判断分段函数在分段点处可导性的简便方法

分段函数在《高等数学》中经常出现,其分段点处的求导问题一向是学生学习的一大难点。通常我们是依据导数定义来判断分段点处的可导性,学生实际用起来感觉很吃力。对分段函数在分段点处可导性的判别方法做了详细梳理,对满足一定条件的分段函数,利用求导公式分别求出分段点左、右两侧的导函数,再将分段点代入作为分段点处的左、右导数,并以此得出分段函数在分段点处的可导性,这样做可使计算过程大大简化,更易于学生接受。     

测量薄膜厚度的数字叠栅技术

现代干涉测试的核心是用合理的算法处理干涉图而获得所需的面形及参数。由于常见的相移法要通过移相器有规律地移动采集多幅干涉图并数字化后求取波面的相位分布,这样必然引入由于移相器的线性及非线性误差所带来的计算误差,因此需要事先对移相器进行标定。采用了数字叠栅方法,利用一幅静态干涉图与一个正弦光栅的四幅光强分布图叠加,从而实现相移式动态干涉测试的效果,借助于相移法处理干涉图原理,可获得波面相位分布,从而实现对薄膜厚度的测量。由于正弦光栅的初始相位是由计算机产生的,所给出的相位移动不含任何移相误差,因此可提高测量的精度。     

利用空域滤波虚光栅叠栅法提取干涉图波面

虚光栅叠栅条纹法是一种利用单幅干涉图提取波面信息的方法,为了解决叠栅条纹的滤波问题,提出了一种基于高斯函数的空域滤波法。利用高斯函数在空域中对叠栅条纹图进行模糊处理,滤除不需要的高频分量,仅保留包含波面相位信息的低频分量。重点研究了高斯函数滤波窗口的选择和干涉图的载频之间的对应关系。该方法具有计算量小、易于选取滤波窗口的优点。对一光学平面的面形测量结果表明,利用空域滤波虚光栅叠栅法提取的波面[峰谷(PV)值为0.080λ,均方根(RMS)值为0.020λ,λ=632.8nm]与利用Zygo GPI干涉仪的四步移相法得到的波面(PV值为0.079λ,RMS值为0.017λ)相吻合。     

基于莫尔光纤光栅的F-P LD双模自激注入锁定

提出一种基于莫尔光纤光栅的F-P(法布里-珀罗)半导体激光器双波长自激注入锁定生成拍频信号以获得所需毫米波的实验方案。实验结果表明,在11.7nm波长调谐范围内可获得边模抑制比约为30dB的双波长输出,该双波长输出可产生高达168GHz的拍频信号。该高频毫米波信号生成方案的系统结构简单,成本低廉。     

低功耗TFT-LCD驱动方法

为了降低薄膜晶体管液晶显示器(TFT-LCD)的功耗,提出了一种新的双栅之型反转驱动方法。研究了双栅之型反转驱动技术的节能原理,完成了相关结构设计、电路设计,制作了35.6cm(14in)WXGA(1 366RGB×768)样品,测试并分析了节能效果。结果表明,该技术可以有效降低TFT-LCD的功耗,在显示彩条画面的情况下,液晶屏模拟电源功耗降低了70%(191mW)。分析了出现的莫尔条纹问题,并提出了解决方案。该研究为降低TFT-LCD及其他显示设备的功耗提供了一种驱动方法及设计参考。     

Modelling Inhomogeneous Mechanical Properties in Adhesive Bonds

Polymers often show an inhomogeneous distribution of their mechanical properties. In adhesive layers these inhomogeneities result from the formation of interphases close to the substrates. In addition, chemical aging processes are driven by diffusive processes entering the specimen from the boundaries and changing the local properties of the polymer. In the present contribution a model is presented that takes into account the local effects of the interphase's formation or of the aging processes, respectively.

The model is based on a phenomenological continuum mechanical approach, i.e., the effects are described by the introduction of an additional field in combination with an additional balance equation and corresponding boundary conditions. In the first part of this paper the formation of interphases is investigated. Comparing the model with experimental results allows for the identification of the model parameters. In the second part the model is enhanced to describe effects due to chemical aging. Some illustrative examples show the general behaviour of the model and motivate a series of experiments allowing for the required parameter identification.     

基于三维CDM的复合材料开口层合板失效分析

建立了复合材料层合板三维连续介质损伤力学模型,并将该模型应用于复合材料开口层合板的损伤破坏分析中。与相关试验中开口层合板强度和损伤破坏情况对比分析表明:本文模型能够有效地模拟开口层合板从初始损伤到完全破坏的全过程,具有较高的计算精度和良好的数值模拟收敛性。基于该模型,详细分析了在单向拉伸载荷作用下开口层合板不同铺层的损伤破坏情况。     

Modelling of load interaction and overload effect on fatigue damage of steel bridges

This paper studies the effects of load sequence and interaction, and overloading effect on the fatigue damage of bridges on the basis of a non-linear fatigue damage model. The model is derived from the theory of continuum damage mechanics for high-cycle fatigue. Fatigue behaviour at two levels of constant stress range is first discussed in detail. The formulation for the effective fatigue strength of the predamaged members is then derived, and the results predicted by the model are compared with the experimental data for two stress level tests and other results obtained from linear and double linear fatigue damage models. The variation of cycle ratio and fatigue life due to overloading is secondly investigated; the equations for evaluating the effect of overloading on fatigue damage accumulation on bridges at normal traffic loading are then derived. It has been demonstrated that the developed model can well describe the effect of load sequence and interaction and has also been verified by comparing the predicted results obtained by the model with the experimental data based on two levels of stress tests. The effect of accidental overloading on the fatigue damage of existing bridges can also be evaluated using the model. The model is applied to evaluate the fatigue damage and service life of the Tsing Ma Bridge, an essential portion of the transport network for the Hong Kong airport, under normal traffic loading and possible accidental overloading.     

Numerical prediction of turbulent flow and heat transfer with phase change in crystallizer of inverse casting

horoductionInverse casting is a technique for Producing nearnet-shape cast strips. T'he main idea of this technique isdeveloped from a successful inveshgation['], in which ithas been Proved that the inverse cashng teclmiquewould be applicable to produce the steel strip with aabackness of 0.5-3 nun, with a good material prOPertyand with a lower energy consumption in contrast withconventional conhnuous cashng process. The POssibilitytO p~ce composite strips is also one of the mostattrachve pro…     

剪力墙结构高阶自振频率及振形的一种近似算法

应用连续化原理并结合 Rayleigh法求解剪力墙结构高阶自振频率 ,推导出形式简单且应用方便的计算公式 ,可以较快地求出具有相当精度的结果 .