Vol 27, No 4 (2019)

The electron density singularity formed at the joining area of relativistic wake wave and bow waves has been proposed as a novel relativistic electron mirror regime to reflect the counter-propagating electromagnetic pulse [1]. Coherent hard electromagnetic radiation is generated by the reflection, compression and frequency upshift from the electron density singularity. In this paper, detailed description of this regime is provided, and new features are shown. The electromagnetic fields reflected by the electron density singularity are investigated via multi-dimensional particle-in-cell simulations.

A self-gravitating opposite polarity dust plasma (SGOPDP) medium (containing both positively and negatively charged dust, vortex-like distributed ions and Maxwellian electrons) has been considered in order to examine the effect of vortex-like (trapped) ion distribution on dust-acoustic (DA) solitary waves (SWs) propagating in SGOPDP medium. The reductive perturbation method, which is valid for small but finite amplitude SWs, is employed to derive a modified Korteweg-de Vries equation having stronger nonlinearity. The basic features of the DA SWs in SGOPDP medium are found to be significantly modified by the combined effect of self-gravitational field and vortex-like ion distribution. The results of this paper have many implications in space and laboratory dusty plasmas.

A possibility of calibrating a piezo transducer by comparing thermoacoustic and vaporization pressure signals generated in a metal (liquid mercury) irradiated with nanosecond laser pulses is demonstrated. In this calibration method, significant difference in the dependence of these two pressure generation mechanisms on the irradiated surface temperature is used.

The radiation hardness of neodymium-doped gadolinium vanadate crystal (Nd:GdVO₄) has been investigated. Crystal with sizes of 4×4×8 mm doped to a level of 0.5% Nd³⁺ and (for comparison) undoped GdVO₄ crystal were γ-irradiated by a ⁶⁰Co source to an absorbed dose of about 10⁶ to 10⁷ rad. The photoinduced absorption spectra of the crystals have been studied. Intense lasing with a differential efficiency up to about 25% was obtained in an irradiated Nd:GdVO₄ crystal. It is shown that irradiation of a crystal up to a dose of 10⁷ rad does not reduce significantly its laser efficiency.

Reflection spectra of a composite one-dimensional photonic crystal (PC) based on porous anodic alumina filled with ferroelectric sodium nitrite have been recorded in the wavelength range of 400 to 1200 nm. Significant spectral shifts of the first and second stopbands are revealed for the composite PC. The stopband spectral half-width is found to decrease by a factor of four to five. The possibility of applying composite alumina-based photonic crystals as selective narrowband mirrors is discussed.

Dynamics of a suspension of dielectric nanoparticles in an intense laser field is considered for the first time. A two-dimensional model is developed for interaction of laser radiation with nanoparticles in a suspension. A stable spatial configuration of nanospheres in a suspension is found and dispersion relations for low-lying excitations of a multiparticle system are determined within the model.

The problems concerned with the dispersion and attenuation of surface wave propagations due to imperfect elasticity are of great interest to seismologists. The present work reports the dispersion and attenuation characteristics of Love-type wave propagation in a fiber-reinforced layer laid on an inhomogeneous viscoelastic half-space. The inhomogeneity in the viscoelastic medium arises due to the hyperbolic trigonometric variation in depth. A complex frequency equation for the Love-type wave has been procured using the suitable boundary conditions. Thus, the dispersion and damping equations have been calculated to analyze the dispersion and attenuation peculiarities of the wave. Results for the uniform homogeneous isotropic media have been compared with existing solutions. Numerical computation and graphical sketches have been set forth for the relevant parametric variations.

The conditions providing the equilibrium stationary state of high-density solid and annular electron beams, transported in cylindrical drift tubes and focused by a homogeneous magnetic field, have been investigated. An efficient numerical model is proposed to determine the distributions of the electrostatic potential, charge density, and electron velocities in the stationary state of these beams, with allowance for the space-charge forces. The results of the numerical calculations for the limiting currents, determined by the longitudinal deceleration (caused by space-charge forces) and conditions for equilibrium transverse magnetic focusing for transported beams of different configurations on the length of a klystrontype vacuum electronic device, are presented. The limitations on the device working length, related to the excitation of diocotron instability, are estimated. The calculation results are compared with the data obtained using the quasi-three-dimensional program “Arsenal-MSU” and analytical formulas suggested by other researchers.

Samples of composite second-generation high-temperature superconducting (HTS) tapes based on the GdBCO (123) compound have been irradiated in a pulsed electron accelerator (system Terek-2, GPI RAS) through a tantalum target in order to determine how the thermal and shock loads arising on the tantalum-HTS interface affect the superconducting parameters of HTS tapes. Scanning Hall magnetometry was applied to characterize HTS samples subjected to electron irradiation. The thermal modes and shock load in a composite superconductor under irradiation are estimated as functions of the energy absorbed by the target. At a silver surface temperature equal to the melting point, the critical current decreases by 87% from the initial value. At lower irradiation energies, the decrease in the critical current is smaller. The role of the temperature effects and shock waves under this irradiation is discussed.

Data of the SWARM-95 experiment, where intense internal waves on a stationary path led to coupling of acoustic source field modes, have been processed. The spectral-density localization domains, which are due to unperturbed and perturbed fields, are obtained using a double Fourier transform of interference pattern on a hologram. The interference patterns of these fields have been reconstructed by filtering these regions and applying double inverse Fourier transforms to them, which made it possible to reconstruct the unperturbed-waveguide transfer function and the time variability of the medium. The velocity of intense internal waves is estimated based on the recorded perturbed-field hologram.

A thermographic study of low-intensity phototherapeutic effects on the human body in situ was carried out. The feature of the work was the measurement of the dynamics of surface temperature changes in a bio-object for 40 min after the cessation of irradiation. The relaxation character of the temperature behavior with quasi-oscillating phenomena during the selected observation period has been established. An explanation of the observed phenomena with the involvement of literature data is proposed. It is shown that 15-min irradiation at a radiation intensity of 14mWcm⁻² is optimal for phototherapy at a wavelength of 640 nm. A conclusion was made about the possibility of considering changes in the local temperature of a bio-object as a correlated parameter to determine the optimal dose of radiation during phototherapy.

Time dependence of the average vorticity amplitude is measured for vortices at lattice sites on the surface of water-glycerin solutions after excitation of two perpendicular surface waves with a frequency of 3 Hz. It is noted that presence of an elastic film on the surface of the liquid should be assumed for achieving the best agreement between the experimental data and the theoretical calculations. Considering the film effect, it is shown that the vorticity amplitude generated by perpendicular nonlinear waves almost does not change when the kinematic viscosity coefficient of the water-glycerin solution increases by more than a factor of 10.