1,083 research outputs found
Non-linear analysis of geomagnetic time series from Etna volcano
International audienceAn intensive nonlinear analysis of geomagnetic time series from the magnetic network on Etna volcano was carried out to investigate the dynamical behavior of magnetic anomalies in volcanic areas. The short-term predictability of the geomagnetic time series was evaluated to establish a possible low-dimensional deterministic dynamics. We estimated the predictive ability of both a nonlinear forecasting technique and a global autoregressive model by comparing the prediction errors. Our findings highlight that volcanomagnetic signals are the result of complex processes that cannot easily be predicted. There is slight evidence based on nonlinear predictions, that the geomagnetic time series are to be governed by many variables, whose time evolution could be better regarded as arising from complex high dimensional processes
Entanglement and particle correlations of Fermi gases in harmonic traps
We investigate quantum correlations in the ground state of noninteracting
Fermi gases of N particles trapped by an external space-dependent harmonic
potential, in any dimension. For this purpose, we compute one-particle
correlations, particle fluctuations and bipartite entanglement entropies of
extended space regions, and study their large-N scaling behaviors. The
half-space von Neumann entanglement entropy is computed for any dimension,
obtaining S_HS = c_l N^(d-1)/d ln N, analogously to homogenous systems, with
c_l=1/6, 1/(6\sqrt{2}), 1/(6\sqrt{6}) in one, two and three dimensions
respectively. We show that the asymptotic large-N relation S_A\approx \pi^2
V_A/3, between the von Neumann entanglement entropy S_A and particle variance
V_A of an extended space region A, holds for any subsystem A and in any
dimension, analogously to homogeneous noninteracting Fermi gases.Comment: 15 pages, 22 fig
Multicritical behavior of two-dimensional anisotropic antiferromagnets in a magnetic field
We study the phase diagram and multicritical behavior of anisotropic
Heisenberg antiferromagnets on a square lattice in the presence of a magnetic
field along the easy axis. We argue that, beside the Ising and XY critical
lines, the phase diagram presents a first-order spin-flop line starting from
T=0, as in the three-dimensional case. By using field theory we show that the
multicritical point where these transition lines meet cannot be O(3) symmetric
and occurs at finite temperature. We also predict how the critical temperature
of the transition lines varies with the magnetic field and the uniaxial
anisotropy in the limit of weak anisotropy.Comment: 21 pages, 8 fig
Self-consistent models of cuspy triaxial galaxies with dark matter haloes
We have constructed realistic, self-consistent models of triaxial elliptical
galaxies embedded in triaxial dark matter haloes. We examined three different
models for the shape of the dark matter halo: (i) the same axis ratios as the
luminous matter (0.7:0.86:1); (ii) a more prolate shape (0.5:0.66:1); (iii) a
more oblate shape (0.7:0.93:1). The models were obtained by means of the
standard orbital superposition technique introduced by Schwarzschild.
Self-consistent solutions were found in each of the three cases. Chaotic orbits
were found to be important in all of the models,and their presence was shown to
imply a possible slow evolution of the shapes of the haloes. Our results
demonstrate for the first time that triaxial dark matter haloes can co-exist
with triaxial galaxies.Comment: Latex paper based on the AASTEX format, 20 pages, 11 figures, 2
tables. Paper submitted to Ap
Static and dynamic structure factors in three-dimensional randomly diluted Ising models
We consider the three-dimensional randomly diluted Ising model and study the
critical behavior of the static and dynamic spin-spin correlation functions
(static and dynamic structure factors) at the paramagnetic-ferromagnetic
transition in the high-temperature phase. We consider a purely relaxational
dynamics without conservation laws, the so-called model A. We present Monte
Carlo simulations and perturbative field-theoretical calculations. While the
critical behavior of the static structure factor is quite similar to that
occurring in pure Ising systems, the dynamic structure factor shows a
substantially different critical behavior. In particular, the dynamic
correlation function shows a large-time decay rate which is momentum
independent. This effect is not related to the presence of the Griffiths tail,
which is expected to be irrelevant in the critical limit, but rather to the
breaking of translational invariance, which occurs for any sample and which, at
the critical point, is not recovered even after the disorder average.Comment: 43 page
Intelligent learning objects: an agent aproach to create interoperable learning objects
Reusing learning material is very important to design learning environments for real-life learning. The reusability of learning objects results from the product of three main features: modularity, discoverability and interoperability. We proposed learning objects built based on agent architectures, called Intelligent Learning Objects (ILO). This paper discusses how the ILO approach can be used to improve the interoperability among learning objects, learning menagement systems (LMS) and pedagogical agents.Education for the 21 st century - impact of ICT and Digital Resources ConferenceRed de Universidades con Carreras en Informática (RedUNCI
Improving interoperability among learning objects using FIPA agent communication framework
The reusability of learning material is based on three main features:
modularity, discoverability and interoperability. Several researchers on Intelligent Learning Environments have proposed the use of architectures based on agent societies. Learning systems based on Multi-Agent architectures support the development of more interactive and adaptable systems and the Learning Objects approach gives reusability. We proposed an approach where learning objects are built based on agent architectures. This paper discusses how the Intelligent Learning Objects approach can be used to improve the interoperability between learning objects and pedagogical agents.Applications in Artificial Intelligence - AgentsRed de Universidades con Carreras en Informática (RedUNCI
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