42,738 research outputs found
Influence of Refractory Periods in the Hopfield model
We study both analytically and numerically the effects of including
refractory periods in the Hopfield model for associative memory. These periods
are introduced in the dynamics of the network as thresholds that depend on the
state of the neuron at the previous time. Both the retrieval properties and the
dynamical behaviour are analyzed.Comment: Revtex, 7 pages, 7 figure
Characterizing Weak Chaos using Time Series of Lyapunov Exponents
We investigate chaos in mixed-phase-space Hamiltonian systems using time
series of the finite- time Lyapunov exponents. The methodology we propose uses
the number of Lyapunov exponents close to zero to define regimes of ordered
(stickiness), semi-ordered (or semi-chaotic), and strongly chaotic motion. The
dynamics is then investigated looking at the consecutive time spent in each
regime, the transition between different regimes, and the regions in the
phase-space associated to them. Applying our methodology to a chain of coupled
standard maps we obtain: (i) that it allows for an improved numerical
characterization of stickiness in high-dimensional Hamiltonian systems, when
compared to the previous analyses based on the distribution of recurrence
times; (ii) that the transition probabilities between different regimes are
determined by the phase-space volume associated to the corresponding regions;
(iii) the dependence of the Lyapunov exponents with the coupling strength.Comment: 8 pages, 6 figure
Charmed hadron signals of partonic medium
We present a short review of our results on the collectivity and the
suppression pattern of charmed mesons in heavy-ion collisions based on the
microscopic Hadron-String Dynamics (HSD) transport approach for different
scenarios of charm interactions with the surrounding matter - the 'comover'
dissociation by mesons with further recreation by D+Dbar channels and
'pre-hadronic' interaction scenarios. While at SPS energies the hadronic
'comover' absorption scenario is found to be compatible with the experimental
data, the dynamics of c and cbar quarks at RHIC are dominated by partonic or
'pre-hadronic' interactions in the strongly coupled quark-gluon plasma stage
and cannot be modeled by pure hadronic interactions. We find that the
collective flow of charm in the purely hadronic scenario appears compatible
with the data at SPS energies but underestimates the data at top RHIC energies.
Thus, the large elliptic flow v2 of D mesons and the low R_AA(pT) of J/Psi seen
experimentally at RHIC have to be attributed to early interactions of
non-hadronic degrees of freedom. Simultaneously, we observe that non-hadronic
interactions are mandatory in order to describe the narrowing of the J/Psi
rapidity distribution from p+p to central Au+Au collisions at the top RHIC
energy. We demonstrate additionally that the strong quenching of high-pT
J/Psi's in central Au+Au collisions indicates that a fraction of final J/Psi
mesons is created by a coalescence mechanism close to the phase boundary.Comment: Talk given at International Conference on Strangeness in Quark Matter
(SQM 2008), Beijing, China, 6-10 Oct 200
Brane Cosmic String Compactification in Brans-Dicke Theory
We investigate an alternative compactification of extra dimensions using
local cosmic string in the Brans-Dicke gravity framework. In the context of
dynamical systems it is possible to show that there exist a stable field
configuration for the Einstein-Brans-Dicke equations. We explore the analogies
between this particular model and the Randall-Sundrum scenario.Comment: RevTex, 5 pages, no figures. To appear in the Physical Review
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