Selection of conditions for studying intraaggregate connections influence on water stability of soil aggregates

The search for approaches to assessment the water resistance of soil aggregates is conducted using the modified Andrianov method. It is shown that the kinetic equation of the first-order reaction could be applied to describe the aggregates destruction in standing water. Methods of formal kinetics at the same time are just partially applicable for the description of soil aggregates destruction because of a significant change in the reaction rate constant over time. In particular, the average constant of reaction rate is convenient for water resistance comparison of different aggregates samples. It is established that the main factors that determine the speed of aggregate destruction are trapped air, gases produced by anaerobic microorganisms as well as intra-aggregate connections and the velocity of water entering the aggregates. In the course of the conducted experiments, it is shown that water resistance assessment should perform on wet aggregates under the normal atmospheric pressure. It allows neutralizing the influence of trapped gases of microbial origin and providing the domination of intra-aggregate connections that sustain water resistance in wet aggregates of real soils.

MECHANISMS OF FORMATION AND STRUCTURE POLYMER SALTS OF DIMETHYLAMINOETHYL METHACRYLATE WITH HETEROCYCLIC COMPOUNDS

The article presents the results of studies of the main regularities of the polymerization of quaternary monomeric salts of dimethylaminoethylmethacrylate with heterocyclic compounds - N-α-chloromethylbenzoxazolone, N-α-bromomethylmercaptobenzthiazolthione and N-α-chloromethylbenztriazole, determined experimentally the values ​​of the kinetic process parameters. The structure and composition of the newly synthesized monomers and polymers were studied using PMR spectra and elemental composition analysis. The processes of polymerization of monomeric salts based on DMA and heterocyclic compounds were studied, the main kinetic regularities of the reactions were established, and it was shown that the system under study obeys the basic laws of the radical process, which is confirmed by the compilation of a mathematical model of the formal kinetics of the reaction. A mathematical model of radical polymerization was compiled, on the basis of which the ordinal values ​​and activation energy of the reaction were determined and the results were obtained that were adequate with the experimental ones.

Redundancy-Free Models for Mathematical Descriptions of Three-Phase Catalytic Hydrogenation of Cinnamaldehyde

A new approach on how to formulate redundancy-free models for mathematical descriptions of three-phase catalytic hydrogenation of cinnamaldehyde is presented. An automatically created redundant (generalized) model is formulated according to the complete reaction network. Models based on formal kinetics and kinetics concerning the Langmuir-Hinshelwood theory for three-phase catalytic hydrogenation of cinnamaldehyde were investigated. Redundancy-free models were obtained as a result of a step-by-step elimination of model parameters using sensitivity and interval analysis. Starting with 24 parameters in the redundant model, the redundancy-free model based on the Langmuir-Hinshelwood mechanism contains 6 parameters, while the model based on formal kinetics includes only 4 parameters. Due to less degrees of freedom of molecular rotation in the adsorbed state, the probability of a direct conversion of cinnamaldehyde to 3-phenylpropanol according to the redundancy-free model based on Langmuir-Hinshelwood approach is practically negligible compared to the model based on formal kinetics.

Determining the relationship between critical conditions of detonation propagation and the average decomposition rates of explosives in detonation waves

The study introduces a model of steady propagation of non-ideal detonation of open cylindrical charges with diameters close to critical ones. The model was obtained in the quasi-one-dimensional approximation with the use of analytical methods. We found a solution for the model’s closing equation, which directly relates the average decomposition rate in the detonation front, determined by the parameters of the formal kinetics equation and dependent on the detonation rate, the gas-dynamic parameters of the initial explosive and its reaction products (isentropic exponents), the duration of the chemical peak and ideal detonation velocity, and also the ratio of the charge diameter to the duration of the chemical peak of the ideal detonation. We obtained an equation which reflects the dependence of the non-ideal detonation velocity on the charge diameter. The critical diameter is determined as the range boundary of the charge diameter values at which this equation still has a solution. The study shows that the expression for the fundamental characteristics of the detonation process, i.e. the ratio of the spread time and the reaction time of the explosive, differs from the expression used in the Khariton principle when taking into account the divergence of the reacting flow in the curved detonation front. As for the critical value of this ratio, in general it is different from the unity and is a variable value depending on the characteristics of the kinetics of decomposition of a substance in shock waves. Based on the calculations, we draw a conclusion that changes in the microstructure of the explosive charge of the same composition, displayed by changes in the parameters of the formal kinetics equation, are accompanied by relative changes in the critical diameter, many times greater than the relative changes in the duration of the chemical peak of ideal detonation

Optical transient absorption experiments reveal the failure of formal kinetics in diffusion assisted electron transfer reactions

The charge separation yield is shown to be strongly influenced by the distance dependence of the reactivity, viscosity and concentration and cannot be disentangled from the preceding events.

Martensite Spread: Analytical Modeling and Computer Simulation

In bulk polycrystals, the first nucleation event in a single grain may induce transformationin neighboring grains, resulting in a cluster of partially transformed grains. This cluster of partiallytransformed grains is normally designated as a ‘spread event’. The collection of these single spreadevents can be defined as the ‘spread’or ‘martensite spread’. In this paper we show how the martensitespreadmay be well described by formal kinetics. Spread taking place as a result of athermalmartensitetransformation, isothermal martensite transformation and even martensite burst are analyzed with thehelp of such a methodology. Formal kinetics is essentially based on a stochastic geometry approach ofthe transformations considered as nucleation and growth (or birth-and-growth ) processes. Therefore,the success of such an analysis strongly suggests the possibility of a computer simulation of the spreadentirely based on probabilistic considerations. Such a simulation has been carried out and the resultsare discussed in this paper with reference to the results obtained by the analytical methods.

Analytical Expressions for Formal Kinetics

In recent papers Rios and Villa resorted to developments in stochastic geometry to revisit theclassical KJMA theory and generalize it for situations in which nuclei were located in space accordingto both homogeneous and inhomogeneous Poisson point processes as well as according to Materncluster process and surface and bulk nucleation in small specimens. Rigorous mathematical methodswere employed to ensure the reliability of the new expressions. These results are briefly described.Analytical expression for inhomogeneous Poisson point process nucleation gives very good agreementwith Cellular Automata simulations. Cellular Automata simulations complement the analyticalsolutions by showing the corresponding microstructural evolution. These new results considerablyexpand the range of situations for which analytical solutions are available.