Russian Journal of Physical Chemistry B最新文献

The structural organization of DNA in stressed (with increased stress resistance), anabiotic, and mummified cells obtained by introducing 4-hexylresorcinol in different concentrations at different stages of cell culture growth is studied using the synchrotron radiation diffraction technique. The experimental studies allow us to conclude that 4-hexylresorcinol is the initiator of the transition of cells into an anabiotic and mummified state in the stationary stage of growth. In the prestationary stage, in the studied concentration range, 4-hexylresorcinol initiates the transition of cells into a mummified state but not into an anabiotic state, which indicates that DNA is unprepared for the crystallization process in these bacteria. The structure of DNA inside a cell in an anabiotic dormant state (the almost complete absence of metabolism) and dormant state (starvation stress) coincide (form nanocrystalline structures). The data indicate the universality of DNA condensation or the universality of DNA protection by the Dps protein in the dormant state, regardless of the type of stress. The mummified state (the complete absence of metabolism, irreversible to life) is very different in structure (has no order within the cell).

A new method for mixing solutions and suspensions containing thermodynamically immiscible dispersion media based on the use of ultrasonic dispersion and thermally stimulated microwave heating has been proposed. The results of a study of a number of functional composites obtained by mixing solutions of biodegradable polymers in chloroform with aqueous suspensions of natural polymers are presented. The possibility of obtaining polymer composites doped with magnetic nanoparticles and drugs by this method is considered. It has been established that the proposed method of mixing makes it possible to combine suspensions of polymers of different kinds in the composition of composites suitable for creating porous, hygroscopic, and magnetically controlled materials for biomedical and environmental applications.

The self-ignition of a propylene–oxygen–argon stoichiometric mixture with a volumetric argon content of 95% is studied. The experiments are performed on a shock tube, which is part of the Shock Tube Experimental Complex of the Institute of Mechanics of Moscow State University, in conditions behind the reflected shock wave. The time dependencies of signals from a piezoelectric pressure sensor, a thermoelectric detector, and an optical section configured to record the radiation of electronically excited radicals OH^• (λ = 302 nm), CH^• (λ = 427 nm, and molecular carbon ({text{C}}_{2}^{centerdot }) (λ = 553 nm) are analyzed. The ignition delay times τ_ign are measured in the temperature range T = 1200–2460 K and pressures p = 4.5–25 atm. The data obtained are compared with the results of other authors.

A new process is proposed for the pyrolysis of ammonia in a filtration combustion moving bed reactor to produce hydrogen. The process can be implemented in reactors with energy recovery with a separate supply of reagents (including swiss-roll reactors, etc.). The mass-energy balance of the process is calculated. The pyrolysis products are analyzed under a condition of thermodynamic equilibrium with varying temperature and pressure. The system pressure is varied from 1 to 10 bar. The temperature range from 300 to 1100 K iss considered. It is shown that the pyrolysis of ammonia ends at a temperature of 620 K at atmospheric pressure. An increase in pressure in the system leads to a slight increase in the temperature of the pyrolysis of ammonia. The portion of hydrogen that needs to be burned to cover the energy for heating and pyrolysis of the initial ammonia in the case of an adiabatic reactor is 0.13. From one mole of ammonia it is possible to obtain 1.31 moles of hydrogen.

Adsorption of toxic gas of carbon monoxide (CO) molecules by using transition metals (TM) of titanium (Ti), vanadium (V) or chromium (Cr)-doped boron nitride (B₅N₁₀) nanocage have been investigated using density functional theory. The partial density of states can evaluate a determined charge assembly between gas molecules and TM–B₄N₁₀ which indicates the competition among dominant complexes of Ti, V, Cr. Based on nuclear quadrupole resonance analysis, TM-doped on B₅N₁₀ has shown the lowest fluctuation in electric potential and the highest negative atomic charge including 0.5883 (chromium), 0.6893 (vanadium) and 0.7499 coulomb (titanium), respectively, have presented the most tendency for being the electron acceptors. Furthermore, the reported results of nuclear magnetic resonance spectroscopy have exhibited that the yield of electron accepting for doping atoms on the TM–B₄N₁₀ through gas molecules adsorption can be ordered as: Cr > V > Ti that exhibits the strength of covalent bond between titanium, vanadium, chromium, and CO towards toxic gas removal from air. In fact, the adsorption of CO gas molecules can introduce spin polarization on the TM–B₄N₁₀ which specifies that these surfaces may be employed as magnetic scavenging surface as a gas detector. Regarding IR spectroscopy, doped nanocages of Ti–B₄N₁₀, V–B₄N₁₀, and Cr–B₄N₁₀, respectively, have the most fluctuations and the highest adsorption tendency for gas molecules which can address specific questions on the individual effect of charge carriers (gas molecule-nanocage), as well as doping atoms on the overall structure. Based on the results of (Delta G_{{{text{ads}}}}^{{text{o}}}) amounts in this research, the maximum efficiency of Ti, V, Cr atoms doping of B₅N₁₀ for gas molecules adsorption depends on the covalent bond between CO molecules and TM–B₄N₁₀ as a potent sensor for air pollution removal. Therefore, for a given number of carbon donor sites in CO, the stabilities of complexes owing to doping atoms of Ti, V, Cr can be considered as: CO@Cr–B₄N₁₀ > CO@V–B₄N₁₀> CO@Ti–B₄N₁₀.

Using thermogravimetric analysis (TGA), the kinetic constants of the thermal decomposition of polymethylmethacrylate (PMMA) in an oxidizing environment are determined over a wide range of sample heating rates. The values of the kinetic constants of polymer decomposition are determined by the Kissinger method. It is shown that as the degree of polymer decomposition increases, the rate constant decreases at a constant temperature.

The combustion modes of powder and granular mixtures (100 – X)(Ti + C) + XNiCr (X = 0–30%) containing Ti powders of different dispersion with different amounts of impurity gases in them are studied. The experimental setup provided the filtration of impurity gases released during combustion in the cocurrent direction or through the side surface of the sample. The difference between the experimental burning velocities of powder mixtures with titanium of a different fineness is explained using a convective-conductive combustion model. For granular mixtures based on Ti powder with a characteristic size of 120 μm, it is shown that combustion occurs in the conductive mode. Comparison of the combustion velocities of granular mixtures containing Ti powder with particles of a characteristic size of 60 μm in the absence and presence of gas filtration through the sample indicates the transition of combustion to the convective regime. The necessary and sufficient conditions for the transition from conductive to convective combustion are formulated, which makes it possible to determine the composition of the mixture whose combustion occurs in the boundary region. In mixtures based on Ti with a particle size of 60 μm, the conductive combustion regime is observed during the combustion of granules 0.6 mm in size and a mixture with X = 30% of granules 1.7 mm in size. For mixtures with X = 0–20% with granules 1.7 mm in size, burning in the convective regime, the interfacial heat transfer coefficients are evaluated using the experimental data. Their values are more than an order of magnitude higher than the theoretical ones. The XRD results of the combustion products showed that in order to obtain synthesis products without side phases of intermetallic compounds, it is necessary to use finely dispersed titanium powder.

Small additions of hydrocarbons, such as propylene, which are widely studied as combustion and explosion inhibitors of hydrogen-air mixtures, sometimes exhibit specific properties. The known mechanism of the inhibitory effect of these additives is associated with the intensification of the termination of branching chains due to the addition of hydrogen atoms; however, conditions also exist in which these compounds, instead of inhibiting, have a neutral and even promoting effect. Such conditions and the reasons leading to the fact that inhibition is practically absent have not yet been studied. This article shows the results of numerical modeling, which make it possible to more fully outline the range of conditions where the addition of propylene practically does not inhibit hydrogen-air mixtures and outline possible reasons for this effect. The solution to three model problems is presented: self-ignition in a constant-volume reactor, laminar flame propagation, and gas ignition with a heated wire. The calculations are carried out with the detailed kinetic mechanism of chemical reactions NUIGMech 1.1 (2020). The objects of the study are three air mixtures containing hydrogen in amounts of 15, 29.6, and 50 vol % (lean, stoichiometric, and rich mixtures, respectively) without additives and with the addition of 1% propylene.

A numerical model for the POX steam-oxygen conversion of methane to synthesis gas in a reversed flow nonpremixed filtration combustion reactor with a reversed flow of a steam-methane mixture and a continuous supply of oxygen to the center of the reactor is carried out. The calculations were performed for the oxygen/methane molar ratio of 0.47 and steam/methane molar ratio of 0.5, in the parametric region close to the limit for the feasibility of the scheme. Various modes of initiation and control of flow reversal are considered, and dependences of the combustion temperature and the composition of products on the characteristics of the process are obtained. A comparison of the established cyclic mode of conversion with the predictions of the equilibrium model shows that the kinetic constraints lead to a higher combustion temperature and incomplete conversion of methane. At high temperatures, the conversion proceeds via the initial soot formation during the pyrolysis of methane and the subsequent reaction of soot with steam.

The ignition of the normal layer-by-layer burning (LB) and its transition to the convective burning (CB) regime in mixtures of ammonium nitrate (AN) with bulk density aluminum are studied. Experiments in a constant-volume bomb with pressure registration are carried out. The porosity of the samples is 0.55–0.59, the particle size of the AN varies from 20–40 to 250–630 µm, and the aluminum content varies from 8 to 47 wt %. Two brands of aluminum were used: ASD-4 and PAP-2. It is shown that the mixtures are capable of being ignited when the igniter pressure is close to or above the critical (minimum) value. The values of the critical pressure of the igniter, the pressure, and the time at which LB and CB occurs for mixtures with different particle sizes of AN and aluminum and different concentrations are measured. The replacement of aluminum ASD-4 with PAP‑2 leads to a significant (by an order of magnitude or even more) decrease in the values of critical pressure and pressures at which LB and CB begins.