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Immunization of real complex communication networks

EUROPEAN PHYSICAL JOURNAL B 2006年第2期49卷 259-264页

作者： Gómez-Gardeñes, J Echenique, P Moreno, Y Univ Zaragoza Inst Biocomputat & Phys Complex Syst BIFI E-50009 Zaragoza Spain Univ Zaragoza Dept Fis Mat Condensada E-50009 Zaragoza Spain Univ Zaragoza Dept Fis Teor E-50009 Zaragoza Spain

Most communication networks are complex. In this paper, we address one of the fundamental problems we are facing nowadays, namely, how we can efficiently protect these networks. To this end, we study an immunization strategy and found that it works almost as good as targeted immunization, but using only local information about the network topology. Our findings are supported with numerical simulations of the Susceptible-Infected-Removed (SIR) model on top of real communication networks, where immune nodes are previously identified by a covering algorithm. The results provide useful hints in the way to designing and deploying a digital immune system.

关键词： structures and organization in complex systems World Wide Web, Internet Interdisciplinary applications of physics

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Phase transitions in unstable cancer cell populations

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EUROPEAN PHYSICAL JOURNAL B 2003年第1期35卷 117-123页

作者： Solé, RV Univ Pombeau Fabra ICREA Complex Syst Lab Barcelona 08003 Spain Santa Fe Inst Santa Fe NM 87501 USA

The dynamics of cancer evolution is studied by means of a simple quasispecies model involving cells displaying high levels of genetic instability. Both continuous, mean-field and discrete, bit-string models are analysed. The string model is simulated on a single-peak landscape. It is shown that a phase transition exists at high levels of genetic instability, thus separating two phases of slow and rapid growth. The results suggest that, under a conserved level of genetic instability the cancer cell population will be close to the threshold level. Implications for therapy are outlined.

关键词： Biological physics: General theory and mathematical aspects Dynamics of evolution Ecology and evolution structures and organization in complex systems

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Efficiency and robustness in ant networks of galleries

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EUROPEAN PHYSICAL JOURNAL B 2004年第1期42卷 123-129页

作者： Buhl, J Gautrais, J Solé, RV Kuntz, P Valverde, S Deneubourg, JL Theraulaz, G Univ Toulouse 3 CNRS Ctr Rech Cognit Anim F-31062 Toulouse 4 France Univ Pompeu Fabra ICREA Complex Syst Lab Barcelona 08003 Spain Univ Nantes Ecole Polytech F-44322 Nantes 03 France Free Univ Brussels CENOLI B-1050 Brussels Belgium

Recent theoretical and empirical studies have focused on the topology of large networks of communication/interactions in biological, social and technological systems. Most of them have been studied in the scope of the small-world and scale-free networks' theory. Here we analyze the characteristics of ant networks of galleries produced in a 2-D experimental setup. These networks are neither small-worlds nor scale-free networks and belong to a particular class of network, i.e. embedded planar graphs emerging from a distributed growth mechanism. We compare the networks of galleries with both minimal spanning trees and greedy triangulations. We show that the networks of galleries have a path system efficiency and robustness to disconnections closer to the one observed in triangulated networks though their cost is closer to the one of a tree. These networks may have been prevented to evolve toward the classes of small-world and scale-free networks because of the strong spatial constraints under which they grow, but they may share with many real networks a similar trend to result from a balance of constraints leading them to achieve both path system efficiency and robustness at low cost.

关键词： structures and organization in complex systems Networks and genealogical trees Dynamics of social systems

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Phase separation dynamics in small-world media

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EUROPEAN PHYSICAL JOURNAL B 2007年第3期58卷 345-351页

作者： Imayama, R. Shiwa, Y. Kyoto Inst Technol Stat Mech Lab Sakyo Ku Kyoto 6068585 Japan

We present results of a numerical study of phase separation dynamics of a two-dimensional quenched system which has a small-world topology, both with and without the conserved order parameter. We examine how the domain coarsening changes with the density of long-range connections (shortcuts). It is demonstrated that the shortcuts have directly opposite effects, i.e., a speeding up of the coarsening process of reaching a fully uniform state, and a freezing of the system in a disordered metastable state.

关键词： structures and organization in complex systems Pattern selection, pattern formation Order-disorder transformations, statistical mechanics of model systems

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Synchronization of multi-phase oscillators: an Axelrod-inspired model

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EUROPEAN PHYSICAL JOURNAL B 2009年第2期70卷 243-248页

作者： Kuperman, M. N. Zanette, D. H. Ctr Atom Bariloche Consejo Nacl Invest Cient & Tecn RA-8400 San Carlos De Bariloche Rio Negro Argentina Inst Balseiro RA-8400 San Carlos De Bariloche Rio Negro Argentina

Inspired by Axelrod's model of culture dissemination, we introduce and analyze a model for a population of coupled oscillators where different levels of synchronization can be assimilated to different degrees of cultural organization. The state of each oscillator is represented by a set of phases, and the interaction - which occurs between homologous phases - is weighted by a decreasing function of the distance between individual states. Both ordered arrays and random networks are considered. We find that the transition between synchronization and incoherent behaviour is mediated by a clustering regime with rich organizational structure, where any two oscillators can be synchronized in some of their phases, while their remain unsynchronized in the others.

关键词： Synchronization, coupled oscillators Dynamics of social systems structures and organization in complex systems

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Cluster structure of EU-15 countries derived from the correlation matrix analysis of macroeconomic index fluctuations

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EUROPEAN PHYSICAL JOURNAL B 2007年第2期57卷 139-146页

作者： Gligor, M. Ausloos, M. Univ Liege GRAPES B-4000 Liege Belgium Natl Coll Roman Voda Neamt 5550 Romania

The statistical distances between countries, calculated for various moving average time windows, are mapped into the ultrametric subdominant space as in classical Minimal Spanning Tree methods. The Moving Average Minimal Length Path (MAMLP) algorithm allows a decoupling of fluctuations with respect to the mass center of the system from the movement of the mass center itself. A Hamiltonian representation given by a factor graph is used and plays the role of cost function. The present analysis pertains to 11 macroeconomic (ME) indicators, namely the GDP (x(1)), Final Consumption Expenditure (x(2)), Gross Capital Formation (x(3)), Net Exports (x(4)), Consumer Price Index (y(1)), Rates of Interest of the Central Banks (y(2)), Labour Force (z(1)), Unemployment (z(2)), GDP/hour worked (z(3)), GDP/capita (w(1)) and Gini coefficient (w(2)). The target group of countries is composed of 15 EU countries, data taken between 1995 and 2004. By two different methods (the Bipartite Factor Graph Analysis and the Correlation Matrix Eigensystem Analysis) it is found that the strongly correlated countries with respect to the macroeconomic indicators fluctuations can be partitioned into stable clusters.

关键词： Economics, econophysics, financial markets, business and management structures and organization in complex systems Time series analysis

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Nonextensive statistical approach to non-coding human DNA

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PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS 2008年第11期387卷 2653-2659页

作者： Oikonomou, Th. Provata, A. Tirnakli, U. Ege Univ Dept Phys Fac Sci TR-35100 Izmir Turkey Natl Ctr Sci Res Demokritos Inst Phys Chem Athens 15310 Greece Univ Athens Sch Med Dept Biol Chem Athens 11527 Greece

We use q-exponential distributions, which maximize the nonextensive entropy S-q (defined as S-q equivalent to (1 - Sigma(i)p(i)(q)) / (q - 1), to study the size distributions of non-coding DNA (including introns and intergenic regions) in all human chromosomes. We show that the value of the exponent q describing the non-coding size distributions is similar for all chromosomes and varies between 2 <= q <= 2.3 with the exception of chromosomes X and Y (C) 2007 Elsevier B.V. All rights reserved.

关键词： structures and organization in complex systems DNA RNA classical statistical mechanics

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complex grid computing

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EUROPEAN PHYSICAL JOURNAL B 2005年第1期44卷 119-128页

作者： Costa, LD Travieso, G Ruggiero, CA Univ Sao Paulo Inst Fis Sao Carlos BR-13560970 Sao Carlos SP Brazil

This article investigates the functional properties of complex networks used as grid computing systems. complex networks following the Erdos-Renyi model and other models with a preferential attachment rule ( with and without growth) or priority to the connection of isolated nodes are studied. Regular networks are also considered for comparison. The processing load of the parallel program executed on the grid is assigned to the nodes on demand, and the efficiency of the overall computation is quantified in terms of the parallel speedup. It is found that networks with preferential attachment allow lower computing efficiency than networks with uniform link attachment. At the same time, considering only node clusters of the same size, preferential attachment networks display better efficiencies. The regular networks, on the other hand, display a poor efficiency, due to their implied larger internode distances. A correlation is observed between the topological properties of the network, specially average cluster size, and their respective computing efficiency.

关键词： structures and organization in complex systems Computer science and technology World Wide Web, Internet Combinatorics, graph theory Networks and genealogical trees

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Evolving pseudofractal networks

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EUROPEAN PHYSICAL JOURNAL B 2007年第3期58卷 337-344页

作者： Zhang, Zhongzhi Zhou, Shuigeng Chen, Lichao Fudan Univ Dept Comp Sci & Engn Shanghai 200433 Peoples R China Fudan Univ Shanghai Key Lab Intelligent Informat Proc Shanghai 200433 Peoples R China

We present a family of scale-free network model consisting of cliques, which is established by a simple recursive algorithm. We investigate the networks both analytically and numerically. The obtained analytical solutions show that the networks follow a power-law degree distribution, with degree exponent continuously tuned between 2 and 3. The exact expression of clustering coefficient is also provided for the networks. Furthermore, the investigation of the average path length reveals that the networks possess small-world feature. Interestingly, we find that a special case of our model can be mapped into the Yule process.

关键词： complex systems structures and organization in complex systems Computational methods in statistical physics and nonlinear dynamics

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Response of Boolean networks to perturbations

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EUROPEAN PHYSICAL JOURNAL B 2008年第3期62卷 365-371页

作者： Fretter, C. Drossel, B. Tech Univ Darmstadt Inst Festkorperphys D-64289 Darmstadt Germany

We evaluate the probability that a Boolean network returns to an attractor after perturbing h nodes. We find that the return probability as function of h can display a variety of different behaviours, which yields insights into the state-space structure. In addition to performing computer simulations, we derive analytical results for several types of Boolean networks, in particular for Random Boolean Networks. We also apply our method to networks that have been evolved for robustness to small perturbations, and to a biological example.

关键词： Networks and genealogical trees Nonlinear dynamics and chaos structures and organization in complex systems

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