Volume 54, Nº 4 (2018)

An algorithm is proposed to estimate the node coordinates of deformed lattices of quasiperiodic textures with subpixel accuracy. The algorithm consists of two steps. In the first step, the frequency and initial phase vectors of a polyharmonic brightness function model are calculated from the characteristics of spectral outliers of image fragments. The obtained estimates are used to determine the coordinates of the nodes of the local lattice. In the second step, the local lattices are combined into a global lattice for the entire image of the quasi-periodic texture. Using high-accuracy estimates of model parameters from small image fragments ensures stable operation of the algorithm for significant deformations of the lattice and sub-pixel accuracy in estimating the coordinates of its nodes. Results of computer simulation and processing of real halftone images of quasiperiodic textures are given demonstrating the effectiveness of the proposed algorithm.

This paper touches upon the problem of a compact polygonal description of objects. A method of lossless compression of geometric data based on perturbation functions is proposed. Advantages of this approach over the known algorithms of transformation of three-dimensional models for fast transmission of information and its compact storage are demonstrated.

This paper describes the concept and methods of space-time processing of radio images of small objects in a multiposition radiometer system, which make it possible to increase the performance of this system. The spatial processing is carried out in each overlook cycle of scanning radiometers in order to determine the spatial coordinates of objects and mutual orientation of coordinate systems. The time processing is carried out in a sequence of overlook cycles of radiometers for determining the trajectory of the objects that change mutual positions.

This paper touches upon a model of simultaneous acoustic masking, which detects speech signal components perceived by a human’s auditory system. A simultaneous masking algorithm on the basis of this model is proposed. It is shown that, after simultaneous masking, a signal becomes a binary structure that reflects the harmonic structure of a vocalized sequence. It is experimentally proven that this structure can be used to detect key speech segments (from the standpoint of perception by an auditory system). This structure serves as a basis for an algorithm of high-quality segmentation of a speech signal into vocalized and unvocalized segments, which does not require learning before use. The joint use of the algorithms for simultaneous masking and speech signal segmentation is tested, and their performance is evaluated.

A tunable (in terms of the angle of convergence of intersecting light beams) two-beam interferometer with fixed mirrors and a fixed photosensitive element is considered. The photosensitive element is based on a symmetric beam-splitter unit where tuning of the interference pattern period is ensured by only one type of motion: interferometer rotation with respect to the motionless source of the collimated light beam. It is demonstrated that the period can be controlled in this way for convergence angles from 30 to 180° for beams with diameters of 10% or more of the beam-splitter unit length. In this region, the greatest width of the range of convergence angle tuning can exceed 40°, and the admissible beam diameter approaches 40% of the beam-splitter unit length. Comparisons with a similar interferometer based on a beam-splitter cube are performed, and possible areas of application of the considered interferometer are determined.

A method used for calibration of scanning modules on the basis of galvanometric deflectors is considered. The method is based on an iterative two-step algorithm of processing of the profilometry map of the test writing of the calibrated module. It is demonstrated that high accuracy and robustness of determining the coordinates of the reference points of the test writing can be obtained by means of finding the approximate positions of such points and identifying the fragment in the vicinity of these points at the first step and searching for the exact values of the coordinates by the correlation method at the second step. The use of this method and a simple algorithm of piecewise-planar interpolation offers a possibility of laser beam positioning with a relative error of 10⁻⁵ from the writing field.

The photo extraction of rubidium atoms from the bulk of a photonic crystal has been investigated. It has been found that in the case of irradiation of the crystal in the stop band where the desorbing light does not penetrate deeply, the separation of atoms occurs practically from its surface, so that the density of desorbed atoms in the cell decreases only exponentially. In the case of irradiation of the crystal outside the stop band, the bulk of the crystal is irradiated almost completely. In this connection, the exponential decrease in the density of atoms in the cell is replaced by its relatively slow reduction of diffusion nature. The bulk diffusion coefficient of rubidium atoms in the photonic crystal was measured to be 2 · 10⁻⁸ cm²/s.

The formation and dynamics of excitations in an atomic or molecular nano chain of a helical shape are studied. The dipole-dipole interaction between the circular polarizations of the optical transitions of neighboring molecules is taken into account. The derived Bloch equations are solved in a continuum approximation using the Frenet–Serret coordinate system. Solutions are obtained that describe the formation of stable localized structures (solitons) due to the curvature of the chain, which can have a critical influence on the luminescent properties of the chiral medium.