Vertical motions in the lower ionosphere and a sporadicE-layer

We propose a calculation technique for the main characteristics of a sporadic E-layer, including the effective recombination coefficient, the relative content of meteor and atmospheric ions in the layer, and the time of its evolution. This technique is based on measurements of vertical plasma velocities by the method of resonance scattering of radio waves by artificial periodic inhomogeneities of the electron density. The contribution of internal gravity waves and turbulent motions to the formation of sporadic layers is estimated. The characteristic values of the turbulent velocity measured by this method at the heights of the turbopause are presented. The possible mechanisms of mid-latitude sporadic E-layer formation at heights of 90 to 120 km are considered. Experimental studies confirmed the main statements of the wind shear theory concerning the determining role of the redistribution of ionization under the action of atmospheric winds with vertical gradient of velocity in the formation of E_s. Deceased. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 1, pp. 26–35, January, 1999.     

Artificial periodic irregularities,wave phenomena in the lower ionosphere,and the sporadic <Emphasis Type="Italic">E</Emphasis> layer

We present new results of studying the artificial periodic irregularities produced in the ionosphere by the radio emission of the high-power heating facility “Sura” during the period of observations of the sporadic E layer. Basing on the measurement results for the velocity of the vertical plasma motion and the electron profile density in the E region of the ionosphere, which were obtained by the method of resonance scattering of radiowaves by an artificially produced periodic structure, we analyze the possibility to produce a sporadic E layer by driving metal ions affected by the vertical shear of the velocity, which occurs at these altitudes due to the propagation of internal gravity waves. The parameters of these waves are evaluated, as well as the mass and concentration of metal ions in the sporadic E layer.     

Amplification/damping processes of atmospheric acoustic-gravity waves in horizontal winds with linear shear

The time-varying frequencies and amplification/damping rate (ADR) of atmospheric acoustic-gravity waves (AGW) in unbounded horizontal winds with linear shear (HWLS) in the linear approach is analytically obtained for the three-dimensional case. The numerical solutions for the temporal evolution of the AGW amplitudes point at the possibility of the energy transformation between the obtained acoustic, gravity and shear wave modes.     

Acoustic wave effects on catalysis: design of surfaces with artificially controllable functions for chemical reactions

The effects of surface acoustic wave (SAW) and resonance oscillation (RO) of bulk acoustic waves on the catalysis of metals were studied in an attempt to design a catalyst surface with artificially controllable functions for chemical reactions. In ethanol decomposition on a thin Cu film catalyst deposited on the propagation path of a shear horizontal leaky SAW, the SAW-on increased the activity for ethylene production remarkably but a little for acetaldehyde production. A poled ferroelectric z-cut LiNbO₃ with a thickness extensional mode RO (TERO) and a x-cut LiNbO₃ with a thickness shear mode RO (TSRO) were employed as a substrate, on which a thin Ag film catalyst was deposited. For ethanol decomposition, TERO increased ethylene production activity and the selectivity for ethylene production from 79 to 96%, whereas TSRO caused little activity enhancement for both ethylene and acetaldehyde production. The combination with the results of laser Doppler measurements showed that the activity enhancement and selectivity changes with SAW and RO of the acoustic waves are associated with dynamic large lattice displacement vertical to the surface.     

Effect of radial density gradient on dispersion of guided helicon mode

The effect of the radial density gradient on the dispersion of guided helicon mode is considered. For the parabolic density profile, the conditions under which the wave frequency is proportional to the axial wavenumber squared (ω ≈ k _z ² ) are obtained.     

Feasibility analysis of solid immersion lens-based dual-layer near-field recording optics with a numerical aperture of 1.84

A dual-layer near-field recording (NFR) optical system with a high numerical aperture (NA) of 1.84 was designed by appropriate cover and spacing layer selection, using layers with refractive indices of 2.0. The designed aplanatic imaging optics exhibited additional aberrations in the multi-layered stack, mainly due to the air-gap and spacer layer. Given optics designed only to compensate for aberrations caused by a 2-μm-thick cover-layer, a 3-μm-thick spacer layer induces 96.2 mλ_rms and 6.5 mλ_rms of spherical aberration and defocus, respectively. A complete electric field calculation analysis for the inside of the multi-layer stack verified that diffraction-limited spot quality can be ensured on the recording layer with phase-only correction. As the aberration caused by the multi-layered stack cannot be corrected perfectly, due to the high oscillation of the aberration function along the radial direction in the exit pupil, three different types of liquid crystal (LC) electrodes were considered for practical implementation. Of the three phase-correction methods, the approximate linear phase-correction method was the most tolerant of axis decenter from the optical axis, providing acceptable diffraction-limited correction performance.     

Understanding and modeling turbulent fluxes and entrainment in a gravity current

We present an experimental study of the mixing processes in a gravity current flowing on an inclined plane. The turbulent transport of momentum and density can be described in a very direct and compact form by a Prandtl mixing length model: the turbulent vertical fluxes of momentum and density are found to scale quadratically with the vertical mean gradients of velocity and density. The scaling coefficient, the square of the mixing length, is approximately constant over the mixing zone of the stratified shear layer. We show how, in different flow configurations, this length can be related to the shear length of the flow (ε/∂_zu³)^1/2. We also study the fluctuations of the momentum and density turbulent fluxes, showing how they relate to mixing and to the entrainment/detrainment balance. We suggest a quantitative measure of local entrainment and detrainment derived from observed conditional correlations of density flux and density or vertical velocity fluctuations.     

Mechanical characterization of sintered piezo-electric ceramic material using scanning acoustic microscope

Lead Zirconate Titanate (PZT) is a piezo-electric ceramic material that needs to be characterized for its potential use in microelectronics. Energy dispersive X-ray analysis (EDX) is conducted to determine the chemical composition of the PZT ceramics. The scanning electron microscope (SEM) is performed to study the surface morphology, grain structure and grain boundaries. The SEM image helps us to understand the surface wave propagation and scattering phenomena by the PZT and the reason for its anisotropy and inhomogeneity due to the grain structure. In this paper scanning acoustic microscopy at 100 MHz excitation frequency is conducted for determining mechanical properties of PZT. Earlier works reported only the longitudinal wave speed in PZT while in this paper longitudinal, shear and surface acoustic wave speeds of sintered PZT are measured from its acoustic material signature (AMS) curves, also known as V(z) curves. AMS or V(z) curve is the variation of the output voltage as a function of the distance between the acoustic lens focal point and the reflecting surface. The average velocities of longitudinal, shear and surface acoustic waves in a PZT specimen are determined from its V(z) curve generated at 100 MHz excitation frequency and found to be over 5000 m/s, over 3000 m/s and between 2500 and 3000 m/s, respectively. From these velocities all elastic constants of the specimen are obtained.     

The sterilization of Escherichia coli by dielectric-barrier discharge plasma at atmospheric pressure

The sterilization of E. coli (ATCC8099) using an atmospheric pressure, air DBD plasma driven by 100 Hz high-voltage power supply was investigated in this paper. The results showed that germicidal efficiency was closely related to the plasma treatment time, the gap spacing, the initial cell density and the surface characters of substrate materials. The germicidal efficiency was 99.999% under the conditions of 5-min plasma treatment, 3-cm gap spacing and on PET films. After plasma exposure for 5 min, the temperature was observed below 43 °C which could not lead to inactivate E. coli. The observation of protein leakage and cell morphology alteration by transmission electron microscopy (TEM) techniques revealed that the etching action on cell membrane by electrons, ions and radicals was primary reason of DBD air plasma sterilization.     

Propagation and conversion of non-axisymmetric modes in non-uniform helicon-sustained plasma

An effect of the radial plasma density gradient on the oblique wave propagation in the helicon-frequency range is investigated. It is shown that the dispersion features of electrostatic and electromagnetic modes are essentially changed in strongly non-uniform helicon plasma. In particular, the transition between helicon eigenmode frequency scales ω ～ k _z and ω ～ k _z ² is demonstrated. The process of total conversion of long-wavelength helicon mode into short-wavelength electrostatic wave in near-axis region of a plasma column is analysed. Due to modification of the wave dispersion relations, the densities at which the mode conversion occurs are considerably reduced if the density gradient is steep enough. The estimation of collisionless axial damping rate of helicon mode connected with linear mode conversion is presented. This damping is compared with the usual collision damping.     

Thickness-shear modes and magnetoelastic waves in a longitudinally magnetized ferromagnetic plate

Magnetoelastic (ME) waves and thickness-shear modes in the ferromagnetic plate are studied. Coupled vibrations of magnetization and shear elastic deformations excited simultaneously by a variable magnetic field propagate in two mutually perpendicular directions: parallel and normal to a surface. For parameters characteristic of isotropic ferromagnet with the sample magnetization and Zeeman field parallel to the surface, resonant frequencies of shear modes are computed and their dispersion law is examined. It is shown that the dependence of dimensional resonances frequencies on wave number k_z of ME wave propagating along saturating field direction occurs. The possibility of excitation of ME waves with different k_z explains multimode character of thickness ME resonances.     

The elliptical dimension of space-time atmospheric stratification of passive admixtures using lidar data

State-of-the-art airborne lidar data of passive scalars have shown that the spatial stratification of the atmosphere is scaling: the vertical extent (Δz) of structures is typically ≈Δx^H_z where Δx is the horizontal extent and H_z is a stratification exponent. Assuming horizontal isotropy, the volumes of the structures therefore vary as ΔxΔxΔx^H_z=Δx^D_s where the “elliptical dimension” D_s characterizes the rate at which the volumes of typical non-intermittent structures vary with scale. Work on vertical cross-sections has shown that 2+H_z=2.55±0.02 (close to the theoretical prediction 23/9).In this paper we extend these (x, z) analyses to (z, t). In the absence of overall advection, the lifetime Δt of a structure of size Δx varies as Δx^H_t with H_t=2/3 so that the overall space-time dimension is D_st=29/9=3.22…. However, horizontal and vertical advection lead to new exponents: we argue that the temporal stratification exponent H_t≈1 or ≈0.7 depending on the relative importance of horizontal versus vertical advection velocities. We empirically test these space-time predictions using vertical-time (z, t) cross-sections using passive scalar surrogates (aerosol backscatter ratios from lidar) at ∼3 m resolution in the vertical, 0.5-30 s in time and spanning 3-4 orders of magnitude in scale as well as new analyses of vertical (x, z) cross-sections (spanning over 3 orders of magnitude in both x, z directions). In order to test the theory for density fluctuations at arbitrary displacements in (Δz, Δt) and (Δx, Δz) spaces, we developed and applied a new Anisotropic Scaling Analysis Technique (ASAT) based on nonlinear coordinate transformations. Applying this and other analyses to data spanning more than 3 orders of magnitude of space-time scales we determined the anisotropic scaling of space-time finding the empirical value D_st=3.13±0.16. The analyses also show that both cirrus clouds and aerosols had very similar space-time scaling properties. We point out that this model is compatible with (nonlinear) “turbulence” waves, hence potentially explaining the observed atmospheric structures.     

Electro-optical properties of strontium-barium niobate crystals and their relation to the domain structure of the crystals

The electro-optical coefficients r _ij and half-wave voltage V_λ/2 of strontium-barium niobate crystals poled in the ferroelectric phase are shown to vary along the polar axis. The r _ij (z) and V_λ/2(z) dependences indicate the presence of a residual domain density D(z) and clearly depend on the sign of the polarizing field, with r _ij being minimum (D being maximum) near the negative electrode. This character of the D(z) distribution and, hence, the r _ij (z) and V_λ/2(z) coordinate dependences can be explained by predominant domain nucleation near the negative electrode, which is revealed when the switching processes are studied using 90° (Rayleigh) light scattering from domain walls.     

An experimental study on corona q-u curves under non-standard lightning impulses

Considering that a majority of lightning surges intruding into substations present non-standard form, an experimental study is performed on the q-u (charge-voltage) curves under damped oscillation impulses in a corona cage. Based on the measured results, a comparison is made between the q-u curves under damped oscillation and double exponential impulses. The oscillation frequency and damping time constant are varied to investigate their effect on the characteristic parameters of the q-u curves. A preliminary discussion is also given for explanation of the formative mechanism of the oblate helix minor loops appearing on the q-u curves.     

Beat excitation of terahertz radiation in a semiconductor slab in a magnetic field

Two infrared lasers of frequencies ω₁ and ω₂ propagating in the TM/TE mode along $\stackrel{?}{z}$ direction in a rippled density semiconductor waveguide are shown to resonantly excite terahertz radiation at the beat frequency when ripple wave number is suitably chosen to satisfy the phase matching. The wave vector of the density ripple is along the direction of laser propagation while a static magnetic field is applied transverse to it. The lasers exert a ponderomotive force on the electrons at the beat frequency. This force, in the presence of density ripple and transverse magnetic field, produces a nonlinear current at the terahertz frequency. The magnetic field enhances the amplitude of the terahertz wave. However terahertz yield is significantly higher in the TM mode laser beating than in the TE mode laser beating.     

Disturbances of the upper atmosphere and ionosphere caused by acoustic-gravity wave sources in the lower atmosphere

The results of observations of acoustic-gravity waves in the troposphere and the ionosphere at middle latitudes during periods of passage of the solar terminator are presented. Tropospheric observations were performed using a lidar. The frequency characteristics of variations of the tropospheric parameters are determined based on observations of the intensity of the scattered lidar signal. The characteristics of variations of the total electron content (TEC) in the atmosphere are determined from data collected by GPS navigation satellites. An analysis of the observational data showed that the spectrum of variations of the atmospheric and ionospheric parameters is indicative of acoustic-gravity waves (AGW) propagating from the lower atmosphere. Modeling studies of the vertical propagation of AGW from the Earth’s surface showed that such waves quickly (within ~15 min) reach altitudes of the upper atmosphere (~300 km). The refraction and dissipation of waves in the upper atmosphere produces perturbations of the background state of the atmosphere and gives rise to the waveguide propagation of infrasonic wave components. The observed manifestations of TEC disturbances caused by AGW propagating from the lower atmosphere can be explained by the diurnal variation of the altitude of the ionosphere and the waveguide propagation of infrasonic waves.     

Reconstruction of the coordinate dependences of quadratic susceptibility tensor \hat \chi ^{(2)} (z, ω1 ± ω2; ω1, ±ω2) components for the one-dimensionally inhomogeneous absorbing medium

A method for the unambiguous reconstruction of the spatial profiles of all components (except for ?? _zzz ) of the quadratic susceptibility complex tensor {ie165-2} (z, ??₁ + ??₂; ??₁, ??₂), which is responsible for the sumfrequency generation in a one-dimensionally inhomogeneous plate is proposed and proven for the first time. Such reconstruction is possible if the symmetry of the medium provides the diagonal character of the linear permittivity tensor {ie165-3} (z, ??). The procedure involves the measurement of the complex amplitude of the new wave with the frequency ??₁ + ??₂ that is reflected from the plate for a certain interval of the angles of incidence of the wave with the frequency ??₂. The reflected wave results from the nonlinear interaction of the wave with frequency ??₂ and the wave with frequency ??₁ that exhibits the normal incidence. A similar approach can be used to determine the profiles of the components of the quadratic susceptibility tensor {ie165-4}(z, ??₁ ? ??₂; ??₁, ? ??₂), which is responsible for the difference-frequency generation.     

Laser-ablation-induced refractive index fields studied using pulsed digital holographic interferometry

Pulsed digital holographic interferometry has been used to investigate the plume and the shock wave generated in the ablation process of a Q-switched Nd-YAG (λ=1064 nm and pulse duration=12 ns) laser pulse on a polycrystalline boron nitride (PCBN) target under atmospheric air pressure. A special setup based on two synchronised wavelengths from the same laser for simultaneous processing and measurement has been used. Digital holograms were recorded for different time delays using collimated laser light (λ=532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps showing the propagation of the shock wave and the plume generated by the process. Radon inversion has been used to estimate the 3D refractive index fields measured from the projections assuming rotational symmetry. The shock wave density has been calculated using the point explosion model and the shock wave condition equation and its behaviour with time at different power densities ranging from 1.4 to 9.1 GW/cm² is presented. Shock front densities have been calculated from the reconstructed refractive index fields using the Gladstone–Dale equation. A comparison of the shock front density calculated from the reconstructed data and that calculated using the point explosion model at different time delays has been done. The comparison shows quite good agreement between the model and the experimental data. Finally the reconstructed refractive index field has been used to estimate the electron number density distribution within the laser-induced plasma. The electron number density behaviour with distance from the target at different power densities and its behaviour with time are shown. The electron number densities are found to be in the order of 10¹⁸ cm^?3 and decay at a rate of 3×10¹⁵ electrons/cm³ ns.     

Analysis of the formation of ion beams in varying electric fields of a stationary plasma thruster

We propose a technique for analyzing the distribution function of the velocity components (radial V _r and azimuthal V _φ) of ions in a beam. This technique is used for studying the ion beam emerging from a stationary plasma thruster (SPT). It is shown that the beam contains ions with a radial velocity component in the range V _r /V _z = ? 1.2 to +0.74, as well as ions with the azimuthal velocity component in the range V _?/V _z = ±0.9. Numerical calculations lead to the conclusion that ions acquire the azimuthal velocity component in the field of the azimuthal wave of the plasma potential evolving in the SPT channel.