Thermal explosion of a reactive mixture under conditions of oscillating ambient temperature

The problem of the thermal explosion of a finite volume of a reactive material in a medium with harmonically oscillating temperature is solved in the classical formulation. A kind of resonance is shown to arise when the oscillation period is commensurate with the adiabatic induction period of thermal explosion at the mean ambient temperature. At both high and very low oscillation frequencies, the critical condition parameter and induction period are only slightly affected by ambient temperature oscillations. By contrast, at moderately low frequencies, even small-amplitude oscillations of ambient temperature can strongly influence the critical condition and, especially, induction period of thermal explosion.     

Electron and atomic structure of polymers: Implication for nuclear tracks formation

A review of experimental and theoretical activities in a study of an electron and atomic structure of polymers is presented. Polymers having conjugated π-electron systems were studied experimentally in different aggregate states within the temperature interval 4.2– 300 K using spectrophotometric and spectroluminescence methods. Special attention has been paid to oxidization processes in polymers caused by ionizing radiation. The theoretical approach developed in Ukraine for electron and atomic structure calculations is based on the theory of multiple scattering of elementary excitations (electrons and phonons). This approach provides a possibility to estimate energy spectra of elementary excitations, parameters of interatomic correlations, electron density distributions, absorption and emission (photoluminescence) spectra. Study of the fluorescence spectra provides a possibility to estimate the electron structure as well as the local characteristics of latent tracks induced by nuclear particles. Dependencies of the shape of photoluminescence bands can be investigated experimentally for different kinds of nuclear particles within a wide energy range. Application of combined experimental and theoretical approach of investigation of solid-state nuclear track detector (SSNTD) physical properties, and determination of nuclear particle characteristics (charge, atomic number, etc.) are discussed.     

Inhibiting Effect of Fullerene C60 and Other Antioxidants on Thermal Oxidative Degradation of Copolymers of Methyl Methacrylate with Methacrylamides

Copolymers of methyl methacrylate with methacrylamides undergo thermal oxidative degradation less actively than polymethyl methacrylate. Additions of fullerene C60 inhibit degradation.     

Nonradiative deactivation of the electronic excitation energy in cyanine dyes: influence of binding to DNA

The processes of nonradiative deactivation of electronic excitation energy in cyanine dyes determine their quantum yield. Because of that, the study of the influence of cyanines binding to DNA on these processes can provide information on the causes leading to the cyanines fluorescence intensity enhancement in the presence of DNA. In the presented paper, the activation energies of nonradiative degradation of electronic excitation, quantum yields and rate constants of nonradiative transitions of several cyanines in free state and in the presence of DNA were established and compared. The mechanisms of nonradiative deactivation of dye excitation energy were discussed.     

Spin-orbit coupling in oxygen near the dissociation limit

By using the method of configuration interactions in the valence basis with triple exponentials, the spectrum of the oxygen molecule is calculated in a range of internuclear distances from 1.2 to 2.45 Å, with the matrix of configuration interactions being diagonalized with regard to the spin-orbit coupling. The matrix elements of the spin-orbit coupling are presented, along with the spin splittings of triplet and quintet states. Particular attention is given to the intermediate range for the breaking of the O=O bond (1.8–2.45 Å), where the strong mixing of multiplets and rearrangement of the valence bonding to the atomic limit O(³ P)+O(³ P) occur. Other dissociation limits up to O(¹ D)+O(¹ D) are also taken into account. The results obtained are discussed in the context of the theory of the chemical bond, catalysis, radiation collisions, and the theory of spectral bands for high vibrational quantum numbers.     

Effect of absorption of low-molecular-weight compounds by some polymer flocculants

The sorption properties of the intramolecular complex - poly(acrylamide) to poly(vinyl alcohol) grafted copolymer (PVA-PAA_N) in block state were investigated with respect to a number of compounds. The relatively small molecules of phenol, phenylalanine in water solution as well as nitrobenzene in hexane are strongly absorbed by PVA-PAA_N films. The large humine acid molecules (sizes are larger by more than ≈ 10 times) are absorbed by PVA-PAA_N very weakly. It was determined the absorption influence on the character of polymer film solution. In a number of cases the oscillation of the dilution and sorption were observed when determining the critical concentrations of guest molecules in the upper layer of polymer films were achieved. The possible mechanisms of absorption were discussed.