  The embedding of a Taub-NUT space in the directions transverse to the world
volume of branes describes branes at (spherical) orbifold singularities.
Similarly, the embedding of a pp-wave in the brane world volume yields an AdS
orbifold. In case of the D1-D5--brane system, the AdS3 orbifolds yields a BTZ
black hole; as we will show, the same holds for D3-branes corresponding to
AdS5. In addition we will show that the AdS orbifolds and the spherical
orbifolds are U-dual to each other. However in contrast to spherical orbifolds
the AdS orbifolds lead to a running coupling, which is in the IR inverse to the
coupling of the spherical orbifold. A discussion of the general pp-wave
solution in AdS space is added.
