Scattering amplitude of four non-relativistic particles

The exact integral equations for the non-relativistic four-particle scattering amplitudes are obtained, assuming only two-body forces. These equations can be solved when in the final state there are two pairs of particles with small relative energy of particles in the c.m. system of each pair. As an example, the reaction d+d→n+p+d is considered.     

利用激光光梯度力消除气溶胶雾霾粒子的机理研究

针对气溶胶雾霾粒子在大气流中所受力的平衡体系(旋转升力平衡重力, 粒子与粒子之间依靠斥力形成稳定的网状的力平衡体系)的问题, 提出了用激光光梯度力破坏力平衡进而消除雾霾的新机理. 首先, 根据牛顿第二定理, 得到了粒子所受力的非线性方程组, 应用Runge-Kutta 法积分求解了雾霾颗粒在大气流中所受的主要力(空气曳引阻力、范德瓦耳斯斥力、旋转升力)的数值, 成功验证了西安市2013年12月17-25日、2014年2月20-26日两次雾霾检测试验结论: 在雾霾过程中, 粒径在0.5-0.835 μm径段的粒子数浓度增加最明显. 其次, 在雾霾粒子形成的均匀介质中, 计算了激光光梯度力的大小. 研究发现, 激光光梯度力的数量级恒大于雾霾颗粒所受主要力的数量级, 激光光梯度力完全可以破坏雾霾颗粒所受力的平衡体系. 因此, 用激光光梯度力消除雾霾是可行的, 这种新的解决雾霾的方法对人们的实际生活、环保及创建美丽的蓝天具有非常重要的意义.     

Characteristics of the vibrational power flow propagation in a submerged periodic ring-stiffened cylindrical shell

By using space-harmonic analysis method, the characteristics of the vibrational power flow propagation in an infinite periodic ring-stiffened cylindrical shell immersed in water are studied. The harmonic motion of the shell and the sound pressure field in the fluid are described by Flügge shell equations and Helmholtz equation, respectively, and four kinds of the rings’ forces and moments are considered. Along the shell axial direction, the propagation of the power flow carried by different internal forces (moments) of the shell wall can be obtained, thus the total power flow in the shell wall and the ratios of the component power flow carried by different shell internal forces (moments) to the total power flow are also studied. It is found that characteristics of the vibrational power flow propagation vary with different circumferential modes order and different frequencies. Moreover, the presence of the stiffeners and structural damping will greatly influence the results.     

Suspended Particles and the Gravitational Instability of Rotating Magnetised Medium

The effect of uniform rotation on the self gravitational instability of an infinite homogeneous magnetised gas particle medium in the presence of suspended particles is investigated. The equations of the problem are linearized and the general dispersion relation for such system is obtained. The rotation is assumed along two different directions and separate dispersion relation for each case is obtained. The dispersion relation for propagation parallel and perpendicular to the uniform magnetic field along with rotation is derived. The effect of suspended particles on the different modes of propagation is investigated. It is found that in presence of suspended particles, magnetic field, rotation and viscosity, Jeans' criterion determines the condition of gravitational instability of gas-particle medium.     

Effects of the Space Charge Forces and the Beam Halo in an AVF Cyclotron with Intense Beam Currents

The equations of motion of particles in an AVF cyclotron in a curvilinear coordinate system are derived for the cases with and without space charge forces. Assuming a set of the parameter values in the equations, numerical calculations are carried out by using Lunge-Kutta methods in the case with space charge forces. The results show that the formation of the beam halo is also a main reason of the beam losses, but the mechanism here is different from that in a linear accelerator. It is not given rise by resonance and chaos but the outward repellent motion and the vortex motion of the particles in the bunch.     

含左手材料光纤的表面模特性

在弱导条件下,利用Maxwell方程组,对纤芯是左手材料,包层是右手材料的光纤表面模进行了研究,得到了TE (TM)、 EH和 HE表面模的色散方程,.根据色散方程,画出了相应表面模和含左手材料光纤导模的色散曲线.比较这些色散曲线,发现了含左手材料光纤表面模一些新的特性.     

强流AVF型迴旋加速器中的空间电荷效应和束晕

详细推导了AVF型迴旋加速器中束团粒子在曲线坐标系中的动力学方程(考虑和不考虑空间电荷相互作用力两种情况).在假定动力学方程中各参数值的前提条件下,用Lunge-Kutta方法对考虑空间电荷时的动力学方程进行了数值计算.结果表明,束晕的形成和发展同样也是强流迴旋加速器中束流损失的一个主要原因.但束晕形成的机制不同于直线加速器的情况,它不是由共振和混沌引起,而是由于粒子的排斥运动和束团内粒子的涡流运动引起的.     

Statistical mechanics of confined systems with rotational excitations

New experimental and numerical investigations of confined systems of particles demonstrate the existence of rotational excitations. We develop here a statistical theory of finite systems, including rotational modes, by introducing the angular momentum into the formalism and constructing the relevant distributions. As special applications we study systems driven to a prescribed kinetic energy by negative friction or special isokinetic thermostats. Several distribution functions which are solutions of the Liouville or Fokker–Planck equations are given. The theory is applied to Coulomb clusters confined by parabolic forces.     

A microscopic theory of nucleation. II

Using the nonequilibrium statistical operator obtained in the preceding paper of the authors [1], equations describing the kinetics of nucleation in a nonequilibrium medium are derived. A Fokker-Planck equation is found for embryo distribution functions in the number of particles, energy, momentum, and c.m. coordinates with additional random forces due to non equilibrium processes in the medium. Hydrodynamic equations are obtained for the medium with account of thermodynamic forces due to discontinuities of thermodynamic parameters at the interphase boundary. The symmetry of cross (interphase) kinetic coefficients is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 44–52, May, 1978.     

Noncentral forces in crystals of charged colloids

The elastic properties of fcc crystals consisting of charge stabilized colloidal particles are determined from real space imaging experiments using confocal microscopy. The normal modes and the force constants of the crystal are obtained from the fluctuations of the particles around their lattice sites using the equipartition theorem. We show that the Cauchy relation is not fulfilled and that only noncentral many-body forces can account for the elastic properties.     

Theoretical calculation of the dielectric tensor and field equations in columns with elliptical cross-sections including inhomogeneous magnetized cold collisionless drift and rotating plasmas

In this paper the effects of the inhomogeneity of the density of charged particles and the initial axial, rotating and radial motion on the dielectric permittivity tensor and the field equations in a long column of multi-layer magnetized plasmas with confocal elliptical cross-sections are investigated. The elements of the dielectric permittivity tensor and the generalized field equations of each region are obtained. The field equations for hybrid modes in each region of the inhomogeneous plasma with coaxial elliptical cylindrical boundaries are presented.     

Optical manipulation in optofluidic microbubble resonators

An optical manipulation system based on optofluidic microbubble resonators(MBR) is proposed. As the high-Q whispering gallery modes(WGMs) are excited in an MBR, the buildup of the field intensity inside the resonator is large enough to trap nanoscale particles. The optical gradient forces generated by the WGMs with different radial orders are investigated numerically. The negative effect of the resonance detuning induced by the particles is taken into account to investigate the optical gradient forces exerting on the particles. By the stability analysis, the WGMs with high radial orders show a better trapping stability under Brownian motion since most of the optical fields reside within the water core.     

MODES OF CONTACT AND UNIQUENESS OF SOLUTIONS FOR SYSTEMS WITH FRICTION-AFFECTED SLIDERS

The kinetic equations of planar multi-body systems with friction-affected sliding joints are reformulated for the computation of closed-form solutions for the kinetic parameters. The state of such systems is characterized not only by the position parameters and velocities, but in addition, the modes of contact in the sliding joints must be specified. Then the cases with one or several sets of solutions, obtained for the same position parameters, velocities, active forces and friction parameters, can be related to positions of the system with different modes of contact between sliders and guiding surfaces. They are physical unequivocal states and can be interpreted as unique solutions for the kinetic problem with specified configuration of the system. If no solutions exist, then the friction parameters considered are too large and exceed limiting values, for which friction locking occurs.     

四流体模型与m=1内扭曲模稳定性分析

利用描述俘获粒子运动的四流体模型推导出包含俘获粒子效应,离子反磁漂移,有限电阻及反常电子粘滞效应的ｍ＝１的内扭曲模本征方程和色散关系,并在等离子体芯部存在与不存在的高能粒子的两种情况下,讨论了俘获粒子效应和各种耗散效应对内扭曲模的影响。     

Three-Dimensional Numerical Analysis for Millimeter Wave TWTs

Based on Macro–particle model, the electron beam can be subdivided into 3D Macro–particles to calculate space–charge forces and 3D large–signal working equations are obtained. Finally, the numerical results for a uniform magnetic focusing field are given.     

Theory of two-photon lasers I

We start from the microscopic Hamiltonian formulated by means of creation and annihilation operators for the field modes, and creation and annihilation operators for the electrons. The virtual transitions via the intermediate atomic level are eliminated by second order perturbation theory so that an effective Hamiltonian results which describes two-photon creation or annihilation. In the next step Heisenberg equations of motion are derived for the field amplitudes, the atomic dipole moments, and the inversion. The effect of heatbaths is taken into account by means of damping terms and fluctuating forces. In the present paper these equations are averaged over the fluctuating forces and the resulting semiclassical equations are solved for the stationary state. We treat the degenerate and nondegenerate case including detuning and atomic levels with homogeneous and inhomogeneous broadening. The field modes may be either running or standing waves. A detailed discussion of the laser condition is given.     

Investigation of two-dimensional acoustic resonant modes in a particle separator

Within an acoustic standing wave particles experience acoustic radiation forces, a phenomenon which is exploited in particle or cell manipulation devices. When developing such devices, one-dimensional acoustic characteristics corresponding to the transducer(s) are typically of most importance and determine the primary radiation forces acting on the particles. However, radiation forces have also been observed to act in the lateral direction, perpendicular to the primary radiation force, forming striated patterns. These lateral forces are due to lateral variations in the acoustic field influenced by the geometry and materials used in the resonator. The ability to control them would present an advantage where their effect is either detrimental or beneficial to the particle manipulation process. The two-dimensional characteristics of an ultrasonic separator device have been modelled within a finite element analysis (FEA) package. The fluid chamber of the device, within which the standing wave is produced, has a width to height ratio of approximately 30:1 and it is across the height that a half-wavelength standing wave is produced to control particle movement. Two-dimensional modal analyses have calculated resonant frequencies which agree well with both the one-dimensional modelling of the device and experimentally measured frequencies. However, these two-dimensional analyses also reveal that these modes exhibit distinctive periodic variations in the acoustic pressure field across the width of the fluid chamber. Such variations lead to lateral radiation forces forming particle bands (striations) and are indicative of enclosure modes. The striation spacings predicted by the FEA simulations for several modes compare well with those measured experimentally for the ultrasonic particle separator device. It is also shown that device geometry and materials control enclosure modes and therefore the strength and characteristics of lateral radiation forces, suggesting the potential use of FEA in designing for the control of enclosure modes in similar particle manipulator devices.     

Numerical study of random lasing in three dimensional amplifying disordered media

In this paper, the lasing action in three-dimensional active random systems has been numerically investigated. Here, random systems of spherical dielectric particles imbedded in an active medium are considered. The quasi steady state approximation for the population inversion of the active medium is applied to solve three dimensional governing equations. Results show that when the density of particles increases to an upper limit, the intensity of lasing modes is enhanced. Also, the effects of pumping rate and particle size on the number of lasing modes and their intensity are studied. Lasing threshold of laser modes in different disordered systems is calculated and it is shown that by an appropriate selection of the central frequency of gain line-shape, the output power intensity of random lasers increases. These results are in agreement with the experimental results observed by others.     

行波管三维非线性计算机模拟的改进

采用宏粒子模型计算空间电荷力,导出行波管三维大讯号工作方程组,开发出ＶｉｓｕａｌＣ＋＋数值分析软件。随后进行计算机模拟,提出将三维空间电荷力处理为二维,大大节省了计算时间,数值结果与三维计算吻合很好。     

行波管三维非线性计算机模拟的改进

 采用宏粒子模型计算空间电荷力,导出行波管三维大讯号工作方程组,开发出Visual C++数值分析软件。随后进行计算机模拟,提出将三维空间电荷力处理为二维,大大节省了计算时间,数值结果与三维计算吻合很好。