Quasi-solitons of magnetostatic waves in a two-layer structure under single-mode excitation

We investigate the quasi-solitons of the envelope of forward body magnetostatic waves in a structure that consists of two magnetically coupled films separated by a nonmagnetic interlayer under the initial excitation of a pulse in one of them. We have found that as the pulse propagates, its energy is transferred from one film to the other through intermode coupling; as a result, “pulsating” quasi-solitons of the coupled modes of the two films emerge. We show that the amplitude of each of the mode pulses at the exit from the waveguide can be regulated over a wide range by varying the magnetizing field.     

On the modulation instability development in optical fiber systems

Extensive numerical simulations were performed to investigate all stages of modulation instability development from the initial pulse of pico-second duration in photonic crystal fiber: quasi-solitons and dispersive waves formation, their interaction stage and the further propagation. Comparison between 4 different NLS-like systems was made: the classical NLS equation, NLS system plus higher dispersion terms, NLS plus higher dispersion and self-steepening and also fully generalized NLS equation with Raman scattering taken into account. For the latter case a mechanism of energy transfer from smaller quasi-solitons to the bigger ones is proposed to explain the dramatical increase of rogue waves appearance frequency in comparison to the systems when the Raman scattering is not taken into account.     

Emergence of rogue waves from optical turbulence

We provide some general physical insights into the emergence of rogue wave events from optical turbulence by analyzing the long term evolution of the field. Depending on the amount of incoherence in the system (i.e., Hamiltonian), we identify three turbulent regimes that lead to the emergence of specific rogue wave events: (i) persistent and coherent rogue quasi-solitons, (ii) intermittent-like rogue quasi-solitons that appear and disappear erratically, and (iii) sporadic rogue waves events that emerge from turbulent fluctuations as bursts of light or intense flashes.     

Theoretical model of terahertz radiation generation by laser pulses with tilted wave fronts

A theoretical model is proposed for terahertz radiation generation by femtosecond laser pulses with tilted wave fronts. Self-consistent evolution of the optical and terahertz pulses is investigated. The red shift of the pumping pulse spectrum and the formation of short-long-wave quasi-solitons are examined.     

Soliton interaction in strongly dispersion-managed optical fibers

We derive an expression for the speed with which neighboring solitons attract or repel each other in dispersion-managed fiber systems. We show that the collapse distance can be increased by an order of magnitude by use of quasi-solitons.     

Quasi-solitonic propagation modes of two-component acoustic video pulses in a paramagnetic crystal

Nonlinear propagation of longitudinal-transverse acoustic pulses down to a length of one cycle (video pulses) in a low-temperature paramagnetic crystal in the direction parallel to an external magnetic field is investigated theoretically. The case of a crystal with paramagnetic impurity ions with effective S=1/2 spin is considered. It is shown that, due to spin-phonon interaction, two-component acoustic pulses can propagate in the form of high-power quasi-solitons. Conditions are determined for the formation of exponentially localized subsonic rational solitons which propagate with a velocity higher than the velocity of transverse sound and which have a transverse component with a rotating plane of polarization.     

Quasi-solitons as nonstationary self-similar solutions of the Korteweg-de Vries-Burgers equation

The Korteweg-de Vries-Burgers equation (KdV-B) is studied analytically and numerically for weak dissipation in the nonstationary case (self-similar solutions). Starting the analytical study from the system (S) of two kinetic equations equivalent to KdV-B equation in the exact adiabatic approximation of a symmetrically damped solitary pulse, we renormalize this system by taking into account the asymmetry produced by the damping (tail) and obtain a simple mechanical picture describing qualitatively and quantitatively the properties of the tailed quasi-solitons: the leading pulse is described by an oscillation in a potential well, while the asymmetry is obtained from a transition between two nearby energy levels located at the top of the well. The superposition properties of the quasi-solitons are discussed in the adiabatic approximation, using a Bäcklund transformation directly deduced from system (S). All these analytical results are checked by the numerical study which shows in particular that the tail, once built, becomes completely disconnected from its “mother” soliton and behaves like noise.     

准孤子对在色散缓变光纤中传输特性的数值研究

用分步富里叶变换法求解色散缓变光纤的光孤子NLS方程，在一定条件下孤子对在该光纤中演变为准孤子，其幅值和宽度发生周期性变化，没有出现通常情况下的周期性离合现象。     

Three-dimensional dissipative quasi-solitons in carbon nanotubes

The propagation of three-dimensional quasi-solitons in a system of carbon nanotubes with two-level impurities has been investigated. The system of effective equations is derived in the form of analogs of the Sine–Gordon classical equation and Bloch equations. The effects observed with a change in the inverse population and damping parameter have been studied.     

不均匀等离子体中孤子的传播

假设两种离子的分界面是有限长度并连续变化的,研究了由这两种离子组成的等离子体中孤子的传播.在低阶近似条件下,等离子体声波将由KdV方程或非线性Schrdinger方程来描述,由此给出了准孤子振幅、传播速度等参量在传播过程中的变化. 关键词：     

Dynamics of incoherent bright and dark self-trapped beams and their coherence properties in photorefractive crystals

Using the coherent density approach, we study the propagation dynamics of incoherent bright and dark beams in biased photorefractive crystals. We show that, under appropriate initial conditions, bright as well as darklike incoherent quasi-solitons can be established in this material system. Our numerical simulations demonstrate that the coherence properties of these beams can be significantly affected by the self-trapping process.     

非均匀尘埃等离子体中孤子的传播

运用约化摄动法研究了非均匀尘埃等离子体中孤子的传播情况. 在低阶近似下, 对于小的、但有限振幅的长波振动, 当分界面不连续变化时,孤子在不连续点的反射波与透射波均可由 KdV 方程来描述, 并给出了低阶近似情况下, 对于小的、但有限振幅的长波振动, 当入射波为单孤子时, 反射孤子与透射孤子的个数及其大小;当分界面是有限长度并连续变化时,对于小的、但有限振幅的长波振动, 尘埃声孤波由KdV型方程来描述,并由此给出了准孤子振幅、传播速度等参量在传播过程中的变化. 关键词： 尘埃等离子体 孤子 KdV方程 约化摄动法     

几何尺寸对圆对称环域Josephson结的准通量子激发的影响

本文研究几何尺寸对圆对称环域Josephson结的扰动SGE的环形准孤子波解的影响.数值计算结果表明,当圆对称环域结的内半径,r₀=7.5λ_J时,已出现对应于环域结准通量子激发的环形准孤子波解,同时在I-V特性曲线上出现第一零场台阶.零场台阶的范围剧烈地依赖于环域结的内半径r₀和结宽度(αr₀-r₀);然而几何尺寸对环形准孤子波解特性的影响则比较复杂. 关键词：     

Transmission of return-to-zero pulses in an optical split-step system based on reflecting fiber gratings

A new variety of the “soliton management” in heterogeneous optical media is proposed. The system is composed as a periodic chain of nonlinear fibers with negligible intrinsic group-velocity dispersion (GVD), alternating with sections of unchirped fiber Bragg gratings (FBGs) operating in the reflection regime. Losses due to incomplete reflection are compensated by linear amplifiers. The model may apply to fiber-optic telecommunication links with periodically installed FBG modules, and it may be used for the design of laser setups. By means of extended simulations, we identify small regions in the underlying parameter space where this model, featuring the periodic separation of the Kerr nonlinearity and FBG-induced GVD (hence the name of the “split-step” system), supports stable transmission of RZ (return-to-zero) pulses, i.e., quasi-solitons. The effect of nonzero fiber’s GVD on the stable transmission regime is considered too. Moderately unstable (partly usable) transmission regimes are found in larger regions of the parameter space; they may be of two different types, with the average nonlinearity either undercompensating or overcompensating the GVD. Interactions between the stable RZ pulses are also studied, leading to the identification of a minimum separation between them necessary for the suppression of interaction effects.     

Automatic sensitivity control in diagnostic ultrasonics

Difficulties associated with swept-gain (ie, time-varied gain) as a means of controlling sensitivity in ultrasonic scanning are considered. Automatic sensitivity control as a possible technique for determining sensitivity is discussed. A simple automatic sensitivity control in the form of automatic gain control (AGC) was constructed and applied in scanning complex tissue structures. It is concluded that automatic sensitivity control allows acceptable ultrasonic images to be produced and involves the operator in little manipulation of controls.     

Identifying and comparing states of time-delayed systems: phase diagrams and applications to human motor control systems

A data driven characterization of time-delayed stochastic systems is proposed in terms of linear delay differential equations and two drift parameters. It is shown how these parameters determine the states of such systems with respect to generalized phase diagrams. This approach allows for a comparison of systems with different parameters as exemplified for two motor control tasks: tracking and force production.     

Miniaturization of Fresnel phase matching using a side-coupled integrated spaced sequence of resonators (SCISSOR)

It is proposed that a side-coupled integrated spaced sequence of resonators (SCISSOR) be used to adapt Fresnel phase matching to the case of highly confining waveguides. As is the case for bulk media, this method of quasi-phase-matching (QPM) allows resonant or nonresonant QPM. This property can be used to control the spectral bandwidth of the phase-matching curve.     

Collision between scalar and vector spatial solitons in Kerr media

Experimental observation and numerical results concerning collisions between scalar and vector spatial solitons in a Kerr planar waveguide are presented. It is shown that this configuration allows for the full control of spatial and polarization dynamics of the interacting vector solitons. On the one hand, the ability to achieve polarization control of a single-hump vector soliton is demonstrated. On the other hand, the effect of collision on the spatial symmetry-breaking dynamics of multimode vector solitons is investigated.     

A generalised mathematical model and analysis for integrated multi-channel vibration structure-control interaction systems

A generalised mathematical model and analysis for integrated multi-channel vibration control-structure interaction systems are developed. The governing equations describing the interactions between a generalised elastic structure and a multi-channel electromagnetic excitation and control system are derived. Based on these equations, the stability and dynamic response of the system are analysed. The introduction of an additional dynamic impedance matrix between structure and control system allows vibration structure-control interaction mechanisms to be investigated. The generalised theory provides a basis to measure exactly the dynamic parameters of the structure negating any influence of the excitation and control system. It also allows the design of a more effective control system taking into account the interactions of the control system with structural motions and vice versa. To illustrate the general formulations developed and their applications, simple one- and two-channel systems are investigated using non-dimensional parameters.