Fernando D. Nobre

Phase diagram of the two-dimensional Ising model with random competing interactions

Abstract An Ising model with ferromagnetic nearest-neighbor interactions J 1 ( J 1 > 0 ) and random next-nearest-neighbor interactions [ + J 2 with probability p and − J 2 with probability ( 1 − p ) ; J 2 > 0 ] is studied within the framework of an effective-field theory based on the differential-operator technique. The order parameters are calculated, considering finite clusters with n = 1 , 2 , and 4 spins, using the standard approximation of neglecting correlations. A phase diagram is obtained in the plane temperature versus p, for the particular case J 1 = J 2 , showing both superantiferromagnetic (low p) and ferromagnetic (higher values of p) orderings at low temperatures.

Travelling-wave and separated variable solutions of a nonlinear Schroedinger equation

Some interesting nonlinear generalizations have been proposed recently for the linear Schroedinger, Klein-Gordon, and Dirac equations of quantum and relativistic physics. These novel equations involve a real parameter q and reduce to the corresponding standard linear equations in the limit q → 1. Their main virtue is that they possess plane-wave solutions expressed in terms of a q-exponential function that can vanish at infinity, while preserving the Einstein energy-momentum relation for all q. In this paper, we first present new travelling wave and separated variable solutions for the main field variable Ψ(x→,t), of the nonlinear Schroedinger equation (NLSE), within the q-exponential framework, and examine their behavior at infinity for different values of q. We also solve the associated equation for the second field variable Φ(x→,t), derived recently within the context of a classical field theory, which corresponds to Ψ∗(x→,t) for the linear Schroedinger equation in the limit q → 1. For x ∈ ℜ, we show t...

Controlling the range of interactions in the classical inertial ferromagnetic Heisenberg model: analysis of metastable states

A numerical analysis of a one-dimensional Hamiltonian system, composed by

Thermodynamic framework for compact q-Gaussian distributions

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A thermodynamical formalism describing mechanical interactions

classical localized Heisenberg rotators on a ring, is presented. A distance

One-step replica-symmetry-breaking solution of the Sherrington?Kirkpatrick model under a Gaussian random field

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Ising spin glasses on Wheatstone–Bridge hierarchical lattices

between rotators at sites

Spin-glass attractor on tridimensional hierarchical lattices in the presence of an external magnetic field

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Chaos and stiffness exponents for short-range Gaussian Ising spin glasses

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Minding impacting events in a model of stochastic variance.

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