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by C. Dasgupta and Oriol T. Valls in *Phys. Rev. E* 79, 016303 (2009).

Motivated by many recent experimental studies of non-classical rotational inertia (NCRI) in superfluid and supersolid samples, we present a study of the hydrodynamics of a superfluid confined in the two-dimensional region (equivalent to a long cylinder) between two concentric arcs of radii *b*
and *a*
(*b* < *a*-
) subtending an angle β-
, with 0≤β≤2π-
. The case β = 2π-
corresponds to a blocked ring. We discuss the methodology to compute the NCRI effects, and calculate these effects both for small angular velocities, when no vortices are present, and in the presence of a vortex. We find that, for a blocked ring, the NCRI effect is small, and that therefore there will be a large discontinuity in the moment of inertia associated with blocking or unblocking circular paths. For blocked wedges (*b* = 0
) with β < π-
, we find an unexpected divergence of the velocity at the origin, which implies the presence of either a region of normal fluid or a vortex for {\it any} nonzero value of the angular velocity. Implications of our results for experiments on "supersolid" behavior in solid He-4 are discussed. A number of mathematical issues are pointed out and resolved.

Posted Thursday, February 26th 2009
by Jenny Allan