute of Aeronautics and Embraer SA | Date: 2012-12-21

A process for joining parts together is provided by positioning and temporarily clamping parts to be joined together. A number (n) of pilot holes may then be drilled through the temporarily clamped parts (e.g., by means of Cleco fasteners), wherein the number (n) of pilot holes is less than a total number (N) of holes required to be drilled to allow the parts to be joined together by permanent fasteners and to receive temporary fasteners therein. A remaining number () of holes to achieve the total number (N) of holes required for the parts to be joined together by permanent fasteners may thereafter be drilled so that permanent fasteners may be installed both, by automated system, in the number (n) of pilot holes and the remaining number () of holes that have been drilled to thereby permanently join the parts together.

Brazilian Technological Institute of Aeronautics and Embraer SA | Date: 2010-11-12

Automated positioning and alignment methods and systems for aircraft structures use anthropomorphous robots with six degrees of freedom to carry the aero structure parts during the positioning and alignment. The parts and structures (if any) supporting the parts are treated as robot tools.

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