796 research outputs found

    Communication in networks with hierarchical branching

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    We present a simple model of communication in networks with hierarchical branching. We analyze the behavior of the model from the viewpoint of critical systems under different situations. For certain values of the parameters, a continuous phase transition between a sparse and a congested regime is observed and accurately described by an order parameter and the power spectra. At the critical point the behavior of the model is totally independent of the number of hierarchical levels. Also scaling properties are observed when the size of the system varies. The presence of noise in the communication is shown to break the transition. Despite the simplicity of the model, the analytical results are a useful guide to forecast the main features of real networks.Comment: 4 pages, 3 figures. Final version accepted in PR

    Optimal network topologies for local search with congestion

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    The problem of searchability in decentralized complex networks is of great importance in computer science, economy and sociology. We present a formalism that is able to cope simultaneously with the problem of search and the congestion effects that arise when parallel searches are performed, and obtain expressions for the average search cost--written in terms of the search algorithm and the topological properties of the network--both in presence and abscence of congestion. This formalism is used to obtain optimal network structures for a system using a local search algorithm. It is found that only two classes of networks can be optimal: star-like configurations, when the number of parallel searches is small, and homogeneous-isotropic configurations, when the number of parallel searches is large.Comment: 4 pages. Final version accepted in PR

    Botulism from Drinking Pruno

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    Foodborne botulism occurred among inmates at 2 prisons in California in 2004 and 2005. In the first outbreak, 4 inmates were hospitalized, 2 of whom required intubation. In the second event, 1 inmate required intubation. Pruno, an alcoholic drink made illicitly in prisons, was the novel vehicle for these cases

    Universal features in the growth dynamics of complex organizations

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    We analyze the fluctuations in the gross domestic product (GDP) of 152 countries for the period 1950--1992. We find that (i) the distribution of annual growth rates for countries of a given GDP decays with ``fatter'' tails than for a Gaussian, and (ii) the width of the distribution scales as a power law of GDP with a scaling exponent β≈0.15\beta \approx 0.15. Both findings are in surprising agreement with results on firm growth. These results are consistent with the hypothesis that the evolution of organizations with complex structure is governed by similar growth mechanisms.Comment: 4 pages, 7 ps figures, using Latex2e with epsf rotate and multicol style files. Submitted to PR

    The Effect of Bankruptcy Laws on the Valuation of Risky Consumer Debt

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    In a market setting with perfect information, a consumer recognizes that he can influence the state-contingent returns, and hence the pric, of his risky debt by the decision variables that determine the collateral and promised payments. This paper examines the effect of bankruptcy laws on the feasible consumption opportunities of borrowers and lenders in order to determine the necessary requirements for the bilateral debt market to be perfectly competitive.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72017/1/j.1540-6288.1989.tb00348.x.pd

    Paradoxes in Learning and the Marginal Value of Information

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    Heterogeneity and the dynamics of technology adoption

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    We estimate the demand for a videocalling technology in the presence of both network effects and heterogeneity. Using a unique dataset from a large multinational firm, we pose and estimate a fully dynamic model of technology adoption. We propose a novel identification strategy based on post-adoption technology usage to disentangle equilibrium beliefs concerning the evolution of the network from observed and unobserved heterogeneity in technology adoption costs and use benefits. We find that employees have significant heterogeneity in both adoption costs and network benefits, and have preferences for diverse networks. Using our estimates, we evaluate a number of counterfactual adoption policies, and find that a policy of strategically targeting the right subtype for initial adoption can lead to a faster-growing and larger network than a policy of uncoordinated or diffuse adoption
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