Electroclinic effects in a homogeneously aligned smectic A cell

The electroclinic effect, in a material having a first order S_A to S_C* transition, is studied using the half leaky guided mode geometry. Using an approximately 1 μm thick, homogeneously aligned cell, the voltage induced director twist is characterized at a few temperatures in the S_A phase. The mean field theory readily explains the data recorded at low fields where a linear dependence on voltage is found. However, at higher fields, an unexpected saturation occurs which is most likely caused by the influence of strong surface anchoring forces.     

超短光脉冲作用下的二能级原子

考虑到光场的振幅随时间分布的影响时,我们重新研究了光场与二能级原子相互作用的跃迁几率问题。在强光信号作用下,经过一定的数学代换后,上能级几率的求解可归结为类希尔方程求解;在弱光信号作用下,利用转动波近似(RWA),给出了二能级原子跃迁几率的解析表达式,并讨论了几种典型脉冲光场的分布。     

Neural Network Models for Finline Discontinuities

The radial basis network is used as the finline discontinuities electromagnetic artifical neural network(EMANN) models. EM software analysis is employed to characterize finline discontinuities. EMANN models are then trained using physical parameters and frequency as inputs and equivalent electric circuit element parameters of finline discontinuities as outputs. Once trained , the EMANN models can simulate equivalent electric circuit element parameters of finline step, notch and strip very fast and efficiently.     

Self-organized periodic photonic structure in a nonchiral liquid crystal

A hybrid-aligned cell of the smectic A liquid material 8CB gives two stable director configurations, one of which is periodic and gives strong diffraction of light. This photonic lattice director profile arises from "frustration" caused by conflicting constraints imposed by the boundary conditions and the constant amplitude smectic density wave. A model is proposed which accords well with the experiment results, predicting correctly the dependence of the periodicity on the cell thickness and reproducing optical polarization microscopy results.     

深过冷Ag-Cu-Ge三元共晶合金的相组成与凝固特征

在Ag_38.5Cu_33.4Ge_28.1三元共晶合金的深过冷实验中，获得的最大过冷度为175 K(0.22T_E). XRD分析表明，不同过冷条件下其共晶组织均由(Ag),(Ge)和η(Cu₃Ge)三相组成. 在小过冷条件下，三个共晶相协同生长，凝固组织粗大.随着过冷度的增大，共晶组织明显细化，(Ge)相与其他两相分离，以初生相方式生长，而(Ag)相与η相始终呈二相层片共晶方式共生生长. 当过冷度超过80 K时，初生相(Ge)由小过冷时的块状转变为具有小面相特征的枝晶方式生长. 部分小面相(Ge)枝晶出现规则的花状，花瓣数介于5—8之间，并且过冷度越大(Ge)相越容易分瓣. 花状(Ge)枝晶的晶体表面为{111}晶面簇，择优生长方向为〈100〉晶向族. 关键词： 三元共晶 晶体形核 深过冷 快速凝固     

Dendritic and eutectic growth in Sb<Subscript>60</Subscript>Ag<Subscript>20</Subscript>Cu<Subscript>20</Subscript> ternary alloy

The rapid solidification of Sb60Ag20Cu20 ternary alloy was realized by high undercooling method, and the maximum undercooling is up to 142 K (0.18TL). Within the wide undercooling range of 40-142 K, the solidified microstructures are composed of (Sb), θand ε phases. High undercooling enlarges the solute solubility of (Sb) phase, which causes its crystal lattice to expand and its crystal lattice constants to increase. Primary (Sb) phase grows in two modes at small undercoolings non-faceted dendrite growth is the main growth form; whereas at large undercoolings faceted dendrite growth takes the dominant place. The remarkable difference of crystal structures between (Sb) and θphases leads to (θ Sb) pseudobinary eutectic hard to form, whereas strips of θform when the alloy melt reaches the (θ Sb) pseudobinary eutectic line. The cooperative growth of θand ε phases contributes to the formation of (ε θ) pseudobinary eutectic easily. In addition, the crystallization route has been determined via microstructural characteristic analysis and DSC experiment.     

Transverse-mode controlling of a large-mode-area multimode fiber laser

Coiling technique is used to control the transverse mode of a large-mode-area (LMA) multimode fiber laser. By winding the fiber to a coil with different radius, high-order modes of a multimode fiber laser are suppressed one by one and finally 15.4-W single-transverse-mode output is achieved when the coil radius is 20 mm. It is found that as the coil radius decreases, the beam quality of a multimode fiber laser gets better but the slope efficiency drops for higher-order modes are discriminated. During the experiment, as the coil radius of multimode fiber changes, output characteristic of the laser has been measured. Meanwhile,the mode loss of different modes is calculated theoretically. It is proved that the experimental measured results fit well with the theoretically calculated results.     

Gerbes and twisted orbifold quantum cohomology

In this paper,we construct an orbifold quantum cohomology twisted by a flat gerbe. Then we compute these invariants in the case of a smooth manifold and a discrete torsion on a global quotient orbifold.