About the Synthesis Method of Planar Multilink Mechanisms Based on Genetic Algorithm

This paper discusses the method of synthesizing planar multilink mechanisms based on GA. The pivotal technology is coding, creating population, account fitness, genetic operation and defining population size. This method does not require initial mechanisms and can search for plural appropriate mechanisms simultaneously. It is efficient about the non-linear problem. As an example, configuration of 4-bar planar mechanisms is decided in a practical application. It can be used the synthesis of 6-bar or more bar planar mechanisms as well.     

棉花杂种优势表达机理研究进展

从棉花杂种优势性状表现、配合力分析、生理生化研究、遗传距离与杂种优势关系等方面分析了棉花杂种优势机理研究进展,并提出了从基因水平研究棉花杂种优势,更能确切地反映杂种优势表达机理。     

Potentially durable resistance mechanisms in plants to specialised fungal pathogens

Specialised plant pathogens are in many ways adapted to exploit their host plants. Infective propagules should reach the appropriate plant tissue, gain access to the tissue and negate or suppress various kinds of constitutive and inducible resistance mechanisms. The resistance type most frequently deployed in plant breeding is the race-specific resistance, where a hypersensitive response of plant tissue is elicited by an avirulence factor produced by the pathogen. The great disadvantage of this type of resistance is, that it is often ephemeral. Detailed screening of germplasm may result in the discovery of alternative defence mechanisms not associated with hypersensitivity, that may be durable. Avoidance mechanisms may reduce the chance of infection. Upright plant habit has been reported to decrease spore deposition in cereals. Crop architecture may also affect aspects such as humidity and aeration in the crop, and hence the chances for successful infection by pathogen propagules. Other examples of avoidance are leaf surface properties that interfere with leaf wettability, germ tube orientation and finding of stomata to enter the leaf. Stomata in some accessions of Hordeum chilense are excessively covered by cuticular wax that prevent rust fungal germ tubes from perceiving the stomata, resulting in failure of penetration of the pathogen into the leaf. There is evidence that incompatible host species, biotrophic pathogenic fungi induce basic compatibility by suppressing defence mechanisms. Failure of this induction results in abortion of the infection attempt. Several cases of apparently durable resistance are discussed that are based on failure of haustorium formation, and are not associated with hypersensitivity. They may represent cases where the pathogen has problems in establishing basic compatibility. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evaluation and inheritance of the Lycopersicon hirsutum resistance against potato virus Y

Summary Potato virus Y (PVY) infects most Solanaceous crops grown in Mediterranean countries in open fields and in greenhouses. Necrogenic strains, which have been isolated from diseased tomatoes in France since the 1980's, seriously cause yield and quality loss of tomato fruits. Lycopersicon hirsutum PI 247087 was found to be resistant to PVY. Virus could not be detected in inoculated leaves by ELISA and/or by back-inoculation on susceptible plants. This resistance was efficient against the 16 tested isolates or strains. Temperature and inoculum concentration did not affect its expression. All the F₁ plants of (Momor × PI 247087), (PI 134417 × PI 247087) and (PI 247087 × PI 134417) had symptom scores and ELISA values similar to those of the susceptible parents. The mechanism of resistance could be immunity-like or inhibition of virus migration from cell to cell. The resistance of L. hirsutum PI 247087 appeared to be governed by two independent recessive genes. In a few F₂ plants of (PI 134417 × PI 247087) and F₂ (Momor × PI 247087), virus was able to multiply in the inoculated leaves but could not establish a systemic infection. This finding may suggest a mechanism which interfers with the long distance migration of the virus in the plant.     

干旱区土地利用/覆盖时空动态变化分析——以准格尔旗为例

为评估植被恢复以及土地利用变化对生态脆弱地区的影响,文中选取准格尔旗为研究区,基于1990、2000、2009年三期美国陆地卫星遥感影像提取各时期的土地利用类型,在30m栅格尺度上定量评价并分析其动态变化。变化的驱动因素主要有自然因素、人口增长和城市化、过度矿产资源开发等负面因素和生态恢复政策的正面因素。结果表明:过去20年间,人类活动及资源开采对生态环境的干扰增加,植被恢复的过程是有效而缓慢的。     

草果挥发油的化学成分及抑菌机理研究进展

草果中含有多种生物活性物质,具有抑菌、抗氧化等作用,挥发油为草果提取物中的主要活性成分.本文综述了草果挥发油的化学成分、抑菌作用以及抑菌机理等方面的研究进展,分析了目前研究中存在的一些问题,展望了草果作为天然防腐剂的发展前景,旨在为草果的进一步开发利用提供理论参考.     

油菜(Brassica napus L.)矮化研究进展

油菜(Brassica napus L.)是具有重要影响的油料作物。通过杂交育种在油菜上的运用,获得了相较于旧品种在生活力、生长势、抗逆性、适应力、产量、品质等方面具有更大优势的新品种,但同时也带来了油菜倒伏与机械化生产率无法提高等问题。水稻和小麦相关的矮化研究与应用是绿色革命的重要组成部分,这为人们改良油菜品种提供了新的思路。对于油菜倒伏和提高油菜机械化生产率等急需解决的问题,油菜矮化育种成为了解决问题的关键。本研究围绕甘蓝型油菜矮化基因的遗传特点、基因定位、矮化机制等方面的研究情况进行综述,为进一步利用油菜矮化基因提供参考。     

非圆齿轮-曲柄滑块压捆机构反求设计

为满足压捆机构的理想运动特性要求,该文提出了一种非圆齿轮—曲柄滑块式新型压捆机构,建立了该新型机构的运动学分析模型,并以理想速度曲线为目标反求得到了满足工作要求的非圆齿轮节曲线。通过实例计算比较,该新型机构与传统曲柄滑块式压捆机构相比,在一个工作循环中压缩时间增加30%,能实现小阻力阶段快速压缩、大阻力阶段则以恒定的低速压缩,且所需最大输入功率可降低28.6%。     

空间4-SPS/CU并联机构的受力分析

运用螺旋理论分析了一种具有三维转动和一维移动(沿Z轴)的四自由度(4-SPS/CU)并联机构的自由度,得出该机构为无过约束机构。采用传统的拆杆法对该机构的每个活动构件进行了静力学分析,得出了该机构的静力学平衡方程组,判定该机构的静力学平衡方程组中方程个数大于未知量个数(属超定方程组)。多余的方程个数就是该机构的局部自由度,并采取去掉局部自由度对应的静力学平衡方程来求解该超定方程组。通过求解该方程组,得出了该机构每个构件上的全部约束力/力矩,并分别得出了驱动力与主运动副以及恰约束从动支链的约束反力随该机构位姿变化的仿真曲线。证实了该机构比无恰约束从动支链的四自由度并联机构拥有更好的承载能力。研究结果可为该机构在工程中的应用与结构设计提供静力学理论分析的参考。     

基于D-H变换矩阵的宽窄行分插机构运动特性分析与设计

为满足水稻插秧机宽窄行插秧的需要,以高速插秧机的行星系分插机构为研究基础,根据宽窄行空间插秧轨迹的要求,提出了一种斜齿椭圆齿轮交错啮合传动的行星轮系分插机构。确定了分插机构空间插秧轨迹的关键参数,利用D-H变换矩阵建立了机构的轨迹模型,分析了关键参数对插秧轨迹的影响,并进行了机构的运动特性研究。利用编写的机构优化程序,通过人机交互的方式优化出一组满足空间插秧要求的机构参数,并根据参数完成了机构的设计。最后,通过虚拟仿真验证斜齿椭圆齿轮交错啮合传动的分插机构可以满足水稻宽窄行插秧的要求。