垂直排列一扭曲向列液晶显示的阈值特性

从液晶体系的总自由能出发,通过欧拉-拉格朗日方程组的推导,得到了手性向列相液晶从垂直排列状态转变成平面扭曲排列时的Freedericksz转变阈值电压公式Vth=π×     

基于MDL原理的快速在线信号分选算法

研究了一种基于最小描述长度(MDL)原理的快速在线雷达脉冲信号聚类分选算法,该方法利用幅度或相位差异特征,实现对雷达脉冲数据向量的聚类分选处理。设计了基于MDL原理的在线信号分选算法流程,在每接收到一定数量雷达脉冲信号后,执行一次聚类分选处理;对算法流程中的每个处理模块进行了完备的运算量分析,为工程设计提供有效的理论指导;并对比分析了离线和在线算法的性能。仿真结果表明:在线算法的信号分选正确率与离线方法基本一致,具有很强的工程应用前景。     

基于非线性最小二乘法的姿态优化算法

在无陀螺捷联惯导系统中,在一种适合高自旋弹丸运动姿态测试的十二加速度计配置方案下,针对由十二加速度计的输出直接解算出角速度的方法中没考虑加速度计的安装误差问题,提出一种提高角速度解算精度的优化算法。该方法基于非线性最小二乘法从姿态角的一组初值出发开始在每一点处进行线性替代的迭代计算,搜索出满足极值点必要条件的最优角速度,从而实现对姿态角的优化解算。实验证明:该方法能有效抑制安装误差,精度高,是可行的。     

Enhanced Performance of I2‐Free Solid‐State Dye‐Sensitized Solar Cells with Conductive Polymer up to 6.8%

An iodine‐free solid‐state dye‐sensitized solar cell (ssDSSC) is reported here, with 6.8% energy conversion efficiency—one of the highest yet reported for N719 dye—as a result of enhanced light harvesting from the increased transmittance of an organized mesoporous TiO₂ interfacial layer and the good hole conductivity of the solid‐state‐polymerized material. The organized mesoporous TiO₂ (OM‐TiO₂) interfacial layer is prepared on large‐area substrates by a sol‐gel process, and is confirmed by scanning electron microscopy (SEM) and grazing incidence small‐angle X‐ray scattering (GISAXS). A 550‐nm‐thick OM‐TiO₂ film coated on fluorine‐doped tin oxide (FTO) glass is highly transparent, resulting in transmittance increases of 8 and 4% compared to those of the bare FTO and conventional compact TiO₂ film on FTO, respectively. The high cell performance is achieved through careful control of the electrode/hole transport material (HTM) and nanocrystalline TiO₂/conductive glass interfaces, which affect the interfacial resistance of the cell. Furthermore, the transparent OM‐TiO₂ film, with its high porosity and good connectivity, exhibits improved cell performance due to increased transmittance in the visible light region, decreased interfacial resistance ( Ω ), and enhanced electron lifetime ( τ ). The cell performance also depends on the conductivity of HTMs, which indicates that both highly conductive HTM and the transparent OM‐TiO₂ film interface are crucial for obtaining high‐energy conversion efficiencies in I₂‐free ssDSSCs.     

激光快速成形过程中熔池形态的演化

采用高速摄影技术对激光快速成形过程中液态熔池的形成及其演化过程进行了实时观察。结果发现,以一定速度向前运动的激光束辐照基材时,基材表面开始熔化并形成液态熔池,经过一个较短的时间间隔(约1．0 s)后熔池深度增大至一定值,熔池长度则围绕一恒定值波动。以恒定送粉率向熔池中连续送进金属粉末时,熔池的长度和宽度逐渐减小,熔池寿命缩短。同时熔池后沿不断抬高即熔覆层厚度不断增加,最大熔深处熔池自由表面法向和激光束轴线之间的夹角由几度逐渐增大到20°～30°左右。熔池自由表面发生周期性的变化,实验观察到熔池后沿有周期性的“岛状凸起”出现和消失现象。数值计算结果证实这主要是熔池中熔体在表面张力梯度下引起的强制对流作用的结果。     

A large class of binary ZCZ sequence families constructed by period doubling

In an Approximately Synchronized Code Division Multiple Access （AS-CDMA） communication system, a family with large number of Zero Correlation Zone （ZCZ） sequences is desired, which can satisfy the rapid increase of users. This paper presents a method to generate a （2L,2M, ZCZ＇）-ZCZ sequence family from an original （L,M,ZCZ）-ZCZ sequence family, where ZCZ＇ = ZCZ if ZCZ is even and ZCZ＇ =ZCZ - 1 if ZCZ is odd. This method can also recursively act on a ZCZ sequence family to construct a series of ZCZ sequence families with large sequence number and zero correlation zone length identical to or one less than that of original ZCZ sequences.     

一种高速ADC动态性能参数测试的新方法

模数转换(ADC)采样电路作为模拟域到数字域的接口,实际应用非常广泛。介绍了ADC动态性能参数定义及测试方法,讨论了基于快速傅里叶变换(FFT)的频域测试法测试高速ADC动态性能参数的可行性,最后给出了实施方案和测试结果。     

Heat spreading in a thin longitudinal fin

In view of the trend towards higher power densities in ever shrinking geometries, understanding heat spreading fundamentals is gaining importance. In this paper heat spreading in thin longitudinal geometries is considered. This geometry is of practical interest in one-dimensional Cartesian geometries. A characteristic length is derived and it is shown that this has physical significance for the distance that heat spreads, and for the total amount of heat cooled away. Furthermore, it is investigated when “thin” is a viable assumption. The use of the characteristic length is illustrated for the case of a line source cooling to a plate and for the case of the fins of a plate heatsink. The results are compared to numerical simulations. The work is an extension of the authors' earlier work on heat spreading in infinite longitudinal geometries and heat spreading in infinite and finite circular geometries.     

超声跟踪TeO2器件新设计及其性能比较

在超声跟踪反常器件设计中,用最小二乘法确定相邻换能器中心距s和超声偏置角γ_o两参数的近似值,并通过计算机程序完成精细调节,得到s和γ_o的优化设计值。计算结果表明,用最小二乘法得到的s和γ_o的近似值比过去用中心频率处△Γ和△Θ_α的函数值及一阶导数值相等所得到的近似值更接近于s和γ_o的优化值。因而优化过程更趋简单。将此新设计方法运用到TeO_2器件的具体设计中,并在相同条件下与正常声光器件的性能作比较。比较结果表明,对于相同的倍频程带宽和通带内1.5dB的不均匀性,反常器件的声光互作用长度较正常器件提高40%。     

一种基于无平方根QR分解的流水RLS算法

传统ＱＲ分解（ＧＩＶＥＮＳ旋转）中存在着平方根运算,在用数字电路实现时,会在时间和面积上花费较大的代价,因此,已有无平方根的ＱＲ分解算法出现,这些算法避免了平方根运算,但遇射为Ｓｙｓｔｏｌｉｃ阵列以实现ＲＬＳ算法时,却不能实现单元内部的流水,本文提出了一种新的无平方要ＱＲ分解,能够实现单元内部的流水,进一步提高了速度。