Home – Home – Jornals – Advanced Search

This article is devoted to a study of the properties of an implicit method for Abel type integral algebraic equations. An Abel type integral equation with stiff components is used for examining the properties of these methods and the stability domains are constructed. Numerical calculations confirming the results obtained are performed. In this article, a fractional “stiff” problem is proposed to study the stability of the mathematical objects considered.

Numerical differentiation of functions with large gradients is investigated. It is assumed that a function contains a component known up to a factor and responsible for the large gradients of the function. Application of classical formulas for calculating derivatives to such functions may lead to significant errors. Special-purpose formulas are studied for numerical differentiation on a uniform grid which are exact for a boundary layer component. Conditions are formulated under which an error estimate of a difference formula for a derivative does not depend on the gradients of the boundary layer component. In the case of an exponential boundary layer, when calculating a derivative of an arbitrarily given order error estimates that are uniform with respect to a small parameter are obtained. The results of numerical experiments are presented.

For optimal estimation of quantities of interest from observational data and a model (optimal filtering problem) in the nonlinear case, a particle method based on a Bayesian approach can be used. A disadvantage of the classical particle filter is that the observations are used only to find the weight coefficients with which the sum of the particles is calculated when determining an estimate. The present article considers an approach to solving the problem of nonlinear filtering which uses a representation of the posterior distribution density of the quantity being estimated as a sum with weights of Gaussian distribution densities. It is well-known from filtration theory that if a distribution density is a sum with weights of Gaussian functions, the optimal estimate will be a sum with weights of estimates calculated by the Kalman filter formulas. The present article proposes a method for solving the problem of nonlinear filtering based on this approach. An ensemble π-algorithm proposed earlier by the author is used to implement the method. The ensemble π-algorithm in this new method is used to obtain an ensemble corresponding to the distribution density at the analysis step. This is a stochastic ensemble Kalman filter which is local as well. Therefore, it can be used in high-dimensional geophysical models.

The article reports the geochemical characterization of soils, vegetation, and groundwater of the recultivated spoils of three coal deposits. Recultivation was carried out 30-40 years ago, and then the spoils were left for self-overgrowth without any additional measures. A common pattern for all sites is the presence of carbonaceous particles, their oxidation leads to an increase in temperature in the spoil rocks. The sum of biologically active temperatures exceeds the values for natural soils of undisturbed areas. Technogenic landscapes are characterized by a smaller share of moisture-loving forest and pratal species, compared to the reference areas. Hydrogeochemical anomalies practically do not go beyond the flooded borrow excavations of spoils. Reclamation by applying a fertile soil layer provides minimization of the negative effects associated with an increase in the temperature of spoil soils and accelerates the remediation of regional plant communities.

In order to develop a technology for the chemical processing of methane from the coal industry into valuable products, conditions for the reactions of combined steam/carbon dioxide and autothermal reforming of methane were optimized. The effects of temperature (600-900 °C), volumetric feed rate (50-400 mL/min), contact time (0.04-0.45 s) and the molar ratio of components (O₂/CH₄ = 0.25-1.0, CO₂/H₂O = 0.5-2.0) of the reaction mixture on the conversion rates of initial reagents (CH₄, CO₂, O₂) and the yield of target reaction products (H₂, CO) were studied. It has been shown that the use of combined reforming allows regulating the H₂/CO molar ratio within a wide range (4.1-0.9). Optimal process conditions have been established to ensure the complete conversion of methane and the maximum yield of useful products for the effective utilization of methane-air mixtures in coal production with the generation of a hydrogen-containing gas.

The composition and transformation dynamics of saturated hydrocarbon biomarkers in the coal of the Sergeevo deposit were studied using gas chromatography and gas chromatography - mass spectrometry. Depending on biomarker parameters in the studied section, the layers of allochthonous, autochthonous and mixed origin were identified, differing from each other in the nature and conditions of plant biomass accumulation. Allochthonous coals, enriched with bitumoids and genetically related to terragenic biomaterial, were formed in an oxidative environment. The transition to autochthonous and mixed coals was accompanied by an increase in the contribution from aquagene biomarkers and repeated changes in the facies conditions of sedimentation. Autochthonous coals are distinguished by an abnormal content of higher alkanes and a non-standard distribution of isoprenoid hydrocarbons.

Vanadium precipitation in the form of ammonium metavanadate and polyvanadate from alunite processing solutions is studied. The degree of precipitation of vanadium-containing sediment is determined, depending on solution pH, the initial concentration of vanadium(V) oxide and ammonium sulphate, temperature, and contact time. The results show that ammonium metavanadate (NH₄VO₃) precipitates from the solution at room temperature at pH 8, and when the ammonium metavanadate solution is heated to 90 °C and then acidified to pH 2 and stirred, ammonium polyvanadate (NH₄)₂V₆O₁₆ precipitates. The obtained products were characterized by X-ray phase analysis, infrared spectroscopy, and scanning electron microscopy.

Results of the studies of municipal sewage sludge (MSS) oxidation during pumping a water-oxygen fluid through its bed under uniform (1.5 K/min) temperature ( T ) rise up to 733 K are presented. The temperature dependences of the yield of volatile and liquid products, as well as data on the content of mineral components in the ash residue and water collected at the reactor outlet are obtained. It follows from the temporal dependences of the reactor wall temperature, the power of the ohmic heaters, and the degree of carbon burn-up that the major part of MSS organic matter is oxidized at T < 602 K. According to the data of IR spectroscopy and ultimate analysis, an increase in the oxidation duration and temperature leads to a decrease in the content of hydroxyl and amide groups and an increase in the proportion of aromatic compounds in liquid products. The volatile products obtained at T > 673 K contain only inorganic substances - CO₂, CO, N₂, and NH₃. It is revealed that the major part of nitrogen in the form of NH₄⁺ ions passes into the aqueous phase, while the elements Si, Ca, Al, Fe, P, S, K, Na, and Mg are concentrated in the ash residue.

The article presents a geochemical interpretation of data on the physicochemical properties and individual composition of oils and condensates from the Bovanenkovo and East-Bovanenkovo fields (the distribution of light hydrocarbons (HC) C₃-C₈, n -alkanes, acyclic isoprenanes, steranes, terpanes, arenes). The main purpose of this study is the identification of the main sources of HC fluids, as well as geological and geochemical processes that have affected their composition and the formation of deposits. It is shown that the formation of naphthides from both fields occurred in several stages with the participation of the organic matter (OM) varying in genotype, in particular due to the widespread processes of secondary migration and reformation of primary deposits. Oils and condensates from the Jurassic deposits of the Bovanenkovo field were established to have a genetic relationship with the terrestrial OM of the Lower and Middle Jurassic strata, which was a source of both liquid and gaseous hydrocarbons and subsequently formed these oil and gas accumulations. It is assumed that the naphthides of the Neocomian part of the section are derivatives of the aquatic OM in the Bazhenov formation. These gas-condensate deposits during their formation were differently enriched with light components generated by the terrestrial OM of the Lower and Middle Jurassic strata. The effect of biodegradation processes on the composition of condensates of the Aptian and Albian-Cenomanian deposits was recorded. Their formation is considered having occurred due to the carbonaceous OM of the Cretaceous strata, which served as a source of primary “immature” condensates with terrestrial composition, which were mixed with secondary-migration HC fluids generated by: the aquatic OM of the Bazhenov formation in the case of gas condensates of the Aptian deposits; terrestrial OM of the Lower and Middle Jurassic strata in the case of the pools of the Albian-Cenomanian reservoir. In addition, the naphthides formed with the participation of aquatic OM are observed to be confined to the East-Bovanenkovo field and the southeastern part of the Bovanenkovo field.

In connection with depleting light oil reserves, oil fields with an increased content of paraffin hydrocarbons and resinous-asphaltene components characterized by high density, viscosity and pour point values are increasingly being put into operation. Their extraction is accompanied by the formation of asphalt-resin-paraffin deposits on the walls of technological equipment and, as a result, leads to additional material expenses associated with increased wear of equipment. The influence of the magnetic field on the structural, rheological and energy characteristics of two kinds of oil, differing from each other in composition, and their emulsions (10 wt. % water) was studied. After magnetic treatment, the component composition of the studied oil-containing systems changes. The effect of the magnetic field on low-paraffin, highly resinous oil is accompanied by an increase in viscosity within the whole temperature range. The viscosity of high-paraffin oil changes only slightly after processing, however, a decrease in the pour point is observed.