GNSS卫星三种站心极坐标的关系

全球导航卫星系统（GNSS）的应用中有三种常用的站心极坐标系,天顶方向分别为参考椭球面外法线方向、铅垂线上方向和地心向径方向。传统大地测量中给出的部分极坐标关系式是高度角很小时的近似公式,不再适用于GNSS卫星,另外,实用中还有混淆或近似使用不同站心极坐标的情况。为此,给出了三种站心极坐标的严格关系式,分析了它们的差异规律及量级,为正确使用它们提供了参考。     

GIS城市道路最短路径算法研究

本文紧密结合城市公交的特点,利用改进Dijkstra算法开发出一个针对城市道路系统的最短路径自动搜索信息系统,该系统通过在ArcGIS环境下建立空间数据库和属性数据库,在VB环境下利用改进Dijsktra算法对McObjecta控件进行二次开发而设计完成,能在0.20s完成500多个交叉口的计算并找出其最短路径,是一种...     

顾及地价空间分布规律的城市基准地价以价定级方法研究

提出了一种城市基准地价以价定级方法。该方法用矢栅混合模型划分评价单元,对地价样点进行趋势面分析筛选,使用最短路径距离代替欧氏距离对地价样点进行空间插值,叠加分析后得到各评估单元的指标地价,用其代替传统的因素综合得分对基准地价评估区域分等定级,同时测算出各级别基准地价。以上海市为例对该方法的实用性进行了验证。     

Assessment of critical path analyses of the relationship between permeability and electrical conductivity of pore networks

Critical path analysis (CPA) is a method for estimating macroscopic transport coefficients of heterogeneous materials that are highly disordered at the micro-scale. Developed originally to model conduction in semiconductors, numerous researchers have noted that CPA might also have relevance to flow and transport processes in porous media. However, the results of several numerical investigations of critical path analysis on pore network models raise questions about the applicability of CPA to porous media. Among other things, these studies found that (i) in well-connected 3D networks, CPA predictions were inaccurate and became worse when heterogeneity was increased; and (ii) CPA could not fully explain the transport properties of 2D networks. To better understand the applicability of CPA to porous media, we made numerical computations of permeability and electrical conductivity on 2D and 3D networks with differing pore-size distributions and geometries. A new CPA model for the relationship between the permeability and electrical conductivity was found to be in good agreement with numerical data, and to be a significant improvement over a classical CPA model. In sufficiently disordered 3D networks, the new CPA prediction was within ±20% of the true value, and was nearly optimal in terms of minimizing the squared prediction errors across differing network configurations. The agreement of CPA predictions with 2D network computations was similarly good, although 2D networks are in general not well-suited for evaluating CPA. Numerical transport coefficients derived for regular 3D networks of slit-shaped pores were found to be in better agreement with experimental data from rock samples than were coefficients derived for networks of cylindrical pores.     

赞皇前寒武纪变质杂岩区变质反应结构与变质作用P-T-t轨迹

赞皇变质杂岩位于华北克拉通中部造山带中南段、太行山东麓低山区。出露于该变质杂岩区中南部的含石榴石的斜长角闪片麻岩、泥质片麻岩,均保存了三期矿物组合:进变质、峰期变质和退变质矿物组合。这两大类变质岩石中,进变质阶段矿物组合(M₁)以石榴石变斑晶核部的包裹体矿物组合为代表,变质高峰期矿物组合(M₂)由石榴石变斑晶"边部"和基质矿物组成,退变质阶段矿物组合(M₃)主要是环绕石榴石边部发育的"白眼圈"状后成合晶矿物组合。泥质片麻岩中的石榴石变斑晶均保存了明显的成分环带,且在边部很窄的范围内X_Mn有所增加、Mg/(Mg+Fe)有所降低,指示存在变质高峰期后的退变质过程。温度与压力计算结果表明,赞皇斜长角闪片麻岩所经历的进变质阶段(M₁)温度约为640~710℃、 压力约为8.2~8.6kbar;高峰期(M₂)变质温度超过810℃,压力大于12.1kbar;退变质阶段(M₃)的温压范围为590~670℃和3.2~5.6kbar。此前的研究已说明泥质片麻岩的进变质阶段(M₁)变质温度为660~690℃,压力为9.0~9.2kbar;高峰期(M₂)变质温度超过780℃,压力大于12.5kbar。变质高峰属于中压相系的顶部至高压相系的底部。斜长角闪片麻岩、泥质片麻岩均记录了典型的顺时针P-T轨迹,并显示近等温减压(ITD)的退变质片段。对泥质片麻岩中多颗锆石的变质增生边的SHRIMP U-Pb定年表明,变质高峰期时代为1821±17Ma。变质作用历史说明赞皇变质岩区卷入了华北克拉通东部陆块和西部陆块之间的俯冲-碰撞、随后的快速隆升过程,为华北克拉通中部造山带早元古代末期(~1850Ma)存在的造山事件提供了新的证据 。     

基于应力路径的实用沉降计算方法

为提高对沉降计算的可靠性与方便性,提出了一种基于应力路径的实用沉降计算方法。依据应力路径法原理,采用由Skempton(司开普顿)孔隙水压力方程得出的有效应力路径方程来表达应力路径,得出了沉降计算的实用计算式。所提出的计算式具有形式简洁、参数易确定、方便实用等优点。工程实例分析验证了该方法的可靠性,可为实际工程的沉降计算提供参考。     

Three-dimensional dynamic features of two arctic oscillation types

We investigated the differences between stratospheric (S-type) and tropospheric (T-type) Arctic Oscillation (AO) events on the intraseasonal time scale, in terms of their influences on surface air temperature (SAT) over the Northern Hemisphere and the dynamic features associated with their spatial structures. S-type AO events showed a stratosphere-troposphere coupled structure, while T-type events exhibited a stratosphere-troposphere uncoupled structure. The annular SAT anomalies over the Northern Hemisphere were found to be associated with S-type AO events, whereas such an annular feature was substantially destructed in T-type AO events. The different horizontal structures in the troposphere of the two types could mainly be attributed to transient eddy feedback forcing. As for the vertically uncoupled structure of Ttype events, the underlying dynamical features that differentiate them from S-type events lie in the vertical propagation of zonally confined Rossby waves. In T-type events, the zonally confined Rossby wave packets can emanate from the significant height anomalies over Northeast Asia, where one vertical waveguide exists, and then propagate upward into the stratosphere. In contrast, such a vertical propagation was not evident for S-type events. The stratospheric anomalies associated with the upward injection of the zonally confined Rossby waves from the troposphere in T-type events can further induce the anomalous vertical propagation of planetary waves (PWs) through the interference between the climatological-mean PWs and anomalous PWs, leading to the final stratosphere-troposphere uncoupled structure of T-type events.     

The impact of African elephants on Acacia tortilis woodland in northern Gonarezhou National Park, Zimbabwe

We investigated the impact of African elephants (Loxodonta africana) on the structure and composition of Acacia tortilis woodland in northern Gonarezhou National Park, southeast Zimbabwe. A. tortilis woodland was stratified into high, medium and low elephant utilisation categories based on evidence of elephant habitat use as determined through dung-count surveys in relation to distance of woodland patches from perennial and natural surface water sources. The following variables were recorded in each study plot: tree height, species name, number of species, plant damage, basal circumference and number of stems per plant. A total of 824 woody plants and 26 woody species were recorded from the sampled A. tortilis woodland patches. Mean tree densities, basal areas, tree heights and species diversity were lower in areas with medium and high elephant utilisation as compared to low elephant utilisation areas. Plants damaged by elephants increased with increasing elephant utilisation. The study findings suggest that A. tortilis woodland is gradually being transformed into an open woodland. We recommended that protected area management in arid and semi-arid areas should consider (i) formulating clear thresholds of potential concern to allow for the conservation of sensitive woodlands such as A. tortilis woodlands and (ii) establishing long-term vegetation monitoring programmes.     

北京两次重污染沙尘天气成因及动力传输特征的对比研究

应用气象、空气质量和ERA-Interim再分析资料,结合HYSPLIT后向轨迹模型和地理信息,对比分析了2018年北京两次重污染沙尘天气的成因、传输特征及影响要素等。结果表明:两次过程的沙尘源地均为蒙古国,但3月28日沙尘天气由蒙古气旋引发,传输出现折向,以东北和偏东两条路径输送入京,5月28日沙尘受低涡和发展的低压冷锋影响,为典型的西北传输路径;高空的引导气流与低层冷空气的强度以及地形是导致沙尘传输出现显著差异的主要影响因素;高空为偏西气流,低层冷平流较弱,受到山脉的阻挡,沙尘气团东移至地势较低的区域后,在气压梯度力的驱动下传输方向发生转折,以偏东路径绕流进入北京;高空的偏北气流和低层冷平流较强,沙尘气团可直接翻越山脉从西北路径入京,沙尘粒子的运移高度相对较高。