National Institute of Science and Technology in Complex Systems

and Technology in, Brazil

National Institute of Science and Technology in Complex Systems

and Technology in, Brazil

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Pereira M.A.,University of Sao Paulo | Martinez A.S.,University of Sao Paulo | Martinez A.S.,National Institute of Science and Technology in Complex Systems
Journal of Theoretical Biology | Year: 2010

The Prisoner's Dilemma (PD) game is applied in several research fields due to the emergence of cooperation among selfish players. In this work the PD is studied in a one-dimensional lattice, where each cell represents a player, which in turn can interact with the neighbors playing the PD (cooperate or defect). The update of states adopts the Pavlovian Evolutionary Strategy (PES) or Darwinian Evolutionary Strategy (DES). Adopting PES, if a player receives a positive payoff greater than his/her aspiration level, he/she keeps the current state, and switches otherwise. Adopting DES, player compares his/her payoff with payoff of opponents. If it is not the highest, he/she copies the state of fittest player, switching the state if it is different of his/her current state. The critical temptation values obtained analytically are reported, and the cluster patterns that emerge from the interactions among the players are shown. Also we defined analytical functions that calculate the maximum/minimum size of defective/cooperative clusters. Also, the parameter space is explored with exhaustive computational simulations, which confirm the analytical results and reinforce that Pavlovian strategy foments cooperation among players. In steady state, system can reach the cooperative or quasi-regular phases, when adopting the PES, and cooperative, defective or chaotic phases, adopting the DES. The new quasi-regular phase occurs when several players switch their states in each round, but the proportion of cooperators does not show significant variation. Additionally, the present work shows that the lowest temptation level (. T=1) may be considered a trivial case only for the particular case where the players interact with only one neighbor, otherwise system presents the same features that for higher temptation values. © 2010 Elsevier Ltd.


Backes A.R.,University of Sao Paulo | Goncalves W.N.,University of Sao Paulo | Martinez A.S.,University of Sao Paulo | Martinez A.S.,National Institute of Science and Technology in Complex Systems | Bruno O.M.,University of Sao Paulo
Pattern Recognition | Year: 2010

In this paper, we present a study on a deterministic partially self-avoiding walk (tourist walk), which provides a novel method for texture feature extraction. The method is able to explore an image on all scales simultaneously. Experiments were conducted using different dynamics concerning the tourist walk. A new strategy, based on histograms, to extract information from its joint probability distribution is presented. The promising results are discussed and compared to the best-known methods for texture description reported in the literature. © 2009 Elsevier Ltd. All rights reserved.


Marco A.G.,University of Sao Paulo | Martinez A.S.,University of Sao Paulo | Martinez A.S.,National Institute of Science and Technology in Complex Systems | Bruno O.M.,University of Sao Paulo
International Journal of Modern Physics C | Year: 2010

A novel cryptography method based on the Lorenz's attractor chaotic system is presented. The proposed algorithm is secure and fast, making it practical for general use. We introduce the chaotic operation mode, which provides an interaction among the password, message and a chaotic system. It ensures that the algorithm yields a secure codification, even if the nature of the chaotic system is known. The algorithm has been implemented in two versions: one sequential and slow and the other, parallel and fast. Our algorithm assures the integrity of the ciphertext (we know if it has been altered, which is not assured by traditional algorithms) and consequently its authenticity. Numerical experiments are presented, discussed and show the behavior of the method in terms of security and performance. The fast version of the algorithm has a performance comparable to AES, a popular cryptography program used commercially nowadays, but it is more secure, which makes it immediately suitable for general purpose cryptography applications. An internet page has been set up, which enables the readers to test the algorithm and also to try to break into the cipher. © 2010 World Scientific Publishing Company.


Destefano N.,University of Sao Paulo | Destefano N.,National Institute of Science and Technology in Complex Systems | Martinez A.S.,University of Sao Paulo | Martinez A.S.,National Institute of Science and Technology in Complex Systems
Physica A: Statistical Mechanics and its Applications | Year: 2011

Intertemporal decision making involves choices among options whose effects occur at different moments. These choices are influenced not only by the effect of reward value perception at different moments, but also by the time perception effect. One of the main difficulties that affect standard experiments involving intertemporal choices is the simultaneity of both effects on time discounting. In this paper, we unify the psychophysical laws and discount value functions using the one-parameter exponential and logarithmic functions from nonextensive statistical mechanics. Also, we propose to measure the degree of inconsistency. This quantity allow us to discriminate both effects of time and value perception on discounting process and, by integration, obtain other main quantities like impulsivity and discount functions. © 2011 Elsevier B.V. All rights reserved.


Arruda T.J.,University of Sao Paulo | Pinheiro F.A.,Federal University of Rio de Janeiro | Martinez A.S.,University of Sao Paulo | Martinez A.S.,National Institute of Science and Technology in Complex Systems
Journal of Optics (United Kingdom) | Year: 2012

An exact expression is derived for the time-averaged electromagnetic energy within a magneto-dielectric coated sphere, which is irradiated by a plane and time-harmonic electromagnetic wave. Both the spherical shell and core are considered to be dispersive and lossy, with a realistic dispersion relation of an isotropic split-ring resonator metamaterial. We obtain analytical expressions for the stored electromagnetic energies inside the core and the shell separately and calculate their contributions to the total average energy density. The stored electromagnetic energy is calculated for two situations involving a metamaterial coated sphere: a dielectric shell and dispersive metamaterial core, and vice versa. An explicit relation between the stored energy and the optical absorption efficiency is also obtained. We show that the stored electromagnetic energy is an observable sensitive to field interferences responsible for the Fano effect. This result, together with the fact that the Fano effect is more likely to occur in metamaterials with negative refraction, suggest that our findings may be explored in applications. © 2012 IOP Publishing Ltd.


Cabella B.C.T.,National Institute of Science and Technology in Complex Systems | Martinez A.S.,National Institute of Science and Technology in Complex Systems | Ribeiro F.,Federal University of Lavras
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

We consider a nontrivial one-species population dynamics model with finite and infinite carrying capacities. Time-dependent intrinsic and extrinsic growth rates are considered in these models. Through the model per capita growth rate we obtain a heuristic general procedure to generate scaling functions to collapse data into a simple linear behavior even if an extrinsic growth rate is included. With this data collapse, all the models studied become independent from the parameters and initial condition. Analytical solutions are found when time-dependent coefficients are considered. These solutions allow us to perceive nontrivial transitions between species extinction and survival and to calculate the transition's critical exponents. Considering an extrinsic growth rate as a cancer treatment, we show that the relevant quantity depends not only on the intensity of the treatment, but also on when the cancerous cell growth is maximum. © 2011 American Physical Society.

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