涡旋光在大学物理实验教学中的探究

涡旋光具有独特的强度和螺旋相位结构而备受人们的关注。基于涡旋光与铷原子相互作用，本文研究分析了入射光的频率、拓扑核数以及偏振状态等参量涡旋光束轮廓和能量分布的影响。实验结果表明这些参量可以实现对涡旋光空间分布的有效调制。我们的实验探索能让大学生对涡旋光有更深的理解，拓展他们的眼界。本实验研究也将在大学物理实验教学方面具有潜在的应用。     

A POSTERIORI ERROR ESTIMATES FOR FINITE ELEMENT APPROXIMATIONS OF THE CAHN-HILLIARD EQUATION AND THE HELE-SHAW FLOW

This paper develops a posteriori error estimates of residual type for conforming and mixed finite element approximations of the fourth order Cahn-Hilliard equation ut ＋ △（ε△Au-ε^-1f（u）） = 0. It is shown that the a posteriori error bounds depends on ε^-1 only in some low polynomial order, instead of exponential order. Using these a posteriori error estimates, we construct at2 adaptive algorithm for computing the solution of the Cahn- Hilliard equation and its sharp interface limit, the Hele-Shaw flow. Numerical experiments are presented to show the robustness and effectiveness of the new error estimators and the proposed adaptive algorithm.     

离散几何的两个铺砌问题

利用图论和代数的方法研究离散几何中的两个铺砌问题:1)给出1×2长方形铺砌多米诺骨牌的充分必要条件;2)对高维空间盒子的情形,给出m_1×m_2×…×m_n砖能够铺砌a_1×a_2×…×a_n盒子的一些必要条件和充要条件.     

二部图上完美匹配的正交匹配分解

给定简单二部图G=（V，E），最大度是k（k≥3），G有一个完美匹配M={e1，e2，…，ek}。称边集E的划分{E1，E2，…，El}是G的一个关于肼的正交匹配分解，如果对每一个El是G的匹配并且包含且仅包含肼中的一条边。在本文中我们将证明对于简单二部图G，存在关于完美匹配肼的正交匹配分解，并给出了求这个分解的多项式时间算法。     

任意波长云母波片的制作技术

本文给出了由已测得的云母片对6328 A激光的相位延迟,推算任意波长的延迟的几种方法。对这几种方法进行了分析、比较。根据误差讨论,确定了制作任意波长波片的方法。     

光纤传感技术中的铌酸锂集成光学

介绍铌酸锂(LiNbO_3)集成光学器件的光纤激光多普勒测速仪、光纤温度传感器和光纤微位移传感器的构造和工作原理。     

Non-Gravitational Effects with Density-Matching in Evaluating the Influence of Sedimentation on Colloidal Coagulation

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions in studies on dynamic behaviour of a colloidal system. However, the associated changes in the solvent composition may bring side effects to the properties investigated and therefore might lead to a faulty conclusion if the relevant correction is not made. To illustrate the importance of this side effect, we present an example of the sedimentation influence on the coagulation rate of suspensions of 2μm （diameter） polystyrene. The liquid mixtures, in the proper proportions of water （H2O）, deuterium oxide （D2O） and methanol （MeOH） as the liquid phase, density-matched and unmatched experiments are performed. Besides the influence of viscosity, the presence of methanol in solvent media, used to enhance the sedimentation effect, causes significant changes （reduction） in rapid coagulation rates compared to that in pure water. Without the relevant corrections for those non-gravitational factors it seems that gravitational sedimentation would retard the coagulation. The magnitude of the contribution from the non-gravitational factor is quantitatively determined, making the relevant correction possible. After necessary the influence of the sedimentation on coagulation rates at corrections for all factors, our experiments show that the initial stage of the coagulation is not observable.     

Theoretical study of acoustic field patterns of 2-D ultrasound phased arrays for hyperthermia therapy

Acoustic field patterns of 2-D ultrasound phased arrays for the high intensity focused ultrasound (HIFU) hyperthermia therapy are studied, and controlling algorithms of field patterns are provided. The 2-D phased array using the conventional single-focus scanning pattern can exactly control the focal distance and the steering direction of the beam, but in general produce a single focus. Extremely high intensity levels will be needed when this pattern is used to treat large tumors. However, a direct synthesis method of the acoustic field based on the pseudo-inverse matrix can produce the multiple-focus field pattern. The rectangular radiator method of the acoustic field was used to simulate the single-focus scanning pattern and the multiple-focus pattern which are produced by a 2-D phased array consisting of 20×20 elements, and simulation results show that the 2-D array using the multiple-focus pattern can produce several foci with lower intensity levels simultaneously. Furthermore, the improved eigenvec     

双光折变晶全半线性相位共轭器的自脉动

在由两声光折变ＢａＴｉＯ３晶体（其中一块晶体为一内反射式自抽运相位共轭镜工作方式，起外反射镜作用）构成的半线性自抽运相位共轭吕中观察到了相位共轭光的自脉动现象。自脉动的平均频率ｆ与入射光功率Ⅰ０的关系为ｆ∞Ⅰ０＾１．４３；相位共轭光的平均维持时间ΔＴ与入射光功率Ⅰ０近似成反比。观察到光折变ＢａＴｉＯ３晶体蝇扇形散射光具有动态的空间结构，扇形散射光的这种特性是引起上述半线性自抽运相位共轭器中相位共轭