127 research outputs found
Absence of Chaos in Bohmian Dynamics
The Bohm motion for a particle moving on the line in a quantum state that is
a superposition of n+1 energy eigenstates is quasiperiodic with n frequencies.Comment: 1 pag
Quantum fidelity approach to the ground state properties of the 1D ANNNI model in a transverse field
In this work we analyze the ground-state properties of the
one-dimensional ANNNI model in a transverse field using the quantum fidelity
approach. We numerically determined the fidelity susceptibility as a function
of the transverse field and the strength of the next-nearest-neighbor
interaction , for systems of up to 24 spins. We also examine the
ground-state vector with respect to the spatial ordering of the spins. The
ground-state phase diagram shows ferromagnetic, paramagnetic, floating,
phases, and we predict an infinite number of modulated phases in
the thermodynamic limit (). The transition lines
separating the modulated phases seem to be of second-order, whereas the line
between the floating and the phases is possibly of first-order.Comment: 10 pages, 20 figure
Dynamics of the Potts model on a fractal lattice
The dynamics of the q-state Potts model on a fractal lattice is studied using Monte Carlo simulations. The Glauber dynamics is used leading to an effective temperature-dependent critical exponent of the form z = AK + B implying the breakdown of conventional dynamic scaling. The value of A is shown to be independent of q, within the error bars
Dynamical properties of an harmonic oscillator impacting a vibrating wall
The dynamics of a spring-mass system under repeated impact with a vibrating wall is investigated using the static wall approximation. The evolution of the harmonic oscillator is described by two coupled difference equations. These equations are solved numerically, and in some cases exact analytical expressions have also been found. For a periodically vibrating wall, Fermi acceleration is only found at resonance. There, the average rebounding velocity increases linearly with the number of collisions. Near resonance, the average rebounding velocity grows initially with the number of collisions and eventually reaches a plateau. In the vicinity of resonance, the motion of the oscillator exhibits scaling properties over a range of frequency ratios. The presence of dissipation at resonance destroys the Fermi-acceleration process and induces scaling behavior similar to that at near resonance. For a moving wall with a random amplitude at collisions, Fermi acceleration is observed independently of the ratio between the wall and oscillator frequencies. In this case the average rebounding velocity grows with the square root of the number of collisions with the wall. Also, in this latter case, dissipation suppresses the Fermi-acceleration mechanism and induces a scaling behavior with the same universality class as that of the dissipative bouncing ball model with random external perturbations
Multicritical Points And Reentrant Phenomenon In The BEG Model
The Blume - Emery - Griffiths model is investigated by use of the cluster
variation method in the pair approximation. We determine the regions of the
phase space where reentrant phenomenon takes place. Two regions are found,
depending on the sign of the reduced quadrupole - quadrupole coupling strength
. For negative we find Para-Ferro-Para and Ferro-Para-Ferro-Para
transition sequences; for positive , a Para-Ferro-Para sequence.
Order parameters, correlation functions and specific heat are given in some
typical cases. By-products of this work are the equations for the critical and
tricritical lines.Comment: 14 pages, figures available upon reques
Phase transitions in the two-dimensional super-antiferromagnetic Ising model with next-nearest-neighbor interactions
We use Monte Carlo and Transfer Matrix methods in combination with
extrapolation schemes to determine the phase diagram of the 2D
super-antiferromagnetic (SAF) Ising model with next-nearest-neighbor (nnn)
interactions in a magnetic field. The interactions between nearest-neighbor
(nn) spins are ferromagnetic along x, and antiferromagnetic along y. We find
that for sufficiently low temperatures and fields, there exists a region
limited by a critical line of 2nd-order transitions separating a SAF phase from
a magnetically induced paramagnetic phase. We did not find any region with
either first-order transition or with re-entrant behavior. The nnn couplings
produce either an expansion or a contraction of the SAF phase. Expansion occurs
when the interactions are antiferromagnetic, and contraction when they are
ferromagnetic. There is a critical ratio R_c = 1/2 between nnn- and
nn-couplings, beyond which the SAF phase no longer exists.Comment: 12 pages, 10 figure
Corrections to scaling for diffusion in disordered media
We study the diffusion of a particle in a d-dimensional lattice where disorder arises from a random distribution of waiting times associated with each site of the lattice. Using scaling arguments we derive, in addition to the leading asymptotic behaviour, the correction-to-scaling terms for the mean square displacement. We also perform detailed Monte Carlo simulations for one, two and three dimensions which give results in substantial agreement with the scaling argument predictions
Comment on Long-Time Dynamics via Direct Summation of Infinite Continued Fractions
A Comment on the Letter by Z.-X. Cai et al., Phys. Rev. Lett. 68, 1637 (1992)
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