Reflection of electromagnetic waves from the layered structure of a high-temperature superconductor-multiferroic with cycloidal antiferromagnetic structure

The reflection of electromagnetic waves from the layered structure of a high-temperature superconductor-multiferroic with cycloidal antiferromagnetic structure in an external magnetic field is studied. The frequency dependence of the reflection coefficient at different values of an external magnetic field is calculated. The possibility of effectively controlling the reflective properties of the structure is established.     

Violent folding of a flame front in a flame-acoustic resonance

The first direct numerical simulations of violent flame folding because of the flame-acoustic resonance are performed. Flame propagates in a tube from an open end to a closed one. Acoustic amplitude becomes extremely large when the acoustic mode between the flame and the closed tube end comes in resonance with intrinsic flame oscillations. The acoustic oscillations produce an effective acceleration field at the flame front leading to a strong Rayleigh-Taylor instability during every second half period of the oscillations. The Rayleigh-Taylor instability makes the flame front strongly corrugated with elongated jets of heavy fuel mixture penetrating the burnt gas and even with pockets of unburned matter separated from the flame front.     

An Experimental Study and Theoretical Simulation of Jet-Wing Interaction Noise

The use of high-bypass-ratio engines in civil aviation has resulted in the occurrence of an additional noise source associated with noise of interaction between a jet and an airplane wing. A theoretical model is proposed for predicting the characteristics of interaction noise based on the near-field parameters for an isolated jet. The required near-field characteristics were obtained experimentally in the AC-2 anechoic chamber of the Central Aerohydrodynamic Institute (TsAGI) using a system of azimuthal microphone arrays. Noise in the far-field zone was also measured for both an isolated jet and a jet with a closely located plate simulating a wing. The results of comparing the directivities and spectra of interaction noise obtained using the proposed model and measured experimentally are in good agreement.     

Superionic and ion-conducting chalcogenide glasses: Transport regimes and structural features

Chalcogenide glasses are essentially known as amorphous semiconductors with interesting electronic and optical properties. In contrast to vitreous oxide systems which belong mostly to ionic insulators and/or conductors, the ion transport is not common for chalcogenide glasses and was observed for the first time in the seventies. Nevertheless, a higher polarisability of sulphur, selenium or tellurium compared to oxygen and respectively a higher ionic mobility and diffusivity, makes appropriate chalcogenide glassy systems favourable candidates for both fundamental research and practical applications in the field of solid-state ionics. The observed drastically different ion transport regimes that are closely related to the mobile cation distribution in the structure of silver and copper chalcogenide and chalcohalide glasses will be discussed in the present contribution which represents a compilation of recent results obtained by the author.     

Tracking the effects of rigidity percolation down to the liquid state: relaxational dynamics of binary chalcogen melts

The stochastic dynamics of binary liquids with formula AxB1-x, x=0-0.4 is investigated by neutron spin-echo spectroscopy. These compositions comprise samples of varying chemical connectivity, ranging from twofold-coordinated liquid Se to higher average coordinated As2S3. The parameters giving the temperature dependence of the relaxation patterns show a quasilinear dependence on the average coordination number. The results thus extend the validity of the rigidity concept into the normal liquid state and emphasize the role played by the fine details of atomic bonding on the dynamics at 10 ps-1 ns scales.     

Rapid increase in the delay time for the breakdown of gas-filled gaps in high electric fields

An experimental study is reported of the delay-time statistics for electrical breakdown in air in intense electric fields E = 100–200 kV/cm. The dependence of the statistical delay time t_st for the breakdown on the gap width is obtained for various fields E. With E = 100 kV/cm and with an air pressure of p = 1 atm, the delay time is 20 nsec and depends weakly on in the range 5 = 3–10 mm. As the gap width is reduced from 3 to 2 mm, t_st increases sharply, reaching 3000 nsec. The gap width at which the sharp increase in t_st sets in decreases with increasing E. The gap-width dependence of t_st has the same nature at different pressures. The minimum delay time has been measured to be 8 nsec.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 2, pp. 36–39, February, 1969.     

Electron-optics study of the development of an electric discharge in a gas at high-electric field intensities and with one-electron ignition

A study was made of the luminous region in a discharge gap with copper electrodes, a field of E = 80 kV/cm, air at atmospheric pressure, and a gap width of 4 or 2 mm. The cathode was irradiated with a spark to ignite the initial electrons. The electron current from the cathode was 0.2 · 10⁹ electrons/sec. The exposure time per frame was 3 · 10^–9 sec. With a gap width of = 4 mm, a luminous region is observed at the cathode 2 nsec after voltage is applied to the gap; this region propagates toward the anode, simultaneously increasing in diameter, at a velocity of 10³ cm/sec. A voltage drop is established across the gap approximately 0.5 nsec after the luminous front arrives at the cathode. In narrower gaps, the voltage drop is established across the gap a considerable time after the luminous region has crossed the gap.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 24–27, November, 1969.     

Nonlinear equation for curved nonstationary flames and flame stability

A time-dependent nonlinear equation for a nonstationary curved flame front of an arbitrary expansion coefficient is derived under the assumptions of a small but finite flame thickness and weak nonlinearity. On the basis of the derived equation, stability of two-dimensional curved stationary flames propagating in tubes with ideally adiabatic and slip walls is studied. The stability analysis shows that curved stationary flames become unstable for sufficiently wide tubes. The obtained stability limits are in a good agreement with the results of numerical simulations of flame dynamics and with semiqualitative stability analysis of curved stationary flames. Possible outcomes of the obtained instability at the nonlinear stage are discussed. The instability may result in extra wrinkles at a flame front close to the stability limits and in self-turbulization of the flame far from the limits. The self-turbulization can also be interpreted as a fractal structure. The fractal dimension of a flame front and velocity of a self-turbulized flame are evaluated.