基于RS-485总线和MCU的频率合成器设计

本文主要介绍一款基于RS-485总线和MCU的频率合成器,重点介绍了频率合成器的总体结构,RS-485总线接口电路,高集成度频率合成芯片AD9850的外围硬件电路和控制软件。该合成器输出频率范围:5~40MHz,最小频率步进为≤20Hz,输出正弦波或方波幅度800mV。该频率合成器具有结构简单,精度高,控制灵活的特点。

RS-485总线在CSR控制系统中的应用

该文介绍一种能利用RS 485总线标准,采用自定义串行通信协议,实现CSR控制子系统中的总线通讯的方法。并给出总线硬件电路和相应的软件实现流程图。

在Windows下PC机作为半双工RS-485网络主机通信程序的设计

描述了一个以PC机作为半双工RS-485网络主机,工作于Windows平台上的通讯程序。该程序特点是通过使用异步通信WIN32API和多线程及多种同步量来实现半双工通信方式。

一种基于RS—485网络的集散型控制系统

从系统构成和通信软件两方面介绍了一种基于RS-485网络的集散型控制系统。该系统的RS-485网络由1台工控机和10台可编程控制器构成。工控机通过RS-485网络控制10台独立的3自由度数控液压小车。本文提出了一种RS-485网络通信协议。

一种非局部弹塑性连续体模型与裂纹尖端附近的应力分布

本文提出一种非局部弹塑性连续体模型。在这个模型中,应力与弹性应变之间为非局部线性关系,而塑性应变与总应变历史相联系。对于形变理论,假定塑性应变张量与总应变偏量张量成比例,其比例因子是总有效应变的标量函数。将这一模型用于分析幂硬化弹塑性材料拉伸型裂纹尖端附近的应力场,利用经典断裂力学中所得的拉伸型裂纹尖端HRR奇性解的结果,在一维简化计算下导出了裂纹正前方的拉应力分布和最大拉应力的表达式,证明临界J积分准则可由非局部最大拉应力准则得到。用已有的实验数据计算了几种钢材在裂纹起始扩展时裂纹尖端附近的最大拉应力,发现其量级与晶格内聚强度相近。所得结果对于理解材料断裂过程的物理机理是有益的。

Direct dynamical test for deterministic chaos

We present a direct and dynamical method to distinguish low-dimensional deterministic chaos from noise. We define a series of time-dependent curves which are closely related to the largest Lyapunov exponent. For a chaotic time series, there exists an envelope to the time-dependent curves, while for a white noise or a noise with the same power spectrum as that of a chaotic time series, the envelope cannot be defined. When a noise is added to a chaotic time series, the envelope is eventually destroyed with the increasing of the amplitude of the noise.

微薄梁三点弯曲的尺度效应研究

应用高灵敏度的力传感器以及时间序列电子散斑干涉法,同时测出了不同厚度纯镍薄片三点弯曲试件的抗力与变形,得到薄梁中心点处的载荷与挠度曲线.应用Fleck和Hutchinson的偶应力理论,结合平面应变弯曲模型,建立了薄梁处于弹性状态和弹塑性状态的控制方程,应用Runge-Kutta法进行数值求解,并将计算得到的载荷-挠度曲线以及无量纲化弯矩-表面应变曲线和实验结果进行了比较.在理论计算过程中,没有拟合任何材料参数,所有的材料参数均来自实验测量的结果,材料特征尺度也是根据Stolken和Evans的工作给出的.结果表明:应用偶应力理论预测的结果和实验结果符合良好,而经典理论的预测结果与实验不相符合.

Digital holographic interferometry and the angular spectrum method applied to measuring the domain inversion in ferroelectric crystal

The application of digital holographic interferometry on the quantitative measurement of the domain inversion in a RuO2: LiNbO3 crystal wafer is presented. The recorded holograms are reconstructed by the angular spectrum method. From the reconstructed phase distribution we can clearly observe the boundary between the inverted and un-inverted domain regions. Comparisons with the results reconstructed by use of the Fresnel transform method are given. Factors that influence the measurement include the spectrum filter size and the spectrum movement are discussed. The spectrum filter size has an effect on the measurement of the details. Although the spectrum movement affects every single reconstructed image, it has no influence on the final measurement.

掺铒钙铝硅玻璃的光学带隙

玻璃中稀土掺杂的离子的光谱性质受其周围的玻璃结构和在玻璃基质中的分布影响很大。利用熔融法制备了组分为9SiO2·26Al2O3·65CaO·1．0Er2O3·0．3Yb2O3和分别加入MgO以及La2O3的掺铒钙铝硅玻璃，并研究了其吸收边和光学带隙。计算得出离子填充比随玻璃的平均摩尔质量的增大而减小，同时利用Judd—Ofelt模型计算出该玻璃体系的Ω2，Ω4和Ω6参数，并进行了分析。随着MgO或La2O3的加入，吸收边向短波长移动，光学带隙增大，同时Ω2和Ω6值也增大。对ln（α）和hω的曲线进行线性拟

Influences of CO2 laser irradiation on the structure and photoluminescence of zinc oxide thin films

CO2 laser irradiation experiments on ZnO thin films are reported. The structural, optical, luminescent and vibrational properties of the samples were investigated by X-ray diffraction (XRD), transmittance, photoluminescence (PL) and Raman measurements. XRD results show that the crystalline of the irradiated films was improved. The (002) peaks of irradiated ZnO films shift to. higher 20 angles due to the stress relaxation in the case of laser beam irradiation. From optical transmittance spectra, all films exhibit high transmittance in the visible range, the optical band edge of irradiated films showed a redshift compared with that of as-grown films. Compared with the as-grown films, the photoluminescence emission (in particular the relative intensities of visible emissions) intensities of irradiated samples enhanced. In the Raman scattering spectral both the A I. and E modes exhibited slight Raman blueshift. (c) 2005 Elsevier B.V. All rights reserved.