对称面形光栅TE模的衍射特性

本文采用耦合波方法计算了对称面形光栅的衍射效率,分析了光栅截面面形为正弦、三角形、矩形、梯形光栅衍射效率与光栅周期、沟槽深度的关系,计算了光栅的峰值衍射效率。理论计算表明:合理地选择光栅周期、沟槽深度,对称面形光栅都可以达到很高衍射效率,接近100%;光栅的峰值衍射效率基本出现在Bragg衍射且光栅的周期等于衍射波长时。     

利用表面波测量液体的表面张力系数

本文利用表面张力在液面上产生毛细波的现象，设计了一种原理上的比较新颖，操作上简单，相对误差为０．２％，可与公认的毛细上升法相比的测量方法。     

多缝衍射反演光谱学的稳定性理论研究── 一种第一类Fredholm积分方程数值解之稳定性分析

作者在前文￣（１，２）中通过计算机模拟实验给出了由多缝衍射反演光谱学的积分方程─一种第一类Ｆｒｅｄｈｏｌｍ积分方程─获得稳定线性方程组的条件，本文将进一步从数学上利用积分方程的本征值理论分析计算机的实验结果，阐明这些条件使线性方程组稳定的机制。     

Diffraction grating interferometers for mechanical characterisations of advanced fabric laminates

It is demonstrated that two grating interferometers with high spatial resolutions can successfully be applied for the mechanical characterisation of the advanced fabric composite materials. Based on these two techniques, the mechanical properties of two kinds of fabric laminates are obtained without assumption of uniform strain fields to be used in the characterisation approaches using the local strain sensors. The degree of the yarn crimp effects of the two laminates is compared in terms of the out-of-plane displacement derivatives. Especially, it is shown that the grating shearing interferometer is appropriate for the crimped fabric structure requiring a three-dimensional analysis. The modification from moiré interferometer to grating shearing interferometer is performed by introducing a Michelson interferometer modified for image shearing.     

Improved Lower Bounds for the Critical Probability of Oriented Bond Percolation in Two Dimensions

We present a coupled decreasing sequence of random walks on Z that dominate the edge process of oriented bond percolation in two dimensions. Using the concept of random walk in a strip, we describe an algorithm that generates an increasing sequence of lower bounds that converges to the critical probability of oriented percolation p_c. From the 7th term on, these lower bounds improve upon 0.6298, the best rigorous lower bound at present, establishing 0.63328 as a rigorous lower bound for p_c. Finally, a Monte Carlo simulation technique is presented; the use thereof establishes 0.64450 as a non-rigorous five-digit-precision (lower) estimate for p_c. Mathematics Subject Classification (1991): 60K35 Supported by CNPq (grant N.301637/91-1). Supported by a grant from CNPq.     

扁平绕带式低温高压容器绝热性能分析和计算

扁平绕带式低温高压容器是一种新型低温液体贮存设备 ,由内外两层容器组成 ,内筒体的外壁焊有液氮预冷夹套。平均蒸发率是衡量扁平绕带式低温高压容器绝热性能的重要指标。文中在分析其传热过程和壁厚温差影响因素的基础上 ,提出了一种计算其蒸发率的工程方法 ,并结合1 0 m3液氢储罐设计实例进行了计算。结果表明扁平绕带式低温高压容器具有良好的绝热性能 ,适用于重要介质的低温贮运     

A 3 kW average power tunable TEA CO2 laser

A high average power line-tunable TEA CO₂ laser is described. Average output power up to 3 kW is achieved at repetition rate of 180 Hz. The maximum output power is almost equal among the four spectrum bands of CO₂ laser (the P and R branches of 00°1–10°0 and 00°1–02°0 transition bands). Several special technologies including rotating spark gap switching, PCB (printed circuit board) preionization and zeroth-order grating coupling are employed.     

Second-order bragg interaction in double grating couplers: TM mode

An analytical treatment of the second-order Bragg interaction is presented for the transverse magnetic mode of a dielectric film waveguide having gratings on both the film-cover and the film-substrate interfaces. Four canonical equations that describe the interactions of two guided waves propagating in the opposite directions in the film and the normally incident and radiated free waves in the cover and the substrate are deduced.     

Dynamic behavior of two parallel symmetric permeable cracks in a piezoelectric strip

The dynamic behavior of two parallel symmetric cracks in a piezoelectric strip under harmonic anti-plane shear waves is studied using the Schmidt method for permeable crack surface conditions. The cracks are parallel to the edge of the strip. By means of the Fourier transform, the problem can be solved with the help of two pairs of dual integral equations. These equations are solved using the schmidt method. The results show that the stress and the electric displacement intensity factors depend on the geometry of the cracks, the frequency of incident waves, the distance between cracks and the thickness of the strip. It is also found that the electric displacement intensity factors for the permeable crack surface conditions are much smaller than those for the impermeable crack surface conditions. Project supported by the Post Doctoral Science Foundation of Heilongjiang Province, the Natural Science Foundation of Heilongjiang Province, the National Science Foundation with the Excellent Young Investigator Award (No. 19725209) and the Scientific Research Foundation of Harbin Institute of Technology (HIT.2000.30).