Examinando por Autor "Perazzo, Roberto P. J."
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Artículo de Publicación Periódica The evolutionary minority game with local coordination(2003) Burgos, Enrique; Ceva, Horacio; Perazzo, Roberto P. J."We discuss a modification of the evolutionary minority game (EMG) in which agents are placed in the nodes of a regular or a random graph. A neighborhood for each agent can thus be defined and a modification of the usual relaxation dynamics can be made in which each agent updates her decision depending upon her neighborhood. We report numerical results for the topologies of a ring, a torus and a random graph changing the size of the neighborhood. We find the surprising result that in the EMG a better coordination (a lower frustration) can be achieved if agents base their actions on local information disregarding the global trend in the self-segregation process."Artículo de Publicación Periódica Learning and imitation: transitional dynamics in variants of the BAM(2004) Heymann, D.; Perazzo, Roberto P. J.; Schuschny, A. R."We study the dynamics of self-organized systems when disturbed by shocks. For this purpose, we consider extensions of the “Bar Attendance Model” [1] (BAM), which provides a stylized setting for the analysis of the emergence of coordination in the behavior of a large collection of agents. We represent the learning process of the agents through genetic algorithms, which respond to global (publicly available) information. In addition, we allow the actions of agents to be influenced by local information, as expressed in the behavior and performance of neighboring individuals. In the context of the BAM, we show that, in the event of a shock, the imitation behavior may become widespread and generate a contagion cascade which mimics a collective panic. We use this framework to represent features of the dynamics of an actual bank run."Artículo de Publicación Periódica On the dynamics of a single-bit stochastic-resonance memory device(2010-07) Ibáñez, Santiago Agustín; Fierens, Pablo Ignacio; Perazzo, Roberto P. J.; Patterson, Germán; Grosz, Diego"The increasing capacity of modern computers, driven by Moore’s Law, is accompanied by smaller noise margins and higher error rates. In this paper we propose a memory device, consisting of a ring of two identical overdamped bistable forward-coupled oscillators, which may serve as a building block in a larger scale solution to this problem. We show that such a system is capable of storing a single bit and its performance improves with the addition of noise. The proposed device can be regarded as asynchronous, in the sense that stored information can be retrieved at any time and, after a certain synchronization time, the probability of erroneous retrieval does not depend on which oscillator is being interrogated. We characterize memory persistence time and show it to be maximized for the same noise range that both minimizes the probability of error and ensures synchronization. We also present experimental results for a hard-wired version of the proposed memory, consisting of a loop of two Schmitt triggers. We show that this device is capable of storing a single bit and does so more efficiently in the presence of noise."Artículo de Publicación Periódica Order and disorder in the local evolutionary minority game(2005) Burgos, Enrique; Ceva, Horacio; Perazzo, Roberto P. J."We study a modification of the Evolutionary Minority Game (EMG) in which agents are placed in the nodes of a regular or a random graph. A neighborhood for each agent can thus be defined and a modification of the usual relaxation dynamics can be made in which each agent updates her decision scheme depending upon the options made in her immediate neighborhood. We name this model the Local Evolutionary Minority Game (LEMG). We report numerical results for the topologies of a ring, a torus and a random graph changing the size of the neighborhood.We focus our discussion in a one-dimensional system and perform a detailed comparison of the results obtained from the random relaxation dynamics of the LEMG and from a linear chain of interacting spin-like variables with temperature. We provide a physical interpretation of the surprising result that in the LEMG a better coordination (a lower frustration) is achieved if agents base their actions on local information.We show how the LEMG can be regarded as a model that gradually interpolates between a fully ordered, antiferromagnetic-like system, and a fully disordered system that can be assimilated to a spin glass."Artículo de Publicación Periódica Stochastic resonance and brownian ratchets(2005) Fendrik, Alejandro J.; Romanelli, Lilia; Perazzo, Roberto P. J."We discuss the connections between Brownian ratchets (BR) and stochastic resonance (SR). We consider a periodic potential energy landscape with no left–right symmetry that is driven by an external force which can be derived from a potential that is periodic both in time and space. We show that this system presents two thermal enhancements within two different windows of the temperature. One is associated with a ‘‘coherent diffusion’’ by which particles jump back and forth between the minima of the periodic potential in synchrony with the external driving. The other is instead associated with a ‘‘coherent directional transport’’ by which particles hop synchronically from one minimum of the ratchet to the next. We calculate the current and the diffusion coefficients and show how transport undergoes a resonant enhancement. While the former is always present, the second only appears when left–right symmetry is broken."Artículo de Publicación Periódica Time delay properties of stochastics-resonance information transmission line(2008) Ibáñez, Santiago Agustín; Fendrik, Alejandro J.; Fierens, Pablo Ignacio; Grosz, Diego; Perazzo, Roberto P. J."In this paper we analyze the properties of a chain of forward-coupled bi-stable over-damped oscillators. It is well known that this system displays stochastic resonance and behaves as a transmission line when an adequate amount of noise is added to each oscillator, and the first oscillator is driven by a periodic (sine) modulating signal. By driving the first oscillator with a modulated sequence of random non-return-to-zero (NRZ) bits, we start by showing that the system exhibits a stochastic-resonance behavior. Then we show that bit delays can be adjusted by either changing the amount of noise and/or the coupling intensity between adjacent oscillators. We find that the system can be regarded as a tunable delay line for a broad range of noise and coupling parameters, a feature that may find applications in information processing and bit regeneration."Artículo de Publicación Periódica Two classes of bipartite networks: nested biological and social systems(2008) Burgos, Enrique; Ceva, Horacio; Hernández, Laura; Perazzo, Roberto P. J.; Devoto, Mariano; Medan, Diego"Bipartite graphs have received some attention in the study of social networks and of biological mutualistic systems. A generalization of a previous model is presented, that evolves the topology of the graph in order to optimally account for a given Contact Preference Rule between the two guilds of the network. As a result, social and biological graphs are classified as belonging to two clearly different classes. Projected graphs, linking the agents of only one guild, are obtained from the original bipartite graph. The corresponding evolution of its statistical properties is also studied. An example of a biological mutualistic network is analyzed in detail, and it is found that the model provides a very good fitting of all the main statistical features. The model also provides a proper qualitative description of the same features observed in social webs, suggesting the possible reasons underlying the difference in the organization of these two kinds of bipartite networks."Artículo de Publicación Periódica Why nestedness in mutualistic networks?(2007) Burgos, Enrique; Ceva, Horacio; Perazzo, Roberto P. J.; Devoto, Mariano; Medan, Diego; Zimmermann, Martín; Delbue, Ana María"We investigate the relationship between the nested organization of mutualistic systems and their robustness against the extinction of species. We establish that a nested pattern of contacts is the best possible one as far as robustness is concerned, but only when the least linked species have the greater probability of becoming extinct. We introduce a coefficient that provides a quantitative measure of the robustness of a mutualistic system."