Absorption and fluorescence of 8-azasteroids in the gas phase

Extensive studies of the spectral-luminescent characteristics of four 8-azasteroids and a model compound 2-(3,3-dimethyl-1,2,3,4-tetrahydro-1-isoquinolidene)-5,5-dimethyl-1,3-cyclohexanedion in the gas phase have been made. From the analysis of the dependences of the absorption spectra on the vapor pressure (T_low) and the fluorescence spectra on T_low and the exciting radiation wavelength (_exc) a conclusion on the presence in the vapors of the investigated 8-azasteroids of three absorption and fluorescence centers (S-, M-, and L-centers) has been drawn. The absorption spectra of these centers strongly overlap. Their long-wave absorption boundaries have been determined. The dependence of the fluorescence spectra of all three centers on _exc, which is inherent in rarefied gases of individual organic molecules, is observed. The S-centers are the molecules of the initial steroids, and the M- and L-centers are the molecules of thermo- and phototransformations of the initial steroids. The model compound in the gas phase is characterized by the same dependences of the fluorescence spectra on T_low and _exc as those inherent in 8-azasteroids. Taking into account the additional data obtained as a result of investigation of the absorption and fluorescence spectra of solutions of the substances extracted from vacuum cells after the investigation of 8-azasteroids and the model compound in the gas phase, conclusions on the nature of the M- and L-centers have been drawn.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 48–57, January–February, 2005.     

Evolution of fractal particles in systems with conserved order parameter

Computer simulations of the evolution of fractal aggregates in systems with conserved order parameter are described in this work. The aggregates are generated by diffusion-limited aggregation. This model describes such important processes as annealing of dendrite inclusions in solids, healing of cracks in ceramics, temperature-induced transformations in composites, relaxation of rough surfaces, aging of colloid particles, etc. It is shown that the evolution in fractal media differs significantly from that occurring in initially homogeneous systems and leads to different values of the scaling exponent. A relationship between the fractal dimension, mechanism of relaxation, and scaling exponent was also derived.     

Numerical investigation of viscous gas secondary flows in a rotating cylinder with sources and sinks

A source-sink model of secondary flow excitation in a rotating cylinder, which describes the interaction between a circulator and a rotating gas, is proposed for a nonlinear system of Navier-Stokes equations, and the results of a numerical calculation of the resulting circulating flows are presented. The modified Newton's method employed in the numerical solution makes use of regularizing perturbations to ensure its stability and convergence at low Ekman numbers and high rates of rotation of the cylinder. The combined effect of mechanical and thermal means of flow excitation and the influence of viscous energy dissipation are considered.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 39–44, July–August, 1989.