## Dr. Claudio Juan Tessone
## Publications»## «Publications## Publications in## The Role of Endogenous and Exogenous Mechanisms in the Formation of R&D Networks[2014] Tomasello, Mario Vincenzo;
Perra, Nicola;
Tessone, Claudio Juan;
Karsai, M'arton;
Schweitzer, Frank
## arXiv:1403.4106more» «lessAbstract We develop an agent based model of strategic link formation in Research and Development (R&D) networks. In our model, firms are represented as nodes, and their R&D alliances as links. Empirical evidence has shown that the growth and evolution of these networks are driven by two types of mechanisms. Endogenous mechanisms depend on the previous history of the network, i.e. they take into account existing alliance patterns. Exogenous mechanisms do not depend on the properties of the network but on those of newcomers, i.e. they include the exploratory search for firms that are not part of the network yet. Despite the observation of these two mechanisms, research has focused only on either of the two. To overcome this limitation, we develop a general modeling framework that includes both mechanisms and allows to tune their relative importance in the formation of links. The model contains additional ingredients derived from empirical observations, such as the heterogeneous propensity to form alliances and the presence of circles of influence, i.e. clusters of firms in the network. We test our model against the Thomson Reuters SDC Platinum dataset, one of the most complete datasets available nowadays, listing cross-country R&D alliances from 1984 to 2009. Interestingly, by fitting only three macroscopic properties of the network, this framework is able to reproduce a number of microscopic measures characterizing the network topology, including the distributions of degree, local clustering, path length and component size, and the emergence of network clusters. Furthermore, by estimating the link probabilities towards newcomers and established firms from the available data, we find that endogenous mechanisms are predominant over the exogenous ones in the network formation. This quantifies the importance of existing network structures in selecting partners for R&D alliances.
## A framework for extracting pairwise coupling information during collective animal motion[2014] Richardson, Tom O.;
Perony, Nicolas;
Tessone, Claudio Juan;
Bousquet, Christophe A.H.;
Manser, Marta B.;
Schweitzer, Frank
## Submitted. arXiv:1311.1417more» «lessAbstract The measurement of information flows within moving animal groups has recently been a topic of considerable interest, and it has become clear that the individual(s) that drive collective movement may change over time, and that such individuals may not necessarily always lead from the front. However, methods to quantify the influence of specific individuals on the behaviour of other group members and the direction of information flow in moving group, are lacking on the level of empirical studies and theoretical models. Using high spatio-temporal resolution GPS trajectories of foraging meerkats, Suricata suricatta, we provide an information-theoretic framework to identify dynamical coupling between animals independent of their relative spatial positions. Based on this identification, we then compare designations of individuals as either drivers or responders against designations provided by the relative spatial position. We find that not only does coupling occur both from the frontal to the trailing individuals and vice versa, but also that the coupling direction is a non-linear function of the relative position. This provides evidence for (i) intermittent fluctuation of the coupling strength and (ii) alternation in the coupling direction within foraging meerkat pairs. The framework we introduce allows for a detailed description of the dynamical patterns of mutual influence between all pairs of individuals within moving animal groups. We argue that applying an information-theoretic perspective to the study of coordinated phenomena in animal groups will eventually help to understand cause and effect in collective behaviour.
## Automated Software Remodularization Based on Move Refactoring[2014] Zanetti, Marcelo Serrano;
Tessone, Claudio Juan;
Scholtes, Ingo;
Schweitzer, Frank
## To appear in the Proceedings of the 13th International Conference on Modularity 2014more» «lessAbstract Modular design is a desirable characteristic of complex software systems that can significantly improve their comprehensibility, maintainability and thus quality. While many software systems are initially created in a modular way, over time modularity typically degrades as components are reused outside the context where they were created. In this paper, we propose an automated strategy to remodularize software based on move refactoring, i.e. moving classes between packages without changing any other aspect of the source code. Taking a complex systems perspective, our approach is based on complex networks theory applied to the dynamics of software modular structures and its relation to an n-state spin model known as the Potts Model. In our approach, nodes are probabilistically moved between modules with a probability that nonlinearly depends on the number and module membership of their adjacent neighbors. The latter are defined by the underlying network of software dependencies. To validate our method, we apply it to a dataset of 39 Java open source projects in order to optimize their modularity. Comparing the source code generated by the developers with the optimized code resulting from our approach, we find that modularity (i.e. quantified in terms of a standard measure from the study of complex networks) improves on average by 166+-77 percent. In order to facilitate the application of our method in practical studies, we provide a freely available Eclipse plug-in.
## Slow-Down vs. Speed-Up of Diffusion in Non-Markovian Temporal Networks[2013] Scholtes, Ingo;
Wider, Nicolas;
Pfitzner, Rene;
Garas, Antonios;
Tessone, Claudio Juan;
Schweitzer, Frank
## Arxiv preprint Pages: 1-10more» «lessAbstract We study the slow-down and speed-up of information diffusion in temporal networks with non-Markovian contact sequences. We introduce a causality-preserving time-aggregated representation that allows to analyze temporal networks from the perspective of spectral graph theory. With this we provide the first analytical explanation for the frequently observed slow-down of information diffusion in empirical non-Markovian temporal networks. We derive an analytical prediction for the magnitude of this slow-down and validate our prediction against two empirical data sets. Counterintuitively, we further show that non-Markovian properties can result in a speed-up of information diffusion that can be related to the spectral properties of the underlying temporal network.
## Enhancing consensus under opinion bias by means of hierarchical decision making[2013] Perony, Nicolas;
Pfitzner, Rene;
Scholtes, Ingo;
Tessone, Claudio Juan;
Schweitzer, Frank
## Advances in Complex Systems, Pages: 1350020, Volume: 16more» «less
Abstract We study the role of hierarchical structures in a simple model of collective consensus formation based on the bounded confidence model with continuous individual opinions. For the particular variation of this model considered in this paper, we assume that a bias towards an extreme opinion is introduced whenever two individuals interact and form a common decision. As a simple proxy for hierarchical social structures, we introduce a two-step decision making process in which in the second step groups of like-minded individuals are replaced by representatives once they have reached local consensus, and the representatives in turn form a collective decision in a downstream process. We find that the introduction of such a hierarchical decision making structure can improve consensus formation, in the sense that the eventual collective opinion is closer to the true average of individual opinions than without it. In particular, we numerically study how the size of groups of like-minded individuals being represented by delegate individuals affects the impact of the bias on the final population-wide consensus. These results are of interest for the design of organisational policies and the optimisation of hierarchical structures in the context of group decision making.
## Categorizing bugs with social networks: A case study on four open source software communities[2013] Zanetti, Marcelo Serrano;
Scholtes, Ingo;
Tessone, Claudio Juan;
Schweitzer, Frank
## ICSE '13 Proceedings of the 35th International Conference on Software Engineering Pages: 1032-1041more» «less
Abstract Efﬁcient bug triaging procedures are an important precondition for successful collaborative software engineering projects. Triaging bugs can become a laborious task particularly in open source software (OSS) projects with a large base of comparably inexperienced part-time contributors. In this paper, we propose an efﬁcient and practical method to identify valid bug reports which a) refer to an actual software bug, b) are not duplicates and c) contain enough information to be processed right away. Our classiﬁcation is based on nine measures to quantify the social embeddedness of bug reporters in the collaboration network. We demonstrate its applicability in a case study, using a comprehensive data set of more than 700, 000 bug reports obtained from the BUGZILLA installation of four major OSS communities, for a period of more than ten years. For those projects that exhibit the lowest fraction of valid bug reports, we ﬁnd that the bug reporters’ position in the collaboration network is a strong indicator for the quality of bug reports. Based on this ﬁnding, we develop an automated classiﬁcation scheme that can easily be integrated into bug tracking platforms and analyze its performance in the considered OSS communities. A support vector machine (SVM) to identify valid bug reports based on the nine measures yields a precision of up to 90.3% with an associated recall of 38.9%. With this, we signiﬁcantly improve the results obtained in previous case studies for an automated early identiﬁcation of bugs that are eventually ﬁxed. Furthermore, our study highlights the potential of using quantitative measures of social organization in collaborative software engineering. It also opens a broad perspective for the integration of social network analysis in the design of support infrastructures.
## The rise and fall of a central contributor: Dynamics of social organization and performance in the Gentoo community[2013] Zanetti, Marcelo Serrano;
Scholtes, Ingo;
Tessone, Claudio Juan;
Schweitzer, Frank
## CHASE/ICSE '13 Proceedings of the 6th International Workshop on Cooperative and Human Aspects of Software Engineering Pages: 49-56more» «less
Abstract Social organization and division of labor crucially influence the performance of collaborative software engineering efforts. In this paper, we provide a quantitative analysis of the relation between social organization and performance in Gentoo, an Open Source community developing a Linux distribution. We study the structure and dynamics of collaborations as recorded in the project's bug tracking system over a period of ten years. We identify a period of increasing centralization after which most interactions in the community were mediated by a single central contributor. In this period of maximum centralization, the central contributor unexpectedly left the project, thus posing a significant challenge for the community. We quantify how the rise, the activity as well as the subsequent sudden dropout of this central contributor affected both the social organization and the bug handling performance of the Gentoo community. We analyze social organization from the perspective of network theory and augment our quantitative findings by interviews with prominent members of the Gentoo community which shared their personal insights.
## How can social herding enhance cooperation?[2013] Schweitzer, Frank;
Mavrodiev, Pavlin;
Tessone, Claudio Juan
## Advances in Complex Systems (ACS), Pages: 22, Volume: 16more» «less
Abstract We study a system in which N agents have to decide between two strategies θ_(i) (i ∈ 1... N), for defection or cooperation, when interacting with other n agents (either spatial neighbors or randomly chosen ones). After each round, they update their strategy responding nonlinearly to two different information sources: (i) the payoff a_(i)(θ_(i), f_(i)) received from the strategic interaction with their n counterparts, (ii) the fraction f_(i) of cooperators in this interaction. For the latter response, we assume social herding, i.e. agents adopt their strategy based on the frequencies of the different strategies in their neighborhood, without taking into account the consequences of this decision. We note that f_(i) already determines the payoff, so there is no additional information assumed. A parameter ζ defines to what level agents take the two different information sources into account. For the strategic interaction, we assume a Prisoner's Dilemma game, i.e. one in which defection is the evolutionary stable strategy. However, if the additional dimension of social herding is taken into account, we find instead a stable outcome where cooperators are the majority. By means of agent-based computer simulations and analytical investigations, we evaluate the critical conditions for this transition towards cooperation. We find that, in addition to a high degree of social herding, there has to be a nonlinear response to the fraction of cooperators. We argue that the transition to cooperation in our model is based on less information, i.e. on agents which are not informed about the payoff matrix, and therefore rely on just observing the strategy of others, to adopt it. By designing the right mechanisms to respond to this information, the transition to cooperation can be remarkably enhanced.
## Quantifying the effects of social influence[2013] Mavrodiev, Pavlin;
Tessone, Claudio Juan;
Schweitzer, Frank
## Scientific Reports, Volume: 3, Number: 1360more» «less
Abstract How do humans respond to indirect social influence when making decisions? We analysed an experiment where subjects had to repeatedly guess the correct answer to factual questions, while having only aggregated information about the answers of others. While the response of humans to aggregated information is a widely observed phenomenon, it has not been investigated quantitatively, in a controlled setting. We found that the adjustment of individual guesses depends linearly on the distance to the mean of all guesses. This is a remarkable, and yet surprisingly simple, statistical regularity. It holds across all questions analysed, even though the correct answers differ in several orders of magnitude. Our finding supports the assumption that individual diversity does not affect the response to indirect social influence. It also complements previous results on the nonlinear response in information-rich scenarios. We argue that the nature of the response to social influence crucially changes with the level of information aggregation. This insight contributes to the empirical foundation of models for collective decisions under social influence.
## The social climbing game[2013] Bardoscia, Marco;
Luca, Giancarlo;
Livan, Giacomo;
Marsili, Matteo;
Tessone, Claudio Juan
## Journal of Statistical Physics, Pages: 440-457, Volume: 151more» «less
Abstract The structure of a society depends, to some extent, on the incentives of the individuals they are composed of. We study a stylized model of this interplay, that suggests that the more individuals aim at climbing the social hierarchy, the more society's hierarchy gets strong. Such a dependence is sharp, in the sense that a persistent hierarchical order emerges abruptly when the preference for social status gets larger than a threshold. This phase transition has its origin in the fact that the presence of a well defined hierarchy allows agents to climb it, thus reinforcing it, whereas in a "disordered" society it is harder for agents to find out whom they should connect to in order to become more central. Interestingly, a social order emerges when agents strive harder to climb society and it results in a state of reduced social mobility, as a consequence of ergodicity breaking, where climbing is more difficult.
## Betweenness preference: Quantifying correlations in the topological dynamics of temporal networks[2013] Pfitzner, Rene;
Scholtes, Ingo;
Garas, Antonios;
Tessone, Claudio Juan;
Schweitzer, Frank
## Physical Review Letters, Pages: 198701, Volume: 110, Number: 19more» «less
Abstract Time-evolving interaction patterns studied in diﬀerent contexts can be well represented bytemporal networks in which nodes are intermittently connected. In this Letter we introducethe notion of betweenness preference in the study of temporal networks. It captures how likelya certain node is to mediate interactions between particular pairs of its neighboring nodes.We argue that betweenness preference is an important correlation to consider in the analysisof temporal network data. In particular, it allows to assess to which extent paths existing intime-aggregated, static representations of temporal networks are actually feasible based onthe underlying sequence of interactions. We argue that betweenness preference correlationsare present in empirical data sets. We further show that neglecting betweenness preferencewill lead to signiﬁcantly wrong statements about spreading dynamics in temporal networks.
## How big is too big? Critical shocks for systemic failure cascades[2013] Tessone, Claudio Juan;
Garas, Antonios;
Guerra, Beniamino;
Schweitzer, Frank
## Journal of Statistical Physics, Pages: 765-783, Volume: 151more» «less
Abstract External or internal shocks may lead to the collapse of a system consisting of many agents. If the shock hits only one agent initially and causes it to fail, this can induce a cascade of failures among neighoring agents. Several critical constellations determine whether this cascade remains finite or reaches the size of the system, i.e. leads to systemic risk. We investigate the critical parameters for such cascades in a simple model, where agents are characterized by an individual threshold $$theta_i determining their capacity to handle a load $$alpha$$theta_i with 1-$$alpha being their safety margin. If agents fail, they redistribute their load equally to K neighboring agents in a regular network. For three different threshold distributions P($$theta), we derive analytical results for the size of the cascade, X(t), which is regarded as a measure of systemic risk, and the time when it stops. We focus on two different regimes, (i) EEE, an external extreme event where the size of the shock is of the order of the total capacity of the network, and (ii) RIE, a random internal event where the size of the shock is of the order of the capacity of an agent. We find that even for large extreme events that exceed the capacity of the network finite cascades are still possible, if a power-law threshold distribution is assumed. On the other hand, even small random fluctuations may lead to full cascades if critical conditions are met. Most importantly, we demonstrate that the size of the "big" shock is not the problem, as the systemic risk only varies slightly for changes of 10 to 50 percent of the external shock. Systemic risk depends much more on ingredients such as the network topology, the safety margin and the threshold distribution, which gives hints on how to reduce systemic risk.
## Diversity-induced resonance in the response to social norms[2013] Tessone, Claudio Juan;
Sanchez, Anxo;
Schweitzer, Frank
## Physical Review E, Pages: 022803, Volume: 87more» «less
Abstract In this paper we focus on diversity-induced resonance, which was recently found in bistable, excitable, and other physical systems. We study the appearance of this phenomenon in a purely economic model of cooperating and defecting agents. An agent's contribution to a public good is seen as a social norm, so defecting agents face a social pressure, which decreases if free riding becomes widespread. In this model, diversity among agents naturally appears because of the different sensitivities towards the social norm. We study the evolution of cooperation as a response to the social norm (i) for the replicator dynamics and (ii) for the logit dynamics by means of numerical simulations. Diversity-induced resonance is observed as a maximum in the response of agents to changes in the social norm as a function of the degree of heterogeneity in the population. We provide an analytical, mean-field approach for the logit dynamics and find very good agreement with the simulations. From a socioeconomic perspective, our results show that, counterintuitively, diversity in the individual sensitivity to social norms may result in a society that better follows such norms as a whole, even if part of the population is less prone to follow them.
## Effects of social influence on the wisdom of crowds[2012] Mavrodiev, Pavlin;
Tessone, Claudio Juan;
Schweitzer, Frank
## Proceedings of Collective Intelligence 2012more» «lessAbstract Wisdom of crowds refers to the phenomenon that the aggregate prediction or forecast of a group of individuals can be surprisingly more accurate than most individuals in the group, and sometimes - than any of the individuals comprising it. This article models the impact of social influence on the wisdom of crowds. We build a minimalistic representation of individuals as Brownian particles coupled by means of social influence. We demonstrate that the model can reproduce results of a previous empirical study. This allows us to draw more fundamental conclusions about the role of social influence: In particular, we show that the question of whether social influence has a positive or negative net effect on the wisdom of crowds is ill-defined. Instead, it is the starting configuration of the population, in terms of its diversity and accuracy, that directly determines how beneficial social influence actually is. The article further examines the scenarios under which social influence promotes or impairs the wisdom of crowds.
## Time-explicit graphs: A framework for dynamic network analysis[2012] Pfitzner, Rene;
Scholtes, Ingo;
Tessone, Claudio Juan;
Garas, Antonios;
Schweitzer, Frank
## Submittedmore» «lessAbstract When dealing with networks of several kind, network theory provides the theoretical framework and the practical tools to analyze them. Mostly analysis focuses on steady networks, i.e. networks with ﬁxed topology. However, real-world scenarios often deal with (highly) dynamic topologies. As of today, the question of how to investigate such scenarios, e.g. deﬁning a meaningful notion of “temporal centrality”, has generally not been answered. In this poster we present research pointing out the obstacles arising in this endeavor as well as a possible framework to address those issues, which we call time-explicit graphs.
## Hierarchical consensus formation reduces the influence of opinion bias[2012] Perony, Nicolas;
Pfitzner, Rene;
Scholtes, Ingo;
Schweitzer, Frank;
Tessone, Claudio Juan
## ECMS 2012 - Proceedings of the 26th European Conference on Modelling and Simulation Pages: 662-668more» «less
Abstract We study the role of hierarchical structures in a simple model of collective consensus formation based on the bounded confidence model with continuous individual opinions. For the particular variation of this model considered in this paper, we assume that a bias towards an extreme opinion is introduced whenever two individuals interact and form a common decision. As a simple proxy for hierarchical social structures, we introduce a two-step decision making process in which in the second step groups of like-minded individuals are replaced by representatives once they have reached local consensus, and the representatives in turn form a collective decision in a downstream process. We find that the introduction of such a hierarchical decision making structure can improve consensus formation, in the sense that the eventual collective opinion is closer to the true average of individual opinions than without it. In particular, we numerically study how the size of groups of like-minded individuals being represented by delegate individuals affects the impact of the bias on the final population-wide consensus. These results are of interest for the design of organisational policies and the optimisation of hierarchical structures in the context of group decision making.
## How random is social behaviour? Disentangling social complexity through the study of a wild house mouse population[2012] Perony, Nicolas;
Tessone, Claudio Juan;
Koenig, Barbara;
Schweitzer, Frank
## PLOS Computational Biology, Pages: e1002786, Volume: 8, Number: 11more» «less
Abstract From the synchronised beauty of fish schools to the rigorous hierarchy of ant colonies, animals often display awe-inspiring collective behaviour. In recent years, principles of statistical physics have helped to unveil some simple mechanisms behind the emergence of such collective dynamics. Among the most elementary tools used to explain group behaviour are random processes, a typical example being the so-called “random walk”. In this paper, we have developed a framework based on such random assumptions to study the spatial and social structure of a population of wild house mice. We introduce the concept of perceptual landscape to describe the spatial behaviour of animals, whilst including all sensory and social constraints they are subject to: the perceptual landscape effectively maps the environment of animals as they perceive it. By applying our assumptions to a multi-agent model, we are able to reveal that much of the high-level social behaviour observed in the mouse population can indeed be explained through the many interactions of randomly moving individuals. This raises the question of how much of what we often regard as complex natural phenomena may, in fact, be the result of exceedingly simple forces.
## A quantitative study of social organisation in open source software communities[2012] Zanetti, Marcelo Serrano;
Sarigol, Emre;
Scholtes, Ingo;
Tessone, Claudio Juan;
Schweitzer, Frank
## OASIcs 2012 - Imperial College Computing Student Workshop 2012, Jones A.V. (Ed.), Pages: 116--122, Volume: 28, Publisher: Schloss Dagstuhlmore» «less
Abstract The success of open source projects crucially depends on the voluntary contributions of a suf- ﬁciently large community of users. Apart from the mere size of the community, interesting questions arises when looking at the evolution of structural features of collaborations between community members. In this article, we discuss several network analytic proxies that can be used to quantify diﬀerent aspects of the social organisation in social collaboration networks. We particularly focus on measures that can be related to the cohesiveness of the communities, the distribution of responsibilities and the resilience against turnover of community members. We present a comparative analysis on a large-scale data set that covers the full history of collabor- ations between users of 14 major open source software communities. Our analysis covers both aggregate and time-evolving measures and highlights diﬀerences in the social organisation across communities. We argue that our results are a promising ﬁrst step towards the deﬁnition of suitable, potentially multi-dimensional, resilience and risk indicators for open source software communities.
## Noise-induced volatility of collective dynamics[2012] Harras, Georges;
Tessone, Claudio Juan;
Sornette, Didier
## Physical Review E, Pages: 011150, Volume: 85, Number: 1more» «less
Abstract Noise-induced volatility refers to a phenomenon of increased level of fluctuations in the collective dynamics of bistable units in the presence of a rapidly varying external signal, and intermediate noise levels. The archetypical signature of this phenomenon is that –beyond the increase in the level of fluctuations– the response of the system becomes uncorrelated with the external driving force, making it different from stochastic resonance. Numerical simulations and an analytical theory of a stochastic dynamical version of the Ising model on regular and random networks demonstrate the ubiquity and robustness of this phenomenon, which is argued to be a possible cause of excess volatil-ity in financial markets, of enhanced effective temperatures in a variety of out-of-equilibriumsystems and of strong selective responses of immune systems of complex biological organisms. Extensive nu-merical simulations are compared with a mean-field theory for different network topologies.
## Synchronised firing induced by network dynamics in excitable systems[2012] Tessone, Claudio Juan;
Zanette, Damian H.
## Europhysics Letters, Pages: 68006, Volume: 99, Number: 6more» «less
Abstract We study the collective dynamics of an ensemble of coupled identical FitzHugh-Nagumo elements in their excitable regime. We show that collective firing, where all the elements perform their individual firing cycle synchronously, can be induced by random changes in the interaction pattern. Specifically, on a sparse evolving network where, at any time, each element is connected with at most one partner, collective firing occurs for intermediate values of the rewiring frequency. Thus, network dynamics can play the role of noise and connectivity in inducing this kind of self-organised behaviour in highly disconnected systems which, otherwise, would not allow for the spreading of coherent evolution.
## Organic design of massively distributed systems: A complex networks perspective[2012] Scholtes, Ingo;
Tessone, Claudio Juan
## Informatik Spektrum, Pages: 1-12, Volume: 35, Number: 2more» «less
Abstract The vision of Organic Computing addresses challenges that arise in the design of future information systems that are comprised of numerous, heterogeneous, resource-constrained and error-prone components. The notion organic highlights the idea that, in order to be manageable, such systems should exhibit self-organization, self-adaptation and self-healing characteristics similar to those of biological systems. In recent years, the principles underlying these characteristics are increasingly being investigated from the perspective of complex systems science, particularly using the conceptual framework of statistical physics and statistical mechanics. In this article, we review some of the interesting relations between statistical physics and networked systems and discuss applications in the engineering of organic overlay networks with predictable macroscopic properties.
## Sustainable growth in complex networks[2011] Tessone, Claudio Juan;
Geipel, Markus Michael;
Schweitzer, Frank
## Europhysics Letters, Pages: 58005, Volume: 96, Number: 5more» «less
Abstract Based on the analysis of the dependency network in 18 Java projects, we develop a novel model of network growth which considers both preferential attachment and the addition of new nodes with a heterogeneous distribution of their initial degree, k0. Empirically we find that the cumulative distributions of initial and final degrees in the network follow power law behaviours: 1−P(k0)∝k1−$α$ as a function of the network size, we find empirically K(N)∝N$β$,where $β$ ∈[1.25, 2] (for small N), while converging to $β$ ∼1 for large N. This indicates a transition from a growth regime with increasing network density towards a sustainable regime, which prevents a collapse due to 0 ,and 1−P(k)∝k1−$γ$, respectively. For the total number of links ever increasing dependencies. Our theoretical framework allows us to predict relations between the exponents $α$, $β$, $γ$, which also link issues of software engineering and developer activity. These relations are verified bymeans of computer simulations and empirical investigations. They indicate that the growth of real Open Source Software networks occurs on the edge between two regimes, which are dominated either by the initial degree distribution of added nodes, or by the preferential attachment mechanism. Hence, the heterogeneous degree distribution of newly added nodes, found empirically, is essential to describe the laws of sustainable growth in networks.
## Network evolution based on centrality[2011] Koenig, Michael D;
Tessone, Claudio Juan
## Physical Review E, Pages: 056108, Volume: 84, Number: 5more» «less
Abstract We study the evolution of networks when the creation and decay of links are based on the position of nodes in the network measured by their centrality. We show that the same network dynamics arise under various centrality measures, and solve analytically the network evolution. During the complete evolution, the network is characterized by nestedness: the neighborhood of a node is contained in the neighborhood of the nodes with larger degree.We find a discontinuous transition in the network density between hierarchical and homogeneous networks, depending on the rate of link decay. We also show that this evolution mechanism leads to double power-law degree distributions, with interrelated exponents.
## From assortative to dissortative networks: The role of capacity constraints[2010] Konig, Michael D;
Tessone, Claudio Juan;
Zenou, Yves
## Advances in Complex Systems, Pages: 483, Volume: 13, Number: 04more» «less
Abstract We consider a dynamic model of network formation where agents form and sever links based on the centrality of their potential partners.We show that the existence of capacity constrains in the amount of links an agent can maintain introduces a transition from dissortative to assortative networks. This effect can shed light on the distinction between technological and social networks as it gives a simple mechanism explaining how and why this transition occurs.
## Critical behaviour in an evolutionary ultimatum game with social structure[2009] Eguiluz, Victor M.;
Tessone, Claudio Juan
## Advances in Complex Systems (ACS), Pages: 221-232, Volume: 12, Number: 2more» «less
Abstract Experimental studies have shown the ubiquity of altruistic behavior in human societies. The social structure is a fundamental ingredient to understand the degree of altruism displayed by the members of a society, in contrast to individual-based features, like for example age or gender, which have been shown not to be relevant to determine the level of altruistic behavior. We explore an evolutionary model aiming to delve how altruistic behavior is affected by social structure. We investigate the dynamics of interacting individuals playing the Ultimatum Game with their neighbors given by a social network of interaction. We show that a population self-organizes in a critical state where the degree of altruism depends on the topology characterizing the social structure. In general, individuals offering large shares but in turn accepting large shares, are removed from the population. In heterogeneous social networks, individuals offering intermediate shares are strongly selected in contrast to random homogeneous networks where a broad range of offers, below a critical one, is similarly present in the population.
## Diversity-induced resonance in a model for opinion formation[2009] Tessone, Claudio Juan;
Toral, Raul
## European Physical Journal B, Pages: 549-555, Volume: 71, Number: 4more» «less
Abstract We study an opinion formation model that takes into account that individuals have diverse preferences when forming their opinion regarding a particular issue. We show that the system exhibits a phenomenon called "diversity-induced resonance"[Tessone et al. Phys. Rev. Lett. 97, 194101 (2006)], by which an external influence (for example advertising, or fashion trends) is better followed by populations having the right degree of diversity in their preferences, rather than others where the individuals are identical or have too different preferences. We support our findings by numerical simulations of the model and a mean-field type analytical theory.
## A complementary view on the growth of directory trees[2009] Geipel, Markus Michael;
Tessone, Claudio Juan;
Schweitzer, Frank
## The European Physical Journal B, Pages: 641-648, Volume: 71, Number: 4more» «less
Abstract Trees are a special sub-class of networks with unique properties, such as the level distribution which has often been overlooked.We analyse a general tree growth model proposed by Klemm et al. [Phys. Rev. Lett. 95, 128701 (2005)] to explain the growth of user-generated directory structures in computers. The model has a single parameter q which interpolates between preferential attachment and random growth. Our analysis results in three contributions: first, we propose a more efficient estimation method for q based on the degree distribution, which is one specific representation of the model. Next, we introduce the concept of a level distribution and analytically solve the model for this representation. This allows for an alternative and independent measure of q.We argue that, to capture real growth processes, the q estimations from the degree and the level distributions should coincide. Thus, we finally apply both representations to validate the model with synthetically generated tree structures, as well as with collected data of user directories. In the case of real directory structures, we show that q measured from the level distribution are incompatible with q measured from the degree distribution. In contrast to this, we find perfect agreement in the case of simulated data. Thus, we conclude that the model is an incomplete description of the growth of real directory structures as it fails to reproduce the level distribution. This insight can be generalised to point out the importance of the level distribution for modeling tree growth.
## Editorial: Risk, markets, games, and networks[2009] Schweitzer, Frank;
Battiston, Stefano;
Tessone, Claudio Juan
## The European Physical Journal B, Pages: 439-440, Volume: 71, Number: 4more» «less
Abstract The 20 research articles collected in this issue share, in addition to their topical relations, one important feature: they present results obtained from research groups associated in the COST action P10 ‘Physics of Risk’. COST is an intergovernmental framework for ‘European Cooperation in Science and Technology’, allowing the coordination of research on a European level. The action P10 was funded between September 2003 and June 2008 and involved more than 80 scientists in 21 countries across Europe. The main objective of the action was to apply methods developed in statistical physics to accomplish a new quantitative understanding of the assessment of risk. This way it departed from usual activities in the ﬁeld of risk management. In fact, in recent years statistical physics has successfully contributed to many interdisciplinary ﬁelds ranging from regulatory networks in biology to ﬁnancial market models. Therefore, a transfer of methods and tools from statistical physics into the area of risk assessment should be a promising endeavour.
## Slower is faster: Fostering consensus formation by heterogeneous interia[2008] Tessone, Claudio Juan;
Schweitzer, Frank
## Advances in Complex Systems (ACS), Pages: 551-563, Volume: 11, Number: 04more» «less
Abstract We investigate an extension of the voter model in which voters are equipped with an individual inertia to change their opinion. This inertia depends on the persistence time of a voter's current opinion (ageing). We focus on the case of only two different inertia values: zero if a voter just changed towards a new opinion and nu otherwise. We are interested in the average time to reach consensus, i.e. the state in which all voters have adopted the same opinion. Adding inertia to the system means to slow down the dynamics at the voter's level, which should presumably lead to a slower consensus formation. As an unexpected outcome of our inertial voter dynamics, there is a parameter region of nu where an increasing inertia leads to a faster consensus formation. These results rest on the heterogeneity of voters which evolves through the described ageing. In a control setting of homogeneous inertia values, we only find monotonously increasing consensus times. In the paper, we present dynamical equations for the mean-field case which allow for analytical insight into the observed slower-is-faster effect.
## Decelerating microdynamics can accelerate macrodynamics in the voter model[2008] Tessone, Claudio Juan;
Schweitzer, Frank
## Physical Review Letters, Pages: 1-4, Volume: 101, Number: 1more» «less
Abstract For the voter model, we study the effect of a memory-dependent transition rate. We assume that the transition of a spin into the opposite state decreases with the time it has been in its current state. Counterintuitively, we find that the time to reach a macroscopically ordered state can be accelerated by slowing down the microscopic dynamics in this way. This holds for different network topologies, including fully connected ones. We find that the ordering dynamics is governed by two competing processes which either stabilize the majority or the minority state. If the first one dominates, it accelerates the ordering of the system. The conclusions of this Letter are not restricted to the voter model, but remain valid to many other spin systems as well.
## Universal scaling in the branching of the tree of life.[2008] Herrada, E Alejandro;
Tessone, Claudio Juan;
Klemm, Konstantin;
Eguiluz, Victor M.;
Hernandez - Garcia, Emilio;
Duarte, Carlos M
## PLOS ONE, Pages: e2757, Volume: 3, Number: 7more» «less
Abstract Understanding the patterns and processes of diversification of life in the planet is a key challenge of science. The Tree of Life represents such diversification processes through the evolutionary relationships among the different taxa, and can be extended down to intra-specific relationships. Here we examine the topological properties of a large set of interspecific and intraspecific phylogenies and show that the branching patterns follow allometric rules conserved across the different levels in the Tree of Life, all significantly departing from those expected from the standard null models. The finding of non-random universal patterns of phylogenetic differentiation suggests that similar evolutionary forces drive diversification across the broad range of scales, from macro-evolutionary to micro-evolutionary processes, shaping the diversity of life on the planet.
## Chaotic synchronizations of spatially extended systems as nonequilibrium phase transitions.[2008] Cencini, Massimo;
Tessone, Claudio Juan;
Tornell, Aaron
## Chaos (Woodbury, N.Y.), Pages: 037125, Volume: 18, Number: 3more» «less
Abstract Two replicas of spatially extended chaotic systems synchronize to a common spatio-temporal chaotic state when coupled above a critical strength. As a prototype of each single spatio-temporal chaotic system a lattice of maps interacting via power-law coupling is considered. Furthermore, each unit in the one-dimensional chain is linked to the corresponding one in the replica via a local coupling. The synchronization transition is studied as a nonequilibrium phase transition, and its critical properties are analyzed at varying the spatial interaction range as well as the nonlinearity of the dynamical units composing each system. In particular, continuous and discontinuous local maps are considered. In both cases the transitions are of the second order with critical indices varying with the exponent characterizing the interaction range. For discontinuous maps it is numerically shown that the transition belongs to the anomalous directed percolation (ADP) family of universality classes, previously identified for Levy-flight spreading of epidemic processes. For continuous maps, the critical exponents are different from those characterizing ADP, but apart from the nearest-neighbor case, the identification of the corresponding universality classes remains an open problem. Finally, to test the influence of deterministic correlations for the studied synchronization transitions, the chaotic dynamical evolutions are substituted by suitable stochastic models. In this framework and for the discontinuous case, it is possible to derive an effective Langevin description that corresponds to that proposed for ADP.
## Global firing induced by network disorder in ensembles of active rotators[2008] Tessone, Claudio Juan;
Zanette, Damian H.;
Toral, Raul
## The European Physical Journal B, Pages: 319-326, Volume: 62, Number: 3more» «less
Abstract We study the influence of repulsive interactions on an ensemble of coupled excitable rotators. We find that a moderate fraction of repulsive interactions can trigger global firing of the ensemble. The regime of global firing, however, is suppressed in sufficiently large systems if the network of repulsive interactions is fully random, due to self-averaging in its degree distribution. We thus introduce a model of partially random networks with a broad degree distribution, where self-averaging due to size growth is absent. In this case, the regime of global firing persists for large sizes. Our results extend previous work on the constructive effects of diversity in the collective dynamics of complex systems.
## Finite size effects in the dynamics of opinion formation[2007] Toral, Raul;
Tessone, Claudio Juan
## Communications in Computational Physics, Pages: 177-195, Volume: 2more» «lessAbstract For some models of relevance in the social sciences we review some exam-ples inwhich systemsize plays an important role in the final outcome of the dynamics. We discuss the conditions underwhich changes of behavior can appear onlywhen the number of agents in the model takes a finite value. Those changes of behavior can be related to the apparent phase transitions that appear in some physical models. We showexamples in the Galam's model of opinion transmission and the Axelrod's model of culture formation stressing the role that the network of interactions has on themain results of both models. Finally, we present the phenomenon of system-size stochastic resonance by which a forcing signal (identified as an advertising agent) is optimally amplified by a population of the right (intermediate) size. Our work stresses the role that the system size has in the dynamics of social systems and the inappropriateness of taking the thermodynamic limit for these systems.
## Collective effects induced by diversity in extended systems[2007] Toral, Raul;
Tessone, Claudio Juan;
Lopes, Joao Viana
## European Physical Journal Special Topics, Pages: 59-67, Volume: 143more» «less
Abstract We show that diversity, in the form of quenched noise, can have a constructive effect in the dynamics of extended systems. We first consider a bistable $ϕ⁴$ model composed by many coupled units and show that the global response to an external periodic forcing is enhanced under the presence of the right amount of diversity (measured as the dispersion in one of the parameters defining the model). As a second example, we consider a system of active-rotators and show that while they are at rest in the homogeneous case, the disorder introduced by the diversity suffices to trigger the appearance of common firings or pulses. Both effects require very simple ingredients and we expect the results presented here to be of interest in similar models.
## Evolutionary and ecological trees and networks[2007] Garcia, Emilio Hernandez;
Herrada, Alejandro E;
Rozenfeld, Alejandro F;
Tessone, Claudio Juan;
Eguiluz, Victor M;
Duarte, Carlos M;
Haond, Sophie Arnaud;
Serrao, Ester
## Nonequilibrium Statistical Mechanics And Nonlinear Physics: XV Conference on Nonequilibrium Statistical Mechanics and Nonlinear Physics, Pages: 78-83, Volume: 913, Publisher: AIP Conference Proceedingsmore» «lessAbstract Evolutionary relationships between species are usually represented in phylogenies, i.e. evolutionary trees, which are a type of networks. The terminal nodes of these trees represent species, which are made of individuals and populations among which gene flow occurs. This flow can also be represented as a network. In this paper we briefly show some properties of these complex networks of evolutionary and ecological relationships. First, we characterize large scale evolutionary relationships in the Tree of Life by a degree distribution. Second, we represent genetic relationships between individuals of a Mediterranean marine plant, Posidonia oceanica, in terms of a Minimum Spanning Tree. Finally, relationships among plant shoots inside populations are represented as networks of genetic similarity.
## Theory of collective firing induced by noise or diversity in excitable media[2007] Tessone, Claudio Juan;
Scire, Alessandro;
Toral, Raul;
Colet, Pere
## Physical Review E, Pages: 016203, Volume: 75, Number: 1more» «less
Abstract Large variety of physical, chemical, and biological systems show excitable behavior, characterized by a nonlinear response under external perturbations: only perturbations exceeding a threshold induce a full system response firing. It has been reported that in coupled excitable identical systems noise may induce the simul-taneous firing of a macroscopic fraction of units. However, a comprehensive understanding of the role of noise and that of natural diversity present in realistic systems is still lacking. Here we develop a theory for the emergence of collective firings in nonidentical excitable systems subject to noise. Three different dynamical regimes arise: subthreshold motion, where all elements remain confined near the fixed point; coherent pulsations, where a macroscopic fraction fire simultaneously; and incoherent pulsations, where units fire in a disordered fashion.We also show that the mechanism for collective firing is generic: it arises from degradation of entrainment originated either by noise or by diversity.
## Synchronization of extended chaotic systems with long-range interactions: An analogy to l'evy-flight spreading of epidemics[2006] Tessone, Claudio Juan;
Cencini, Massimo;
Torcini, Alessandro
## Physical Review Letters, Pages: 224101, Volume: 97more» «less
Abstract Spatially extended chaotic systems with power-law decaying interactions are considered. Two coupled replicas of such systems synchronize to a common spatiotemporal chaotic state above a certain coupling strength. The synchronization transition is studied as a nonequilibrium phase transition and its critical properties are analyzed at varying the interaction range. The transition is found to be always continuous, while the critical indexes vary with continuity with the power-law exponent characterizing the interaction. Strong numerical evidences indicate that the transition belongs to the anomalous directed percolation family of universality classes found for L'evy-flight spreading of epidemic processes.
## Noise-induced inhibitory suppression of frequency-selective stochastic resonance[2006] Tessone, Claudio Juan;
Ullner, Ekkehard;
Zaikin, Alexei;
Kurths, Jurgen;
Toral, Raul
## Physical Review E, Pages: 046220, Volume: 74, Number: 4more» «less
Abstract We study the control of oscillations in a system of inhibitory coupled noisy excitable and oscillatory units. Using dynamical properties of inhibition, we find regimes when the oscillations can be suppressed but the information signal of a certain frequency can be transmitted through the system. The mechanism of this phenomenon is a resonant interplay of noise and the transmission signal provided by certain value of inhibitory coupling. Analyzing a system of three or four oscillators representing neural clusters, we show that this suppression can be effectively controlled by coupling and noise amplitudes
## Diversity-induced resonance[2006] Tessone, Claudio Juan;
Mirasso, Claudio R;
Toral, Raul;
Gunton, James D
## Physical Review Letters, Pages: 194101, Volume: 97, Number: 19more» «less
Abstract We present conclusive evidence showing that different sources of diversity, such as those represented by quenched disorder or noise, can induce a resonant collective behavior in an ensemble of coupled bistable or excitable systems. Our analytical and numerical results show that when such systems are subjected to an external subthreshold signal, their response is optimized for an intermediate value of the diversity. These findings show that intrinsic diversity might have a constructive role and suggest that natural systems might profit from their diversity in order to optimize the response to an external stimulus.
## Stochastic resonance in an extended fitzhugh-nagumo system: The role of selective coupling[2006] Tessone, Claudio Juan;
Wio, Horacio S.
## Physica A: Statistical Mechanics and its Applications, Pages: 46-54, Volume: 374more» «lessAbstract Here we present a study of stochastic resonance (SR) in an extended FitzHugh-- Nagumo system with a field dependent activator diffusion. We show that the system response (here measured through the output signal-to-noise ratio (SNR)) is enhanced due to the particular form of the non-homogeneous coupling. Such a result supports previous ones obtained in a simpler scalar reaction-diffusion system and shows that such an enhancement, induced by the field dependent diffusion-or selective coupling-, is a robust phenomenon.
## Dynamics of coupled self-pulsating semiconductor lasers[2005] Scire, Alessandro;
Tessone, Claudio Juan;
Colet, Pere
## IEEE Journal of Quantum Electronics, Pages: 272-279, Volume: 41, Number: 3more» «less
Abstract We introduce and analyze a model for the dynamics of two coupled self-pulsating semiconductor lasers. We investigate the role of the complex coupling coefficient in the static and dynamic properties of the device. We find conditions for the emergence of coherent laser pulses, in which the two lasers display synchronous coherent self-pulsations (self-pulsating super modes). Nonlinear dynamics and two different routes to chaos are also individuated and discussed.
## System size stochastic resonance in a model for opinion formation[2005] Tessone, Claudio Juan;
Toral, Raul
## Physica A: Statistical Mechanics and its Applications, Pages: 106-116, Volume: 351more» «less
Abstract We study a model for opinion formation, which incorporates three basic ingredients for the evolution of the opinion held by an individual: imitation, influence of fashion and randomness. We show that in the absence of fashion, the model behaves as a bistable system with random jumps between the two stable states with a distribution of times following Kramer's law. We also demonstrate the existence of system size stochastic resonance, by which there is an optimal value for the number of individuals N for which the average opinion follows better the fashion.
## Coherence resonance in coupled excitable systems: Dependence with system size[2004] Tessone, Claudio Juan;
Toral, Raul;
Mirasso, Claudio R;
Gunton, James D
## Proceedings of the International School of Physics Enrico Fermi, Course CLV: The Physics of Complex Systems (New Advances and Perspectives), Pages: 461-467, Publisher: IOS Press (Amsterdam)more» «lessAbstract We report on the existence of a coherence resonance effect as a function of system size. We consider globally coupled FitzHugh-Nagumo systems under the effect of white noise and study the synchronization of the response as well as the regularity of the emitted pulses. By numerical integration of the stochastic equations, we find that the regularity as measured both by the jitter and the time correlation, is optimal for an intermediate value of the number of coupled elements. A simple theory, based on the Gaussian approximation, is able to explain qualitetively the observed phenomenon.
## Neighborhood models of minority opinion spreading[2004] Tessone, Claudio Juan;
Toral, Raul;
Amengual, P.;
Wio, Horacio S.;
San Miguel, Maxi
## The European Physical Journal B, Pages: 535-544, Volume: 39, Number: 4more» «less
Abstract We study the effect of finite size population in Galam's model [Eur. Phys. J. B 25, 403 (2002)] of minority opinion spreading and introduce neighborhood models that account for local spatial effects. For systems of different sizes N, the time to reach consensus is shown to scale as lnN in the original version, while the evolution is much slower in the new neighborhood models. The threshold value of the initial concentration of minority supporters for the defeat of the initial majority, which is independent of N in Galam's model, goes to zero with growing system size in the neighborhood models. This is a consequence of the existence of a critical size for the growth of a local domain of minority supporters.
## Stochastic resonance and generalized information measures[2003] Tessone, Claudio Juan;
Plastino, Angel;
Wio, Horacio S.
## Physica A: Statistical Mechanics and its Applications, Pages: 37-54, Volume: 326more» «lessAbstract We use Tsallis' information measure andthe recently advanced "escort-Tsallis" one in order to investigate the stochastic resonance (SR) phenomenon. In particular, on the basis of these generalized information measures (GIM), both characterized by a non-extensivity parameter q, we study the effect of modifying the type of noise. The GIM are used to measure SR phenomenon comparing the input and output probability distributions, finding that for the range of noise intensities enhancing SR, $q → 0$ gives the optimum measure. An important advantage of using GIM instead of Shannon's measure is the possibility of detecting smaller signal amplitudes with the former than with the latter one.
## Stochastic resonance in bistable and excitable systems: Effect of non-gaussian noises[2003] Fuentes, Miguel A.;
Tessone, Claudio Juan;
Wio, Horacio S.;
Toral, Raul
## Fluctuation and Noise Letters, Pages: L365-L371, Volume: 3, Number: 4more» «less
Abstract We analyze stochastic resonance in systems driven by non-Gaussian noises. For the bistable double well we compare the signal-to-noise ratio resulting from numerical simulations with some quasi-analytical results predicted by a consistent Markovian approximation in the case of a colored non-Gaussian noise. We also study the FitzHugh-- Nagumo excitable system in the presence of the same noise. In both systems, we find that, as the noise departs from Gaussian behavior, there is a regime (different for the excitable and the bistable systems) in which there is a notable robustness against noise tuning since the signal-to-noise ratio curve broadens and becomes less sensitive to the actual value of the noise intensity. We also compare our results with some experiments in sensory systems.
## On the equipartition and virial theorems[2002] Mart'nez, Sandra;
Pennini, Flavia;
Plastino, Angel;
Tessone, Claudio Juan
## Physica A: Statistical Mechanics and its Applications, Pages: 48-51, Volume: 305more» «lessAbstract We revisit the celebrated equipartition and virial theorems from a non-extensive viewpoint. We show that both theorems still hold in a non-extensive scenario, independently of the value of Tsallis' index q.
## Q-thermostatistics and the black-body radiation problem[2002] Mart'nez, Sandra;
Pennini, Flavia;
Plastino, Angel;
Tessone, Claudio Juan
## Physica A: Statistical Mechanics and its Applications, Pages: 85-105, Volume: 309more» «lessAbstract We give an exact information-theory treatment of the n-dimensional black-body radiation process in a non-extensive scenario. We develop a q-generalization of the laws of (i) Stefan-- Boltzmann, (ii) Planck, and (iii) Wien, and show that conventional, canonical results are obtained at temperatures above 1/K. Classical relationships between radiation, pressure, and internal energy are recovered (independently of the q value). Analyzing the particles' density for $q 1$, we see that the non-extensive parameter q introduces a fictitious chemical potential. We apply our results to experimental data on the cosmic microwave background and reproduce it with acceptable accuracy for different temperatures (each one associated to a particular q value).
## On the influence of noise on the critical and oscillatory behavior of a predator-prey model: Coherent stochastic resonance at the proper frequency of the system[2001] Rozenfeld, Alejandro F;
Tessone, Claudio Juan;
Albano, Ezequiel;
Wio, Horacio S.
## Physics Letters A, Pages: 45-52, Volume: 280more» «less
Abstract Noise-induced changes in the critical and oscillatory behavior of a prey-- predator system are studied using power spectrum density and spectral amplification factor (SAF) analysis. In the absence of external noise, the population densities exhibit three kinds of asymptotic behavior, namely: absorbing state, fixed point (FP) and an oscillatory regime with a well defined proper (natural) frequency. The addition of noise destabilizes the FP phase inducing a transition to a new OR. Surprisingly, it is found that when a periodic signal is added to the control parameter, the system responds robustly, without relevant changes in its behavior. Nevertheless, the coherent stochastic resonance phenomenon is found only at the proper frequency. Also, a method based on SAF allows us to locate very accurately the transition points between the different regimes.
## Stochastic resonance driven by time-modulated correlated white noise sources[2000] Tessone, Claudio Juan;
Wio, Horacio S.;
Hanggi, Peter
## Physical Review E, Pages: 4623, Volume: 62more» «less
Abstract We analyze the effects caused by the simultaneous presence of correlated additive and multiplicative noises for stochastic resonance. Besides the standard potential modulation we also consider a time-periodic variation of the correlation between the two noise sources. As a foremost result we find that stochastic resonance, as characterized by the signal-to-noise ratio and the spectral amplification, becomes characteristically broadened. The broadening can be controlled by varying the relative phase shift between the two types of modulation force.
## Stochastic resonance in bistable systems: The effect of simultaneous additive and multiplicative[1998] Tessone, Claudio Juan;
Wio, Horacio S.
## Modern Physics Letters B, Pages: 1195-1202, Volume: 12more» «less
Abstract We analyze the effect of the simultaneous presence of correlated additive and multiplica-tive noises on the stochastic resonance response of a modulated bistable system.We find that when the correlation parameter is also modulated, the system's response, measured through the output signal-to-noise ratio, becomes largely independent of the additive noise intensity.
## Blackbody radiation in a nonextensive scenario Mart'nez, Sandra;
Pennini, Flavia;
Plastino, Angel;
Tessone, Claudio Juan
## Physica A: Statistical Mechanics and its Applications Pages: 224-229more» «lessAbstract An exact analysis of the N-dimensional blackbody radiation process in a nonextensive a la Tsallis scenario is performed for values of the nonextensive's index in the range (0 < q < 1). The recently advanced "Optimal Lagrange Multipliers" technique has been employed. The results are consistent with those of the extensive, q = 1 case. The generalization of the celebratedlaws of Planck, Stefan-Boltzmann andWien is investigated.
## Talks»## «Talks## Talks## Network dynamics and the creation of knowledge in R&D networks [Sept. 11, 2012 - Sept. 14, 2012]
## Latsis Symposium, ETH Zurich, Zurich, Switzerland## Network dynamics and the creation of knowledge in R&D networks [Sept. 3, 2012]
## European Conference on Complex Systems (ECCS'12), Brussels, Belgium## Effects of volatility in real-world networks: modeling based on monogamous networks [Feb. 28, 2012]
## First International Workshop on Complex Sciences in the Engineering of Computing Systems (CSECS), held at ARCS 2012, Munich, Germany## Evolution based on centrality: bistability between hierarchical and destructured networks [March 21, 2010 - March 26, 2010]
## Deutsche Physikalische Gesellschaft (DPG) conference, Regensburg, Germany## Social network evolution based on agent centrality [Sept. 16, 2009]
## European Social Simulation Association Conference, University of Surrey, Guildford, UK## From networks evolving by centrality to rank-based dynamics [Aug. 21, 2009]
## International Centre For Theoretical Physics ``Abdus Salam'', Trieste, Italy## Network evolution induced by agents competing for high centrality [Dec. 10, 2008]
## BCNet Workshop: Trends and perspectives in Complex Networks, Barcelona, Spain## Social Network Formation of Agents Competing for High Centrality [June 21, 2008]
## International Conference on Economic Science with Heterogeneous Interacting Agents, Warsaw, Poland## Chaotic synchronization in extended systems as out-of-equilibrium phase transitions, Network Synchronization: from dynamical systems to neuroscience [May 27, 2008]
## Leiden, Netherlands## Reluctance to opinion change leads to faster consensus [Sept. 21, 2007 - Sept. 23, 2007]
## 4-th Annual Meeting COST Action P10 "Physics of Risk", Palermo, Italy |
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