Photobleaching mechanisms of Radachlorin photosensitizer in aqueous solution

The time dependence of the fluorescence intensity of aqueous solutions of Radachlorin photosensitizer at different concentrations and the influence of the dissolved oxygen concentration on the fluorescence dynamics are analyzed. The experimental results are interpreted based on the numerical solution of the system of kinetic equations describing the photochemical processes that lead to the formation and degradation of singlet oxygen in solution. The influence of possible mechanisms of photosensitizer photobleaching is analyzed. It is shown that the main photobleaching mechanism under our experimental conditions is the chemical reaction between the photosensitizer in the triplet state and dissolved oxygen molecules. Two rate constants of electron-transfer chemical reactions, which are important for understanding the nature of the occurring photoprocesses, are determined.     

Oxidative Conversion of Wood Gasification Products in a Mixing Reactor

Russian Journal of Applied Chemistry - The results of thermodynamic calculations and experimental data on conversion of wood gasification tars in pyrolysis gas to tar-free fuel gas by partial...     

Plasma oscillations in two-dimensional electron systems with a superstructure under Stark quantization conditions

The effect of quantizing electric field on plasma oscillations of two-dimensional electron gas in a system with a periodic potential has been theoretically investigated. The coupled-plasmon spectrum ω(q) is calculated for high temperatures (Δ ? T, where Δ is the conduction miniband width and T is temperature in energy units). The calculations are based on the quantum theory of plasma oscillations in the random-phase approximation, with allowance for the umklapp processes.     

Filtration combustion of charcoal-polyethylene systems

The characteristics of the filtration combustion of a carbon-polyethylene-inert material mixture with superadiabatic heating are experimentally studied. It is demonstrated that the composition of the products and the nature of the thermal degradation of the polymer strongly influence the burning rate and thermal structure of the wave. In the filtration combustion wave, a part of the polymer can be pyrolyzed and carried away by the gas flow, with the rest of it being oxidized in the combustion zone.     

Nonlinear conductivity of single-walled zigzag carbon nanotubes

The conductivity of the single-walled zigzag carbon nanotube system was studied in an alternating electric field with the intensity vector along the axis of nanotubes. The electronic carbon nanotube system was macroscopically considered in terms of the Boltzmann kinetic equation in the constant relaxation time approximation while omitting the interaction with the phonon subsystem. The nonlinear responses to the applied harmonic field were calculated and analyzed.     

Theoretical and experimental investigation of the photoacoustic effect in solids with residual stresses

Modern experiment and theory in the field of residual stress detection by the photoacoustic method are summarized and analyzed. A multimode approach based on the simultaneous application of several photothermal and photoacoustic methods is proposed for the study of thermal and thermoelastic effects in solids with residual stress. Some experimental results obtained within the framework of this approach for Vickers indentation zones in ceramics are presented. The effect of annealing on the photoacoustic, piezoelectric signal for ceramics and the influence of the given external loading on the behavior of the photoacoustic signal near the radial crack tips is investigated. It is experimentally shown that both compressive and shear stresses contribute to the photoacoustic signal near the radial crack tips. The model of the photoacoustic, thermoelastic effect in solids with residual stress is proposed. It is based on the modified Murnaghan model of non-linear elastic bodies, which takes into account a possible dependence of the thermoelastic constant on stress. This model is further developed to explain the photoacoustic signal behavior near the radial crack tips. It is demonstrated that this model of the photoacoustic effect agrees qualitatively with the available experimental data.     

Effect of an external mechanical load on elastic stresses near radial cracks in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiC-TiC ceramics: Photoacoustic study

The variation of the photoacoustic signal near the mouths of radial cracks in Vickers-indented externally loaded Al₂O₃-SiC-TiC ceramics is studied. A theoretical model of a photoacoustic signal that is recorded near the mouths of vertical cracks is suggested. Indentation zones in Al₂O₃-SiC-TiC ceramics are visualized by laser scanning photoacoustic microscopy. The sensitivity of the photoacoustic method with piezoelectric detection of signals to both normal and shear stresses acting on a crack is demonstrated. Experimental and theoretical data for the effect of external stresses on the photoacoustic signal near the mouths of radial cracks are compared. For the ceramics under study, agreement is fairly good. It is shown that the strain coefficients near the mouths of vertical cracks can be determined from photoacoustic experimental data.     

Theoretical and experimental study of photoacoustic and electron-acoustic effects in solids with internal stresses

Results of a theoretical and experimental study of photoacoustic and electron-acoustic effects in solids with internal stresses are presented. In the theoretical part, an approach to describing these effects on the basis of a generalized concept of thermoelastic energy of a solid with internal stresses and the nonlinear Murnaghan model for the elastic part of its energy is developed. The results of studying objects with internal stresses in the context of an integrated experimental approach incorporating the techniques of photodeflection and thermal-wave and photoacoustic microscopy with piezoelectric recording of the signal are reported. It is shown that a similar approach allows one to detect the arrangement of the strained surface areas of the object and to evaluate the extent to which its thermal and thermoelastic parameters are affected by internal stresses. The results of applying this approach to a study of Vickers indentations in silicon nitride ceramics are reported.     

Partial Pressure of Saturated Sodium Nitrite Vapor over the System NaNO2-NaNO3

The partial pressure of sodium nitrite was measured in the system NaNO₂-NaNO₃ at temperatures of 798, 823, and 848 K and the logarithm of the NaNO₂ pressure was obtained as a function of inverse temperature. The coefficients A and B of the Clausius-Clapeyron equation and the partial molar heats of evaporation were calculated. The activities and activity coefficients of sodium nitrite were determined for various compositions of the system NaNO₂-NaNO₃.     

Influence of constant quantizing electric field on plasma waves in a two-dimensional superlattice

The effect of a constant electric field on plasma waves in a two-dimensional electronic gas in a system with periodic potential is investigated. A dispersion relation ω(k) is obtained using the high temperature approach. The main and resonant modes of plasma waves are investigated numerically. Regions of one-particle and collective excitations are identified. Calculations are performed on the basis of the plasma wave quantum theory in a random-phase approximation with allowance for the Umklapp processes.