Spatial ordering due to hydrodynamic interactions between a pair of colliding drops in a confined shear

Pair-collision between viscous drops in a confined shear is numerically simulated to show that the confinement drastically alters the trajectories of the drops. In contrast to free shear, drops here move towards the centerline giving rise to a zero cross-stream separation and a net stream-wise separation. The latter varies as inverse of capillary number and the cube of the confinement (distance between the walls). The stream-wise separation does not depend on the initial positions of the drops. An analytical theory for the phenomenon is offered

Bio-Economies of Scope and the Discard Problem in Mulitple Species Fisheries

This paper considers the problem of multi-species fisheries management when targeting individual species is costly and at-sea discards of fish by fishermen are unobserved by the regulator. Stock conditions, ecosystem interaction, technological specification, and relative prices under which at sea discards are acute are identified. A dynamic model is developed to balance ecological interdependencies among multiple fish species, and scope economies implicit in a costly targeting technology. Three regulatory regimes, species-specific harvest quotas, landing taxes, and revenue quotas, are contrasted against a hypothetical sole owner problem. An optimal plan under all regimes precludes discarding. For both very low and very high levels of targeting costs, first best welfare is close to that achieved through any of the regulatory regimes. In general, however, landing taxes welfare dominate species-specific quota regulation; a revenue quota fares the worst.scope economies; multiple species fishery management; costly targeting; discarding