3DT-CM: A Low-complexity Cross-matching Algorithm for Large Astronomical Catalogues Using 3d-tree Approach

Location-based cross-matching is a preprocessing step in astronomy that aims to identify records belonging to the same celestial body based on the angular distance formula. The traditional approach involves comparing each record in one catalog with every record in the other catalog, resulting in a one-to-one comparison with high computational complexity. To reduce the computational time, index partitioning methods are used to divide the sky into regions and perform local cross-matching. In addition, cross-matching algorithms have been adopted on highperformance architectures to improve their efficiency. But the index partitioning methods and computation architectures only increase the degree of parallelism, and cannot decrease the complexity of pairwise-based crossmatching algorithm itself. A better algorithm is needed to further improve the performance of cross-matching algorithm. In this paper, we propose a 3d-tree-based cross-matching algorithm that converts the angular distance formula into an equivalent 3dEuclidean distance and uses 3d-tree method to reduce the overall computational complexity and to avoid boundary issues. Furthermore, we demonstrate the superiority of the 3d-tree approach over the 2d-tree method and implement it using a multi-threading technique during both the construction and querying phases. We have experimentally evaluated the proposed 3d-tree cross-matching algorithm using publicly available catalog data. The results show that our algorithm applied on two 32-core CPUs achieves equivalent performance than previous experiments conducted on a six-node CPU-GPU cluster.

How the Internet Promotes China’s Exports:A Firm-level Perspective

The development of information and communications technologyv(ICT),particularly the Internet,has reduced trade costs.However,it remains unclear whether these reduced costs are reflected in the “extensive margins”of firms'exports(which refer to the probability of firms exporting)or the “intensive margins”(which refer to the value of firms'export).To test this,we used the concepts of information cost and binary margins,an augmented trade model of firm heterogeneity,a two-stage Heckman estimation,and data from the World Bank Enterprise Survey of Chinese firms in 2012.The results revealed that reduced trade costs from the use of ICT were positively related to extensive margins but that the connection with intensive margins was not significant.The results lead to the conclusion that reduced information costs related to a firm's exporting behavior were primarily reflcted in variable trade cosis.This study offers theoretical and empirical evidence for China 3 policies towards the Internet,which are relevant for the export of manufactured goods.The government should encourage the use of ICT to enhance firms export opporunities while facing current trade policy uncerainty.