Entity

Time filter

Source Type

Beijing, China

Wang J.,Wuhan Naval University of Engineering | Ouyang W.,Unit 92117 | Zhao X.,Unit 92678
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2011

The concept and partition of GPS service volume have been established and specified in GPS SPS PS (standard positioning service performance standard) published recently. And the terrestrial service volume (TSV) includs near-Earth space, in which spatial exploration is much active. The new changes give the point that the technology of satellite navigation and positioning is feasible and promising to support users in near-Earth space. Based on the partition of the GPS TSV and SSV (space service volume), we discussed the judgment of the visible satellites in the both space and the feasibility of the received signal power, and carried out the UERE budget of the GPS signal in near space under the standard positioning service condition. Then the navigation performance statistics at the different heights at the middle latitude single point and over the global volume were carried out respectively with the Monte-Carlo method. The results show that the navigation accuracy will improve gradually with the users' height increasing in TSV, and into SSV, the accuracy deteriorates rapidly, and the service interrupt will appear at some height. The conclusions also show that the GDOP at the certain height in TSV will change its precision dilution property, which means that the positioning accuracy is much higher than that of UERE, and that the vertical accuracy is becoming higher than the horizontal accuracy gradually with the users' height increasing in TSV.


Jie W.,Wuhan Naval University of Engineering | Wen O.-Y.,Unit 92117
2010 2nd International Conference on Industrial and Information Systems, IIS 2010 | Year: 2010

In the paper, The conception of UTC, TAI and Loran-C time is described, and the principle of Loran-C timing is also represented in details, as the pivotal part for timing, the Synchronization technoloy of Loran-C is analysed, a method for Absolute Time Synchronization(ATS) is introduced, which is suitable for Chinese Loran-C system and necessary technology for modern Loran-C timing. Some data for evaluation experiment of the method is provided. © 2010 IEEE.


Liang H.,Unit 92117 | Liang H.,National University of Defense Technology | Zhu W.,Unit 92117 | Yao Y.,National University of Defense Technology | And 3 more authors.
Guofang Keji Daxue Xuebao/Journal of National University of Defense Technology | Year: 2013

In HLA simulation, data distribution management (DDM) service provides data filtering capability, which can effectively reduce the transmission and reception of redundant data. During the advancing of large-scale HLA simulation system, much region matching calculation is needed. However, in most of the existing regional matching algorithms, all regions are calculated in every matching calculation process, which results in a waste of computing resources. Meanwhile, the current matching algorithms are mostly based on serial region matching, and the advantage of multi-core cannot be fully taken. Aiming at the limitation of existing algorithms, a parallel region matching algorithm for large-scale HLA simulation is proposed. By this algorithm, the matching process of multiple regions which changes in the same simulation advancing can be calculated in parallel, the advantage of parallel computing environment can be taken. During the process of matching calculation, a method which is based on intersecting information was used. By the history of moving regions, matching calculation only happened within a limited range, and the redundant calculation could be avoided. Theoretical analysis and experimental results showed that the algorithm is particularly suitable for large-scale distributed simulation applications which execute on multi-core computing platform.


Li J.-L.,Unit 92117 | Li J.-L.,CAS Lanzhou Institute of Chemical Physics | Zhou F.,CAS Lanzhou Institute of Chemical Physics | Li C.-S.,Unit 92117 | And 3 more authors.
Mocaxue Xuebao/Tribology | Year: 2011

The tribological properties of some ionic liquids were investigated as additives in polyethylene glycol. Scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS) analyses were conducted to examine the morphology and chemical composition of the wear scars. The results showed that the ionic liquids presented excellent friction-reducing and antiwear properties. This is probably because that the ionic liquids adsorbed on the frictional surfaces and formed protective tribolayers during test.

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