Cluster headaches occur in cycles: sufferers can experience several headaches a day for weeks or even months on end.

VOA: standard.2009.12.17

Hearst and his partner, Ben Gluckstern, launched a bike-sharing program called NY Cycles in 2009.

VOA: standard.2010.01.31

"We are going on the rise again, but that's due to normal cycles,"

VOA: standard.2009.12.21

Storm frequency,he says, comes in cycles of 30 years.

VOA: standard.2009.12.21

"That is how we will restore trust and confidence in our markets." "That is how we will help to put an end to the cycles of boom and bust that we have seen.

VOA: standard.2010.04.24