Dispersion of the high-frequency sound velocity in the aqueous solution of 4-methylpyridine

Dispersion of the high-frequency sound velocity in the aqueous solution of 4-methylpyridine with the concentration 0.06 mole fraction corresponding to the singular point in the temperature-concentration phase diagram is studied. Along with observation of positive dispersion of the speed of sound in going over from ultrasound to hypersound frequencies (5.4 MHz to 4.8 GHz), negative dispersion (a decrease in velocity with increasing frequency) was also observed in a narrow interval of hypersound frequencies from 4.8 to 6.1 GHz.     

Soliton generation via continuous stokes acoustic self-scattering of hypersonic waves in a paramagnetic crystal

A new mechanism is proposed for continuous frequency down-conversion of acoustic waves propagating in a paramagnetic crystal at a low temperature in an applied magnetic field. A transverse hypersonic pulse generating a carrier-free longitudinal strain pulse via nonlinear effects is scattered by the generated pulse. This leads to a Stokes shift in the transverse hypersonic wave proportional to its intensity, and both pulses continue to propagate in the form of a mode-locked soliton. As the transverse-pulse frequency is Stokes shifted, its spectrum becomes narrower. This process can be effectively implemented only if the linear group velocity of the transverse hypersonic pulse equals the phase velocity of the longitudinal strain wave. These velocities are renormalized by spin-phonon coupling and can be made equal by adjusting the magnitude of the applied magnetic field. The transverse structure of the soliton depends on the sign of the group velocity dispersion of the transverse component. When the dispersion is positive, planar solitons can develop whose transverse component has a topological defect of dark vortex type and longitudinal component has a hole. In the opposite case, the formation of two-component acoustic “bullets” or vortices localized in all directions is possible.     

表面增强拉曼光谱法研究铁吡啶类缓蚀剂

利用表面增强拉曼散射光谱技术和传统的电化学手段研究了４－甲基吡啶，２，４，６－二甲基吡啶在盐酸体系中对铁的缓蚀作用，结果表明，在该体系中，４－甲基吡啶对铁的缓蚀作用大于２，４，６－三甲基吡啶，并对其可能的吸附取向进行了讨论。     

Exact self-similar solutions of the generalized nonlinear Schrödinger equation with distributed coefficients

A broad class of exact self-similar solutions to the nonlinear Schr?dinger equation (NLSE) with distributed dispersion, nonlinearity, and gain or loss has been found. Appropriate solitary wave solutions applying to propagation in optical fibers and optical fiber amplifiers with these distributed parameters have also been studied. These solutions exist for physically realistic dispersion and nonlinearity profiles in a fiber with anomalous group velocity dispersion. They correspond either to compressing or spreading solitary pulses which maintain a linear chirp or to chirped oscillatory solutions. The stability of these solutions has been confirmed by numerical simulations of the NLSE.     

Some features of the temperature dependence of the hypersonic velocity in an aqueous solution of tertiary butyl alcohol

The dependence of the hypersonic velocity V in an aqueous solution of tertiary butyl alcohol on the solution temperature t has been measured from the Mandelshtam-Brillouin scattering spectra. A change in the temperature derivative of the velocity, dV/dt, in a narrow range from ≈43 to ≈44°C, with jumps at its boundaries, is revealed. The measurement results and their comparison with the previous data indicate the existence of structural transitions with respect to temperature and concentration in these solutions.     

Brillouin scattering in Li2SO4: Liquid and plastic crystalline phases

The hypersonic velocity in Li₂SO₄ was measured through the liquid-plastic transition for an arbitrary crystalline orientation. The velocity showed a sharp discontinuity at the phase transition. The phonon frequency was a periodic function of crystalline orientation.     

光纤光栅非线性对色散特性的影响

通过在能量较高、考虑非线性时,求解光纤光栅非线性耦合模方程连续波条件下的解,得到光纤光栅失谐量δ与光脉冲传播常量q的非线性色散关系和光栅致群速度色散系数βg2与δ的关系.用MATLAB绘图,得到非线性参量γ和光脉冲能量P0的乘积γP0对色散和βg2的影响.结果表明:随着βg2的增加,非线性色散曲线的上、下两支向δ的负值区移动,当超过某一临界值时,曲线上支开始形成环,这时光纤光栅引起的群速度色散中的反常色散区消失,全部变成正常色散.     

Extended frequency range measurements for determining the Kneser-type acoustic relaxation time

In the present paper, the authors discuss studies carried out for many years dealing particularly with two compounds: benzene and carbon disulphide and compare them with the results obtained by numerous acoustics researchers. These compounds are typical liquids in which acoustic Kneser-type relaxation occurs, caused by an irreversible vibrational and translational (VT) transition. Since magnitudes describing the relaxation process were diverse in many papers, we have undertaken an attempt to clarify these differences and to indicate how to avoid errors resulting from instrumental imperfections and the disregard of the considerable measurement errors when investigating velocity dispersion in the hypersonic (GHz) range. The results of these researches changed the interpretation of previous papers.     

慢布拉格类孤子的传播特性

在耦合模理论的基础上，分析了线性周期结构的色散关系，给出了一维无限长的克尔类非线性介质周期结构中的慢布拉格类孤子解。并且指出，增加脉冲能量会导致群速度色散效应增强，在非线性作用下，禁带宽度会变小，波的频率也会发生偏移，其偏移量主要取决于失谐因子、传播速度、波振幅强度以及非线性系数等参量。     

基于高斯伪谱法的高超声速飞行器再入制导研究

针对高超声速飞行器再入标准轨迹制导方法中存在的制导准备周期长、弹上需存储标准轨迹参数、制导鲁棒性较差等缺点,本文提出了一种基于高斯伪谱法与滚动时域控制技术相结合的高超声速飞行器再入预测-校正制导方案。其中,在线高斯伪谱法采用纵/侧向、全程一体化的制导算法思路,从而实现了对高超声速飞行器再入弹道的全程预测-校正。同时结合滚动时域控制技术从工程上实现了高超声速飞行器再入制导中对开环制导信息的闭环应用,完成了飞行器预测-校正制导方案。通过对高超声速飞行器再入制导过程进行仿真分析,其结果表明应用本文设计的基于高斯伪谱法与滚动时域控制技术相结合的高超声速飞行器再入预测-校正制导方案,飞行器再入过程中具有良好的制导性能。     

Gas-kinetic numerical studies of three-dimensional complex flows on spacecraft re-entry

The gas-kinetic numerical algorithm solving the Boltzmann model equation is extended and developed to study the three-dimensional hypersonic flows of spacecraft re-entry into the atmosphere in perfect gas. In this study, the simplified velocity distribution function equation for various flow regimes is presented on the basis of the kinetic Boltzmann–Shakhov model. The discrete velocity ordinate technique and numerical quadrature methods, such as the Gauss quadrature formulas with the weight function 2/π^1/2exp(?V²) and the Gauss–Legendre numerical quadrature rule, are studied to resolve the barrier in simulating complex flows from low Mach numbers to hypersonic problems. Specially, the gas-kinetic finite-difference scheme is constructed for the computation of three-dimensional flow problems, which directly captures the time evolution of the molecular velocity distribution function. The gas-kinetic boundary conditions and numerical procedures are studied and implemented by directly acting on the velocity distribution function. The HPF (high performance fortran) parallel implementation technique for the gas-kinetic numerical method is developed and applied to study the hypersonic flows around three-dimensional complex bodies. The main purpose of the current research is to provide a way to extend the gas-kinetic numerical algorithm to the flow computation of three-dimensional complex hypersonic problems with high Mach numbers. To verify the current method and simulate gas transport phenomena covering various flow regimes, the three-dimensional hypersonic flows around sphere and spacecraft shape with different Knudsen numbers and Mach numbers are studied by HPF parallel computing. Excellent results have been obtained for all examples computed.     

Inelastic behaviour of bismuth germanium oxide at hypersonic frequencies

Brillouin scattering was used between 10 and 300 K to probe 35 GHz hypersonic phonons. The velocity and attenuation of longitudinal phonons propagating in the [111] direction have been measured. The hypersonic attenuation appears to be dominated by anharmonic phonon-phonon interactions down to 150 K.     

Chirped and chirpfree soliton solutions of generalized nonlinear Schrödinger equation with distributed coefficients

Using the F-expansion method, we systematically present exact solutions of the generalized nonlinear nonlinear Schrödinger equation with varying intermodal dispersion and nonlinear gain or loss. This approach allows us to obtain large variety of solutions in terms of Jacobi-elliptical and Weierstrass-elliptical functions. The chirped and unchirped spatiotemporal soliton solutions and trigonometric-function solutions have been also obtained as limiting cases. The dynamics of these spatiotemporal soliton is discussed in context of optical fiber communication. To visualize the propagation characteristics of chirp and unchirped dark-bright soliton solutions, few numerical simulations are given. It is found that wave profile of solitons depend on the group velocity dispersion and the gain or loss functions.     

Brillouin scattering study of the orientationally disordered phase of cyclohexanol

Brillouin scattering was used to measure the velocity and attenuation of longitudinal hypersonic waves in the orientationally disordered (OD) phase of a cyclohexanol single crystal and at the OD-liquid transition. Our results show that the coupling with a high-frequency relaxation mechanism, which dominates the behaviour of the hypersonic waves in the liquid, is still efficient in the OD phase.     

新型蓝色有机电致磷光配合物二(2-二氟苯基-4-甲基吡啶) 合铱的合成及光谱学性能

合成了三个以含氟苯基吡啶及吡啶基咪唑为配体的蓝色磷光电致发光铱配合物(P)₂Ir(pym),其中主配体(P)分别为2-(2',4'-二氟苯基)-4-甲基吡啶、2-(3',4'-二氟苯基)-4-甲基吡啶、2-(3',5'-二氟苯基)-4-甲基吡啶;辅助配体pymH为2-(2'-吡啶基)咪唑。通过元素分析、核磁、质谱、红外进行结构表征;用紫外可见吸收光谱、荧光光谱以及循环伏安进行其光谱学性能表征。以pymH取代辅助配体picH(2-吡啶甲酸)的方法,得到含吡啶基咪唑的铱配合物,在室温下二氯甲烷溶液中获得强的蓝光发射,其最大发光波长分别是461,480,490 nm,其中(46f₂pmpy)₂Ir(pym)较经典蓝光磷光材料FIrpic蓝移5 nm。     

Elastic constants of the SrLaAlO4 and SrLrGagaO4 crystals measured at ultrasonic and hypersonic oustic frequencies

Elastic constants measured by Brillouin light-scattering experiments were compared with results estimated from the pulse-echo-overlap method for the ultrasonic frequency to find dispersion in their values. In this way Brillouin hypersonic experiments complete the ultrasonic results. The present investigation includes a careful analysis of the accuracy of the results. The measured values of elastic constants suggest a weak dispersion in acoustic wave velocities. However, given the magnitude of the experimental errors, it is difficult to conclude about the dispersion.     

Stable control of pulse speed in parametric three-wave solitons

We analyze the control of the propagation speed of three wave packets interacting in a medium with quadratic nonlinearity and dispersion. We find analytical expressions for mutually trapped pulses with a common velocity in the form of a three-parameter family of solutions of the three-wave resonant interaction. The stability of these novel parametric solitons is simply related to the value of their common group velocity.     

各向异性颗粒PDF输运方程及其颗粒湍流扩散

根据Minier的模型,获得颗粒所见流体脉动速度的朗之万模型,并推导颗粒所见流体湍流脉动速度自关联函数,该函数具有各向异性的特征,进一步由流体脉动速度朗之万模型和颗粒运动方程获得相应的颗粒PDF输运方程.为描述在网格生成湍流中的颗粒扩散运动,将颗粒PDF输运方程作相应的简化,获得一个具有颗粒湍流各向异性的解析解,将方程的解与Wellsand Stock的颗粒湍流扩散实验结果进行比较,获得了很好的结果.揭示了具有各向异性特征的颗粒PDF输运方程的优越性.     

Surface effect on size-dependent wave propagation in nanoplates via nonlocal elasticity

Within the framework of nonlocal elasticity, the surface layer model is proposed to investigate the wave propagation characteristics in a single-layered nanoplate. The general solutions of nonlocal governing equations are expressed using partial wave technique and the nonclassical boundary conditions are derived. The dispersion relation with the effects of surface and nonlocal small-scale is obtained, and the size-dependent dispersion behaviour is demonstrated. The impacts of surface elasticity, residual surface stress and nonlocal parameter on the dispersion curves of the lowest-order two modes are illustrated. Numerical examples reveal that both the surface effect and nonlocal small-scale effect can obviously decrease the magnitude of phase velocity, and the thinner nanoplate corresponds to the smaller wave velocity and the narrower frequency bandwidth.     

Dynamics of counterpropagating waves in parametrically driven systems: dispersion vs. advection

The dynamics of parametrically driven counterpropagating waves in a one-dimensional extended nearly conservative annular system are described by two coupled, damped, parametrically driven nonlinear Schrödinger (NLS) equations with opposite transport terms due to the group velocity, and small dispersion. The system is characterized by two length scales defined by a balance between (a) forcing and dispersion (the dispersive scale), and (b) forcing and advection at the group velocity (the transport scale). Both are large compared to the basic wavelength of the pattern. The dispersive scale plays an important role in the structure of solutions arising from secondary instabilities of frequency-locked spatially uniform standing waves (SW), and manifests itself both in traveling pulses or fronts and in extended spatio-temporal chaos, depending on the signs of the dispersion coefficient and nonlinearity.