According to the characteristics of subway trains tracking, we have proposed a cellular model to simulate the tracking operation of trains in Beijing subway line 2.

本文根据地铁列车追踪运行的特点，建立了固定自动闭塞系统下的元胞自动机模型，并对北京地铁2号线进行了模拟仿真。

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On the program, more about the National Security Agency and reports of a vast computer-based telephone call tracking operation.

NPR: Sen. Cornyn: NSA Phone Tracking a Useful Tool

However, Fast and Furious lost track of more than 1, 000 firearms it was tracking in the operation, and two of the lost weapons turned up at the scene of the 2010 killing of U.S. Border Patrol agent Brian Terry.

CNN: Boehner: Contempt vote on Holder will proceed

Earlier this year, BBC Newsline carried out a series of reports into a USPCA operation which been tracking one gang for some time.

BBC: Badger