Hysteresis in a system driven by either generalized force or displacement variables: martensitic phase transition in single-crystalline Cu-Zn-Al

We report on experiments aimed at comparing the hysteretic response of a Cu-Zn-Al single crystal undergoing a martensitic transition under strain-driven and stress-driven conditions. Strain-driven experiments were performed using a conventional tensile machine while a special device was designed to perform stress-driven experiments. Significant differences in the hysteresis loops were found. The strain-driven curves show reentrant behavior yield point which is not observed in the stress-driven case. The dissipated energy in the stress-driven curves is larger than in the strain-driven ones. Results from recently proposed models qualitatively agree with experiments.

Nucleation in supersaturated solutions 3He in 4He at negative pressure.

Depending on the 3He concentration, thermal nucleation in 3-4He supersaturated liquid mixtures at negative pressures may be originated either by bubble or by 3rich drop formation. We have investigated this phenomenon within a density-functional approach, determining the regions in the pressure¿3He-concentration plane where bubbles or drops likely drive the nucleation process. As an illustrative example, we also give the homogeneous nucleation pressure corresponding to 50 and 100 mK temperature.