43,767 research outputs found
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
Morphology and properties evolution upon ring-opening polymerization during extrusion of cyclic butylene terephthalate and graphene-related-materials into thermally conductive nanocomposites
In this work, the study of thermal conductivity before and after in-situ
ring-opening polymerization of cyclic butylene terephthalate into poly
(butylene terephthalate) in presence of graphene-related materials (GRM) is
addressed, to gain insight in the modification of nanocomposites morphology
upon polymerization. Five types of GRM were used: one type of graphite
nanoplatelets, two different grades of reduced graphene oxide (rGO) and the
same rGO grades after thermal annealing for 1 hour at 1700{\deg}C under vacuum
to reduce their defectiveness. Polymerization of CBT into pCBT, morphology and
nanoparticle organization were investigated by means of differential scanning
calorimetry, electron microscopy and rheology. Electrical and thermal
properties were investigated by means of volumetric resistivity and bulk
thermal conductivity measurement. In particular, the reduction of nanoflake
aspect ratio during ring-opening polymerization was found to have a detrimental
effect on both electrical and thermal conductivities in nanocomposites
Coupling Matrix Representation of Nonreciprocal Filters Based on Time Modulated Resonators
This paper addresses the analysis and design of non-reciprocal filters based
on time modulated resonators. We analytically show that time modulating a
resonator leads to a set of harmonic resonators composed of the unmodulated
lumped elements plus a frequency invariant element that accounts for
differences in the resonant frequencies. We then demonstrate that harmonic
resonators of different order are coupled through non-reciprocal admittance
inverters whereas harmonic resonators of the same order couple with the
admittance inverter coming from the unmodulated filter network. This coupling
topology provides useful insights to understand and quickly design
non-reciprocal filters and permits their characterization using an
asynchronously tuned coupled resonators network together with the coupling
matrix formalism. Two designed filters, of orders three and four, are
experimentally demonstrated using quarter wavelength resonators implemented in
microstrip technology and terminated by a varactor on one side. The varactors
are biased using coplanar waveguides integrated in the ground plane of the
device. Measured results are found to be in good agreement with numerical
results, validating the proposed theory
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