http://publicationslist.org/data/Guido.Caldarelli/atom.xml Guido Caldarellihttp://publicationslist.org/Guido.Caldarelli$basepathfavicon.icoRecent additions to Guido Caldarelli's PublicationsList.org pagehttp://publicationslist.org/publications.png2010-03-28T16:32:58Z http://publicationslist.org/Guido.Caldarelli/refid3 2009-12-21T18:13:01Z

We study the properties of the Barabási model of queuing [A.-L. Barabási, Nature (London) 435, 207 (2005); J. G. Oliveira and A.-L. Barabási, Nature (London) 437, 1251 (2005)] in the hypothesis that the number of tasks grows with time steadily. Our analytical approach is based on two ingredients. First we map exactly this model into an invasion percolation dynamics on a Cayley tree. Second we u...<br/><br/>A Gabrielli, G Caldarelli (2009) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 79: 4 Pt 1 <br/>

http://publicationslist.org/Guido.Caldarelli/refid38 2009-12-23T09:07:55Z

In this paper we study the properties of the Barabasi model of queuing under the hypothesis that the number of tasks is steadily growing in time. We map this model exactly onto an invasion percolation dynamics on a Cayley tree. This allows us to recover the correct waiting time distribution P-W(tau) similar to tau(-3/2) at the stationary state (as observed in different realistic data) and also to ...<br/><br/>A Gabrielli, G Caldarelli (2009) <i>JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT</i> <i></i> <i></i> : <br/>

http://publicationslist.org/Guido.Caldarelli/refid122 2009-12-25T21:06:35Z

We show that the PageRank in a network can be represented as the solution of a differential equation discretized over a directed graph. By exploiting a formal relationship with the time-independent Schrodinger equation it is possible to interpret hub formation and related phenomena as a wave-like localization process in the presence of disorder and trapping potentials. The result opens new perspec...<br/><br/>N Perra, V Zlatić, A Chessa, C Conti, D Donato, G Caldarelli (2009) <i>EPL (Europhysics Letters)</i> 88: 4 48002-5<br/>

http://publicationslist.org/Guido.Caldarelli/refid39 2009-12-25T21:07:06Z

For many complex networks present in nature only a single instance, usually of large size, is available. Any measurement made on this single instance cannot be repeated on different realizations. In order to detect significant patterns in a real-world network it is therefore crucial to compare the measured results with a null model counterpart. Here we focus on dense and weighted networks, proposi...<br/><br/>V Zlatić, G Bianconi, A Diaz-Guilera, D Garlaschelli, F Rao, G Caldarelli (2009) <i>EUROPEAN PHYSICAL JOURNAL B</i> 67: 3 271-275<br/>

http://publicationslist.org/Guido.Caldarelli/refid1 2009-12-21T18:13:01Z

Recent years have witnessed the emergence of a new class of social networks, which require us to move beyond previously employed representations of complex graph structures. A notable example is that of the folksonomy, an online process where users collaboratively employ tags to resources to impart structure to an otherwise undifferentiated database. In a recent paper, we proposed a mathematical m...<br/><br/>Vinko Zlatić, Gourab Ghoshal, Guido Caldarelli (2009) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 80: 3 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid2 2009-12-21T18:13:01Z

In the last few years we have witnessed the emergence, primarily in online communities, of new types of social networks that require for their representation more complex graph structures than have been employed in the past. One example is the folksonomy, a tripartite structure of users, resources, and tags-labels collaboratively applied by the users to the resources in order to impart meaningful ...<br/><br/>Gourab Ghoshal, Vinko Zlatić, Guido Caldarelli, M E J Newman (2009) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 79: 6 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid40 2009-12-23T09:07:55Z

Here we provide a detailed analysis, along with some extensions and additonal investigations, of a recently proposed [1] self-organized model for the evolution of complex networks. Vertices of the network are characterized by a fitness variable evolving through an extremal dynamics process, as in the Bak-Sneppen [2] model representing a prototype of Self-Organized Criticality. The network topology...<br/><br/>G Caldarelli, A Capocci, D Garlaschelli (2008) <i>EUROPEAN PHYSICAL JOURNAL B</i> <i></i> <i></i> 64: 3-4 585-591<br/>

http://publicationslist.org/Guido.Caldarelli/refid42 2009-12-23T09:07:55Z

In recent work we presented a new approach to the analysis of weighted networks, by providing a straightforward generalization of any network measure defined on unweighted networks. This approach is based on the translation of a weighted network into an ensemble of edges, and is particularly suited to the analysis of fully connected weighted networks. Here we apply our method to several such netwo...<br/><br/>S E Ahnert, D Garlaschelli, T M A Fink, G Caldarelli (2008) <i>JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL</i> <i></i> <i></i> 41: 22 <br/>

http://publicationslist.org/Guido.Caldarelli/refid44 2009-12-23T09:07:55Z

We analyze CiteULike, an online collaborative tagging system where users bookmark and annotate scientific papers. Such a system can be naturally represented as a tri-partite graph whose nodes represent papers, users and tags connected by individual tag assignments. The semantics of tags is studied here, in order to uncover the hidden relationships between tags. We find that the clustering coeffici...<br/><br/>A Capocci, G Caldarelli (2008) <i>JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL</i> <i></i> <i></i> 41: 22 <br/>

http://publicationslist.org/Guido.Caldarelli/refid46 2009-12-23T09:07:55Z

The objective of this paper is to analyse the network topology of the Italian segment of the European overnight money market through methods of statistical mechanics applied to complex networks. We investigate differences in the activities of banks of different sizes and the evolution of their connectivity structure over the maintenance period. The main purpose of the analysis is to establish the ...<br/><br/>G Iori, G De Masi, O V Precup, G Gabbi, G Caldarelli (2008) <i>JOURNAL OF ECONOMIC DYNAMICS & CONTROL</i> <i></i> <i></i> 32: 1 259-278<br/>

http://publicationslist.org/Guido.Caldarelli/refid45 2009-12-23T09:07:55Z

In this paper we investigate the nature and structure of the relation between imposed classifications and real clustering in a particular case of a scale-free network given by the on-line encyclopedia Wikipedia. We find a statistical similarity in the distributions of community sizes both by using the top-down approach of the categories division present in the archive and in the bottom-up procedur...<br/><br/>A Capocci, F Rao, G Caldarelli (2008) <i>EPL</i> <i></i> <i></i> 81: 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid43 2009-12-23T09:07:55Z

We analyze several florae (collections of plant species populating specific areas) in different geographic and climatic regions. For every list of species we produce a taxonomic classification tree and we consider its statistical properties. We find that regardless of the geographical location, the climate and the environment all species collections have universal statistical properties that we sh...<br/><br/>C C Cartozo, D Garlaschelli, C Ricotta, M Barthelemy, G Caldarelli (2008) <i>JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL</i> <i></i> <i></i> 41: 22 <br/>

http://publicationslist.org/Guido.Caldarelli/refid41 2009-12-23T09:07:55Z

A Barrat, S Boccaletti, G Caldarelli, A Chessa, V Latora, A E Motter (2008) <i>JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL</i> <i></i> <i></i> 41: 22 <br/>

http://publicationslist.org/Guido.Caldarelli/refid47 2009-12-23T09:07:55Z

We analyze here a particular kind of linguistic network where vertices represent words and edges stand for syntactic relationships between words. The statistical properties of these networks have been recently studied and various features such as the small-world phenomenon and a scale-free distribution of degrees have been found. Our work focuses on four classes of words: verbs, nouns, adverbs and...<br/><br/>R F I Cancho, A Capocci, G Caldarelli (2007) <i>INTERNATIONAL JOURNAL OF BIFURCATION AND CHAOS</i> <i></i> <i></i> 17: 7 2453-2463<br/>

http://publicationslist.org/Guido.Caldarelli/refid123 2009-12-23T10:41:19Z

G De Masi, G Iori, G Caldarelli (2007) <i>Noise and Stochastics in Complex Systems and Finance</i> 6601: 1 <br/>

http://publicationslist.org/Guido.Caldarelli/refid127 2009-12-23T12:32:03Z

A variety of different social, natural and technological systems can be described by the same mathematical framework. This holds from Internet to the Food Webs and to the connections between different company boards given by common directors. In all these situations a graph of the elements and their connections displays a universal feature of some few elements with many connections and many with f...<br/><br/>Guido Caldarelli (2007) :<br/>

http://publicationslist.org/Guido.Caldarelli/refid48 2009-12-23T09:07:55Z

The interplay between topology and dynamics in complex networks is a fundamental but widely unexplored problem. Here, we study this phenomenon on a prototype model in which the network is shaped by a dynamical variable. We couple the dynamics of the Bak-Sneppen evolution model with the rules of the so-called fitness network model for establishing the topology of a network; each vertex is assigned ...<br/><br/>D Garlaschelli, A Capocci, G Caldarelli (2007) <i>NATURE PHYSICS</i> <i></i> <i></i> 3: 11 813-817<br/>

http://publicationslist.org/Guido.Caldarelli/refid49 2009-12-23T09:07:55Z

We present an approach to the analysis of weighted networks, by providing a straightforward generalization of any network measure defined on unweighted networks, such as the average degree of the nearest neighbors, the clustering coefficient, the "betweenness," the distance between two nodes, and the diameter of a network. All these measures are well established for unweighted networks but have hi...<br/><br/>S E Ahnert, D Garlaschelli, T M A Fink, G Caldarelli (2007) <i>PHYSICAL REVIEW E</i> <i></i> <i></i> 76: 1 <br/>

http://publicationslist.org/Guido.Caldarelli/refid53 2009-12-23T09:07:55Z

Using a data set which includes all transactions among banks in the Italian money market, we study their trading strategies and the dependence among them. We use the Fourier method to compute the variance-covariance matrix of trading strategies. Our results indicate that well defined patterns arise. Two main communities of banks, which can be coarsely identified as small and large banks, emerge. (...<br/><br/>G Iori, R Reno, G De Masi, G Caldarelli (2007) <i>PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS</i> <i></i> <i></i> 376: 467-479<br/>

http://publicationslist.org/Guido.Caldarelli/refid51 2009-12-23T09:07:55Z

We present an empirical analysis of the network formed by the trade relationships between all world countries, or World Trade Web (WTW). Each (directed) link is weighted by the amount of wealth flowing between two countries, and each country is characterized by the value of its Gross Domestic Product (GDP). By analysing a set of year-by-year data covering the time interval 1950-2000, we show that ...<br/><br/>D Garlaschelli, T Di Matteo, T Aste, G Caldarelli, M I Loffredo (2007) <i>EUROPEAN PHYSICAL JOURNAL B</i> <i></i> <i></i> 57: 2 159-164<br/>

http://publicationslist.org/Guido.Caldarelli/refid5 2009-12-21T18:13:01Z

We introduce an exact probabilistic description for L=2 of the Barabási model for the dynamics of a list of L tasks. This permits us to study the problem out of the stationary state and to solve explicitly the extremal limit case where a critical behavior for the waiting time distribution is observed. This behavior deviates at any finite time from that of the stationary state. We study also the c...<br/><br/>A Gabrielli, G Caldarelli (2007) <i>Phys Rev Lett</i> <i></i> <i></i> 98: 20 <br/>

http://publicationslist.org/Guido.Caldarelli/refid4 2009-12-21T18:13:01Z

The configuration space network (CSN) of a dynamical system is an effective approach to represent the ensemble of configurations sampled during a simulation and their dynamic connectivity. To elucidate the connection between the CSN topology and the underlying free-energy landscape governing the system dynamics and thermodynamics, an analytical solution is provided to explain the heavy tail of the...<br/><br/>David Gfeller, David Morton de Lachapelle, Paolo De Los Rios, Guido Caldarelli, Francesco Rao (2007) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 76: 2 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid131 2009-12-23T15:05:53Z

G. Caldarelli, A. Vespignani (Eds) (2007) :<br/>

http://publicationslist.org/Guido.Caldarelli/refid54 2009-12-23T09:07:55Z

We use the theory of complex networks in order to quantitatively characterize the formation of communities in a particular financial market. The system is composed by different banks exchanging on a daily basis loans and debts of liquidity. Through topological analysis and by means of a model of network growth we can determine the formation of different group of banks characterized by different bu...<br/><br/>G De Masi, G Iori, G Caldarelli (2006) <i>PHYSICAL REVIEW E</i> <i></i> <i></i> 74: 6 <br/>

http://publicationslist.org/Guido.Caldarelli/refid124 2009-12-23T10:50:09Z

Diego Garlaschelli, Sebastian E Ahnert, Thomas M A Fink, Guido Caldarelli (2006) <i>http://www.citebase.org/abstract?id=oai:arXiv.org:cond-mat/0606805</i><br/>

http://publicationslist.org/Guido.Caldarelli/refid8 2009-12-21T18:13:01Z

We present an analysis of the statistical properties and growth of the free on-line encyclopedia Wikipedia. By describing topics by vertices and hyperlinks between them as edges, we can represent this encyclopedia as a directed graph. The topological properties of this graph are in close analogy with those of the World Wide Web, despite the very different growth mechanism. In particular, we measur...<br/><br/>A Capocci, V D P Servedio, F Colaiori, L S Buriol, D Donato, S Leonardi, G Caldarelli (2006) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 74: 3 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid126 2009-12-23T11:21:38Z

S. Battiston, D. Garlaschelli, G. Caldarelli (2005) <i>Lecture Notes in Economics and Mathematical Systems</i> 550: 189-202<br/>

http://publicationslist.org/Guido.Caldarelli/refid58 2009-12-23T09:07:55Z

We develop an algorithm to detect community structure in complex networks. The algorithm is based on spectral methods and takes into account weights and link orientation. Since the method detects efficiently clustered nodes in large networks even when these are not sharply partitioned, it turns to be specially suitable for the analysis of social and information networks. We test the algorithm on a...<br/><br/>A Capocci, V D P Servedio, G Caldarelli, F Colaiori (2005) <i>PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS</i> <i></i> <i></i> 352: 2-4 669-676<br/>

http://publicationslist.org/Guido.Caldarelli/refid57 2009-12-23T09:07:55Z

D Garlaschelli, G Caldarelli, L Pietronero (2005) <i>NATURE</i> <i></i> <i></i> 435: 7044 E4-E4<br/>

http://publicationslist.org/Guido.Caldarelli/refid9 2009-12-21T18:13:01Z

We present here a study of the clustering and loops in a graph of the Internet at the autonomous systems level. We show that, even if the whole structure is changing with time, the statistical distributions of loops of order 3, 4, and 5 remain stable during the evolution. Moreover, we will bring evidence that the Internet graphs show characteristic Markovian signatures, since the structure is very...<br/><br/>Ginestra Bianconi, Guido Caldarelli, Andrea Capocci (2005) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 71: 6 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid59 2009-12-23T09:07:55Z

We propose a network description of large market investments, where both stocks and shareholders are represented as vertices connected by weighted links corresponding to shareholdings. In this framework, the in-degree (k(in)) and the sum of incoming link weights (nu) of an investor correspond to the number of assets held (portfolio diversification) and to the invested wealth (portfolio volume), re...<br/><br/>D Garlaschelli, S Battiston, M Castri, V D P Servedio, G Caldarelli (2005) <i>PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS</i> <i></i> <i></i> 350: 2-4 491-499<br/>

http://publicationslist.org/Guido.Caldarelli/refid70 2009-12-23T09:07:55Z

We review the recent approach of correlation based networks of financial equities. We investigate portfolio of stocks at different time horizons, financial indices and volatility time series and we show that meaningful economic information can be extracted from noise dressed correlation matrices. We show that the method can be used to falsify widespread market models by directly comparing the topo...<br/><br/>G Bonanno, G Caldarelli, F Lillo, S Micciche, N Vandewalle, R N Mantegna (2004) <i>EUROPEAN PHYSICAL JOURNAL B</i> <i></i> <i></i> 38: 2 363-371<br/>

http://publicationslist.org/Guido.Caldarelli/refid68 2009-12-25T21:14:14Z

The 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 participat...<br/><br/>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 (2004) <i>EUROPEAN PHYSICAL JOURNAL B</i> 38: 2 143-145<br/>

http://publicationslist.org/Guido.Caldarelli/refid67 2009-12-23T09:07:55Z

G Caldarelli, A Erzan, A Vespignani (2004) <i>EUROPEAN PHYSICAL JOURNAL B</i> <i></i> <i></i> 38: 2 141-141<br/>

http://publicationslist.org/Guido.Caldarelli/refid66 2009-12-23T09:07:55Z

Networks representing social systems display specific features that put them apart from biological and technological ones. In particular, the number of links attached to a node is positively correlated to that of its nearest neighbours. We develop a model that reproduces this feature, starting from microscopical mechanisms of growth. The statistical properties arising from the simulations are in g...<br/><br/>M Catanzaro, G Caldarelli, L Pietronero (2004) <i>PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS</i> <i></i> <i></i> 338: 1-2 119-124<br/>

http://publicationslist.org/Guido.Caldarelli/refid65 2009-12-23T09:07:55Z

In this work we apply network theory to detect in a quantitative fashion some of the characters of the system composed by companies and their boards of directors. Modelling this as a bipartite graph, we can derive two networks (one for the companies and one for the directors) and apply to them the standard graph analysis instruments. The emerging picture shows an environment where the exchange of ...<br/><br/>G Caldarelli, M Catanzaro (2004) <i>PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS</i> <i></i> <i></i> 338: 1-2 98-106<br/>

http://publicationslist.org/Guido.Caldarelli/refid69 2009-12-23T09:07:55Z

We 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 i...<br/><br/>G Caldarelli, R Pastor-Satorras, A Vespignani (2004) <i>EUROPEAN PHYSICAL JOURNAL B</i> <i></i> <i></i> 38: 2 183-186<br/>

http://publicationslist.org/Guido.Caldarelli/refid125 2009-12-23T11:15:41Z

We develop an algorithm to detect community structure in complex networks. The algorithm is based on spectral methods and takes into account weights and links orientations. Since the method detects efficiently clustered nodes in large networks even when these are not sharply partitioned, it turns to be specially suitable to the analysis of social and information networks. We test the algorithm on ...<br/><br/>Andrea Capocci, Vito D P Servedio, Guido Caldarelli, Francesca Colaiori (2004) <i>Lecture Notes in Computer Science</i> 3243: 181-187<br/>

http://publicationslist.org/Guido.Caldarelli/refid128 2009-12-23T12:22:15Z

We present here a brief summary of the various possible applications of network theory in the field of finance. Since we want to characterize different systems by means of simple and universal features, graph theory could represent a rather powerful methodology. In the following we report our activity in three different subfields, namely the board and director networks, the networks formed by pric...<br/><br/>Guido Caldarelli, Stefano Battiston, Diego Garlaschelli, Michele Catanzaro (2004) <i>Lecture Notes in Physics</i> 650: 399-423<br/>

http://publicationslist.org/Guido.Caldarelli/refid13 2009-12-25T21:11:41Z

The widespread occurrence of an inverse square relation in the hierarchical distribution of subcommunities within communities (or subspecies within species) has been recently invoked as a signature of hierarchical self-organization within social and ecological systems. Here we show that, whether such systems are self-organized or not, this behavior is the consequence of the treelike classification...<br/><br/>Guido Caldarelli, Cécile Caretta Cartozo, Paolo De Los Rios, Vito D P Servedio (2004) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> 69: 3 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid11 2009-12-21T18:14:26Z

In this Brief Report we present a version of a network growth model, generalized in order to describe the behavior of social networks. The case of study considered is the preprint archive at cul.arxiv.org. Each node corresponds to a scientist, and a link is present whenever two authors wrote a paper together. This graph is a nice example of degree-assortative network, that is, to say a network whe...<br/><br/>Michele Catanzaro, Guido Caldarelli, Luciano Pietronero (2004) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 70: 3 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid10 2009-12-21T18:14:26Z

We study a recent model of random networks based on the presence of an intrinsic character of the vertices called fitness. The vertex fitnesses are drawn from a given probability distribution density. The edges between pairs of vertices are drawn according to a linking probability function depending on the fitnesses of the two vertices involved. We study here different choices for the probability ...<br/><br/>Vito D P Servedio, Guido Caldarelli, Paolo Buttà (2004) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 70: 5 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid71 2009-12-25T21:14:29Z

Erosion by flowing water is one of the major forces shaping the surface of Earth. Studies in the last decade have shown, in particular, that the drainage region of rivers, where water is collected, exhibits scale invariant features characterized by exponents that are the same for rivers around the world. Here we show that from the data obtained by the MOLA altimeter of the Mars Global Surveyor one...<br/><br/>G Caldarelli, P De Los Rios, M Montuori, V D P Servedio (2004) <i>EUROPEAN PHYSICAL JOURNAL B</i> 38: 2 387-391<br/>

http://publicationslist.org/Guido.Caldarelli/refid12 2009-12-21T18:14:26Z

Many social, technological, and biological interactions involve network relationships whose outcome intimately depends on the structure of the network and on the strengths of the connections. Yet, although much information is now available concerning the structure of many networks, the strengths are more difficult to measure. Here we show that, for one particular social network, notably the e-mail...<br/><br/>G Caldarelli, F Coccetti, P De Los Rios (2004) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 70: 2 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid14 2009-12-25T21:12:28Z

We present data analysis and modeling of two particular cases of study in the field of growing networks. We analyze World Wide Web data set and authorship collaboration networks in order to check the presence of correlation in the data. The results are reproduced with good agreement through a suitable modification of the standard Albert-Barabási model of network growth. In particular, intrinsic r...<br/><br/>Andrea Capocci, Guido Caldarelli, Paolo De Los Rios (2003) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> 68: 4 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid16 2009-12-21T18:14:26Z

The structure of ecological communities is usually represented by food webs. In these webs, we describe species by means of vertices connected by links representing the predations. We can therefore study different webs by considering the shape (topology) of these networks. Comparing food webs by searching for regularities is of fundamental importance, because universal patterns would reveal common...<br/><br/>Diego Garlaschelli, Guido Caldarelli, Luciano Pietronero (2003) <i>Nature</i> <i></i> <i></i> 423: 6936 165-168<br/>

http://publicationslist.org/Guido.Caldarelli/refid15 2009-12-21T18:14:26Z

We compare the topological properties of the minimal spanning tree obtained from a large group of stocks traded at the New York Stock Exchange during a 12-year trading period with the one obtained from surrogated data simulated by using simple market models. We find that the empirical tree has features of a complex network that cannot be reproduced, even as a first approximation, by a random marke...<br/><br/>Giovanni Bonanno, Guido Caldarelli, Fabrizio Lillo, Rosario N Mantegna (2003) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 68: 4 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid73 2009-12-23T09:07:55Z

We study the acoustic emission produced by micro-cracks using a two-dimensional disordered lattice model of dynamic fracture, which allows to relate the acoustic response to the internal damage of the sample. We find that the distributions of acoustic energy bursts decays as a power law in agreement with experimental observations. The scaling exponents measured in the present dynamic model can rel...<br/><br/>M Minozzi, G Caldarelli, L Pietronero, S Zapperi (2003) <i>EUROPEAN PHYSICAL JOURNAL B</i> <i></i> <i></i> 36: 2 203-207<br/>

http://publicationslist.org/Guido.Caldarelli/refid129 2009-12-23T12:23:34Z

In addition to traditional properties such as the degree distribution P( k), in this work we propose two other useful quantities that can help in characterizing the topology of food webs quantitatively, namely the allometric scaling relations C( A) and the branch size distribution P(A) A which are defined on the spanning tree of the webs. These quantities, whose use has proved relevant in characte...<br/><br/>Guido Caldarelli, Diego Garlaschelli, Luciano Pietronero (2003) <i>Lecture Notes in Physics</i> 625: 148-166<br/>

http://publicationslist.org/Guido.Caldarelli/refid19 2009-12-21T18:14:26Z

We study here the Bak-Sneppen model, a prototype model for the study of self-organized criticality. In this model several species interact and undergo extinction with a power-law distribution of activity bursts. Species are defined through their "fitness" whose distribution in the system is uniform above a certain threshold. Run time statistics is introduced for the analysis of the dynamics in ord...<br/><br/>G Caldarelli, M Felici, A Gabrielli, L Pietronero (2002) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 65: 4 Pt 2A <br/>

http://publicationslist.org/Guido.Caldarelli/refid130 2009-12-25T21:10:11Z

L Laura, S Leonardi, G Caldarelli, P De Los Rios (2002) <i>In On-line proceedings of the 2nd International Workshop on Web Dynamics</i> <br/>

http://publicationslist.org/Guido.Caldarelli/refid80 2009-12-23T09:07:55Z

G Caldarelli, R Frondoni, A Gabrielli, M Montuori, R Retzlaff, C Ricotta (2002) <i>EUROPHYSICS LETTERS</i> <i></i> <i></i> 59: 1 157-158<br/>

http://publicationslist.org/Guido.Caldarelli/refid17 2009-12-21T18:14:26Z

A new mechanism leading to scale-free networks is proposed in this Letter. It is shown that, in many cases of interest, the connectivity power-law behavior is neither related to dynamical properties nor to preferential attachment. Assigning a quenched fitness value x(i) to every vertex, and drawing links among vertices with a probability depending on the fitnesses of the two involved sites, gives ...<br/><br/>G Caldarelli, A Capocci, P De Los Rios, M A Muñoz (2002) <i>Phys Rev Lett</i> <i></i> <i></i> 89: 25 <br/>

http://publicationslist.org/Guido.Caldarelli/refid18 2009-12-21T18:14:26Z

We address the problem of the role of the concept of local rigidity in the family of sandpile systems. We define rigidity as the ratio between the critical energy and the amplitude of the external perturbation and we show, in the framework of the dynamically driven renormalization group, that any finite value of the rigidity in a generalized sandpile model renormalizes to an infinite value at the ...<br/><br/>S Ciliberti, G Caldarelli, V Loreto, L Pietronero (2002) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 66: 1 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid20 2009-12-21T18:14:26Z

In this paper we present a model for the growth and evolution of Internet providers. The model reproduces the data observed for the Internet connection as probed by tracing routes from different computers. This problem represents a paramount case of study for growth processes in general, but can also help in the understanding the properties of the Internet. Our main result is that this network can...<br/><br/>A Capocci, G Caldarelli, R Marchetti, L Pietronero (2001) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 64: 3 Pt 2 <br/>

http://publicationslist.org/Guido.Caldarelli/refid23 2009-12-21T18:14:26Z

We study the Bak-Sneppen model in the probabilistic framework of the run time statistics (RTS). This model has attracted a large interest for its simplicity being a prototype for the whole class of models showing self-organized criticality. The dynamics is characterized by a self-organization of almost all the species fitnesses above a nontrivial threshold value, and by a lack of spatial and tempo...<br/><br/>M Felici, G Caldarelli, A Gabrielli, L Pietronero (2001) <i>Phys Rev Lett</i> <i></i> <i></i> 86: 9 1896-1899<br/>

http://publicationslist.org/Guido.Caldarelli/refid22 2009-12-21T18:14:26Z

A cellular model introduced for the evolution of the fluvial landscape is revisited using extensive numerical and scaling analyses. The basic network shapes and their recurrence especially in the aggregation structure are then addressed. The roles of boundary and initial conditions are carefully analyzed as well as the key effect of quenched disorder embedded in random pinning of the landscape sur...<br/><br/>G Caldarelli (2001) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 63: 2 Pt 1 <br/>

http://publicationslist.org/Guido.Caldarelli/refid83 2009-12-23T09:07:55Z

This paper focuses on the statistical properties of wild-land fires and, in particular, investigates if spread dynamics relates to simple invasion model. The fractal dimension and lacunarity of three fire scars classified from satellite imagery are analysed. Results indicate that the burned clusters behave similarly to percolation clusters on boundaries and look denser in their core. We show that ...<br/><br/>G Caldarelli, R Frondoni, A Gabrielli, M Montuori, R Retzlaff, C Ricotta (2001) <i>EUROPHYSICS LETTERS</i> <i></i> <i></i> 56: 4 510-516<br/>

http://publicationslist.org/Guido.Caldarelli/refid82 2009-12-23T09:07:55Z

We introduce a simplified protein model where the water degrees of freedom appear explicitly (although in an extremely simplified fashion). Using this model we are able to recover both the warm and the cold protein denaturation within a single framework, while addressing important issues about the structure of model proteins.<br/><br/>G Caldarelli, P De Los Rios (2001) <i>JOURNAL OF BIOLOGICAL PHYSICS</i> <i></i> <i></i> 27: 2-3 229-241<br/>

http://publicationslist.org/Guido.Caldarelli/refid84 2009-12-23T09:07:55Z

The stable marriage problem has been introduced in order to describe a complex system where individuals attempt to optimise their own satisfaction, subject to mutually conflicting constraints. Due to the potential large applicability of such model to describe all the situation where different objects has to be matched pairwise, the statistical properties of this model have been extensively studied...<br/><br/>G Caldarelli, A Capocci (2001) <i>PHYSICA A</i> <i></i> <i></i> 300: 1-2 325-331<br/>

http://publicationslist.org/Guido.Caldarelli/refid85 2009-12-23T09:07:55Z

In the stable marriage problem two sets of agents must be paired according to mutual preferences, which may happen to conflict. We present two generalizations of its sex-oriented version, aiming to take into account correlations between the preferences of agents and costly information. Their effects are investigated both numerically and analytically. (C) 2001 Elsevier Science B.V. All rights reser...<br/><br/>G Caldarelli, A Capocci, P Laureti (2001) <i>PHYSICA A</i> <i></i> <i></i> 299: 1-2 268-272<br/>

http://publicationslist.org/Guido.Caldarelli/refid87 2009-12-23T09:07:55Z

We study, both with numerical simulations and theoretical methods, a cellular automata model for surface growth in the presence of a local instability, driven by an external flux of particles. The growing tip is selected with probability proportional to the local curvature. A probability p of developing overhangs through lateral growth is also introduced. For small external fluxes, we nd a fractal...<br/><br/>R Cafiero, G Caldarelli (2001) <i>EUROPHYSICS LETTERS</i> <i></i> <i></i> 54: 2 187-193<br/>

http://publicationslist.org/Guido.Caldarelli/refid21 2009-12-21T18:14:26Z

We introduce a polymer model where the transition from swollen to compact configurations is due to interactions between the monomers and the solvent. These interactions are the origin of the effective attractive interactions between hydrophobic amino acids in proteins. We find that in the low and high temperature phases polymers are swollen, and there is an intermediate phase where the most favora...<br/><br/>P De Los Rios, G Caldarelli (2001) <i>Phys Rev E Stat Nonlin Soft Matter Phys</i> <i></i> <i></i> 63: 3 Pt 1 <br/>

http://publicationslist.org/Guido.Caldarelli/refid98 2009-12-23T09:07:55Z

We present the result of numerical simulations for a fracturing process in a three-dimensional solid subjected to a mode-I load in a quasi-static regime. The solid is described using the Born model on an FCC lattice with a starting notch. We obtain a value of the roughness exponent zeta similar or equal to 0.5 in agreement with the value measured in microfracturing experiments. Our result supports...<br/><br/>A Parisi, G Caldarelli (2000) <i>PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS</i> <i></i> <i></i> 280: 1-2 161-165<br/>

http://publicationslist.org/Guido.Caldarelli/refid94 2009-12-23T09:07:55Z

We present a detailed study of a two-dimensional lattice model introduced to describe mud cracking in the limit of extremely thin layers. In this model to each bond in the lattice is assigned a (quenched) random breaking threshold. Fractures proceed by selecting the 'weakest' part of the material (i.e. the smallest value of the threshold). A local damage rule is also implemented, by using two diff...<br/><br/>R Cafiero, G Caldarelli, A Gabrielli (2000) <i>JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL</i> <i></i> <i></i> 33: 45 8013-8028<br/>

http://publicationslist.org/Guido.Caldarelli/refid93 2009-12-23T09:07:55Z

We formulate the angular structure of lacunarity in fractals, in terms of a symmetry reduction of the three point correlation function. This provides a rich probe of universality, and first measurements yield new evidence in support of the equivalence between self-avoiding walks (SAW's) and percolation perimeters in two dimensions. We argue that the lacunarity reveals much of the renormalization g...<br/><br/>R C Ball, G Caldarelli, A Flammini (2000) <i>PHYSICAL REVIEW LETTERS</i> <i></i> <i></i> 85: 24 5134-5137<br/>

http://publicationslist.org/Guido.Caldarelli/refid92 2009-12-23T09:07:55Z

We introduce a simplified protein model where the solvent (water) degrees of freedom appear explicitly (although in an extremely simplified fashion). Using this model we are able to recover the thermodynamic phenomenology of proteins over a wide range of temperatures. In particular we describe both the warm and the cold protein denaturation within a single framework, while addressing important iss...<br/><br/>P De Los Rios, G Caldarelli (2000) <i>PHYSICAL REVIEW E</i> <i></i> <i></i> 62: 6 8449-8452<br/>

http://publicationslist.org/Guido.Caldarelli/refid91 2009-12-23T09:07:55Z

In this paper we present a theoretical approach that allows us to describe the transition between critical and noncritical behavior when stocastic noise is introduced in extremal models with disorder. Namely, we show that the introduction of thermal noise in invasion percolation (IP) brings the system outside;the critical point. This result suggests a possible definition of self-organized critical...<br/><br/>A Gabrielli, G Caldarelli, L Pietronero (2000) <i>PHYSICAL REVIEW E</i> <i></i> <i></i> 62: 6 7638-7641<br/>

http://publicationslist.org/Guido.Caldarelli/refid95 2009-12-25T21:11:11Z

We study the properties of the "rigid Laplacian" operator; that is we consider solutions of the Laplacian equation in the presence of fixed truncation errors. The dynamics of convergence to the correct analytical solution displays the presence of a metastable set of numerical solutions, whose presence can be related to granularity. We provide some scaling analysis in order to determine the value o...<br/><br/>S Ciliberti, G Caldarelli, P De Los Rios, L Pietronero, Y C Zhang (2000) <i>PHYSICAL REVIEW LETTERS</i> 85: 23 4848-4851<br/>

http://publicationslist.org/Guido.Caldarelli/refid96 2009-12-23T09:07:55Z

In this paper we show that the Internet web, from a user's perspective, manifests robust scaling properties of the type P(n) proportional to n(-tau), where n is the size of the basin connected to a given point, P represents the density of probability of finding n points downhill and tau = 1.9 +/- 0.1 s a characteristic universal exponent. This scale-free structure is a result of the spontaneous gr...<br/><br/>G Caldarelli, R Marchetti, L Pietronero (2000) <i>EUROPHYSICS LETTERS</i> <i></i> <i></i> 52: 4 386-391<br/>

http://publicationslist.org/Guido.Caldarelli/refid97 2009-12-23T09:07:55Z

We study the roughness of fracture surfaces of three-dimensional samples through numerical simulations of a model for quasi-static cracks known as Born Model. We find for the roughness exponent a value zeta similar or equal to 0.5 measured for "small length scales" in microfracturing experiments. Our simulations confirm that at small length scales the fracture can be considered as quasi-static. Th...<br/><br/>A Parisi, G Caldarelli, L Pietronero (2000) <i>EUROPHYSICS LETTERS</i> <i></i> <i></i> 52: 3 304-310<br/>

http://publicationslist.org/Guido.Caldarelli/refid102 2009-12-23T09:07:55Z

We introduce a model for the dynamics of mud cracking in the limit of of extremely thin layers. In this model the growth of fracture proceeds by selecting the part of the material with the smallest (quenched) breaking threshold. In addition, weakening affects the area of the sample neighbour to the crack. Due to the simplicity of the model, it is possible to derive some analytical results. In part...<br/><br/>A Gabrielli, R Cafiero, G Caldarelli (1999) <i>EUROPHYSICS LETTERS</i> <i></i> <i></i> 45: 1 13-19<br/>

http://publicationslist.org/Guido.Caldarelli/refid100 2009-12-23T09:07:55Z

It has been recently noticed that heterogeneous media undergoing a fracturing process display a set of properties characteristic of systems at the critical state. in the present work we focus on the way in which the critical regime is reached. It is possible to define a branching ratio, for the breaking processses in the material, that represents the probability to trigger future breakdowns given ...<br/><br/>G Caldarelli, C Castellano, A Petri (1999) <i>PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS</i> <i></i> <i></i> 270: 1-2 15-20<br/>

http://publicationslist.org/Guido.Caldarelli/refid99 2009-12-23T09:07:55Z

In this paper we investigate the influence of different boundary conditions on the final breakdown of a lattice model for the fracture of heterogeneous media. Experimental evidence shows that disordered media subject to stress display some features that are characteristic of critical systems, therefore suggesting an interpretation of the global breakdown of the system as a kind of critical transit...<br/><br/>G Caldarelli, C Castellano, A Petri (1999) <i>PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES</i> <i></i> <i></i> 79: 11-12 1939-1944<br/>

http://publicationslist.org/Guido.Caldarelli/refid101 2009-12-23T09:07:55Z

G Caldarelli, A Petri (1999) <i>PHYSICAL REVIEW LETTERS</i> <i></i> <i></i> 83: 7 1483-1483<br/>

http://publicationslist.org/Guido.Caldarelli/refid108 2009-12-23T09:07:55Z

We introduce a model for fractures in quenched disordered media. This model has a deterministic extremal dynamics, driven by the energy function of a network of springs (Born Hamiltonian). The breakdown is the result of the cooperation between the external field and the quenched disorder. This model can be considered as describing the low-temperature Limit for crack propagation in solids. To descr...<br/><br/>G Caldarelli, R Cafiero, A Gabrielli (1998) <i>PHYSICAL REVIEW E</i> <i></i> <i></i> 57: 4 3878-3885<br/>

http://publicationslist.org/Guido.Caldarelli/refid103 2009-12-23T09:07:55Z

We study the boundary effects in invasion percolation (IP) with and without trapping. We And that the presence of boundaries introduces a new set of surface critical exponents, as in the case of standard percolation. Numerical simulations show a fractal dimension, for the region of the percolating cluster near the boundary, remarkably different from the bulk one. In fact, on the surface we find a ...<br/><br/>A Gabrielli, R Cafiero, G Caldarelli (1998) <i>JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL</i> <i></i> <i></i> 31: 37 7429-7446<br/>

http://publicationslist.org/Guido.Caldarelli/refid104 2009-12-23T09:07:55Z

We introduce the Webworld model, which links together the ecological modelling of food web structure with the evolutionary modelling of speciation and extinction events. The model describes dynamics of ecological communities on an evolutionary time-scale. Species are defined as sets of characteristic features, and these features are used to determine interaction scores between species. A simple ru...<br/><br/>G Caldarelli, P G Higgs, A J McKane (1998) <i>JOURNAL OF THEORETICAL BIOLOGY</i> <i></i> <i></i> 193: 2 345-358<br/>

http://publicationslist.org/Guido.Caldarelli/refid106 2009-12-23T09:07:55Z

We study the stationary state of a Poisson problem for a system of N perfectly conducting metal balls driven by electric forces to move within a medium of very low electrical conductivity onto which charges are sprayed from outside. When grounded at a confining boundary, the system of metal balls is experimentally known to self-organize into stable fractal aggregates. We simulate the dynamical con...<br/><br/>M Marani, J R Banavar, G Caldarelli, A Maritan, A Rinaldo (1998) <i>JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL</i> <i></i> <i></i> 31: 18 L337-L343<br/>

http://publicationslist.org/Guido.Caldarelli/refid107 2009-12-23T09:07:55Z

A mean field theory is discussed for a sandpile model, a cellular automaton prototype of systems showing self-organized criticality. The previous formulation of the mean field does not take into account the dissipation effects that take place on boundaries. This gives rise to some inconsistencies that are eliminated by carefully considering the boundaries effects, as it is shown in this paper. We ...<br/><br/>G Caldarelli (1998) <i>PHYSICA A</i> <i></i> <i></i> 252: 3-4 295-307<br/>

http://publicationslist.org/Guido.Caldarelli/refid109 2009-12-23T09:07:55Z

A prototype model of stock market is introduced and studied numerically. In this self-organized system, we consider only the interaction among traders without external influences. Agents trade according to their own strategy, to accumulate their assets by speculating on the price's fluctuations which are produced by themselves. The model reproduced rather realistic price histories whose statistica...<br/><br/>G Caldarelli, M Marsili, Y C Zhang (1997) <i>EUROPHYSICS LETTERS</i> <i></i> <i></i> 40: 5 479-484<br/>

http://publicationslist.org/Guido.Caldarelli/refid111 2009-12-23T09:07:55Z

Boundary effects for invasion percolation are introduced and discussed here. The presence of boundaries determines a set of critical exponents characteristic of the boundary. In this paper we present numerical simulations showing a remarkably different fractal dimension for the region of the percolating cluster near the boundary. In fact, near the surface we find a value of D-sar= 1.67 +/- 0.03, w...<br/><br/>R Cafiero, G Caldarelli, A Gabrielli (1997) <i>PHYSICAL REVIEW E</i> <i></i> <i></i> 56: 2 R1291-R1294<br/>

http://publicationslist.org/Guido.Caldarelli/refid110 2009-12-23T09:07:55Z

We study the scaling behavior in currency exchange rates. Our results suggest that they satisfy scaling with an exponent close to 0.5, but that it differs qualitatively from that of a simple random walk. Indeed price variations cannot be considered as independent variables and subtle correlations are present. Furthermore, we introduce a novel statistical analysis for economic data which makes the ...<br/><br/>S Galluccio, G Caldarelli, M Marsili, Y C Zhang (1997) <i>PHYSICA A</i> <i></i> <i></i> 245: 3-4 423-436<br/>

http://publicationslist.org/Guido.Caldarelli/refid112 2009-12-23T09:07:55Z

A simple scheme for the evolution of a fluvial landscape in heterogeneous environments is critically examined to capture the essential mechanism responsible for the recurrent scale-free landforms in the river basin. It is shown that, regardless of boundary and initial conditions, geomorphological constraints in the form of quenched randomly pinned regions play a key role in the robust emergence of...<br/><br/>G Caldarelli, A Giacometti, A Maritan, I RodriguezIturbe, A Rinaldo (1997) <i>PHYSICAL REVIEW E</i> <i></i> <i></i> 55: 5 R4865-R4868<br/>

http://publicationslist.org/Guido.Caldarelli/refid118 2009-12-23T09:07:55Z

We use a stochastic description of models with a dynamic in quenched disorder to analyze the mechanism of their self-organization to a critical state in terms of memory effects. We introduce a framework to characterize both memory effects and avalanche events which suggests that self-organization can result in general from memory. This issue is settled by the introduction and the analysis of a mod...<br/><br/>M Marsili, G Caldarelli, M Vendruscolo (1996) <i>PHYSICAL REVIEW E</i> <i></i> <i></i> 53: 1 R13-R16<br/>

http://publicationslist.org/Guido.Caldarelli/refid117 2009-12-25T21:10:35Z

An efficient transfer matrix technique is introduced to study directed optimal paths in two and three dimensions. The roughness exponent zeta is 0.6325 +/- 0.0007 for the two-dimensional case and zeta = 0.555 +/- 0.008 for the three-dimensional one, in agreement with the recent conjecture zeta = v(perpendicular to)/v(parallel to), where v(perpendicular to) and v(parallel to) are the correlation le...<br/><br/>P De Los Rios, G Caldarelli, A Maritan, F Seno (1996) <i>PHYSICAL REVIEW E</i> 53: 3 R2029-R2032<br/>

http://publicationslist.org/Guido.Caldarelli/refid113 2009-12-25T21:10:54Z

We show that a vectorial model for inhomogeneous elastic media self-organizes under external stress. An onset of crack avalanches of every duration and length scale compatible with the lattice size is observed. The behavior is driven by the introduction of annealed disorder, i.e., by lowering the breaking threshold in the neighborhood of a bond broken by the stress, with a process similar to self-...<br/><br/>G Caldarelli, F D Di Tolla, A Petri (1996) <i>PHYSICAL REVIEW LETTERS</i> 77: 12 2503-2506<br/>

http://publicationslist.org/Guido.Caldarelli/refid114 2009-12-23T09:07:55Z

A temperature-like parameter is introduced in ordinary sandpiles models. A temperature-dependent probability distribution is assigned for the sand toppling on sites of any height. In mean-field theory criticality is obtained for all the values of temperature and no characteristic avalanche size appears. Numerical simulations support the existence of criticality at any temperature with apparently c...<br/><br/>G Caldarelli, A Maritan, M Vendruscolo (1996) <i>EUROPHYSICS LETTERS</i> <i></i> <i></i> 35: 7 481-485<br/>

http://publicationslist.org/Guido.Caldarelli/refid116 2009-12-23T09:07:55Z

In a critically self-organized model of punctuated equilibrium, boundaries determine peculiar scaling of the size distribution of evolutionary avalanches. This is derived by an inhomogeneous generalization of standard branching processes, extending previous mean field descriptions and yielding nu = 1/2 together with tau' = 7/4, as distribution exponent of avalanches starting from species at the en...<br/><br/>G Caldarelli, C Tebaldi (1996) <i>PHYSICAL REVIEW LETTERS</i> <i></i> <i></i> 76: 26 4983-4986<br/>

http://publicationslist.org/Guido.Caldarelli/refid115 2009-12-23T09:07:55Z

We 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 appropriat...<br/><br/>G Caldarelli, A Vespignani (1995) <i>FRACTALS-AN INTERDISCIPLINARY JOURNAL ON THE COMPLEX GEOMETRY OF NATURE</i> <i></i> <i></i> 3: 4 829-837<br/>

http://publicationslist.org/Guido.Caldarelli/refid119 2009-12-25T21:04:33Z

At dissipative boundaries, models of self-organized criticality show peculiar scalings, different from the bulk ones, in the distributions characterizing avalanches. For Abelian models with Dirichlet boundary conditions, evidence of this is obtained by a mean field approach to semi-infinite sandpiles, and by numerical simulations in two and three dimensions. On the other hand, within the mean fiel...<br/><br/>AL Stella, C Tebaldi, G Caldarelli (1995) <i>PHYSICAL REVIEW E</i> 52: 1 72-75<br/>

http://publicationslist.org/Guido.Caldarelli/refid120 2009-12-25T21:02:41Z

We 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 appropri...<br/><br/>G Caldarelli, A Vespignani, L Pietronero (1995) <i>PHYSICA A</i> 215: 3 223-232<br/>

http://publicationslist.org/Guido.Caldarelli/refid121 2010-01-04T14:34:32Z

We 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 distingui...<br/><br/>G Caldarelli, C Castellano, A Vespignani (1994) <i>PHYSICAL REVIEW E</i> 49: 4 2673-2679<br/>