Dipole soliton formation in a nematic liquid crystal in the nonlocal limit

The interaction of two symmetric solitary waves, termed nematicons, in a liquid crystal is considered in the limit of nonlocal response of the liquid crystal. This nonlocal limit is the applicable limit for most experimentally available liquid crystals. In this nonlocal limit, two separate cases for the initial separation of the nematicons are considered, these being large and small separation. Both spinning and nonspinning nematicons are considered. It is found that in the case of large initial separation, the nematicons can form a spinning or nonspinning bound state with a finite steady separation, this being called a nematicon dipole, when they are π out of phase. On the other hand, well separated, nonspinning, in-phase nematicons attract and merge, while well separated, spinning, in-phase nematicons can either form a bound state or merge into a single nematicon. In the limit of small initial separation, the nematicons rapidly merge when they are in phase. Modulation equations describing the nematicon interaction are derived via suitable trial functions in an averaged Lagrangian. These modulation equations are further modified to include the effect of the diffractive radiation shed as the nematicons evolve. Finally the modulation equations are approximated in order to investigate the various interaction regimes. Good to excellent agreement is found between their solutions and full numerical solutions of the nematicon equations.     

高速光纤通信系统中高阶PMD的优化建模

为了评估随机变化的偏振模色散(PMD)(包括一阶和二阶PMD)使系统信号裂化的程度,降低其对高速光纤通信系统传输速率和传输容量的不利影响,在斯托克斯空间中推导了偏振模色散(PMD)矢量的数学表达式。对PMD效应所导致的脉冲展宽进行了数学分析,给出了差分群时延(DGD)的变化、一阶PMD矢量和二阶PMD矢量方向的变化对脉冲展宽的影响。通过数学推导得出,在大多数情况下,二阶PMD无法完全补偿,需通过控制单元的调整使其对系统的影响达到极小值。通过实验分析,得到了和数学推导中同样的结果,从而证明了模型的正确性。     

调制型准层流电子枪聚焦透镜系统的研究

基于变像管工作原理并从其整体性能优化的角度出发,得出在其中采用准层流电子束的必要性;通过分析已有电子光学聚焦系统所存在的结构和性能上的缺陷,确立了优化电子透镜系统的基本模型.在分析各参量相对变化对其渐进聚焦调制特性影响的基础上,阐明了通过膜孔透镜的引入而形成对电子束横向尺寸具有渐进压缩特性的准层流电子枪的可能性.     

车辆间大气激光移动通信调制方式研究

对大气激光移动通信的调制方式进行了研究,介绍了OOK、PPM、DPPM、DPIM及DH-PIM调制方式并分析了其各项性能指标,提出一种H-PPM调制方式并与其它调制方式进行了比较.该方式在继承标准PPM优良误码特性的同时,在接收端解调时不需要符号同步,简化了接收机的设计,降低了系统实现的难度.理论分析和仿真结果表明,此H-PPM调制方式可以满足移动车辆间短距离、高可靠性、小数据容量激光通信的需要.     

基于实际空间截止频率的稀疏孔径双圆周阵列的优化

提出了一种新的稀疏孔径光瞳结构-两个圆周阵内外嵌套而成的双圆周结构,并研究了该结构的调制传递函数.该结构以实际空间截止频率作为约束条件,保证调制传递函数在最小截止频率以内无零频,以阵列的u-v覆盖点间距最大化及最小冗余度来设计目标函数,并采用这种优化方法对3-3、5-3以及6-3双圆周阵列进行了优化排列.将优化结果与相同子孔径数目的均匀圆周阵以及Golay结构进行仿真实验和比较.结果表明,优化后的双圆周阵列,具有最大的实际空间截止频率和实际等效口径.     

Experimental He-pressure broadening for the R(10) and P(2) lines in the ν3 band of CO2, and experimental pressure shifts for R(10) measured at several temperatures between 300 K and 100 K

Helium broadening coefficients for the R(10) and the P(2) lines in the ν₃ band of ¹³CO₂ have been measured over a large range of temperature (70 K-300 K). Helium pressure shifts for the R(10) line at several temperatures between 100 K and 300 K have also been determined. These measurements were obtained with a cold Herriott cell, using the collisional cooling technique to reach the lowest temperatures. They provide an extended dataset for the temperature dependence of widths and shifts. This dataset was compared to theoretical He-broadening coefficients combining quantum scattering calculations and the latest potential energy surface for the system He-CO₂ from Korona et al. [T. Korona, R. Moszynski, F. Thibault, J.-M. Maunay, B. Bussery-Honvault, J. Boissoles, P.E.S. Wormer, J. Chem. Phys. 115 (2001) 3074-3084].     

Experimental investigation of the line center of Hg intercombination spectral line 253.7 nm perturbed by Kr

The collision broadening and shift of the Hg intercombination spectral line 253.7 nm (6¹S₀–6³P₁) perturbed by Kr has been investigated using a high-resolution scanning Fabry–Perot interferometer. The values of the pressure broadening and shift coefficients β and δ, respectively, for the studied line have been obtained. The obtained coefficients β and δ are compared with their corresponding published experimental values and also those calculated using Lindholm–Foley impact theory.     

Optical methods in studies of structural transformations in thin organic films

The examples of phase transitions in Langmuir-Blodgett films of polyvinylidene fluoride (PVDF) and in the surface layer of polystyrene were chosen to demonstrate the great potential of using luminescent molecular probes for studying the heterogeneity of the surfaces of solids and thin films, as well as structural transformations and phase transitions in systems of different natures. The method provides unique information on the local properties of surfaces and thin films when used in combination with other techniques.     

介孔SiO2薄膜孔结构的慢正电子技术表征

通过蒸发诱导自组装技术制备了具有不同有序结构的介孔SiO₂薄膜,并采用同步辐射X射线反射率以及慢正电子束流技术对其进行表征.实验结果表明,随着旋涂速率的增加,介孔结构由三维立方向二维六角结构转变,同时平均孔隙率随转速增加而减小.利用各向同性无机孔收缩模型和Fourier变换红外光谱,探讨了薄膜结构和正电子湮没参数的内在联系. 关键词： 同步辐射 X射线反射率 Doppler展宽 正电子素飞行时间谱     

用于核磁共振的直接数字合成频率源

直接数字频率源的使用可以简化核磁共振谱仪的设计,降低核磁共振谱仪设计的成本. 文中介绍一种采用Analog Device公司的AD7008芯片设计的基于PC机的直接数字合成频率源,它可实现频率和相位的高速切换,频率分辨率为0.01Hz,相位分辨率为0.09°,最后给出核磁共振实验结果.