A. E. Hramov

Formation and nonlinear dynamics of the squeezed state of a helical electron beam with additional deceleration

Results of numerical simulations and analysis of the formation and nonlinear dynamics of the squeezed state of a helical electron beam in a vircator with a magnetron injection gun as an electron source and with additional electron deceleration are presented. The ranges of control parameters where the squeezed state can form in such a system are revealed, and specific features of the system dynamics are analyzed. It is shown that the formation of a squeezed state of a nonrelativistic helical electron beam in a system with electron deceleration is accompanied by low-frequency longitudinal dynamics of the space charge.

High-frequency impedance and absorption of a semiconductor lattice upon an external periodic perturbation

The impedance and absorption of a semiconductor superlattice under an external harmonic perturbation are investigated. It is shown that a weak external periodic signal synchronizes the domain motion in a semiconductor superlattice, and this process is accompanied by an increase in absorption and a reduction in the amplitude of the superlattice impedance. The characteristic dependence of the active and reactive impedance components on the frequency and amplitude of the external harmonic perturbation is presented.

Theoretical and numerical investigation of “intermittent” intermittency in coupled chaotic systems

The behavior of a chaotic system is theoretically described that simultaneously exhibits type-I intermittency and ring intermittency. The theory, as applied to a system of two unidirectionally coupled chaotic Rössler oscillators, shows good agreement with the results of numerical simulations.

Adaptive filtering of electroencephalogram signals using the empirical-modes method

A new method for the removal of physiological artifacts in the experimental signals of human electroencephalograms (EEGs) has been developed. The method is based on decomposition of the signal in terms of empirical modes. The algorithm involves EEG signal decomposition in terms of empirical modes, searching for modes with artifacts, removing these modes, and restoration of the EEG signal. The method was tested on experimental data and showed high efficiency in the removal of various physiological artifacts in EEGs.

Stability of the Steady State in a Strongly Coupled Semiconductor Superlattice Described Using a Semiclassical Approach

The stability of the steady state of a semiconductor superlattice described using a semiclassical approach is analyzed. It is shown that generation arises due to the appearance of perturbations characterized by a positive increment of growth. The relationship between the frequency of the current oscillations and the frequency of the perturbation oscillation is determined.

Nonlinear Dynamics of a Generator on a Virtual Cathode with Modulated Emission

A numerical study of a low-voltage vircator with controlled emissions from a thermocathode is performed for when an external signal effects on the electron beam and modulates the emission. The strong influence of the modulation parameters on characteristics of oscillations of the beam with virtual cathode is noted. It is shown that when the modulation frequency is tuned to the one of harmonics of a virtual cathode’s free oscillations, there is a considerable increase in the power of high-frequency harmonics of the virtual cathode’s free oscillations in the output spectrum.

Dynamics of an Electron Beam with a Virtual Cathode in a Vircator without a Magnetic Field and with Drift Space Filled by Neutral Gas

The physical processes in a vircator without an external magnetic field and with a drift space filled by neutral gas are studied. Three typical dynamic regimes are found: (1) the suppression of virtual cathode oscillations, (2) pulse generation, in which the suppression and resumption of virtual cathode oscillations are observed, and (3) continuous virtual cathode generation. The frequency dynamics of the vircator’s output radiation is investigated for the last case, and it is shown that the generation frequency of the vircator can rise when the gas pressure exceeds a certain critical value.

Experimental and Theoretical Study of Chaotic Microwave Oscillations and Pattern Formation in Non-relativistic Electron Beam with Virtual Cathode

Results are presented from experimental and numerical study of oscillatory phenomena in electron beam with virtual cathode (VC) in diode gap with decelerating field. Experiments have revealed a chaotic broadband generation of the microwave oscillations of VC. Numerical simulations based on a simple PIC model have shown that the onset of the chaotic generation with increasing beam deceleration rate are governed by the processes of regrouping of the electrons in the beam with VC

Analyzing cluster formation in adaptive networks of Kuramoto oscillators by means of integral signals

A numerical study of an adaptive network of coupled oscillators (Kuramoto oscillators) is performed. The problem of studying phase synchronization in networks by considering wavelet spectra of the integral signal and the evolution of the phase difference in clusters of the adaptive network is examined. The process behind the formation of phase clusters is analyzed using integral characteristics.

Chaos and its suppression in a system of two coupled Rydberg atoms

The nonlinear behavior and chaos in a system of two coupled Rydberg atoms is investigated. A map of the regimes in which oscillations with different periods are plotted is produced, and the chaotic behavior of the system is revealed. A procedure for suppressing chaos in the system by means of an external parametric effect is presented.