IMT Institutional Repository: No conditions. Results ordered -Date Deposited. 2024-09-09T17:56:02ZEPrintshttp://eprints.imtlucca.it/images/logowhite.pnghttp://eprints.imtlucca.it/2014-12-10T14:37:10Z2014-12-10T14:37:10Zhttp://eprints.imtlucca.it/id/eprint/2406This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/24062014-12-10T14:37:10ZThe structure of inter-urban traffic: a weighted network analysisWe study the structure of the network representing the interurban commuting traffic of the Sardinia region, Italy, which amounts to 375 municipalities and 1,600,000 inhabitants. We use a weighted network representation where vertices correspond to towns and the edges to the actual commuting flows among those. We characterize quantitatively both the topological and weighted properties of the resulting network. Interestingly, the statistical properties of commuting traffic exhibit complex features and non-trivial relations with the underlying topology. We characterize quantitatively the traffic backbone among large cities and we give evidences for a very high heterogeneity of the commuter flows around large cities. We also discuss the interplay between the topological and dynamical properties of the network as well as their relation with socio-demographic variables such as population and monthly income. This analysis may be useful at various stages in environmental planning and provides analytical tools for a wide spectrum of applications ranging from impact evaluation to decision-making and planning support.Andrea De MontisMarc BarthélemyAlessandro Chessaalessandro.chessa@imtlucca.itAlessandro Vespignani2013-11-07T11:03:39Z2013-11-20T09:08:17Zhttp://eprints.imtlucca.it/id/eprint/1883This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/18832013-11-07T11:03:39ZThe structure of interurban traffic: a weighted network analysisWe study the structure of the network representing the interurban commuting traffic of the Sardinia region, Italy, which amounts to 375 municipalities and 1 600 000 inhabitants. We use a weighted network representation in which vertices correspond to towns and the edges correspond to the actual commuting flows among those towns. We characterize quantitatively both the topological and weighted properties of the resulting network. Interestingly, the statistical properties of the commuting traffic exhibit complex features and nontrivial relations with the underlying topology. We characterize quantitatively the traffic backbone among large cities and we give evidence for a very high heterogeneity of the commuter flows around large cities. We also discuss the interplay between the topological and dynamical properties of the network as well as their relation with sociodemographic variables such as population and monthly income. This analysis may be useful at various stages in environmental planning and provides analytical tools for a wide spectrum of applications ranging from impact evaluation to decision making and planning support. Andrea De MontisMarc BarthélemyAlessandro Chessaalessandro.chessa@imtlucca.itAlessandro Vespignani2013-11-06T11:15:38Z2013-11-20T08:56:18Zhttp://eprints.imtlucca.it/id/eprint/1874This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/18742013-11-06T11:15:38ZCritical exponents in stochastic sandpile models We present large scale simulations of a stochastic sandpile model in two dimensions. We use momentum analysis to evaluate critical exponents and finite size scaling method to consistently test the obtained results. The general picture resulting from our analysis allows us to characterize the large scale behavior of the present model with great accuracy. Alessandro Chessaalessandro.chessa@imtlucca.itAlessandro VespignaniStefano Zapperi2013-11-06T11:04:52Z2013-11-20T08:54:23Zhttp://eprints.imtlucca.it/id/eprint/1872This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/18722013-11-06T11:04:52ZUniversality in sandpilesWe perform extensive numerical simulations of different versions of the sandpile model. We find that previous claims about universality classes are unfounded, since the method previously employed to analyze the data suffered from a systematic bias. We identify the correct scaling behavior and provide evidences suggesting that sandpiles with stochastic and deterministic toppling rules belong to the same universality class.Alessandro Chessaalessandro.chessa@imtlucca.itH. Eugene StanleyAlessandro VespignaniStefano Zapperi2013-11-06T11:00:00Z2013-11-20T08:53:06Zhttp://eprints.imtlucca.it/id/eprint/1871This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/18712013-11-06T11:00:00ZMean-field behavior of the sandpile model below the upper critical dimensionWe present results of large scale numerical simulations of the Bak, Tang, and Wiesenfeld [Phys. Rev. Lett. 59, 381 (1987); Phys. Rev. A 38, 364 (1988)] sandpile model. We analyze the critical behavior of the model in Euclidean dimensions 2<~d<~6. We consider a dissipative generalization of the model and study the avalanche size and duration distributions for different values of the lattice size and dissipation. We find that the scaling exponents in d=4 significantly differ from mean-field predictions, thus suggesting an upper critical dimension dc>~5. Using the relations among the dissipation rate ε and the finite lattice size L, we find that a subset of the exponents displays mean-field values below the upper critical dimensions. This behavior is explained in terms of conservation laws.Alessandro Chessaalessandro.chessa@imtlucca.itEnzo MarinariAlessandro VespignaniStefano Zapperi2013-11-06T10:56:50Z2014-12-05T09:45:08Zhttp://eprints.imtlucca.it/id/eprint/1870This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/18702013-11-06T10:56:50ZEnergy constrained sandpile modelsWe study two driven dynamical systems with conserved energy. The two automata contain the basic dynamical rules of the Bak, Tang, and Wiesenfeld sandpile model. In addition a global constraint on the energy contained in the lattice is imposed. In the limit of an infinitely slow driving of the system, the conserved energy E becomes the only parameter governing the dynamical behavior of the system. Both models show scale-free behavior at a critical value Ec of the fixed energy. The scaling with respect to the relevant scaling field points out that the developing of critical correlations is in a different universality class than self-organized critical sandpiles. Despite this difference, the activity (avalanche) probability distributions appear to coincide with the one of the standard self-organized critical sandpile.Alessandro Chessaalessandro.chessa@imtlucca.itEnzo MarinariAlessandro Vespignani2012-02-27T09:34:29Z2012-02-27T09:34:29Zhttp://eprints.imtlucca.it/id/eprint/1188This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11882012-02-27T09:34:29ZFractal and topological properties of directed fracturesWe use the Born model for the energy of elastic networks to simulate ‘‘directed’’ fracture growth. We define directed fractures as crack patterns showing a preferential evolution direction imposed by the type of stress and boundary conditions applied. This type of fracture allows a more realistic description of some kinds of experimental cracks and presents several advantages in order to distinguish between the various growth regimes. By choosing this growth geometry it is also possible to use without ambiguity the box-counting method to obtain the fractal dimension for different subsets of the patterns and for a wide range of the internal parameters of the model. We find a continuous dependence of the fractal dimension of the whole patterns and of their backbones on the ratio between the central- and noncentral-force contributions. For the chemical distance we find a one-dimensional behavior independent of the relevant parameters, which seems to be a common feature for fractal growth processes.Guido Caldarelliguido.caldarelli@imtlucca.itClaudio CastellanoAlessandro Vespignani2012-02-27T09:29:04Z2012-02-27T09:29:04Zhttp://eprints.imtlucca.it/id/eprint/1187This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11872012-02-27T09:29:04ZFixed scale transformation for fracture growth processes governed by vectorial fieldsWe use the Fixed Scale Transformation (FST) approach to study the problem of fractal growth in fracture patterns generated by using the Born Model. The application of the method to this model is very complex because of the vectorial nature of the system considered. In particular, the implementation of this scheme requires a careful choice of the fracture path and the identification of the appropriate way to take into account screening effects. The good agreements of our results with computer simulations shows the validity and flexibility of the FST method which represents a general theoretical approach for the study of fractal patterns evolution.Guido Caldarelliguido.caldarelli@imtlucca.itAlessandro VespignaniLuciano Pietronero2012-02-27T09:19:37Z2012-02-27T09:19:37Zhttp://eprints.imtlucca.it/id/eprint/1186This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11862012-02-27T09:19:37ZFixed scale transformation approach for born model of fracturesWe use the Fixed Scale Transformation theoretical approach to study the problem of fractal growth in fractures generated by using the Born Model. In this case the application of the method is more complex because of the vectorial nature of the model considered. In particular, one needs a careful choice of the lattice path integral for the fracture evolution and the identification of the appropriate way to take effectively into account screening effects. The good agreement of our results with computer simulations shows the validity and flexibility of the FST method in the study of fractal patterns evolution.Guido Caldarelliguido.caldarelli@imtlucca.itAlessandro Vespignani2012-02-15T16:02:44Z2012-02-15T16:02:44Zhttp://eprints.imtlucca.it/id/eprint/1127This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11272012-02-15T16:02:44ZStructure of cycles and local ordering in complex networksWe study the properties of quantities aimed at the characterization of grid-like ordering in complex networks. These quantities are based on the global and local behavior of cycles of order four, which are the minimal structures able to identify rectangular clustering. The analysis of data from real networks reveals the ubiquitous presence of a statistically high level of grid-like ordering that is non-trivially correlated with the local degree properties. These observations provide new insights on the hierarchical structure of complex networks.Guido Caldarelliguido.caldarelli@imtlucca.itRomualdo Pastor-SatorrasAlessandro Vespignani2012-02-15T15:54:46Z2012-02-15T15:54:46Zhttp://eprints.imtlucca.it/id/eprint/1126This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11262012-02-15T15:54:46ZPreface on "Applications of Networks"Guido Caldarelliguido.caldarelli@imtlucca.itAyşe ErzanAlessandro Vespignani2012-02-15T15:49:49Z2012-02-15T15:49:49Zhttp://eprints.imtlucca.it/id/eprint/1125This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11252012-02-15T15:49:49ZVirtual Round Table on ten leading questions for network researchThe following discussion is an edited summary of the public debate started during the conference "Growing Networks and Graphs in Statistical Physics, Finance, Biology and Social Systems" held in Rome in September 2003. Drafts documents were circulated electronically among experts in the field and additions and follow-up to the original discussion have been included. Among the scientists participating to the discussion L.A.N. Amaral, A. Barrat, A.L. Barabasi, G. Caldarelli, P. De Los Rios, A. Erzan, B. Kahng, R. Mantegna, J.F.F. Mendes, R. Pastor-Satorras, A. Vespignani are acknowledged for their contributions and editing. Luis A. N. AmaralAlain BarratGuido Caldarelliguido.caldarelli@imtlucca.itAlbert-László BarabásiPaolo De Los RiosAyşe ErzanByungnam KahngRosario Nunzio MantegnaJosè F. F. MendesRomualdo Pastor-SatorrasAlessandro Vespignani2012-01-20T10:45:29Z2012-01-25T13:10:14Zhttp://eprints.imtlucca.it/id/eprint/1076This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/10762012-01-20T10:45:29Z(edited by) Large scale structure and dynamics of complex networks: from information technology to finance and natural scienceThis book is the culmination of three years of research effort on a multidisciplinary project in which physicists, mathematicians, computer scientists and social scientists worked together to arrive at a unifying picture of complex networks. The contributed chapters form a reference for the various problems in data analysis visualization and modeling of complex networks.Guido Caldarelliguido.caldarelli@imtlucca.itAlessandro Vespignani