Hacotization of discretization and quantization conditions in radar systems with digital phased antenna grates

The article establishes a connection between the directional properties of digital phased array antennas (FAR) in radar systems by means of space-time signal processing, based on the use of stochastic quantization scales in time, space and level, leading to a decrease in the influence of sampling noise and quantization in the process of diagram formation and the formation of frequency selectivity "narrowed" (in the usual and spatial frequencies - angular directions) frequency channels, formed by increasing the size of spatial and temporal samples.

Mathematical modeling of biological tissues electrical conductivity based on the ion electrodiffusion equations

Problem formulating. The vital processes of biological tissues are closely related to their electrical properties. An important task is to create a physical and mathematical model that will link the electrical properties of tissues to their physiological state. Goal. Construction of a model of biological tissue electrical properties based on the equations of ion electrodiffusion. Result. The paper presents the model of biological tissue electrical properties based on the ion electrodiffusion equations, and compares the simulation results with the experimental results presented in the literature. Practical meaning. The presented model can be used to describe processes occurring in tissue at the level of concentration and conductivity of ions in individual cells and cell membranes. In particular, the process of tissue degradation during laser radiation heating can be described.

Development of the instrumental support of the domestic computing platform "Elbrus 801-PC" in the problems of neural network modeling of nonlinear dynamic systems

The development of tools for solving research problems with the use of domestic software and hardware is an urgent direction. Such tasks include the tasks of neural network modeling of nonlinear controlled systems. The paper provides an extended analysis of the capabilities of the Elbrus architecture and the blocks of the built-in EML library for mathematical modeling of nonlinear systems. A comparative analysis of the instrumentation and efficiency of computational experiments is performed, taking into account the use of an 8-core processor and the potential capabilities of a 16-core processor. The specifics of the EML library blocks in relation to solving specific types of scientific problems is considered and the optimized software is analyzed. The design of generalized models of nonlinear systems with switching is proposed. For generalized models, a new switching algorithm has been developed that can be adapted to the Elbrus computing platform. An algorithmic tree is constructed, and algorithmic and software are developed for the study of models with switching. The results of adaptation of the modules of the software package for modeling managed systems to the elements of the platform are presented. The results of computer modeling of nonlinear systems based on the Elbrus 801-RS computing platform are systematized and generalized. The results can be used in problems of creating algorithmic and software for solving research modeling problems, in problems of synthesis and analysis of models of controlled technical systems with switching modes of operation, as well as in problems of neural network modeling and machine learning.

Controlling the adsorption of mineral porous particles by chelation

Problem formulating. To increase the sorption capacity of calcium carbonate microparticles used as core for the development of targeted drug delivery, EDTA chelation of calcium ions was used to form a developed active surface of the particles. Goal. Is in modification of the surface of micron and submicron calcium carbonate vaterite particles using EDTA chelation of calcium ions and studying the effect of particle processing on their sorption capacity. Result. It was shown using scanning electron microscopy that EDTA treatment of the CaCO3 surface leads to an increase on the surface roughness of the particles, as well as an increase on their sorption capacity according to spectrophotometric data. Practical meaning. Use of adsorption to encapsulate the active substance inside the carriers. It is shown that an increase in the sorption capacity of particles leads to an increase in the amount of a substance inside its volume.

Terminal filtering of stochastic processes observed on a finite time interval

Annotation. Currently, the problem of evaluating stochastic processes observed under noisy conditions on a finite time interval is solved only for datasets in the form of time series using a limited number of statistical variational or spectral analysis methods, as well as various modifications of regression methods. In this case, parametric criteria are used that depend on individual parameters of the distribution density of the observed process, and not on the density itself, which significantly limits the possibilities of increasing the estimation accuracy. To solve the problem of high-precision estimation of stochastic processes on a finite time interval of their observation, an approach is proposed, firstly, providing optimal estimation according to the criterion depending on the posterior distribution density - the most informative characteristic of the observed process, and secondly, taking into account the dynamic structure of the process and the finiteness of the interval observation. A numerical example is considered to illustrate the effectiveness of the developed approach. Relevance. Currently, the problem of evaluating stochastic processes observed under noisy conditions on a finite time interval (terminal filtering problem) is solved only for datasets in the form of time series using a limited number of statistical variational or spectral analysis methods, as well as various modifications of regression methods. In this case, parametric criteria are used that depend on individual parameters of the distribution density of the observed process, and not on the density itself, which significantly limits the possibilities of increasing the estimation accuracy. Target. In this regard, for stochastic processes of a general form - described by nonlinear stochastic differential equations, it is necessary to develop a method of terminal filtering according to a criterion that takes into account the finiteness of the observation time interval and depends on the posterior distribution density - the most informative characteristic of the observed process (and not on its individual parameters). Results. The proposed solution to the problem of high-precision terminal filtering of stochastic processes - their optimal estimation over a finite observation time interval - is based on the use of a terminal criterion that depends directly on the posterior distribution density and takes into account the finiteness of the observation time interval. When describing the observed stochastic processes, their most general representation was used - nonlinear stochastic differential equations, which significantly expands the field of application of the results obtained in comparison, for example, with time series. The general solution to the problem of optimal terminal filtering is obtained using the Pontryagin maximum principle, the solution to the problem of suboptimal filtering, which significantly reduces computational costs, is based on the method of invariant immersion. Practical significance. A numerical example is considered to illustrate the effectiveness of the developed method. The proposed approach can be widely used in various fields of scientific and technical research: radio engineering, Earth sensing, satellite navigation, astronomy, seismology, geodesy, etc.

Application of the extended Mattis-Bardeen theory for the calculation of reflection coefficient of superconducting NbTiN thin films

Problem formulating. NbTiN is becoming the subject of interest because of unique properties in RF. Therefore, the problem of investigation of this material’s electrical properties rises sharply. Goal. This work is aimed at theoretical description of the superconductive films’ reflection coefficient with considering imaginary part of the superconductive gap and to apply the results to calculate the reflection coefficient from NbTiN film at frequencies up to 2500 GHz. Result. The formulas for calculation of the reflection coefficient with high precision was obtained. Parameters of NbTiN were calculated. Practical meaning. Currently there are many factors which reduce the quality of NbTiN films and thus restricting their application. Therefore, the proposed method of calculations is useful in research activities in this area.

Agglomerative clusterization with DBSCAN algorithm and iterative method

The tasks of grouping, classifying, and clustering data are widely encountered nowadays in different areas of activity. These tasks need to be solved in librarianship and even in social networks. One of the complex and important tasks is a grouping of normative and reference information. Solving this problem will allow us to perform complex operations with the normativereference information: building a hierarchical structure from scratch, adding new entities or groups to the existing, and combining several lists of normative-reference information independently of the original hierarchical structure presence. This article includesdescription of using DBSCAN as an agglomerative-iterative clusterization algorithm. The iterative part of this algorithm is necessary forfull entity list clusterization on every hierarchical level. Clustering metrics such as adjusted Rand index, Jaccard index, Foulkes-Mallows index are considered. A new metric based on the previously mentioned metrics has been proposed. A combination of Word2Vec and TF-IDF algorithms is used to convert the textual names of objects to numerical form.

Negative conductivity of graphene with direct electric current

Problem formulating. Currently, there are no compact, efficient terahertz radiation sources operating at room temperature. To create such sources and amplifiers, structures based on graphene with DC-current can be used. Goal. Finding conditions for achieving the negative real part of graphene conductivity and amplification of THz radiation in graphene with a direct electric current. Result. It is shown that for a certain value of direct electric current in graphene, the reflection coefficient of the THz wave incident on the structure based on graphene with DC-current exceeds unity, which indicates the amplification of THz radiation in the structure. The amplification of the THz radiation in graphene is achieved due to negative values of the real part of the graphene conductivity. Practical meaning. Results can be used to create sources and amplifiers of terahertz radiation.

Design and analysis of a mathematical model of the motion of a heterogeneous fluid in a well

The development of methods for modeling the motion of fluid in a well is an urgent area of both theoretical and applied interest. In mathematical modeling of real processes of fluid motion, it is possible to use a description using continuous distributions and use a well-developed apparatus of continuum mechanics and differential calculus. The purpose of the work is to synthesize and analyze a model of the motion of a heterogeneous fluid in a well based on the methods of continuum mechanics and differential calculus. The issues of constructing and studying models of the motion of a multiphase fluid in a well are considered. Systems of equations of conservation of phase masses, momentum and energy of a two-phase mixture are studied. The approach to the search for the optimal pressure of liquid supply to the well and to the estimation of the velocity distribution of liquid and particles is described. The results can find applications in modeling processes related to fluid movement, as well as in the development of technologies in the oil and gas industry, as well as technologies aimed at ensuring environmental safety.

Features of the photoconductivity of the quasi-one-dimensional compound TiS3

Problem formulating. The features of linear and nonlinear conductivity, magnetic conductivity, thermopower, and the Hall effect observed on TiS3 whiskers indicate phase transitions to a state of CDW in this compound, but there is no direct evidence yet. The study of photoconductivity would allow us to learn more about the nature of these phase transitions. Goal. Study of the effect of radiation in the range from near-IR to near-UV on the conductivity of single-crystal TiS3 whiskers at 4.2 <T<300 K and search for features of photoconductivity in the temperature range of the suggested phase transitions. Result. Features of the photoconductivity of TiS3 at temperatures of 50 K and 15 K, at which the −dlnσ/d(1/T) maxima were previously observed, are found. A decrease in photoconductivity at these temperatures indicates a change in the electronic spectrum, which may be associated with the formation of CDW. Practical meaning. In the case of developing TiS3-based photosensors, it is important to study the photoconductivity in a wide temperature range.