We have carried out ultrasound measurements for 4He confined in a nano-porous glass, Gelsil. The sound velocity of Gelsil glass in a vacuum is determined by the two-level system (TLS) contribution. Regardless of whether 4He in the pore is liquid or solid, there exists an additional sound velocity change due to the relaxation of ultrasound stresses by a thermal activation mechanism. It was found that the different heat treatment of Gelsil glass affects both this relaxation and the superfluidity of 4He in the pore.
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