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Lebedev Konstantin Andreyevich
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Articles count: 13
Сформировать список работ, опубликованных в Научном журнале КубГАУ
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ADAPTIVE TIME SERIES MODELS OF A MOUNTAIN RIVER LEVEL
01.00.00 Physical-mathematical sciences
Description
The article presents a technique of short-term forecasting of water level in the river bed of a mountain type using Markov’s chains
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MATHEMATICAL MODEL OF THE DYNAMICS OF HIV INFECTION WITHOUT TREATMENT
01.00.00 Physical-mathematical sciences
Description
This article discusses the mathematical and numerical modeling of the immune system of the course of HIV infection without treatment. Presently a significant number of scientific papers are devoted to the study of this problem. However, HIV infection is highly volatile and there is no effective drug, in that HIV has the ability to mutate and reproduce itself in the presence of chemical substances that are meant to inhibit or destroy it. The mathematical models used in this paper are conceptual and exploratory in nature. The proposed mathematical model allow us to obtain a complete description of the dynamics of HIV infection, and also an understanding of the progression to AIDS. Thus, the results of the numerical solution of differential equations in this work show that: the disease develops, and at low concentration of the virus, a certain level of stability does not depend on the initial concentration of infestation. In the absence of treatment, for interesting competition between virus and the loss of virus caused by immune response should be strictly greater than the rate of multiplication of the virus in the blood; the reproduction rate of the uninfected cells should be stricly greater than the mortality rate of the uninfected cells
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01.00.00 Physical-mathematical sciences
Description
The article presents a mathematical model of the ion transport across phase boundary exchange membrane / solution. The border is considered as an object in space, endowed with all the physical and chemical properties that are inherent physical and chemical phases. It is regarded as a special physical and chemical environment, having a distributed exchange capacity in which there is space charge dissociation of water molecules. The size of this object is estimated in the range of 1-300 nm. The surface morphology of industrial membrane type MK-40, МA-41 and МA-41P was investigated experimentally by scanning electron microscopy (REM). There was analyzed the amplitude of average surface roughness. In this article, the reaction layer is modeled as a region that forms as a relief morphology of the membrane. Membrane properties are due to the properties of the solution and the properties of the membrane. To determine the dependence of Q(x) is proposed procedure for assessing the proportion of solid phase in the total volume of which can be seen in the vertical cross section microprofile on the membrane surface line. Height multivendors determine the reaction layer zone on frame of model. Influence of surface morphology on the V-A characteristics and the sizes of the convective instability of cation-exchange membrane evaluated numerically simulating the hydrodynamic flow conditions using a solution of the Navier-Stokes equations. The transfer of a strong electrolyte such as NaCl ions through the thin layer of the reaction layer is considered. The place of nanomodel in the structure of a three-layer membrane system is showed. The distribution of the concentration of ions in the system, the charge density distribution and the dependence of the integrate charge with extent nanolayer is present. How to change the shape of the space charge and its integral value with one is investigated
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Description
Theoretically and experimentally, we investigated the process of adjusting the pH of natural water of hydrocarbonate class electrodialyzer with bipolar membranes with channel length of 40 cm. We experimentally measured concentration of components, pH of the solutions in alkaline and acid channels of electrodeposition depending on the current density. The article describes a mathematical model for long channels; to scale the mass transfer characteristics of the process there was applied and verified a method of compartmentalization, which gave the possibility to calculate the dependence of the component along the channel length at different velocities of flow of the solution. Numerical calculations were compared with experimental data on electrodialyser of 10 cm and 40 cm length
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01.00.00 Physical-mathematical sciences
Description
In the article we build a mathematical model of elec-tro-diffusion of ions in the diffusion layer of a mem-brane system complicated by the occurrence of the previous slow homogeneous chemical reaction with the condition of electrical neutrality of the solution. We have set a two-point boundary value problem and developed a method to solve it; we have given an algorithm and a numerical method for solving it in Comsol 3.5 environment. The formula for limiting kinetic current was derived. Some of the model’s capabilities to describe the properties of the system are given
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01.00.00 Physical-mathematical sciences
Description
In this article we consider a mathematical model of effect of non-compliance with the prevention of HIV/AIDS among a heterogeneous population based on known model by Kimbir et al (2006). The effectiveness of a condom use and implications of non-compliance with a population of preventive measures (condoms) are the aim of this research work. In this work, with definite coefficients, nonlinear model is used, which consists of system of six differential equations for different population groups (six groups of the population) to obtain the model equations. Compared with the existing model by Kimbir, the proposed model to a large extent, takes into account the birth rate of the studied population. Numerical simulation of the model equations shows that reducing the rate of transmission of HIV/AIDS can be effectively achieved within a certain time, and only where relatively high condom efficacy and high compliance by susceptible and infected are observed. From the obtained results, we can see that the control of HIV/AIDS in the heterosexual population depends on the net compliance and effectiveness of the recommended prevention (condom use). As a recommendation, the model focuses on intensive training and ongoing campaigns to raise the awareness of the population by governmental and non-governmental agencies on the effective use of the condom
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01.00.00 Physical-mathematical sciences
Description
Following the absence of a definite treatment for the human immunodeficiency virus (HIV) or the acquired immune deficiency syndromes (AIDS) since their appearance, many scientific studies with the help of mathematical models have been formulated to the extent possible to prevent and eradicate the disease. In this article we have formulated a mathematical model that explores the dynamics of the impact of the use of condom and therapeutic treatment simultaneously, as a means (tools) against the spread of HIV/AIDS in the heterosexual population. The proposed model uses a nonlinear differential equation system consisting of seven (7) differential equations in seven (7) groups of the population. The model takes into account natural birth rate of the studied population, and the proportion of infected males, which simultaneously uses condom and antiretroviral therapy. The model explores the behavioral change of proportion of infected individuals in the population following the application of control measures (condom use and antiretroviral therapy). It is proved that the effectiveness of preventive measures greatly depends on a number of parameters described. In addition, the results of numerical experiments showed that in the absence of both preventive measures, the entire population is contaminated with the infection. The interaction of the model parameters show that the population with high levels of condom use in the presence of significant adherence to antiretroviral therapy as prophylaxis significantly reduces the level of HIV/AIDS. Thus, prevention of infection is significantly improved with the increasing number of the infected population using condoms and antiretroviral therapy simultaneously
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01.00.00 Physical-mathematical sciences
Description
In this article we propose a method of determining the share or the significance (weight) of indicators of Beaver and risks R in the portfolio formed by these parameters allowing us to minimize the mean square error evaluating the effectiveness of the portfolio (risk) in the assessment of the financial condition of the companies investigated. The proposed method is the minimization of a quadratic form in variables satisfying lengthy conditions, i.e. the quadratic programming. This technique is implemented using four methods of optimization: analytical method, using built-in function minimization block given, the penalty function method and the gradient method. More so, this technique allows, as shown by the results of the computational experiments, the expert without routine statistical data processing to obtain additional information on the credit worthiness of the investigated enterprise and make a more informed conclusion about its financial condition, which speeds up the decision on granting a loan required by a company. Based on the techniques proposed in this paper, other techniques of assessing the creditworthiness of businesses may be constructed using the results of optimization theory based on well-established applied research methods: Method of evaluating the creditworthiness of Russia, Credit scoring method, the American method, method of Altman and others
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01.00.00 Physical-mathematical sciences
Description
In this article we propose a method that uses the apparatus of the theory of fuzzy sets, together with the five-factor model of Altman in assessing the creditworthiness of an enterprise. Altman's model works in two ways: It applies the root mean square (RMS) integral approximation for the exact calculation of quantitative assessment of creditworthiness (probability of bankruptcy), and using the device of fuzzy sets for ordered sets by the degree of confidence in the resulting probability. In this paper we conducted simulation procedure for the credit assessment and showed the capabilities of the model. The model input parameters , forms system inputs (input variables), allowing you to get the value of the parameter z of Altman. With the help of Altman's model, approximating function L6, the decision function I(p) and the algorithm for calculating preference we obtain the number of the set i to which belongs a number of ordered sets as fuzzy logic . On the selected simulation parameters, stable statistics can be obtained. Altman's model with the use of computational function allows real values of the input parameters of the enterprise replaced by random values of the simulation model. This technique allows, as shown by the results of computational experiments, the creditor to obtain additional information on the creditworthiness of the investigated enterprise and make a more informed conclusion about its financial condition, which speeds up the decision on the possibility of issuing the required credit. The development of method of estimating fuzzy logic can be applied to other models of assessing the creditworthiness of a company: Davydov's model, Zaitseva's, Saifullina's, Kadykova's and others with appropriate modification
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01.00.00 Physical-mathematical sciences
Description
In this article we have proposed a method using the apparatus of fuzzy sets theory in conjunction with the five-factor model of Altman to assess the creditworthiness of the investigated companies. The Altman model was improved in two ways: by using RMS integral approximation for the exact calculation of the quantitative credit assessment (probability of bankruptcy) and the application of the apparatus of fuzzy sets for ordered sets by the degree of confidence resulting probability
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