半柔性大分子链穿越微孔行为的研究

采用动态蒙特卡罗模拟方法，模拟半柔性大分子链在电场作用下穿越纳米孔道进入球腔的输运过程. 主要研究电场强度及半柔性大分子链的刚性强度对穿孔过程的影响.发现：平均穿孔时间τ随电场强度的增大而减小，τ与链的长度N满足标度关系τ~N^α，并且电场强度E和弯曲能b对标度指数有显著影响. 研究结果表明，当电场强度为中等时，刚性弱和刚性强的大分子的穿孔过程是完全不同的. 研究半柔性大分子链穿越微孔的行为，有助于更深入认识生物大分子在生命体内的输运过程.     

含stubs量子波导系统的电子自旋极化输运性质

理论上研究了含stubs的Rashba自旋轨道耦合（spin-orbit coupling, SOC）量子波导系统的自旋极化输运性质. 利用晶格格林函数方法，发现由于stubs和SOC产生的势阱使系统中出现束缚态，这些束缚态与传播态之间相互干涉导致电导中出现Fano共振结构，同时在对应的自旋极化率中也出现Fano共振或反共振结构. 此外，由于系统结构的突变使电子被反向散射和量子干涉效应，电导中出现一系列的共振峰. 但是，当系统加上外磁场后，所有这些效应都被抑制, 系统重新出现量子化电导, 同时自旋电导也出 关键词： 量子波导 自旋极化输运 自旋轨道耦合     

电磁波辐照下量子线的电子自旋极化输运性质

理论上研究Rashba自旋-轨道相互作(SOI)量子线在外电磁波辐照下的电子自旋极化输运性质.在自由电子模型下利用散射矩阵方法,发现当Rashba SOI较弱时,自旋极化率与外电磁场频率和电子入射能量无关,而当Rashba SOI较强时,自旋极化率则强烈依赖于外场频率和电子入射能量,其物理根源是Rashba SOI使子带混合引起的.此外,当电子的入射能量增加到打开另一通道阈值时,电子的透射率出现一个反常的台阶结构,这来源于电子与光子的非弹性散射而使电子在子带间的跃迁. 关键词： 量子线 电磁波 自旋极化输运 散射矩阵     

Spin-dependent electron transport of a waveguide with Rashba spin--orbit coupling in an electromagnetic field

We investigate theoretically the spin-dependent electron transport in a straight waveguide with Rashba spin-orbit coupling (SOC) under the irradiation of a transversely polarized electromagnetic (EM) field.Spin-dependent electron conductance and spin polarization are calculated as functions of the emitting energy of electrons or the strength of the EM field by adopting the mode matching approach.It is shown that the spin polarization can be manipulated by external parameters when the strength of Rashba SOC is strong.Furthermore,a sharp step structure is found to exist in the total electron conductance.These results can be understood by the nontrivial Rashba subbands intermixing and the electron intersubband transition when a finite-range transversely polarized EM field irradiates a straight waveguide.     

Automatic detection of the belt-like region in an image with variational PDE model

In this paper, we propose a novel method to automatically detect the belt-like object, such as highway, river, etc., in a given image based on Mumford-Shah function and the evolution of two phase curves. The method can automatically detect two curves that are the boundaries of the belt-like object. In fact, this is a partition problem and we model it as an energy minimization of a Mumford-Shah function based minimal partition problem like active contour model. With Eulerian formulation the partial differential equations (PDEs) of curve evolution are given and the two curves will stop on the desired boundary. The stop term does not depend on the gradient of the image and the initial curves can be anywhere in the image. We also give a numerical algorithm using finite differences and present various experimental results. Compared with other methods, our method can directly detect the boundaries of belt-like object as two continuous curves, even if the image is very noisy.