Volume 7 Issue 3


Volume 7 Issue 1

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Lesko S.A.,
Alyoshkin A.S.,
Filatov V.V.

Stochastic and percolating models of blocking computer networks dynamics during distribution of epidemics of evolutionary computer viruses

The paper presents a complex model of the dynamics of virus epidemies propagation in computer networks, based on topological properties of computer networks and mechanisms of the viruses spread. On one hand, this model is based on the use of percolation theory methods, which makes it possible to determine such structural-information characteristics of networks as the dependence of the percolation threshold on the average number of connections per one node (network density). On the other hand, the dynamic processes of stochastic propagation in computer networks of evolving viruses are observed when anti-virus programs become outdated and postponed. The paper discusses the concept of percolation threshold, provides an equation for the dependence of the percolation threshold of a network on its density obtained by analyzing numerical simulation data. The dynamics of virus epidemies were studied through two approaches. The first one is based on the description of transition diagrams between states of nodes, after which a system of kinetic differential equations for the virus epidemies is constructed. The second is based on considering the probabilities of transitions between possible states of the entire network. A second-order differential equation is obtained in this article, and a boundary value problem is formulated. Its solution describes the dependence of the network blocking probability on the blocking probability of an individual node. The solution also makes it possible to estimate the time required to reach the percolation threshold. The model incorporates the evolutionary properties of viruses: previously immunized or disinfected nodes can be infected again after a certain time interval. Besides, the model incorporates a lag of the anti-virus protection. Analysis of the solutions obtained for the models created shows the possibility of various modes of virus propagation. Moreover, with some sets of values of differential equation coefficients, an oscillating and almost periodic nature of virus epidemies is observed, which largely coincides with real observations.

Keywords: computer model evolving viruses, oscillating dynamics of computer viruses epidemies, lag times, state transition graphs, stochastic processes, percolation threshold of networks with random topologies.



Bekkiev A.Yu.,
Makoviy V.A.

Impulse noise parameter assessment in a batch radio channel 14

Modern radio communication means to provide safe data transmission due to adapting radio channel to the actual noise environment. It is impossible to conduct proper comparative tests on various radio stations offered by manufacturers and to compare objectively the results obtained in field without actual signal parameters and noise environment instrument inspection at the reception point. The paper considers tactical level radio communications system operation when jammed with powerful impulse noise of various nature. It suggests a device enabling to assess the main parameters of impulse noise, namely desired signal and additive noise mixture envelope effective value, impulse noise envelope effective value, impulse noise duty factor. To provide measurement independence from a specific realization of a decoder it is suggested to use the envelope of a signal received by a radio station. The developed device uses standard radio channel data batches as measuring signals and does not require changing radio channel or radio network algorithms and timing charts. A method to assess the effective value of desired signal envelope and additive noise mean-square value when the received signal involves impulse noise is suggested. The paper demonstrates that valid assessment of desired signal and additive noise mixture is possible in case of setting aside selection values affected by impulse noise. A device separating symbols affected by impulse noise from those that are not affected is suggested. Formulas that allow synthesizing the device operation algorithms are obtained. The structure chart of the measurer is developed; the algorithms used to assess measured parameters are given.

Keywords: tactical control unit, impulse noise, measuring instrument, impulse noise parameters.



Vigdorovich E.N.

Radiation resistance of epitaxial structures based on GaAs 10

This paper presents the results of a study on the irradiation of heterostructures based on gallium arsenide with neutrons and gamma rays. The horizontal channel of the IRT-2000 reactor with an energy of 2.65 MeV served as a source of neutrons. Two types of structures were considered: autoepitaxial (AES) and heteroepitaxial (HES). They were obtained by the MOC-hydride method under reduced pressure using gallium and aluminum organometallic compounds and arsine. The obtained results show that irradiation with neutrons and gamma-quanta just slightly changes the concentration of the charge carriers of the autoepitaxial structures and the density of the charge carriers of the heteroepitaxial structures. As for the mobility of charge carriers, some increase in their mobility is observed at the initial moment of irradiation. As the irradiation flux density increases, the mobility either stabilizes at a certain level or decreases. The increase in mobility after the first irradiation of the heterostructures indicates an increase in the lifetime of charge carriers, apparently due to a decrease in the concentration of recombination centers in the structures, most likely, the density of structural defects at the heteroboundaries. When irradiating with fast neutrons, a similar picture is observed. Initially, the mobility of charge carriers slightly increases as the concentration of charge carriers slightly changes. Then the characteristics stabilize. An increase in the uniformity of properties over the area of the structures is observed. It is assumed that this is due to the appearance of clusters of defects and impurities.

Keywords: gallium arsenide, irradiation, autoepitaxial structures, heteroepitaxial structures, charge carrier concentration and mobility.


Ilyin N.A.,
Klimov A.A.,
Tiercelin N.,
Pernod P.,
Mishina E.D.,
Gaponov M.S.,
Brekhov K.A.,
Sigov A.S.,
Preobrazhensky V.L.

Dynamics of magnetization in multilayer TbCo/FeCo structures under the influence of femtosecond optical excitation 21

The need to study ultrafast processes in magnetism is due to the prospects for creating ultrafast magnetic recording and ultrafast spintronic devices. In order to excite the magnetic subsystem femtosecond optical pulses are used. The excitement is manifested as in spin precession. In metals, the material is heated first due to significant optical absorption, and significant Joule losses occur. The most important task is to search for materials in which spin processes are excited without heating. Obvious candidates are weakly absorbing materials, such as ferrite garnets. However, the range of such materials and the range of their functionality are limited.The purpose of this work is to study the dynamics of systems with nonthermal mechanisms of spin precession excitation. Such excitation is possible in ferromagnetic / antiferromagnetic heterostructures with exchange interaction, provided that the recombination time of photocarriers is shorter than the time of heat diffusion. Multilayer TbCo / FeCo structures of the near IR range were investigated for a femtosecond optical pulse. The spin dynamics are compared with the direction of the wave vector of the exciting pulse along and perpendicular to the axis of easy magnetization of the structures (“easy axis” and “hard axis” geometry, respectively). It is shown that in case of “easy axis” geometry the determinative mechanism is the thermal interaction. When the system is exposed to an excitation pulse, this mechanism leads to a decrease in the projection of magnetization on the direction of propagation of the test beam. In case of “hard axis” geometry, the magnetization turns to the magnetic field at the initial stage. Then it precesses and relaxes to an equilibrium angular orientation. Such dynamics indicate a rapid recovery of the uniaxial anisotropy field after laser irradiation. The presented results demonstrate an ultrafast change in the magnetic anisotropy induced during the fabrication of the heterostructure under study, which may be of interest for optical control of the orientation of the magnetization.

Keywords: magnetic heterostructures, optical control of magnetization, ultrafast demagnetization, ultrafast change in magnetic anisotropy, femtosecond laser light.


Mokrushina A.A.,
Yurasov A.N.

Features of modeling of the magnetorefractive effect in multilayered metal nanostructures 13

The magnetorefractive effect (MRE) is important and interesting from both fundamental and practical points of view. This effect consists in a change in the reflection coefficient or the passage of an electromagnetic wave from magnetized structures with magnetoresistance effects. It can be giant, tunnel and colossal magnetoresistance depending on the type of structure. MRE is most clearly manifested in the IR region of the spectrum and can reach tens of percent. It is possible to show its unambiguous dependence on the magnitude of the magnetoresistance. This article discusses the features of MRE in multilayer metal nanostructures with giant magnetoresistance. The MRE simulation is carried out using a model that relates this effect to magnetoresistance, as well as in the framework of the model taking into account spin-dependent scattering. The last model in earlier works allowed describing a number of experimental data well qualitatively and in some places quantitatively. In this paper, taking into account the frequency dependence of the resistance allowed us to improve the first model, which allowed us to obtain a good qualitative and quantitative description of the effect value – this is a fundamentally new result. The article highlighted the key opportunity for the application of magnetorefractive effect as a contactless method to study nanostructures, a method of nondestructive testing of all electronic components. A comparison with experimental data is also made. A good description is demonstrated in the framework of the two models considered, which can effectively describe the relationship between MRE and magnetoresistance.

Keywords: nanostructures, magnetorefractive effect, magnetoreflection, magnetotransmission, magnetoresistance, spin-dependent scattering.



Chukita V.I.,
Senokosov E.A.,
Feshchenko V.S.

The stand for research of positional-sensitive photosensor 19

The paper considers position-sensitive photodetectors (PSP), which are designed to detect the source of electromagnetic radiation in the optical range and determine the coordinates of the irradiated area in real time, as well as to track moving optical objects. In particular, data are presented on photodetectors based on photosensitive epitaxial CdSe/mica layers with an unconventional layout and switching of electrical contacts. The output signal of such PSP is the transverse potential difference that appears between its two contacts after exposure of one of the areas of the photodetector. These PSPs can be an alternative or competition to existing photocells due to high accuracy, speed, ease of manufacture and low cost. But there are significant obstacles for their wide application. First, it is an analog type of output signal, which prevents its further processing. And, second, it is difficult to calibrate “manually” a newly made photosensor: it takes a long time associated with the accumulation and processing of large amounts of data. The introduction of computer technology and the creation of an information-measuring system allow us to process the output signals of such photodetectors with high accuracy and speed in real time. To solve this problem we have developed a stand for the study of position-sensitive photodetectors, which is presented in this paper. This stand allows digitizing the signal received from the photodetector, in real time, with high accuracy to determine the coordinates of the irradiated area on the photodetector and explore its characteristics such as the specified value of the dark current of the photodetector, light current at a certain illumination, and output voltage. At this stand, position-sensitive photodetectors based on the CdS/mica system were studied. It is shown that the characteristics and parameters of photoreceivers measured on this stand coincide with theoretical ones, within the error limits. Recommendations on the use of the stand are given.

Keywords: epitaxial layer, position-sensitive photodetector, equipotential current line, microcontroller, delta-sigma analog-to-digital converter, electronic switch, programmable amplifier, indicator device.



Karpov D.A.,
Struchenkov V.I.

Dynamic programming as a method of spline approximation in the CAD systems of linear constructions

Under study is a problem of the line structure routing of roads, railways and other linear constructions. Designing a trace plan and longitudinal profile are considered as non-linear programming tasks. Since the number of elements of the plan and the longitudinal profile is not known, the problem is solved in three stages. First, a search is performed for a polyline consisting of short elements. On the second stage it is used to determine the initial approximation of the desired line, which is optimized at the last stage. The required line consists of a given type elements and it is a spline with a number of features:- In contrast to the polynomial elements considered in the theory of splines, when designing roads unknown spline is a sequence of elements: straight, clothoid, circle, clothoid, straight and so on.- In this task, the spline does not have to be a single-valued function.- The parameters of the elements of the desired spline must satisfy the constraints in the form of inequalities.These features of the task do not allow the use of non-linear programming methods to solve it. Converting a broken line to a spline is carried out using dynamic programming. For this purpose a special formalization of this task is proposed. A new algorithm of dynamic programming is given. The result is used as an initial approximation to optimize the parameters of the spline using a previously developed non-linear programming program.

Keywords: route, plan view and longitudinal section, spline, dynamic programming, object function, constraint.