Defect formation in tellurium in various gravity conditions

The effect of gravity (from micro-to a rather high gravity, 5g ₀) acting during tellurium crystallization on the concentration of neutral (N _D ) and electrically active (N _AD ) acceptor-type structural defects in samples grown both under complete remelting of the starting ingot and under directed seed recrystallization of an ingot was studied. The concentrations N _AD and N _D and their distribution over the sample length were derived from the electrical characteristics (conductivity and the Hall effect) measured along the ingots in the temperature range 1.6–300 K. The contributions of various mechanisms to hole scattering were found from an analysis of the temperature behavior of the mobility. The results obtained were compared with the characteristics of samples grown following a similar program under normal conditions. The presence of N _AD defects is characteristic of the initial crystallization stage of all samples. N _AD is substantially lower (N _AD ～ 10¹⁵ cm^?3) than N _D ～ 10¹⁸ cm^?3 and decreases exponentially in the course of sample crystallization. Complete remelting under microgravity revealed indications of strong supercooling and spontaneous crystallization, as well as spatial oscillations of the electrical resistivity over the sample length caused by N _D modulation. These observations are related to the specific features of the melting and crystallization in zero gravity, namely, the melt breaking away from the wall of the ampoule and the increasing role of Marangoni convection.     

Effect of the reaction conditions on the formation of the ZnO nanostructures

ZnO nanorods were synthesized through a simple chemical method by reacting Zn(C₂H₃O₂)₂·2H₂O and NaOH at low temperature and the effects of changing the order of addition of reactants on the morphological evolution of ZnO nanorods were investigated. The samples were characterized by using XRD, SEM, EDX, TEM, BET and Raman techniques. Optical properties of the ZnO nanostructures were too investigated by UV–Vis spectroscopy at room temperature.The hexagonal wurtzite phase of ZnO was confirmed by X-ray diffraction (XRD) for all the samples. SEM and TEM analysis indicated that different morphologies were obtained by changing the order of addition of reactants.     

Modeling the ionospheric propagation of acoustic gravity waves from the Tohoku tsunami of 2011

The observations of the upper atmosphere after the severe Tohoku earthquake of March 11, 2011 are analyzed. The observations cover the Hawaii region and span the time interval from about 7 h after the main shock to about half an hour before the arrival of the tsunami wave generated this earthquake. We explore the factors that are responsible for the emergence of the ionospheric response, which comprises a series of waves propagating ahead of the tsunami. The contribution of the moving tsunami wave into the formation of such a pre-tsunami response is established by the numerical simulation of the equations of geophysical hydrodynamics with two-dimensional geometry.     

Effect of phase noise on parametric instabilities

We report an experimental study on the effect of an external phase noise on the parametric amplification of surface waves. We observe that both the instability growth rate and the wave amplitude above the instability onset are decreased in the presence of noise. We show that all the results can be understood with a deterministic amplitude equation for the wave in which the effect of noise is just to change the forcing term. All the data for the growth rate (respectively the wave amplitude), obtained for different forcing amplitudes and different intensities of the noise, can be collapsed on a single curve using this renormalized forcing in the presence of noise.     

Effect of multiplicative noise on parametric instabilities

We report a study on the effect of external multiplicative noise on parametric instabilities using two different experimental systems: an electronic RLC circuit, parametrically pumped with a voltage-variable capacitor, and surface waves generated by vertically vibrating a layer of fluid (the Faraday instability). Both systems are forced by the superposition of a sinusoidal and a noisy component. We study the statistical properties of the response of both systems to noisy parametric forcing and compare them with theoretical predictions. When the detuning from parametric resonance is such that the bifurcation in the absence of noise is supercritical, both systems behave in the same way under the influence of noise. We find that the effect of noise is twofold: on one hand, it triggers the instability before its deterministic onset under the form of oscillatory bursts; on the other hand, it inhibits the nonlinearly saturated oscillatory response above the deterministic onset. When the detuning is such that the bifurcation is subcritical, we find that the two systems behave differently. In the case of the electronic oscillator, noise mostly triggers random transitions between the two states of the bistable region that exists in the absence of noise, whereas in the surface wave experiment new states are created by noise and the bistable region is strongly enlarged.     

A mathematical mechanism for instabilities in stripe formation on growing domains

A cascade process involving stripe splitting in reaction-diffusion systems with isotropically growing one-dimensional domains is studied. Such cascades, propagating from a smaller domain to a larger domain, have been proposed as an answer to the criticism that the Turing mechanism lacks robustness because many stable patterns can coexist on a large domain and, therefore, the final state is very sensitive to the initial conditions. In contrast, if the system starts with a small domain, very few stable patterns are possible, which limits the sensitivity to the initial conditions. In order to show the validity and limitations of this scenario, we clarify the underlying mathematical mechanism that drives various types of stripe-splitting via a reduction from partial differential equations to ordinary differential equations, as well as investigating global arrangements of the set of n-mode stripe branches with D_n-symmetry of the stripe locations. The mathematical simplification above allows us to reveal how each n-mode stripe branch is destabilized as the domain grows and to characterize the associated eigenprofiles that actually determine the manner of splitting at the infinitesimal level. We find that all the D_n-symmetry-breaking instabilities typically occur simultaneously up to leading order before the saddle-node point of the n-mode stripe branch is reached. The instability with the largest real part is of the alternate type: every other peak splits at the infinitesimal level. A symmetry-preserving instability appears at the saddle-node point, which drives the simultaneous type of splitting, i.e., mode-doubling. Due to competition between these two types of instabilities, the problem depends subtly on the growth speed. Alternate splitting typically arises for slow growth and simultaneous splitting for fast growth. For intermediate growth rates, the manner of splitting becomes mixed and sensitive to fluctuations.     

Diagnostics of the HF-pumped ionospheric region using wide-band radio emission

We present the results of comprehensive studies of the spatio-temporal structure of the artificial ionospheric plasma turbulence created by powerful radio emission over the “Sura” heating facility. The elaborated methods of the transmitter-receiver operation control, wide-band signal recording, digital filtering and spectral analysis of the stimulated electromagnetic emissions and short radio pulses are used for diagnostics. Novel data are obtained on the evolution of the Langmuir and upper-hybrid turbulence spectrum, the altitude distribution of the plasma wave decay rates, and the amplitude-phase characteristics of the test signals under wide-band sounding of the ionospheric plasma. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 8, pp. 649–668, August 2007.     

On the theory of instabilities arising at quark-gluon plasma formation

Collisions of two degenerate quark Fermi liquids are studied. It is shown that there arise instabilities, which manifest themselves in propagation of growing oscillations corresponding to the modes existing in a Fermi liquid at rest. Quark jets are likely to appear in the directions of the growing oscillations propagation.

The instabilities studied in this work are similar to the beam instability in ordinary electron plasma.     

Secondary instabilities and vortex formation in collisionless-fluid magnetic reconnection

It is shown that the pattern of current layers formed within a magnetic island in the nonlinear phase of magnetic field line reconnection in a collisionless two-dimensional fluid plasma is subject to the onset of a secondary instability, the effect of which increases with decreasing electron temperature. In the cold electron limit the saturation of the island growth is accompanied by a turbulent redistribution of the current layers and by the development of long lived fluid vortices while, in the opposite limit, the current layer structure remains regular.     

Effect of destabilizing fields on hydrodynamic instabilities in nematics

The effect of destabilizing fields on the roll instability (RI) threshold for shear flow and on the homogeneous instability (HI) threshold for plane Poiseuille flow of nematic HBAB (μ _s>0) is studied on the basis of the continuum theory of nematics for flow cells of infinite lateral width. It turns out that the critical shear rate and wave vector at RI threshold decrease with increasing destabilizing field but do not approach zero at the Freedericksz transition. However calculations show that beyond the Freedericksz threshold HI may be favourable over a range of destabilizing field with shear in the stabilizing role. For plane Poiseuille flow a similar analysis points to the existence of a HI threshold in the presence of destabilizing field beyond the Freedericksz threshold again with shear acting as a stabilizing field. These results are compared with theoretical results obtained previously for MBBA.     

On the role of large-scale ionospheric inhomogeneities in the formation of middle-latitude F-spread

We present the results of a special experiment carried out in the settlement of Zimenki, Nizhniy Novgorod province, on ionospheric vertical sounding by HF signals under F-spread using practically synchronous measurements of the multiple-ray nature of normal waves reflected from magnetoactive ionospheric plasma with ordinary and extraordinary polarizations at frequencies shifted by 0.7MHz. The experiment confirms the dominating role of large-scale electron-density inhomogeneities of the moving ionospheric disturbance type in the formation of middle-latitude F-spread.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 5, pp. 564–567, May, 1996.This work was supported by the Russian Foundation for Fundamental Research (project N. 95-02-03716 RFFI).