[en] Starting from the system of kinetic equations for components of a two-component gas of quasiparticles with arbitrary dispersion law, the exact expression for the diffusion coefficient is obtained. This general results are used to study the phenomenon of quantum diffusion in solid ³He-⁴He. In particular, the width of the energy band of impuriton is calculated, and the physical reasons for a strong temperature dependence of the diffusion coefficient (D approx T^-9) are explained

[en] We consider the model of temperature and heat flow evolution in a double-layer system. The first layer is superfluid ⁴He and the second layer is a metallic plate. At the left end of the first layer the oscillating heat source is situated. Temperature at the right end of the second layer is constant. It was found that temperature and heat flow resonances of unusual form appeared. Analytical expressions for width and amplitudes of these resonances are obtained.

[en] The kinetic theory of first sound in a quantum liquid is presented. The results for velocity and sound attenuation are obtained and found to be valid over a wide range of frequencies, including hydrodynamic, kinetic, and intermediate regimes, and throughout the whole temperature range in which a quasiparticle description is applicable. Comparison of theory and experiments is carried out

[en] Dissipative processes in low-concentration ³He-⁴He solutions are considered in the entire temperature interval in which the quasiparticle description is valid. All the kinetic coefficients and the second-sound damping factor are calculated by using the Boltzmann equations for a three-component quasiparticle gas. The roton-impuriton times that determine the various coefficients are obtained. The calculated values are compared with the experimental data

No abstract available

[en] We propose a model for the quasiparticles of superfluid ⁴He which describes both phonons and rotons in a unified way. The theory is based on the fact that the thermal de Broglie wavelengths of the atoms overlap each other. This allows us to treat superfluid ⁴He as a continuous medium at all length scales. Then the parameters of the continouous medium (density, pressure, and velocity) can be given a probabilistic value at each point in space. The quasiparticles of superfluid ⁴He are small fluctuations in these parameters; the frequency and wave vector of a fluctuation correspond to the energy and momentum of the quasiparticle, respectively. Using the Lagrange formalism we derive equations for the potential associated with these fluctuations, and this leads to a generalized wave equation. From the Hamiltonian formalism we derive a system of equations for the variables of a continuous medium, and show that in the general case there is a non-local dependence between pressure and density. Applying the methods of the mechanics of continuous media, we calculate the creation probabilities for both phonons and rotons by phonons in a solid, in a unified way. This theory explains why R^- rotons are not created by a heater. The theory is compared with those of others, and the results with experiments

[en] We solve the one-dimensional problem of quasiparticles' transfer through the interface between a solid and superfluid helium. Superfluid helium is treated as a continuous medium with correlations. When a solid's phonon is incident on the interface, phonons, R^- and R⁺ rotons are created in helium, and their creation probabilities are obtained. When a quasiparticle of superfluid helium is incident, it can be reflected as any one of the three quasiparticles, and the corresponding probabilities are derived. The R^- rotons creation and detection probability are both shown to be small, and this explains why they could not be detected experimentally for a long time

[en] The resonances occurring during oscillations of quartz tuning forks in superfluid helium and its mixtures are studied. Quartz tuning forks are used to study various properties of helium, and also as a precision temperature sensor. Experimental observations of resonance phenomena were carried out in a wide range of temperatures and pressures, but the results of observations have not yet been exhaustively described theoretically. In this work we consider the pressure, entropy, and velocities oscillations in order to determine the conditions under which oscillations of a solid wall excite the first and second sound in superfluid helium and sound in supercritical helium, and to calculate the contributions of these processes to the formation of resonances during oscillations of closed tuning forks. In particular, the experimentally observed excitation of standing waves of pressure and entropy oscillations by an oscillating closed tuning fork, the appearance and properties of resonances depending on the temperature and pressure of helium are considered. (author)

[en] We discuss a number of unusual phenomena, which have been discovered recently in anisotropic quasiparticle systems in superfluid ⁴He. These include the creation of high-energy phonons by a pulse of low-energy phonons, the suprathermal distribution of high-energy phonons in long phonon pulses, the mesa shape of the angular distribution of low-energy phonons, the creation of a 'hot line' when two-phonon pulses cross. The thermodynamic properties of anisotropic quasiparticle systems of He II are derived for all degrees of anisotropy

No abstract available