Modified sine-Gordon Equation Research Articles

Nonlinear waves of the sine-Gordon equation in the model with three attracting impurities

Purpose of this work is to use analytical and numerical methods to consider the problem of the structure and dynamics of coupled localized nonlinear waves in the sine-Gordon model with impurities (or spatial inhomogeneity of the periodic potential). Methods. Using the analytical method of collective coordinates for the case of the arbitrary number the same point impurities on the same distance each other, differential equation system was got for localized waves amplitudes as the functions on time. We used the finite difference method with explicit scheme for the numerical solution of the modified sine-Gordon equation. We used a discrete Fourier transform to perform a frequency analysis of the oscillations of localized waves calculate numerically. Results. We found of the differential equation system for three harmonic oscillators with the elastic connection for describe related oscillations of nonlinear waves localized on the three same impurity. The solutions obtained from this system of equations for the frequencies of related oscillation well approximate the results of direct numerical modeling of a nonlinear system. Conclusion. In the article shows that the related oscillation of nonlinear waves localized on three identical impurities located at the same distance from each other represent the sum of three harmonic oscillations: in-phase, in-phase-antiphase and antiphase type. The analysis of the influence of system parameters and initial conditions on the frequency and type of associated oscillations is carried out.

Numerical search for the stationary quasi-breather of the graphene superlattice equation

The propagation of electromagnetic solitons in a graphene superlattice device is governed by a modified sine-Gordon equation, referred to as the graphene superlattice equation. Kink-antikink collisions suggest the existence of a quasi-breather solution. Here, a numerical search for static quasi-breathers is undertaken by using a new initial condition obtained by a regular perturbation of the null solution. Our results show that the frequency of the initial condition has a minimum critical value for the appearance of a robust quasi-breather able to survive during more than one thousand periods. The amplitude and energy of the quasi-breather solution decrease, but its frequency increases, as time grows. The robustness of the new quasi-breather supports its experimental search in real graphene superlattice devices.

Fractal structure of the soliton scattering for the graphene superlattice equation

The graphene superlattice equation, a modified sine-Gordon equation, governs the propagation of solitary electromagnetic waves in a graphene superlattice. This equation has kink solutions without explicit analytical expression, requiring the use of quadrature methods. The inelastic collision of kinks and antikinks with the same but opposite speed is studied numerically for the first time; after their interaction they escape to infinity when its speed is either larger than a critical value or it is inside a series of resonance windows; otherwise, they form a breather-like state that slowly decays by radiating energy. Here, the fractal structure of these resonance windows is characterized by using a multi-index notation and their main features are compared with the predictions of the resonant energy exchange theory showing good agreement. Our results can be interpreted as new evidence in favour of this theory.

New Exact Solutions for the Coupled Nonlinear Schrödinger Equations with Variable Coefficients

In this paper, coupled nonlinear Schrodinger equations with variable coefficients are studied, which can be used to describe the interaction among the modes in nonlinear optics and Bose-Einstein condensation. Some novel bright-dark solitons and dark-dark solitons are obtained by modified Sine-Gordon equation method. Moreover, some figures are provided to illustrate how the soliton solutions propagation is determined by the different values of the variable group velocity dispersion terms, which can be used to model various phenomena.

Solitary wave solutions for the variable-coefficient coupled nonlinear Schrödinger equations and Davey–Stewartson system using modified sine-Gordon equation method

In this study, the sine-Gordon equation method is modified to deal with variable-coefficient systems containing imaginary parts, such as nonlinear Schrödinger systems. These are of considerable importance in many fields of research, including ocean engineering and optics. As an example, we apply the modified method to variable-coefficient coupled nonlinear Schrö dinger equations and Davey–Stewartson system with variable coefficients, treating them as one-dimensional and two-dimensional systems, respectively. As a result of this application, novel solitary wave solutions are obtained for both cases. Moreover, some figures are provided to illustrate how the solitary wave propagation is determined by the different values of the variable group velocity dispersion terms, which can be used to model various phenomena.

Integrable generalizations of the sine-Gordon, short pulse, and reduced Maxwell–Bloch equations

The multi-parameter generalizations of the sine-Gordon (SG), short pulse (SP), and reduced Maxwell–Bloch (RMB) equations are considered. These generalizations are integrable by the inverse scattering transformation method and connected with the modified SG equation, its limiting case, and the modified RMB equations by the changes of the dependent and independent variables expressed in terms of the conserved densities and fluxes of the latter. The particular cases of the generalizations considered include the Rabelo–Fokas (RF) equation, the modified SP equation, and some other equations. The properties of the soliton solutions of some of the generalizations are studied. It is revealed that the interaction of the well-defined solitons of the RF equation and the corresponding version of the RMB equations leads to an appearance of the intervals in some regions of the soliton parameters, where the solution becomes multi-valued, and to the blow-up of the solution. In addition, the compacton-like soliton solutions can exist in some cases.

Modeling of the mode dynamics generated by Madison Symmetric Torus machine utilizing a modified sine-Gordon equation

In this paper, a new dynamic model is presented for the experimental data generated by the Madison Symmetric Torus (MST) machine. The model is based on a modified sine-Gordon (SG) dynamic equation. The modified sine-Gordon equation model effectively captures the behavior of the slinky mode in reversed-field pinch experiments. In addition, this paper demonstrates how the derived model accurately describes the behavior of the localized magnetohydrodynamic mode (slinky mode) that appears in reversed-field pinch toroidal magnetic confinement systems. The modified SG equation model is solved analytically by using the perturbation method. The resulting model is fit to match a variety of experimental results in the MST reversed-field pinch experiment. The efficacy of the newly developed model in effectively representing the slinky mode is verified by comparing obtained analytical solution to experimentally measured data.

The influence of the DNA torque on the dynamics of transcription bubbles in plasmid PTTQ18

In this work, we study numerically the influence of the DNA torque on the movement of transcription bubbles in the potential field formed by the sequence of plasmid PTTQ18. To imitate the movement, we apply a modified sine-Gordon equation with the two additional terms that describe the effects of dissipation and the action of the DNA torsion torque, and with the coefficients that depend on the sequence of bases. We obtain the trajectories of the transcription bubbles and investigate the dependence of the trajectories on the initial bubble velocity and the DNA torsion torque. It is shown that not the initial bubble velocity but the DNA torsion torque governs the trajectories of the transcription bubbles.

New integrable model of propagation of the few-cycle pulses in an anisotropic microdispersed medium

We investigate the propagation of the few-cycle electromagnetic pulses in the anisotropic microdispersed medium. The effects of the anisotropy and spatial dispersion of the medium are created by the two sorts of the two-level atoms. The system of the material equations describing an evolution of the states of the atoms and the wave equations for the ordinary and extraordinary components of the pulses is derived. By applying the approximation of the sudden excitation to exclude the material variables, we reduce this system to the single nonlinear wave equation that generalizes the modified sine–Gordon equation and the Rabelo–Fokas equation. It is shown that this equation is integrable by means of the inverse scattering transformation method if an additional restriction on the parameters is imposed. The multisoliton solutions of this integrable generalization are constructed and investigated.

On the modeling of the motion of a transcription bubble under constant torque

The motion of a transcription bubble under constant torque is investigated. The motion of the bubble was modeled by a modified sine-Gordon equation. Numerical solutions of this equation (kinks) were found. Trajectories of the kink motion in homogeneous and inhomogeneous sequences were calculated for different model values of the torque M τ and the initial velocity v 0. It was shown that a change in the torsion moment M τ has a significant impact on the character of the kink trajectory. At the same time, a change in the initial kink velocity v 0 in a rather wide range of values does not affect the character of the kink trajectory.

Conformational Transitions Control in Polynucleotide Chains by External Frequency-Modulated Exposure

Use of DNA molecules in molecular electronics is very promising. Close relationship between the charge transfer and conformational changes follows from experiment. For the theoretical descriptions of conformational transitions of DNA molecule the kink-like solutions of the modified sine-Gordon equation are mostly used. Our investigations show that the motion of the kink can be controlled by the external exposure.

On the possibility of the observation of the resonance interaction between kinks of the sine-Gordon equation and localized waves in real physical systems

The resonance dynamics of kinks of the sine-Gordon equation in a system with a single point impurity with allowance for the generation of localized waves in the presence of an external force and dissipation has been studied. Equations of motion for the coordinate of the kink center and the amplitude of the impurity mode have been found. The analysis of solutions of these equations and results of the numerical simulation of the modified sine-Gordon equation have showed that damping and the external force act against the appearance of the resonance reflection of the kink from the attractive impurity. However, the resonance energy exchange between solitons causing it still takes place.

On kinks and other travelling-wave solutions of a modified sine-Gordon equation

We give an exhaustive, non-perturbative classification of exact travelling-wave solutions of a perturbed sine-Gordon equation (on the real line or on the circle) which is used to describe the Josephson effect in the theory of superconductors and other remarkable physical phenomena. The perturbation of the equation consists of a constant forcing term and a linear dissipative term. On the real line candidate orbitally stable solutions with bounded energy density are either the constant one, or of kink (i.e. soliton) type, or of array-of-kinks type, or of “half-array-of-kinks” type. While the first three have unperturbed analogs, the last type is essentially new. We also propose a convergent method of successive approximations of the (anti)kink solution based on a careful application of the fixed point theorem.

A comparator based on soliton antisoliton pair generation in soliton diode

Modified sine-Gordon equation is solved for a soliton diode, which is a long Josephson junction in which the magnetic field of the control current reverses its direction at the center. Applying a properly directed bias current can start the spontaneous generation of soliton and antisolitons at the transition region of the diode and leads to a flux-flow voltage. The threshold bias current at which such a voltage generation starts is a function of the control current and the size of the transition region. Such phenomena can find applications in high-speed decision making electronic comparators.

Управление динамикой кинка модифицированного уравнения синус-Гордона внешним воздействием с меняющимися параметрами

В работе представлены результаты, подтверждающие возможность управления движением кинка модифицированного уравнения синус-Гордона внешним воздействием с изменяющимися параметрами. Рассмотрены три типа внешних воздействий: постоянное, периодическое с постоянной частотой и периодическое частотно-модулированное. С использованием метода Мак-Лафлина–Скотта получены зависимости координаты и скорости кинка от времени при разных значениях параметров внешнего воздействия. Показано, что изменяя параметры, можно регулировать скорость и направление движения кинка.

Коллективное влияние примесей на динамику кинков уравнения синус-Гордона

С помощью численных методов исследована динамика кинков модифицированного уравнения синус-Гордона в модели с локализованной пространственной модуляцией периодического потенциала (или примесью). Рассмотрен случай наличия двух одинаковых примесей. Показано, что возможно наблюдение коллективных эффектов влияния примесей, которые сильно зависят от расстояния между ними. Продемонстрировано наличие определенного критического значения расстояния между примесями, которое приводит к двум качественно различным сценариям динамического поведения кинка.

Existence and uniqueness of solutions of a class of third order dissipative problems with various boundary conditions describing the Josephson effect

We prove existence and uniqueness of solutions of a large class of initial–boundary-value problems characterized by a quasi-linear third order equation (the third order term being dissipative) on a finite space interval with Dirichlet, Neumann or pseudoperiodic boundary conditions. The class includes equations arising in superconductor theory, in the form of various modified sine–Gordon equation describing the Josephson effect, and in the theory of viscoelastic materials.

Dynamics of generalized sine-Gordon soliton in inhomogeneous media

In this paper we introduce a few novel generalized sine-Gordon equations and study the dynamics of its solitons in inhomogeneous media. We consider length, mass, gravitational acceleration and spring stiffness of a coupled pendulums chain as a function of position x. Then in the continuum limit we derive semi-analytical and numerical soliton solutions of the modified sine-Gordon equation in the inhomogeneous media. The obtained results confirm that the behavior of solitons in these media is similar to that of a classical point particle moved in an external potential.

Long-range interactions and wave patterns in a DNA model

We propose a spin-like model of DNA nonlinear dynamics with long-range interactions between adjacent base pairs. We show that the model equation is a modified sine-Gordon equation. We perform the linear stability analysis of a plane wave, which predicts high-amplitude and extended oscillating waves for high values of the long-range parameter. This is confirmed numerically and biological implications of the obtained patterns are suggested.

Surface losses and self-pumping effects in a long Josephson junction: A semianalytical approach

The flux-flow dynamics in a long Josephson junction is studied both analytically and numerically. A realistic model of the junction is considered by taking into account a nonuniform current distribution, surface losses and self-pumping effects. An approximate analytical solution of the modified sine-Gordon equation is derived in the form of a unidirectional dense fluxon train accompanied by two oppositely directed plasma waves. Next, some macroscopic time-averaged quantities are calculated making possible to evaluate the current-voltage characteristic of the junction. The results obtained by the present method are compared with direct numerical simulations both for the current-voltage characteristics and for the loss factor modulated spatially due to the self-pumping. The comparison shows very good agreement for typical junction parameters but indicates also some limitations of the method.