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New NMR studies of 3He in high-porosity aerogel reveal a phase transition from an A-like to a B-like phase on cooling. The evidence includes frequency shift and magnetic susceptibility data, and similar behavior is found in two quite different aerogel samples. The A-like phase is stable only very near to T(c) but can be supercooled to below 0.8T(c). This behavior has been seen clearly at 32- and 24-bar pressures, and the presence of negative frequency shifts suggests that an A-like phase exists near T(c) at pressures as low as 12 bars in a magnetic field of 28.4 mT.

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This review covers a wide range of experimental and theoretical studies of low-temperature properties of glasses. The emphasis is on the various effects of interactions between two-level tunneling systems, TS's. We present experimental evidence, both direct and indirect, for the existence of interactions.Recent measurements of equilibrium internal friction and dielectric dissipation which deviate from the predictions of the noninteracting tunneling model are presented. The theoretical interpretation of this behavior in dielectric glasses at ultralow temperature is discussed in the context of recent theories of the interaction-induced TS relaxation.In addition, recent nonequilibrium dielectric and acoustic measurements are reviewed and a theoretical explanation for their results based on the formation of a dipole gap is discussed.The ability to explain the universality of low-temperature glassy behavior in terms of the interaction of some mobile defects is discussed in the light of recent experimental, numerical, and analytical results.