The motion of colloid particles in a viscous fluid flow is considered. Small sizes of colloid particles as compared to the characteristic scale of the flow make it possible to calculate their velocity relative to the liquid. If the density of a colloid particle is higher than the density of the liquid, the flow splits into regions in which the velocity of colloid particles coincides with the velocity of the liquid and regions of flow stagnation in which the colloid velocity is higher than the velocity of the fluid. This effect is used to explain qualitatively the decrease in the drag to the flows past macroscopic bodies and flows in pipes.

Владимир Валентинович Лебедев (к 60-летию со дня рождения), Андреев А.Ф., Габитов И.Р., Захаров В.Е., Иорданский С.В., Кац Е.И., Колоколов И.В., Коршунов С.Е., Трунин М.Р., Фалькович Г.Е., Фейгельман М.В., Хмельницкий Д.Е., Элиашберг Г.М.

The electrical properties of bilayer heterojunctions in a strong magnetic field at low temperatures have been considered. It has been shown that both the ohmic and Hall conductivities decrease exponentially due to the formation of neutral pairs if the electric fields in the two layers are parallel. In the antiparallel fields, the Hall conductivity is still determined by the activation energy of the excited electrons and decreases exponentially, but the ohmic conductivity decreases much slower, proportional to the temperature square.

It is shown that q absorption lines arise in two-dimensional crystal lattices at a rational fractional number p/q of magnetic-field flux quanta per electron. The absorption lines correspond to different exciton formation energies and are determined by the electron-hole Coulomb interaction. The number of the absorption lines is calculated for electron densities corresponding to the fractional quantum Hall effect.

The relaxation of the nonequilibrium order parameter (wave function of pairs) of a “pure” superconductor is considered for the homogeneous case. The relaxation is due to the electron-phonon interaction. The orderparameter relaxation time is shown to be much longer than the time interval between electron-electron collisions. This relation is explained by the smallness of the superconducting transition temperature compared to both the Fermi energy and the Debye energy in the BCS model.

A joint scientific session of the Physical Science Division of the Russian Academy of Sciences and the Joint Physical Society of the Russian Federation was held on 26 October 2006 at the conference room of the Lebedev Physics Institute, RAS. The following reports were presented at the session. (1) Pudalov V M (Lebedev Physics Institute, RAS) "Metal ± insulator transitions and related phenomena in a strongly correlated two-dimensional electron system"; (2) Iordanskii S V, Kashuba A (Landau Institute for Theoretical Physics, RAS) "Two-dimensional multicomponent electron gas as a model for silicon heterostructures"; (3) Olshanetskii E B (Institute of Semiconductor Physics (ISP), RAS SB, Novosibirsk), Renard V (GHML, MPI-FKF/CNRS, Grenoble, France), Kvon Z D (ISP, RAS SB, Novosibirsk), Gornyi I V (Institut fur Nanotechnologie, Karlsruhe, Germany; Ioffe Physical Technical Institute, RAS, St. Petersburg), Toropov A I (ISP, RAS SB, Novosibirsk), Portal J C (GHML, MPI-FKF/CNRS, Grenoble, France) "Interaction effects in the transport and magnetotransport of two-dimensional electrons in AlGaAs/GaAs and Si/SiGe heterojunctions." Summaries of the reports are given below. • Metal – insulator transitions and related phenomena in a strongly correlated two-dimensional electron system , V M Pudalov Physics-Uspekhi, 2006, Volume 49, Number 2, Pages 203–208 • Two-dimensional multicomponent electron gas as a model for silicon heterostructures, S V Iordanskii, A B Kashuba Physics-Uspekhi, 2006, Volume 49, Number 2, Pages 208–211 • Interaction effects in the transport and magnetotransport of two-dimensional electrons in AlGaAs/GaAs and Si/SiGe heterojunctions, E B Olshanetskii, V Renard, Z D Kvon, I V Gornyi, A I Toropov, J C Portal Physics-Uspekhi, 2006, Volume 49, Number 2, Pages 211–216

Всеволод Феликсович Гантмахер (к семидесятилетию со дня рождения), Абрикосов А.А., Андреев А.Ф., Горьков Л.П., Долгополов В.Т., Иорданский С.В., Кведер В.В., Левинсон И.Б., Осипьян Ю.А., Рашба Э.И., Тимофеев В.Б., Хмельницкий Д.Е., Элиашберг Г.М.