Bistatic radar as a tool for earth investigation using small satellites

Bistatic radar is a facility for the Earth remote sensing, which uses large spatial diversity between its transmitter and receiver. Nomogram method is proposed to determine the radar's parameters. Analysis of the nomograms has shown that modern onboard radio facilities allow to obtain spatial resolution of about 100 m at the wavelength λ = 3 cm for LEO satellite (H = 350 km). Experiments of bistatic radiolocation of the Earth near the radioshadow zone were provided using telecommunication link “MIR” orbital station — GEO satellite at wavelength λ = 32 cm. For the first time in practice of bistatic radiolocation of the Earth from space reflected signal in radioshadow zone was observed.The analysis of experimental results verified the developed radiophysical model with the value of sea water conductivity σ = 7.0 mo/m and absorption coefficient due to atmospheric oxygen χ = 0.0096±0.0024 dB/km.     

Nonlinear Fracture Resistance Parameters for Elements of Aviation Structures under Biaxial Loading

This study is concerned with practical application of nonlinear deformation and fracture resistance parameters for residual durability estimation of the fuselage elements with operation damage. By means of numerical calculations for the fragment of fuselage skin with central crack the governing parameters of the elastic-plastic crack-tip stress field are determined as a function of biaxial loading. Two variants of modeling of the crack-tip stress field were performed for the panel of homogeneous isotropic material and a set of the special cohesive elements. As a result the assessment of the biaxial loading influence of fracture damage zone state on crack tip stress field in fuselage panel is given.     

Exoplanetary searches with gravitational microlensing: Polarization issues

There are different methods for finding exoplanets such as radial spectral shifts, astrometrical measurements, transits, timing etc. Gravitational microlensing (including pixel-lensing) is among the most promising techniques with the potentiality of detecting Earth-like planets at distances about a few astronomical units from their host star or near the so-called snow line with a temperature in the range 0–100 ^°C on a solid surface of an exoplanet. We emphasize the importance of polarization measurements which can help to resolve degeneracies in theoretical models. In particular, the polarization angle could give additional information about the relative position of the lens with respect to the source.     

Measurement of the transpolar potential in laboratory magnetosphere

Results of measurements of the transpolar potential in a laboratory magnetosphere are presented. Its approximately linear dependence on the kinetic energy of ions of the incoming flow is found. The measurements of the electric potential in plasma have shown the presence of an asymmetry along the dawn-dusk line. Near the boundary layer at the dawn side, the potential is systematically higher than the average values, while at the dusk side it is systematically lower. The observed difference in the plasma potential in the lowlatitude equatorial part of the magnetosphere by its sign and magnitude approximately corresponds to the transpolar potential at the poles of a dipole. The obtained laboratory data give a direct confirmation of the magnetospheric generator model.     

The iron Kα-line diagnostics of the rotating black hole metric in Seyfert galaxies

Observations of Seyfert galaxies in X-ray region reveal the wide emissive lines in their spectra, which can arise in inner parts of accretion disks, where the effects of General Relativity (GR) must be taken into account. A spectrum of a solitary emission line of a hot spot in Kerr accretion disk is simulated depending on the radial coordinate r and the angular momentum a = J/M of a black hole, under the assumption of equatorial circular motion of a hot spot. It is shown that the characteristic two-peak line profile with the sharp edges arises at a large distance (about r ≈ (3–10) r_g). The inner regions emit the line, which is observed with one maximum and extremely wide red wing. We present results of simulations for the isothermal and Shakura–Sunayev disks.     

Field-aligned currents and magnetospheric generator in experiments on a laser-produced plasma flowing around a magnetic dipole

A laboratory experiment on modeling the magnetospheric generator of the field-aligned currents and the Earth’s transpolar potential in the absence of IMF is illustrated. The measurements of the total field-aligned current in the generator shorted mode and the transpolar potential in the circuit disconnection mode made it possible to determine the generator internal resistance. A model that explains the saturation current and internal resistance by the feedback between the field-aligned current and plasma flank motions has been proposed. This feedback is described through the effective resistance, which is proportional to the flow rate and the ratio of the boundary layer to the dimension of the magnetosphere. For the experimental conditions, the calculated generator resistance was in good agreement with the measured value. The estimates for the Earth’s magnetosphere indicate that the MHD generator internal resistance in the boundary layer is usually much lower than the reverse integral conductivity of the ionosphere.