IGCP448：岩溶生态系统全球对比研究进展

综述了IGCP 448项目"全球岩溶地质及有关生态系统对比"(2000-2004)执行四年来所取得的学术成果.其中比较重要的新认识有:(1)岩溶地区的植被,常常是涵养水分,增加含水层的贮水能力,改善水文生态环境的重要因素,但在澳大利亚南部岩溶区广泛分布的桉树,则以其强烈的蒸发作用,而被用于降低地下水位,防治土壤盐碱化;(2)在北方(Boreal) 或温带湿润气候生态区,地下岩溶系统则被用于排除沼泽地区过多积水,偏碱性的碳酸盐岩也有利于中和酸性环境,凡是岩溶发育的地方,都成了主要农业基地;(3)通过洞穴探险发现一类完全不同于靠光合作用产生有机质的生物群--化学自养微生物(甲烷菌);(4)中国西南典型岩溶区的研究表明,表层土壤微生物可以加速碳酸盐岩的溶解作用,并揭示了植物根系与土壤微生物是产生碳酸酐酶(CA)的两个重要供给源.     

Prediction of permafrost distribution on the Qinghai-Tibet Plateau in the next 50 and 100 years

The Qinghai-Tibet Plateau(QTP)has the highestand largest permafrost coverage in the low-middlelatitudes all over the world.With the progress ofChina’s Western Development,human activities areincreasing significantly on the QTP.For instance,theQinghai-Tibet Railway project started in June2001iscurrently under construction,but permafrost problemwill be one of the critical factors for the engineeringconstruction.Frost heave and permafrost settlementmay destroy engineering construction[1,2]…     

Optimal and sustainable extraction of groundwater in coastal aquifers

Four examples are investigated for the optimal and sustainable extraction of groundwater from a coastal aquifer under the threat of seawater intrusion. The objectives and constraints of these management scenarios include maximizing the total volume of water pumped, maximizing the profit of selling water, minimizing the operational and water treatment costs, minimizing the salt concentration of the pumped water, and controlling the drawdown limits. The physical model is based on the density-dependent advective-dispersive solute transport model. Genetic algorithm is used as the optimization tool. The models are tested on a hypothetical confined aquifer with four pumping wells located at various depths. These solutions establish the feasibility of simulating various management scenarios under complex three-dimensional flow and transport processes in coastal aquifers for the optimal and sustainable use of groundwater.     

Evolution of the high-temperature plasma in the 15 June 1973 flare

The analysis of the high temperature plasma in Fe xxiii–xxiv in the 15 June 1973 flare is presented. The observations were obtained with the NRLXUV spectroheliograph on Skylab. The results are: (1) There was preheating of the active region in which the flare occurred. In particular, a large loop in the vicinity of the flaring region showed enhanced brightness for many hours before the flare. The loop disappeared when the flare occurred, and returned in the postflare phase, as if the energy flux which had been heating the large loop was blocked during the flare and restored after the flare was gone. The large magnetic fields did not change significantly. (2) The flare occurred in low-lying loop or loops. The spatial distribution of flare emission shows that there was a temperature gradient along the loop. (3) The high temperature plasma emitting Fe xxiii and xxiv had an initial upward motion with a velocity of about 80 km s^–1. (4) There was large turbulent mass motion in the high temperature plasma with a random velocity of 100 to 160 km s^–1. (5) The peak temperature of the hot plasma, determined from the Fe xxiii and xxiv intensity ratio, was 14 × 10⁶ K. It decreased slightly and then, for a period of 4 min, remained at 12.6 × 10⁶ K before dropping sharply to below 10 × 10⁶ K. The density of the central core of the hot plasma, determined from absolute intensity of Fe xxiv 255 Å line, was of the order of 10¹¹ cm^–3.The persistence of the high level of turbulence and of the high temperature plateau in the decaying phase of the flare indicates the presence of secondary energy release. From the energy balance equation the required energy source is calculated to be about 3 to 7 ergs cm^–3 s^–1.Ball Brothers Research Corporation.     

中天山坡地冰缘地貌的若干问题

由 1985—1989年野外调查结果和定位重复观测资料可知,本区坡地冰缘地貌的分布特征为:1.各类坡地冰缘形态彼此具有成因联系;2.不同序次的冰缘地貌类型具有各自的时空分异;3.不同的坡地冰缘地貌类型在一定条件下可有所转化。再则,本区风化以寒冻剥裂和寒冻楔入为主,呈现在时空和状态上为不可逆过程的耗散结构。     

一颗与众不同的脉冲星Geminga

最近，一个困扰人们达十几年之久的γ射线源Ｇｅｍｉｎｇａ被证认为Ｘ、γ射线脉冲星，其光学对应体也被确定为一颗光谱偏蓝的２５等星。对Ｇｅｍｉｎｇａ脉冲星的确证说明存在着一类没有射电辐射的脉冲单星。     

变刚度钢管混凝土短柱隔震结构弹塑性动力分析

采用HBTA2.5程序,对一变刚度钢管混凝土短柱隔震结构进行了弹塑性时程分析。分析结果表明,其隔震装置的水平变形和耗能能力可以大大减轻地震对结构的影响。提出钢管混凝土短柱隔震结构在工程应用将有很好的发展前景。     

基于FME的DWG数据到ArcGIS转换的应用研究

本文针对工程实践中DWG数据到ArcGIS转换的实际需要,基于转换工具FME,采用FME Workbench构建转换模块对DWG数据转换的方法,研究了利用FME Workbench构建转换模块的关键技术和对转换后GIS数据的检查。通过以阜新腰梅力板的DWG数据为例,实现了对DWG数据到ArcGIS的Geodatabase数据的转换,并对转换后的数据进行检查、整理。结果证明,本文所采用的转换方法良好,节省了工作时间、提高了工作效率。     

无限长土坡滑移变形模拟

从建立土体应力平衡微分方程入手,在平面应变的假定下求解均质无限长土坡的应力平衡方程。通过拟定坡土的滑移速度和粘塑性应变率的关系式,以剑桥模型为依托,得出滑移变形速率的显式表达式,由此推出土坡滑动位移的计算式。因为模型计算值与实测值无论变形趋势还是大小都有不少误差,所以经修正粘滞性参数来改进模型的模拟精度。最后通过一个算例,将现场实测滑移数据和模型计算值进行比较,分析表明二者较为一致。     

嵌入式马尔科夫链的地质属性建模与应用

传统的地质统计学所形成的算法理论和方法(如克里格算法)过分依赖样品的数据,变异函数参数众多,给地质模拟造成很大困难。基于马尔科夫链的地质属性建模采用转移概率描述样品区域的各种参数变量,通过转移概率矩阵直接推导地质属性分布比例、平均长度,其简化了地质空间各向异性处理过程,克服了传统地质统计学中参数众多且复杂难以计算和地质体分布过程中存在不对称性等缺陷,使得整个地质属性建模的过程更简洁、清晰,容易理解,且建模的结果可以很好地反映地质体空间分布的复杂性。该文利用马尔科夫链对南京市河西地区的新近地质层进行了地质属性建模,实例应用表明,使用该模型进行地质属性建模可为进一步的数值模拟提供支持。