Metastable states in the J_{1}-J_{2} Ising model.

We study the J_{1}-J_{2} Ising model on the square lattice using the random local field approximation (RLFA) and Monte Carlo (MC) simulations for various values of the ratio p=J_{2}/|J_{1}| with antiferromagnetic coupling J_{2}, ensuring spin frustration. RLFA predicts metastable states with zero order parameter (polarization) at low temperature for p∈(0,1). This is supported by our MC simulations, in which the system relaxes into metastable states with not only zero, but also with arbitrary polarization, depending on its initial value, external field, and temperature.

Beyond the decoupling approximation in the model free approach for the interpretation of NMR relaxation of macromolecules in solution.

The model free (MF) approach allows straightforward extraction of generalized order parameters and correlation times for internal and overall bond vector reorientational fluctuations from NMR spin relaxation measurements for macromolecules in solution. The drawback of this approach is the use of a decoupling approximation that neglects correlations between internal and overall molecular motions. These correlations are significant when fluctuation amplitudes are less than the size of the "cage" that restricts the bond vector.

Phase mixing, induced relaxation, and chaos in one-dimensional dynamical systems.

This paper investigates the mechanism of induced phase mixing, which leads to effective dissipation in classical nonlinear dynamical systems with a fast modulation of the potential. The suggested model can be applied to a classical dynamical description of cold atomic clouds in optical traps. We show that the parametric nonadiabatic modulation of the laser intensity can provide a tool for dynamical control of the effective relaxation in such systems.

Configurational disorder and the local field effects in nonlinear optical systems.

We argue that in nonlinear optical systems with atoms randomly distributed in crystals or amorphous hosts one should go beyond the Clausius-Mossoti limit in order to take into account the effect of local eld uctuations induced by congurational disorder in atom position. This eect is analyzed by means of a random local mean field approach with neglect of correlations between dipole moments of different atoms. The formalism is applied to 3-level type systems with quantum coherence possessing an absorptionless index of refraction and lasing without inversion.