  Grain rotation and grain boundary (GB) sliding are two important mechanisms
for grain coarsening and plastic deformation in nanocrystalline materials. They
are in general coupled with GB migration and the resulting dynamics, driven by
capillary and external stress, is significantly affected by the presence of
junctions. Our aim is to develop and apply a novel continuum theory of
incoherent interfaces with junctions to derive the kinetic relations for the
coupled motion in a tricrystalline arrangement. The considered tricrystal
consists of a columnar grain embedded at the center of a non-planar GB of a
much larger bicrystal made of two rectangular grains. We examine the shape
evolution of the embedded grain numerically using a finite difference scheme
while emphasizing the role of coupled motion as well as junction mobility and
external stress. The shape accommodation at the GB, necessary to maintain
coherency, is achieved by allowing for GB diffusion along the boundary.
