A charged particle moving near a perfectly conducting sphere

The problem of a charged particle moving in an arbitrary prescribed trajectory near a perfectly conducting sphere is formulated in terms of the magnetic-field integral equation on the sphere. The integral equation is solved with the aid of the solutions of the associated eigenvalue problem. A detailed study of the canonical problem, where the charged particle moves around a sphere in a circular orbit, reveals that a sufficiently accurate solution can be obtained by solving two independent quasi-static problems. Validity criteria are established for the quasi-static solutions in terms of the particle's speed and distance from the sphere. These quasi-static problems can be easily generalized and solved for particles of arbitrary motion and conductors of arbitrary shape. Induced surface currents and charges on the sphere as well as the rate of energy loss of the charged particles are calculated.     

Motion of a charged particle in electric and magnetic fields

The motion of a charged particle in time-varying uniform electric and magnetic fields has been determined exactly by writing the Lorentz force equation in a matrix form. The general solution is obtained by solving the ordinary first-order linear differential equation.     

Transient response of a thin wire to a moving charged particle

The transient current on a thin wire induced by a charged particle moving parallel to the wire axis is studied. An explicit analytical solution for the induced current is obtained by utilizing the natural-mode method in conjunction with the method of asymptotic expansion. It is found that the solution can be split into two parts: one part consists of damped sinusoidal oscillations and the other exhibits quasistatic-like behavior. Numerical results are presented and compared with some selected results obtained directly by numerically solving a spacetime domain integral equation for the induced wire current.     

超晶格中带电粒子的相干电磁辐射

指出了对周期介质加上周期变化的电场,可望获得时空周期变化的周期场;在这种场中运动的带电粒子表现出了人们预期的行为.对这种情况下的电磁辐射进行了讨论,并以掺杂超晶格为例进行具体分析.首先,在经典力学框架内和偶极近似下,把粒子的纵向运动方程化为广义摆方程;在小振幅近似下,把无扰动系统的摆方程进一步化为Duffing方程.用Jacobian椭圆函数和第一类椭圆积分严格地给出了粒子运动轨道和它的运动周期;讨论了粒子的辐射能量和辐射强度.结果表明,当超晶格的势阱深度为1 eV,为λp=100 nm,γ=104时,电子的辐射频率为8.85×1019,位于x-能区.     

带电粒子的准沟道辐射

引入新的相互作用势——正弦平方势,并从运动方程的旋转周期解出发,解析地处理了带电粒子的准沟道辐射。讨论了这种辐射与沟道辐射的区别,计算了它对总辐射强度的贡献。     

非谐激励与周期弯晶中粒子运动的混沌行为

利用Melnikov方法讨论了非谐激励系统的混沌行为,并在极限情况κ→0下,把非谐激励转化为谐波激励,而运动方程化为倒置摆方程.倒置摆方程描写了带电粒子在周期弯晶中翻越势垒的横向运动行为.结果表明:系统的稳定性与参数有关,适当调整参数就能保证系统是稳定的;即使保持参数不变,调整系统初始状态也可以使系统完成从无序向有序,或者从有序向无序转换.     

参数共振与晶体摆动场中粒子运动的稳定性

从倒置摆方程出发讨论了无扰动系统的相平面特征,并用Jacobi椭圆函数和椭圆积分解析地描述了带电粒子的电磁辐射;用多尺度法导出了扰动系统的频率响应、临界条件和一阶近似解,揭示了系统不可逆性、不稳定性和弛豫行为.用拉莫公式讨论了带电粒子的辐射强度.指出了适当调节参数可以保证系统的稳定性.     

带电粒子在超品格量子阱沟道中的准沟道辐射

引入正弦平方势,在经典力学框架内,把粒子的运动方程化为标准的摆方程.用Jacobian椭圆函数和椭圆积分解析地给出了系统的解和粒子运动周期,并从方程的旋转周期解出发讨论了带电粒子的准沟道辐射.将准沟道辐射和沟道辐射进行了比较,发现二者的主要差别在于准沟道粒子的横向速度的平均值不为零,而它的辐射能量在k~c=0.5时,比沟道辐射大2.4倍.

Abstract：

In the frame of the classical mechanics the motion equation of particles is reduced to the pendulum equation by using the sine-squared potential. The solution of the equation and the period of the particle motion are expressed exactly by means of Jacobian elliptic function and the elliptic integral. The quasi-channeling radiation of the charged particles is discussed based on the rotational periodic solution. From the comparison between quasi-channeling radiation and channeling radiation, it is found that their main difference is that the average transverse velocity of the quasi-channeling particles is not zero,and its radiation energy is 2.4 times more than that of the channeling radiation if k~c =0.5.     

混合激励与应变超晶格系统沟道运动的临界特征

从势和场的观点出发讨论了带电粒子在应变超晶格中的运动行为.在经典力学框架内和偶极近似下,引入正弦平方势,把粒子运动方程化为具有阻尼项和混合激励项的广义摆方程.利用Melnikov方法讨论了系统的临界性质与混沌行为.结果表明,系统的混沌行为与它的参数有关,适当调节参数,就可以原则上保证系统的稳定性.     

时空周期场与非相对论粒子的电磁辐射

寻找新光源,特别是短波长激光光源引起了人们的广泛兴趣.在时空周期场中运动的带电粒子表现出了预期的行为.指出了置于外场中的超晶格是典型的时空周期场.假设掺杂超晶格的导带底是周期调制的,在经典力学框架内,将非相对论粒子在时空周期场中的运动方程化为带有阻尼项和受迫项的摆方程.在无阻尼情况下,利用摄动法导出了系统的一阶近似解,讨论了高次谐波辐射和辐射强度;用Hamiltonian原理和相平面方法讨论了系统的稳定性.在阻尼情况下,利用Melnikov方法讨论了系统的临界特征和混沌行为.结果表明,非相对论粒子的高次谐波辐射存在局部极大,可望作为短波长激光光源.由于系统的稳定性与它的参数有关,只需适当调节这些参数,系统的稳定性就能得到保证.     

Electrostatic separation of a charged-particle layer between electrodes

The problem of electrostatic separation of a layer of charged particles of small size compared with the layer thickness was studied. The particle layer initially is confined between two electrodes, and experiments were carried out on a dispersion of particles in a liquid to determine the mass fraction remaining on each electrode after electrode separation. The dependence of the mass fraction on particle charge and applied potential was measured. A physical model was formulated and found to be in good agreement with experimental measurements.     

强电磁脉冲电离大气三维FDTD仿真

强电磁脉冲在大气中传播时会导致大气分子电离,且电离气体又会反作用于传播的电磁波,因此是 一个传播状态动态实时变化的物理过程。要准确模拟该过程需要综合考虑电磁波传播、大气电离、带电粒子运动等 物理过程。为解决该问题,文中结合麦克斯韦方程、等离子体方程、磁流体动力学方程等,构建多物理场分析方程 组,该方程组能够考虑强电磁脉冲传播时大气电离、扩散、附着、复合等物理效应。进而结合三维时域有限差分方法 (FDTD)来构建动态仿真模型,对强电磁脉冲在大气中的传播过程进行仿真并分析其宏观大气电离效果。     

Interaction of charged particle flows with plasmons in two-dimensional electron gas

The theory of interaction of charged particle beams with 2D electron gas, located in the field of the delta-like potential wallU(y) =U _oδ(y) has been developed. The kinetic equation for plasmons in 2D electron gas was obtained; the conditions of arising of their instability are given and the corresponding expressions for the increment of plasmons are found.     

Transition radiation caused by a chiral plate

A simple calculation is made of the electromagnetic field radiated due to a charged particle traversing a plate of chiral material. The transition radiation from this chiral plate is round to differ from the usual dielectrie transition radiation. Discussion is presented placing in evidence the characteristics of the radiation and comments are made concerning the possible applicability of the transition radiation mechanism.     

Effect of non-spherical atmospheric charged particles and atmospheric visibility on performance of satellite-ground quantum link and parameters simulation

In order to study the relationship between the non-spherical atmospheric charged particles and satellite-ground quantum links attenuation. The relationship among the particle concentration, equivalent radius, charge density of the charged particle, the attenuation coefficient and entanglement of the satellite-ground quantum link can be established first according to the extinction cross section and spectral distribution function of the non-spherical atmospheric charged particles. The quantitative relationship between atmospheric visibility and communication fidelity of satellite-ground quantum link were analyzed then. Simulation results show that the ellipsoid, Chebyshev atmospheric charged particle influences on attenuation of the satellite-ground quantum link increase progressively. When the equivalent particle radius is 0.2 μm and the particle concentration is 50 μg/m³, the attenuation coefficient and entanglement of the satellite-ground quantum link is 9.21 dB/km, 11.46 dB/km and 0.453, 0.421 respectively; When the atmospheric visibility reduces from 8 km to 2 km, the communication fidelity of satellite-ground quantum link decreases from 0.52 to 0.08. It is shown that the non-spherical atmospheric charged particles and atmospheric visibility influence greatly on the performance of the satellite-ground quantum link communication system. Therefore, it is necessary to adjust the parameters of the quantum-satellite communication system according to the visibility values of the atmosphere and the shapes of the charged particles in the atmosphere to improve reliability of the satellite-ground quantum link.     

Segmentation of brain MR images using a charged fluid model

In this paper, we developed a new deformable model, the charged fluid model (CFM), that uses the simulation of a charged fluid to segment anatomic structures in magnetic resonance (MR) images of the brain. Conceptually, the charged fluid behaves like a liquid such that it flows through and around different obstacles. The simulation evolves in two steps governed by Poisson's equation. The first step distributes the elements of the charged fluid within the propagating interface until an electrostatic equilibrium is achieved. The second step advances the propagating front of the charged fluid such that it deforms into a new shape in response to the image gradient. This approach required no prior knowledge of anatomic structures, required the use of only one parameter, and provided subpixel precision in the region of interest. We demonstrated the performance of this new algorithm in the segmentation of anatomic structures on simulated and real brain MR images of different subjects. The CFM was compared to the level-set-based methods [Caselles et al. (1993) and Malladi et al (1995)] in segmenting difficult objects in a variety of brain MR images. The experimental results in different types of MR images indicate that the CFM algorithm achieves good segmentation results and is of potential value in brain image processing applications.     

介观测量仪器对单电子态的量子测量

对于一个实际的测量装置,即被介观测量仪器所测量的两态(量子比特)或多态量子系统做了理论研究.为了正确描述测量引起的反作用,发展了一个保持细致平衡条件的量子主方程的方法,建立的这套方案适用于任意电压和任意温度.     

Quantum Measurement of Single Electron State by a Mesoscopic Detector

对于一个实际的测量装置,即被介观测量仪器所测量的两态(量子比特)或多态量子系统做了理论研究.为了正确描述测量引起的反作用,发展了一个保持细致平衡条件的量子主方程的方法,建立的这套方案适用于任意电压和任意温度.     

Influence of thunderstorm cloud on the performance of satellite-to-ground quantum link and parameters simulation

In order to investigate the effect of thunderstorm cloud on the performance of satellite-to-ground quantum link,according to the extinction cross section and the number concentration distribution function of the charged particle in the thunderstorm cloud,the relationships among the particle concentration,charge density and link attenuation of charged particles in atmosphere were established.The relationship between the atmospheric concentration of charged particles,the charge density on the average channel capacity,channel fidelity,channel survival function and bit error rate of quantum key distribution system were put out.The simulation results show that the thunderstorm cloud has a significant effect on the performance of the satellite-to-ground quantum link.So in order to improve the reliability of satellite-ground quantum communication,the system parameters should be adjusted according to the forecast of the thunderstorm cloud.     

周期弯晶摆动场辐射的混沌振荡

周期弯曲晶体中做沟道运动的带电粒子,在沟道辐射的同时,还将产生摆动场辐射.引入正弦平方势,并考虑运动阻尼和非线性影响,在经典力学框架内和偶极近似下,把粒子的运动方程化为具有阻尼项和受迫项的摆方程.利用梅利尼科夫(Melnikov)方法分析了异宿轨道的分叉与系统进入斯梅耳(Smale)马蹄意义下的混沌行为.结果表明,系统进入混沌的临界条件与它的具体参数有关,只需适当调节这些参数就可以原则上避免或控制混沌,从而进一步保证系统有效输出x-激光或γ-激光.