Excitation and Emission of an Atom in Its Interaction with an Ultrashort Electromagnetic Field Pulse

Based on the approximation of sudden perturbations, the excitation and ionization of an atom in its interaction with an ultrashort electromagnetic field pulse are examined. The probabilities of excitation and ionization are obtained together with the spectra and cross sections of pulse re-emission by the atom.     

Two-electron transitions in collisions of fast multiply-charged ions with helium-like atoms

Single and double excitation and ionization of a helium-like atom are considered based on the eikonal approximation. Simple analytical formulas are derived for the cross sections of inelastic collision. A comparison with the experiment is conducted. Scientific Research Institute of Applied Physics at Tashkent State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 44–48, February, 2000.     

Asymptotic regimes and structure of concentration tails in the Dykhne model

A transport problem is solved for a high-contrast regularly inhomogeneous medium. Transport regimes and structure of the concentration tails in high-permeability regions are analyzed for two geometries of such regions: a plane layer and a right cylinder. It is shown that changes with time of transport regimes lead to complex asymptotic particle distributions at long distances (concentration “tails”). The time dependence of the total number of active particles and depth of particle penetration into the low-permeability region are calculated.     

Mathematical modeling of systematic drainage of irrigated soil over an impermeable layer

We solve the problem of plane steady-state seepage of groundwater in a homogeneous isotropic soil layer from a periodic system of irrigation canals under conditions of both infiltration and horizontal drainage. A detailed hydrodynamic analysis is performed of the structure and properties of seepage flow and the effect of physical parameters of the flow scheme.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 72, pp. 72–75, 1990.