Search for inert oxide matrices for carrying out solid-phase ion-exchange reactions by the internal reaction scheme

Having a goal of studying the possibility of and develop methods for controlling internal solidphase reactions inside a solid matrix that is diffusionally saturated with several components simultaneously from different source phases, we experimentally checked whether it is possible to synthesize, for use as these matrices, ZrO₂-Nb₂O₅ solid solutions having distorted fluorite structure and NiO-CuO-Cu₂O solid solutions having rock salt structure (these solid solutions had been studied by computational techniques using the ion lattice mechanic approximation), with a controlled ratio of anionic and cationic conductivities.     

Comparison of efficiency of artificial neural networks for forecasting the geomagnetic activity index Dst

Using artificial neural networks (ANN), we study problems of forecasting the evolution of the geomagnetic D _st index on the basis of parameters of the solar-wind plasma and magnetic field obtained from the OMNI satellite system. Using this sample problem, we compare the neural network modifications with error backpropagation, such as classic network and feedback network. We analyze the efficiency of a feedback in the hidden layer of the Elman neural network which has a dynamic memory due to the time delay. The role of a delay in the input layer of a neural network is studied. It is shown that the forecasting efficiency increases significantly if a feedback in the hidden layer and the time delay in the input layer are used. The hidden-layer feedback and the input-layer time delay reproduce the time delay in the physical problem considered. Using thresholds in activation functions does not influence the ANN efficiency. The solar-wind parameters that have the strongest influence on the geomagnetic-storm formation are found. The influence of the number of hidden-layer neurons on the quality of forecasting the global disturbances in the near-Earth magnetic field is studied. It is pointed out that the networks with error backpropagation allow, after the relevant tuning and learning, fairly efficient forecasting of phenomena similar to geomagnetic storms several hours before a large-scale magnetospheric event. Pedagogical University, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 5, pp. 385–394, May, 2000.     

Detection of magneto-gravity waves in the ionosphere by analysis of the maximum observable frequencies on oblique-sounding paths

The existence of magneto-gravity waves stipulated by the substorm activity can lead to the occurrence of traveling ionospheric disturbances, whose velocity exceeds the sound speed. For detection of magneto-gravity waves, we used experimental data on propagation of decameter radio waves on the midlatitude and subauroral oblique sounding paths Inskip–Rostov-on-Don, Cyprus–Rostovon-Don, Irkutsk–Rostov-on-Don, and Norilsk–Rostov-on-Don in December 2006 and March 2007 under conditions of weak geomagnetic disturbance. Time delays between the AE indices of polar electrojets and the maximum observable frequencies for the considered paths were established by calculation of linear correlations. These delays correspond to the times required for transport of gravity disturbances from the auroral region to the reflection points of radio waves on respective paths. Among the obtained time shifts, we mention the 5–10-min ones which correspond to increased velocity of the disturbances compared with the usual velocities of acoustic-gravity waves for the paths under study. Such cases can be related to the transport of magneto-gravity waves. Study of the spectral composition of the AE-index disturbances and recorded maximum observable frequencies shows consistency of their spectral features in the cases of increased correlation for small time delays. It is also found that the spectral features of the AE-index disturbances coincide with the spectral features of the disturbances of the horizontal component of the geomagnetic field on ground-based magnetic stations. According to calculated dispersion curves, the frequencies of magneto-gravity waves were estimated, and they turned out to be equal to ω ≈ (1–2) ・ 10⁻⁴ Hz.     

Phase diagrams of the CoMnO system in air

A retrospective critical analysis of phase diagrams of the CoMnO system in air has been made. A high-temperature phase equilibrium of the CoMnO system in air and phase diagrams of this system under different cooling conditions (quenching in water, quenching in air, cooling at rate of 25°K h^?1) have been constructed. A comparative analysis of these diagrams shows that whatever the cooling rate, cooling does not preserve the high-temperature state of the system and is accompanied (depending on cooling conditions, temperature and Co/Mn ratio) by one or more of the following phenomena: (1) oxidation of the Co_NMn_1?NO solution to spinel-type solid solutions (2) merging of a cubic and tetragonal spinel phase and formation of a homogeneous tetragonally distorted spinel (3) tetragonal distortion of the spinel lattice (4) decomposition of the cubic spinel into a cubic and tetragonal spinel. (5) decomposition of the cubic spinel into a cubic, tetragonal and slightly distorted tetragonal spinel. Therefore, the form of the phase diagram of the CoMnO system in air is entirely determined by the method of cooling.     

Transformation of alfvén into slow magnetosonic disturbances in the magnetosphere due to reflection from magnetically conjugate ionospheric regions

We perform numerical and analytical studies of MHD phenomena within the framework of a one-dimensional model of the magnetosphere bounded by conjugate reflection surfaces. Specific features of the nonlinear transformation of an Alfvén wave into a slow magnetosonic one upon propagation along the magnetic fieldB ₀ are considered. Effects of reflection of a nonlinear magnetospheric wave from magnetically conjugate ionospheres are analyzed in detail. It is shown that the main effect for the case of a nonlinear Alfvén wave in a low-temperature plasma is the plasma sweeping off the volumes close to the reflecting boundaries. Numerical results which demonstrate the generation dynamics of the slow magnetosonic wave and plasma sweeping upon reflection of a powerful Alfvén wave from the ionosphere are in qualitative agreement with the analytical estimates. In a cold plasma, the effect is so significant that it requires a numerical study even if the initial Alfvén wave is linear. The key role of the ratio between the Alfvén and sound velocities for the value of the density disturbance is revealed. Pedagogical University, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 4, pp. 285–295, April, 2000.     

Long-Term Forecasting of Solar Activity Indices Using Neural Networks

Using artificial neural networks (ANN), we study the possibility for long-term forecasting of the annual mean Wolf numbers and the monthly average solar radiation flux at 2800 MHz. A feedback ANN with error backpropagation was designed and implemented for this purpose. The software allows one to vary the number of input parameters and neurons and the values of the training parameters. The forecast error is calculated and the actual data are graphically compared to the predicted ones. The annual Wolf number was forecasted directly one year ahead using an auxiliary training (warming-up) of the ANN by the previous 18 values of the annual Wolf number entering the training sequence. The prediction efficiency was 92%. Adding the coronal index and the annual solar-radiation flux (i.e., the SF index) to the input parameters leads to some improvement of the forecast. The iterative long-term forecast of the annual Wolf number for 1986-2000 yielded an efficiency of 71%. Using the direct and iterative techniques, the annual Wolf number was forecasted for the rest of the 23rd and the beginning of the 24th cycles (2000-2010).     

Magnetogravity waves in the ionosphere under conditions of finite conductivity

We obtain dispersion relations for magnetogravity waves in the ionosphere with allowance for the combined influence of magnetic field, gravity, and finite conductivity within the framework of the hydrodynamic approximation. The required conditions are fulfilled in the ionosphere at altitudes over or about 250 km. The auroral electrojet is considered as a source of magnetogravity waves which are frequently observed as traveling ionospheric disturbances. The contribution of magnetogravity waves to the ionospheric disturbances is determined on the basis of analyzing the data from the vertical sounding of the ionospheric F₂ layer and the geomagnetic disturbances along the chosen magnetic meridian and on its sides. The features of the obtained dynamic spectra of magnetogravity waves agree with the characteristic frequencies and velocities determined by the calculated dispersion curves. As a result, we confirm the fact that magnetogravity waves stipulate some traveling ionospheric disturbances and can be used for diagnostics of the ionospheric parameters.     

Nonlinear transformation of magnetohydrodynamic waves in moving plasma

We study the space-time dynamics of low-frequency formations in a moving plasma on the basis of magnetohydrodynamic (MHD) concepts. For this purpose a special computer program was written, which realizes MHD equations in a 1D approximation and allows us to carry out computer simulations in interactive mode. In the experiments we consider weak nonlinearity, in which the observed dynamic processes permit quasilinear interpretation in terms of Alfven and magnetoacoustic waves with their interaction, and strong-nonlinearity modes, in which a quasilinear approach is meaningless. We obtain new results on the influence of drift of the medium on the shock-wave shape and oscillations arising near it. Drift motion of the medium promotes the development of a shock-wave instability and other dynamic modes.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 5, pp. 579–587, May, 1996.This work was supported by the Russian Foundation for Fundamental Research (project No 94-023-06108).     

Artificial neural network technique for predicting the critical frequency of the ionospheric <Emphasis Type="Italic">F</Emphasis><Subscript>2</Subscript> layer

We employ artificial neural networks (ANNs) to develop an algorithm yielding 1-, 2-, 3-, 12-, and 24-hour forecasts of the critical frequency of the ionospheric F₂ layer. A search for suitable training set and ANN architecture is performed. The use of auxiliary input data, such as the solar-wind and interplanetary magnetic-field parameters, as well as the geomagnetic-activity indices, makes it possible not only to improve the prediction efficiency but also to find some regularities in the critical-frequency behavior. The results of this work can be applied to the prompt correction of the ionosphere model, aimed at improving the ionospheric HF radio communication.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 1, pp. 1–15, January 2005.     

Calculation of Classical Polar-Activity Indices Using Their Modern Variants

At present, the auroral-electrojet AE, AU, and AL indices are calculated using a smaller number of stations than earlier. This influences the accuracy of estimates of the magnetospheric activity components, which are performed using the relationships with modern indices AE₈ (obtained from the data of 8 stations) substituted instead of the classical indices AE₁₂ (obtained from the data of 12 stations). In this paper, we develop an artificial neural-network (ANN) algoritm for recalculating the classical polar-activity indices from modern ones. It is demonstrated that the developed ANN is capable of retrieving the AE₁₂-index from data of 8 stations (AE₈) with efficiency reaching 90% in some cases. The results obtained allow one to estimate the error in the representation of the auroral-electrojet activity by modern AE₈ indices as compared with the ones introduced into geophysical research by their creators. We also develop a retrieval technique for polar indices, which employs data on solar-wind parameters.