典型海洋大气环境中AZ80镁合金电偶腐蚀行为研究

镁合金作为最轻的金属结构材料,具有比强度高、比刚度高、减震性能好、电磁屏蔽等优点。随着海洋强国战略的实施,先进镁合金结构材料逐步在海洋装备上开始应用。已列装的新型高强AZ80镁合金,通过与QBe1.7铍青铜紧固件连接,共同构成整体在典型海洋大气环境中服役。在高盐、高湿的海洋环境环境中,镁合金与电位更正的QBe1.7铍青铜偶接后,极易发生电偶腐蚀。电位相对更负的高强AZ80镁合金,作为电偶腐蚀的阳极被加速溶解。本研究对高强AZ80镁合金电偶腐蚀样品经过12个月青岛海洋大气暴露试验,发现空白对照组、电偶1组(紧固件铍青铜直径Ψ=10mm)和电偶2组(紧固件铍青铜直径Ψ=20mm)的平均腐蚀速率分别为108.1071、133.8929、173.6250g/(m~2·a)。电偶对表面的主要腐蚀产物为:Mg(OH)_2、MgSO_4和MgCl_2。空白样品、电偶1组和电偶2组平均腐蚀深度分别为:0.175、0.330、0.315mm/a。样品中部腐蚀深度最大,边部腐蚀深度则相对较小。不同样品在青岛试验站的腐蚀产物对基体保护能力的量度(n值)分别为1.1337、1.1378、1.0895,表明随着暴露时间的延长,试样在海洋大气环境中的腐蚀速率会加快,试样表面的腐蚀产物对基体根本起不到保护作用。通过灰色关联分析法,计算了青岛海洋大气腐蚀站点的环境因素与AZ80镁合金腐蚀深度和腐蚀失重之间的关联度,结果表明:青岛海洋大气环境因素对高强AZ80镁合金空白样品腐蚀失重影响前三位分别为:SO_4~(2-)非水溶性硫酸盐转化率;对电偶1组样品影响前三位的环境因素分别为:SO_2硫酸盐转化率NO_2;对电偶2组样品影响前三位的环境因素分别为:水溶性降尘SO_2NH_3。对比电偶对2组和1组,唯一的差别是电偶对的面积比,但决定镁合金腐蚀速度的大气成分完全不同,相关机制会在未来工作中详细研究。     

WGS-84坐标系和西安80坐标系转换方法及精度分析——基于新疆兵团C、D级GPS网成果

根据新疆兵团C、D级GPS网中的重合三角点、GPS2000网联合平差点、天文点成果,采用二维高斯平面坐标转换模型和Bursa七参数转换模型,完成WGS-84坐标系与80西安坐标系转换参数的计算与精度分析。     

一种ADS40影像物方反投影坐标计算的快速算法

针对ADS40影像的物方空间投影几何约束,提出了一种基于扫描线投影中心平面几何约束的ADS40物方反投影坐标计算快速算法,有效地改进了最佳扫描线的搜索效率.实验表明,该算法可以有效地提高ADS40影像物方反投影坐标计算的效率.     

ADS40近红外波段遥感影像分类方法

针对传统的基于像元的分类方法的不足,结合ADS40近红外波段遥感影像的分类过程,简要介绍了面向对象的分类方法,并将其与传统的基于像元的方法进行了比较。结果表明：面向对象的方法不仅能够有效地避免“椒盐”现象,还能大幅度提高分类精度.     

用于ADS40传感器的多视觉立体匹配算法模型

提出了一种新的用于航空三线阵数字影像匹配的算法模型。该模型能同时匹配任意数量(大于2)的影像,并且在匹配过程中间接地运用了核线约束条件。运用这一算法模型,可以融合不同立体像对的信息并得到最终的决策结果。同时,探讨了影像遮挡问题的解决方法,并以ADS40机载三线阵数字传感器所获取的数字影像为例,对所提出的算法模型进行了实验验证。最后提出需进一步研究解决的问题。     

Spanish Monitoring of Comets: Making Sense of Amateur Photometric Data

Amateur astronomers have always represented an important observing group in cometary astronomy. Much of our knowledge of cometary light curves has come from amateur data, initially in the form of total visual magnitude estimates and now increasingly in the form of CCD observations. The increasingly widespread use by amateur astronomers of CCD cameras of excellent sensitivity and good cosmetic quality has revolutionised astrometry, allowing far more intensive astrometric monitoring of comets to be carried out down to magnitude 18 and fainter, with a corresponding enormous increase in the quality of calculated orbits. Although amateur CCD photometry is extensively available in the Internet, its use has been less widespread. The reason is the lack of standardisation in the way that this data is taken that leads to amateur CCD light curves having enormous dispersion. All amateur CCD photometry is aperture photometry, but it is seen that neither does it represent well the equivalent of m1 (total visual magnitude), even with a large aperture, nor is it close to the definition of m₂ (the nucleus magnitude). The problem is examined using data from the Spanish Comet Observers Group archives to show that by careful standardisation of data acquisition amateur CCD data can produce high quality, well-sampled and physically meaningful light curves. Examples are presented of the results for recent comets including 19P/Borrelly, 51P/Harrington, C/2001 TU80 (LINEAR-NEAT), C/2000 WM1 (LINEAR) & C/2001 A2 (LINEAR).     

A mathematical and numerical model for reactive fluid flow systems

We formulate mathematical and numerical models for multispecies, multi-phase and non-isothermal reactive fluid flow in porous media focusing on the chemical reactions and the transport of solutes. Mass conservation and stability in the time integration are emphasized. We use cell-centered finite volume differencing in space and an implicit Runge-Kutta method in time. Assuming two space dimensions, we introduce flux approximation for arbitrarily shaped convex quadrilaterals. On equidistant and variable sized rectangular grids we choose limited κ= related schemes to approximate the advective flux and the central difference scheme for the diffusive flux. On non-rectangular grids we recommend the VF9 scheme for the estimation of the diffusive flux. Our model exists as a code. This revised version was published online in July 2006 with corrections to the Cover Date.     

河系几何相似性的层次度量方法

已有的线群目标几何相似性度量方法主要基于数理统计的思想,通过统计整体变化信息计算几何相似性,缺少对局域特征的表达,并不适用于具有高度分形特征的河系。为此,本文将河系几何特征划分为3层次的信息特征：单条河流的形状特征、局部区域的结构特征、全局范围的分布特征。首先,结合角链码法与Hausdorff距离计算单条河流的形状相似度;然后,根据 “二八定律”确定局部特征区域,通过坐标系转换计算M： N的河系局域结构相似度;最后综合整体描述子得到全局分布相似度,并在该基础上,构建差异指标进行河系多尺度相似性计算与综合质量评价。实验表明,该方法的计算结果优于均值指标法,能有效应用于制图综合的质量评价。     

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