  The kinetics of single-species annihilation, $A+A\to 0$, is investigated in
which each particle has a fixed velocity which may be either $\pm v$ with equal
probability, and a finite diffusivity. In one dimension, the interplay between
convection and diffusion leads to a decay of the density which is proportional
to $t^{-3/4}$. At long times, the reactants organize into domains of right- and
left-moving particles, with the typical distance between particles in a single
domain growing as $t^{3/4}$, and the distance between domains growing as $t$.
The probability that an arbitrary particle reacts with its $n^{\rm th}$
neighbor is found to decay as $n^{-5/2}$ for same-velocity pairs and as
$n^{-7/4}$ for $+-$ pairs. These kinetic and spatial exponents and their
interrelations are obtained by scaling arguments. Our predictions are in
excellent agreement with numerical simulations.
