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The theory of sound propagation in macroscopically isotropic and homogeneous porous media saturated with superfluid 4 He has been developed neglecting all damping processes. The case when the normal fluid component is locked inside a porous medium by viscous forces is investigated in detail. It is shown that in this case one shear wave and two longitudinal, fast and slow, waves exist. Fast wave as well as slow wave is accompanied with temperature oscillations. The velocities of these waves are obtained.

The pseudo-spin model for double layer quantum Hall system with total landau level filling factor ν = 1 is discussed. Unlike the "traditional" one where interlayer voltage enters as static magnetic field along pseudo-spin hard axis, in our model we consider applied interlayer voltage as a frequency of precessing pseudo-magnetic field lying into the easy plane. It is shown that a Landau-Lifshitz equation for the considered pseudo magnetic system well describes existing experimental data. Besides that, the mentioned model predicts novel directed intra-layer transport phenomenon in the system: unidirectional intra-layer energy transport is realized due to interlayer voltage induced motion of topological kinks. This effect could be observed experimentally detecting counter-propagating intra-layer inhomogeneous charge currents which are proportional to the interlayer voltage and total topological charge of the pseudo-spin system.

A two-quantum process of electron spin–lattice relaxation in amorphous solids is investigated. A relaxation mechanism involving two-level tunneling systems and phonons from the region of the boson peak is considered. It is shown that this mechanism is effective under certain conditions.

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