The Basic Shape Classification of Space Debris with Light Curves     

LU Yao  ZHAO Chang-yin 《Chinese Astronomy and Astrophysics》2021,45(2):190-208

We study the machine learning method for classifying the basic shape of space debris in both simulated and observed data experiments, where light curves are used as the input features. In the dataset for training and testing, simulated light curves are derived from four types of debris within different shapes and materials. Observed light curves are extracted from Mini-Mega TORTORA (MMT) database which is a publicly accessible source of space object photometric records. The experiments employ the deep convolutional neural network, make comparisons with other machine learning algorithms, and the results show CNN (Convolutional Neural Network) is better. In simulational experiments, both types of cylinder can be distinguished perfectly, and two other types of satellite have around 90% probability to be classified. Rockets and defunct satellites can achieve 99% success rate in binary classification, but in further sub-classes classifications, the rate becomes relatively lower.  相似文献   

Finding and sharing GIS methods based on the questions they answer   总被引：1，自引：0，他引：1  

S. Scheider  A. Ballatore  R. Lemmens 《International Journal of Digital Earth》2019,12(5):594-613

Geographic information has become central for data scientists of many disciplines to put their analyzes into a spatio-temporal perspective. However, just as the volume and variety of data sources on the Web grow, it becomes increasingly harder for analysts to be familiar with all the available geospatial tools, including toolboxes in Geographic Information Systems (GIS), R packages, and Python modules. Even though the semantics of the questions answered by these tools can be broadly shared, tools and data sources are still divided by syntax and platform-specific technicalities. It would, therefore, be hugely beneficial for information science if analysts could simply ask questions in generic and familiar terms to obtain the tools and data necessary to answer them. In this article, we systematically investigate the analytic questions that lie behind a range of common GIS tools, and we propose a semantic framework to match analytic questions and tools that are capable of answering them. To support the matching process, we define a tractable subset of SPARQL, the query language of the Semantic Web, and we propose and test an algorithm for computing query containment. We illustrate the identification of tools to answer user questions on a set of common user requests.  相似文献   

A multiphase approach for evaluating the horizontal and rocking impedances of pile group foundations          下载免费PDF全文

V.T. Nguyen  G. Hassen  P. de Buhan 《国际地质力学数值与分析法杂志》2016,40(10):1454-1471

This paper advocates the use of a multiphase model, already developed for static or quasi‐static geotechnical engineering problems, for simulating the behaviour of piled raft foundations subject to horizontal as well as rocking dynamic solicitations. It is shown that such a model, implemented in a FEM code, yields appropriate predictions for the foundation impedance characteristics, provided that shear and bending effects in the piles are taken into account, thus corroborating the findings of the asymptotic homogenization theory. Besides, it is notably pointed out that such a multiphase‐based computational tool makes it possible to assess the dynamic behaviour of pile groups in a much quicker way than when using direct numerical simulations, which may face oversized problems when large pile groups are concerned. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Why asymptotic limit of the acid dissolution capacity can lead to a sharp dissolution front in chemical dissolution of porous rocks?          下载免费PDF全文

Chongbin Zhao  B.E. Hobbs  A. Ord 《国际地质力学数值与分析法杂志》2017,41(15):1590-1602

The use of the asymptotic limit can greatly simplify the theoretical analysis of chemical dissolution front instabilities in fluid‐saturated rocks and therefore make it possible to obtain mathematical solutions, which often play a crucial role in understanding the propagation behavior of chemical dissolution fronts in chemical dissolution systems. However, there has been a debate in recent years that the asymptotic limit of the acid dissolution capacity (i.e., the acid dissolution capacity number approaching zero) alone cannot lead to a sharp dissolution front of the Stefan type in the acidization dissolution system, in which the dissolvable minerals of carbonate rocks are chemically dissolved by the injected acid flow. The acid dissolution capacity number is commonly defined as the ratio of the volume of the carbonate rock dissolved by an acid to that of the acid. In this paper, we use four different proof methods, including (i) direct use of the fundamental concepts; (ii) use of the mathematical governing equations of an acidization dissolution system; (iii) use of the different time scaling approach; and (iv) use of a moving coordinate system approach, to demonstrate that the asymptotic limit of the acid dissolution capacity can indeed lead to sharp dissolution fronts of the Stefan type in acidization dissolution systems on a much larger time scale (than the dissolution time scale). Our new finding is that on the reaction time scale, the condition of the conventional time derivative of porosity approaching zero alone can ensure that the acidization dissolution front has a sharp shape of the Stefan type. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

A 3D discrete FEM iterative algorithm for solving the water pipe cooling problems of massive concrete structures          下载免费PDF全文

Jing Cheng  T. C. Li  Xiaoqing Liu  L. H. Zhao 《国际地质力学数值与分析法杂志》2016,40(4):487-508

Water pipe cooling has been widely used for the temperature control and crack prevention of massive concrete structures such as high dams. Because both under‐cooling and over‐cooling may reduce the efficiency of crack prevention, or even lead to great harm to structures, we need an accurate and robust numerical tool for the prediction of cooling effect. Here, a 3D discrete FEM Iterative Algorithm is introduced, which can simulate the concrete temperature gradient near the pipes, as well as the water temperature rising along the pipes. On the basis of the heat balance between water and concrete, the whole temperature field of the problem can be computed exactly within a few iteration steps. Providing the pipe meshing tool for building the FE model, this algorithm can take account of the water pipe distribution, the variation of water flow, water temperature, and other factors, while the traditional equivalent algorithm based on semi‐theoretical solutions can only solve problems with constant water flow and water temperature. The validation and convergence are proved by comparing the simulated results and analytical solutions of two standard second‐stage cooling problems. Then, a practical concrete block with different cooling schemes is analyzed and the influences of cooling factors are investigated. In the end, detailed guidance for pipe system optimization is provided. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

修正的极大似然法拟合幂律频数分布     

李友平 《天文学报》2014,55(5)

针对包含饱和样本数据的频数幂律分布拟合,提出一个新的幂律分布指数的极大似然估计方法的修正公式.对比研究显示,修正公式适用于剔除异常饱和值的幂律频数拟合.如果不剔除饱和值,幂律指数的估计只能使用修正前的公式,其误差随幂律指数变化,指数较小时误差较大.由此建议,对于包含饱和样本的频数分布拟合,首先剔除异常的饱和值,然后对剩余不含饱和值的子集使用修正公式进行参数估计.  相似文献   

脉冲星射电辐射束半径与周期关系的研究     

魏丁丁  游霄鹏 《天文学报》2014,(6)

脉冲星的周期非常稳定.前人通过研究发现脉冲星射电辐射束半径大小应该正比于周期的-1/3或-1/2次方.通过整理收集了87颗信噪比很好的、偏振位置角明显为"S"曲线的脉冲星数据,用脉冲星辐射束几何模型计算得到了每颗脉冲星的辐射束半径及误差.发现脉冲星周期小于0.85 s时,辐射束半径正比于周期的-1/2次方.周期大于0.85 s时,辐射束半径与周期之间并没有明显的幂律关系,但这可能与选择效应有关.当假设脉冲星的磁倾角为90?时,计算得到的辐射束半径随周期分布的下边界正比于周期的-1/2次方,与前人的结论一致.  相似文献   

一种载人小行星探测轨道优化设计方法     

甘庆波  张扬  朱正帆  韩威华  董鑫 《天文学报》2014,(6)

给出了一种基于变比冲核电推进载人飞船探测小行星的轨道优化设计方法.首先基于双脉冲单圈Lambert轨道转移,对地球出发段和返回段进行搜索剪枝,再从两个可行区域中优选最佳飞行路径.设定"推进-滑行-推进"的分段飞行策略,以工质消耗最少为指标,利用混合法优化核电推进飞行轨迹,最后以分段优化参数为初值,基于整体任务约束将全飞行过程转化为非线性优化问题,将各飞行段进行拼接,获得整体参数优化解,并给出了数值和图形结果.  相似文献   

多星混合资料的定轨     

王歆 《天文学报》2014,(6)

在空间目标光学观测资料定轨中常常会遇到多个目标的观测被标记为同一个目标的情况,由于包含了多个目标的数据,定轨过程无法收敛或者完全错误.从极大似然估计角度,采用EM(Expectation Maximum)方法提出一种将轨道改进和识别过程相互融合的处理方法,并在具体实现过程中给出一种稳健估计方法.数值模拟表明方法简便、有效、可行.采用站间差历元差的手段,对当前电离层变化值进行求解与预测,可以将电离层延时误差的变化控制在一定范围,满足频率传递的要求.  相似文献   

Integer‐ambiguity resolution in astronomy and geodesy     

A. Lannes  J.‐L. Prieur 《Astronomische Nachrichten》2014,335(2):198-209

Recent theoretical developments in astronomical aperture synthesis have revealed the existence of integer‐ambiguity prob‐lems. Those problems, which appear in the self‐calibration procedures of radio imaging, have been shown to be similar to the nearest‐lattice point (NLP) problems encountered in high‐precision geodetic positioning and in global navigation satellite systems. In this paper we analyse the theoretical aspects of the matter and propose new methods for solving those NLP problems. The related optimization aspects concern both the preconditioning stage, and the discrete‐search stage in which the integer ambiguities are finally fixed. Our algorithms, which are described in an explicit manner, can easily be implemented. They lead to substantial gains in the processing time of both stages. Their efficiency was shown via intensive numerical tests. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献