椭偏光学显微成像系统聚焦评价函数的研究

自动聚焦技术在椭偏光学显微成像系统中是一项关键的技术。利用几种常用聚焦评价函数作为研究手段研究了这一过程。实验中采用硅基底表面人血纤维蛋白膜层和多元蛋白质芯片样品作为研究对象，研究了几种函数在自动聚焦过程中函数值的变化，以及噪音、样品区域选择对聚焦效果的影响。实验验证拉普拉斯评价函数和Sobel评价函数可以满足系统的要求；采用多幅图像平均的方法可以有效降低噪音，当平均次数达到9次以上，系统噪音的影响就可以被降至有效评价的程度；沿同一锐边，选择不同的调焦区域，对聚焦过程基本没有影响；利用评价函数在实验中确定了倾斜平面成像的最佳聚焦平面，并与理论像平面吻合。实验证明利用聚焦评价函数可以成功实现自动聚焦技术在椭偏光学显微成像系统中的应用。

海流引起海底管道悬空的数值模拟

海底管道悬跨将影响管道的安全运营。在海底管道稳定性设计中，需要合理分析具有初始嵌入深度的海底管道产生悬空的物理机制。本文对海流作用下铺设于砂质海床上的海底管道悬空进行了数值模拟。求解不可压缩流体N-S方程，分析了海流作用下管道周围的流场特性，研究了管道两侧的压力分布特性和海床表面剪应力的分布特点。在管道绕流流场分析的基础上，通过对土体渗流方程的求解，得到了管道周围砂质海床内的渗流场以及渗流水力梯度场的分布情况。与海床表面剪应力计算结果进行比较分析发现，管道下方渗流出口处土体的流土渗透破坏将诱导管道发生悬空

Microstructure and mechanical properties of Zr-Cu-Al bulk metallic glasses

Zr49Cu46Al5 and Zr48.5Cu46.5Al5 bulk metallic glasses(BMGs) with diameter of 5 mm were prepared through water-cooled copper mold casting. The phase structures of the two alloys were identified by X-ray diffractometry(XRD). The thermal stability was examined by differential scanning calorimetry(DSC). Zr49Cu46Al5 alloy shows a glass transition temperature, T, of about 689 K, an crystallization temperature, T-x, of about 736 K. The Zr48.5Cu46.5Al5 alloy shows no obvious exothermic peak. The microstructure of the as-cast alloys was analyzed by transmission electron microscopy(TEM). The aggregations of CuZr and CuZr2 nanocrystals with grain size of about 20 nm are observed in Zr49Cu46Al5 nanocrystalline composite, while the Zr48.5Cu46.5Al5 alloy containing many CuZr martensite plates is crystallized seriously. Mechanical properties of bulk Zr49Cu46Al5 nanocrystalline composite and Zr48.5Cu46.5Al5 alloy measured by compression tests at room temperature show that the work hardening ability of Zr48.5Cu46.5Al5 alloy is larger than that of Zr48.5Cu46.5Al5 alloy.

Characteristics of deep penetration laser welding of dissimilar metal Ni-based cast superalloy K418 and alloy steel 42CrMo

Experimental trials of autogenous deep penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 5.0 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser output power, welding velocity and defocusing distance on the morphology, welding depth and width as well as quality of the welded seam were investigated. Results show that full keyhole welding is not formed on both K4.18 and 42CrMo side, simultaneously, due to the relatively low output power. Partial fusion is observed on the welded seam near 42CrMo side because of the large disparity of thermal-physical and high-temperature mechanical properties of these two materials. Tile rnicrohardness of the laser-welded joint was also examined and analyzed. It is suggested that applying negative defocusing in the range of Raylei length can increase the welding depth and improve tile coupling efficiency of the laser materials interaction. (c) 2007 Elsevier Ltd. All rights reserved.