Table of contents

Macroscopic kinetics describes relaxation in terms of macroscopic states, i.e., the distributions of density, temperature, and so on. Two types of system are examined in this review, namely, (1) closed systems (or systems interacting exclusively with a thermostat) and (2) flow systems in which the nonequilibrium state is maintained by an external agency (source of supply or pump). In both cases, states are established that do not depend (in a particular range) on the initial conditions. These are the attractor states. Spatially homogeneous states (kinetic phases) are discussed for flow systems, together with transitions between them that are the analogs of the motion of interphase boundaries. In closed systems, the establishment of equilibrium can be preceded by the appearance of other attractors in the form of intermediate asymptotic behavior. A comparison is made between similar states in different processes (chemical reactions, viscous flows, absorption of light, and so on). Stability conditions are discussed.

The present state of the theory of strongly charged polyelectrolytes of the DNA type is reviewed. An infinitely long, uniformly charged cylinder immersed in a dielectric continuum is adopted as a model of DNA. Small mobile ions are treated as impermeable spheres. A comparison of the results of rigorous and approximate theoretical approaches to the description of this model shows that the self-consistent-field method, i.e., the Poisson-Boltzmann equation, is a reliable basis for deriving quantitative results. The theory of polyelectrolytes based on a solution of the nonlinear Poisson-Boltzmann equation is used to analyze the role played by electrostatic interactions in conformational changes in DNA. Transitions of two types are considered: a helix-coil transition and a transition between the ordinary right-hand-helix DNA (the B form) and the recently discovered left-hand-helix (the Z form). In the latter case the theory predicts a nonmonotonic behavior of the difference between the free energies of these conformations as a function of the salt concentration. It also predicts the existence of a critical point of a B-Z equilibrium for ionic strengths in the physiological region.

This paper reviews the first experiments on Mössbauer filtration of synchrotron radiation (that is, experiments on separating, out of the continuous energy spectrum of the synchrotron radiation, a beam of extremely highly monochromatized radiation with a relative linewidth of the order of 10⁻¹² at an energy of 14.4 keV) by coherent nuclear resonance scattering of the synchrotron radiation by the nuclei of a Mössbauer isotope. The corresponding theoretical investigations as well as possible variations of Mössbauer filtration of synchrotron radiation are discussed. The combination of the advantages of synchrotron radiation and Mössbauer spectroscopy, which is characterized by a uniquely high energy resolution, opens up new prospects for the use of synchrotron radiation in basic and applied investigations. This outlook refers first of all to the nuclear physics of solids and in particular to the topic of nuclear excitons in a crystal, to studies of the magnetic and electric field structure in crystals, metrological applications of synchrotron radiation, etc. The possibility of implementing new Mössbauer experiments with the use of synchrotron radiation is discusssed.