444,943 research outputs found
Dynamic communities in multichannel data: An application to the foreign exchange market during the 2007--2008 credit crisis
We study the cluster dynamics of multichannel (multivariate) time series by
representing their correlations as time-dependent networks and investigating
the evolution of network communities. We employ a node-centric approach that
allows us to track the effects of the community evolution on the functional
roles of individual nodes without having to track entire communities. As an
example, we consider a foreign exchange market network in which each node
represents an exchange rate and each edge represents a time-dependent
correlation between the rates. We study the period 2005-2008, which includes
the recent credit and liquidity crisis. Using dynamical community detection, we
find that exchange rates that are strongly attached to their community are
persistently grouped with the same set of rates, whereas exchange rates that
are important for the transfer of information tend to be positioned on the
edges of communities. Our analysis successfully uncovers major trading changes
that occurred in the market during the credit crisis.Comment: 8 pages, 6 figures, accepted for publication in Chao
The evolution of P2P networks for file exchange: the interaction between social controversy and technical change
Since the irruption of Napster in 1999, Peer-to-Peer computer networks for file exchange have been at the heart of a heated debate that has eventually evolved into a wide social controversy across the world, involving legal, economical, and even political issues. This essay analyzes the effects of this controversy on the technical innovations that have shaped the evolution of those systems. It argues that the usual image of a single two-sided conflict does not account for most of the technical changes involved. P2P entrepreneurs and creators show a wide range of motivations and business strategies -if any- and users are not a monolithic group with a common set of goals and values. As a result, the actual historical evolution of those networks does not follow a simple linear path but a more complex and multidirectional development
Collisions of strings with Y junctions
We study the dynamics of Nambu--Goto strings with junctions at which three
strings meet. In particular, we exhibit one simple exact solution and examine
the process of intercommuting of two straight strings, in which they exchange
partners but become joined by a third string. We show that there are important
kinematical constraints on this process. The exchange cannot occur if the
strings meet with very large relative velocity. This may have important
implications for the evolution of cosmic superstring networks and non-abelian
string networks.Comment: 4 pages, 1 figure, uses revtex 4. Clarifying comments added to
correct a conceptual error, reference updated. Version accepted by Phys Rev
Letters, with additional references and minor change
Exchanges in complex networks: income and wealth distributions
We investigate the wealth evolution in a system of agents that exchange
wealth through a disordered network in presence of an additive stochastic
Gaussian noise. We show that the resulting wealth distribution is shaped by the
degree distribution of the underlying network and in particular we verify that
scale free networks generate distributions with power-law tails in the
high-income region. Numerical simulations of wealth exchanges performed on two
different kind of networks show the inner relation between the wealth
distribution and the network properties and confirm the agreement with a
self-consistent solution. We show that empirical data for the income
distribution in Australia are qualitatively well described by our theoretical
predictions.Comment: 8 pages, 11 figure
The changing federated relationship between local and regional cooperatives
The evolution of the federated relationship between local and regional cooperatives is examined from the perspective of local cooperatives’ need for commodity-based farm supplies and regional cooperatives’ identity as food companies. Because locals want many competing bids for the supplies they purchase, they resist a strong and close affiliation with regional cooperatives, which then find themselves with excess capacity. Regionals have responded by instituting tighter bonds with selected local cooperatives operating as "internal supply networks," in exchange for certain benefits. This adaptation reduces the impact of divergent goals among regionals and locals within the federated system.Cooperatives, federation, networks, competition, regionalization., Agribusiness,
Making new connections towards cooperation in the prisoner's dilemma game
Evolution of cooperation in the prisoner's dilemma game is studied where
initially all players are linked via a regular graph, having four neighbors
each. Simultaneously with the strategy evolution, players are allowed to make
new connections and thus permanently extend their neighborhoods, provided they
have been successful in passing their strategy to the opponents. We show that
this simple coevolutionary rule shifts the survival barrier of cooperators
towards high temptations to defect and results in highly heterogeneous
interaction networks with an exponential fit best characterizing their degree
distributions. In particular, there exist an optimal maximal degree for the
promotion of cooperation, warranting the best exchange of information between
influential players.Comment: 6 two-column pages, 7 figures; accepted for publication in
Europhysics Letter
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