The chemical evolution of the Universe – I. High column density absorbers

We construct a simple, robust model of the chemical evolution of galaxies from high to low redshift, and apply it to published observations of damped Lyman α quasar absorption line systems (DLAs). The elementary model assumes quiescent star formation and isolated galaxies (no interactions, mergers or gas flows). We consider the influence of dust and chemical gradients in the galaxies, and hence explore the selection effects in quasar surveys. We fit individual DLA systems to predict some observable properties of the absorbing galaxies, and also indicate the expected redshift behaviour of chemical element ratios involving nucleosynthetic time delays.
Despite its simplicity, our 'monolithic collapse' model gives a good account of the distribution and evolution of the metallicity and column density of DLAs, and of the evolution of the global star formation rate and gas density below redshifts z ∼3. However, from the comparison of DLA observations with our model, it is clear that star formation rates at higher redshifts ( z >3) are enhanced. Galaxy interactions and mergers, and gas flows very probably play a major role.     

Variable 21-cm absorption at z=0.3127

We report multi-epoch Giant Metrewave Radio Telescope (GMRT) H  i observations of the z  = 0.3127 damped absorber towards the quasar PKS 1127−145, which reveal variability in both the absorption profile and the flux of the background source, over a time-scale of a few days.
The observed variations cannot be explained by simple interstellar scintillation (ISS) models where there are only one or two scintillating components and all of the ISS occurs in the Galaxy. More complicated models, where either there are more scintillating components or some of the ISS occurs in the interstellar medium of the z =0.3127 absorber, may be acceptable. However, the variability can probably be best explained in models incorporating motion (on sub-VLBI scales) of a component of the background continuum source, with or without some ISS.
All models producing the variable 21-cm absorption profile require small-scale variations in the 21-cm optical depth of the absorber. The length-scale for the opacity variations is ∼0.1 pc in pure superluminal motion models, and ∼10 pc in pure ISS models. Models involving subluminal motion, combined with scintillation of the moving component, require opacity variations on far smaller scales of ∼ 10–100 au .     

The Hybrid Nature of 0846＋51W1： a BL Lac Object with a Narrow Line Seyfert 1 Nucleus

We found a NLS1 nucleus in the extensively studied eruptive BL Lac object, 0846+51W1, out of a large sample of NLS1s compiled from the spectroscopic dataset of SDSS DR1. Its optical spectrum can be well decomposed into three components: a power law component from the relativistic jet, a stellar component from the host galaxy, and a component from a typical NLS1 nucleus. The emission line properties of 0846+51W1, FWHM     

DEM技术在景观工程道路选线中的应用

数字高程模型(DEM)既是二维地理空间上具有连续变化特征的地理现象的模型化表达和过程模拟,又是空间起伏连续变化现象的数字化表示和分析工具的集合。道路工程是DEM应用最早的领域。在道路勘测设计中,通过高精度DEM,可以进行平面、纵断面的交互定线,横断面的自动生成、土方计算与调配、道路的多方案比选,并通过设计表面模型和DEM叠加,实现道路景观模型及动画演示,从而对设计质量进行评价,并对拟建道路与周围环境的协调状况进行分析。     

含交叉断层的复杂地质体3维建模算法研究

在矿井生产中,出现交叉断层的区域往往是地质构造非常复杂的地方,也是危险高发的区域.对含交叉断层的3维地质建模的算法进行了研究.其主要思想是分别建立岩层和断层的TIN模型,以断层交线作为约束条件,进行带约束三角剖分,从而建立起交叉断层模型.这将有利于矿山的工程管理,减少危险的发生,作为后续采矿生产的依据.     

车载激光扫描数据分类支持下的路面数据提取

车载激光扫描系统可以快速采集道路及两旁的建筑物、植被、电杆等地物的点云数据,而点云数据的分类提取是车载激光扫描系统应用的关键。本文选用全景激光移动测量系统获取的激光点云数据,分析了路面点云数据的特征,采用渐进格网法进行了路面点云数据的提取研究;通过试验区的实例验证,取得了较好的分类效果。     

基于对偶拓扑结构的路网路段重要性评估方法

现有的路网路段重要性评估方法考虑的是路网中的路段的统计特性或路网的局部结构对重要性的影响。在路段的重要性与路网的全体路段相关联的基础上,提出m阶邻居节点的复杂路网路段重要度评估方法。为验证算法的有效性,实验仿真采用成都市路网的对偶拓扑结构,在1 484个路段中提取10条关键路径对评估方法进行验证。评估结果显示:与度值法、介数法相比,该方法能显著地区分复杂路网中路段之间的重要性差异,准确地确定网络中的关键路径,具有更高的评估准确性。     

基于红绿色觉异常人群的路况地图色彩设计研究

红绿色觉异常人群对于明度变化的感受比正常视觉者更加敏感,可以弥补色相辨别的缺陷。通过针对黄色明度对比实验得出红绿色觉异常人群对明度对比各等级的视觉感受,找出对红绿色觉异常人群既可以容易识别又不会觉得刺眼的明度对比范围。实验结果引入地图设色,结合色彩象征意义,做出红绿色觉异常人群和正常人群通用的路况地图。在路况信息清晰表达前提下,尽可能保留色彩象征意义,并保证地图的观赏性。通过路况地图色彩明度对比实验制作出红绿色觉异常人群既能无障碍识别又带有警示象征意义的路况地图。     

改进角度纹理特征提取高分辨率遥感影像带状道路

针对目前高分辨率遥感影像的道路自动提取算法研究中的不足,该文提出了一种基于并行角度纹理特征的半自动道路提取算法:用户输入完成道路中心线上的起始点、道路方向、道路宽度等初始化工作,利用并行角度纹理特征获取道路前进方向,用抛物线参数方程构建道路轨迹模型来预测道路轨迹点,使用角度纹理特征值构建的紧质度系数和抛物线的曲率变化来约束道路轨迹点,验证失败则转入手工跟踪;往复执行以提取道路中心线。试验证明,本算法是一种稳健的道路半自动提取算法。