城市虚拟现实研究初探

虚拟城市是 3维城市地理信息系统的前沿领域 ,该文对在微机上如何建立虚拟城市作了初步探讨 ,把建立虚拟城市的方法分为 3维真实场景建模、海量数据环境下的场景漫游以及确定任意时刻声音文件的调入时机三个部分。重点介绍了控制三维场景漫游、自适应层次细节模型、简单碰撞检测的实现方法 ,并提出了采用泰森模型调用声音文件的新思路。最后给出在VC 开发环境下用OpenGL建立虚拟城市的应用实例。     

裂隙岩质边坡地下水渗流数值模拟

本文从反倾向岩质高边坡的渗流特征和渗流普遍规律出发,根据渗流力学知识,建立数学模型,通过渗流数值模拟计算分析了渗透压力、水头变化规律以及对岩质边坡稳定性的影响.     

构造、气候与砾岩* ——以积石山和临夏盆地为例

探讨构造、气候与砾岩的关系对于研究青藏高原隆升的时间和方式具有重要意义。裂变径迹热年代学表明积石山地区于8MaB.P.开始构造变形,与碎屑颗粒裂变径迹结果和生长地层结果一致,而明显早于积石砾岩出现的时间(3.6MaB.P.)。通过区分岩体隆升与地面隆升之间的差别,文章提出一种新的模型,以解释隆升、气候和砾岩之间的关系。积石山岩体于8MaB.P.开始隆升,隆升初期,尽管岩体隆升1500~2000m,但是由于积石山上覆的新生代地层易于剥蚀,在花岗岩基底被剥露到地表之前,地表只有少量隆升或没有隆升。随着沉积地层被剥蚀殆尽,基岩暴露于地表,地面隆升速率加快。约3.6MaB.P.,积石山隆升约200~900m,造成了地形雨和发源于积石山的横向河流的出现,这些横向河流把积石山的花岗岩搬运到盆地中沉积下来,形成积石砾岩。     

Historical trophic evolutions and their ecological responses from shallow lakes in the middle and lower reaches of the Yangtze River: Case studies on Longgan Lake and Taibai Lake

The evolutions of diatom floras and the total phosphorous (TP) concentrations in the historical period were reconstructed for two lakes, Longgan and Taibai in the middle Yangtze River,based on high resolutional fossil diatom study from two sediment cores and an established regional diatom-TP transfer function. The TP concentration in Longgan Lake changed slightly in the range of 36-62 μg/L and kept its middle trophic level in the past 200 years. The changes of diatom assemblages reflect a macrophyte-dominated history of the lake. During the nineteenth century, the lake TP concentration increased comparatively, corresponding to the increase in abundance of benthic diatoms. The progressive increase of epiphytic diatoms since the onset of the twentieth century indicates the development of aquatic plants, coinciding with the twice drops of water TP level. The TP concentration in Taibai Lake kept a stable status about 50 μg/L before 1953 AD, while diatoms dominated by facultative planktonic Aulacoseira granulata shifted quickly to epiphytic diatom species, indicating a rapid expansion of aquatic vegetation. During 1953-1970 AD, the coverage of aquatic plants decreased greatly inferred by the low abundance of epiphytic diatoms as well as declined planktonic types, and the reconstructed TP concentration shows an obvious rising trend firstly, suggesting the beginning of the lake eutrophication. The lake was in the eutrophic condition after 1970, coinciding with the successive increase of planktonic diatoms. The comparison of the two lakes suggests the internal adjustment and purification function of aquatic plants for nutrients in water. The discrepancy of TP trends in the two lakes after 1960 reflects two different patterns of lake environmental response to human disturbance. Sediments in Taibai Lake clearly recorded the process of lake ecological transformation from the macrophyte-dominated stage to the algae-dominated stage. The limits of TP concentration (68-118 μg/L) in the transitional state can be considered as the critical value between the two stable ecosystems. Further work will be necessary to provide more evidence from the sediments in more eutrophic lakes for the primary inference. The reconstructive TP level and the inference of aquatic plants from fossil diatoms in different lakes, as well as their comparison provide a scientific basis for ecological restoration of eutrophic lakes in research regions.     

Variation characteristics of heavy metals and nutrients in the core sediments of Taihu Lake and their pollution history

The sedimentary environment change, trophic evolution and heavy metals pollution history of the northern Taihu Lake in the last 100 years are studied according to the sedimentary geo-chemical proxies of the core sediments, such as grain size, nutrients, heavy metals, diatom, etc. The nutrients in the sediments depended mainly on the lake internal circulation and the heavy metals were from natural geogenic sources before the 1920s, which were not influenced by human activities generally, and grain size was one of the key factors influencing heavy metals content in the sediments. The alternation of manner and strength of human activities in Taihu Lake catchment before and after the 1920s made the lake sediments coarser, and hence heavy metals and TP content decreased contrasted with that before the 1920s. TP content in sediments and water increased from the 1950s to late 1970s due to anthropogenic pollutants discharge, and the lake belonging to mesotrophic state. TN and TOC content and C/N ratio increased due to the increasing external pollutants into Taihu Lake by human activities, TP content also increased obviously in water and sediments, and the diatom association was dominated by eutrophic species since the late 1970s, indicating the eutrophication state of Taihu Lake in this period. Meanwhile the increasing in heavy metals content, such as Cu, Mn, Ni, Pb and Zn, and their proportion of valid fractions in the sediments indicates that they all result from human pollutants since the late 1970s. The heavy metals in the surface sediments have certain potential biological toxicity due to the higher SEM/AVS ratio.     

山东蒙阴科马提岩地球化学特征及其意义

山东蒙阴科马提岩具有典型的鬣刺结构，高镁低钛，铝不亏损，具有正的Rb、Ba、Sr、U异常，轻稀土元素亏损，重稀土元素平坦，稀土元素总量很低，高场强元素与稀土元素发生分异，Nb/Nb^＊〉1，与加拿大蒙罗镇科马提岩地球化学特征和同位素特征相似。研究表明，蒙阴科马提岩可能起源于长期亏损的地幔源区，岩浆不可能来源于以橄榄石、辉石和石榴石（或者majorite）为主要矿物相的地幔源区。最新Sm-Nd同位素研究显示，蒙阴科马提岩样品的εNd值为-0．4～＋3．6，新鲜样品一般为＋3．3，也证实了科马提岩来自长期亏损的地幔源区，并且地幔柱在上升过程中受到地壳混染程度很小，推测研究区科马提岩的喷出可能是新太古代大陆增生事件的重要组成部分。     

非结构网格上的三维浅水流动数值模型

针对当前复杂环境水流模拟的需求,建立了新型的基于特征型高分辨率数值算法的三维非结构网格浅水动力模型。模型采用有限体积法离散sigma坐标下的三维浅水方程,运用Roe黎曼近似解评估水平界面通量。模型网格拟合边界能力强,可根据需要局部加密;格式数值性能优良,具有守恒性、单调迎风性、高数值分辨率等特性。同时,应用干湿判别法处理动边界,以适应浅滩地形漫/露过程模拟的需要。封闭水池内部风生环流、干河床上溃坝过程和长江口实际潮流场的模拟从不同侧面展示了模型的特点,结果表明它能够准确地预测水流的三维流动结构,而且计算简单高效,具有良好的数值稳定性。     

一种自适应正则MAP超分辨率重建方法

提出了一种简单、通用的基于自适应正则化技术的MAP超分辨率重建新方法，该方法可以自适应地选择正则化参数，并充分利用中间重建结果的信息，不断对其进行更新，通过迭代过程得到最终的重建影像。利用模拟序列影像和真实序列影像分别对本文方法进行了验证，结果表明，本文方法可以根据不同影像序列的特点，自适应确定相应的正则化参数，并能找到最优解，适用性较强。     

用模糊ARTMAP算法对CBERS-2数据进行分类

用模糊ARTMAP（fuzzy adaptive resonance theorymap）神经网络算法对CBERS-2数据进行了分类实践。首先介绍了模糊ARTMAP神经网络的算法原理和具体训练分类过程；然后用2004年9月新疆石河子地区的影像数据进行土地利用分类试验，并将分类结果与基于统计的最大似然法（MLC）、反向传播神经网络（BP）的分类结果作比较，总分类精度比MLC和BP算法分别提高9．9％和4．6％。结果表明，模糊ARTMAP对试验区CBERS-2影像上的裸地识别能力很强，对高分辨率的CBERS-2影像可获得很好的分类结果。     

广西暴雨卫星云图与热带流场变化综合预报方法

利用卫星云图资料结合热带风场的变化,采用分级客观定量的计算方法,得到影响关键区内的云系像素值大小和云顶亮温。同时,结合该关键区内热带风场的变化,对云系是否影响广西进行预测,判断其对暴雨范围、强度、持续时间的影响程度,从而作出暴雨过程的预报。经过对1996~2002年4~9月169例暴雨个例的资料统计分析表明:在广西大范围暴雨过程中80%的云系叠加在西南风急流之上。云顶亮温在-70℃以下的云系像素值达到500时,就有大范围暴雨天气过程的可能。此结果应用到日常预报业务中,对提高暴雨预报准确率有较大帮助。