Effect Of A Negative Poisson Ratio In The Tension Of Ceramics

The effect of a negative Poisson ratio is experimentally revealed in the tension deformation of a natural layered ceramic. This effect can increase the volume strain energy per unit volume by 1100% and, simultaneously, decrease the deformation strain energy per unit volume by about 44%, so that it effectively enhances the deformation capacity by about 1 order of magnitude in the tension of the material. The present study also shows that the physical mechanisms producing the effect are attributed to the climbing on one another of the nanostructures in the natural material, which provides a guide to the design of synthetic toughening composites.

PATTERNS OF SPATIAL-DISPERSION, LOCOMOTION AND FORAGING BEHAVIOR IN 3 GROUPS OF THE YUNNAN SNUB-NOSED LANGUR (RHINOPITHECUS-BIETI)

Aspects of the behaviour of three groups of Yunnan snub-nosed langurs, Rhinopithecus bieti, were observed over the course of three field seasons from 1986 to 1988. The major findings of the study were: (1) The habitats of R. bieti were mainly at heights of 3,600-4,150 m above sea level. (2) Groups were very large, with group sizes ranging from more than 100 to 269 individuals. (3) Spatial dispersion densities ranged from about 27 to 106 m2/individual during sleeping and resting, to feeding dispersions as large as 5,000-15,000 m2. (4) The locomotor repertoire of R. bieti consisted largely of walking, jumping and climbing. On very rare occasions, semibrachiation was observed, but true brachiation was never observed. The locomotor repertoires of juveniles were more diverse than those of subadults or adults. (5) Communication consisted mainly of eye-to-eye contact accompanied by murmurs; while loud calls were heard only rarely. (6) Groups moved between sleeping and feeding sites in single file. It is concluded that R. bieti is a mainly terrestrial species.

Tidally induced upwelling off Yangtze River estuary and in Zhejiang coastal waters in summer

MASNUM wave-tide-circulation coupled numerical model (MASNUM coupled model, hereinafter) is developed based on the Princeton Ocean Model (POM). Both POM and MASNUM coupled model are applied in the numerical simulation of the upwelling off Yangtze River estuary and in Zhejiang coastal waters in summer. The upwelling mechanisms are analyzed from the viewpoint of tide, and a new mechanism is proposed. The study suggests that the tidally inducing mechanism of the upwelling includes two dynamic aspects: the barotropic and the baroclinic process. On the one hand, the residual currents induced by barotropic tides converge near the seabed, and upwelling is generated to maintain mass conservation. The climbing of the residual currents along the sea bottom slope also contributes to the upwelling. On the other hand, tidal mixing plays a very important role in inducing the upwelling in the baroclinic sea circumstances. Strong tidal mixing leads to conspicuous front in the coastal waters. The considerable horizontal density gradient across the front elicits a secondary circulation clinging to the tidal front, and the upwelling branch appears near the frontal zone. Numerical experiments are designed to determine the importance of tide in inducing the upwelling. The results indicate that tide is a key and dominant inducement of the upwelling. Experiments also show that coupling calculation of the four main tidal constituents(M-2, S-2, K-1, and O-1), rather than dealing with the single M-2 constituent, improves the modeling precision of the barotropic tide-induced upwelling.

Effects of the dinoflagellate Alexandrium tamarense on early development of the scallop Argopecten irradians concentricus

The effects of Alexandrium tamarense (strain ATHK) on early development of the bay scallop Argopecten irradians concentricus were studied under laboratory conditions. The algal culture was verified by HPLC to produce paralytic shellfish poisoning (PSP) at a level of 37.48 fmol/cell. Survival of the scallop larvae was not affected when they were grown with A. tamarense at concentrations of 500-10,000 cells/ml for 48 h. However, the activity of D-shape larvae was inhibited after 48-h exposure to A. tamarense at the algal cell density of 10,000 cells/ml. Scallop growth was inhibited significantly by A. tantarense during a 14-day exposure starting at the eye-spot larval stage. The size of juvenile scallops in the group of 10,000 cells/ml was only about 32% of that of the controls, although no obvious effect of A. tamarense was found on the rate of larval metamorphosis. All juvenile scallops survived in algal concentrations of 600-2400 cells/ml, however, attachment rates were significantly lower than control values after a 5-h exposure to A. tamarense at concentrations >600 cells/ml, while they were not obviously reduced after only 1 h of exposure. At concentrations >600 cells/ml, the climbing ability of juveniles was clearly reduced by exposure to A. tamarense after only 1 h. The climbing rate and height were only 55% and 45%, respectively, of those of the controls, when exposed to A. tantarense at a concentration of 600 cells/ml. The results indicated that A. tamarense blooms may have detrimental impacts on shellfish at early life stages, therefore, special attention should be paid to the toxic algal blooms in shellfish breeding area. (C) 2003 Elsevier Science B.V. All rights reserved.

Impacts of HAB species Heterosigma akashiwo on early development of the scallop Argopecten irradians Lamarck

The effects of Heterosigma akashiwo on the early development of Argopecten irradians Lamarck: eggs, D-shaped larvae, eye-spot larvae and juveniles, were investigated under laboratory conditions. Exposing fertilized eggs to various densities of H. akashiwo algal culture revealed that the development of the embryos to the gastrula was significantly slowed at densities of more than 1 X 10(4) cells/ml algal cells, and mostly was arrested when the embryos reached the trochophore larvae stage. At this stage, several trochophore larvae were adhered together by the algal cells, resulting in the inhibition of their swimming activity. Larvae had still not developed into D-shaped larvae after 30 h, and therefore did not finish the hatching process. The attachment and adherence of the algal cells to the larvae might be an important process in the mechanism of the impact on egg hatching success. The activity of the D-shaped larvae was significantly inhibited after 48 h exposure to H. akashiwo at a density of 15 X 10(4) cells/ml and after 96 h at 10 X 10(4) cells/ml. The survival rate of the eye-spot larvae was decreased significantly after 48 h exposure to the algal culture at densities of more than 1 X 10(4) cells/ml. However, all the juveniles could survive and their climbing and attachment activity were not affected after 1 and 5 h exposure to the algal culture at all the various algal cell densities tested from 5 to 20 X 10(4) cells/ml. The results indicated that susceptibility of embryos or larvae to the alga H. akashiwo differs depending on the developmental stage. The embryos and the eye-spot larvae of A. irradians are more sensitive stages to the toxicity of H. akashiwo. Observed effects of H. akashiwo exposure on early development of A. irradians serve to point out to the potential danger of this alga for scallop populations. The possible toxicological mechanisms of H. akashiwo on the scallop embryos and larvae are discussed. (c) 2005 Elsevier B.V All rights reserved.

基于主动试探的微小型爬壁机器人步态控制

针对欠平滑壁面上微小型爬壁机器人吸盘足吸附失败后的自主行为控制问题,根据机器人的结构设计及运动步态特点,提出基于主动试探的机器人吸盘足着地点自主选择步态控制方法。分析机器人的三种运动模式,以及直线运动和转向运动的基本步态。定义机器人的状态矢量,建立机器人吸盘足的有限状态机模型和状态转移图,并按"就近"原则设定状态转移函数的优先级。以上述研究为基础,提出在缺少壁面环境信息条件下的机器人步态控制主动试探方法。对步态控制方法进行仿真分析,并在实验室模拟环境和实际的飞机外表面环境进行试验验证,结果表明,所提出方法对于改善机器人的控制性能和提高机器人的自主能力是可行和有效的。

一种FPGA的嵌入式可重构机器人控制系统

提出一种基于FPGA的可重构嵌入式微处理器控制系统.在FPGA中嵌入两个NiosⅡ软核,用VHDL语言编写用户自定义组件.在一个由NiosⅡ软核组成的处理器上实现PWM信号生成、编码器信号处理以及多电机同步伺服运算等,在另一个处理器实现机器人任务管理.该控制系统针对微小型爬壁机器人的控制系统设计,不仅具有良好的实时多任务处理能力,而且具有可重构的特点,因而可应用于一类微小型机器人控制系统以提高其设计的灵活性.

轮腿复合移动机器人自主越障姿态设定及轮腿运动协调算法实现

轮腿复合移动机器人具有很好的地面适应能力和越障能力。本文通过对机器人系统结构的分析和其越障高度的静态分析,计算出机器人能够越障的最大高度,并提出了针对典型地形环境(沟、坎、台)越障问题的机器人构型优化以及轮腿运动协调控制算法,而且通过实验验证了算法的有效性。

可重构模块化机器人系统的翻越台阶能力研究

从分析系统的工作原理和子机器人运行机理入手,对可重构模块化星球探测机器人系统的翻越台阶能力进行了研究。对于单体子机器人,提出了通过加反向速度和规划手臂姿态的方法,使其能够顺利翻越台阶型障碍物,增强了单体子机器人的翻越台阶能力。由几个子机器人组成的新系统极大地扩展了单体子机器人的环境适应能力,分析了有利于子机器人组合翻越台阶型障碍物的组合形式,提出了首尾相连成环形连接的构型是翻越台阶的最佳组合,并提出了根据环境条件采取不同策略的决策方法,即对于较低的台阶,采取子机器人组合一起翻越,对于高台阶,采取将一个子机器人送上台阶的策略。最后,通过静力学分析,得出了单体子机器人和子机器人组合所能翻越台阶型障碍物的极限尺寸,实际实验很好地验证了分析结果。

可重构模块化机器人系统的爬坡能力研究

介绍了一种新型的可重构模块化星球探测机器人系统,详细分析了子机器人组合的三种基本构型:手臂在前,首尾相连成串状;手臂在后,首尾相连成串状;两个子机器人首尾相连成环状。以两个子机器人为例,对爬坡过程中子机器人系统的各种组合形式进行了静力学分析,在此基础上,对机器人组合的爬坡能力进行了仿真研究,结果表明子机器人组合的爬坡能力与其连接构型紧密相关。实际试验很好地验证了仿真结果,同时,以实际试验为基础,得出了如下结论:在爬坡过程中,手臂在前的串状连接的机器人组合的运动稳定性较差,首尾相连的环状连接的机器人组合是子机器人组合爬坡的首选构型。

一种轮足复合式爬壁机器人机构建模与分析

基于行星轮系运动及双足真空吸附原理,提出了一种新型爬壁机器人机构,介绍了机构的构型及结构特点,推导了运动学方程,分析了沿直线行走、平面旋转和跨越交叉壁面三种运动模式.仿真结果表明该机构具有移动速度快、运动灵活、跨越交叉壁面能力强等特点.

基于立体视觉的移动机器人楼梯识别

本文提出了一种结构化环境下,基于立体视觉的机器人楼梯识别算法,并将算法该应到自主移动机器人上。该算法首先利用二维图像分析的方法搜索楼梯的疑似区域;进而利用立体视觉对各个疑似区域进行精确三维重建,结合三维信息重构楼梯平面,排除虚假疑似楼梯区域;最后判定机器人和楼梯的相对位姿关系,引导机器人爬楼梯。最终我们将该算法应用到了自主移动机器人上,通过在各种光照条件下的实验,进一步验证了该算法的准确性和快速性。

小型爬壁机器人系统设计与应用

针对一种小型的双足爬壁机器人,设计开发了基于DSP2812处理芯片的控制系统.该机器人系统采用双足真空吸盘式结构和用3个电机驱动5个关节的欠驱动结构.双足真空吸盘式结构使其可以在光滑的墙面和天棚行走,又能够在交接面之间完成跨步行走.而欠驱动结构减少了电机的数目,从而减小了机器人的尺寸和降低了机器人的质量和能量消耗,但它也给机器人的控制和运动规划带来了新的挑战.已完成的系统设计包括运动模式设计、关节控制、通信模块设计和吸盘足控制等.实验结果证明了所提出方案的可行性.