Ionospheric effects of geomagnetic storms at mid latitudes

Previously, we studied the ionospheric effects of the sequence of geomagnetic storms on September 9–14, 2005 using a global self-consistent model “Thermosphere-Ionosphere-Protonosphere” (GSM TIP). Differences between the predicted and observed effects of the ionospheric storms may be due to the use of the three-hour K _p index of geomagnetic activity in modeling the time dependence of model input parameters, use of the dipole approximation of the geomagnetic field, and disregard in simulations for solar flares that occurred during this period. We tried to eliminate two of these three reasons. First, we used the A _E index of geomagnetic activity with minute resolution in modeling the time dependence of the model input parameters. Second, we took into account the effects of solar flares. In addition, GSM TIP model was supplemented by an empirical model describing the precipitation of high-energy electrons. The results of the simulation of the behavior of various ionospheric parameters over the Yakutsk, Irkutsk, Millstone Hill, and Arecibo stations on September 9 and 10, 2005 in the new formulation of the problem, presented in the current work, are in better agreement with the available experimental data than the results of previous calculations.     

Homogenization of a convection–diffusion equation in perforated domains with a weak adsorption

The aim of this paper is to study the asymptotic behavior of the solution of a convection–diffusion equation in perforated domains with oscillating velocity and a Robin boundary condition which describes the adsorption on the bord of the obstacles. Without any periodicity assumption, for a large range of perforated media and by mean of variational homogenization, we find the global behavior when the characteristic size ε of the perforations tends to zero. The homogenized model, is a convection–diffusion equation but with an extra term coming from the weak adsorption boundary condition. An example is presented to illustrate the methodology.     

Stabilization of the motion of an unstable linear mechanical system

Kiev. Translated from Prikladnaya Mekhanika, Vol. 26, No. 4, pp. 79–85, April, 1990.     

Instability of a Cantilever with a Propeller in an Incident Flow

A physical explanation is given to the mechanism of back coupling of the perturbed motion of a propeller in its plane of rotation and the force in the same plane. This unusual feedback may cause a mechanical system with a propeller to self-excite in the plane of possible oscillations of its axis upon propeller reversal. Instability occurs easier at the resonance of the system when the resultant moment of external forces lags in phase behind the angle of attack by approximately 5/4.     

Calculation of the motion of a gas behind the front of a luminous detonation wave taking account of the lateral expansion of the plasma column

Nonsteady-state gasdynamic processes are considered in a plasma column (hot channel), formed behind the front of a shock wave moving toward a laser beam. A quasi-one-dimensional approximation is used-the parameters in the channel are assumed to be compensated with respect to cross section, but depend on the time and distance along the axis. Motion in the cold dense casing surrounding the channel is assumed to be one-dimensional and cylindrically symmetrical. The solutions of the corresponding systems of equations in partial derivatives permit the parameters to be determined approximately both in the case when the mean free path of the radiation is small in comparison with the radius of the beam (luminous detonation) and also in the case when the mean free path is comparable with the radius. Examples are given of the corresponding numerical calculations. It is shown that in the latter case, a cycle of incomplete absorption can be achieved when behind the shock wave front, moving with constant velocity up to the Jouguet plane, only a part of the radiation energy incident on the front is released.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 18–28, May–June, 1976.     

Averaged model of vibration of a damped elastic medium

We consider an initial boundary-value problem used to describe the nonstationary vibration of an elastic medium with large number of small cavities filled with a viscous incompressible fluid. We study the asymptotic behavior of the solution in the case where the diameters of the cavities tend to zero, their number tends to infinity, and the cavities occupy a three-dimensional region. We construct an averaged equation to describe the leading term of the asymptotics. This equation serves as a model of propagation of waves in various media, such as damped soil, rocks, and some biological tissues.     

Neutron diffraction experiments in diamond and sapphire anvil cells

Diamond anvil cells (DAC) provide the highest static pressures ≥1?Mbar. Because of the low intensity of neutron sources, for a long time it was thought impossible to use DAC or other anvil cells in neutron experiments. We describe pressure cells with diamond and sapphire anvils and neutron instrumentation allowing neutron diffraction experiments to be carried out under pressures as high as 50?GPa, temperatures down to 0.1?K, and applied magnetic fields up to 7.5?T.     

Microgeometry and effective permittivity of discontinuous metal films

This work deals with the investigation of dielectric and optical properties of discontinuous metal films over a wide range of filling factors each side of the percolation threshold. A phenomenological two-parameter representation is used for the effective permittivity &εtilde; of such systems. In order to test the proposed approach, we have taken for gold films on a glass substrate the transmittance spectra in the visible and near-IR regions. It is shown that the representation used for the effective permittivity enables us to adequately describe the experimental transmittance spectra. The parameters entering the above representation are determined and the relationship between them and film microgeometry is discussed. Received: 6 November 2000 / Accepted: 30 May 2001 / Published online: 25 July 2001     

Stability of flow of a viscous liquid down an inclined plane

Using the Navier-Stokes equation the stability of a layer of viscous liquid flowing down a solid surface under gravity is studied in the linear formulation. The effect of surface tension and the inclination of the solid surface on the limits of stability are examined also. Curves are calculated for the neutral stability with respect to two types of perturbations — surface waves and shear waves.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskol Fiziki, No. 2, pp. 172–176, March–April, 1975.