白水江国家级自然保护区羚牛生境特征及潜在分布

羚牛(Budorcas taxicolor)是国家一级保护野生动物,对其生境评估有助于科学保护该物种的栖息地.以白水江国家级自然保护区为例,通过样线法对羚牛的痕迹点进行调查,并记录痕迹点所处的生境特征,利用最大熵模型对保护区羚牛生境进行了适宜性评价和预测.结果显示,羚牛的适宜生境主要分布在让水河、刘家坪和丹堡河保护站,总分布面积为634.33km^(2),占保护区总面积的34.51%,占核心区面积的70.36%.采用的生物地理模型可靠(AUC>0.80),在6个环境变量中,贡献最大的是年均温,其次为年降水量,第三是坡度.白水江保护区羚牛生态源地的最低海拔为1600m,最高出现在3300m.需要加强该区域的干扰控制、管理和监测,减缓人为活动对该生态源地的进一步挤压.

考虑材料性能退化影响的锈蚀水工组合梁时变可靠度分析

随着运行年限的增加,水工组合梁在外部环境和荷载的作用下材料力学性能会发生一定程度的退化,基于时变理论对水工组合梁的安全可靠度分析已成为其安全评价的重要内容。为此,采用Monte Carlo随机有限元法,结合材料性能退化规律,分析研究了锈蚀水工组合梁时变可靠度规律。通过工程算例分析,得到了材料性能随时间线性衰减情况下水工组合梁的屈服强度和弹性模量,研究了材料性能退化与否对水工组合梁失效概率和可靠度的影响,并对计算所得到的失效概率和可靠度进行数值拟合。结果表明,水工金属结构屈服强度和弹性模量随锈蚀程度的加深而减小,且与失重率呈线性关系;无论是否考虑材料性能退化规律,水工组合梁可靠度指标均为线性变化,可根据拟合后的线性规律计算出任意时段水工组合梁可靠度指标。

Distribution and development strategy for Jatropha curcas L. in Yunnan Province, Southwest China

Yunnan Province is the main distributing area ofJatropha curcas L. This plant is abundant in several drainage areas of the dry-hot, dry-warm and sub-humid valleys in the south subtropical area of Yunnan Province. The seeds that were picked from trees blossoming between April and May and fructifying between September and October will have large seed yield and fine quality. For developing bio-diesel stock forest ofJ. curcas in areas with adaptive climate, seeding measures for afforestation should be taken and techniques on breeding, fast-growing, and high-yielding plantation cultivation are very important.