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Spin-up problem in superfluid 4He.

We report the results of an experimental investigation of the nature of the vortex-boundary interaction and its role in the spin-up problem of superfluid /sup 4/He. We find evidence for two independence vortex-drag mechanisms: a drag associated with vortex lines pulling against pinning sites with a force equal to the line ''tension'' and a viscous drag associated with vortex motion through the normal-fluid Ekman layers.