Absorption of electromagnetic radiation by a bimetallic cylindrical particle of finite length

The absorption cross section of electromagnetic radiation is calculated for a bimetallic cylindrical particle of finite length. A general case is considered, where the ratio of the radius of the particle core to the particle radius and the ratio of the radius of the particle to its length can take arbitrary values. The conditions of diffuse reflection of electrons from the internal and external surfaces of the metal shell of the particle and from its faces are used as the boundary conditions of the problem. The effect of the ratio of the radius of the core of a bimetallic cylindrical particle to the particle radius and the ratio of the radius of the particle to its length on the electromagnetic properties of the particle is analyzed.     

Charge to radius dependency for conductive particles charged by induction

Particle charge is a critical parameter that needs to be determined in order to accurately predict behavior of a charged particle exposed to electrical forces. The effectiveness of various electrostatic applications depends directly on this charge or, more specifically, the charge to mass ratio. Previous studies report conflicting data for the size dependency of charge. In this paper, the relation between the value of charge on a conductive particle and the particle radius in the process of induction charging is investigated. The results of numerical simulations of a liquid atomization process are presented and a novel approach to the analytical solution of the problem is introduced. It is found that the exponent in the particle charge to radius dependency is equal to two when the particle is in the direct contact with the bulk material. The radius exponent decreases rapidly as the atomizing ligament length is increased. For ligament lengths many times greater than the particle radius, the radius exponent approaches one. Agreement between numerical and analytical results is found to be very good. The results of this study clarify some of the conflicting data in the previously published literature and suggest that the particle charge is practically linearly dependent on radius for atomized liquid particles and proportional to particle surface area for solid particles. In addition it is shown that the charge to mass ratio for liquid particles can be maximized by ensuring the ligament length during atomization is maximum.     

极区夏季中层顶区域尘埃粒子参数的研究

采用轨道受限运动方法研究了极区夏季中层顶区域的尘埃粒子电荷数与尘埃粒子半径。利用尘埃等离子体充电理论,建立了尘埃粒子充电方程模型,得到尘埃粒子充电时尘埃电荷数和半径的比值。然后结合ECT02实验数据,分析了发生极区中层夏季回波现象时极区中层顶区域尘埃粒子电荷数和半径的比值,并得到尘埃粒子的半径以及尘埃粒子所带电荷量。结果表明,极区中层顶区域的尘埃粒子平均所带电荷不到一个,它的半径约为20nm。     

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采用轨道受限运动方法研究了极区夏季中层顶区域的尘埃粒子电荷数与尘埃粒子半径。利用尘埃等离子体充电理论,建立了尘埃粒子充电方程模型,得到尘埃粒子充电时尘埃电荷数和半径的比值。然后结合ECT02实验数据,分析了发生极区中层夏季回波现象时极区中层顶区域尘埃粒子电荷数和半径的比值,并得到尘埃粒子的半径以及尘埃粒子所带电荷量。结果表明,极区中层顶区域的尘埃粒子平均所带电荷不到一个,它的半径约为20nm。     

Force exerted on a conducting spherical particle near the plate of a plane capacitor

The potential energy and the interaction force of a conducting spherical particle and a similarly charged plane plate are calculated for relatively small distances. The force is calculated from the potential energy and the plate is represented as a conducting sphere whose radius is 100 times greater than the radius of the particle. It is assumed that the particle is not charged by the plate. The domains of parameters in which the particle is always repulsed from the plate and in which the attraction takes place are determined.     

Analysis of ultrasonic attenuation in particle-reinforced plastics by a differential scheme

Attenuation of ultrasonic longitudinal waves in some particle-reinforced polymer composites is studied theoretically by a micromechanical model based on a differential (incremental) scheme. A set of differential equations is established by which the attenuation spectrum of the composite can be computed from the known properties of viscoelastic matrix and elastic particles. For a composite reinforced with glass particles with radius 0.15 mm, the proposed scheme is shown to predict the attenuation in better agreement with the foregoing experimental results than the previous simplistic independent scattering model. Based on this scheme, the dependence of the longitudinal attenuation spectrum of a particulate polymer composite on the wavelength-to-particle radius ratio and the particle volume fraction is examined in detail. It is then shown theoretically that the attenuation of the composite decreases monotonically with the particle volume fraction when the particle radius is sufficiently small compared to the incident wavelength, while it shows non-monotonic particle-fraction dependence when the ratio of the particle radius to the wavelength is larger. To examine this theoretical finding from an experimental point of view, the longitudinal attenuation in a glass-particle-reinforced polyester composite with particle radius 0.0225 mm is measured for different particle volume fractions. The measured attenuation characteristics are shown to support the qualitative features of the theoretical prediction.     

Analysis of ultrasonic attenuation in particle-reinforced plastics by a differential scheme

Attenuation of ultrasonic longitudinal waves in some particle-reinforced polymer composites is studied theoretically by a micromechanical model based on a differential (incremental) scheme. A set of differential equations is established by which the attenuation spectrum of the composite can be computed from the known properties of viscoelastic matrix and elastic particles. For a composite reinforced with glass particles with radius 0.15 mm, the proposed scheme is shown to predict the attenuation in better agreement with the foregoing experimental results than the previous simplistic independent scattering model. Based on this scheme, the dependence of the longitudinal attenuation spectrum of a particulate polymer composite on the wavelength-to-particle radius ratio and the particle volume fraction is examined in detail. It is then shown theoretically that the attenuation of the composite decreases monotonically with the particle volume fraction when the particle radius is sufficiently small compared to the incident wavelength, while it shows non-monotonic particle-fraction dependence when the ratio of the particle radius to the wavelength is larger. To examine this theoretical finding from an experimental point of view, the longitudinal attenuation in a glass-particle-reinforced polyester composite with particle radius 0.0225 mm is measured for different particle volume fractions. The measured attenuation characteristics are shown to support the qualitative features of the theoretical prediction.     

Dynamic Light Scattering Measurement of Nanometer Particles in Liquids

Dynamic light scattering (DLS) techniques for studying sizes and shapes of nanoparticles in liquids are reviewed. In photon correlation spectroscopy (PCS), the time fluctuations in the intensity of light scattered by the particle dispersion are monitored. For dilute dispersions of spherical nanoparticles, the decay rate of the time autocorrelation function of these intensity fluctuations is used to directly measure the particle translational diffusion coefficient, which is in turn related to the particle hydrodynamic radius. For a spherical particle, the hydrodynamic radius is essentially the same as the geometric particle radius (including any possible solvation layers). PCS is one of the most commonly used methods for measuring radii of submicron size particles in liquid dispersions. Depolarized Fabry-Perot interferometry (FPI) is a less common dynamic light scattering technique that is applicable to optically anisotropic nanoparticles. In FPI the frequency broadening of laser light scattered by the particles is analyzed. This broadening is proportional to the particle rotational diffusion coefficient, which is in turn related to the particle dimensions. The translational diffusion coefficient measured by PCS and the rotational diffusion coefficient measured by depolarized FPI may be combined to obtain the dimensions of non-spherical particles. DLS studies of liquid dispersions of nanometer-sized oligonucleotides in a water-based buffer are used as examples.     

Absorption of electromagnetic radiation by an inhomogeneous spherical particle

The cross section of absorption of electromagnetic radiation by an inhomogeneous spherical particle is calculated. The general case of an arbitrary value of the ratio of the particle radius to the radius of the dielectric core is considered. The condition of diffuse reflection of electrons from the inner and outer surfaces of the metal layer of the particle is taken as the boundary condition of the problem. The limiting cases are considered and the results obtained are discussed.     

基于多粒子群算法的视频跟踪研究

粒子群算法是一种新的进化算法,算法思路适合于进行视频跟踪,但是由于在视频跟踪过程中以跟踪窗口作为粒子,因此该粒子具有中心点横坐标、中心点纵坐标和窗口半径三维特征向量,计算冗余较大,难以满足视频跟踪的实时性要求。提出了一种多粒子群视频跟踪算法,即在跟踪过程中使用多个粒子群,粒子群与粒子群之间粒子半径不同,在各粒子群以评价函数收敛到最佳中心点后,再完成各自半径的一维粒子群计算。这样就可将三维粒子群计算分为一个两维和一个一维粒子群计算,最后通过比较得出最佳粒子,作为搜索结果。分析了这一算法成立的必要条件,即当选择Bhattacharyya系数计算方法作为粒子群算法的评价函数时,大于目标的固定窗体的中心点可以收敛到目标的形心。实验证明,这种基于多粒子群的跟踪算法可以应用于实时视频跟踪,其跟踪效果优于传统算法。     

Effect of the character of conduction electron reflection on the electromagnetic properties of an inhomogeneous cylindrical particle

The cross section of magnetic absorption of a small elongated cylindrical particle with a dielectric core and metallic shell is calculated. The general case of an arbitrary value of the ratio of the dielectric core radius to the radius of the particle is considered. The condition of mixed (mirror-diffuse) reflection of conduction electrons from the boundaries of the metal layer of the particle is chosen as the boundary condition to the problem. The limiting cases are considered, and the results obtained are discussed.     

The effect of the character of electron reflection on the electromagnetic properties of an inhomogeneous spherical particle

The magnetic absorption cross section of a small spherical particle with a dielectric core and a metallic shell is calculated. The general case is considered when the ratio of the radius of the dielectric core to the total radius of the particle may take arbitrary values. The condition of specular-diffuse reflection of conduction electrons from the surfaces of the metal layer of the particle is chosen as the boundary conditions of the problem. The limit cases are considered, and the results are discussed.     

Numerical simulation of particle size effects on contact electrification in granular systems

Based on the contact charge transfer model between two particles due to a single collision proposed by Apodaca, the contact charges carried on a particle is derived due to multiple collisions, including the repeat collisions between two particles and the collisions with different particles, in mixed-size granular system of identical material. The effect of the particle size on the charges carried on the particle is simulated. The results indicate that for a mixed-size granular system, due to multiple collisions among particles, there exists a threshold particle radius, the particles with radius higher than which and the particles with radius lower than which carry opposite charges. The threshold particle radius is equal to mean value of particle size in the mixed-size granular system. Basically, the polarity of the charges carried on the largest particle is same as the polarity of the transfer charge carrier, and in case of the positive charge transferred, the largest particle will be positively charged and the smallest particle will be negatively charged, and vice versa. In the same size region, the more dispersive the particle size is, the more the net charges can be produced. In normal-distributed granular system, the magnitude of contact charge is determined mainly by the particle size distribution, size region, total particle number and the relative impact velocity.     

格子玻尔兹曼方法模拟弯流道中粒子的惯性迁移行为

本文发展了一个能够模拟微流场环境下粒子惯性迁移行为的三维耦合模型.该模型采用基于动理论的格子玻尔兹曼方法(LBM)描述流体流动,采用牛顿动力学模型描述粒子的平动和转动,采用基于LBM反弹格式的运动边界法实现流体与粒子模型的耦合.模拟了重力作用下粒子的沉降过程和Couette流条件下粒子的转动过程,通过将模拟结果与文献中的基准解进行对比定量验证了模型的可靠性.模拟了不同大小的球形粒子在环形流道中的迁移,成功复现了经典的流道截面二次流形成过程,分析了粒径大小对粒子在流道中平衡位置的影响机理.结果表明,粒子在弯流道中的平衡位置与粒径大小密切相关,小半径粒子的平衡位置靠近流道外侧而大半径粒子则靠近流道内侧.通过实验对模拟结果进行了定性验证.本模型为深入研究微流场环境下粒子的运动特性以及开发微流控粒子分选器件提供了参考依据.     

Teilchen-Modelle und effektive Radien in der Allgemeinen Relativitätstheorie

Particle Models and Effective Radius in the General Theory of Relativity We discuss the role of the classical particle radius defined in the classical field models of particles for the general relativistic particle problem suggested by EINSTEIN. The main point is that in General Relativity the point-like particles without field masses may be self-consistent but not the model particles with an effective radius given by the Schwarzschild radius of the mechanical particle mass.     

Characteristics of gain spectrum of modulation instability in soft matter

We investigate the spatial modulation instability in colloidal suspension based on the nonlinear Schrödinger equation. By a standard linear stability analysis, we obtain the expression for instability gain and identified the relationship between the measurable instability characteristic parameters and the particle radius, the optical beam width. It is shown that the modulation growth rate, the maximum growth rate, cut-off frequency and the fastest growth frequency increase as the particle radius decreases and (or) the beam width increases if the optical intensity is constant. Moreover, the ultimate values of the cut-off frequency and the fastest growth frequency are proportional to the beam width, while are independent of the sphere radius. The results provide a new approach to measure the sphere radius and to control the characteristic parameters of modulation instability through the beam width.     

Heat-transfer processes upon laser heating of inert-matrix-hosted inclusions

A model to describe the heating of metal inclusions in inert media by a laser radiation pulse with allowance for the heat-transfer and melting processes in the matrix and inclusion materials is proposed. The time regularities of the heating of the matrix and inclusions were examined, and the dependences of the maximum temperature on the particle surface on the laser pulse energy density and on the particle radius were obtained. Approximate formulae for the maximum heating temperature and for the radius of most heated particles are proposed. We show that melting processes result in a reduction of the maximum heating temperature and in an insignificant variation of the radius of most heated particles.     

Altitude and formation conditions of noctilucent clouds in the Earth atmosphere

A model for the motion of dust particles in the atmosphere, forming noctilucent clouds, is developed. The equilibrium particle positions are calculated for different initial conditions. The analysis of the time evolution of the particle radius and the particle positions gives rise to oscillating behavior, which was also obtained in earlier models.     

近红外波段气溶胶的衰减特性研究

在已知大气气溶胶折射率和气溶胶谱分布的基础上, 对近红外波段的气溶胶衰减特性进行了研究。利用Mie散射理论计算并讨论了气溶胶的消光、散射、吸收效率因子随尺度参数的变化和消光系数随半径和波长的变化, 并且在MATLAB中对各种变化情况进行了仿真。结果表明, 三种气溶胶粒子的消光和散射能力依次为沙尘性粒子, 水溶性粒子, 烟煤。消光系数在粒子半径和入射波长相近时达到最大, 并且粒子半径对消光、散射、吸收系数的影响比入射波长更明显。这些结论可以为红外辐射在大气中的衰减计算和分析提供依据。     

球形粒子在聚焦拉盖尔-高斯光束中的散射特性研究

研究了球形粒子在聚焦拉盖尔-高斯光束中的散射特性. 根据广义Mie理论, 推导出球形粒子在聚焦拉盖尔-高斯光束中散射系数的解析公式. 针对光束的电场分布及粒子散射强度进行了数值仿真, 讨论了散射强度随散射角、散射球粒子半径和拓扑荷的变化特性, 并通过散射系数解释了散射强度分布的振荡现象. 结果表明, 在聚焦拉盖尔-高斯光束照射下, 球形粒子的后向散射强度随着粒子半径的增大而逐渐增大; 后向散射强度开始增大时对应的粒子半径与拓扑荷有关. 通过与高斯光束的对比, 可以看出球形粒子在聚焦拉盖尔-高斯光束中散射特性的差异, 使其在粒径测量、光通信和大气后向散射探测等方面具有潜在应用价值.