The paper analyses a network with given input and output flows in each of its nodes. The basis of this analysis is the algorithm for determining the set of solutions of the linear equations system, using the Gaussian method. The power of the set determines the structural entropy of the system. By introducing uncertainty into the value of part of the information flows, the deviation of the network from its equilibrium state is simulated. The set of potential solutions, as a part of the total set of the system solutions, determines the statistical entropy of the system. The probability entropy is calculated for a network with four nodes and a total flow of 10 erlangs with a sampling step of 1 erlang. Calculated entropy values for 1, 2, 3, and 4 uncertain flows out of a total of 16 flows that are transmitted between nodes of the fully connected network. As a result of the conducted statistical analysis of entropy values, the optimal number of statistical intervals for entropy values is determined: 4, 11, 24, and 43 intervals for 1, 2, 3, and 4 uncertain flows, respectively. This makes it possible to highlight the set of flows in the system that have the greatest influence on the entropy value in the system. The obtained results are of practical importance, as they enable the detection of deviations of the network from its equilibrium state by monitoring the passage of traffic on individual branches of a complex telecommunication network. Since, as shown in our previous works, the task of determining the complete set of solutions of the system for the number of nodes greater than 4 has a significant computational complexity, the application of the algorithm to such networks requires an increase in the discretization step of the values of information flows in the network. Another way to reduce computational complexity can be to reduce the set of analysed solutions to a subset of solutions close to the equilibrium state of the system. © 2022 Lviv Polytechnic National University.

The paper proposes a model of an electromagnetic radiation sensor that uses the precession of the magnetization vector in a ferromagnet (ferromagnetic resonance) as a result of absorbing the energy of an incident electromagnetic wave, the generation of a spin current as a result of this precession, the generation of a spin-polarized current as a result of the passage of a spin current in a non-magnetic metal, and a change in the direction of magnetization of a ferromagnetic layer with a low coercive force (free layer) due to the passage of a spin-polarized current. Then the radiation will be detected by its effect on the electrical resistance of the entire structure, which depends on the mutual directions (parallel or antiparallel) of magnetization of the free and fixed (with a large coercive force) ferromagnetic layers (phenomenon of giant magnetic resistance). The dependence of the spin-polarized current in the device on the frequency and amplitude of the incident electromagnetic wave with linear polarization was calculated. A method of calculating the range of amplitude and frequency values of radiation that can be detected by the sensor has been developed. The parameters of this model are the detection time and the number of spin gates in one sensor. Calculations are given for a ferromagnetic layer made of permalloy and for spin valves with four different critical current values that determine the process of remagnetization of the free layer: 20, 50, 100, and 200 microamps.

The article is devoted to modelling the growth of thin films on the surfaces of crystals having a similar crystal structure with a small parameter of mismatch of the lattice of substances from which the film and the crystal substrate are formed. A review of modelling methods based on both analytical expressions and computational methods is made. A number of methods for modelling the most typical processes: surface formation in the form of pyramidal formations (so-called needle crystals), two-dimensional with initial islands of growth and three-dimensional uneven growth processes. To model the process of growth of needle crystals, it is proposed to use a method based on Gaussian statistics of surface height increments. The model of three-dimensional growth of the crystal surface, which uses the iterative algorithm of Foss, and which makes it possible to investigate the processes of stepped, uneven growth of crystals, is also considered. In contrast to stepwise growth, a model of submonolayer growth of a film based on the Monte Carlo method is considered. For submonolayer growth of the film, pseudo-random sequences are used, which simulate the initial arrangement of the nuclei of the nucleus of the next layer on the crystal surface. The computational characteristics of this method are determined, namely the dependence of the number of iterations on the initial surface filling coefficient. 

The properties of the spin-valve structure, based on two ferromagnetic layers divided by a layer of non-magnetic metal, in the geometry of the current perpendicular to the plane are modeled. In addition to well-known classical twochannel conductivity model proposed by Nevill Mott, the developed model takes into account spin scattering on the surface between structures. The developed model uses equivalent electrical circuits to simulate a spin valve with parallel and antiparallel alignment. On the basis of this model, the dependences of the giant magnetic resistance on two geometric parameters of the structure—the ratio between the thickness of the free and the thickness of the fixed layers, and their ratio to the length of spin diffusion—are derived. Based on the developed model, numerical data are obtained for the spin valve, where the ferromagnetic layers are made of cobalt, permalloy, iron, and nickel. The portion of surface scattering in the giant magnetic resistance is also investigated. A general conclusion is made about the slight increase of the giant magnetic resistance due to the influence of surface scattering for structures based on cobalt, permalloy, and iron, but not for nickel. This outlines the scope of applicability of the developed model. 

The authors of the article consider decelerating structures made of homogeneous material, which have a periodic structure in space. Such systems are used to concentrate the energy of high-frequency electromagnetic waves in order to increase the sensitivity of devices designed for their registration, increase the efficiency of the interaction of a beam of free electrons with a slowed electromagnetic field, for the manufacture of structural elements in waveguide devices, and for generators of monochromatic radiation in the terahertz and optical ranges (effect Vavilov-Cherenkov radiation). The parameters of the wave process are studied on the basis of an exact analytical solution based on the cylindrical Bessel and Hankel functions for a decelerating system with axial symmetry in the form of a spiral. To obtain numerical solutions, the optimization problem of the system of nonlinear equations of a complex variable is solved. The conducted studies establish the relationship between the transverse and longitudinal wave numbers and the attenuation coefficient of the electromagnetic wave. A detailed analysis of the solutions of the equation showed that, in addition to the classical solution that determines the surface wave, other solutions are possible for which the concentration of the electromagnetic field inside the structure is higher.