树木体内水分长距离运输的负压传递机制     

尚念科 《山东林业科技》2011,41(3):90-92

蒸腾能使木质部产生不超过-0.1MPa的有限负压,这个负压在木质部内自上而下依次向下传递。水分在导管或管胞内所受的吸附力、毛管力、真空力等综合作用力要大于或等于所受的重力,这个综合作用力可以将水分托住而不受重力作用而下移,使水分在负压作用下以分段移动的方式从根部上升到植物顶端。空穴和栓塞是两个不同的概念,其形成过程、恢复机制都有其本质的不同。空穴的发生与负压和水分的分段移动有密切的关系。  相似文献   

基于约束的虚拟装配运动导航技术   总被引：1，自引：0，他引：1  

杨润党  武殿梁  范秀敏  严隽琪 《农业机械学报》2006,37(3):113-118

在虚拟装配过程中,当虚拟手抓取的零部件受到约束时,操作者佩戴的位姿跟踪器(FOB)检测到的理论位姿数据与虚拟手的位姿不能满足一致性,难以满足沉浸感的要求。在建立装配约束和自由度等价关系的基础上提出了表达自由度的统一数据结构,并根据零部件所受到不同约束时的剩余自由度进行了自由度的重新归约;根据零件满足当前约束的等价自由度以及位置跟踪器检测到的数据,提出了一种基于增量驱动和广义坐标系的自由度求解算法求解零件在受约束条件下的运动导航矩阵,以此矩阵驱动零部件在满足约束条件下的运动。这个算法已经被应用于集成虚拟装配系统IVAE中。  相似文献   

基于高速图像的雾滴尺寸分布统计与运动分析   总被引：2，自引：3，他引：2  

史春建  邱白晶  汤伯敏  刘保玲 《农业机械学报》2006,37(5):63-66

针对植保机械雾滴尺寸分布统计及运动分析方法存在的不足,提出了利用高速摄像机结合数字图像处理技术对雾化场的空间雾滴尺寸分布和雾滴的运动进行分析的方法。实现了空间雾滴尺寸分布的快速统计分析,避免了对雾化场的干扰。利用图像序列中的时间差信息对雾滴在水平和垂直方向上的速率进行了分析,为进一步分析雾滴的沉降及漂移特性提供了有效方法。  相似文献   

旋转式开沟机工作部件的运动分析   总被引：1，自引：0，他引：1  

孙红霞  陈勋  张志林  杜白石 《农机化研究》2002,(3):53-54,56

对旋转式开沟机的工作部件进行了运动分析，探讨了机具的工作原理，参数设计，开沟铲尖的运动轨迹，沟的几何参数及开沟铲的运动参数，为机具的设计提供了理论依据。  相似文献   

Are hedgerows effective corridors between fragments of woodland habitat? An evidence-based approach   总被引：1，自引：1，他引：1  

Zoe G. Davies  Andrew S. Pullin 《Landscape Ecology》2007,22(3):333-351

Anthropogenic modification of the countryside has resulted in much of the landscape consisting of fragments of once continuous habitat. Increasing habitat connectivity at the landscape-scale has a vital role to play in the conservation of species restricted to such remnant patches, especially as species may attempt to track zones of habitat that satisfy their niche requirements as the climate changes. Conservation policies and management strategies frequently advocate corridor creation as one approach to restore connectivity and to facilitate species movements through the landscape. Here we examine the utility of hedgerows as corridors between woodland habitat patches using rigorous systematic review methodology. Systematic searching yielded 26 studies which satisfied the review inclusion criteria. The empirical evidence currently available is insufficient to evaluate the effectiveness of hedgerow corridors as a conservation tool to promote the population viability of woodland fauna. However, the studies did provide anecdotal evidence of positive local population effects and indicated that some species use hedgerows as movement conduits. More replicated and controlled field investigations or long-term monitoring are required in order to allow practitioners and policy makers to make better informed decisions about hedgerow corridor creation and preservation. The benefits of such corridors in regard to increasing habitat connectivity remain equivocal, and the role of corridors in mitigating the effects of climate change at the landscape-scale is even less well understood.  相似文献   

Effect of road density on abundance of white-footed mice     

Trina Rytwinski  Lenore Fahrig 《Landscape Ecology》2007,22(10):1501-1512

While several studies have demonstrated that roads can act as barriers to small mammal movement, the relationship between road density and small mammal abundance has not yet been investigated. In southeastern Ontario, Peromyscus leucopus (white-footed mice) suffer high over-winter mortality rates, resulting in small springtime populations and frequent local extinctions. Peromyscus leucopus movement is known to be inhibited by roads, which should result in lower rates of immigration into and recolonization of habitats in landscapes with high road density. We tested two predictions: (1) Forest sites situated in landscapes with high road densities have a higher chance of P. leucopus being absent during the early spring than forest sites situated in landscapes with low road densities and (2) P. leucopus populations during the summer are smaller in forest sites situated in landscapes with high road densities than in landscapes with low road densities. We sampled P. leucopus in focal patches within nineteen landscapes (7 rural, low-road-density landscapes; 7 rural, high-road-density landscapes; 5 urban landscapes). There was no significant relationship between road density and the presence/absence of P. leucopus during the early spring. We found a significant positive effect of road density on P. leucopus relative abundance during the summer, even when we excluded the urban landscapes and based the analysis on only the 14 rural landscapes. Our results suggest that any negative effect of roads on P. leucopus populations, created by their inhibition to moving across roads, is far outweighed by some positive effect of roads on P. leucopus abundance. We suggest that the two most likely explanations are that roads are positively correlated with an important as-yet-undetermined component of habitat quality, or that roads positively affect P. leucopus by negatively affecting their predators.  相似文献   

花尾榛鸡(Bonasa bonasia)在韩国温带林中的季节性移动特征(英文)     

Shin-Jae Rhim  Woo-Shin LEE 《林业研究》2002,13(2)

This study were carried out in the Experimental Forest (37( 48' 10" N, 127( 48' 50" E) of Gangwon Forest Development Institute, Gamjeong-ri, Chuncheon, Gangwon-do Province, Korea from Dec. 1999 to Jul. 2002. Eight individuals (three males and five females) of hazel grouse were captured and they were marked with a 14-g necklace-type transmitter. The surveying results showed that females were more active than males throughout the year, but males were more mobile than females in spring. The degree of movement for females and males was similar from summer to winter. The overlap degree of habitat was very large from spring to autumn. Hazel grouse had greater shifts in area use in winter. They used similar area from spring to autumn, made a shift in their habitat use in winter, and then shifted back to the previous habitat.  相似文献   

Using behavioral landscape ecology to predict species’ responses to land-use and climate change   总被引：1，自引：0，他引：1  

Jessie L. Knowlton  Catherine H. Graham 《Biological conservation》2010,143(6):1342-1354

Climate change and habitat destruction are widely recognized as major threats to species’ survival. As a result of these anthropogenic impacts, species are often forced into novel landscapes where their persistence is difficult to predict. Knowledge of how individuals move or disperse through the landscape, choose habitat in which to settle, and produce offspring which survive to repeat the process can greatly improve our ability to predict species’ persistence. The field of behavioral landscape ecology uses a strong theoretical base to explore, often experimentally, how the behavior of a particular species is affected by heterogeneous and rapidly changing landscapes and can offer valuable insight for managing species in the face of human-induced environmental changes. When interpreted by modelers, results of landscape-level behavioral experiments can be quantified for use in predictive models. To this end, we summarize the methods and results of research using direct experimental manipulation techniques broken into the following categories: translocations, playback experiments, food resource manipulations, manipulations of reproductive success, direct manipulations of the landscape, and manipulations of predation risk. We review and place in a theoretical framework the results from this emerging body of research regarding how organisms move in and respond to different types of landscapes, both natural and human-altered. We go onto highlight the potential of each experimental method to quantify different processes, which may be useful when interpreted by modelers attempting to parameterize predictive models. Finally, we suggest future directions for experimental research that will allow for greater integration of behavioral landscape ecology and predictive modeling.  相似文献   

韩国“新村运动”经验及其对中国新农村建设的启示     

杨贤智  骆浩文  张辉玲 《中国农学通报》2006,22(9):547-547

简要介绍了韩国“新村运动”的发展历程和取得的成就；概述了韩国“新村运动”把农民的思想启蒙作为起点、农村经济发展作为目标的成功经验；分析总结了韩国“新村运动”对中国新农村建设的启示；结合“十一五”规划纲要和2006年中央一号文件精神，指出在中国社会主义新农村建设过程中，要尊重农民意愿、培养有创业本领的新型农民、解决新农村建设的资金来源问题、做到科学合理规划、完善乡村自理和村民自治机制。  相似文献   

How peri-urban areas can strengthen animal populations within cities: A modeling approach     

R.P.H. Snep  P.F.M. Opdam  J.M. Baveco  W. Timmermans  V. Kuypers 《Biological conservation》2006,127(3):345-355

We explore the extent to which inner-city fauna can be enhanced by source areas in peri-urban zones as a response to a decreasing quality and size of green habitats within cities. The objectives were to get a better understanding of the interaction between animal populations of urban and peri-urban areas, and the role of urban green structures within this relationship, and to find out the extent to which peri-urban areas can contribute to urban animal populations. We illustrate the idea of peri-urban support by using a simulation model for individual animal movement, applied in a particular case-study with butterflies as model species. Results show differences in accessibility of inner-city areas between model butterfly species that differ in mobility. The impact of peri-urban individuals on populations of inner-city habitats differed among several peri-urban source-scenarios: the enlargement of the inner-city butterfly population by peri-urban individuals was determined as 7-36% for ‘moderate dispersers’ and 19-56% for ‘good dispersers’. Results also show that well-connected habitat patches within existing urban green structures were more likely to be visited by peri-urban individuals than isolated habitat patches. We conclude that peri-urban nature areas, if large enough, can have a potentially positive influence on the presence of fauna in inner-city neighborhoods. In addition, results suggest that connectivity between inner-city and peri-urban habitat patches enhances contribution of peri-urban migrants to inner-city populations. By providing a range of different habitats, from inner-city up to peri-urban area, moderately mobile habitat specialists could better compete against the small set of successful habitat generalists that are increasing in urban environments all over the world.  相似文献