On the Aggregation of Inertial Particles in Random Flows
  We describe a criterion for particles suspended in a randomly moving fluid to aggregate. Aggregation occurs when the expectation value of a random variable is negative. This random variable evolves under a stochastic differential equation. We analyse this equation in detail in the limit where the correlation time of the velocity field of the fluid is very short, such that the stochastic differential equation is a Langevin equation. 
B. Mehlig, M. Wilkinson, K. Duncan, T. Weber, M. Ljunggren