Vol 62, No 12 (2017)

Existing analytical results on the propagation of electromagnetic pulse in resonantly absorbing gas medium are used to analyze possible character and features of the dispersion-induced distortions of an ultrashort frequency-modulated radio pulse with the initial rectangular shape and the carrier frequency that is close to the resonance frequency of a single strong absorption band of water vapor in the millimeter-wavelength range (183.36 GHz).

A procedure for extraction of variations in the ionospheric total electron content (TEC) caused by the presence of local regions containing small-scale irregularities of the electron concentration has been developed. The procedure employs the transionospheric sounding data obtained with the use of a double-frequency GPS/GLONASS receiver. The procedure is based on extraction of individual components of the TEC time series by applying to the series the procedure of simple sliding-window smoothing with the width of the window selected according to the period of the TEC variations caused by the various-scale ionospheric irregularities. The efficiency of the procedure is demonstrated by the actual measurement data.

A two-dimensional problem of plane wave diffraction in the optical band by two silver ribbons with elliptical cross-section is considered. The scattering and absorption spectra are calculated by rigorous numerical methods. Two variants of the relative position of the ribbons are considered. The influence of the distance between the ribbons on the form of the resonance response of the system is studied.

It is noted that the radiation pattern (RP) of an antenna array (AA) with electric control is a function of solid angles and frequency. The dependence of the properties of the RP of a linear AA on the method of control of the phases of the currents on the AA elements is analyzed.

With the popularity of the Internet, how to securely transmit and store multimedia data, and effectively access them has become an issue of great concern. High-dynamic-range (HDR) images are predicted to be a future trend and have already received considerable attention. In this study, an object-based method for sharing secret HDR images is proposed. This method comprised three steps. First, HDR images were divided into several objects and the coordinates of the objects and related information were recorded. Second, a method for sharing secret images was used to share the produced objects and recorded information, which were ranked according to importance. Third, a Lagrange interpolation method was used to reconstruct the various objects. The method can be used to maintain high information security and provide a convenient and effective image-restoration method to users. Experimental results confirmed the effectiveness of the method proposed in this study.

Orthogonal frequency division multiplexing (OFDM) a multicarrier system [1, 2] provides base for all advanced wireless communication system. The performance of OFDM is degraded by peak-to-averagepower ratio (PAPR). High PAPR requires high power amplifiers (HPAs). The nonlinearity of the HPA exhibits amplitude and section distortions, that cause loss of orthogonality among the subcarriers, and hence, intercarrier interference (ICI) is introduced inside the transmitted signal. Not only that, high PAPR put together lands up in in-band distortion and out-of-band radiation. Rather than using HPA’s, the only way to improve performance of OFDM system is to reduce PAPR. The PAPR reduction of OFDM system gives fair reduction in PAPR under partial transmits sequence (PTS) and DCT-SLM techniques. Here in this paper we proposed a combination of PTS and DCT-SLM and an algorithm to cut back the PAPR. This hybrid combined technique reduces PAPR effectively and minimizes the complexity of PTS technique.

The step-by-step method is used for the analysis of propagation of electromagnetic waves in a multilayer structure of a finite length with periodic irregularities of the permittivity, permeability, and conductivity. The distribution of the wave amplitudes in the structure layers is considered and two its main types, sinusoidal and exponential, are revealed. Passbands and stopbands in frequency dependences of reflection and transmission coefficients are found. Parameters of these passbands and stopbands are determined by the combination of the periodicity of irregularities and the finiteness of the structure length. In the case of the tensor permeability, an additional stopband caused by gyrotropic properties of the magnetic medium is found. For the case of a conducting medium, the excess of the normalized amplitude of propagating waves over the unit level is considered and possible factors that cause its appearance are discussed.

An analytical model describing the behavior of a three-dimensional bounded bunch in a nonuniform magnetic field is constructed. The model reduces the description of the dynamics of the phase portrait to solving a system of ordinary differential equations. A particular solution of the system, illustrating the capabilities of the model, is presented.

An approach to the development of function-oriented microcontrollers with the hardware support of fuzzy computations, the using of which makes it possible to improve the accuracy and speed of data processing and control systems and diminish the laboriousness of designing of the given systems, is proposed. The issues concerning the hardware prototyping of fuzzy solvers are discussed, and the examples illustrating the experimental estimates of their characteristics as against existing solutions are presented.

It has been revealed in experiments that, based on the thermal influence of gases on the surface acoustic wave propagating in a hot acoustic transmission line, it is possible to efficiently detection hydrogen without using gas-sensible coatings. It order to increase the sensitivity, the acoustic transmission line of the sensor is made of a piezoelectric crystal of В₁₂SiO₂₀ with large temperature coefficient of delay and the total phase shift and delay of the wave between radiating and receiving transducers are increased owing to propagation of this wave through two cylindrical roundings. When concentrations are in a range of 0.1–3.2%, the acoustothermic response to hydrogen by an order of magnitude exceeds responses to O₂, CH₄, NO, and water vapor of the same concentrations. Owing to the absence of a gas-sensible coating, the long-term stability of detection is high and is less than ±2% during six months.

The problem of decision theoretic online learning is discussed. There is the set of methods, experts, and algorithms capable of making solutions (or predictions) and suffering losses due to the inaccuracy of their solutions. An adaptive algorithm whereby expert solutions are aggregated and sustained losses not exceeding (to a certain quantity called a regret) those of the best combination of experts distributed over the prediction interval is proposed. The algorithm is constructed using the Fixed-Share method combined with the Ada-Hedge algorithm used to exponentially weight expert solutions. The regret of the proposed algorithm is estimated. In the context of the given approach, there are no any stochastic assumptions about an initial data source and the boundedness of losses. The results of numerical experiments concerning the mixing of expert solutions with the help of the proposed algorithm are presented. The strategies of games on financial markets, which were suggested in our previous papers, play the role of expert strategies.

Two problems of data representation by means of convex polyhedra are considered. In the first problem, it is required to exclude from a finite set of points X the points that are not vertices of the convex hull of X. An algorithm based on solving a series of linear programming problems is developed. Its computational complexity is asymptotically lower than the complexity of a convex hull constructing, and it requires much less additional memory than for constructing a convex hull. The second problem consists in finding the minimal subset of inequalities in a system of linear inequalities whose solution set coincides with the solution set of the initial system. It is shown that this problem can be solved similarly to the first one, and the solution algorithm can be extended to the case of nonlinear inequalities. Randomized improved versions of both algorithms are proposed.

The convolution kernel based on the geodesic distance has many advantages because it admits recursive computation and, therefore, fast image processing. Besides, the interpolation quality in some channels increases in the presence of additional image channels with a higher resolution as compared to the interpolated image layer, which is important for solution of the problem of multispectral image interpolation. In this paper, the quality is estimated using several criteria, in particular, the structural similarity index. In the experimental part of the paper, the evident advantage of the proposed interpolation over traditional methods (in particular, the bicubic and bilinear interpolation) is shown.

A variation-based approach to formation of the topological characteristics of two-dimensional signals is proposed. Application of these characteristics for the metric estimation of the local parameters of images is considered. Concepts of the object convexity size and amplitude indices are introduced and a technique for their calculation is proposed. The use of these parameters for detecting the noise and the objects of different dimensions in grayscale and multispectral images is demonstrated. Theoretical conclusions are confirmed experimentally.

A tandem queuing system that contains two single-channel stations with finite buffers and allows blocking of the first server is considered. The first station receives nonstationary Poisson packet flow that is processed at a controlled rate. In the case of the queue overflow in the first system, the input packet is lost. The second station does not allow overflow due to control of the acceptance probability (a decrease in such a probability leads to slowing of packet sending from the first station). The queuing system is described with the aid of the controlled Markov process. The optimal control problem is considered over a finite time horizon using the criterion of minimum average losses under the constraints on the total service time and energy consumption of the first station. Optimization algorithms are proposed for synthesis of the control law for nonstationary data flow in two-agent robotic system.

The paper presents an analysis of the combinatorial evolution and prediction of modular systems in application to requirements to communications. A hierarchical model of the system of requirements is used (local alternative variants of modifications, their characteristics, tree-like structure over local modifications). The forecasting is based on combinatorial optimization models (hierarchical morphological design) in the form of selecting the best local modifications and combining them with allowance for their compatibility. An illustrative example describes a four-stage evolution and forecasting of a hierarchical system of requirements to the topology of a communication system.