818 research outputs found
Complex phase-ordering of the one-dimensional Heisenberg model with conserved order parameter
We study the phase-ordering kinetics of the one-dimensional Heisenberg model
with conserved order parameter, by means of scaling arguments and numerical
simulations. We find a rich dynamical pattern with a regime characterized by
two distinct growing lengths. Spins are found to be coplanar over regions of a
typical size , while inside these regions smooth rotations associated
to a smaller length are observed. Two different and coexisting
ordering mechanisms are associated to these lengths, leading to different
growth laws and violating dynamical
scaling.Comment: 14 pages, 8 figures. To appear on Phys. Rev. E (2009
Mean-field phase diagram for Bose-Hubbard Hamiltonians with random hopping
The zero-temperature phase diagram for ultracold Bosons in a random 1D
potential is obtained through a site-decoupling mean-field scheme performed
over a Bose-Hubbard (BH) Hamiltonian whose hopping term is considered as a
random variable. As for the model with random on-site potential, the presence
of disorder leads to the appearance of a Bose-glass phase. The different phases
-i.e. Mott insulator, superfluid, Bose-glass- are characterized in terms of
condensate fraction and superfluid fraction. Furthermore, the boundary of the
Mott lobes are related to an off-diagonal Anderson model featuring the same
disorder distribution as the original BH Hamiltonian.Comment: 7 pages, 6 figures. Submitted to Laser Physic
Gutzwiller approach to the Bose-Hubbard model with random local impurities
Recently it has been suggested that fermions whose hopping amplitude is
quenched to extremely low values provide a convenient source of local disorder
for lattice bosonic systems realized in current experiment on ultracold atoms.
Here we investigate the phase diagram of such systems, which provide the
experimental realization of a Bose-Hubbard model whose local potentials are
randomly extracted from a binary distribution. Adopting a site-dependent
Gutzwiller description of the state of the system, we address one- and
two-dimensional lattices and obtain results agreeing with previous findings, as
far as the compressibility of the system is concerned. We discuss the expected
peaks in the experimental excitation spectrum of the system, related to the
incompressible phases, and the superfluid character of the {\it partially
compressible phases} characterizing the phase diagram of systems with binary
disorder. In our investigation we make use of several analytical results whose
derivation is described in the appendices, and whose validity is not limited to
the system under concern.Comment: 12 pages, 5 figures. Some adjustments made to the manuscript and to
figures. A few relevant observations added throughout the manuscript.
Bibliography made more compact (collapsed some items
Phase-ordering kinetics on graphs
We study numerically the phase-ordering kinetics following a temperature
quench of the Ising model with single spin flip dynamics on a class of graphs,
including geometrical fractals and random fractals, such as the percolation
cluster. For each structure we discuss the scaling properties and compute the
dynamical exponents. We show that the exponent for the integrated
response function, at variance with all the other exponents, is independent on
temperature and on the presence of pinning. This universal character suggests a
strict relation between and the topological properties of the
networks, in analogy to what observed on regular lattices.Comment: 16 pages, 35 figure
Percolation on the average and spontaneous magnetization for q-states Potts model on graph
We prove that the q-states Potts model on graph is spontaneously magnetized
at finite temperature if and only if the graph presents percolation on the
average. Percolation on the average is a combinatorial problem defined by
averaging over all the sites of the graph the probability of belonging to a
cluster of a given size. In the paper we obtain an inequality between this
average probability and the average magnetization, which is a typical extensive
function describing the thermodynamic behaviour of the model
Customer Complaining and Probability of Default in Consumer Credit
In many countries, Banking Authorities have adopted an Alternative Dispute Resolution (ADR) procedure to manage complaints that customers and financial intermediaries cannot solve by themselves. As a consequence, banks have had to implement complaint management systems in order to deal with customers’ demands. The growth rate of customer complaints has been increasing during the last few years. This does not seem to be only related to the quality of financial services or to lack of compliance in banking products. Another reason lies in the characteristics of the procedures themselves, which are very simple and free of charge. The paper analyzes some determinants regarding the willingness to complain. In particular, it examines whether a high customers’ probability of default leads to an increase in non-valid complaints. The paper uses a sample of approximately 1,000 customers who received a loan and made a claim against the lender. The analysis shows that customers with higher Probability of Default are more likely to make claims against Financial Institutions. Moreover, it shows that opportunistic behaviors and non-valid complaints are more likely if the customer is supported by a lawyer or other professionals and if the reason for the claim may result in a refund or damage compensation
Phase ordering and universality for continuous symmetry models on graphs
We study the phase-ordering kinetics following a temperature quench of O(N)
continuous symmetry models with and 4 on graphs. By means of extensive
simulations, we show that the global pattern of scaling behaviours is analogous
to the one found on usual lattices. The exponent a for the integrated response
function and the exponent z, describing the growing length, are related to the
large scale topology of the networks through the spectral dimension and the
fractal dimension alone, by means of the same expressions as are provided by
the analytic solution of the inifnite N limit. This suggests that the large N
value of these exponents could be exact for every N.Comment: 14 pages, 11 figure
Aging dynamics and the topology of inhomogenous networks
We study phase ordering on networks and we establish a relation between the
exponent of the aging part of the integrated autoresponse function
and the topology of the underlying structures. We show that in full generality on networks which are above the lower critical dimension
, i.e. where the corresponding statistical model has a phase transition at
finite temperature. For discrete symmetry models on finite ramified structures
with , which are at the lower critical dimension , we show that
is expected to vanish. We provide numerical results for the physically
interesting case of the percolation cluster at or above the percolation
threshold, i.e. at or above , and for other networks, showing that the
value of changes according to our hypothesis. For
models we find that the same picture holds in the large- limit and
that only depends on the spectral dimension of the network.Comment: LateX file, 4 eps figure
Earthworm populations in Eucalyptus spp plantation at Embrapa Forestry, Brazil (Oligochaeta).
Presented at the 6th International Oligochaete Taxonomy Meeting, Palmeira de Faro, Portugal, 2013
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