Effects of vegetation control on ecosystem water use efficiency within and among four grassland ecosystems in China

Through 2-3-year (2003-2005) continuous eddy covariance measurements of carbon dioxide and water vapor fluxes, we examined the seasonal, inter-annual, and inter-ecosystem variations in the ecosystem-level water use efficiency (WUE, defined as the ratio of gross primary production, GPP, to evapotranspiration, ET) at four Chinese grassland ecosystems in the Qinghai-Tibet Plateau and North China. Representing the most prevalent grassland types in China, the four ecosystems are an alpine swamp meadow ecosystem, an alpine shrub-meadow ecosystem, an alpine meadow-steppe ecosystem, and a temperate steppe ecosystem, which illustrate a water availability gradient and thus provide us an opportunity to quantify environmental and biological controls on ecosystem WUE at different spatiotemporal scales. Seasonally, WUE tracked closely with GPP at the four ecosystems, being low at the beginning and the end of the growing seasons and high during the active periods of plant growth. Such consistent correspondence between WUE and GPP suggested that photosynthetic processes were the dominant regulator of the seasonal variations in WUE. Further investigation indicated that the regulations were mainly due to the effect of leaf area index (LAI) on carbon assimilation and on the ratio of transpiration to ET (T/ET). Besides, except for the swamp meadow, LAI also controlled the year-to-year and site-to-site variations in WUE in the same way, resulting in the years or sites with high productivity being accompanied by high WUE. The general good correlation between LAI and ecosystem WUE indicates that it may be possible to predict grassland ecosystem WUE simply with LAI. Our results also imply that climate change-induced shifts in vegetation structure, and consequently LAI may have a significant impact on the relationship between ecosystem carbon and water cycles in grasslands.

柔性制造系统中死锁避免的充要条件第一部分：资源竞争过程的建模

柔性制造系统的主要特点是多种不同类型的工件同时在系统中加工，这些工件竞争系统的有限资源，导致象系统死锁等这样的不希望事件的发生，本文用一种Ｐｅｔｒｉ网模型，称之为着色面向资源的Ｐｅｔｒｉ网（着色ＲＯＰＮ）来描述系统中的这一竞争过程；这一模型揭示了资源竞争过程的本质特点，从而为寻求死锁避免的充要条件提供了基础。

空值环境下关系数据库的更新 Ⅰ：扩展关系模型及基本运算

本文从空值语义及更新操作的关系出发，提出了一种新的扩展关系模型，用以组织更新操作下的含有空值的关系数据库中的信息．同时，定义了这种模型下的基本关系代数运算．为实现空值环境下关系数据库的数据更新奠定了基础。

管道煤气生产中汞的分布

为了解城市管道煤气生产中可能存在的汞污染，对贵阳市管道煤气及煤气生产所使用的洗精煤、煤气生产过程中产生的化学产品焦碳、焦油及焦炉煤气脱硫洗涤物硫浆中汞的含量和分布进行了研究。研究发现，管道煤气中汞的含量低于二次金汞齐～冷原子吸收光谱法检测限0．05ng／m^3，较贵阳市城区大气汞的含量还低。在原煤转化为城市管道煤气过程中，煤中的汞在煤气生产的各个环节都有不同程度的脱除；其中原煤的洗选过程是最主要的脱汞过程，约75％左右的汞在该过程中被脱除；焦碳中汞含量占洗精煤汞含量的14．1％；煤焦油中汞含量占洗精煤中汞的15．5％；硫浆的生成过程则脱除了煤气生产用洗精煤中51％的汞。

赣中周潭群石榴石、斜长石和黑云母微区化学成分特征及其地球动力学意义

周潭群变质岩中石榴石、斜长石和黑云母微区化学成分变化明显,石榴石变斑晶具典型的生长环带,由晶体中心向两侧边缘XMg 、XFe值以光滑曲线递增,XCu 、XMn值以光滑曲线递减,反映其增温过程;晶体最边缘的化学成分反映变质峰期的温度条件。通过石榴石变斑晶生长环带剖面分析,应用Grt-Bi 温度计和GASP 压力计,确定本区变质作用p T 轨迹为顺时针形式,发生于大陆碰撞造山带环境。