D-BRANES AND PRODUCTION OF STRINGS

We review two types of D-branes processes where open strings are creat ed. In the first type, a closed string incident on a collection of D-b ranes is converted into a number of open strings running along them. F or the case of threebranes we compare the absorption rate with that in semiclassical gravity, and find exact agreement. The second type of p rocess is creation of stretched open strings by crossing D-branes. We show that this is possible whenever a p-brane passes through an (8 - p )-brane positioned orthogonally to it. The extra attractive force exer ted by the stretched open string is crucial for finding that the net f orce cancels in this BPS system.