The coherent potential method in the diffusion problem on a random substitution lattice

Based on the balance equation, we consider the diffusion problem on a hyperlattice with randomly distributed inaccessible sites. Using diagram methods, we find a self-consistent expression for the configurationally averaged Green’s function in the coherent potential approximation. We show that this approach is applicable in a broad range of concentrations of accessible sites. Using this approximation, we find the exact asymptotic form of the static diffusion coefficient for a low concentration of blocked sites. This allows making good estimates of the percolation threshold in the random-site diffusion problem on an arbitrary hyperlattice. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 149, No. 2, pp. 252–261, November, 2006.     

Electrolysis of Water in a System with a Solid Polymer Electrolyte at Elevated Pressure

Electrolysis of water in a system with a solid polymer electrolyte (SPE) at pressures elevated up to 3.0 MPa is studied. A mechanism of the effect of elevated pressure on the electrolysis electrochemistry is proposed. A mathematical model and relevant software, which allow one to model current–voltage curves of an SPE-based electrolyzing cell on the basis of reference and experimental data, are designed.     

An experimental study of technical fluctuations in a quartz crystal oscillator with automatic gain control

The contribution of technical fluctuations of individual circuit components of a quartz crystal oscillator with AGC to the technical characteristics of the output signal is determined. The noise of the elements studied is simulated. It is demonstrated that the AGC system significantly improves the amplitude-frequency characteristics of the oscillator output signal. Requirements are determined for the noise characteristics of individual oscillator stage components for the purpose of obtaining high short-term frequency stability.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 21, No. 12, pp. 1778–1784, December, 1978.     

The quenching of Pb(6p 2 1 D 2) atoms in collisions with molecules

The collisions of metastable Pb(6p ^{2 1} D ₂) atoms with various molecules were studied by the diagnostics of radiation from a hollow cathode lamp and a laser on lead vapor. Experiments were performed for a gas flow of lead atoms with argon. The Pb(6p ^{2 1} D ₂) states were excited in a gas discharge in the presence of reagent gas molecules. The absolute rate constants for the quenching and chemical reactions of lead atoms in the ground and excited states were determined. The quantum efficiency of chemical reactions was close to one for the N₂O, CH₂Cl₂, SF₆, and CuBr molecules. Long-lived chemical compounds were formed in these reactions.     

The size effect in the ultralow-frequency electrical excitation spectrum of bridgman instability

With crystal hydrates growing in size, the amplitude of the ultralow-frequency (ULF) electric field responsible for a drastic drop in their mechanical stability under high uniaxial compression is found to markedly decrease. This effect is demonstrated with oxalic acid crystal hydrates H₂C₂O₄ · 2H₂O in experiments on Bridg-man explosive instability. As the size of the crystal hydrates grows, the ULF stability spectrum exhibits no less than three narrow dips imposed on a broader dip. This spectrum correlates with the permittivity burst spectra. These phenomena can be explained if, at ULFs, the compressible crystal hydrates are considered as nonlinear disperse systems in chains of variable-moment giant (comparable to a disperse particle in size) dipole oscillators.     

Molecular and Supramolecular Structures of Triiodides and Polyiodobismuthates of Phenylenediammonium and Its N,N-dimethyl Derivative

Despite remarkable progress in photoconversion efficiency, the toxicity of lead-based hybrid perovskites remains an important issue hindering their applications in consumer optoelectronic devices, such as solar cells, LED displays, and photodetectors. For that reason, lead-free metal halide complexes have attracted great attention as alternative optoelectronic materials. In this work, we demonstrate that reactions of two aromatic diamines with iodine in hydroiodic acid produced phenylenediammonium (PDA) and N,N-dimethyl-phenylenediammonium (DMPDA) triiodides, PDA(I₃)₂⋅2H₂O and DMPDA(I₃)I, respectively. If the source of bismuth was added, they were converted into previously reported PDA(BiI₄)₂⋅I₂ and new (DMPDA)₂(BiI₆)(I₃)⋅2H₂O, having band gaps of 1.45 and 1.7 eV, respectively, which are in the optimal range for efficient solar light absorbers. All four compounds presented organic–inorganic hybrids, whose supramolecular structures were based on a variety of intermolecular forces, including (N)H⋅⋅⋅I and (N)H⋅⋅⋅O hydrogen bonds as well as I⋅⋅⋅I secondary and weak interactions. Details of their molecular and supramolecular structures are discussed based on single-crystal X-ray diffraction data, thermal analysis, and Raman and optical spectroscopy.     

Expectation values of descendent fields in the sine-Gordon model

We obtain exactly the vacuum expectation values in the sine-Gordon model and in Φ_1,3 perturbed minimal CFT. We discuss applications of these results to short-distance expansions of two-point correlation functions.     

On the multidimensional theory of the first-order phase transitions

Multidimensional theory of first-order phase transitions in the vicinity of a one-dimensional saddle point is considered. Transformations of the variables describing new-phase nuclei are suggested; these transformations allow one to completely separate the variables in the Fokker-Planck equation and reduce the problem to a one-dimensional one. The distribution function and the nucleation rate are found for both stationary and non-stationary nucleation stages. As an illustration, the problem of boiling of a volatile liquid is considered in the case where new-phase nuclei are characterized by two parameters.