遥感光谱信息提取不同覆盖下植被水分信号的研究进展

综述了基于遥感光谱信息的植被水分信号提取的研究进展,包括直接利用光谱反射率反演植被水分信息到建立植被水分指数(WI),再发展至利用辐射传输模型来获取植被冠层水分信息。着重评述了针对低植被覆盖条件下的提取其冠层水分信息的方法,包括利用冠层生理参数估算植被水分信号;基于去除土壤背景影响的光谱植被水分指数或辐射传输模型估算植被水分信息,以及基于多角度的星-地观测提取稀疏条件下的植被水分信息。最后讨论了针对提取低覆盖植被冠层水分信息方法的可能发展趋势。     

0-1分布的贝叶斯检验在医疗检查中的应用

本文给出了样本相互独立,但不同分布的情况下后验概率函数的表达式及其与序贯后验概率函数之间的关系。在此基础上,给出了先验分布和条件分布为0-1分布情况下贝叶斯后验概率大小的比较方法,结合贝叶斯检验分析法安排医疗检查,使其在不降低诊断准确率的前提下,节省检查费用,提出了合理安排医疗检查的建议。     

气相爆轰模拟的化学反应加速算法

针对反应流中刚性化学反应源项传统算法计算量大的特点,提出加速化学反应计算速度的动态数据表存储/删除算法,在二维气相爆轰的数值模拟中进行检验,研究节点删除和整体删除两种不同方式的效果,并与传统直接积分的算法进行比较.计算结果表明,该算法既可以很好地满足计算精度的要求,同时也对计算机内存没有苛刻的要求.当数据表数据容量一定时,计算的加速比随控制容差的增加而增加,在相同的容差条件下,节点删除算法比整体删除算法加速效果明显.并且在处理瞬态反应流问题时显示了很好的优越性.     

基于机器视觉的高精度测量与装配系统设计

在对某些精密产品实现自动化生产过程中,存在难以对装配该产品所需的多种装配小零件进行高精度自动测量与装配的问题。针对该问题,搭建了基于机器视觉技术的自动化测量与装配系统。基于Halcon图像处理软件平台,对零件图像进行了中值滤波、图像增强等预处理;采用了Canny算法对零件求取像素精度的边缘,并运用椭圆曲线拟合法获取了亚像素精度边缘;建立了两种相机镜头畸变模型,采用径向排列约束(RAC)标定法与张正友标定法对相机进行了标定,并对标定精度进行了对比;实验结果表明：本系统的装配同轴度精度能达到0.05mm,零件尺寸测量标准差低于3.8μm,满足工业需求,可以解决工业实际问题。     

A new alternating group explicit-implicit algorithm with high accuracy for dispersive equation

In this paper, a new alternating group explicit-implicit （nAGEI） scheme for dispersive equations with a periodic boundary condition is derived. This new unconditionally stable scheme has a fourth-order truncation error in space and a convergence ratio faster than some known alternating methods such as ASEI and AGE. Comparison in accuracy with the AGEI and AGE methods is presented in the numerical experiment.     

Energetic analysis of fragment docking and application to structure-based pharmacophore hypothesis generation

We have developed a method that uses energetic analysis of structure-based fragment docking to elucidate key features for molecular recognition. This hybrid ligand- and structure-based methodology uses an atomic breakdown of the energy terms from the Glide XP scoring function to locate key pharmacophoric features from the docked fragments. First, we show that Glide accurately docks fragments, producing a root mean squared deviation (RMSD) of <1.0 Å for the top scoring pose to the native crystal structure. We then describe fragment-specific docking settings developed to generate poses that explore every pocket of a binding site while maintaining the docking accuracy of the top scoring pose. Next, we describe how the energy terms from the Glide XP scoring function are mapped onto pharmacophore sites from the docked fragments in order to rank their importance for binding. Using this energetic analysis we show that the most energetically favorable pharmacophore sites are consistent with features from known tight binding compounds. Finally, we describe a method to use the energetically selected sites from fragment docking to develop a pharmacophore hypothesis that can be used in virtual database screening to retrieve diverse compounds. We find that this method produces viable hypotheses that are consistent with known active compounds. In addition to retrieving diverse compounds that are not biased by the co-crystallized ligand, the method is able to recover known active compounds from a database screen, with an average enrichment of 8.1 in the top 1% of the database.     

Weighted essential non‐oscillatory schemes for tidal bore on unstructured meshes

In this paper, the third‐order weighted essential non‐oscillatory (WENO) schemes are used to simulate the two‐dimensional shallow water equations with the source terms on unstructured meshes. The balance of the flux and the source terms makes the shallow water equations fit to non‐flat bottom questions. The simulation of a tidal bore on an estuary with trumpet shape and Qiantang river is performed; the results show that the schemes can be used to simulate the current flow accurately and catch the stronger discontinuous in water wave, such as dam break and tidal bore effectively. Copyright © 2008 John Wiley & Sons, Ltd.     

应变对析氢反应催化剂TiC2性能影响的研究

应变工程是一种有效地用来调整原子薄膜材料的电子、磁性和光学性能的策略.利用第一性原理计算,我们表明应变也可以有效地调节Ti C₂的析氢反应(HER)的催化活性,这是电解水电化学制氢所必需的.我们主要考虑0-8%范围的拉伸应变,研究发现,在25%的氢覆盖率下双轴拉伸比单轴拉伸能更有效的提高HER活性,但b方向拉伸后的Ti C₂结构具有更高的氢最大覆盖率,且b方向的拉伸应变对不同氢覆盖率的Ti C₂单层片的催化性能都有很大的提高.电子结构计算表明,拉伸应变可以激活相对惰性的内部价电子,从而引起体系的失稳和催化活性的提高.在本工作中获得的见解可能有助于利用应变作为一种有效手段来提高二维材料的催化活性,并探索更有效地调整其电子结构和催化活性的新方法.