  We study the motions of small solids, ranging from micron-sized dust grains
to 100-m objects, in the vicinity of a local density enhancement of an
isothermal gaseous solar nebula. Being interested in possible application of
the results to the formation of clumps and spiral arms in a circumstellar disk,
we numerically integrate the equations of motion of such solids and study their
migration for different values of their sizes and masses and also for different
physical properties of the gas, such as its density and temperature. We show
that, considering the drag force of the gas and also the gravitational
attraction of the nebula, it is possible for solids, within a certain range of
size and mass, to migrate rapidly (i.e. within ~1000 years) toward the location
of a local maximum density where collisions and coagulation may result in an
accelerated rate of planetesimal formation.
