Solitary flexural waves on a supersonic domain wall in yttrium orthoferrite

Solitary flexural waves on a supersonic domain wall in yttrium orthoferrite are observed and investigated. These waves have a sharp leading edge and a protracted trailing edge, reminiscent of the waves accompanying moving vertical Bloch lines in iron garnet films. The total velocity of the solitary flexural waves in yttrium orthoferrites for all observed amplitudes equals the maximum velocity of the domain walls. Two solitary waves with identical amplitudes colliding head-on are annihilated. The waves possess topological charges, and they move and form dynamic profiles under the influence of gyroscopic forces. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 10, 760–765 (25 May 1997)     

Reflection of antiferromagnetic vortices on a supersonic domain wall in yttrium orthoferrite

Reflection of solitary flexural waves propagating in a supersonic domain wall of yttrium orthoferrite from the domain wall part moving with the transverse-sound velocity is observed experimentally. This observation confirms that such a reflection of a solitary flexural wave leads to a change in the sign of the topological charge of the antiferromagnetic vortex accompanied by this wave, which proves a direct relationship between these two objects.     

Interaction of a moving domain wall with surface magnetoelastic waves in yttrium orthoferrite

The amplitude-frequency characteristics of magnetoelastic surface waves excited by moving domain walls in a lamellar yttrium orthoferrite samples are discovered and measured. The results of analysis of the effect of magnetoelastic surface waves on the dynamics of domain walls in this orthoferrite are considered. The nonlinear interaction between magnetoelastic surface waves accompanying a moving domain wall is analyzed.     

Solitary waves and rogue waves in a plasma with nonthermal electrons featuring Tsallis distribution

In this Letter, we discuss the electron acoustic (EA) waves in plasmas, which consist of nonthermal hot electrons featuring the Tsallis distribution, and obtain the corresponding governing equation, that is, a nonlinear Schrödinger (NLS) equation. By means of Modulation Instability (MI) analysis of the EA waves, it is found that both electron acoustic solitary wave and rogue wave can exist in such plasmas. Basing on the Darboux transformation method, we derive the analytical expressions of nonlinear solutions of NLS equations, such as single/double solitary wave solutions and single/double rogue wave solutions. The existential regions and amplitude of solitary wave solutions and the rogue wave solutions are influenced by the nonextensive parameter q and nonthermal parameter α. Moreover, the interaction of solitary wave and how to postpone the excitation of rogue wave are also studied.     

Excitation of bending vibration by a moving domain wall in a plate of yttrium orthoferrite

Elastic vibrations have been experimentally found induced by a moving domain wall in a sample of yttrium orthoferrite 10⁻⁴ m thick. Calculations have been carried out to suggest their relevance to flexural Lamb waves.     

Gyroscopic dynamics of antiferromagnetic vortices in the orthoferrite domain wall

The method of generation of antiferromagnetic vortices on the supersound domain wall in the orthoferrites was proposed. Moving antiferromagnetic vortices were accompanied by the solitary deflection waves. These waves were used for investigation of generation and nonlinear dynamics of the antiferromagnetic vortices on a moving domain wall with the help of two- and three-fold digital high-speed photography and Faraday rotation in the orthoferrites plates cut perpendicular to the optical axis. The full velocity of antiferromagnetic vortex nonlinearly increases and saturates on the spin velocity level c. The vortices with smallest topological charges saturate earlier than with big one. The vortices velocity along the domain wall u increases up to the maximum and goes to the dependence u²+v²=c². Vortex dynamics is quasirelativistic on quasirelativistic domain wall. The theory of gyroscopic force in the domain wall of orthoferrites was elaborated by Zvezdin et al. and was confirmed our earlier experimental results.     

Self focusing of acoustically excited Faraday ripples on a bubble wall

A theoretical explanation is presented to explain pattern formation during the generation of Faraday waves on a bubble wall. The theory derives the Hamiltonian formulation of the nonlinear bubble dynamics. The nonlinear Schrödinger equation for the envelope of surface modes on the bubble wall has been obtained. The solitary wave solution predicts that the shape distortions should be localized near the equator of the bubble.     

Solitary waves, steepening and initial collapse in the Maxwell–Lorentz system

We present a numerical study of Maxwell’s equations in nonlinear dispersive optical media describing propagation of pulses in one Cartesian space dimension. Dispersion and nonlinearity are accounted for by a linear Lorentz model and an instantaneous Kerr nonlinearity, respectively. The dispersion relation reveals various asymptotic regimes such as Schrödinger and KdV branches. Existence of soliton-type solutions in the Schrödinger regime and light bullets containing few optical cycles together with dark solitons are illustrated numerically. Envelope collapse regimes of the Schrödinger equation are compared to the full system and an arrest mechanism is clearly identified when the spectral width of the initial pulse broadens beyond the applicability of the asymptotic behavior. We show that beyond a certain threshold the carrier wave steepens into an infinite gradient similarly to the canonical Majda–Rosales weakly dispersive system. The weak dispersion in general cannot prevent the wave breaking with instantaneous or delayed nonlinearities.     

Tb0.3Dy0.7Fe2合金磁畴偏转研究

研究了Tb_0.3Dy_0.7Fe₂合金在压磁和磁 弹性效应中的磁畴偏转和磁导率特性. 基于Stoner-Wolhfarth 模型能量极小原理, 绘制了自由能与磁畴偏转角度的关系曲线, 研究了压应力和磁场载荷作用下磁畴角度的偏转特性, 计算分析了不同载荷作用下磁畴偏转的磁导率特性, 并与实验数据进行比较论证. 研究表明,应力和磁场的作用都将使磁畴方向[111]和[111]发生角度跃迁, 直观有效地解释了材料巨磁致伸缩效应的机理; 应力和磁场作用下磁畴的偏转将使材料磁导率呈减小趋势, 其中磁场能对磁导率的影响大于应力能, 这一现象在小载荷作用下尤为明显. 实验结果表明, 磁导率的计算数据与实验数据符合得较好, 验证了计算方法的正确性. 理论分析对Terfenol-D磁畴偏转模型的完善 和磁化过程中磁滞回线的绘制非常有意义.     

三维浅海环境下孤立子内波对低频声能流的传播影响

针对三维浅海环境下孤立子内波对低频声信号传播特性的影响问题,基于Oxyz坐标系下的三维浅海低频声场有限元计算方法,以声能流为研究对象,仿真分析了内波存在对低频声信号传播特性的影响规律。研究结果表明:受内波影响,在xOz平面,声能流垂直分量的传播偏转角度呈现周期性的起伏规律;随着声源深度的增加,内波对声能流偏转角度的影响深度也随之增加。对xOy平面,当声源位于温跃层以上时,随着接收深度的增加,各深度平面上声能流水平分量的偏转角越大;随着声源深度的增加,内波对各深度平面上声能流的影响逐渐减弱。     

孤立波在一维复合颗粒链中传播特性的模拟研究

采用分子动力学方法模拟研究了孤立波在重轻颗粒相间排列的一维复合颗粒链中的传播特性.结果发现,在轻重颗粒的质量比较大或较小时,散射作用较弱,颗粒的速度和孤立波的速度衰减较慢.在轻重颗粒的质量比为中等时,散射作用较强,颗粒的速度和孤立波的速度衰减较快.孤立波在通过重-轻颗粒界面时,存在有增速效应,可以提高孤立波的传播速度.并且,轻重颗粒的质量比越小增速效应越强.在散射作用和增速效应的共同作用下,改变轻重颗粒的质量比可以调控孤立波在重-轻颗粒链中的传播时间.     

Solitary ion-acoustic wave propagation in the presence of electron trapping and background nonextensivity

Solitary ion-acoustic wave propagation in the presence of electron trapping is investigated within the theoretical framework of the Tsallis statistical mechanics. A physically meaningful Schamel-like distribution is outlined. In the small amplitude limit, the nonlinear dispersion relation is derived to analyze the global dependency of the main solitary wave quantities. It is found that for a given amplitude and trapping state, the solitary potential structure speeds up and broadens as the electron nonextensivity strengthens. Our results may be of basic interest for experiments that involve particle trapping. The flexibility provided by the nonextensive q-parameter enables one to obtain a good agreement between theory and experiment.     

高脉冲重复频率调Q Tm,Ho:GdVO4激光器

报道了一个高效率连续波和调Q高重频两种运行方式的Tm,Ho:GdVO4激光器.Tm,Ho:GdVO4晶体尺寸4 mm×4 mm×7 mm,a轴通光,液氮制冷到100 K,由发射中心波长为793 nm的光纤耦合激光二极管端面泵浦.Tm,Ho:GdVO4激光连续波输出功率4.0 W,光光转换效率26%.声光调Q条件下输出平均高功率3.9 W,脉冲重复频率10 kHz,脉冲宽度50 ns. 通过减小声光Q开关的开启时间,激光脉冲宽度由50 ns减小至23 ns.在10 kHz重频下,测量最大脉冲能量0.39 mJ , 峰值功率7.8 kW.     

Dark and composite rogue waves in the coupled Hirota equations

The intriguing dark and composite rogue wave dynamics in a coupled Hirota system are unveiled, based on the exact explicit rational solutions obtained under the assumption of equal background height. It is found that a dark rogue wave state would occur as a result of the strong coupling between two field components with large wavenumber difference, and there would appear plenty of composite structures that are attributed to the specific wavenumber difference and the free choice of three independent structural parameters. The coexistence of different fundamental rogue waves in such a coupled system is also demonstrated.     

Quantum effects on the black hole shadow and deflection angle in the presence of plasma

In this study, the optical properties of a renormalization group improved (RGI) Schwarzschild black hole (BH) are investigated in a plasma medium. Beginning with the equations of motion in a plasma medium, we aim to present the modifications in the shadow radius of the RGI BH. To this end, we compute the deflection angle of light in the weak gravity regime for uniform and non-uniform plasma media. Importantly, owing to the plasma media, we discover that the equations of motion for light obtained from the radiating and infalling/rest gas have to be modified. This, in turn, changes and modifies the expression for the intensity observed far away from the BH. Finally, we obtain the shadow images for the RGI BH for different plasma models. Although quantum effects change the background geometry, such effects are minimal, and practically detecting these effects using the current technology based on supermassive BH shadows is impossible. The parameter Ω encodes the quantum effects, and in principle, one expects such quantum effects to play significant roles only for very small BHs. However, the effects of plasma media can play an important role in the optical appearance of BHs, as they affect and modify the equations of motion.     

Effects of dust-charge gradient and polarization forces on the waves and Jeans instability in strongly coupled dusty plasma

The effects of dust charge gradient (DCG) force and polarization force have been investigated on the properties of dust acoustic wave (DAW) and linear Jeans instability in strongly coupled dusty plasma. In the kinetic regime, DCG and polarization forces modify the DAW mode and couple with compressional viscoelastic wave mode. The Jeans instability criterion and critical wavenumber have been modified due to DCG force, polarization force and strong coupling effects. The results have been discussed in the warm photodisassociation region and in the laboratory complex plasmas. The strong correlation effect and the charge variation parameter stabilize the growth rate of Jeans instability. But, the polarization parameter stabilize the growth rate for positively charged dust grains and destabilize for negatively charged dust grains. The implications of charge gradient and polarization parameters are discussed for lower and higher charges in the laboratory complex plasma which decreases the growth of the propagating DAW.     

用纵横波声时比法测螺栓轴力精度研究

用纵横波测量螺栓轴力的技术已取得较大发展,本文介绍了纵横波比值法原理,通过理论推导,获得比值法计算的简易公式。建立试验平台,用现场用螺栓进行标定和测量,得出比值法在工程实践状态下的测量误差为10%以内,基本能满足工程应用的要求。此外,针对试验结果,本文还初步探讨了误差出现的原因以及提高精度的方法。本文介绍的比值法,无需精确测量标定螺栓长度和纵横波声速,现场应用更加简洁,具有较大的工程应用价值。     

Universal magnetic domain wall dynamics in the presence of weak disorder

The motion of elastic interfaces in disordered media is a broad topic relevant to many branches of physics. Field-driven magnetic domain wall motion in ultrathin ferromagnetic Pt/Co/Pt films can be well interpreted within the framework of theories developed to describe elastic interface dynamics in the presence of weak disorder. Indeed, the three theoretically predicted dynamic regimes of creep, depinning, and flow have all been directly evidenced in this model experimental system. We discuss these dynamic regimes and demonstrate how field-driven creep can be controlled not only by temperature and pinning, but also via interactions with magnetic entities located inside or outside the magnetic layer. Consequences of confinement effects in nano-devices are briefly reviewed, as some recent results on domain wall motion driven by an electric current or assisted by an electric field. Finally new theoretical developments and perspectives are discussed.     

非线性基底势对离散非线性晶格孤波动力学性质的影响

使用一种简化的准离散多重尺度法,研究了具有非线性基底势的一维离散非线性晶格的孤波解, 表明孤波能够在这种一维非线性晶格链中存在,而且非线性基底势对孤波的载波频率、群速度、振幅等动力学性质都将产生影响。 另一方面,我们还对非线性动力学方程进行了数值求解, 发现用简化的准离散多重尺度法得到的近似解与精确的计算机数值计算结果符合得较好。     

Theoretical and numerical calculation of the acoustic radiation force acting on a circular rigid cylinder near a flat wall in a standing wave excitation in an ideal fluid

The acoustic radiation force acting on a cylinder near a flat wall in a standing wave is calculated by analytical methods and numerical simulations. An exact theoretical solution is presented as well as an approximate solution. The approximate solution is in algebraic form and quite easy to compute. The numerical simulation is based on FVM (Finite Volume Method) on unstructured triangular meshes. The exact theoretical, approximate and numerical solutions are compared with each other and good agreements are obtained. Furthermore, the effects of the flat wall are investigated in detail by the three methods.