Acoustic radiation force of a quasi-Gaussian beam imparted to a solid spherical scatterer in a fluid

The radiation force generated upon the scattering of a quasi-Gaussian acoustic beam on a homo-geneous elastic sphere in a fluid is investigated. It is shown that the force depends nonmonotonically on the ratio between the sphere’s diameter and the beam’s waist. For a given beam power, the radiation force has its maximum value when the diameters are roughly egual to each other. This is due to the resonant excitation of shear waves on the sphere’s surface under the impact of acoustic wave in the surrounding fluid.     

Active control of power flow transmission in finite connected plate

The vibration propagation and active control of power flow in finite connected plate structure are studied. The dynamic response of the connected plate is obtained by the wave approach. The active power flow at the junction of the connected plate is suppressed by the feedforward active vibration control. It indicates that the active power flow at the junction of the connected plate cannot be well suppressed by the optimal control force for minimizing the acceleration, but it can be effectively suppressed by the optimal control force for minimizing the active power flow. The small error of the optimal control force has slight effects on the control results.     

Coherent beam combining of hybrid phase control in master oscillator-power amplifier configuration

A novel scalable architecture for coherent beam combining with hybrid phase control involving passive phasing and active phasing in master oscillator-power amplifier configuration is presented. Wide-linewidth mutually injected passive phasing fibre laser arrays serve as master oscillators for the power amplifiers, and the active phasing using stochastic parallel gradient descent algorithm is induced. Wide-linewidth seed laser can suppress the stimulated Brillouin scattering effectively and improve the output power of the fibre laser amplifier, while hybrid phase control provides a robust way for in-phase mode coherent beam combining simultaneously. Experiment is performed by active phasing fibre laser amplifiers with passive phasing fibre ring laser array seed lasers. Power encircled in the main-lobe increases1.57 times and long-exposure fringe contrast is obtained to be 78% when the system evolves from passive phasing to hybrid phasing.     

A basic hybrid finite element formulation for mid-frequency analysis of beams connected at an arbitrary angle

When beams are connected at an arbitrary angle and subjected to an external excitation, both longitudinal and bending waves are generated in the system. Since longitudinal wavelengths are considerably longer than bending wavelengths in the mid-frequency region, the number of bending wavelengths in the beams is considerably larger than the number of longitudinal wavelengths. In this paper, plannar beams connected at arbitrary angles are considered. The energy finite element analysis (EFEA) is employed for modelling the bending behavior of the beams and the conventional finite element analysis (FEA) is utilized for modelling the longitudinal vibration in the beams. Thus, a basic hybrid FEA formulation is presented for mid-frequency analysis of systems that contain two types of energy. The bending vibration is associated with the long members in the system and the longitudinal vibration is associated with the short members. The long members are considered to have high modal overlap and to contain several wavelengths within their dimension, and uncertainty effects are present. The short members contain a small number of wavelengths, and exhibit a low modal overlap. Due to the low modal overlap the resonant frequencies are spaced far apart in the frequency domain, therefore the short members exhibit resonant or non-resonant behavior depending on the frequency of the excitation.In this work, the bending and the longitudinal vibration within the same beam member are treated as a long and as a short member, respectively. A hybrid joint formulation is developed between long and short members. Power reflection and transmission coefficients are derived for each joint. The distribution of the energy throughout the system demonstrates a strong dependency on the power transfer coefficients. Several systems are analyzed by the hybrid FEA and by analytical solutions, and good correlation between them is observed.     

Resonant scattering of a lepton by a lepton in the pulsed light field

The process of resonant scattering of a lepton by a lepton in the field of pulsed light wave in general relativistic case is studied theoretically. The approximation when a pulsewidth is considerably greater than the characteristic time of wave oscillation is considered. The analytical expression for the resonant differential cross-section of concerned process is derived within the framework of the first order of the perturbation theory with respect to external laser field; it contains the resonant peak, the altitude and the width of which are defined by the external pulsed wave characteristics. It is demonstrated, that the resonant differential cross-section of scattering of an electron by an electron (an electron by a positron, an electron by a muon) in the pulsed light field may be several orders of magnitude greater than the corresponding one in the external field absence. The derived results may be verified experimentally for example by scientific facility at SLAC National Accelerator Laboratory.     

Nonlinear interaction of a Gaussian EM beam with an electrostatic upper hybrid wave: Stimulated Raman scattering

Summary In this paper we have studied the nonlinear interaction of a Gaussian electromagnetic beam with an electrostatic upper hybrid wave in a collisionless magnetized plasma. On account of the interaction of the incident Gaussian electromagnetic beam with the plasma, a time-independent component of the ponderomotive force becomes finite and leads to the modification in the background density. This results in the excitation of the upper hybrid mode of the plasma. The excited electrostatic wave leads to the enhanced Raman backscattering. An expression for the scattered power is derived and the effect of the external static magnetic field on the enhancement of the density perturbation and scattered power is discussed. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

带有反射腔的相对论返波管的数值模拟

 阐述了带有反射腔的相对论返波管的数值模拟研究。利用线性理论[1]设计了返波管的慢波结构，应用SUPERFISH软件设计了谐振反射器。用KARAT软件对谐振反射腔返波管进行了宏观粒子模拟，得到了优化的返波管结构参数，并研究了外加磁场对输出效率的影响。模拟结果表明：谐振反射腔不仅起到截止颈的作用，还有预调制的作用；在低外加磁场条件下，该返波管也能输出较高功率的微波。显示了其在重复频率工作方面的重要意义。     

辐照用紧凑连续波电子加速器的物理设计

为适应工业电子加速器需求增多的现状,提出了一种新型的结构紧凑的连续波电子加速器,运行频率为180MHz。依靠置于加速腔外的多个偏转磁铁,使电子束多次穿越加速腔,从而得到持续的加速。设计过程中,用CST软件对谐振加速腔进行了优化,用Parmela软件模拟了束流的粒子动力学。粒子纵向稳定度和横向聚焦也通过模拟进行了分析和验证。结果显示:此种新型加速器能得到9MeV,100kW的稳定电子束流。     

Scattering properties of an individual metallic nano-spheroid by the incident polarized light wave

The scattering properties of a metallic nano-spheroid under the illumination of different polarized light waves are investigated using 3D boundary element method. The influences of different geometrical sizes of the nano-spheroid and incident directions of the illuminating light wave on the scattering spectrum are studied for different incident polarized light waves. The results show that the metallic nano-spheroid has two intrinsic resonant modes, corresponding to different polarization states and resonant wavelengths. The scattering enhancement, the resonant wavelength, and the location of the enhanced optical field are strongly dependent on the polarization properties of the illuminating light waves, and they can be modulated by appropriately choosing the polarization directions of the incident light wave.     

Transmission of structure-borne sound from a beam into an infinite plate

An analytical study of transmission of structure-borne sound from a semi-infinite beam into an infinite, isotropic plate is presented. The beam is assumed to carry a torsional, a quasi-longitudinal and bending wave and the transmission is obtained with the help of the admittances of the beam and the plate. The analysis is restricted to the case of low frequencies but is otherwise general; thus due regard is given not only to the bending wave of the plate but also to the other propagating waves and to the local reactions. An interesting result from the study is that a bending wave on the beam will transfer a substantial part of its power into quasi-longitudinal and transverse waves in the plate, especially if the plate is thin compared with the beam. This is thought to be a factor that is important and not so easily quantifiable in the analysis of a complex structure. The local reactions on the other hand are of small importance for the power transmission from a torsional and quasi-longitudinal wave on the beam but may be important for the transmission of a bending wave, especially if the Young's modulus of the beam is larger than that of the plate.     

CONTROL OF MULTI-SPAN BEAM VIBRATION BY A RANDOM WAVE REFLECTOR

In this paper, a new wave reflector called random wave reflector (RWR) is introduced for the control of transverse vibration and wave propagation in an infinite, multi-span, simple-support beam. In order to illustrate the theory, RWR is first tested in a simple configuration of controlling plane wave propagation through layers of gas media. Results demonstrate that RWR has great advantages over other types of noise abatement methods. RWR is then applied to control the vibration of the multi-span beam in which the support locations are given in a random manner. Two types of external excitations, an incident vibration wave and an external point force, are considered separately. Transmission loss, localization factor, mode shape and input power flow are used to investigate the effectiveness of RWR. The results show that no vibrational power flow can be tapped into or propagate through a random system at any frequency. The passbands, which always exist in traditional systems, are eliminated in a random system for which much better performance is obtained over a broad frequency range.     

Non-stationary response of a beam to a moving random force

The non-stationary random vibration of a beam is investigated. The beam is subjected to a random force with constant mean value which is moving with constant speed along the beam. The statistical characteristics of the first and second order for the deflection and bending moment of the beam are computed by using the correlation method. The numerical results of the coefficient of variation of the deflection at beam span mid-point are given for five basic types of convariances of the force (white noise, constant, exponential cosine, exponential, and cosine wave). The effect of the speed of the movement of the force along the beam as well as the effect of the beam damping is investigated in detail. It is concluded that the resulting beam vibration turns out to be a non-stationary process even though the motion considered is that of a stationary random force.     

A direct solution for the efficiency and gain of a CARM oscillator

Approximate analytic solutions for the resonant interaction of a relativistic electron beam interacting with a constant amplitude TEM wave, as in the cyclotron autoresonance maser (CARM) oscillator configuration, are presented. The approximation neglects force bunching relative to inertial bunching, which is usually valid for CARM parameter values of interest in many applications     

1,4-丁二硫醇分子器件电输运性质的力敏特性研究

基于杂化密度泛函理论,研究了1,4-丁二硫醇分子体系的结构随电极作用力的变化及拉断过程;并利用弹性散射格林函数方法进一步计算了不同电极作用力下分子体系的电输运特性.结果显示,界面结构不同,拉断分子体系所用的拉力也不同:分子末端硫原子处于Au(111)面的空位上方时,拉断分子体系需约1.75 nN的拉力;若金电极表面存在孤立金原子与1,4-丁二硫醇分子末端的硫原子相连,拉断分子体系只需约1.0 nN的力,且伴有孤立金原子被拉出.两种情况分别与不同实验测量相符合.分子在压缩过程中发生扭曲并引起表面金原子滑移,然而压缩扭曲过程与拉伸回复过程不可逆.电极拉力约为0.7—0.8 nN时,分子体系在不同界面构型下以及在不同扭转状态下,电导都出现极小值,这与实验结论一致.分子的末端原子与电极间耦合强度随电极作用力的变化是引起分子体系电导变化的主要因素.实验在0.8 nN附近同时测得较小概率的高电导值与双分子导电有关.     

Axial radiation force of a bessel beam on a sphere and direction reversal of the force

An expression is derived for the radiation force on a sphere placed on the axis of an ideal acoustic Bessel beam propagating in an inviscid fluid. The expression uses the partial-wave coefficients found in the analysis of the scattering when the sphere is placed in a plane wave traveling in the same external fluid. The Bessel beam is characterized by the cone angle beta of its plane wave components where beta=0 gives the limiting case of an ordinary plane wave. Examples are found for fluid spheres where the radiation force reverses in direction so the force is opposite the direction of the beam propagation. Negative axial forces are found to be correlated with conditions giving reduced backscattering by the beam. This condition may also be helpful in the design of acoustic tweezers for biophysical applications. Other potential applications include the manipulation of objects in microgravity. Islands in the (ka, beta) parameter plane having a negative radiation force are calculated for the case of a hexane drop in water. Here k is the wave number and a is the drop radius. Low frequency approximations to the radiation force are noted for rigid, fluid, and elastic solid spheres in an inviscid fluid.     

Comprehensive modeling of vertical external cavity surface emitting laser with resonant periodic gain

One of the promising laser constructions having much attention in the past years is thin-disc semiconductor lasers with the resonant periodic gain in a form of multiple quantum wells. The 3D numerical model is developed based on combining bi-directional beam propagation method with the round-trip operator technique. The standing wave effect in resonant gain structure and diffraction in the external laser cavity are taken into account explicitly. Characteristics of optical modes are found numerically for cylindrical vertical extended cavity surface emitting laser with above-threshold pumping. Variation of distance to the external mirror is found to result in notable changes in power and optical quality of the output beam. The decisive role of gain and index non-linearities in these changes is identified.     

Powerful electromagnetic millimeter-wave oscillations produced by stimulated scattering of microwave radiation by relativistic electron beams

The stimulated scattering of electromagnetic waves in microwave generators, in which a high-current electron beam excites either a backward wave (BWO) or a quasi-critical frequency wave (orotron) is investigated experimentally. The scattering occurs at the same electron beam and the high-frequency feedback is provided by the inhomogeneities of the electrodynamic system of the microwave generator itself. A power of several tens of megawatts has been achieved in the 3-mm range. The mode selection permitted to obtain single-mode scattering.     

粗糙表面激光散射特性的理论研究

用矢量微扰动方法分析激光束在粗糙表面上散射的分布特性。详细讨论高斯光束的角谱和适用于准直激光束散射问题的波前分割概念认为，当用入射总功率作归一化因子时，准直粗激光束散射可近似地作为平面波处理，而细激光束散射则与平面波存在很大的差异，利用所得结果讨论了一维粗糙表面的激光隐身作用及椭圆偏振光入射时镜反射方向和后向散射场的偏振态。最后介绍两种线偏振光在粗糙表面上散射分布的差异。实验验证了主要结论。     

柱面波对多层球的轴向声辐射力

在理论和数值上研究柱面波对多层球的声辐射力.基于声波的散射理论，得到声辐射力的解析解，并给出数值仿真.结果表明：在特定的ka和kr₀处，柱面行波的辐射力可以是负值（k是波数，a是多层球的半径，r₀是多层球到声源的距离）.随着kr₀增加到无穷大，仿真结果退化为平面波的情形.对双层球而言，每层的相对厚度影响曲线共振峰的大小和位置，但对三层球而言没有显著影响.当最内层的介质换成空气时，由于声阻抗差异较大，共振峰更加明显.该研究可以为研发新一代单行波声束声学镊子提供理论指导，该技术在生物医学超声和材料科学领域有广泛的应用.     

In-fiber integrated accelerometer

A compact in-fiber integrated fiber-optic Michelson interferometer based accelerometer is proposed and investigated. In the system, the sensing element consists of a twin-core fiber acting as a bending simple supported beam. By demodulating the optical phase shift, we obtain that the acceleration is proportional to the force applied on the central position of the twin-core fiber. A simple model has been established to calculate the sensitivity and resonant frequency. The experimental results show that such an accelerometer has a sensitivity of 0.09 rad/g at the resonant frequency of 680 Hz.