3,819 research outputs found
Cluster and group synchronization in delay-coupled networks
We investigate the stability of synchronized states in delay-coupled networks
where synchronization takes place in groups of different local dynamics or in
cluster states in networks with identical local dynamics. Using a master
stability approach, we find that the master stability function shows a discrete
rotational symmetry depending on the number of groups. The coupling matrices
that permit solutions on group or cluster synchronization manifolds show a very
similar symmetry in their eigenvalue spectrum, which helps to simplify the
evaluation of the master stability function. Our theory allows for the
characterization of stability of different patterns of synchronized dynamics in
networks with multiple delay times, multiple coupling functions, but also with
multiple kinds of local dynamics in the networks' nodes. We illustrate our
results by calculating stability in the example of delay-coupled semiconductor
lasers and in a model for neuronal spiking dynamics.Comment: 11 pages, 7 figure
Controlling synchrony by delay coupling in networks: from in-phase to splay and cluster states
We study synchronization in delay-coupled oscillator networks, using a master
stability function approach. Within a generic model of Stuart-Landau
oscillators (normal form of super- or subcritical Hopf bifurcation) we derive
analytical stability conditions and demonstrate that by tuning the coupling
phase one can easily control the stability of synchronous periodic states. We
propose the coupling phase as a crucial control parameter to switch between
in-phase synchronization or desynchronization for general network topologies,
or between in-phase, cluster, or splay states in unidirectional rings. Our
results are robust even for slightly nonidentical elements of the network.Comment: 4 pages, 4 figure
Analog power spectral density analysis of electroretinogram data
Analog power spectral density analysis of electroretinogram dat
Adaptive synchronization in delay-coupled networks of Stuart-Landau oscillators
We consider networks of delay-coupled Stuart-Landau oscillators. In these
systems, the coupling phase has been found to be a crucial control parameter.
By proper choice of this parameter one can switch between different synchronous
oscillatory states of the network. Applying the speed-gradient method, we
derive an adaptive algorithm for an automatic adjustment of the coupling phase
such that a desired state can be selected from an otherwise multistable regime.
We propose goal functions based on both the difference of the oscillators and a
generalized order parameter and demonstrate that the speed-gradient method
allows one to find appropriate coupling phases with which different states of
synchronization, e.g., in-phase oscillation, splay or various cluster states,
can be selected.Comment: 8 pages, 7 figure
Heavy-flavor dynamics in nucleus-nucleus collisions: from RHIC to LHC
The stochastic dynamics of c and b quarks in the fireball created in
nucleus-nucleus collisions at RHIC and LHC is studied employing a relativistic
Langevin equation, based on a picture of multiple uncorrelated random
collisions with the medium. Heavy-quark transport coefficients are evaluated
within a pQCD approach, with a proper HTL resummation of medium effects for
soft scatterings. The Langevin equation is embedded in a multi-step setup
developed to study heavy-flavor observables in pp and AA collisions, starting
from a NLO pQCD calculation of initial heavy-quark yields, complemented in the
nuclear case by shadowing corrections, k_T-broadening and nuclear geometry
effects. Then, only for AA collisions, the Langevin equation is solved
numerically in a background medium described by relativistic hydrodynamics.
Finally, the propagated heavy quarks are made hadronize and decay into
electrons. Results for the nuclear modification factor R_AA of heavy-flavor
hadrons and electrons from their semi-leptonic decays are provided, both for
RHIC and LHC beam energies.Comment: 4 pages, 2 figures (3 eps files); submitted for publication in the
proceedings of "Quark Matter 2011", 23-28 May 2011, Annecy (France
Direct photons ~basis for characterizing heavy ion collisions~
After years of experimental and theoretical efforts, direct photons become a
strong and reliable tool to establish the basic characteristics of a hot and
dense matter produced in heavy ion collisions. The recent direct photon
measurements are reviewed and a future prospect is given.Comment: 8 pages, 8 figures, Invited plenary talk at Quark Matter 200
Synchronisation in networks of delay-coupled type-I excitable systems
We use a generic model for type-I excitability (known as the SNIPER or SNIC
model) to describe the local dynamics of nodes within a network in the presence
of non-zero coupling delays. Utilising the method of the Master Stability
Function, we investigate the stability of the zero-lag synchronised dynamics of
the network nodes and its dependence on the two coupling parameters, namely the
coupling strength and delay time. Unlike in the FitzHugh-Nagumo model (a model
for type-II excitability), there are parameter ranges where the stability of
synchronisation depends on the coupling strength and delay time. One important
implication of these results is that there exist complex networks for which the
adding of inhibitory links in a small-world fashion may not only lead to a loss
of stable synchronisation, but may also restabilise synchronisation or
introduce multiple transitions between synchronisation and desynchronisation.
To underline the scope of our results, we show using the Stuart-Landau model
that such multiple transitions do not only occur in excitable systems, but also
in oscillatory ones.Comment: 10 pages, 9 figure
e+e- Pairs: a clock and a thermometer of heavy ion collisions
Recently, there is growing evidence that a new state of matter is formed in
sqrt(s_NN)= 200 GeV Au+Au collisions at RHIC: a strongly coupled Quark Gluon
Plasma of partonic degrees of freedom which develops a collective motion.
Dilepton spectra are not affected by strong interaction and can therefore probe
the whole time evolution of the collision. Thus they may be sensitive to onset
of deconfinement, chiral symmetry restoration, as well as the production of
thermal photons. The PHENIX experiment measured the production of e+e- pairs in
p+p and Au+Au collisions at sqrt(s_NN)= 200 GeV. An enhanced dilepton yield in
the mass range 150<m_ee<750 MeV/c^2 is measured. The excess increases faster
with centrality than the number of participating nucleons and is concentrated
at p_T<1GeV/c. At higher p_T the excess below 300 MeV/c^2 has been related to
an enhanced production of direct photons possibly of thermal origin.Comment: Proceedings of Quark Matter 2008, 8 pages, 7 figure
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