Review of results of HF scattering by artificial ionospheric turbulence obtained with UTR-2 radio telescope

The results of bistatic-radar and transillumination studies of the F-layer under the influence of powerful radio waves (Sura heating facility, Nizhny Novgorod) are presented. A highly directional receiving antenna (UTR-2, Kharkov) made it possible to detect and interpret a number of fine-structure characteristics of the Doppler spectrum of a signal scattered by a heated region. It is shown that, in addition to regular drift, there exists relative ordered motion of inhomogeneities in a perturbed region. The relative velocity is estimated. Deformation of the spectrum of a scattered signal in the states of development and relaxation is established and studied, and possible mechanisms of this phenomenon are discussed. Quasi-periodic variations of the amplitude and frequency of a scattered signal with periods of 30 sec to 5 min are detected. A comparison is made with the results of simultaneous radio transillumination of a heated region by signals from the point source Cassiopeia.Scientific-Research Radio-Physics Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 4, pp. 479–492, April, 1994.     

Studying characteristics of the large-scale ionospheric irregularities induced by high-power HF radio emission with GPS diagnosis

We present the results of experimental studies of artificial large-scale irregularities of the ionospheric electron number density with dual-frequency GPS diagnosis. The total electron content was analyzed in the GPS signal trajectory when the satellites passed over the heated region. Spectral composition of the observed variations was determined by wavelet analysis. Characteristic scales of artificial irregularities of the electron number density in the F layer are estimated. It is experimentally proved that the irregularities remain for at least 15–20 min after the transmitter is switched off. A more confident excitation and increased intensity of the irregularities were also confirmed when the beam was inclined south of the magnetic-zenith direction.     

Plasma diagnostics of the solar corona using decimetric radio waves (review)

The solar corona is a very dynamic plasma on time scales down to a few tens of microseconds. The various emissions at decimetric wavelength are briefly reviewed. Several of them seem to be caused by energetic (non-thermal) electrons accelerated in flares or flare-like processes releasing free magnetic energy. The use of decimetric radiation as diagnostics of the acceleration process, the ambient plasma, and the non-thermal particles requires a solid understanding of the emission process. Although we are still far from this in most cases, some information can already be derived from the observations.Institute of Astronomy, Federal Institute of Technology (ETH), Zurich, Switzerland. Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 7, pp. 809–820, July, 1994.     

Excitation of short-wave oscillations in the ionospheric plasma by the field of a high-power radio wave with extraordinary polarization due to induced scattering by ions

We analyze excitation of electron-cyclotron or upper hybrid oscillations of the ionospheric plasma at a frequency that is close to the pump frequency as a result of induced scattering of a high-power radio wave with extraordinary polarization by ions. The excited oscillations have a small wavelength of the order of the Larmor electron radius, which allows them to propagate near and below the reflection level of an extraordinary radio wave. We found the instability increment and threshold field, which results from collisional absorption of plasma waves. It is shown that the threshold field is minimal near the reflection level of an extraordinary radio wave when the radio wave frequency f₀ is between electron harmonics nf_Be with n≥2. In an ionospheric F layer it is of the order of 1 W/m. Such fields are easily obtained in ionospheric heating experiments allowing for radio-wave field swelling in the reflection region. In the vicinity of electron harmonics f_o≅nf_Be, the threshold field is increasing. For f_o<nf_Be with f_o≅nf_Be the instability does not develop because of the absence of plasma oscillations with a frequency that is close to the pump frequency (the latter also refers to the case f_o<2f_Be). The expressions obtained are generalized to the case in which the instability under consideration is excited by the field of an ordinary radio wave in the region of its quasilongitudinal propagation. We discuss the possibility of using the emergence of very short-wave plasma oscillations for explaining the experimentally observed phenomena. Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences, Troitsk, Moscow Region, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 5, pp. 541–560, May, 1997.     

Gyroharmonic properties of the middle-scale artificial ionospheric turbulence during heating of the ionospheric F 2 layer by a high-power O-mode radio wave

We present the results of studying the properties of artificial F-spread that appears on ionograms during heating of the ionospheric F₂ region by a high-power O-mode radio wave. It is shown that the regions of resonant interaction of a high-power radio wave with plasma, where the pump-wave energy is almost totally absorbed and the plasma is subject to intense heating, affect significantly the development of a self-focusing instability of a high-power radio wave and the generation of middle-scale (with characteristic scales across the magnetic field l_⊥ ≈ 0.4–1.5 km) artifical ionospheric inhomogeneities. It is established that the intensity of such inhomogeneities depends on the sign and magnitude of detuning of the pump-wave frequency with respect to the electron gyroresonance harmonic frequency Δf = f_PW − nf_ce and has the minimum value for Δf ≈ −20 kHz, thus demonstrating the asymmetry of the gyroharmonic properties of their excitation mechanism. Relationship between the observed phenomena and known characteristics of the artificial ionospheric turbulence for f_PW ≈ nf_ce is analyzed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 5, pp. 367–375, May 2008.     

Global modeling 2~(nd)-order ionospheric delay and its effects on GNSS precise positioning

Ionospheric delay is one of the major error sources in GNSS navigation and positioning.Nowadays,the dual-frequency technique is the most widely used in ionospheric refraction correction.However,dual-frequency measurements can only eliminate the first-order term of ionospheric delay,while the effect of the second-order term on GNSS observations may be several centimeters.In this paper,two models,the International Reference Ionosphere (IRI) 2007 and International Geomagnetic Reference Field (IGRF) 11 are used...     

Radiation effects on poly(methyl methacrylate) induced by pulsed laser irradiations

Poly(methyl methacrylate) (PMMA) was irradiated using a medical UV-ArF excimer laser operating at the fundamental wavelength of 193 nm. Characterized by a beam diameter of 1.8 mm and energy of 180 mJ with a Gaussian energy profile, it operates in a single mode or at 30 Hz repetition rate. Mechanical profilometry was carried out on ablation craters in order to study the rugosity and the ablation yield in the various operative conditions. Optical transmission and reflection measurements at six wavelengths were conducted in order to characterize the optical properties of the irradiated surfaces. Measured crater depths in PMMA were lower with respect to the forecasted ones in corneal tissue, while the lateral crater aperture was maintained. The rugosity produced at the crater bottom after irradiation was about 0.3 μm, and the ablation yield was about 10¹⁵ molecules/laser pulse, while etching depth and diameter show a roughly linear dependence on the number of laser shots. These experiments constitute a base for deeper clinical investigations.     

Violation of the coherence of radio waves induced by a cascade shower in the lunar regolith

It has been shown that small fluctuations of the refractive index of the lunar regolith owing to, e.g., a nonuniform density distribution, give rise to the loss of the coherence of a Cherenkov radio pulse induced by a cascade shower from an ultrahigh-energy particle and to a strong decrease in the spectral density of the radio signal. This can be one of the causes of why no events from ultrahigh-energy cosmic particles on the surface of the moon have been detected.     

R.F. (280 MHz) EPR imaging of extended samples: Apparatus and preliminary results

This paper presents the preliminary results obtained using an Electron Paramagnetic Resonance imaging apparatus operating at 280 MHz. The acquisition technique and the procedure used to obtain the spin density spatial localization are presented and specimen images of extended samples are given. The accuracy of the images and the spatial resolution are also discussed.     

Consistent quasi-periodic variations of the geomagnetic pulsation level and doppler frequency shift of decametric radio waves aspect-scattered by artificial field-aligned ionospheric irregularities

We present the results of experimental studies of consistent quasi-periodic variations of the geomagnetic-pulsation level and effective Doppler frequency shift of decametric radio waves aspectscattered by artificial field-aligned ionospheric irregularities. For processing of signals, we used a system spectral analysis and a correlation analysis. It is shown that quasi-periodic variations of the effective Doppler frequency shift are caused by geomagnetic-field pulsations with an amplitude of 0.5–1.0 nT and a period of 50–150 s. Estimated amplitudes of the quasi-periodic and aperiodic drift velocities of the ionospheric irregularities appeared close to 5–10 and 15–30 m/s, respectively.     

Lasers for plasma diagnostics and laser methods of investigation (review)

Delivered at the Fifth All-Union Conference on diagnostics of a high-temperature plasma (June 18–22, 1990, Minsk).     

Cu-Ag (111) polymorphism induced by segregation and advacancies

Chemical and structural phase transitions induced by Ag surface segregation in the dilute Cu(Ag) (111) system have been investigated by Monte Carlo simulations. The polymorphism observed when depositing Ag on Cu (111) is proven to exist also in equilibrium segregation. If the segregation isotherms are not very sensitive to the superstructures, we show that the superstructure observed in the high part of the isotherm depends strongly on the number of advacancies.