Autowave Structures Research Articles

GROWTH TIME OF ACOUSTIC PERTURBATIONS IN ISENTROPICALLY
 UNSTABLE HEAT-RELEASING MEDIUM

Isentropic instability is a type of thermal instability that leads to the growth of acoustic waves. As a result of wave growth in such media, autowave structures are formed, the parameters of which depend only on the properties of the medium and can be predicted both analytically and numerically. This study aims to answer the question of how quickly these structures can form in an isentropically unstable medium with parameters similar to Orion Bar. It is shown that the growth time depends on the characteristic size of the initial perturbation. The fastest growing structures take 3-6 thousand years to reach half their maximum amplitude. Further growth to the maximum value takes 15-20 thousand years.

Spiral and target wave chimeras in a 2D network of nonlocally coupled van der Pol oscillators

Abstract We study numerically autowave structures in a two-dimensional lattice of van der Pol oscillators for the cases of local and nonlocal coupling between the individual oscillators. It is shown that classical spiral wave and target wave regimes are observed in the network. When the nonlocal coupling between the elements is introduced, complex spatio-temporal structures, including chimera states, can be realized. We reveal and describe single- and multi-core spiral wave chimeras (SWC), as well as a novel type of chimera state which is based on target waves and called a target wave chimera (TWC). We investigate and compare the features of SWC and TWC incoherent cores. Finally, we study how the system dynamics changes when the coupling parameters are varied and discuss the impact of external noise on the observed wave structures.

Heat Criterion of the Change of Strain-Hardening Stages in Austenitic Stainless Steel

The infrared thermography method was used to study changes in the temperature of austenitic stainless steel in the process of tensile deformation. It was revealed that the temperature of the sample stops growing in the transition region between the linear stages of strain hardening. This phenomenon can be connected with a change in the entropy of the deformed medium as a result of a reconstruction of the ordered autowave structures. In the region of true deformation exceeding 0.4, a phenomenon of discontinuous flow (Portevin–Le Chậtelier effect) is observed, which is accompanied by the motion of the single fronts of localized deformation. The observed fronts are heat sources, and the value of the temperature at the arbitrary point of the sample is determined by its position relative to the front of deformation.

Autowave Self-Organization in the Folding of Proteins

A review of physical regularities in formation of the the spatial structure of proteins during their folding, that is, the folding of a homochiral polypeptide chain into a unique native configuration, is presented, including the mathematical models of this process. The materials of this review are summarized in a new phenomenological model for the formation of hierarchies of sign-alternating chiral structures and also in a new mathematical model for the formation of α-helices as autowave structures. Some folding thermodynamic aspects associated with symmetry factors are discussed.

Investigation of the mechanism of emergence of autowave structures at the reaction front.

A qualitative mechanism for autowave pattern formation at the reaction front, observed in certain chemical systems including combustion, is suggested. It is assumed that patterns are formed as a result of interaction of two subsystems, one of which is responsible for the reaction front propagation while the other determines the formation of waves at the front. A corresponding phenomenological model is constructed in which reaction front propagation is described by a submodel of the Fisher-Kolmogorov-Petrovskii-Piskunov type and waves on the front are described by a submodel of the FitzHugh-Nagumo type. In the three-dimensional numerical analysis, it is demonstrated that the model is able to qualitatively explain the emergence of wave patterns of both spiral and target types, which are experimentally observed at the reaction front. The dependence of these patterns on the velocity and thickness of the front is examined.

The asymptotic theory of the generation of long-wave structures in critical layers of weakly dissipative jet flows

The mechanisms of the large-scale vortex structures formation in zonal jet flows (atmospheric blockings, cyclonic, and anticyclonic vortices) is investigated. Nonlinear perturbations formed during the onset of barotropic instability of a long-wave mode in weakly-dissipative and weakly supercritical jet flows with a symmetric velocity profile are considered in the β-plane approximation. This analysis is performed within the framework of the asymptotic theory based on the concept of a nonlinear critical layer. The equations describing the interaction of a wave with vorticity perturbations in a critical layer are derived. The regimes of a quasi-stationary and nonstationary nonlinear critical layer are considered separately. Combined equations of evolution covering the principle regimes of instability development are proposed. The existence of autowave-type structures characterized by a balance between the energy receipt to the wave and its dissipation are obtained within the framework of a numerical simulation. The dependence of the parameters of generated autowave structures on the shape of the zonal jet profile and the flow supercriticality level is studied.

Periodic autowave structures in a wide-aperture laser with inertial phase nonlinearity

The formation of a periodic structure of the optical field of a wide-aperture laser with inertial Kerr phase nonlinearity is considered. The conditions for the appearance of one-dimensional periodic wave structures propagating along the aperture are found and their properties are studied.

Steady-state autowave patterns in a two-dimensional excitable medium with a band of different excitability

A kinematic approach is used to construct steady-state traveling wave patterns in a two-dimensional excitable medium with a band of different excitability. New stationary autowave structures of bell-like shape are shown to exist when the excitability in a band is decreased compared to surrounding areas. The front profiles of the patterns and their propagation velocities are evaluated. Total internal reflection of waves from a band of higher excitability is predicted. The failure of steady-state propagation because of the critical curvature effect is discussed.

Possibility of the appearance of spin autowaves in a model of a ferromagnet with nonuniform dissipation

A model of a ferromagnet with nonuniform dissipation is introduced for the Landau-Lifshitz equations. It is shown that in this model a ferromagnet can be regarded as an oscillating active medium where the formation of autowave structures — spin autowaves, pacemakers, and spiral waves — is possible. Their wave characteristics, expressed in terms of the parameters of the medium, are found for a special case.

Non-spiral autowave structures in unrestricted excitable media

New non-spiral propagating autowave structures in unrestricted excitable media are predicted theoretically. The front shape of the new structures is evaluated analytically. The structures are shown to be stable with respect to small wave front perturbations.

Kinematics of autowave structures in excitable media

We consider an approximate approach to the description of complex space-time structures in different types of excitable media based on the kinematics of autowave fronts. Because of the generality and relative simplicity of the kinematic approach, it is possible to obtain analytical results for different types of autowave motion in two and three-dimensional excitable media. The kinematic approach is used to treat steady-state autowave structures and also to study the evolution of autowaves in inhomogeneous, time-dependent and anisotropic media.

Kinematika avtovolnovykh struktur v vozbudimykh sredakh

Kinematika avtovolnovykh struktur v vozbudimykh sredakh

Dynamic pattern processing with adaptive excitable media

We use an excitable medium for dynamic pattern processing. For this purpose the autowave structures arising from the light-sensitive Belouzov-Zhabotinsky reaction could serve as attractors. The dynamics is simulated as a non-linear network with local interaction in terms of cellular automata. With the help of a set of threshold electrodes the actual state is projected into a space of bytes. At the end of the adaptation procedure for the parameters we achieved the ability of this system for pattern recognition. Dynamic and statis pattern processing are compared with respect to information capacity and adaption time.