In this form, the signs of the disease appear and begin to grow worse, with no periods of disappearance.

VOA: special.2009.01.06

In Kenya,a project aims to educate girls about H.I.V.prevention while helping them stay in school during their monthly periods.

VOA: special.2009.03.16

Other scientists have shown that sun spot activity can be measured in periods of time that last about eleven years.

VOA: special.2009.09.29

These problems may appear and then disappear, sometimes resulting in long periods when there are no problems at all.

VOA: special.2009.01.06

Charles Darwin developed the theory of how living things develop from simpler organisms over long periods of time.

VOA: special.2009.02.25

Archeologists are able to estimate the age of these objects by dividing layers of dirt into time periods.

VOA: special.2009.08.18

The two time periods tested whether people were more likely to act differently in the short term than in the long term.

VOA: special.2009.03.03

Their purpose was to explore some of the problems of manned flight, during short periods,in lower space.

VOA: special.2010.07.07

The next time you think about going without sleep, consider this: Laboratory animals that are kept awake for long periods of time ...die.

VOA: special.2009.08.26

There are also twenty historical rooms which show different periods of American building and furniture design.

VOA: special.2010.08.04

Rebecca Skloot tells this complex story by going back and forth between subjects and time periods.

VOA: special.2010.07.21

But once the seeds are planted, she does suggest covering the soil with a little mulch to protect it during rains and dry periods.

VOA: special.2010.03.02

Mister Chavez often went for long periods without food to protest the conditions under which the farm workers were forced to do their jobs.

VOA: special.2009.09.06

An astronomer at Harvard College, Henrietta Leavitt, had discovered that these periods of brightness could be used to measure the star's distance from Earth.

VOA: special.2009.04.29