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## Beats in the system of three non-linear oscillators and their quantum analog

oscillators. The only known realization of similar process in the short homogenous chain with more then two elements refers to the three-well quantum system with the same coupling between the wells providing the special condition on the equations describing the system. However, this condition does not appear to hold in classical homogenous cou- pled systems, that makes the full periodic energy exchange in the systems of three classi- cal oscillators questionable. Here we prove that fully reciprocal periodic energy transport between the ends of a short homogenous chain of nonlinear oscillators is possible in the conservative classical system with the ‘soft’ nonlinearity. The analogy with the quantum system of the coherent (harmonic) quantum Rabi oscillations in a superposition of three quantum states helps to reveal the special condition on the effective on-site potentials, which does not exist in the classical linear system or system of more than two oscillators with ‘hard’ nonlinearity. We study the periodic energy transport and its localization with use of the regular asymptotic analysis in the reduced phase space. The reported effects can be significant for many fundamental and applied areas of sciences where the coherent energy transport is important.

In our earlier studies, we found the effect of non-conventional synchronization, which is a specific type of nonlinear stable beating in the system of two weakly coupled autogenerators with hard excitation given by generalized van der Pol-Duffing characteristics. The corresponding synchronized dynamics are due to a new type of attractor in a reduced phase space of the system. In the present work, we show that, as the strength of nonlinear stiffness and dissipation are changing, the phase portrait undergoes a complicated evolution leading to a quite unexpected appearance of difficult to detect “repellers” separating a stable limit cycle and equilibrium points in the phase plane. In terms of the original coordinates, the limit cycle associates with nonlinear beatings while the stationary points correspond to the stationary synchronous dynamics similar to the so-called nonlinear local modes.

In the present paper, we study the mechanism of formation and bifurcations of highly nonstationary regimes manifested by different energy transport intensities, emerging in an anharmonic trimer model. The basic model under investigation comprises a chain of three coupled anharmonic oscillators subject to localized excitation, where the initial energy is imparted to the first oscillator only. We report the formation of three basic nonstationary transport states traversed by locally excited regimes. These states differ by spatial energy distribution, as well as by the intensity of energy transport along the chain. In the current study, we focus on numerical and analytical investigation of the intricate resonant mechanism governing the inter-state transitions of locally excited regimes. Results of the analytical study are in good agreement with the numerical simulations of the trimer model.

A problem of synchronization of quasiperiodic oscillations is discussed in application to an example of coupled systems with autonomous quasiperiodic dynamics. Charts of Lyapunov exponents are presented that reveal characteristic domains on the parameter plane such as oscillator death, complete synchronization, phase synchronization of quasiperiodic oscillations, broadband synchronization, broadband quasiperiodicity. Features of each kind of dynamical behavior are discussed. Analysis of corresponding bifurcations is presented, including quasiperiodic Hopf bifurcations, saddle–node bifurcations of invariant tori of different dimensions, and bifurcations of torus doublings. Both the case of dominance of quasiperiodic oscillations in one of the generators and the case of pronounced periodic resonances embedded in the region of quasiperiodicity are considered.

Challenges to simulate networks of weakly coupled oscillators using circuit simulators are considered. The approach based on the special locking function is presented. The application of system of the phase equations based on locking functions for estimation of locking range of weakly coupled oscillator networks is shown.

The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.

Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.

Let k be a field of characteristic zero, let G be a connected reductive algebraic group over k and let g be its Lie algebra. Let k(G), respectively, k(g), be the field of k- rational functions on G, respectively, g. The conjugation action of G on itself induces the adjoint action of G on g. We investigate the question whether or not the field extensions k(G)/k(G)^G and k(g)/k(g)^G are purely transcendental. We show that the answer is the same for k(G)/k(G)^G and k(g)/k(g)^G, and reduce the problem to the case where G is simple. For simple groups we show that the answer is positive if G is split of type A_n or C_n, and negative for groups of other types, except possibly G_2. A key ingredient in the proof of the negative result is a recent formula for the unramified Brauer group of a homogeneous space with connected stabilizers. As a byproduct of our investigation we give an affirmative answer to a question of Grothendieck about the existence of a rational section of the categorical quotient morphism for the conjugating action of G on itself.

Let G be a connected semisimple algebraic group over an algebraically closed field k. In 1965 Steinberg proved that if G is simply connected, then in G there exists a closed irreducible cross-section of the set of closures of regular conjugacy classes. We prove that in arbitrary G such a cross-section exists if and only if the universal covering isogeny Ĝ → G is bijective; this answers Grothendieck's question cited in the epigraph. In particular, for char k = 0, the converse to Steinberg's theorem holds. The existence of a cross-section in G implies, at least for char k = 0, that the algebra k[G]G of class functions on G is generated by rk G elements. We describe, for arbitrary G, a minimal generating set of k[G]G and that of the representation ring of G and answer two Grothendieck's questions on constructing generating sets of k[G]G. We prove the existence of a rational (i.e., local) section of the quotient morphism for arbitrary G and the existence of a rational cross-section in G (for char k = 0, this has been proved earlier); this answers the other question cited in the epigraph. We also prove that the existence of a rational section is equivalent to the existence of a rational W-equivariant map T- - - >G/T where T is a maximal torus of G and W the Weyl group.