黄土不同指标的古环境意义探讨

在确认“黄土也是古土壤”的前提下,对新近发现的位于黄土高原西北部沙漠黄土边界带的彭阳剖面进行了烧失量、色度、磁化率、粒度、CaCO3等环境变化代用指标的系统测试。通过建立土壤发育指数和红化指数,探讨了各指标与古土壤发育强度之间的关系。根据古土壤的发育强度,初步建立了800 ka BP生态脆弱区的高分辨率环境图谱。此图谱与公认的海洋氧同位素曲线、洛川剖面可以进行良好的对比,并揭示出更多的环境变化信息。     

Comparison of methods to model the gravitational gradients from topographic data bases

A number of methods have been developed over the last few decades to model the gravitational gradients using digital elevation data. All methods are based on second-order derivatives of the Newtonian mass integral for the gravitational potential. Foremost are algorithms that divide the topographic masses into prisms or more general polyhedra and sum the corresponding gradient contributions. Other methods are designed for computational speed and make use of the fast Fourier transform (FFT), require a regular rectangular grid of data, and yield gradients on the entire grid, but only at constant altitude. We add to these the ordinary numerical integration (in horizontal coordinates) of the gradient integrals. In total we compare two prism, two FFT and two ordinary numerical integration methods using 1" elevation data in two topographic regimes (rough and moderate terrain). Prism methods depend on the type of finite elements that are generated with the elevation data; in particular, alternative triangulations can yield significant differences in the gradients (up to tens of Eötvös). The FFT methods depend on a series development of the topographic heights, requiring terms up to 14th order in rough terrain; and, one popular method has significant bias errors (e.g. 13 Eötvös in the vertical–vertical gradient) embedded in its practical realization. The straightforward numerical integrations, whether on a rectangular or triangulated grid, yield sub-Eötvös differences in the gradients when compared to the other methods (except near the edges of the integration area) and they are as efficient computationally as the finite element methods.     

金川县农业生产条件与资源开发

金川具森林丰富、果类品质好,但农牧资源开发水平低、山区经济落后、制约农业生产的自然-社会经济条件众多。今后应以林果业为主,稳定、提高农牧业生产水平,大力发展农林牧副产品深加工工业等,坚持振兴山区经济的战略开发方向,并要采取相应的主要对策。     

陕西秦巴山区垂直自然带的土地演替

以陕西秦巴山区为案例，对土地演替的内涵、研究内容和演替历史做了论述，运用遥感技术编制土地类型图，运用计算机手段对秦岭南、北坡和大巴山北坡的不同垂直带层的土地演替做了模拟．认为土地演替是土地内部物流与能流转化迁移的结果，土地演替分为自然演替和人为演替两种过程．     

Study of temperature and precipitation variations in Italy based on surface instrumental observations

In this paper we present a study concerning the climatic behaviour of two principal observables, temperature and precipitation as obtained from the measurements carried out at 50 Italian meteorological stations, since 1961. Analyses of WMO Climate Normals (CliNo) from 1961 to 1990 have been performed dividing the 50 Italian stations in three different classes: mountain (11 stations), continental (17) and coastal areas (21).The comparison of the CliNo 1961–1990 with the trend of temperature and precipitation for the period 1991–2000 showed a sharp significant increase of summer temperatures over Italy starting from 1980. This phenomenon was particularly evident for mountain stations, where a significant temperature increase has been recorded also during the autumn. Moreover, the analysis of precipitation data permitted to point out that, starting from 1980, mountain stations have been affected by a significant increase of precipitation events during autumn and winter, while for the rest of the Italian territory a reduction of precipitations has been recorded during early spring.     

湍流度随高度的变化及其对城市宏观地形的依赖

分别构建广州主建成区垂直比例尺为1﹕2 000、1﹕1 000和1﹕500的3个建筑物模型,利用大型边界层风洞,在西北和东南两风向下,基于中性流模拟分析了复杂城市地形下湍流度随高度的变化及其对宏观地形的依赖。结果表明：风廓线指数α与不同高度的湍流度之间的关系密切,利用现有模型,根据4类粗糙度边界层和不同垂直比例尺,可确定相应的湍流度随高度变化模型的主要系数,预测精度高。城市地形下最大湍流度面发育在0~0.2 h之间狭窄的范围内。用湍流度形态指数β来表征湍流度随高度的变化,无论城市屋脊还是平坦地形,随着风程区的延伸,廓线的指数α升高,湍流度形态指数β降低。表明同一高度湍流度值具有由迎风区、丘顶区向背风区增高,沿风程逐渐增大的规律,对地形部位和风程的依赖性强,与来流翻越简单地形时的特征一致。     

2.5-D稳定电流场h-自适应有限元的后验误差分析

本文针对2.5-D稳定电流场问题,用Galerkin方法推导了其变分问题;基于残值推导了h-自适应有限元方法求解2.5-D稳定电流场边值问题的后验误差公式,阐述了2.5-D稳定电流场的基于超收敛恢复的后验误差估计方法.为2.5-D稳定电流场h-自适应有限元方法的后验误差的实现奠定了理论基础.