纯球坐标系内各项重力校正值计算方案和计算过程

在国内,首次阐述了"纯球坐标系内各项重力校正值的计算方案和计算过程"。该计算方案有如下优点:①以观测点P为中心,以球面距离am=am-1+Δa.bm-1(m=2,3,…,M)为半径将计算区划分为M个环带,再以Δλ0为由P点出发射线的角度间隔将所有环带等分为N(整数)份的计算区划分方案是最严密拼接,因而校正值的计算精度相当高。②在地形复杂和相对高差大的情况下,通过减小Δa、b和Δλ0数值,可进一步提高计算精度。③可以直接采用带有经、纬度坐标的高程数据,进行大面积测区的各项重力校正值计算,而不受6°带和标准图幅限制。     

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GPU accelerated marine data visualization method

The study of marine data visualization is of great value. Marine data, due to its large scale, random variation and multiresolution in nature, are hard to be visualized and analyzed. Nowadays, constructing an ocean model and visualizing model results have become some of the most important research topics of ‘Digital Ocean'. In this paper, a spherical ray casting method is developed to improve the traditional ray-casting algorithm and to make efficient use of GPUs. Aiming at the ocean current data, a 3D view-dependent line integral convolution method is used, in which the spatial frequency is adapted according to the distance from a camera. The study is based on a 3D virtual reality and visualization engine, namely the VV-Ocean. Some interactive operations are also provided to highlight the interesting structures and the characteristics of volumetric data. Finally, the marine data gathered in the East China Sea are displayed and analyzed. The results show that the method meets the requirements of real-time and interactive rendering.     

Higher Harmonics Induced by Waves Propagating over A Submerged Obstacle in the Presence of Uniform Current

To investigate higher harmonics induced by a submerged obstacle in the presence of uniform current, a 2D fully nonlinear numerical wave flume（NWF） is developed by use of a time-domain higher-order boundary element method（HOBEM） based on potential flow theory. A four-point method is developed to decompose higher bound and free harmonic waves propagating upstream and downstream around the obstacle. The model predictions are in good agreement with the experimental data for free harmonics induced by a submerged horizontal cylinder in the absence of currents. This serves as a benchmark to reveal the current effects on higher harmonic waves. The peak value of non-dimensional second free harmonic amplitude is shifted upstream for the opposing current relative to that for zero current with the variation of current-free incident wave amplitude, and it is vice versa for the following current. The second-order analysis shows a resonant behavior which is related to the ratio of the cylinder diameter to the second bound mode wavelength over the cylinder. The second-order resonant position slightly downshifted for the opposing current and upshifted for the following current.     

正二十面体全球剖分模型的Geometry Clipmap球面绘制

地形绘制一直是图形学研究的热点问题,尤其是球面地形绘制,其在形状和数据组织方面比平面地形绘制更加复杂。在已有球面地形绘制算法的基础上,提出一种基于Geometry Clipmap的球面地形剖分与绘制方法。该方法以构建正二十面体球面网格为基础,将正二十面体划分为十个菱形区域,采用球面菱形网格的剖分,针对每个菱形区域的周边网格进行重新剖分和组合,形成一个虚拟的3×3的大菱形区域,扩大了Clipmap的活动范围,并在一定程度上解决了Clipmap的跨边界问题。实验结果表明了本文方法的可行性和有效性。     

异心球形电容器电容的精确解

提出了导体系统电容问题求解的一种新方法，借助双球面坐标系和平行板电容公式，求出了异心球形电容器电容的解析式。此外，对另外几种类型异体系统的电容也作了讨论。     

Zonal-Harmonics Perturbations

A recently developed iterative technique for solving the perturbed Kepler problem is explained, in a step-by-step detail, using the simple example of oblateness perturbations. The results are then extended to deal with higher-degree zonal harmonics.     

脑动脉粥样硬化斑块中钙化物矿物学特征研究

脑动脉钙化与脑动脉系统病变有密切联系。本文从矿物学角度出发,使用偏光显微镜(POM),扫描电子显微镜(SEM)、透射电子显微镜(TEM)、显微红外光谱(micro-FTIR)、同步辐射微区X射线衍射(μ-SRXRD)以及同步辐射微区X射线荧光光谱(μ-SRXRF)对脑动脉粥样硬化斑块中的钙化样品进行了研究。结果表明,钙化主要有球状和块状两种集合体形态,球状钙化具有同心环状或同心放射状构造,直径约0.3~5μm;块状钙化中可见球状钙化被杂乱分布的柱状纳米晶体包裹。钙化主要矿物相为B型碳羟磷灰石(B-CHA),并含Na、Mg、Zn、Fe和Sr等元素,与主动脉钙化中的矿物组成类似。钙化在其形成初期呈分散的小球状,后期大量球体逐渐被CHA纳米晶体充填胶结形成了致密的块状钙化。     

球近似艾黎-海斯卡宁均衡模型分析

针对传统的均衡重力异常方式基于平面近似,积分范围较小、计算公式的适用性受限、表征的信息量有限的问题,该文在球坐标下分析艾黎-海斯卡宁(Airy-Hesikanen)均衡模型。以计算点向径为半径,将地形分为布格球壳和粗糙地形两部分,计算其地形影响和均衡改正。在实验区,选用补偿深度21km、密度差0.678g/cm3的模型参数,采用该文公式和传统公式计算均衡重力异常,并比较分析其计算值。结果表明,以球近似Airy-Hesikanen均衡模型计算均衡重力异常值,在小积分范围以及平坦地区,与传统公式计算值的精度相当;但随着积分半径增加,球近似Airy-Hesikanen均衡模型计算值精度不断提高、变化更平缓,说明球近似AiryHesikanen均衡模型代替平面近似Airy-Hesikanen均衡模型应用于重力问题研究更为符合地球实际情况。     

各向异性组合滤波法反演陆地水储量变化

地球时变重力场模型反演陆地水储量变化已为全球气候变化研究作出巨大贡献,考虑到时变重力场模型球谐系数中存在相关性,其高阶次项具有较大的误差,需采用最优的滤波方法进行空间平滑。本文提出一种新的各向异性组合滤波方法,其基本思想是将改进的高斯滤波法与均方根(root mean square,RMS)滤波法组合,即对球谐系数的低阶次采用改进的高斯滤波法,而高阶次采用RMS滤波法。首先分析了最新的GRACE RL05系列时变重力场模型系数误差特性,基于全球水储量变化反演结果,分析比较了高斯滤波、改进的高斯滤波、RMS滤波和DDK滤波与本文提出的组合滤波法的有效性及精度,并利用模型结果进行了验证,计算结果表明,组合滤波法的中误差最小。研究结果表明,本文提出的组合法相比于先前的滤波方法,可有效地过滤高阶次的噪声,消除南北条带误差,同时减少信号泄漏,提高信噪比,保留更多有效的地球物理信号,进而提高反演精度。