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61.
星上计算机的处理能力不断提高,地基控制系统资源日益紧张,这些都对卫星自主定轨提出了迫切的要求,利用卡尔曼滤波进行卫星自主定轨将具有十分广阔的应用前景。但由于低轨卫星受摄动力较大,使得其动力学方程十分复杂,本文对如何建立适当的模型进行了分析。标准卡尔曼滤波只有在满足一定约束条件时,才能得到最优解。但利用星载GPS进行卫星定轨时,这些约束条件并不能得到完全的满足,针对这些问题本文讨论了相关噪声和滤波发散,观测值粗差等问题。 相似文献
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大别山北部榴辉岩的Pb同位素特征 总被引：2，自引：2，他引：2
大别山北部榴辉岩的全岩 Pb同位素研究结果表明 ,Pb同位素比值 N(2 0 6 Pb) /N (2 0 4 Pb) =16 .773～ 18.339,N (2 0 7Pb) /N (2 0 4 Pb) =15 .346～ 15 .5 16 ,N (2 0 8Pb) /N (2 0 4 Pb) =37.133～ 38.346 ,平均值分别为 17.6 5 ,15 .4 5和 37.81)明显接近于下地壳成分 N(2 0 6 Pb) /N(2 0 4 Pb) ,N(2 0 7Pb) /N(2 0 4 Pb) ,N(2 0 8Pb) /N(2 0 4 Pb)值分别为 17.6 2 ,15 .35和 38.75 ) ,同时 ,北部榴辉岩的 U /Pb比 (0 .0 0 2～ 0 .0 0 9)及 U质量分数 (0 .0 4× 10 - 6 ～ 0 .2 3× 10 - 6 )稍低于下地壳平均值 ,而 Pb质量分数 (6 .72× 10 - 6～ 2 6 .6 4× 10 - 6 )则接近于或略高于地壳平均值 ,但是 ,U/Pb比则明显偏离上地壳平均值、也不同于大别山南部榴辉岩及有关岩石 (较低的 Pb质量分数和较高的 U/Pb比 )。此外 ,考虑到研究区榴辉岩的岩石地球化学及 Sr,Nd同位素年代学方面研究已证明它们大多数为印支期扬子陆壳俯冲变质成因。由此进一步表明 ,大别山北部榴辉岩的原岩大多数应来自于扬子大陆下地壳。这对正确认识大别山碰撞造山带的构造格局和演化具有重要意义。 相似文献
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1 INTRODUCTION The coherent structure of turbulence is the most important discovery of turbulence studies in the last several decades. The coherent structure is a joint spatial state (Liang, 1999). In this space, there exist all kinds of motions that are organized and related. Namely, strip structures, large vortical structures, and other organizing flows are present. In 1932, researchers found that turbulence wasn抰 a fully random phenomenon and came to realize that the repeated emergen… 相似文献
64.
AN IMPROVED SEMI-IMPLICIT TIME DIFFERENCE SCHEME OF SPECTRAL MODEL AND NUMERICAL APPLICATIONS 总被引：1，自引：0，他引：1
In fact,the popular semi-implicit time difference scheme of spectral model still includes someimportant linear terms using time explicit difference scheme,and the major terms are directlyrelated to fast internal-and external-gravity waves in the atmospheric forecasting equation.Additionally,due to using time difference on two terms at different time.the popular schemeartificially introduces unbalance between pressure gradient force and Coriolis force terms whilenumerically computing their small difference between large quantities.According to thecomputational stability analysis conducted to the linear term time difference scheme in simpleharmonic motion equation,one improved semi-implicit time difference scheme is also designed inour study.By adopting a kind of revised time-explicit-difference scheme to these linear terms thatstill included in spectral model governing equations,the defect of spectral model which only partlyusing semi-implicit integrating scheme can be overcome effectively.Moreover,besides all spectralcoefficients of prognostic equations,especially of Helmholtz divergence equation,can be workedout without any numerical iteration,the time-step (computation stability) can also be enlarged(enhanced) by properly introducing an adjustable coefficient. 相似文献
65.
李沛川 《武汉大学学报(信息科学版)》1993,(Z1)
制图综合常要求将地形图要素从其正确的图面位置偏移一点。本文就线状要素的移位问题进行讨论。首先提出移位场的概念,这对于由于移位所产生的“连锁反应”能较好地解决;然后,提出一种栅格探测——矢量计算方祛,加快移位计算的速度。 相似文献
66.
在原有测量控制网(称旧网)的基础上建立同级扩大网或低级加密网(称新网)时,新旧网之间的重合点(称连接点)坐标值粗差的检验是平差前的一个重要环节。本文将连接点坐标视为带协方差阵的观测值,采用数据探测法定位其粗差。借助于 Gauss-Markov模型下两个备选假设检验的理论,推导了连接点相关坐标观测值粗差可定位性基本公式,讨论了各类平面网中连接点坐标观测值粗差的可发现性和可区分性。 相似文献
67.
地形图中符号可分为点状符号、面状符号和线状符号,不同比例尺的地形图,其符号的构造规律是一致的,只是符号的结构与尺寸不同。本文在于探索这些符号的构造规律,并进行有机组织。 相似文献
68.
本地理底图数据库系统是一个小型的数据库系统,它具备了地图数据库的基本功能,适应同一底图服务多种专题图编制的要求,提供多种检索途径;运用大量的位操作,使得数据库结构具有动态性、灵活性。将频繁交换的数据纳入内存,加快了系统运进速度;通过多边形组织,可自行建立专题要素与底图要素的图形关系,建立区域间层次关系,减小数据采集工作量。 相似文献
69.
Mingbo Yang Yuehu Kang Qing Zhang Institute of Geographic Sciences Natural Resource Research Chinese Academy of Sciences Beijing China Graduate University of Chinese Academy of Sciences Beijing China Earthquake Administration of Beijing Municipality Beijing China Beijing Beifang Middle School Beijing China 《地震学报(英文版)》2009,(3):301-306
This paper quantitatively analyzed groundwater table fluctuations caused by groundwater overdraft, and probed into the possibility of drawing earthquake precursory information from groundwater table variations on the background of groundwater overdraft. Main effect factors of groundwater regime in Beijing region include groundwater extraction and rainfall. The decline of groundwater table was directly related to regional groundwater overdraft. Using the method of correlation analysis, the paper analyzed the... 相似文献
70.
Using lightning locating system based on time-of-arrival technique to study three-dimensional lightning discharge processes 总被引：2，自引：0，他引：2
ZHANG GuangShu WANG YanHui QIE XiuShu ZHANG Tong ZHAO YuXiang LI YaJun & CAO DongJie Laboratory for Climate Environment Disasters of Western China Cold Arid Regions Environmental Engineering Research Institute Chinese Academy of Sciences Lanzhou China Laboratory for Middle Atmosphere Global Environment Observation 《中国科学:地球科学(英文版)》2010,(4)
A time-of-arrival(TOA) system based on GPS technology for locating VHF radiation sources from lightning has been developed and used in observation sites in the northern Shandong Province,China.The 3D images of the lightning progression have been obtained successfully for the first time in China.The 3D-channel evolutions of typical negative CG,positive CG and IC lightning flashes have been discussed together with the data of fast electric field change.It was found that significant differences existed between the negative and positive CG lightning flashes in terms of the initiation and propagation of the radiation sources.The preliminary breakdown of a negative CG lightning flash propagated at a speed about 5.2×104 m/s.The stepped leader of negative CG lightning flashes was trigged by negative initial breakdown.Thereafter,it propagated downward at a speed of 1.3×105 m/s.The initial process of the positive CG lightning flashes was also a propagation process of negative streamer.These streamers propagated dominantly horizontally in the positive charge region and accumulated positive charges at the origin of the lightning,and as a consequence,initiated downward positive streamers.A new type of lightning discharge that was triggered by a narrow bipolar pulse(NBP) is discussed in this study.The NBP was originated at altitude of about 10.5 km in the upper positive charge region.As a distinct difference from normal IC flash,its channels extended horizontally all around and produced a lot of radiation sources.The source power of the NBP could approach 16.7 kW,which is much greater than that of normal lightning discharge ranging between 100 mW and 500 W.The 3D propagation of this new type of lightning discharge was observed and obtained for the first time in China.The possible initiation mechanism of this new type of light-ning is discussed here. 相似文献