联合高低卫-卫跟踪和卫星重力梯度数据恢复地球重力场的谱组合法

GOCE采用的高低卫-卫跟踪和卫星重力梯度测量技术在恢复重力场方面各有所长并互为补充,如何有效利用这两类观测数据最优确定地球重力场是GOCE重力场反演的关键问题。本文研究了联合高低卫-卫跟踪和卫星重力梯度数据恢复地球重力场的最小二乘谱组合法,基于球谐分析方法推导并建立了卫星轨道面扰动位T和径向重力梯度Tzz、以及扰动位T和重力梯度分量组合{Tzz-Txx-Tyy}的谱组合计算模型与误差估计公式。数值模拟结果表明,谱组合计算模型可以有效顾及各类数据的精度和频谱特性进行最优联合求解。采用61天GOCE实测数据反演的两个180阶次地球重力场模型WHU_GOCE_SC01S（扰动位和径向重力梯度数据求解）和WHU_GOCE_SC02S（扰动位和重力梯度分量组合数据求解）,结果显示后者精度优于前者,并且它们的整体精度优于GOCE时域解,而与GOCE空域解的精度接近,验证了谱组合法的可行性与有效性。     

南极长城站建立深空跟踪站对月球车地-月通信条件的改善

假定在地球南极中国长城科学考察站建立跟踪站,模拟计算月球南极月球车和该跟踪站之间通信的可达性,并和国内跟踪站与南极月球车之间的通信条件进行比较。计算结果表明：①在长城站所建立的跟踪站与月球南极的月球车通信受地形的影响比与我国境内的跟踪站的影响要小;②中国南极长城站和我国境内的跟踪站经度相差180°,综合长城站和我国境内的跟踪站,可以减少由于地球自转而造成的测站背离月球的影响,使观测时段更长。南极长城站建立深空探测跟踪站的通信可达性模拟计算可为我国深空探测网建站的规划及可行性研究提供参考。     

长江流域沿江镉异常源追踪与定量评估的研究框架

Cd属于积蓄性有毒元素,引起慢性中毒的潜伏期可达10~30 年之久。中国正在进行的多目标地球化学调查成果显示,长江流域存在全流域的Cd异常。对长江上、中、下游冲洪积物中Cd质量分数的初步研究,发现长江流域Cd异常以自然风化作用为主。针对长江流域Cd异常的特点,在统一技术规范的基础上采用枯、丰水期悬浮物测量技术、河漫滩/泛滥平原沉积物沉积柱分层采样技术,同位素测年技术来建立长江各支流Cd输入通量的时空变化模型和定量评估方法,估算长江各支流的Cd输入通量,使分散于沿江各省的区域地球化学评价置于同一平台,从而为全面研究长江流域Cd异常的形成机理创造条件。     

Modeling the connectivity and intersection of hydraulically loaded cracks with in situ fractures in rock

The interaction of an advancing hydraulically loaded crack and in situ fracture network can yield highly complex patterns. We model the connectivity of cells in a finite element domain and in a fracture network by a simplicial complex data structure. The complete adjacency information between cells is determined by one level down facet and one level up cofacet neighborhood information. Combined with a disjoint set data structure, explicit algorithms are derived to efficiently track network connectivity and load transfer between independent fracture sets. We also propose an approach to regularize the application of hydraulic load to newly intersected in situ cracks to smoothen the transition of pressure on intersected cracks from ambient to hydraulic pressure and to avoid the sudden loading of the entire length of these cracks. Numerical results demonstrate the performance of crack connectivity and load transfer models and the effect of regularization model. The results show that as the angle between an incoming hydraulically loaded crack and an in situ crack increases, the effect of in situ crack shifts from slight realignment to diversion/offsetting of the loaded crack. As the angle difference approaches the normal angle, the loaded crack tends to penetrate through the in situ crack. The proposed schemes are also used for transient simulation of 2D reservoirs with multiple perforations surrounded by in situ cracks with and without a bias in the distribution of their orientation. It was shown that from 2 perforations with angles closer to in situ cracks at low loading rates to all perforations at higher loading rates can result in active hydraulic crack propagation. The h‐adaptive method of asynchronous space‐time discontinuous Galerkin method is used to exactly track complex fracture patterns in these dynamic fracture simulations.     

多径效应的动态特性对码跟踪环路的影响分析

接收机与卫星之间的相对运动,使得多径效应存在动态特性。针对卫星轨道的不同,分析多径效应对测距误差的影响,着重讨论静止接收机接收GEO卫星信号时出现的固有多径现象,仿真分析多径信号的衰落频率对码跟踪环路的影响。仿真结果表明,当衰落频率接近或大于码环路带宽时,多径对码跟踪精度的影响会在一定程度上被滤除;不同的卫星轨道导致多径效应的动态特性存在差异,会使测距误差在时域上表现出短时快变和长时缓变两种特征。为研究多径效应产生机理与卫星轨道因素的相关性提供了验证途径。     

基于Silverlight的GIS项目跟踪管理系统

为了提高软件企业项目管理的水平,文章介绍了基于Silverlight的GIS项目跟踪管理系统。该系统是以Silverlight为开发平台,以ArcGIS Server REST服务为关键技术,以SQL Server 2005为数据库的B/S结构的应用系统。系统开发实践表明,Silverlight平台是软件企业进行项目管...     

基于状态约束的直流电动机有限时间位置跟踪控制

本文提出了一种基于状态约束的直流电动机神经网络自适应有限时间控制方法.首先采用障碍李雅普诺夫函数对直流电动机的状态量进行约束,确保直流电动机的角位置和角速度限制在给定的约束区间内,引入神经网络逼近系统中未知的非线性函数.此外,通过引入有限时间控制技术,提高了系统的收敛速度和控制精度.仿真结果验证了该方法能够实现对直流电动机快速有效的位置跟踪控制.     

Tidal flushing time of marine fish culture zones in Hong Kong

Accurate determination of flushing time is crucial for maintaining sustainable production in fish culture zones(FCZs),as it represents the physical self-purification capability via tidal exchange with clean water in the outer sea.However,owing to the temporal and spatial complexity of the coastal flushing process,existing methods for determining flushing time may not be generally applicable.In this paper,a systematic method for determining the flushing time in FCZs is presented,in which bathymetry,runoff,tidal range and stratification are properly accounted for.We determine the flushing time via numerical tracer experiments,using robust 3D hydrodynamic and mass transport models.For FCZs located in sheltered and land-locked tidal inlets,the system boundary can be naturally defined at the connection with the open sea.For FCZs located in open waters,hydrodynamic tracking is first used to assess the extent of tidal excursion and thus delimit the initial boundary between clean water and polluted water.This general method is applied to all designated marine FCZs in Hong Kong for both the dry and wet seasons,including 20 sheltered FCZs(in semi-enclosed waters of Tolo Harbour,Mirs Bay,and Port Shelter) and 6 FCZs in open waters.Our results show that flushing time is the longest in inner Port Shelter(about 40 days in dry season),and the shortest for the FCZs in open waters(less than one week in dry season).In addition,the flushing time in dry season is commonly longer than that in wet season:20%~40% for most well-sheltered FCZs;2.6~4 times for the others.Our results indicate a positive correlation between the flushing time and distance to open boundary,supporting the view that the flushing time of a FCZ is closely related to its location.This study provides a solid basis for mariculture management such as the determination of carrying capacity of FCZs.     

YT－1型压电陀螺钻孔测斜仪的研制和发展前景

ＹＴ－１型压电陀螺钻孔测斜仪是国内外首次采用压电角速率陀螺作测量钻孔方位的主件的。研制了了一套与其定向性民生相适应的地面定向,电子跟踪测量等新的定向方法系统。     

用质心跟踪法预报强对流天气的试验研究

利用１９８７－１９９１年６－８月间影响北京地区的１３次西北路径强对流天气过程数字化雷达回波资料，用质心跟踪法，分别对不同强度等级廓线的飑线回波带整体，和选择其中对预报地区有影响的快（条）状回波，作移动客观外推预报试验及分析。结果表明，质心跟踪法对强对流雷达回波具有较好的客观外推预报能力。其中，有选择的块（条）状回波的移动外推预测效果比飑线回波带整体要好，而两者又均以不衰减的回波区外推预报效果最好，