12,479 research outputs found
The Wigner Entropy Production Rate
The characterization of irreversibility in general quantum processes is an
open problem of increasing techno- logical relevance. Yet, the tools currently
available to this aim are mostly limited to the assessment of dynamics induced
by equilibrium environments, a situation that often does not match the reality
of experiments at the microscopic and mesoscopic scale. We propose a theory of
irreversible entropy production that is suited for quantum systems exposed to
general, non-equilibrium reservoirs. We illustrate our framework by addressing
a set of physically relevant situations that clarify both the features and the
potential of our proposal
Spatial stochastic predator-prey models
We consider a broad class of stochastic lattice predator-prey models, whose
main features are overviewed. In particular, this article aims at drawing a
picture of the influence of spatial fluctuations, which are not accounted for
by the deterministic rate equations, on the properties of the stochastic
models. Here, we outline the robust scenario obeyed by most of the lattice
predator-prey models with an interaction "a' la Lotka-Volterra". We also show
how a drastically different behavior can emerge as the result of a subtle
interplay between long-range interactions and a nearest-neighbor exchange
process.Comment: 5 pages, 2 figures. Proceedings paper of the workshop "Stochastic
models in biological sciences" (May 29 - June 2, 2006 in Warsaw) for the
Banach Center Publication
Entrograms and coarse graining of dynamics on complex networks
Using an information theoretic point of view, we investigate how a dynamics
acting on a network can be coarse grained through the use of graph partitions.
Specifically, we are interested in how aggregating the state space of a Markov
process according to a partition impacts on the thus obtained lower-dimensional
dynamics. We highlight that for a dynamics on a particular graph there may be
multiple coarse grained descriptions that capture different, incomparable
features of the original process. For instance, a coarse graining induced by
one partition may be commensurate with a time-scale separation in the dynamics,
while another coarse graining may correspond to a different lower-dimensional
dynamics that preserves the Markov property of the original process. Taking
inspiration from the literature of Computational Mechanics, we find that a
convenient tool to summarise and visualise such dynamical properties of a
coarse grained model (partition) is the entrogram. The entrogram gathers
certain information-theoretic measures, which quantify how information flows
across time steps. These information theoretic quantities include the entropy
rate, as well as a measure for the memory contained in the process, i.e., how
well the dynamics can be approximated by a first order Markov process. We use
the entrogram to investigate how specific macro-scale connection patterns in
the state-space transition graph of the original dynamics result in desirable
properties of coarse grained descriptions. We thereby provide a fresh
perspective on the interplay between structure and dynamics in networks, and
the process of partitioning from an information theoretic perspective. We focus
on networks that may be approximated by both a core-periphery or a clustered
organization, and highlight that each of these coarse grained descriptions can
capture different aspects of a Markov process acting on the network.Comment: 17 pages, 6 figue
Global Quantum Correlation in the Ising model
We study quantum correlations in an isotropic Ising ring under the effects of
a transverse magnetic field. After characterizing the behavior of two-spin
quantum correlations, we extend our analysis to global properties of the ring,
using a figure of merit for quantum correlations that shows enough sensitivity
to reveal the drastic changes in the properties of the system at criticality.
This opens up the possibility to relate statistical properties of quantum
many-body systems to suitably tailored measures of quantum correlations that
capture features going far beyond standard quantum entanglement.Comment: Published in the International Journal of Quantum Information as part
of the special issue devoted to "Quantum Correlations: entanglement and
beyond
Electromagnetic Productions of KLambda and KSigma on the Nucleons
We briefly review the progress and problems in the electromagnetic production
of KLambda on the nucleon. The problem of the data discrepancy in this channel
as well as the corresponding physics consequence are highlighted. We also
discuss the effect of the new beam-recoil polarization data Cx and Cz on our
analysis. For this purpose we use the isobar model Kaon-Maid and a recent
multipoles model that can describe recent experimental data. We also present a
new multipoles model for the KSigma channels to complete our analysis.Comment: 8 pages, 6 figures, invited talk at 6th International Conference on
Perspectives in Hadronic Physics, Trieste, Italy, 12-16 May 200
Radio detection prospects for a bulge population of millisecond pulsars as suggested by Fermi LAT observations of the inner Galaxy
Analogously to globular clusters, the dense stellar environment of the
Galactic center has been proposed to host a large population of as-yet
undetected millisecond pulsars (MSPs). Recently, this hypothesis found support
in the analysis of gamma rays from the inner Galaxy seen by the Large Area
Telescope (LAT) aboard the Fermi satellite, which revealed a possible excess of
diffuse GeV photons in the inner 15 deg about the Galactic center (Fermi GeV
excess). The excess can be interpreted as the collective emission of thousands
of MSPs in the Galactic bulge, with a spherical distribution that strongly
peaks towards the Galactic center. In order to fully establish the MSP
interpretation, it is essential to find corroborating evidence in
multi-wavelength searches, most notably through the detection of radio
pulsation from individual bulge MSPs. Based on globular cluster observations
and the gamma-ray emission from the inner Galaxy, we investigate the prospects
for detecting MSPs in the Galactic bulge. While previous pulsar surveys failed
to identify this population, we demonstrate that, in the upcoming years, new
large-area surveys with focus on regions a few degrees north or south of the
Galactic center should lead to the detection of dozens of bulge MSPs.
Additionally, we show that, in the near future, deep targeted searches of
unassociated Fermi sources should be able to detect the first few MSPs in the
bulge. The prospects for these deep searches are enhanced by a tentative
gamma-ray/radio correlation that we infer from high-latitude gamma-ray MSPs.
Such detections would constitute the first clear discoveries of field MSPs in
the Galactic bulge, with far-reaching implications for gamma-ray observations,
the formation history of the central Milky Way and strategy optimization for
future radio observations.Comment: 24 pages, 17 figures, 5 tables. Minor clarifications. Matches version
published in Ap
Relativistic Quark-Model Results for Baryon Ground and Resonant States
Latest results from a study of baryon ground and resonant states within
relativistic constituent quark models are reported. After recalling some
typical spectral properties, the description of ground states, especially with
regard to the nucleon and hyperon electromagnetic structures, is addressed. In
the following, recent covariant predictions for pion, eta, and kaon partial
decay widths of light and strange baryon resonances below 2 GeV are summarized.
These results exhibit a characteristic pattern that is distinct from
nonrelativistic or relativized decay studies performed so far. Together with a
detailed analysis of the spin, flavor, and spatial structures of the wave
functions, it supports a new and extended classification scheme of baryon
ground and resonant states into SU(3) flavor multiplets
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