Vol 82, No 1 (2018)

It is shown that to find the transverse refractive-index profile of a semiconductor laser waveguide, it is sufficient to know the angle of the device’s radiation divergence and two values of the function describing the directional radiation pattern. A calculation technique is proposed and its use in the diagnostics of laser diode degradation is discussed.

A way of forming a new class of solitons—chirped (or aberrational) solitons—when a pulse passes through a layered nonlinear structure in a cubically nonlinear medium is demonstrated by means of computer simulation. It is shown that the pulse frequency modulation of the resulting solitons is nonlinear.

Surface electromagnetic waves that propagate within the interface between a conventional dielectric or a metamaterial and a topological insulator with an undamped surface electric current are considered. Dispersion relations are given for guided waves that are surface waves polarized differently on either side of the media interface and create a coupling state due to the magnetoelectric effect.

An enhanced linear acoustic tomograph is designed for the early medical diagnosis of pathological neoplasms of soft biological tissues. Problems associated with additional prospects for tomographic imaging are discussed.

Patterns of wave propagation along the surface of a viscous liquid covered with an insoluble elastic surfactant film are studied analytically. The relationship between the damping decrement of capillary–gravitational waves and the distribution pattern of the surfactant concentration maxima relative to the crests of the waves is established as a function of the film’s elasticity.

A relativistic gyrotron fed by a 500 keV, 2 kA helical electron flow in the TE and TM modes is simulated on the basis of a self-consistent system of time-dependent equations with a non-fixed field structure and using a three-dimensional version of the KARAT PIC code. The possibility of reaching an output power 200–250 MW at a wavelength of 10 mm is shown.

The absorption spectrum of liquid water in the range of 10³–10¹³ Hz (from dc conductivity of up to 5 THz IR resonance) is completely and uniformly described by a simple physical model. The model assumes the existence in water of a high concentration of H₃O⁺ and OH⁻ ions (up to 4.5% of the total number of molecules) that exchange protons with H₂O molecules on the scale of picoseconds.

The formation of a horseshoe-shaped vortex from an initial straight cylindrical vortex occurring in the viscous layer of a retarding fluid flow in a channel with a nonuniform cross section is studied experimentally. The spatial bends of the vortex filament and the effect of the ambient fluid pressure first form an arch with supports at the bottom of the channel, then a horseshoe-shaped vortex, and finally a circular vortex with the destruction of the supports.

The results from simulating a system for the encrypted transmission of information are presented. The parameter of a Thomas oscillator in the mode of dynamic chaos is regulated by a law independent of the information signal. The information signal is additively mixed to the resulting signal at the output of the leading chaotic oscillator.

The noise-induced intermittent behavior of multistable systems is studied using the example of a reference system (a Chua generator). It is shown that upon exposing the Chua generator to external noise, a noise-induced intermittency is observed at certain values of the control parameters. The statistical characteristics obtained for this type of behavior are compared to the appropriate theoretical formulas.

The plasma excitation density in a graphene-based superlattice on a striped substrate is investigated as a function of the period and width of the potential wells that form the superlattice. Calculations are based on the quantum theory of plasma waves in the random phase approximation with regard to Umklapp processes.

The effect a periodic electric field has on the dynamics of electron domains in a semiconductor superlattice with applied voltage and a magnetic field tilted relative to the superlattice axis is investigated. It is shown that this periodic electric field greatly affects the I–V characteristic of the superlattice and can induce several interesting phenomena, including the onset of synchronous regimes. The obtained results are compared to the data for a zero tilted magnetic field.

A robust algorithm designed to localize a source in an acoustic waveguide without perfect knowledge of array calibration is constructed, that is a generalization of the known RARE (RAnk REduction) method in application to signal reception under the condition of incomplete information on a propagation medium. It has been established by means of statistical modeling that the proposed method gives a significant advantage in the accuracy of the source position estimation as well as in the achieved probability of its correct localization in comparison with the traditional RARE algorithm that assumes a priori knowledge of channel characteristics. The restriction on the permissible norm of mismatch between presumed and actual replica fields, for which a correct solution of the inverse problem is possible, has been found. The proposed algorithm is validated by its application to the experimental data observed in the Ladoga Lake. It has been shown that under real conditions the presented approach is rather efficient and ensures an acceptable source reconstruction quality without the need for a computationally intensive joint estimation of both the source and waveguide parameters.