3,543 research outputs found
Motif-based communities in complex networks
Community definitions usually focus on edges, inside and between the
communities. However, the high density of edges within a community determines
correlations between nodes going beyond nearest-neighbours, and which are
indicated by the presence of motifs. We show how motifs can be used to define
general classes of nodes, including communities, by extending the mathematical
expression of Newman-Girvan modularity. We construct then a general framework
and apply it to some synthetic and real networks
Discrete-time Markov chain approach to contact-based disease spreading in complex networks
Many epidemic processes in networks spread by stochastic contacts among their
connected vertices. There are two limiting cases widely analyzed in the physics
literature, the so-called contact process (CP) where the contagion is expanded
at a certain rate from an infected vertex to one neighbor at a time, and the
reactive process (RP) in which an infected individual effectively contacts all
its neighbors to expand the epidemics. However, a more realistic scenario is
obtained from the interpolation between these two cases, considering a certain
number of stochastic contacts per unit time. Here we propose a discrete-time
formulation of the problem of contact-based epidemic spreading. We resolve a
family of models, parameterized by the number of stochastic contact trials per
unit time, that range from the CP to the RP. In contrast to the common
heterogeneous mean-field approach, we focus on the probability of infection of
individual nodes. Using this formulation, we can construct the whole phase
diagram of the different infection models and determine their critical
properties.Comment: 6 pages, 4 figures. Europhys Lett (in press 2010
Heat transport in the spin chain: from ballistic to diffusive regimes and dephasing enhancement
In this work we study the heat transport in an XXZ spin-1/2 Heisenberg chain
with homogeneous magnetic field, incoherently driven out of equilibrium by
reservoirs at the boundaries. We focus on the effect of bulk dephasing
(energy-dissipative) processes in different parameter regimes of the system.
The non-equilibrium steady state of the chain is obtained by simulating its
evolution under the corresponding Lindblad master equation, using the time
evolving block decimation method. In the absence of dephasing, the heat
transport is ballistic for weak interactions, while being diffusive in the
strongly-interacting regime, as evidenced by the heat-current scaling with the
system size. When bulk dephasing takes place in the system, diffusive transport
is induced in the weakly-interacting regime, with the heat current
monotonically decreasing with the dephasing rate. In contrast, in the
strongly-interacting regime, the heat current can be significantly enhanced by
dephasing for systems of small size
Dependence of the drag over super hydrophobic and liquid infused surfaces on the textured surface and Weber number
Direct Numerical Simulations of a turbulent channel flow have been performed. The lower wall of the channel is made of staggered cubes with a second fluid locked in the cavities. Two viscosity ratios have been considered, m=μ1/μ2=0.02 and 0.4 (the subscript 1 indicates the fluid in the cavities and 2 the overlying fluid) mimicking the viscosity ratio in super–hydrophobic surfaces (SHS) and liquid infused surfaces (LIS) respectively. A first set of simulations with a slippery interface has been performed and results agree well with those in literature for perfect slip conditions and Stokes approximations. To assess how the dynamics of the interface affects the drag, a second set of DNS has been carried out at We=40 and 400 corresponding to We+≃10−3 and 10−2. The deformation of the interface is fully coupled to the Navier-Stokes equation and tracked in time using a Level Set Method. Two gas fractions, GF=0.5 and 0.875, have been considered to assess how the spacing between the cubes affects the deformation of the interface and therefore the drag. For the dimensions of the substrate here considered, under the ideal assumption of flat interface, staggered cubes with GF=0.875 provide about 20% drag reduction for We=0. However, a rapid degradation of the performances is observed when the dynamics of the interface is considered, and the same geometry increases the drag of about 40% with respect to a smooth wall. On the other hand, the detrimental effect of the dynamics of the interface is much weaker for GF=0.5 because of the reduced pitch between the cubes
Optimal map of the modular structure of complex networks
Modular structure is pervasive in many complex networks of interactions
observed in natural, social and technological sciences. Its study sheds light
on the relation between the structure and function of complex systems.
Generally speaking, modules are islands of highly connected nodes separated by
a relatively small number of links. Every module can have contributions of
links from any node in the network. The challenge is to disentangle these
contributions to understand how the modular structure is built. The main
problem is that the analysis of a certain partition into modules involves, in
principle, as many data as number of modules times number of nodes. To confront
this challenge, here we first define the contribution matrix, the mathematical
object containing all the information about the partition of interest, and
after, we use a Truncated Singular Value Decomposition to extract the best
representation of this matrix in a plane. The analysis of this projection allow
us to scrutinize the skeleton of the modular structure, revealing the structure
of individual modules and their interrelations.Comment: 21 pages, 10 figure
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