  Structure and superfluid response of nanoscale size helium-four clusters
enclosed in spherical cavities are studied by computer simulations. The curved
surface causes the formation of well-defined concentric shells, thus imparting
to the system a very different structure from that of free standing clusters.
On a strongly attractive substrate, superfluidity is only observed at low
density, in the single layer coating the inner surface of the cavity. If the
substrate is very weak (e.g., Li), on the other hand, a superfluid two-shell
structure can form, whose physical properties interpolate between two and three
dimensions. It is shown how experimental signatures of this physical behavior
can be detected through measurements of the momentum distribution.
