Domains in ferroelectric nanodots

Almost free-standing single crystal mesoscale and nanoscale dots of ferroelectric BaTiO(3) have been made by direct focused ion beam patterning of bulk single crystal material. The domain structures which appear in these single crystal dots, after cooling through the Curie temperature, were observed to form into quadrants, with each quadrant consisting of fine 90 degrees stripe domains. The reason that these rather complex domain configurations form is uncertain, but we consider and discuss three possibilities for their genesis: first, that the quadrant features initially form to facilitate field-closure, but then develop 90 degrees shape compensating stripe domains in order to accommodate disclination stresses; second, that they are the result of the impingement of domain packets which nucleate at the sidewalls of the dots forming "Forsbergh" patterns (essentially the result of phase transition kinetics); and third, that 90 degrees domains form to conserve the shape of the nanodot as it is cooled through the Curie temperature but arrange into quadrant packets in order to minimize the energy associated with uncompensated surface charges (thus representing an equilibrium state). While the third model is the preferred one, we note that the second and third models are not mutually exclusive.

芝罘西湾COD浓度变化和相关分析的初步探讨

Using the method of the correlation analysis this paper discusses the relations between COD concentration change and the tide in the western Zhi Wu Gulf of Yan Tai. The tropic equation was given. It can be seen that the correlation between the concentration of COD and the tide level is minus in the north of this Bay. However it is positive in the south of this Bay. The concentration of COD in oreases with the increases of mean range of tide. The concentration of COD for flood tide is less than it for ebb current in the north of the Bay and vice verse in the south of the Bay.

Genetic structure analysis of natural Sargassum muticum (Fucales, Phaeophyta) populations using RAPD and ISSR markers

Sargassum muticum is important in maintaining the structure and function of littoral ecosystems, and is used in aquaculture and alginate production, however, little is known about its population genetic attributes. In this study, random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers were used to investigate the genetic structure of four populations of S. muticum and one outgroup of S. fusiforme (Harv.) Setchell from Shandong peninsula of China. The selected 24 RAPD primers and 19 ISSR primers amplified 164 loci and 122 loci, respectively. Estimates of genetic diversity with different indicators (P%, percentage of polymorphic loci; H, the expected heterozygosity; I, Shannon's information index) revealed low or moderate level of genetic variations within each S. muticum population, and a high level of genetic differentiations were determined with pairwise unbiased genetic distance (D) and fixation index (F-ST ) among the populations. The Mantel test showed that two types of matrices of D and F-ST were highly correlated whether from RAPD (r = 0.9706, P = 0.009) or ISSR data (r = 0.9161, P = 0.009). Analysis of molecular variance (AMOVA) was conducted to apportion the variations among and within the S. muticum populations. It indicated that variations among populations were higher than those within populations, being 55.82% verse 44.18% by RAPD and 55.21% verse 44.79% by ISSR, respectively. Furthermore, the Mantel test suggested that genetic differentiations among populations were related to the geographical distances (r > 0.6), namely, conformed to the IBD (isolation by distance) model, as expected from UPGMA (unweighted pair group method with arithmetic averages) cluster analysis. On the whole, the high genetic structuring among the four S. muticum populations along the distant locations was clearly indicated in RAPD and ISSR analyses (r > 0.9, P < 0.05) in our study.

UUV推进系统容错控制分配算法研究

针对水下机器人(UUV)推进系统容错控制分配问题,本文提出了基于SVD分解(奇异值分解)与定点分配的混合算法。与传统的方法相比,它回避了求伪逆矩阵的问题,降低了计算量;能够满足推进器饱和约束限制。利用水下实验平台推进系统模型进行了仿真实验,验证了算法的正确性和有效性。

水下机械手运动学逆解的一种优化解法

本文给出一种运用约束最优化的变尺度法求解Schilling水下机械手运动学逆解的方法。这种方法不仅具有牛顿方法的快速性和理想的总体收敛性,通过迭代求取H阵,不仔在奇异性问题,运用惩罚函数法选取步长,保证了从任意点进行搜索,同时有效地处理了约束的存在。这种方法较其它优化算法和搜索法有明显的快速性,在PⅡ550微机上的求解实验证明此算法完全可以用在此机械手运动学的实时求解中。

越野移动机器人自动驾驶专家系统的研究

本文研究越野移动机器人驾驶专家系统等有关问题．首先介绍了系统的硬件支持环境，然后阐述了自动驾驶专家系统的总体结构，有关知识库的内容以及使用知识的各功能模块的作用与运行机理．该系统已部分得以应用，能够完全代替驾驶员完成各种驾驶操作，并能进行自主导航、运动规划、自动绕障、动态跟踪目标、原路返回以及示教再现等复杂任务。