树木、林内、林冠上与森林区风速廓线研究(英文)

风速是森林生态系统研究中最为重要的变量之一,同时也是控制气流运输过程最基本的要素。由于树木生理指标和生长过程对风速的改变十分敏感,因此风速随高度的变化规律,即风速廓线的研究十分重要。一般认为,在裸地或林冠上的风廓线均呈对数规律变化,但是在单株树木和林分内风速随高度的变化则不呈对数规律。本文根据最近在海岸松林内风的研究结果,总结了针叶树种单株树木内、林分内和林冠上层以及海岸林区的风速廓线变化规律,其主要结论如下:1)单株针叶树树冠内的风速廓线呈指数形式分布,2)在林分内的风速廓线可用风的减弱系数来表示,3)[(\267\347)(\300\252\317\337\324\332\301\326\271\332\262\343)]上的分布可由风廓线参数(摩擦速度、粗糙长度、零平面位移)确定,4)在海岸林区,极端风速的分布可以使用了建筑上的风荷载模型进行预测。另外,本文提出了该研究领域尚需进一步探讨的问题,主要包括:1)风速廓线与树木特征及林分特征间的关系,2)利用简单的方法预测了风速廓线参数,3)风速廓线在树木生理、生态研究的作用、树木生长过程中风的微生态学效应以及森林生态和管理应用等方面。图4表1参60。

樟子松人工固沙林稳定性的研究

提出了人工林稳定性的内涵及其评价标准．分析了影响沙地樟子松人工林稳定性的各种干扰因子，通过对沙地樟子松人工林造林成活、生长情况、对不良外界环境的抗御能力、林分寿命、林分结构和生产力的综合评价分析，认为沙地樟子松引种人工林基本上是稳定的；而生长在立地较好的丘间低地的林分，其稳定性大于沙丘顶部的林分；从抗枯梢病角度看，幼林的抗性大于中林；从林分密度和生产力角度来看．红花尔基沙地樟子松林稳定性高于章古台．

基于LandsatTM/ETM数据的锡林河流域土地覆盖变化

根据1987年、1991年、1997年和2000年4期LandsatTM/ETM影像的土地利用/土地覆盖分类结果,运用地理信息系统空间分析方法,分析了内蒙古锡林河流域1987~2000年间各土地利用类型及草甸草原、典型草原、荒漠草原的数量变化和空间变化特征。分析结果显示,锡林河流域土地利用/土地覆盖变化的主要特征为草甸草原、典型草原面积的大幅减少和荒漠草原、农田和沙漠化土地面积的大幅增加及城镇的扩张。其中面积增加最大的是荒漠草原,增加了2328km2;相当于1987年荒漠草原面积的56%。农田和城镇面积逐年增大,分别从1987年的114.3km2和25.2km2增加到2000年的332.1km2和43.6km2。面积减少最多的是羊草+丛生禾草、羊草+杂类草等优良高产温带典型草原类型,共减少2040km2。草甸草原面积亦呈逐年减少的趋势,从1987年的1103km2减少到2000年375km2,面积减少了65.9%。农田、沙化地及城镇等非草原土地利用类型面积增加了62.5%。

Impacts of socio-economic factors on sediment yield in the Upper Yangtze River

In recent years, the role of human activities in changing sediment yield has become more apparent for the construction of hydraulic engineering and water conservation projections in the Upper Yangtze River, but it has not been evaluated at the macro scale. Taking Sichuan Province and Chongqing City as an example, this paper studies the relationship between socio-economic factors and sediment yield in the Upper Yangtze River based on section data in 1989 and 2007. The results show that sediment yield is significantly correlated with population density and cultivated area, in which the former appears to be more closely related to sediment yield. Moreover, in the relation of sediment yield vs. population density, a critical value of population density exists, below which the sediment yield increases with the increase of population density and over which the sediment yield increases with the decrease of population density. The phenomenon essentially reflects the influence of natural factors, such as topography, precipitation and soil property, and some human activities on sediment yield. The region with a higher population density than critical value is located in the east of the study area and is characterized by plains, hills and low mountains, whereas the opposite is located in the west and characterized by middle and high mountains. In the eastern region, more people live on the lands with a low slope where regional soil erosion is slight; therefore, sediment yield is negatively related with population density. In contrast, in the western region, the population tends to aggregate in the areas with abundant soil and water resources which usually lead to a higher intensity of natural erosion, and in turn, high-intensity agricultural practices in these areas may further strengthen local soil erosion. It is also found that population tends to move from the areas with bad environment and high sediment yield to the areas with more comfortable environment and less sediment yield. The natural factors have greater influence on sediment yield of western region than that of eastern region. Generally, the natural factors play a dominant role on sediment yield in the Upper Yangtze River.

Microstructures and mechanical properties of as-cast Mg–5Al–0.4Mn–xNd (x=0, 1, 2 and 4) alloys

Mg-5Al-0.4Mn-xNd (x=0, 1, 2 and 4wt.%) alloys were prepared by metal mould casting method. The microstructures and mechanical properties were investigated. The results demonstrated that Al11Nd3 phase was formed and mainly aggregated along the grain boundaries with the addition of Nd. Meanwhile, the grain sizes were greatly reduced with the increasing Nd content.

马钱苷的电喷雾串联质谱及傅立叶变换离子回旋共振质谱研究

利用电喷雾串联质谱(ESI-MSn)技术研究马钱苷的质谱碎裂机理,探讨其碎裂方式,并利用傅立叶变换离子回旋共振质谱(FTICR-MS)及SORI-CID高分辨率、高质量准确度对其碎裂机理进行验证研究。采用H/D交换和串联质谱的方法,发现马钱苷羟基上的活泼氢在质谱中性碎片丢失过程中较易被转移,表现出较大的化学活性。通过加入特定的Na+和Li+等碱金属离子,极大地提高了马钱苷化合物质谱分析的灵敏度,获得了更多的结构信息,建立了马钱苷化合物质谱鉴定和分析的新方法。