11,862 research outputs found
Analytical and numerical studies of disordered spin-1 Heisenberg chains with aperiodic couplings
We investigate the low-temperature properties of the one-dimensional spin-1
Heisenberg model with geometric fluctuations induced by aperiodic but
deterministic coupling distributions, involving two parameters. We focus on two
aperiodic sequences, the Fibonacci sequence and the 6-3 sequence. Our goal is
to understand how these geometric fluctuations modify the physics of the
(gapped) Haldane phase, which corresponds to the ground state of the uniform
spin-1 chain. We make use of different adaptations of the strong-disorder
renormalization-group (SDRG) scheme of Ma, Dasgupta and Hu, widely employed in
the study of random spin chains, supplemented by quantum Monte Carlo and
density-matrix renormalization-group numerical calculations, to study the
nature of the ground state as the coupling modulation is increased. We find no
phase transition for the Fibonacci chain, while we show that the 6-3 chain
exhibits a phase transition to a gapless, aperiodicity-dominated phase similar
to the one found for the aperiodic spin-1/2 XXZ chain. Contrary to what is
verified for random spin-1 chains, we show that different adaptations of the
SDRG scheme may lead to different qualitative conclusions about the nature of
the ground state in the presence of aperiodic coupling modulations.Comment: Accepted for publication in Physical Review
Portuguese term extraction methods: comparing linguistic and statistical approaches.
This paper discuss different extraction methods, linguistic informed and pure statistical, through a comparative analysis using usual metrics: Precision, Recall and F-measure. The experiments were made over a corpus from Pediatrics in portuguese, and the extracted terms were compared with a reference list.Propor 2010
Chaos and Synchronized Chaos in an Earthquake Model
We show that chaos is present in the symmetric two-block Burridge-Knopoff
model for earthquakes. This is in contrast with previous numerical studies, but
in agreement with experimental results. In this system, we have found a rich
dynamical behavior with an unusual route to chaos. In the three-block system,
we see the appearance of synchronized chaos, showing that this concept can have
potential applications in the field of seismology.Comment: To appear in Physical Review Letters (13 pages, 6 figures
Impactos da agropecuária nos planaltos sobre o regime hidrológico do Pantanal.
O Pantanal e seus planaltos adjacentes; Regime hidrológico do Pantanal; O regime hidrológico diante da expansão da agropecuária; O planalto do Taquari: um estudo de caso; Ações governamentais.bitstream/item/37548/1/CT37.pd
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