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Search Results: 1 - 10 of 401942 matches for " J. F. F. Mendes "
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Critical behavior of models with infinitely many absorbing states
Mendes, J.F.F.;
Brazilian Journal of Physics , 2000, DOI: 10.1590/S0103-97332000000100010
Abstract: in this article we review several models with many absorbing configurations. in all these models attention will be focused on the in uence of the initial state on the dynamic evolution. the relation of systems with many absorbing configurations to those displaying avalanches (self-organized criticality) is also investigated. some new results are presented both for systems with and without parity conservation. recently derived scaling relations are tested.
Critical behavior of models with infinitely many absorbing states
Mendes J.F.F.
Brazilian Journal of Physics , 2000,
Abstract: In this article we review several models with many absorbing configurations. In all these models attention will be focused on the in uence of the initial state on the dynamic evolution. The relation of systems with many absorbing configurations to those displaying avalanches (self-organized criticality) is also investigated. Some new results are presented both for systems with and without parity conservation. Recently derived scaling relations are tested.
Communication and correlation among communities
M. Ostilli,J. F. F. Mendes
Physics , 2009, DOI: 10.1103/PhysRevE.80.011142
Abstract: Given a network and a partition in communities, we consider the issues "how communities influence each other" and "when two given communities do communicate". Specifically, we address these questions in the context of small-world networks, where an arbitrary quenched graph is given and long range connections are randomly added. We prove that, among the communities, a superposition principle applies and gives rise to a natural generalization of the effective field theory already presented in [Phys. Rev. E 78, 031102] (n=1), which here (n>1) consists in a sort of effective TAP (Thouless, Anderson and Palmer) equations in which each community plays the role of a microscopic spin. The relative susceptibilities derived from these equations calculated at finite or zero temperature, where the method provides an effective percolation theory, give us the answers to the above issues. Unlike the case n=1, asymmetries among the communities may lead, via the TAP-like structure of the equations, to many metastable states whose number, in the case of negative short-cuts among the communities, may grow exponentially fast with n. As examples we consider the n Viana-Bray communities model and the n one-dimensional small-world communities model. Despite being the simplest ones, the relevance of these models in network theory, as e.g. in social networks, is crucial and no analytic solution were known until now. Connections between percolation and the fractal dimension of a network are also discussed. Finally, as an inverse problem, we show how, from the relative susceptibilities, a natural and efficient method to detect the community structure of a generic network arises. For a short presentation of the main result see arXiv:0812.0608.
Critical phenomena on heterogeneous small-world networks
M. Ostilli,J. F. F. Mendes
Physics , 2010, DOI: 10.1209/0295-5075/92/40013
Abstract: We consider critical phenomena on heterogeneous small-world networks having a scale-free character but also arbitrary short-loops. After deriving the self-consistent equation for the order parameter and the critical surface, we prove that the critical behavior on complex networks is in fact infinitely robust with respect to the presence of arbitrary short-loops.
Diluted antiferromagnet in a ferromagnetic enviroment
M. O. Hase,J. F. F. Mendes
Physics , 2007, DOI: 10.1088/1751-8113/41/14/145002
Abstract: The question of robustness of a network under random ``attacks'' is treated in the framework of critical phenomena. The persistence of spontaneous magnetization of a ferromagnetic system to the random inclusion of antiferromagnetic interactions is investigated. After examing the static properties of the quenched version (in respect to the random antiferromagnetic interactions) of the model, the persistence of the magnetization is analysed also in the annealed approximation, and the difference in the results are discussed.
Exact results and new insights for models defined over small world networks. First and second order phase transitions. II: Applications
M. Ostilli,J. F. F. Mendes
Physics , 2008,
Abstract: We apply a novel method (presented in part I) to solve several small-world models for which the method can be applied analytically: the Viana-Bray model (which can be seen as a 0 or infinite dimensional small-world model), the one-dimensional chain small-world model, and the small-world spherical model in generic dimension. In particular, we analyze in detail the one-dimensional chain small-world model with negative short-range coupling showing that in this case, besides a second-order spin glass phase transition, there are two critical temperatures corresponding to first- or second-order phase transitions.
Exact results and new insights for models defined over small-world networks. First and second order phase transitions. I: General result
M. Ostilli,J. F. F. Mendes
Physics , 2008,
Abstract: We present, as a very general method, an effective field theory to analyze models defined over small-world networks. Even if the exactness of the method is limited to the paramagnetic regions and to some special limits, it gives the exact critical behavior and the exact critical surfaces and percolation thresholds, and provide a clear and immediate (also in terms of calculation) insight of the physics. The underlying structure of the non random part of the model, i.e., the set of spins staying in a given lattice L_0 of dimension d_0 and interacting through a fixed coupling J_0, is exactly taken into account. When J_0\geq 0, the small-world effect gives rise to the known fact that a second order phase transition takes place, independently of the dimension d_0 and of the added random connectivity c. However, when J_0<0, a completely different scenario emerges where, besides a spin glass transition, multiple first- and second-order phase transitions may take place.
Evolution of a sandpile in a thick flow regime
S. N. Dorogovtsev,J. F. F. Mendes
Physics , 1999, DOI: 10.1103/PhysRevE.61.2909
Abstract: We solve a one-dimensional sandpile problem analytically in a thick flow regime when the pile evolution may be described by a set of linear equations. We demonstrate that, if an income flow is constant, a space periodicity takes place while the sandpile evolves even for a pile of only one type of particles. Hence, grains are piling layer by layer. The thickness of the layers is proportional to the input flow of particles $r_0$ and coincides with the thickness of stratified layers in a two-component sandpile problem which were observed recently. We find that the surface angle $\theta$ of the pile reaches its final critical value ($\theta_f$) only at long times after a complicated relaxation process. The deviation ($\theta_f - \theta $) behaves asymptotically as $(t/r_{0})^{-1/2}$. It appears that the pile evolution depends on initial conditions. We consider two cases: (i) grains are absent at the initial moment, and (ii) there is already a pile with a critical slope initially. Although at long times the behavior appears to be similar in both cases, some differences are observed for the different initial conditions are observed. We show that the periodicity disappears if the input flow increases with time.
Language as an Evolving Word Web
S. N. Dorogovtsev,J. F. F. Mendes
Physics , 2001,
Abstract: Human language can be described as a complex network of linked words. In such a treatment, each distinct word in language is a vertex of this web, and neighboring words in sentences are connected by edges. It was recently found (Ferrer and Sol\'e) that the distribution of the numbers of connections of words in such a network is of a peculiar form which includes two pronounced power-law regions. Here we treat language as a self-organizing network of interacting words. In the framework of this concept, we completely describe the observed Word Web structure without fitting.
Short time dynamics of a two dimensional majority vote model
J. F. F. Mendes,M. A. Santos
Physics , 1997, DOI: 10.1103/PhysRevE.57.108
Abstract: Short time Monte Carlo methods are used to study the nonequilibrium ferromagnetic phase transition in a majority vote model in two dimensions. The existance of an initial critical slip regime is verified. The measured values of dyamic exponents $z=2.170(5)$ and $\theta = 0.191(2)$ are in excellent agreement with those of the kinetic Ising model universality class.
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