Police have evacuated homes near RAF Fairford, an air base in England used by the US, and arrested several men on suspicion of explosives offences.
The US has returned all B-1 bombers stationed at RAF Fairford to their American home bases.
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Every article counts as a vote whose weight fades over time — an article published today counts as 1.0, one from two days ago counts 0.5, four days ago 0.25, and so on (a 2-day half-life). Pulse is the sum of those weights, so fresh coverage lifts it and old bursts fade away smoothly.