Superflow and dissipation in porous glasses

The study of superflow of 4He in porous vycor glass has a long venerable history, dating back to the early days of superfluidity. In this work, the authors address a number of outstanding questions. In doing so, they use a low frequency (250 Hz) Helmholtz oscillator technique which uses filled pores and allows measurements to be made on small samples under a variable pressure gradient and at any temperature - not only below the superfluid transition (a feature also of torsional oscillator and acoustic techniques). The technique has also been used to investigate aerogel porous glass, but the main emphasis of this report is on vycor