With the time-dependent perturbation theory, the dynamics of a two-level system coupled to an Bose field is revisited.

从含时微扰论的角度出发，重新求解了与玻色场相耦合的两态系统的动力学。

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The interaction between a weak probe laser pulse and a two-level system strongly driven by a near-resonant laser pulse is studied by dressed model.

我们用缀饰模型研究强近共振激光脉冲驱动下二能级系统与弱试探脉冲的相互作用。

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Much better to stick with a two-level system of pass and fail, or (if you will insist on such elitism) one extra level of “pass with distinction” for the top quartile.

最好还是继续两级方案，即通过和不通过，或者（若坚持精英主义）再为顶尖者增加“优秀通过”这个额外的级别。

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Gloucestershire, Staffordshire, Warwickshire and Worcestershire are all upper-level authorities in a two-tier system with district councils like Cheltenham, Tamworth, Wyre Forest and Stratford-on-Avon underneath them.

BBC: Elections to show why county councils count

Monday's briefing will also confirm that Mr Gove has dropped plans for a two-tier exam system - with more academically-able students taking an O-level type exam and the rest taking an easier test.

BBC: GCSE exam changes to be announced by Michael Gove