Moving and Interaction of Compact-like Pulses in Klein-Gordon Lattice System

We study the moving and interaction of the compact-like pulses in the system of an anharmonic lattice with a double well on-site potential by a direct algebraic method and numerical experiments. It is found that the localization of the compact-like pulse is related to the nonlinear coupling parameter Cnl and the potential barrier height V0 of the double well potential. The velocity of the moving compact-like pulse is determined by the linear coupling parameter Cl, the localization parameter q (the nonlinear coupling parameter Cnl) and the potential barrier height Vo.Numerical experiments demonstrate that appropriate Cl is not detrimental to a stable moving of the compact-like pulse.However, the head on interaction of two compact-like pulses in the lattice system with comparatively small Cl leads to the appearance of a discrete stationary localized mode and small amplitude nonlinear oscillation background, while moderate Cl results in the emergence of two moving deformed pulses with damping amplitude and decay velocity and radiating oscillations, and biggish Cl brings on the appearing of four deformed kinks with radiating oscillations and different moving velocities.     

Moving and Interaction of Compact-like Pulses in Klein-Gordon Lattice System

We study the moving and interaction of the compact-like pulses in the system of an anharmonlc lattice with a double well on-site potential by a direct algebraic method and numerical experiments. It is found that the localization of the compact-like pulse is rClated to the nonlinear coupling parameter Cnl and the potential barrier height Vo of the double well potential. The velocity of the moving compact-like pulse is determined by the linear coupling parameter Cl, the localization parameter q (the nonlinear coupling parameter Cnl) and the potential barrier height Vo.Numerical experiments demonstrate that appropriate Cl is not detrimental to a stable moving of the compact-like pulse.However, the head on interaction of two compact-like pulses in the lattice system with comparatively small Cl leads to the appearance of a discrete stationary localized mode and small amplitude nonlinear oscillation background, while moderate Cl results in the emergence of two moving deformed pulses with damping amplitude and decay velocity and radiating oscillations, and biggish Cl brings on the appearing of four deformed kinks with radiating oscillations and different moving velocities.     

Phonon-assisted damping of Rabi oscillations in semiconductor quantum dots

Electron-phonon interaction is a major source of optical dephasing in semiconductor quantum dots. Within a density matrix theory the electron-phonon interaction is considered up to the second order of a correlation expansion, allowing the calculation of the quantum kinetic dephasing dynamics of optically induced nonlinearities in GaAs quantum dots for arbitrary pulse strengths and shapes. We find Rabi oscillations renormalized and a damping that depends on the input pulse strength, a behavior not known from exponential dephasing mechanisms.     

孔缝对金属腔体强电磁脉冲耦合特性影响研究

核电磁脉冲和高功率微波等强电磁脉冲易造成电子设备功能失效甚至损毁,在实际工程实施中用金属腔体对电子设备进行屏蔽是常用的强电磁脉冲抑制手段。基于电磁仿真计算,对含矩形孔缝金属腔体的强电磁脉冲耦合特性进行了系统研究,阐述了孔缝宽长比、腔体尺寸等因素对多种不同类型强电磁脉冲（核电磁脉冲、宽带高功率微波、窄带高功率微波）作用下腔体内耦合场的影响;并以此为基础,重点分析了强电磁脉冲与含孔缝金属腔体之间的作用机制。研究结果表明:不同类型强电磁脉冲耦合信号差异明显,金属腔体对强电磁脉冲的响应是腔体谐振模式、孔缝谐振频率与强电磁脉冲共同作用的结果;当腔体谐振模式、孔缝谐振频率在强电磁脉冲的带内时,腔体内部的耦合场会出现增强效应;特别地,腔体与孔缝间的相互作用还可造成腔体与缝隙的谐振频率发生偏移。因此,在为电子设备设计金属屏蔽外壳时,应基于不同强电磁脉冲的频带范围,对腔体与孔缝的尺寸进行综合设计,抑制腔体、孔缝谐振及谐振频率偏移,提升其强电磁脉冲防护性能。     

Interaction of a Gaussian acoustic wave with a turbulent non-premixed flame

A Direct Numerical Simulation (DNS) of a turbulent non-premixed flame interacting with a Gaussian acoustic wave is carried out in this work. This numerical simulation takes into account detailed transport phenomena including the Soret effect as well as complete chemical kinetics on a very fine mesh. Turbulent non-premixed flame calculations are carried out both with and without an acoustic wave and results are recorded at the same time. By a simple difference it is then possible to obtain the influence of the acoustic wave/turbulent flame interaction. Using an extension of the non-linear Rayleigh criterion to a system with many species and elementary reactions, the obtained results can be further analysed. The initially planar acoustic wave develops strong perturbations along its transverse direction because of the interaction process, even at very early times. The amplitude of the pressure perturbation presents locally high positive as well as negative values, demonstrating the importance of focussing/defocussing effects and local amplification (resp. damping) phenomena. In the same way, the heat release rate is locally modified (either increased or decreased) during the interaction process. Finally, the presented Rayleigh criterion is used to identify regions where local amplification (respectively damping) takes place. Both amplification and damping zones coexist directly close to each other inside the reaction zone. The observed, resulting global effect is thus based on an average over highly varying local conditions within the flame front, leading to a smoothing effect. The complexity of the coupling procedure leading to this global wave amplification or damping is demonstrated by the present analysis.     

Landau damping of collective mode in a quasi-two-dimensional repulsive Boseben Einstein condensate

We investigate the Landau damping of the collective mode in a quasi-two-dimension repulsive Bose—Einstein condensate by using the self-consistent time-dependent Hatree—Fock—Bogoliubov approximation and a complete and orthogonal eigenfunction set for the elementary excitation of the system. We calculate the three-mode coupling matrix element between the collective mode and the thermal excited quasi-particles and the Landau damping rate of the collective mode. We discuss the dependence of the Landau damping on temperature, on atom number in the condensate, on transverse trapping frequency and on the length of the condensate. The energy width of the collective mode is taken into account in our calculation. With little approximation, our theoretic calculation results agree well with the experimental ones and are helpful for deducing the damping mechanics and the inter-particle interaction.     

Transient response of dielectric materials exposed to ultrafast laser radiation

We present results describing several characteristics of energy coupling into dielectric materials (fused silica) irradiated by ultrashort laser pulses in a regime close to the surface optical breakdown threshold. The results intend to illustrate the energy balance in the interaction process by observing the spatio-temporal variations of a laser pulse transversing a dielectric slab as a function of its energy. The measurements are based on real-time observations of the self-action of the laser pulse and associated effects on its temporal envelope, as well as on ex-situ phase-contrast microscopy of induced permanent material reactions. The experimental results are accompanied by numerical simulations of the pulse traces inside the dielectric material at different energetic conditions. The optical observations allow insights into the development and the dynamics of the laser-induced free carrier population, emphasizing the role of the bulk effects related to the nonlinear wave propagation into the transparent material during laser exposure. PACS 79.20.Ds; 52.50.Jm     

Various Kinds Waves and Solitons Interaction Solutions of Boussinesq Equation Describing Ultrashort Pulse in Quadratic Nonlinear Medium

The consistent tanh expansion (CTE) method is applied to the (2+1)-dimensional Boussinesq equation which describes the propagation of ultrashort pulse in quadratic nonlinear medium. The interaction solutions are explicitly given, such as the bright soliton-periodic wave interaction solution, variational amplitude periodic wave solution, and kink-periodic wave interaction solution. We also obtain the bright soliton solution, kind bright soliton solution, double well dark soliton solution and kink-bright soliton interaction solution by using Painlevé truncated expansion method. And we investigate interactive properties of solitons and periodic waves.     

基于强耦合Duffing振子的微弱脉冲信号检测与参数估计

耦合Duffing振子在检测强噪声中的微弱脉冲信号时具有可检测信噪比低等优点,但目前检测模型还存在系统性能与初始状态有关、只能工作在倍周期分岔状态等缺陷.为此本文构建了一种能克服上述缺点的新的微弱脉冲信号检测模型,通过对两个Duffing振子同时施加较大的恢复力和阻尼力耦合,可使振子间产生广义的"阱内失同步"现象,基于这种现象可实现微弱脉冲信号的检测与恢复.以信噪比改善和波形相似度为衡量指标,研究了周期策动力幅值与周期、耦合系数、计算步长、阻尼系数等参量对模型信号检测与波形恢复效果的影响.对方波、双指数脉冲和高斯导数脉冲进行检测和恢复的实验结果表明,本文所构建的模型能够在较低信噪比条件下有效地检测并恢复出高斯白噪声背景中的微弱脉冲信号,进而改善了现有的Duffing振子对非周期脉冲信号的检测能力并扩展了其应用领域.     

高阶群速度色散引起的高斯超短脉冲宽度的展宽和形变

基于动量守恒和光参变过程中的三波耦合波方程,和负单轴非线性光学晶体CsLiB6O10的色散方程,研究了在光参变效应中超短激光脉冲由于群速度色散引起的展宽和形变。数值模拟显示,在超短脉冲波形为双曲正割形和无啁啾调制时,高阶群速度色散引起的超短脉冲为50fs时,晶体长度为10mm,紫外光213nm作为基波入射时的脉冲展宽是波长为532nm绿光在同等条件下的1.6倍。脉冲展宽程度与入射波长和晶体长度有关,波长越短和晶体长度越长则脉冲展宽和波形变化越严重,高阶色散引起的超短高斯脉冲展宽,将破坏其波形对称性并引起旁瓣现象。     

长脉冲相对论速调管中束流脉冲缩短的研究

介绍L波段长脉冲相对论速调管放大器研究中，长脉冲强流相对论电子束(IREB)经过输入腔和中间腔间隙后的脉冲缩短问题.分析了造成束流脉冲缩短的主要机理之一是高频系统的角向非均匀模式与电子束相互作用而使得束流扩散形成的，并经过实验参数的调节，减轻了长脉冲IREB的脉冲缩短问题，得到了较强的基波调制电流.从长脉冲加速器引出500 kV，3.5 kA，1.3 μs的电子束，经过输入腔和两个群聚腔的调制后，得到了2.0 kA的基波调制电流，束流脉冲宽度由0.3 μs增加到1 μs，束流脉冲缩短问题得到明显减轻. 关键词： 相对论速调管放大器 脉冲缩短 高功率微波 长脉冲强流相对论电子束     

Active control of geometrically nonlinear transient vibration of composite plates with piezoelectric actuators

In this paper, the incremental finite element equations for geometric non-linear analysis of piezoelectric smart structures are developed using a total Lagrange approach by using virtual velocity incremental variational principles. A four-node first order shear plate element model with reduced and selective integration is also developed. Geometrically non-linear transient vibration response and control of plates with piezoelectric patches subjected to pulse loads are investigated. Active damping is introduced on the plates by coupling a self-sensing and negative velocity feedback algorithm in a closed control loop. The numerical results show that piezoelectric actuators can introduce significant damping and suppress transient vibration effectively. The effects of the number and locations of the piezoelectric actuators on the control system are also discussed.     

On surface plasmon damping in metallic nanoparticles

Two possible mechanisms of damping of surface plasmon (SP) oscillations in metallic nanoparticles (MNPs), not connected with the electron–phonon interaction, are investigated theoretically: (a) radiation damping of SPs and (b) resonant coupling of SP oscillations with electronic transitions in the matrix. For the mechanism (a) it is shown that the radiation damping rate is proportional to the number of electrons in a MNP and therefore this channel of energy outflow from the MNP becomes essential for relatively large particles. The strong frequency and size dependence of the radiation damping rate obtained allows us to separate the contributions of radiative processes and the electron–phonon interaction to the energy leakage. The investigation of the mechanism (b) shows that the rate of energy leakage of SP oscillations from a MNP does not depend on particle size and is fully determined by the optical characteristics of the matrix. It is demonstrated that for very small MNPs of -–3 5nm size, where the strong three-dimensional size quantization effect suppresses the electron–phonon interaction, the resonance coupling in certain cases provides an effective energy outflow. PACS 78.67.Bf     

Ultrashort Gaussian pulse-width expansion and shape deformation induced by group velocity dispersion

Pulse-width expansion and pulse-shape deformation of an ultrashort Gaussian pulse induced by both low and high order group velocity dispersion were theoretically analyzed in terms of energy conservation and coupled equations for three wave radiations. As an example, the optical parametric interaction processes in a negative uniaxial crystal of CsLiB₆O₁₀ with 50 fs of ultrashort Gaussian pulse were simulated. The results indicate that the degree of the pulse expansion induced by low and high order group velocity dispersion is determined by both the wavelength of the incident wave and the crystal length. A pulse could be expanded to 1.41 times its initial value as a crystal length equals the dispersion length and further heavily expanded with decreasing wave-length and increasing crystal length. The pulse expansion induced by high order group velocity dispersion using an incident wavelength of 213 nm is 1.6 times that when using 532 nm in a 50 fs pulse width without chirp modulation, and the symmetry deformation and the frequency pushing phenomena of the ultrashort pulse shape are also found. The text was submitted by the authors in English.     

地铁车辆直型辐板阻尼环车轮声振特性分析

为探究地铁车辆阻尼环扩张状态对阻尼环车轮声振特性影响,在半消声室内进行阻尼环车轮自由状态下的声振特性实验研究,结合有限元仿真对实验结果进行分析。研究表明,环-轮组合振动固有频率与原车轮相比变化不大,但阻尼环使车轮的模态阻尼比显著增加,有效抑制了车轮各模态的振动幅值。改变阻尼环扩张状态,阻尼环降噪效果发生非线性变化,幅值在5.6 dB(A)之内。阻尼环扩张状态可通过调节非闭合阻尼环两端扩张装置来改变。阻尼环处于非最大扩张状态W_3时,可获得最佳降噪效果。     

The Observation and Dynamics of 1H NMR Spin Noise in Methanol

The observation of ¹H spin noise in relation to prior established magnetization and radiation damping has revealed a correlated dynamics. The spin noise of methyl satellites in ¹³C-enriched methanol was observed in the presence of an antiphase magnetization, created by the combination of ¹H–¹³C J coupling evolution and radiofrequency (RF) pulses. A gradient pulse was applied to remove residue spin coherence coming from the RF pulses, and as a result spin noise phenomena were uncovered. While magnetization was in an inverted metastable state, the spin–spin relaxation time was shortened to prevent a super radiation burst. The relation between magnetization, radiation damping, and absorption or emission of the spin noise of methyl satellites has been studied. In relation to magnetization and radiation damping, spin noise bump and dip have been observed simultaneously in the same molecule. Both can be created through a proper inversion of magnetization. The revealed spin noise dynamics of spin system coupling to the probe circuit via radiation damping allows performance of a transformation from dip into bump by proper application of pulses combined with ¹H–¹³C J coupling evolution.     

Storing optical information as a mechanical excitation in a silica optomechanical resonator

We report the experimental demonstration of storing optical information as a mechanical excitation in a silica optomechanical resonator. We use writing and readout laser pulses tuned to one mechanical frequency below an optical cavity resonance to control the coupling between the mechanical displacement and the optical field at the cavity resonance. The writing pulse maps a signal pulse at the cavity resonance to a mechanical excitation. The readout pulse later converts the mechanical excitation back to an optical pulse. The storage lifetime is determined by the relatively long damping time of the mechanical excitation.     

Effects of interlayer coupling in a magnetic trilayer system

Magnetic properties of a trilayer consisting of two different magnetic films separated by a nonmagnetic spacer are investigated by means of the variational cumulant expansion. The long-range interlayer interaction as well as the nearest neighbor coupling including the anisotropy and external fields are considered. The mean magnetization and ordering temperatures are calculated for various interlayer-coupling energies in qualitative agreement with experiments.     

Molecular dynamics study of the role of material properties on nanoparticles formed by rapid expansion of a heated target

Rapid expansion of a heated target and its decomposition into fragments is investigated by using molecular dynamics simulations. Particular attention is focused on the void formation and nucleation that governs the target disintegration. The cluster formation process is investigated as a function of material properties (initial temperature, interaction potential and composition). Calculation results demonstrate the influence of these properties on void nucleation and growth and on the characteristic parameters of nanoparticles to be formed. In particular, larger initial temperature and expansion rate lead to the formation of smaller fragments. These effects are found to be similar for three different materials (silicon, nickel and metal alloy). In addition, the stoichiometrical cluster composition obtained in the expansion of a binary alloy is found to be fairly well preserved. The calculation results can be used for the interpretation of the experimental findings showing the formation of nanoparticles by short and ultra-short pulse laser ablation of both simple and more complex materials.