Random matrix theory for low-frequency sound propagation in the ocean: a spectral statistics test

Problem of long-range sound propagation in the randomly-inhomogeneous deep ocean is considered. We examine a novel approach for modeling of wave propagation, developed by K.C.Hegewisch and S.Tomsovic. This approach relies on construction of a wavefield propagator using the random matrix theory (RMT). We study the ability of the RMT-based propagator to reproduce properties of the propagator corresponding to direct numerical solution of the parabolic equation. It is shown that mode coupling described by the RMT-based propagator is basically consistent with the direct Monte-Carlo simulation. The agreement is worsened only for relatively short distances, when long-lasting cross-mode correlations are significant. It is shown that the RMT-based propagator with properly chosen range step can reproduce some coherent features in spectral statistics.Comment: 23 pages, 13 figure

Order-to-chaos transition in the model of a quantum pendulum subjected to noisy perturbation

Motion of randomly-driven quantum nonlinear pendulum is considered. Utilizing one-step Poincar\'e map, we demonstrate that classical phase space corresponding to a single realization of the random perturbation involves domains of finite-time stability. Statistical analysis of the finite-time evolution operator (FTEO) is carried out in order to study influence of finite-time stability on quantum dynamics. It is shown that domains of finite-time stability give rise to ordered patterns in distributions of FTEO eigenfunctions. Transition to global chaos is accompanied by smearing of these patterns; however, some of their traces survive on relatively long timescales

Dynamics of BEC mixtures loaded into the optical lattice in the presence of linear inter-component coupling

We consider dynamics of a two-component Bose-Einstein condensate where the components correspond to different hyperfine states of the same sort of atoms. External microwave radiation leads to resonant transitions between the states. The condensate is loaded into the optical lattice. We invoke the tight-binding approximation and examine the interplay of spatial and internal dynamics of the mixture. It is shown that internal dynamics qualitatively depends on the intra-component interaction strength and the phase configuration of the initial state. We focus attention on two intriguing phenomena occurring for certain parameter values. The first phenomenon is the spontaneous synchronization of Rabi oscillations running inside neighbouring lattice sites. Another one is the demixing of the condensate with formation of immiscible solitons when nonlinearity becomes sufficiently strong. Demixing is preceded by the transient regime with highly irregular behavior of the mixture.Comment: Accepted for publication in the Journal of Russian Laser Researc

A numeric-analytical method for solving the Cauchy problem for ordinary differential equations

In the paper we offer a functional-discrete method for solving the Cauchy problem for the first order ordinary differential equations (ODEs). This method (FD-method) is in some sense similar to the Adomian Decomposition Method. But it is shown that for some problems FD-method is convergent whereas ADM is divergent. The results presented in the paper can be easily generalized on the case of systems of ODEs

Stability preserving structural transformations of systems of linear second-order ordinary differential equations

In the paper we have developed a theory of stability preserving structural transformations of systems of second-order ordinary differential equations (ODEs), i.e., the transformations which preserve the property of Lyapunov stability. The main Theorem proved in the paper can be viewed as an analogous of the Erugin's theorem for the systems of second-order ODEs. The Theorem allowed us to generalize the 3-rd and 4-th Kelvin -- Tait -- Chetayev theorems. The obtained theoretical results were successfully applied to the stability investigation of the rotary motion of a rigid body suspended on a string.Comment: 40 page

Quantum transport in a driven disordered potential: onset of directed current and noise-induced current reversal

We study motion of a quantum wavepacket in a one-dimensional potential with correlated disorder. Presence of long-range potential correlations allows for existence of both localized and extended states. Weak time-dependent perturbation in the form of a fluctuating plane wave is superimposed onto the potential. This model can be realized in experiments with optically trapped cold atoms. Time-dependent perturbation causes transitions between localized and extended states. Owing to violation of space-time symmetries, there arises atomic current which is codirectional with the wave-like perturbation. However, it is shown that the perturbation can drag atoms only within some limited time interval, and then the current changes its direction. Increasing of the perturbation bandwidth and/or amplitude results in decreasing of the time of current reversal. We argue that onset of the current reversal is associated with inhomogeneity of diffusion in the momentum space

A Superexponentially Convergent Functional-Discrete Method for Solving the Cauchy Problem for Systems of Ordinary Differential Equations

In the paper a new numerical-analytical method for solving the Cauchy problem for systems of ordinary differential equations of special form is presented. The method is based on the idea of the FD-method for solving the operator equations of general form, which was proposed by V.L. Makarov. The sufficient conditions for the method converges with a superexponential convergence rate were obtained. We have generalized the known statement about the local properties of Adomian polynomials for scalar functions on the operator case. Using the numerical examples we make the comparison between the proposed method and the Adomian Decomposition Method.Comment: 33 pages, 6 figure

Exponentially convergent functional-discrete method for eigenvalue transmission problems with discontinuous flux and potential as a function in the space L1L_1

Based on the functional-discrete technique (FD-method), an algorithm for eigenvalue transmission problems with discontinuous flux and integrable potential is developed. The case of the potential as a function belonging to the functional space $L_1$ is studied for both linear and nonlinear eigenvalue problems. The sufficient conditions providing superexponential convergence rate of the method were obtained. Numerical examples are presented to support the theory. Based on the numerical examples and the convergence results, conclusion about analytical properties of eigensolutions for nonself-adjoint differential operators is made.Comment: 27 pages, 11 tables, 9 figure

The FD-method for solving nonlinear Klein-Gordon equation

In the paper we present a functional-discrete method for solving the Goursat problem for nonlinear Klein-Gordon equation. The sufficient conditions providing that the proposed method converges superexponentially are obtained. The results of numerical example presented in the paper are in good agreement with the theoretical conclusions.Comment: 20 page

Exponentially convergent functional-discrete method for solving Sturm-Liouville problems with potential including Dirac \delta-function

In the paper we present a functional-discrete method for solving Sturm-Liouville problems with potential including function from L_{1}(0,1) and \delta-function. For both, linear and nonlinear cases the sufficient conditions providing superexponential convergence rate of the method are obtained. The question of possible software implementation of the method is discussed in detail. The theoretical results are successfully confirmed by the numerical example included in the paper.Comment: 29 pages, 7 figures, 3 table