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A large high-energy cluster impacting on a solid surface (the number of particles in a cluster N ≥ 10² – 10⁶, the collision energy per particle E_col ≥ 10 – 10³ eV) forms for a short time (≤ 50 – 500 fs) a medium characterized by extremely high temperature (≥ 10⁴ – 10⁵ K), density (up to 4 to 5 times the solid state value), and pressure (≥ 1 – 10 Mbar). As this takes place, the cluster heating rate reaches the value ≥ 10¹⁵ – 10¹⁶ Ê s⁻¹. In these extreme conditions, physical and chemical processes that are impossible in thermal equilibrium can occur both in the cluster itself and the collision zone. In this paper, extreme processes induced in clusters as a result of their strong excitation at collisions with a solid surface are reviewed, including ionization, light and charged-particle emission, fragmentation, breaking and making of chemical bonds, microshock wave generation, nuclear fusion, and surface bombardment. Conditions for these processes to proceed are examined and models to describe them discussed. It is shown that the characteristics of the processes depend significantly on the velocity, size, and composition of the cluster, as well as the material and temperature of the surface. Cluster excitation by an impact with a surface and that by a superhigh-power ultrashort laser pulse are compared and practical applications of the above processes are discussed.

One of the new methods of fiber optics uses cladding modes for controlling propagation of radiation in optical fibers. This paper reviews the results of studies on the propagation, excitation, and interaction of cladding modes in optical fibers. The resonance between core and cladding modes excited by means of fiber Bragg gratings, including tilted ones, is analyzed. Propagation of cladding modes in microstructured fibers is considered. The most frequently used method of exciting cladding modes is described, based on the application of long-period fiber gratings. Examples are presented of long-period gratings used as sensors and gain equalizers for fiber amplifiers, as well as devices for coupling light into and out of optical fibers.

Recently, several attempts have been made to determine the critical size in ferroelectricity. Due to the development of ferroelectric nanostructure technology, this fundamental problem had also become crucial for applied research. It is shown that although the theory predicts the existence of a finite critical size, ferroelectric polarization and its switching can be observed in monolayer films, at least in the case of ferroelectric vinylidene fluoride-trifluoroethylene copolymer P[VDF–TrFE] films prepared by the Langmuir–Blodgett method. The experimental search for the critical size in perovskite ferroelectrics is briefly reviewed. It is shown that the Landau–Ginzburg theory predicts the critical size to be infinitely small if the extrinsic effect of the film–electrode strain mismatch is taken into account. Special features of the switching dynamics of ultrathin ferroelectric films are also considered.

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 für 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, • Two-dimensional multicomponent electron gas as a model for silicon heterostructures, S V Iordanskii, A B Kashuba Physics-Uspekhi, 2006, Volume 49, Number 2, • 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,