Table of contents

This paper reviews research on helium clusters (of up to 20 atoms) and molecular hydrogen clusters (of up to 17 molecules) weakly bound by van der Waals forces to a light chromophore molecule such as OCS, N₂O, CO₂, or CO. Such clusters form in supersonic gas jets and are studied through the spectrum of the particular chromophore used. It is found that as the cluster grows, its rotational frequency increases (the effective moment of inertia decreases) starting from a certain number of atoms (molecules) attached. Also, in CO-based clusters a nearly free rotation of the chromophore molecule was observed. Experimental studies of such clusters are reviewed, as are those of the N₂–CO and CO–CO complexes in which both monomers nearly freely rotate. The relation of these rotations to the superfluidity of helium and hydrogen is discussed, and comparisons are made with spectroscopic experiments on chromophores and hydrogen clusters in liquid helium nanodroplets.

Methods for producing beams of nanometer-sized superfluid helium droplets and techniques for embedding single molecules and clusters in them open up many possibilities for spectroscopy, as well as providing insight into many physical and chemical processes occurring on the atomic and molecular level at extremely low temperatures (T ≤ 0.4 K). In this paper, results of investigations into the possibility of selecting molecules embedded in superfluid helium nanodroplets (clusters) are reviewed. The method proposed starts with the selective vibrational excitation of cluster-embedded molecules by intense IR laser radiation (which greatly reduces the size of the excited clusters), followed by size-separating the clusters via scattering the cluster beam from a crossing molecular (atomic) beam. It is shown that molecules of a particular isotope (component) composition can be selected with this method. The advantages and disadvantages of the method are discussed. Methods for creating and doping helium nanodroplets and some other examples of their applications are also outlined.

The problem of chaotic advection of passive scalars in the ocean and its topological, dynamical, and fractal properties are considered from the standpoint of the theory of dynamical systems. Analytic and numerical results on Lagrangian transport and mixing in kinematic and dynamic chaotic advection models are described for meandering jet currents, topographical eddies in a barotropic ocean, and a two-layer baroclinic ocean. Laboratory experiments on hydrodynamic flows in rotating tanks as an imitation of geophysical chaotic advection are described. Perspectives of a dynamical system approach in physical oceanography are discussed.

It is shown that according to the relativistic theory of gravity, the gravitational field slows down the rate of time flow but stops doing so when the field is strong, thus displaying its tendency toward self-limitation of the gravitational potential. This property of the gravitational field prevents massive bodies from collapsing and allows a homogeneous isotropic universe to evolve cyclically.

In the investigation of cyclotron ion heating in systems designed for plasma isotope separation, the high-frequency (HF) electric field amplification effect was found to occur in equilibrium plasma. In the present article this effect is treated as a result of the interaction of the plasma placed in a constant external magnetic field with the HF modes of the vacuum chamber. Consistent elaboration of this approach allowed obtaining a clear interpretation of the HF electric field amplification effect and constructing a simple model of HF field excitation in a plasma column embedded in the external magnetic field.