Quantum breathers in a finite Heisenberg spin chain with antisymmetric interactions

A study of the likelihood of quantum breathers in a quantum Heisenberg spin system including a Dzyaloshinsky-Moriya interaction (DMI) is done through an extended Bose-Hubbard model while using the scheme of few body physics. The energy spectrum of the resulting Bose-Hubbard Hamiltonian, on a periodic one-dimensional lattice containing more than two quanta shows interesting detailed band structures. From a non degenerate, and a degenerate perturbation theory in addition to a numerical diagonalization, a careful investigation of these fine structures is set up. The attention is focussed on the effects of various interactions that are; the DMI, the Heisenberg in-plane (X, Y) as well as the out of plane exchange interaction on the energy spectrum of such a system. The outcome displays a possibility of an energy self-compensation in the system. We also computed the weight function of the eigenstates in direct space and in the space of normal modes. From a perturbation theory it is shown that the interaction between the quanta leads to an algebraic localization of the modified extended states in the normal-mode space of the non-interacting system that are coined quantum q-breathers excitations

Nonlinear spring model for frictional stick-slip motion

Frictional stick-slip dynamics is discussed using a model of one oscillator pulled by a nonlinear spring force. We focus our attention on the nonlinear spring parameter k0. The dynamics of the model is carefully studied, both numerically and analytically. Our numerical investigation, which involves bifurcation diagrams, shows a rich spectrum of dynamical behavior including periodic, quasi-periodic and chaotic states. On the other hand, and for a good selection of parameters , the motion of the particle involves periodic stick-slip, erratic and intermittent motions, characterized by force fluctuations, and sliding. This study suggests that the transition between each of motion strongly depends on the nonlinear parameter k0. The system also displays resonance at fractional frequencies of the oscillator

Nonlinear dynamics for magnetic systems with a single-spin potential with variable shapes

Results of computer simulations to investigate the spin dynamics of a classical ferromagnet subject to easy-plane anisotropy and a parameterized Zeeman energy are reported. The variability of the Zeeman term induces a deformable substrate potential in the system. The results show substantial deviations between the conventional sine-Gordon and deformable sine-Gordon description. Solitary-like solutions, shock waves, nanopteron waves and a variety of phenomena, including large easy-plane deviations are also observed. The results display ballistic, diffusive as well as stochastic behaviors. The region of parameters and limits of applicability of deformability effects induced by parameterization of the Zeeman energy are examined. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005

Non-Hermitian Hamiltonian of two-level systems in complex quaternionic space: An introduction in electronics

An imaginary resistor (Z) based electronic dimer is used to describe the gyroscopic and resistive coupled two-level systems in quaternionic space. We successfully used the quaternionic coefficients to characterize the different classes of non-Hermitian systems: the pseudo-Hermitian and anti-Hermitian, both having exceptional points (EPs) separating the exact and the broken phases. Remarkably, the EPs conical dynamic is fully described to follow a hyperbolic/parabolic shape in the case of parity-time symmetry (PTS)/anti-PTS, respectively. Interestingly, our results demonstrated that the gyroscopic coupling mechanism allows identical non-dissipative but non-oscillatory systems with negative capacitor to exhibit PTS-like behavior

Dry friction: motions – map, characterization and control

We consider a simple model of spring-mass block placed over a constant velocity v rolling plate. The map of the dynamic is presented in the (v,r) space where r accounts for the possible variation of the periodic shape profile of the rolling carpet. In order to characterize each type of motion, we found that evaluating the area of the phase space trajectories is more relevant than attempting on one hand, to solve analytically the asymptotic behavior, or on the other hand, to obtain an equivalent of the entropy and the free energy. First-order transition reveals to be the characteristic route from one type of motion to another. Later, we investigate the influence of the classical TMD1 and TLCD2 on the dynamic of this mass. Moreover, we numerically study the effects of a modified TMD. Reduced order parameter provides a quick overview of the whole system than phase space representations and bifurcation diagrams. Comparison of performances in the (v,r) space is made. It reveals the efficiency of the modified TMD. It comes out that the new TMD we designed stabilizes the system better than the two above control systems

Nonlinear spring model for frictional stick-slip motion

46.55.+d Tribology and mechanical contacts, 68.35.Gy Mechanical properties; surface strains, 81.40.Pq Friction, lubrication, and wear,