Vol 43, No 10 (2024)

The statistical model developed in this work allows us to calculate the shape of the multiple quantum (MQ) NMR spectra (the dependence of the amplitudes of the corresponding multiple quantum coherences on their orders) by decomposing the desired time-correlation functions (TCF) over the infinite set of orthogonal operators and by using some well-known facts from the physics of traditional model systems. The resulting expression contains series with terms depending on the gradually growing up with the time number of spins in clusters of correlated spins. The influence of the possible degradation of these clusters on the shape of the spectra is taken into account. Analytical and numerical calculations were performed for various parameter values included in the final expressions. The developed theory adequately describes the results of numerical calculations of the MQ spectra performed by us and experiments: the transformation of the Gaussian profile into an exponential one, the asymptotics (wings) of the spectrum depending on the coherence order M, the dependence of the relaxation rate of the MQ spectrum on M, as well as the narrowing and stabilization of the MQ spectrum under the influence of perturbation.

Benzene and its derivatives are extremely important substances in modern chemical technologies. However, emissions of these substances have an extremely negative impact on the atmosphere and ecology. Benzene is a substance of the second class of danger and its effect on the human body is fraught with serious consequences. In the event of man-made disasters, an urgent task is to convert benzene into less toxic substances. In this work, using a low-pressure flow reactor, the kinetic patterns of the reactions of atomic fluorine with benzene, fluorobenzene, and chlorobenzene at a temperature T = 293 K and a pressure of 0.8–1.3 Torr were established. The concentrations of reagents and products were controlled by molecular beam mass spectrometry. To determine reaction rate constants, the method of competing reactions was used. The reaction of fluorine atoms with cyclohexane was chosen as a competitor. As a result of the analysis using experimental and literature data, the following values of the rate constants of the studied reactions were obtained.

The results of a three-dimensional numerical study of the propagation of detonation waves in a two-phase mixture of liquid iso-octane with air are presented. The detonation calculation technique is based on Navier-Stocks equations with the simulation of liquid phase evolution using the Lagrangian formalism. Numerical models consider droplet movement, evaporation and breakup as well as finite-rate mixing and chemical transformations. The reliability of the method is confirmed by the comparison of predicted and measured velocities of heterogeneous detonation in a vertical channel of square cross-section. The influence of the prehistory on the formation of a two-phase detonable mixture in the channel on the propagation velocity and structure of detonation waves is considered. The influence of droplet coagulation is also taken into account. New data on the spatiotemporal structure of a two-phase detonation wave have been obtained.

There are many reasons for natural gas (methane) leaks in gas distribution networks. One of the most important tasks of gas distribution organizations is to promptly identify and eliminate gas leaks before they cause emergency situations. Eliminating gas leaks as soon as possible will minimize the negative impact on the environment. This paper proposes a new original method for detecting emergency gas emissions into the atmosphere and leaks on gas pipeline systems. The technique involves the simultaneous use of both experimental and calculated data to determine the concentration and characteristic sizes of gas emissions. The methodology was tested at laboratory conditions using a propane cylinder and a gas burner. The Scorpion monophotonic sensor was used as recording equipment. As a result of processing experimental data and mathematical modeling using computational fluid dynamics methods, the dependence of propane concentration on the distance to the burner was constructed and the characteristic dimensions of the gas cloud were determined.There are many reasons for natural gas (methane) leaks in gas distribution networks. One of the most important tasks of gas distribution organizations is to promptly identify and eliminate gas leaks before they cause emergency situations. Eliminating gas leaks as soon as possible will minimize the negative impact on the environment. This paper proposes a new original method for detecting emergency gas emissions into the atmosphere and leaks on gas pipeline systems. The technique involves the simultaneous use of both experimental and calculated data to determine the concentration and characteristic sizes of gas emissions. The methodology was tested at laboratory conditions using a propane cylinder and a gas burner. The Scorpion monophotonic sensor was used as recording equipment. As a result of processing experimental data and mathematical modeling using computational fluid dynamics methods, the dependence of propane concentration on the distance to the burner was constructed and the characteristic dimensions of the gas cloud were determined.

Studying the physical properties of long-lived plasma formations can help us to understanding the nature of electro-physical phenomena in thunder clouds, the lower ionosphere, tornadoes, volcanic activity and the associated appearance of natural plasmoids (such as ball lightning, sprites, jets, etc.). The study of the stimulated detonation of long-lived energy-consuming plasmoids obtained in laboratory using a combined type plasma generator consisting of an erosive plasma generator and a magnetoplasma compressor is presented in this paper. It was found that a necessary condition for detonation is the excess of certain threshold values of pressure and temperature. The existence of a directed explosion mode has been established, which is realized only at optimal delay times (of the order of t_d ~ 2000 μs) between the beginning of a pulsed erosion discharge and the discharge of a magnetoplasma compressor. The parameters of shock waves, as well as the optical and X-ray spectra of long-lived energy-consuming plasmoids in the stimulated detonation mode were measured.

In recent years numerous satellite data on the yellow glow of the sodium layer (located at an altitude of 85–95 km from the Earth’s surface) have become available. Studies of optical activity at sodium D-line frequencies are necessary for a better understanding of the plasma-chemical processes occurring in the mesosphere. It should be taken into account that these processes occur in a neutral environment, where the molecular nitrogen is general component. In this work the analytical numerical expressions for the elements of 3´3 matrix of interaction between Na(²P_j) and N₂(X ¹S_g⁺) and interaction potential between Na(²S_1/2) and N₂(X ¹S_g⁺) were obtained at medium and large interpartical distances that determine radiation lines collisional broadening. The exchange, quadrupole–quadrupole, dispersion, and spin–orbit interactions were taken into account. Exchange interaction between the valence Na electron and N₂(X ¹S_g⁺) molecule was described by the local Hellman pseudopotential. The effect of the overlap between Na(²S_1/2, ²P_j) and N₂(X ¹S_g⁺) electron densities was taken into account evaluating long-range quadrupole–quadrupole and dispersion interactions.