Drag effect and topological complexes in strongly interacting two-component lattice superfluids.

The mutual drag in strongly interacting two-component superfluids in optical lattices is discussed. Two competing drag mechanisms are the vacancy-assisted motion and proximity to a quasimolecular state. In a case of strong drag, the lowest energy topological excitation (vortex or persistent current) can consist of several circulation quanta.

Surface roughness and effective stick-slip motion.

The effect of random surface roughness on hydrodynamics of viscous incompressible liquid is discussed. When the hydrodynamic decay length (the viscous wave penetration depth) is larger than the correlation radius (size) of random surface inhomogeneities, it is possible to replace a random rough surface by effective stick-slip boundary conditions on a flat surface with two constants: the stick-slip length and the renormalization of viscosity near the boundary. The stick-slip length and the renormalization coefficient are expressed explicitly via the correlation function of random surface inhomogeneities.