Том 61, № 6 (2016)
- Жылы: 2016
- Мақалалар: 22
- URL: https://journals.rcsi.science/1064-2269/issue/view/12318
Review
Wide-aperture planar lasers
Аннотация
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.
Electrodynamics and Wave Propagation
Numerical electrodynamic investigation of the interior 3D problem of the Sestroretskii cube
Аннотация
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.
Synthesis and analysis of a frequency-scanned planar waveguide array focused in the Fresnel zone
Аннотация
A 2D array of radiators excited by the modes of a planar array of parallel waveguides and focused in the Fresnel zone is considered. The problem of determining the positions of array radiators for focusing the field at a finite distance from the array aperture is solved for the cases of plane and cylindrical fronts of the initial distribution of the phases of waveguide modes. A phenomenological model of the slotted-waveguide array is used to determine the position of the focal line, the aberration of the scattering spot, and the frequency scanning sector.
Resonance absorption at scattering by a metamaterial cylinder
Аннотация
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.
Quasi-static plasmon resonances in a graphene ribbon in the infrared range
Аннотация
The 2D problem of diffraction of a plane electromagnetic wave diffraction by a graphene ribbon is considered for the case of the TM polarization. Quasi-static plasmon resonanses are investigated with the use of rigorous numerical methods. The surface currents and scattering and absorption cross-sections are calculated. It is shown that, owing to the high Q-factor, multipole plasmon resonances appear not only in the near field but also in the far field.
Compensation of reflection from an RF absorbent material with the help of a lattice of double split rings
Аннотация
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.
Dispersion characteristics of optical waveguides based on ZnO nanorods
Аннотация
Using the method of separation of variables in the cylindrical coordinate system, the problem of propagation of electromagnetic waves in a 2D periodic lattice of ZnO nanwaveguides covered with a thin metal film is solved. Comparison of calculation results with results of simulation with the use of the COMSOL Multiphysics™ package based on the finite-element method is performed. The obtained results are used for forecasting the resonance wavelengths of a 2D periodic lattice of ZnO nanorods grown on a dielectric substrate.
Dynamics Chaos in Radiophysics and Electronics
Transient processes under stochastic synchronization of oscillators in colored-noise medium
Аннотация
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.
Physical Processes in Electron Devices
Thermoelastic properties of micron-size actuators based on the Ti2NiCu//Pt composite with shape-memory effect
Аннотация
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.
Novel Radio Systems and Elements
Optical fiber with distributed Bragg-type reflector
Аннотация
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.
Mathematical Models and Computational Methods
The influence of parameter initialization on the training time and accuracy of a nonlinear regression model
Аннотация
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.
Regression on the basis of nonstationary Gaussian processes with Bayesian regularization
Аннотация
We consider the regression problem, i.e. prediction of a real valued function. A Gaussian process prior is imposed on the function, and is combined with the training data to obtain predictions for new points. We introduce a Bayesian regularization on parameters of a covariance function of the process, which increases quality of approximation and robustness of the estimation. Also an approach to modeling nonstationary covariance function of a Gaussian process on basis of linear expansion in parametric functional dictionary is proposed. Introducing such a covariance function allows to model functions, which have non-homogeneous behaviour. Combining above features with careful optimization of covariance function parameters results in unified approach, which can be easily implemented and applied. The resulting algorithm is an out of the box solution to regression problems, with no need to tune parameters manually. The effectiveness of the method is demonstrated on various datasets.
Speech enhancement with adaptive spectral estimators
Аннотация
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.
Sojourn times in different modes in the queueing system with batch Poisson arrivals, general service times, and hysteretic policy
Аннотация
Consideration is given to the model of the SIP server modelled as a single-server queueing system with finite capacity R and two batch Poisson flows (priority and non-priority), general service times, and bi-level hysteretic control of arrival rates, which is defined by two numbers: L and H (0 < L < H < R). The hysteretic policy under consideration implies that, at each instant, the system can be in one of the three operation modes: normal, overload, and blocking. The system accepts customers from both flows when it is in normal mode, accepts only priority flow when is it overloaded, and rejects all new customers in the discard modes. It is assumed that the switching between operation modes can occur only at the instant of service completion. The analytical method for computing the distributions (in terms of Laplace–Stieltjes transforms) of system’s sojourn times in each operation mode and return times to the normal mode is proposed. Illustative examples are presented.
Description of the design space by extremal ellipsoids in data representation problems
Аннотация
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.
Stereovision algorithms applicability investigation for motion parallax of monocular camera case
Аннотация
An attempt is made to estimate of whether the stereo-matching algorithms are applicable to the motion parallax of a monocular side-looking camera. The distortions in the degree of epipolar restrictions are theoretically analyzed depending on the relative rotation of the coordinate system of images. The algorithmic technique for estimating the quality of the computed disparity map is developed. The new stereo-matching algorithm used for the parallax of a monocular camera is described.
Theory and Methods of Information Processing
A novel algorithm for solution of a combinatory set partitioning problem
Аннотация
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.
Anderson–Darling statistic and its “inverse”
Аннотация
For more than 60 years, the Anderson–Darling test is most frequently used among all Cramér–von Mises (omega-square) tests. This statistic modifies a classical empirical process defined within the [0, 1] interval by multiplying it by weighting function ψ(t) = (t(1–t))–1/2. The weighting function redistributes the test sensitivity to deviations of the distribution function of the observed stochastic quantity from a hypothetical distribution function in different its segments. However, the tests with other weighting functions may also be of interest in practice. New formulas for the eigenvalues of the Anderson–Darling statistic are proposed. The statistic “inverse” to the Anderson–Darling statistic with weighting function ψ(t) = (t(1–t))1/2 is considered. Tests with other weighting functions may also be of interest when weighted Cramér–von Mises statistics are used. The table of quantiles of statistics with weighting functions ψ(t) = tα(1–t)β, α >–1, β >–1 is presented. The quantiles are given for 36 different combinations of parameters α >–1 and β >–1. The table was calculated using accurate numerical methods and without application of modeling techniques.
Analysis and Synthesis of Control Systems
Identification of the model parameters and filtering of the motion coordinates of the car of a monorail road
Аннотация
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.
Adaptive control of the car motion of a monorail road
Аннотация
Construction of the mathematical model of the car motion, identification of the model parameters, and filtering of the coordinates of the car motion in a monorail road are considered. The law of control of the car motion that ensures an acceptable quality of operation of the control system is selected. Simulation confirming the serviceability of the obtained algorithms and the whole control system is performed.
Data Transmission in Computer Networks
Symbol synchronization in the OFDM–MFSK-based multiple access system
Аннотация
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.