6,691 research outputs found
Vacuum phenomenology of the chiral partner of the nucleon in a linear sigma model with vector mesons
We investigate a linear sigma model with global chiral symmetry. The mesonic degrees of freedom are the standard scalar and
pseudoscalar mesons and the vector and axial-vector mesons. The baryonic
degrees of freedom are the nucleon, , and its chiral partner, , which
is usually identified with N(1535). The chiral partner is incorporated in the
so-called mirror assignment, where the nucleon mass is not solely generated by
the chiral condensate but also by a chirally invariant mass term, . The
presence of (axial-) vector fields modifies the expressions for the axial
coupling constants of the nucleon, , and its partner,
. Using experimental data for the decays and
, as well as lattice results for we infer
MeV, i.e., an appreciable amount of the nucleon mass originates
from sources other than the chiral condensate. We test our model by evaluating
the decay and the s-wave nucleon-pion scattering lengths
.Comment: 16 pages, 2 figures. To appear in Phys. Rev.
Coherence in scale-free networks of chaotic maps
We study fully synchronized states in scale-free networks of chaotic logistic
maps as a function of both dynamical and topological parameters. Three
different network topologies are considered: (i) random scale-free topology,
(ii) deterministic pseudo-fractal scale-free network, and (iii) Apollonian
network. For the random scale-free topology we find a coupling strength
threshold beyond which full synchronization is attained. This threshold scales
as , where is the outgoing connectivity and depends on the
local nonlinearity. For deterministic scale-free networks coherence is observed
only when the coupling strength is proportional to the neighbor connectivity.
We show that the transition to coherence is of first-order and study the role
of the most connected nodes in the collective dynamics of oscillators in
scale-free networks.Comment: 9 pages, 8 figure
The current progress of the ALICE Ring Imaging Cherenkov Detector
Recently, the last two modules (out of seven) of the ALICE High Momentum
Particle Identification detector (HMPID) were assembled and tested. The full
detector, after a pre-commissioning phase, has been installed in the
experimental area, inside the ALICE solenoid, at the end of September 2006. In
this paper we review the status of the ALICE/HMPID project and we present a
summary of the series production of the CsI photo-cathodes. We describe the key
features of the production procedure which ensures high quality photo-cathodes
as well as the results of the quality assessment performed by means of a
specially developed 2D scanner system able to produce a detailed map of the CsI
photo-current over the entire photo-cathode surface.
Finally we present our recent R&D efforts toward the development of a novel
generation of imaging Cherenkov detectors with the aim to identify, in heavy
ions collisions, hadrons up to 30 GeV/c.Comment: Presented at the Imaging-2006 Conference, Stockholm, Sweden, June
200
Spatial updating, spatial transients, and regularities of a complex automaton with nonperiodic architecture
We study the dynamics of patterns exhibited by rule 52, a totalistic cellular automaton displaying intricate behaviors and wide regions of active/inactive synchronization patches. Systematic computer simulations involving 230 initial configurations reveal that all complexity in this automaton originates from random juxtaposition of a very small number of interfaces delimiting active/inactive patches. Such interfaces are studied with a sidewise spatial updating algorithm. This novel tool allows us to prove that the interfaces found empirically are the only interfaces possible for these periods, independently of the size of the automata. The spatial updating algorithm provides an alternative way to determine the dynamics of automata of arbitrary size, a way of taking into account the complexity of the connections in the lattice
Periodic Neural Activity Induced by Network Complexity
We study a model for neural activity on the small-world topology of Watts and
Strogatz and on the scale-free topology of Barab\'asi and Albert. We find that
the topology of the network connections may spontaneously induce periodic
neural activity, contrasting with chaotic neural activities exhibited by
regular topologies. Periodic activity exists only for relatively small networks
and occurs with higher probability when the rewiring probability is larger. The
average length of the periods increases with the square root of the network
size.Comment: 4 pages, 5 figure
Onset of fluidization in vertically shaken granular material
When granular material is shaken vertically one observes convection, surface
fluidization, spontaneous heap formation and other effects. There is a
controversial discussion in literature whether there exists a threshold for the
Froude number below which these effects cannot be
observed anymore. By means of theoretical analysis and computer simulation we
find that there is no such single threshold. Instead we propose a modified
criterion which coincides with critical Froude number for small
driving frequency .Comment: 7 pages, 5 figure
Multistability, phase diagrams, and intransitivity in the Lorenz-84 low-order atmospheric circulation model
We report phase diagrams detailing the intransitivity observed in the climate scenarios supported by a prototype atmospheric general circulation model, namely, the Lorenz-84 low-order model. So far, this model was known to have a pair of coexisting climates described originally by Lorenz. Bifurcation analysis allows the identification of a remarkably wide parameter region where up to four climates coexist simultaneously. In this region the dynamical behavior depends crucially on subtle and minute tuning of the model parameters. This strong parameter sensitivity makes the Lorenz-84 model a promising candidate of testing ground to validate techniques of assessing the sensitivity of low-order models to perturbations of parameters
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