Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session D23: Networks and Complex Systems |
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Sponsoring Units: GSNP Chair: Michael F. Shlesinger, ONR Room: LACC 410 |
Monday, March 21, 2005 2:30PM - 2:42PM |
D23.00001: Weighted networks: Structure and modeling Marc Barthelemy In addition to topological complexity, real-world networks display a gradation in the intensity strength between nodes-the weights of the links. I will present two examples, the airline connection network and the scientific collaboration network, representative of critical infrastructure and social system respectively. These weighted networks exhibit broad distributions and non-trivial correlations of weights that cannot be explained in terms of the underlying topological structure. These results call for the need of the modeling of complex networks which goes beyond purely topological models. I will present a model which provides an explanation for the features observed in several real-world networks. This model of weighted network formation introduces a dynamical coupling between topology and weights by rearranging weights when a new link is introduced in the system. [Preview Abstract] |
Monday, March 21, 2005 2:42PM - 2:54PM |
D23.00002: Self-organization of collaboration networks Jose J. Ramasco, Sergei N. Dorogovtsev, Romualdo Pastor-Satorras We study collaboration networks in terms of evolving, self-organizing bipartite graph models. We propose a model of a growing network, which combines preferential edge attachment with the bipartite structure, generic for collaboration networks. The model depends exclusively on basic properties of the network, such as the total number of collaborators and acts of collaboration, the mean size of collaborations, etc. The simplest model defined within this framework already allows us to describe many of the main topological characteristics (degree distribution, clustering coefficient, etc.) of one-mode projections of several real collaboration networks, without parameter fitting. We explain the observed dependence of the local clustering on degree and the degree--degree correlations in terms of the ``aging'' of collaborators and their physical impossibility to participate in an unlimited number of collaborations. [Preview Abstract] |
Monday, March 21, 2005 2:54PM - 3:06PM |
D23.00003: Patent Citation Networks Katherine Strandburg, Jan Tobochnik, Gabor Csardi, Peter Erdi Patent applications contain citations which are similar to but different from those found in published scientific papers. In particular, patent citations are governed by legal rules. Moreover, a large fraction of citations are made not by the patent inventor, but by a patent examiner during the application procedure. Using a patent database, which contains the patent citations, assignees and inventors, we have applied network analysis and built network models. Our work includes determining the structure of the patent citation network and comparing it to existing results for scientific citation networks; identifying differences between various technological fields and comparing the observed differences to expectations based on anecdotal evidence about patenting practice; and developing models to explain the results. [Preview Abstract] |
Monday, March 21, 2005 3:06PM - 3:18PM |
D23.00004: Dynamics of rumor-like information dissemination in complex networks Maziar Nekovee, Yamir Moreno, Ginestra Bianconi, Matteo Marsili An important dynamic process that takes place in complex networks is the spreading of information via rumor-like mechanisms. In addition to their relevance to propagation of rumors and fads in human society, such mechanism are also the basis of an important class of collective communication protocols in complex computer networks, such as the Internet and the peer-to-peer systems. In this talk we present results of our analytical, numerical and large-scale Monte Carlo simulation studies of this process on several classes of complex networks, including random graphs, scale-free networks, and random and small-world topological graphs. Our studies point out to important differences between the dynamics of rumor spreading and that of virus spreading in such networks, and provide new insights into the complex interplay between the spreading phenomena and network topology. [Preview Abstract] |
Monday, March 21, 2005 3:18PM - 3:30PM |
D23.00005: Network Structures from Selection Principles Vittoria Colizza, Jayanth R. Banavar, Amos Maritan, Andrea Rinaldo We present an analysis of the topologies of a class of networks which are optimal in terms of the requirements of having as short a route as possible between any two nodes while yet keeping the congestion in the network as low as possible. Strikingly, we find a variety of distinct topologies and novel phase transitions between them on varying the number of links per node. Our results suggest that the emergence of the topologies observed in nature may arise both from growth mechanisms and the interplay of dynamical mechanisms with a selection process. [Preview Abstract] |
Monday, March 21, 2005 3:30PM - 3:42PM |
D23.00006: Scaling and distribution of the width in regular and small-world synchronization networks in 2D Hasan Guclu, Gyorgy Korniss, Mark A. Novotny, Zoltan Toroczkai We study the evolution, the scaling and the steady-state distribution of the width in two-dimensional regular and small-world (SW) networks motivated by a synchronization problem in distributed computing \footnote[2]{G. Korniss et al.,\textit{Science} \textbf{299}, 677 (2003).} \footnote[3]{H. Guclu and G. Korniss, \textit{Phys. Rev. E} \textbf{69} 065104(R) (2004).}. We find that in the regular network the system exhibits Kardar-Parisi-Zhang (KPZ) type roughening (de-synchronized state) with a very slow convergence to the KPZ width distribution. When SW links are added to the regular network one obtains a finite width in the thermodynamic limit (synchronized state). The distribution of the width in the SW network, however, is of non-Gaussian type with an exponential tale. [Preview Abstract] |
Monday, March 21, 2005 3:42PM - 3:54PM |
D23.00007: Rigidity percolation and ``intermediate phase'' in randomly connected networks Julien Barr\'e, Alan Bishop, Turab Lookman, Avadh Saxena Between the usual floppy and rigid phases, an intermediate phase has recently been identified in rigidity percolation, both theoretically and experimentally. We present a simple model that enables us to analytically characterize this intermediate phase. [Preview Abstract] |
Monday, March 21, 2005 3:54PM - 4:06PM |
D23.00008: The Dynamics of Information Access in the Online Media Zoltan Dezso, Eivind Almaas, Andras Lukacs, Balazs Racz, Istvan Szakadat, Albert-Laszlo Barabasi While most research on information access focuses on search engines, a significant fraction of new information we are exposed to comes from news, whose source is increasingly shifting online. News, however, have a fleeting quality: in contrast with the 24-hour news cycle of the printed press, in the online and audiovisual media the non-stop stream of new developments often obliterates a news event within hours. Through archives, the Internet offers better long-term search-based access to old events than any other media before. Yet, if we are not exposed to a news item while prominently featured, it is unlikely that we will know what to search for. The accelerating news cycle raises several important questions: How long is a piece of news accessible without targeted search? What is the dynamics of news accessibility? [Preview Abstract] |
Monday, March 21, 2005 4:06PM - 4:18PM |
D23.00009: ``Thermal'' and ``superthermal'' two-class structure of the personal income distribution Victor Yakovenko, Antonio Silva In Ref.\ [1] we proposed an analogy between the thermal Boltzmann-Gibbs probability distribution of energy in physics and the probability distribution of money in economics in statistical equilibrium. In Ref.\ [2] we find that the probability distribution of personal income in the USA has a well-defined two-class structure. The majority of population (97-99\%) belongs to the lower class characterized by the exponential Boltzmann-Gibbs (``thermal'') distribution, whereas the upper class (1-3\% of population) has a Pareto power-law (``superthermal'') distribution. By analyzing the income data for 1983--2001 from IRS, we show that the ``thermal'' part is stationary in time, save for a gradual increase of the effective temperature, whereas the nonequilibrium ``superthermal'' tail swells and shrinks following the stock market. We discuss the concept of equilibrium inequality in a society, based on the principle of maximal entropy, and quantitatively show that it applies to the majority of the US population. \\[4pt] [1] A. Dragulescu and V. M. Yakovenko, ``Statistical mechanics of money'', Eur. Phys. J. B {\bf 17}, 723--729 (2000). [cond-mat/0001432] \\[0pt] [2] A. C. Silva and V. M. Yakovenko, ``Temporal evolution of the `thermal' and `superthermal' income classes in the USA during 1983--2001'', accepted to Europhysics Letters. [cond- mat/0406385] [Preview Abstract] |
Monday, March 21, 2005 4:18PM - 4:30PM |
D23.00010: Effect of Disorder Strength on Optimal Paths in Complex Networks Sameet Sreenivasan, Tomer Kalisky, Lidia A. Braunstein, Sergey V. Buldyrev, Shlomo Havlin, H. Eugene Stanley We study the transition between the strong and weak disorder regimes in the scaling properties of the average optimal path $\ell_{\rm opt}$ in a disordered ER random network and SF network. We find that for any finite value of the disorder strength control parameter $a$, there is a crossover network size $N^*(a)$ at which the transition occurs. For $N \ll N^*(a)$ the scaling behavior of $\ell_{\rm opt}$ is in the strong disorder regime, with $\ell_{\rm opt} \sim N^{1/3}$ for ER networks and for SF networks with $\lambda \ge 4$, and $\ell_ {\rm opt} \sim N^{(\lambda-3)/(\lambda-1)}$ for SF networks with $3 < \lambda < 4$. For $N \gg N^*(a)$ the scaling behavior is in the weak disorder regime, with $\ell_{\rm opt}\sim\ln N$ for ER networks and SF networks with $\lambda > 3$. We proceed to derive the scaling relation between $N^*(a)$ and $a$. We find that $N^*(a)\sim a^3$ for ER networks and for SF networks with $\lambda\ge 4$, and $N^*(a)\sim a^{(\lambda-1)/(\lambda-3)}$ for SF networks with $3 <\lambda < 4$. [Preview Abstract] |
Monday, March 21, 2005 4:30PM - 4:42PM |
D23.00011: Diffusion Processes on Power-Law Small-World Networks Balazs Kozma, Matthew B. Hastings, G. Korniss We consider diffusion driven processes on power-law small-world networks: a random walk process related to folded polymers and surface growth related to synchronization problems. The random links introduced in small-world networks often lead to mean-field coupling (as if the random links were annealed) but in some systems mean-field predictions break down, like diffusion in one dimension. This break-down can be understood treating the random links perturbatively where the mean field prediction appears as the lowest order term of a naive perturbation expansion. Our results were obtained using self-consistent perturbation theory \footnote{B. Kozma, M. B. Hastings, and G. Korniss, Phys. Rev. Lett. {\bf 92}, 108701 (2004).} and can also be understood in terms of a scaling theory. We find a rich phase diagram, with different transient and recurrent phases, including a critical line with continuously varying exponents. [Preview Abstract] |
Monday, March 21, 2005 4:42PM - 4:54PM |
D23.00012: Statistical model with a standard Gamma distribution Anirban Chakraborti, Marco Patriarca, Kimmo Kaski We study a statistical model consisting of $N$ basic units which interact with each other by exchanging a physical entity, according to a given microscopic random law, depending on a parameter $\lambda $. We focus on the equilibrium or stationary distribution of the entity exchanged and verify through numerical fitting of the simulation data that the final form of the equilibrium distribution is that of a standard Gamma distribution. The model can be interpreted as a simple closed economy in which economic agents trade money and a saving criterion is fixed by the saving propensity $\lambda $. Alternatively, from the nature of the equilibrium distribution, we show that the model can also be interpreted as a perfect gas at an effective temperature $T (\lambda )$, where particles exchange energy in a space with an effective dimension $D (\lambda )$. [Preview Abstract] |
Monday, March 21, 2005 4:54PM - 5:06PM |
D23.00013: Unprecedented conservation law of evolution and Methuselah age. Mark Azbel' Extensive data establish that mortality in evolutionary unprecedented protected populations is predominantly universal for humans, flies, nematodes, yeast. The law which is preserved in evolution of species as biologically remote as humans and yeast is a conservation law of evolution. Conservation laws are well known in physics, but conservation law of evolution is unprecedented. It describes mortality dynamics of live animals which strongly interact with changing environment. Yet the law reduces only to current population characteristics, and does not depend on any variables specific for environment or interaction with it. This must be related to homeostasis which is specific for live systems. The law implies selection which, in contrast to species specific natural selection, proceeds via universal stepwise evolutionary rungs. The law suggests that universal mortality is a disposable evolutionary byproduct, and directed genetic and/or biological changes may yield healthy and vital Methuselah lifespan. This is consistent with recent experiments, and may be related to genes, which were beneficial for non-universal longevity in the wild, but became detrimental in evolutionary unprecedented protected conditions. Universality implies that single cell yeast may provide a master key to the mechanism of mortality and adaptation in all animals. [Preview Abstract] |
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