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Search Results: 1 - 10 of 291257 matches for " E. K.;Mendes "
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Quantum Statistical Mechanics for Nonextensive Systems II
E. K. Lenzi,R. S. Mendes,A. K. Rajagopal
Physics , 1999, DOI: 10.1103/PhysRevE.59.1398
Abstract: In this paper, the Green function theory of quantum many-particle systems recently presented is reworked within the framework of nonextensive statistical mechanics with a new normalized $q$-expectation values. This reformulation introduces a renormalization of temperature of the earlier theory and a self-consistency condition. The linear response theory is also presented, along with its two-particle Green function version. Finally, a Boltzmann transport-like equation is also developed here.
Symbolic sequences and Tsallis entropy
Ribeiro, H. V.;Lenzi, E. K.;Mendes, R. S.;Mendes, G. A.;da Silva, L. R.;
Brazilian Journal of Physics , 2009, DOI: 10.1590/S0103-97332009000400018
Abstract: we address this work to investigate symbolic sequences with long-range correlations by using computational simulation. we analyze sequences with two, three and four symbols that could be repeated l times, with the probability distribution p(l) ∝ 1/l μ. for these sequences, we verified that the usual entropy increases more slowly when the symbols are correlated and the tsallis entropy exhibits, for a suitable choice of q, a linear behavior. we also study the chain as a random walk-like process and observe a nonusual diffusive behavior depending on the values of the parameter μ.
Symbolic Sequences and Tsallis Entropy
H. V. Ribeiro,E. K. Lenzi,R. S. Mendes,G. A. Mendes,L. R. da Silva
Physics , 2010, DOI: 10.1590/S0103-97332009000400018
Abstract: We address this work to investigate symbolic sequences with long-range correlations by using computational simulation. We analyze sequences with two, three and four symbols that could be repeated $l$ times, with the probability distribution $p(l)\propto 1/ l^{\mu}$. For these sequences, we verified that the usual entropy increases more slowly when the symbols are correlated and the Tsallis entropy exhibits, for a suitable choice of $q$, a linear behavior. We also study the chain as a random walk-like process and observe a nonusual diffusive behavior depending on the values of the parameter $\mu$.
Perturbation and Variational Methods in Nonextensive Tsallis Statistics
E. K. Lenzi,L. C. Malacarne,R. S. Mendes
Physics , 1998, DOI: 10.1103/PhysRevLett.80.218
Abstract: A unified presentation of the perturbation and variational methods for the generalized statistical mechanics based on Tsallis entropy is given here. In the case of the variational method, the Bogoliubov inequality is generalized in a very natural way following the Feynman proof for the usual statistical mechanics. The inequality turns out to be form-invariant with respect to the entropic index $q$. The method is illustrated with a simple example in classical mechanics. The formalisms developed here are expected to be useful in the discussion of nonextensive systems.
Average Entropy of a Subsystem from its Average Tsallis Entropy
L. C. Malacarne,R. S. Mendes,E. K. Lenzi
Physics , 2002, DOI: 10.1103/PhysRevE.65.046131
Abstract: In the nonextensive Tsallis scenario, Page's conjecture for the average entropy of a subsystem[Phys. Rev. Lett. {\bf 71}, 1291(1993)] as well as its demonstration are generalized, i.e., when a pure quantum system, whose Hilbert space dimension is $mn$, is considered, the average Tsallis entropy of an $m$-dimensional subsystem is obtained. This demonstration is expected to be useful to study systems where the usual entropy does not give satisfactory results.
Path Integral Approach to the Nonextensive Canonical Density Matrix
E. K. Lenzi,L. C. Malacarne,R. S. Mendes
Physics , 1999, DOI: 10.1016/S0378-4371(99)00551-8
Abstract: Feynman's path integral is herein generalized to the nonextensive canonical density matrix based on Tsallis entropy. This generalization is done in two ways by using unnormalized and normalized constraints. Firstly, we consider the path integral formulation with unnormalized constraints, and this generalization is worked out through two different ways, which are shown to be equivalent. These formulations with unnormalized constraints are solutions to two generalized Bloch equations proposed in this work. The first form of the generalized Bloch equation is linear, but with a temperature-dependent effective Hamiltonian; the second form is nonlinear and resembles the anomalous correlated diffusion equation (porous medium equation). Furthermore, we can extend these results to the prescription of field theory using integral representations. The second development is dedicated to analyzing the path integral formulation with normalized constraints. To illustrate the methods introduced here, we analyze the free particle case and a non-interacting scalar field. The results herein obtained are expected to be useful in the discussion of generic nonextensive contexts.
q-Exponential Distribution in Urban Agglomeration
L. C. Malacarne,R. S. Mendes,E. K. Lenzi
Physics , 2001, DOI: 10.1103/PhysRevE.65.017106
Abstract: Usually, the study of city population distribution has been reduced to power laws. In such analysis, a common practice is to consider cities with more than one hundred thousand inhabitants. Here, we argue that the distribution of cities for all ranges of populations can be well described by using a $q$-exponential distribution. This function, which reproduces the Zipf-Mandelbrot law, is related to the generalized nonextensive statistical mechanics and satisfies an anomalous decay equation.
Biodistribution Study of the Radiopharmaceutical Sodium Pertechnetate in Wistar Rats Treated with Rutin
Luciana C. Bernardo,Ana E.O. Santos,Danielle C. Mendes,Carolina K. Ribeiro
Pakistan Journal of Biological Sciences , 2004,
Abstract: The interest of scientific community in the research of biological effects of medicinal plants is increasing. Among the different substances isolated from natural products, stands out flavonoids. Rutin is a flavonoid used in conventional and traditional medicine. In nuclear medicine, radiopharmaceuticals present an expected biodistribution and uptake in determined target organs. However, studies show that biodistribution can be altered by the use of natural or synthetic substances. In this study, we evaluated the biodistribution of the radiopharmaceutical sodium pertechnetate (99mTcO4Na) in Wistar rats treated with rutin. Male Wistar rats were divided in two groups: treated with rutin (n=5) and treated with NaCl 0.9% (n=5). 99mTcO4Na was administered and the radioactivity percentage per gram of each organ was determined (%ATI.g-1). The results show that rutin interfered on the uptake of 99mTcO4Na in liver (P=0.0026), when compared with group 2. The results can be explained by the pharmacological effects of this flavonoid like hepatoprotective actions
Critical phenomena and noise-induced phase transitions in neuronal networks
K. -E. Lee,M. A. Lopes,J. F. F. Mendes,A. V. Goltsev
Physics , 2013, DOI: 10.1103/PhysRevE.89.012701
Abstract: We study numerically and analytically first- and second-order phase transitions in neuronal networks stimulated by shot noise (a flow of random spikes bombarding neurons). Using an exactly solvable cortical model of neuronal networks on classical random networks, we find critical phenomena accompanying the transitions and their dependence on the shot noise intensity. We show that a pattern of spontaneous neuronal activity near a critical point of a phase transition is a characteristic property that can be used to identify the bifurcation mechanism of the transition. We demonstrate that bursts and avalanches are precursors of a first-order phase transition, paroxysmal-like spikes of activity precede a second-order phase transition caused by a saddle-node bifurcation, while irregular spindle oscillations represent spontaneous activity near a second-order phase transition caused by a supercritical Hopf bifurcation. Our most interesting result is the observation of the paroxysmal-like spikes. We show that a paroxysmal-like spike is a single nonlinear event that appears instantly from a low background activity with a rapid onset, reaches a large amplitude, and ends up with an abrupt return to lower activity. These spikes are similar to single paroxysmal spikes and sharp waves observed in EEG measurements. Our analysis shows that above the saddle-node bifurcation, sustained network oscillations appear with a large amplitude but a small frequency in contrast to network oscillations near the Hopf bifurcation that have a small amplitude but a large frequency. We discuss an amazing similarity between excitability of the cortical model stimulated by shot noise and excitability of the Morris-Lecar neuron stimulated by an applied current.
Logarithmic diffusion and porous media equations: a unified description
I. T. Pedron,R. S. Mendes,T. J. Buratta,L. C. Malacarne,E. K. Lenzi
Physics , 2005, DOI: 10.1103/PhysRevE.72.031106
Abstract: In this work we present the logarithmic diffusion equation as a limit case when the index that characterizes a nonlinear Fokker-Planck equation, in its diffusive term, goes to zero. A linear drift and a source term are considered in this equation. Its solution has a lorentzian form, consequently this equation characterizes a super diffusion like a L\'evy kind. In addition is obtained an equation that unifies the porous media and the logarithmic diffusion equations, including a generalized diffusion equation in fractal dimension. This unification is performed in the nonextensive thermostatistics context and increases the possibilities about the description of anomalous diffusive processes.
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