Collective behavior in the system of self propelling particles with   nonholonomic constraints
  We consider the dynamics of systems of self propelling particles with nonholonomic constraints. A continuum model for a discrete algorithm used in works by T. Vicsek et al. is proposed. For a case of planar geometry the finite flocking behavior is obtained. The circulation of the velocity field is found not to be conserved as a consequence of the nonholomicity. The stability of ordered motion with respect to noise is discussed. An analogy with the kinetics of charges in superconductors is noted. 
V. L. Kulinskii, V. I. Ratushnaya, A. V. Zvelindovsky, D. Bedeaux