On a Modification of the Scintillation Method

We solve the problem of diffraction of fluctuating radiation by an optically thin irregular layer (phase screen) with developed turbulent structure. It is shown that in the case of diffraction of radiation with saturated fluctuations and a narrow-band frequency spectrum by a weakly turbulent moving phase screen, the measured frequency spectrum of intensity fluctuations in the observation plane allows one to obtain information on the form of the spectrum of irregularities of an optically thin irregular layer in a wide size range significantly exceeding the size of the first Fresnel zone. Similarly to the well-known phase method of diagnostics of randomly irregular media, the conventional scintillation method modified in such a way yields undistorted information on the form of the irregularity spectrum. However, in contrast to the phase method, it also allows one to obtain data on the drift velocity of irregularities in the studied irregular layer.     

Analysis of appearance of moving ionospheric disturbances of the “sickle” type at middle latitudes

We present the results of analysis of the data of vertical ionospheric sounding at the Zimenki test site (Nizhny Novgorod). The January and July ionograms are used to plot the dependences of the number of “sickle” type disturbances on the time of the day for the period from 1996 to 1992. A comparison with the scattering in an ionospheric F-layer for the same period is performed. A trend in the time series of the phenomenon observed is recorded. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 12, pp. 1455–1462, December, 1997.     

Structural self-organization, domain structure, and magnetic characteristics of manganites of the La-Sr-Mn-Ti-Ni-O system

The structure and phase composition of La_0.65Sr_0.35Mn_{1 ? x ? y} Ni_xTi_yO₃ manganites (0 ≤ x ≤ 0.3; 0 ≤ x + y ≤ 0.3) obtained by solid-state reactions in air are studied by x-ray diffraction. All the samples are single-phase materials and have an orthorhombic or pseudocubic structure, depending on the chemical composition and the sintering temperature. The saturation magnetization and the temperature dependences of the magnetic susceptibility are measured. The magnetic structure of manganites is characterized by the existence of inhomogeneities in the form of ring domains or drops whose size is in the range 30–100 μm. A study of the surface by scanning tunneling microscopy reveals the occurrence of ring, spiral, or lamellar structures with a characteristic size of the order of 10 nm. A possible approach to the interpretation of the obtained experimental results based on the concept of self-organization processes leading to the segregation of ion pairs and the formation of elastic concentration domains is discussed.     

On one feature of the F-spread phenomenon in the midlatitude ionosphere

We report on the results of observations of reflected SW signals by vertical sounding (VS) of the ionosphere in Zimenki, Nizhny Novgorod region, in the summers of 1994 and 1995. We discovered an anomalous increase in the multipath propagation of the received SW signals during ionospheric F-spread: The duration of a multipath reflected signal increased considerably when we used a highly directional antenna compared to the case of a weakly directional antenna. The fast amplitude fluctuation index increased with increasing delay of the reflected SW signals. The observations are interpreted in terms of a stochastic model of midlatitude F-spread as the phenomenon of multipath radio wave scattering (reflection) from large-scale electron density inhomogeneities under conditions of a strongly developed inhomogeneous structure of the ionosphere.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 10, pp. 1064–1070, October, 1995.     

Study of the Wind Characteristics of the Atmospheric Turbulence using a Multibeam Sodar

We present the results of acoustic sounding of the atmosphere in summer of 2001. The experiments were carried out using a multibeam bistatic sodar with two parabolic antennas of 15 m in diameter. The distance between the antennas was about 425 m. The transmitting acoustic antenna having 8^° beam width was pointed to the zenith. The four-beam operation of the receiving paraboloid was implemented by mounting four separate microphones in its focal plane. The width of each beam of the receiving antenna was 2.5^°. The beams of the transmitting and receiving antennas crossed at a height about 500 m. The sounding frequency was equal to 576 Hz. The acoustic-pulse duration and repetition period were 2 s and 8 s, respectively. A new procedure for experimental-data processing on the basis of analysis of temporary variations in the Doppler frequency shift of a scattered signal is proposed and approved. The approach based on using structural functions is applied. The preliminary results of analysis of one observation session are presented.     

Mixed algebras and quivers related to cell complexes

In this paper we study finite dimensional algebras arising from categories of perverse sheaves on finite regular cell complexes (cellular perverse algebras). We prove that such algebras are quasi-hereditary and have finite global dimension. We discuss some restrictions, under which cellular perverse algebras are Koszul. We also study the relationship between Koszul duality functors in the derived categories of categories of graded and non-graded modules over an algebra and its quadratic dual.     

On the fractal structure of small-scale traveling ionospheric disturbances

We present the results of the studies of fractal properties of the small-scale inhomogeneities of traveling ionospheric disturbances in special experiments on radio-raying of the midlatitude ionosphere by signals from orbital satellites in 2004–2006. Along with the conventional correlation processing of the received signals, we performed their multifractal analysis, as well as fractal processing of signals by the correlation-integral method. Important information on fractal properties of the small-scale turbulence for the least studied part of the upper-ionosphere inhomogeneity spectrum in the interval of characteristic scales l ≈ 1–10 km is obtained. In particular, it is noted that the fractal structure of these inhomogeneities can be originated from the nonlinear “destruction” of several large-scale sinusoidal structures in a quasistable traveling disturbance. It is also noted that the multifractal spectra of amplitude fluctuations of the received signals obtained in the experiments in different years, in different time of the day, and in different seasons of the observations are quite similar. This is evidence that intermittency is a universal property of the plasma turbulence, at least for the midlatitude upper ionosphere. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 1, pp. 22–30, January 2008.     

Multifractal Structure of Intermittency in a Developed Ionospheric Turbulence

We present the results of studying the multifractal structure of intermittency in a developed ionospheric turbulence during special experiments on radio-raying of the midlatitude ionosphere by signals from orbital satellites in 2005–2006. It is shown, in particular, that the determination of multidimensional structural functions of the energy fluctuations of received signals permits one to obtain the necessary information on multifractal spectra of the studied process of radio-wave scattering in the ionosphere. Experimental data on multifractal spectra of slow fluctuations in the received-signal energy under conditions of a developed small-scale turbulence are compared with the existing concept of the radio-wave scattering within the framework of the statistical theory of radio-wave propagation in the ionosphere. It is inferred that under conditions of a developed ionospheric turbulence, the multifractal structure of the intermittency of slow fluctuations in the received-signal energy is a consequence of the intermittency of small-scale fluctuations in the electron number density of the ionospheric plasma on relatively large spatial scales of about several ten kilometers. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 6, pp. 485–493, June 2008.     

Multipower spectrum of small-scale ionospheric turbulence

We consider the problem of diagnostics of the local structure of small-scale ionospheric turbulence using the multifractal analysis of received signals from the Earth’s orbital satellites after the radio sounding of the inhomogeneous ionosphere by these signals. In particular, it is shown that analysis of the multifractal structure of the received-signal amplitude records by the method of multidimensional structural functions allows one to determine the indices of the multipower local spectra of the small-scale ionospheric turbulence, which are inherent in it due to the nonuniform spatial distribution of small-scale fluctuations of the electron number density. It is noted that information on the multipower spectrum of small-scale ionospheric turbulence is not available for the conventional radio scintillation method based on the classical spectral analysis of received signals during the remote radio sounding of the ionosphere. At the same time, the method of multidimensional structural functions is efficient under conditions of actual nonstationarity of the process of scattering of the HF radio waves by the randomly inhomogeneous ionospheric plasma. The method of multidimensional structural functions is used for the multifractal processing of received signals of orbital satellites during special experiments on radio sounding of the midlatitude ionosphere under natural conditions and its modification by high-power HF radio waves. First data on the indices of the multipower local spectra of small-scale ionospheric turbulence are obtained. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 1, pp. 14–22, January 2009.