508 research outputs found
A cellular automaton for the factor of safety field in landslides modeling
Landslide inventories show that the statistical distribution of the area of
recorded events is well described by a power law over a range of decades. To
understand these distributions, we consider a cellular automaton to model a
time and position dependent factor of safety. The model is able to reproduce
the complex structure of landslide distribution, as experimentally reported. In
particular, we investigate the role of the rate of change of the system
dynamical variables, induced by an external drive, on landslide modeling and
its implications on hazard assessment. As the rate is increased, the model has
a crossover from a critical regime with power-laws to non power-law behaviors.
We suggest that the detection of patterns of correlated domains in monitored
regions can be crucial to identify the response of the system to perturbations,
i.e., for hazard assessment.Comment: 4 pages, 3 figure
Interplay of charge, spin and lattice degrees of freedom on the spectral properties of the one-dimensional Hubbard-Holstein model
We calculate the spectral function of the one dimensional Hubbard-Holstein
model using the time dependent Density Matrix Renormalization Group (tDMRG),
focusing on the regime of large local Coulomb repulsion, and away from
electronic half-filling. We argue that, from weak to intermediate
electron-phonon coupling, phonons interact only with the electronic charge, and
not with the spin degrees of freedom. For strong electron-phonon interaction,
spinon and holon bands are not discernible anymore and the system is well
described by a spinless polaronic liquid. In this regime, we observe multiple
peaks in the spectrum with an energy separation corresponding to the energy of
the lattice vibrations (i.e., phonons). We support the numerical results by
introducing a well controlled analytical approach based on Ogata-Shiba's
factorized wave-function, showing that the spectrum can be understood as a
convolution of three contributions, originating from charge, spin, and lattice
sectors. We recognize and interpret these signatures in the spectral properties
and discuss the experimental implications.Comment: 8 pages, 7 figure
Topological quantum transition driven by charge-phonon coupling in the Haldane Chern insulator
In condensed matter physics many features can be understood in terms of their
topological properties. Here we report evidence of a topological quantum
transition driven by the charge-phonon coupling in the spinless Haldane model
on a honeycomb lattice, a well-known prototypical model of Chern insulator.
Starting from parameters describing the topological phase in the bare Haldane
model, we show that the increasing of the strength of the charge lattice
coupling drives the system towards a trivial insulator. The average number of
fermions in the Dirac point, characterized by the lowest gap, exhibits a finite
discontinuity at the transition point and can be used as direct indicator of
the topological quantum transition. Numerical simulations show, also, that the
renormalized phonon propagator exhibits a two peak structure across the quantum
transition, whereas, in absence of the mass term in the bare Hadane model,
there is indication of a complete softening of the effective vibrational mode
signaling a charge density wave instability.Comment: 5 pages, 4 figure
Applications of Self-Organizing Maps for Ecomorphological Investigations through Early Ontogeny of Fish
We propose a new graphical approach to the analysis of multi-temporal morphological and ecological data concerning the life history of fish, which can typically serves models in ecomorphological investigations because they often undergo significant ontogenetic changes. These changes can be very complex and difficult to describe, so that visualization, abstraction and interpretation of the underlying relationships are often impeded. Therefore, classic ecomorphological analyses of covariation between morphology and ecology, performed by means of multivariate techniques, may result in non-exhaustive models. The Self Organizing map (SOM) is a new, effective approach for pursuing this aim. In this paper, lateral outlines of larval stages of gilthead sea bream (Sparus aurata) and dusky grouper (Epinephelus marginatus) were recorded and broken down using by means of Elliptic Fourier Analysis (EFA). Gut contents of the same specimens were also collected and analyzed. Then, shape and trophic habits data were examined by SOM, which allows both a powerful visualization of shape changes and an easy comparison with trophic habit data, via their superimposition onto the trained SOM. Thus, the SOM provides a direct visual approach for matching morphological and ecological changes during fish ontogenesis. This method could be used as a tool to extract and investigate relationships between shape and other sinecological or environmental variables, which cannot be taken into account simultaneously using conventional statistical methods
Behavior of quantum entropies in polaronic systems
Quantum entropies and state distances are analyzed in polaronic systems with
short range (Holstein model) and long range (Frhlich model)
electron-phonon coupling. These quantities are extracted by a variational wave
function which describes very accurately polaron systems with arbitrary size in
all the relevant parameter regimes. With the use of quantum information tools,
the crossover region from weak to strong coupling regime can be characterized
with high precision. Then, the linear entropy is found to be very sensitive to
the range of the electron-phonon coupling and the adiabatic ratio. Finally, the
entanglement entropy is studied as a function of the system size pointing out
that it not bounded, but scales as the logarithm of the size either for weak
electron-phonon coupling or for short range interaction. This behavior is
ascribed to the peculiar coupling induced by the single electron itinerant
dynamics on the phonon subsystem.Comment: 4 figures, to be published in Phys. Rev.
Two channel model for optical conductivity of high mobility organic crystals
We show that the temperature dependence of conductivity of high mobility
organic crystals Pentacene and Rubrene can be quantitatively described in the
framework of the model where carriers are scattered by quenched local
impurities and interact with phonons by Su-Schrieffer-Hegger (SSH) coupling.
Within this model, we present approximation free results for mobility and
optical conductivity obtained by world line Monte Carlo, which we generalize to
the case of coupling both to phonons and impurities. We find fingerprints of
carrier dynamics in these compounds which differ from conventional metals and
show that the dynamics of carriers can be described as a superposition of a
Drude term representing diffusive mobile particles and a Lorentz term
associated with dynamics of localized charges.Comment: 6 pages, 5 figure
Phase transitions in the Potts spin glass model
We have studied the Potts spin glass with 2-state Ising spins and s-state
Potts variables using a cluster Monte Carlo dynamics. The model recovers the +-
J Ising spin glass (SG) for s=1 and exhibits for all s a SG transition at
T_{SG}(s) and a percolation transition at higher temperature T_p(s). We have
shown that for all values of at T_p(s) there is a thermodynamical
transition in the universality class of a ferromagnetic s-state Potts model.
The efficiency of the cluster dynamics is compared with that of standard spin
flip dynamics.Comment: 8 pages, Latex, with 8 EPS fig
The efforts of a multidisciplinary approach in a rehabilitation institute for deaf children: a psychosocial intervention aimed at breaking the pattern of stalled productivity
Introduction
The multidisciplinary approach for the treatment of hearing impaired children exposes the work group to several tasks: the group needs to integrate different competencies and techniques, to share common treatment goals, to manage the relational dynamics with the children and with their parents, to explore the families’ expectancies. These efforts can put the work group in stressful conditions and, consequently, can negatively affect the quality of the intervention to be carried out.
Aim
Our aim was to illustrate a psychosocial analysis performed in a religious Institute for hearing impaired children, aimed at breaking the stalled productivity of the Institute, at avoiding inefficient and fragmented treatments, at preventing unelaborated relational dynamics within the staff and between the staff and the children’s families.
Methodology
Through the Content Analysis of semi-structured interviews administered to staff-members and families we analyzed the quality of the teamwork, the relational arrangements towards the families and local services (25 interview with 5 staff members); the family-Institute relationship and the family’s representation and satisfaction of the Institute (7 interview with 13 hearing and hearing impaired parents).
Results
The institute action seems to be more characterized by the maintenance of the relationship with the families per se, than oriented to productive goals.The hearing parents seem to be more satisfied than the hearing-impaired parents, possibly because the first are more prepared to receive the Institute's help.
Conclusions
The stalled productivity can be overcome only with the elaboration of those relational/emotional dynamics which prevent staff members and children’s parents from focusing on productive goals. The staff-members’ training should be improved in order to develop specific competencies to perform an integrated, multidisciplinary approach in treatments, to negotiate with the families, and share with them, work program and objectives of the treatment
Rashba effect induced localization in quantum networks
We study a quantum network extending in one-dimension (chain of square loops
connected at one vertex) made up of quantum wires with Rashba spin-orbit
coupling. We show that the Rashba effect may give rise to an electron
localization phenomenon similar to the one induced by magnetic field. This
localization effect can be attributed to the spin precession due to the Rashba
effect. We present results both for the spectral properties of the infinite
chain, and for linear transport through a finite-size chain connected to leads.
Furthermore, we study the effect of disorder on the transport properties of
this network.Comment: To appear in Phys. Rev. Let
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