Vegetation effects on mean daily maximum and minimum surface air temperatures over China

Changes in the daily maximum (Tmax) and minimum (Tmin) surface air temperatures and the associated temperature extremes have severe consequences on human society and the natural environment. In this study, we assess vegetation effects on mean Tmax and Tmin over China by computing a vegetation feedback parameter using the satellite-sensed Normalized Difference Vegetation Index (NDVI) and observed temperatures for the period 1982–2002. In all seasons, vegetation exerts a much stronger forcing on Tmax than on Tmin, and thus has a substantial effect on the diurnal temperature range (DTR) over China. Significant positive feedbacks on Tmax and the DTR occupy many areas of China with the feedback parameters exceeding 1°C (0.1 NDVI)–1, while significant negative effects only appear over the summertime climatic and ecological transition zone of northern China and some other isolated areas. Also, the vegetation feedbacks are found to vary with season. In areas where significant feedbacks occur, vegetation contributes to typically 10%–30% of the total variances in Tmax, Tmin, and the DTR. These findings suggest that vegetation memory offers the potential for improving monthly-to-seasonal forecasting of Tmax and Tmin, and the associated temperature extremes over China. Meanwhile, the limitations and uncertainties of the study should be recognized.     

论“无缝之网”的“编织”机理——一种对技术与社会关系的解读

在规律所提供的"可能性空间"中,社会因素为技术形成"编织"了一张"无缝之网"。由社会客体性因素为技术形成划定"边界群"的约束机理、社会主体性因素为技术形成拓展"空间集"的扩展机理和社会控制性因素为技术形成设置"反馈网"的调节机理以及它们之间的整体联动,构成了"无缝之网""编织"的一般机理。认识这一机理对于我们具有重要的启示意义。     

分散时滞两级控制大系统的镇定研究

本文研究了大系统的分散时滞两级镇定问题,导出了镇定的三个充分条件,并提出了两级镇定的设计思路和方法.     

激光控制土地平整技术算法研究

建立土地平整系统的数学模型，讨论系统的稳定性和反应速度。在讨论该问题时将用到MATLAB提供的动态系统仿真工具Simulink。对仿真结果进行分析和可视化研究。     

树木生长对气候变化的响应研究进展

树木生长对气候变化的响应将深刻影响区域植被动态、陆地生态系统生物地化循环、气候反馈及其人类福祉.持续的气候变暖、极端气候事件及自然和人为干扰的增加深刻地影响树木生长动态的时空格局.本文综述了近几十年全球气候变化的整体概况,着重探讨了气候变化对树木生长的影响机制以及树木生长对气候系统的反馈,并就树木生长响应气候变化研究中可能存在的问题和研究前景进行了探讨.提出未来树木生长响应气候变化关系的研究应考虑树木生长响应气候变化的时空差异,加强对树木死亡时空格局及内在机理的认识,重点关注不断增加的极端气候事件及火、虫灾干扰对树木生长的非线性影响机制,并融合地面观测、遥感及陆面动态植被模型模拟等多种分析手段综合分析树木生长对气候变化响应机制的尺度效应及内在机理.