Efficient computation of the 2-D Green's function for 1-D periodic structures using the Ewald method

The Ewald method is applied to accelerate the evaluation of the Green's function of an infinite periodic phased array of line sources. The Ewald representation for a cylindrical wave is obtained from the known representation for the spherical wave, and a systematic general procedure is applied to extend previous results. Only a few terms are needed to evaluate Ewald sums, which are cast in terms of error functions and exponential integrals, to high accuracy. Singularities and convergence rates are analyzed, and a recipe for selecting the Ewald splitting parameter /spl epsiv/ is given to handle both low and high frequency ranges. Indeed, it is shown analytically that the choice of the standard optimal splitting parameter /spl epsiv//sub 0/ will cause overflow errors at high frequencies. Numerical examples illustrate the results and the sensitivity of the Ewald representation to the splitting parameter /spl epsiv/.     

Efficient computation of the periodic Green's function in layereddielectric media

A technique for the efficient computation of the periodic Green's function in layered dielectric media is presented. The technique is based on expanding the spectral Green's function into a finite number of inverse-transformable complex exponential functions. This enables the use of Poisson's summation formula to express the periodic Green's function as a combined sum of spectral terms and spatial terms, each set of which is rapidly convergent. Numerical results are obtained for the on-plane case, in which the direct summation of the series converges extremely slowly. Using the accelerated summation formula of this study, a computation time reduction of 160-fold is obtained. The technique can be applied to a wide class of problems in which periodic structures are to be modeled     

基于双平行线阵的相干分布源二维DOA估计

针对现有相干分布源二维波达方向(DOA)估计算法存在的一些问题,基于双平行均匀线阵提出了一种相干分布源二维DOA估计新算法。利用旋转不变的思想并结合传播算子法来估计相干分布源的二维中心DOA。无需谱搜索和对样本协方差矩阵做特征分解,和传统算法相比,其计算复杂度更低。此外,还给出了详细的参数配对过程,因而能够应用于多源场合。算法在小角度扩展条件下估计性能良好,其性能甚至接近于一维交替搜索算法。算法还是一种对角分布先验知识盲的估计。仿真结果证实了算法的有效性。     

Controlling the conductance of single-molecule junctions with high spin filtering efficiency by intramolecular proton transfer

The pursuit of miniaturization of magnetic electronic components spurs intensive theoretical and experimental researches on designing molecule-scale magnetic devices. Controlling the transport properties is one of the most vital focuses for magnetic molecular devices. In this work, magnetic devices constructed by a single epindolidione (Epi) molecule (5,11-dihydrodibenzo[b,g][1,5]naphthyridine-6,12-dione) bridging two zigzag graphene nanoribbon (zGNR) electrodes are theoretically designed. The Epi molecule can be converted between the keto and enol forms, which is confirmed by first principle molecular dynamics method. The influences of intramolecular proton transfer and the bridging manner between the core molecule and zGNR electrodes on the magnetic transport properties are investigated. Spin-resolved current-voltage (I-V) curves show that both the keto and enol devices display remarkable spin filtering effect. However, the effect of intramolecular proton transfer on the electron transport properties depends on the bridging manner between the Epi molecule and zGNR electrodes. When the Epi molecule is connected to zGNR electrodes with 4,7-sites (A bridging manner), the electron transport properties of molecular junctions are hardly affected by the intramolecular proton transfer. On the contrary, the conductance of the molecular junctions is significantly modulated by the intramolecular proton transfer when the Epi molecule is connected to zGNR electrodes with 4,4′-sites (B bridging manner). Further analysis reveals that the high spin filtering effect originates from stronger coupling between spin-up edge electronic states of zGNR electrodes and states of the core molecule. With B bridging manner, the conjugation characteristics of the Epi molecule as well as the transmission pathway of tunneling electrons can be largely modulated by the intramolecular proton transfer. Our work proposes a feasible way to control the conductance of single-molecule junctions by taking advantage of intramolecular proton transfer.     

球状分层微带天线并矢格林函数的有效处理

采用提取格林函数渐进项的方法,成功克服了分层介质中球并矢格林函数计算无穷级数收敛慢的缺陷,提取出的级数形式的格林函数用球汉克尔函数的加法定理转换成闭合形式的格林函数,通过化简,使之与自由空间的格林函数有着相同的形式。因此,可采取相同的方式处理格林函数的奇异性,然后,采用以RWG为基函数的矩量法计算了圆形贴片与方形贴片微带天线的输入特性,并与文献结果、FEKO仿真结果比较,验证了方法的有效性和正确性。     

Exact analytic solutions for the nonintegrable dispersive long wave equations in (2+(1)-D spaces

Nonlinear evolution equations are of broad interest in physics and various fields of sciences. In this paper, based on the idea of balancing-act method and the computerized symbolic computation, some exact analytic solutions for the nonintegrable dispersive long wave equations in (2 1)-dimensionalspaces have been obtained.