A higher concentration, said the service's deputy director, would cause friction, especially if migrants' religion and customs differed from those of the local population.

This high concentration causes trees to die in six regions that total about in size (see photo, below).

Our concentration at this spot did cause the bubble to wobble slightly, however.

However, even concentrations of one-tenth part per million can cause irritation to the eyes, nose and throat, according to officials.

A heavy concentration of machine-gun fire caused many casualties, and held up our advance.

High enough concentrations of the toxin (10 milligrams per mouse) cause death.

High concentrations of etioplasts will cause leaves to appear yellow rather than green.

When phosphates are introduced into water systems, higher concentrations cause increased growth of algae and plants.

Any concentration of troops or traffic jams could cause disaster.

Some studies suggest that too much concentration on close work can cause nearsightedness, but the evidence is hotly disputed.