Volume 61, Nº 6 (2016)

Wide-aperture planar lasers (vertical-cavity surface emitting lasers, distributed feedback lasers, 2D spaser arrays, and plasmon lasers on stopped-light mode) are reviewed. Structure, parameters (directional pattern and amplitude modulation frequency), and physical principles of such lasers are discussed.

The numerical modeling of the frequency characteristics of the Sestroretskii cube is performed. It is shown that the interior Sestroretskii cube exhibits the properties of a double waveguide T-branch. The hypothesis that signals propagate inside the Sestroretskii cube with the velocity that is the double light speed in vacuum is justified. The limitations of the spectrum of these signals are formulated.

The problem of scattering of the field induced by a filament of magnetic current by a metamaterial cylinder is solved using the method of continued boundary conditions. The effect of the frequency dispersion of permittivity and permeability of the cylinder material on the phenomenon of resonance absorption is investigated.

The frequency dependences of the coefficients of reflection from a lattice of double split rings excited by an RF magnetic field and from an RF-absorbent composite based on resistive films or fibers are analyzed. It is shown that partial reflections from the surface of the composite and the closely spaced lattice can compensate each other and, thus, the reflection from the composite can be significantly reduced. It is experimentally confirmed that the reflection can be decreased by more than 15 dB as compared to the reflection from the composite in the absence of the lattice.

Equations that describe mutual and induced chaotic synchronization of n (n = 2, 3, 4,...) autooscillation systems in colored-noise medium are derived. It is demonstrated that external colored noise acting upon a system of coupled oscillators and a chain of unidirectionally coupled oscillators causes a decrease in the duration of transient processes that lead to the chaotic synchronization (both mutual and induced) of nonidentical oscillators and a decrease in the time needed for stabilization of the symmetric state of the system when the parameters of oscillators are identical.

Thermomechanical properties of microactuators with shape-memory effect (SME) based on the Ti₂NiCu/Pt layered composite are analyzed. Atomic-force microscopy is used to experimentally determine rigidity of the composite microactuators that represent cantilevers with sizes of 50 × 2 × 1 μm and a thickness of the SME active alloy layer of 0.5 μm in a temperature interval of 20–100°C. Forces that are exerted by the composite actuator on a microscopic object are quantitatively estimated. The experimental data are in reasonable agreement with the calculated results.

Optical fiber (OF) with a relatively high level of the backward signal at a certain wavelength is developed and studied. An increase in the backward signal is reached due to the recording of multiple weak fiber Bragg gratings (FBGs) in the course of fiber pulling. A scheme that is simpler than the direct FBG recording through a phase mask is proposed and implemented. Fibers with FBG recorded with different ratios of the region with recorded gratings to the total length of OF are fabricated. An increase in the level of the backward signal relative to the level of the Rayleigh scattering by more than 30 dB is reached. Results of experimental study of the proposed OFs and examples of practical application are presented.

In order to construct a nonlinear regression model we have to accurately (in some sense) initialize parameters of the model. In this work we performed comparison of several widely used methods and several newly developed approached for initialization of parameters of a regression model, represented as a decomposition in a linear dictionary of some parametric functions (sigmoids). We proposed a general deterministic approach for initialization, providing repeatability of results, reduction of a learning time and in some cases increase of a regression model accuracy; we developed two new algorithms (based on a piecewise-linear approximation and based on local properties of approximable dependency) in the framework of the proposed approach; we developed randomized initialization algorithm (spherical initialization) for effective approximation of high-dimensional dependencies; we improved the classical initialization method SCAWI (by locating centers of sigmoids in sample points), providing a regression model accuracy improvement on specific classes of dependencies (smooth functions and discontinuous functions with a number of local peculiarities in an input domain) when using RProp algorithm for learning; we performed comparison of classical and newly proposed initialization methods and highlighted the most efficient ones.

Common statistical estimators for speech enhancement rely on several assumptions about statistical properties of speech and noise processes. In real applications, these assumptions may not be always satisfied due to the effects of a nonstationary environment. In this work, we propose new robust spectral estimators for speech enhancement by incorporation of calculation of rank-order statistics to existing speech enhancement estimators. The proposed estimators are better adapted to nonstationary characteristics of speech signals and noise processes in real environments. By means of computer simulations, we show that the proposed estimators outperform the known estimators in terms of objective criteria of quality.

Problems of description of data sets by constructing the optimum ellipsoid are considered. The optimization problems are formulated as convex programming problems using linear matrix inequalities. The proposed methods are compared with similar methods designed earlier in accordance with two criteria: the volume of the ellipsoid and the number of points in the learning sample, which lie outside the ellipsoid.

A novel efficient algorithm for solution of the problem of equal partitioning of a set with predefined weights of elements is proposed. The algorithm is based on calculation of a linear group preserving an invariant: the set of zeros of a cubic form. Algorithms for solution of related problems, including the problem of the search for the second solution if the first solution is known, are discussed.

Automation of control of the train motion is one of the main problems of safety and economy of transportation of passengers by a monorail road. In this paper, the basic attention is given to construction of the mathematical model of car motion, identification of the model parameters, and filtering of the car motion coordinates in the monorail road. Simulation that confirms serviceability of the proposed algorithms is performed.

The dynamic range of the decentralized wideband code-division multiple access communications system based on OFDM–FSK modulation and noncoherent reception is studied depending on the clock oscillator accuracy and its jitter. The issues concerned with the symbol synchronization of the transmitter and receiver, as well as the dynamic range of the received signal, are investigated. The GOST 207 and GOST 231 unified standard radio wave propagation models, which are interpreted as communications channel models, are discussed.