Scattering of a dipole by a dipole

The spectrum of eigenvalues of the Schrödinger equation with a dipole-dipole potential is not bounded below. An appropriate cut-off leads to a correct low energy problem. Furthermore, it is shown that in polar coordinates the corresponding Schrödinger equation is separable for two spins 1/2.     

Scattering of a Bessel beam by a sphere

The exact scattering by a sphere centered on a Bessel beam is expressed as a partial wave series involving the scattering angle relative to the beam axis and the conical angle of the wave vector components of the Bessel beam. The sphere is assumed to have isotropic material properties so that the nth partial wave amplitude for plane wave scattering is proportional to a known partial-wave coefficient. The scattered partial waves in the Bessel beam case are also proportional to the same partial-wave coefficient but now the weighting factor depends on the properties of the Bessel beam. When the wavenumber-radius product ka is large, for rigid or soft spheres the scattering is peaked in the backward and forward directions along the beam axis as well as in the direction of the conical angle. These properties are geometrically explained and some symmetry properties are noted. The formulation is also suitable for elastic and fluid spheres. A partial wave expansion of the Bessel beam is noted.     

Nonadiabatic heating of a plasma produced by the ionization of a gas by a short intense laser pulse

A hydrodynamic model of the interaction of a short, intense laser pulse with moderate-density gases is constructed. The model systematically takes into account both tunneling-ionization processes and the relativistic motion of the electrons that are produced by the ionization of the gas in the relativistically strong field of the pulse. X-ray spectroscopy data agree well with the proposed theory. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 7, 566–571 (10 October 1998)     

Numerical simulation of the two-phase flow produced by spraying a liquid by a nozzle

A numerical experiment on the simulation of the two-phase flow formed during spraying of a liquid by a nozzle has been described. The radial and axial velocity profiles of the droplets and gas in the free spray and in the two-phase flow through a cylindrical apparatus have been calculated and represented taking into account the early drag crisis of droplets and peculiarities of turbulent friction in the gas, which was detected in previous experiments. The distinguishing feature of the numerical model of the two-phase flow is that it employs the differential equations describing the nonstationary flow of a compressible gas as the initial equations. In transition to their difference analog, the familiar Lax–Wendorff algorithm has been used. A comparison of the results of calculations based on this model with experimental data has demonstrated their concordance.     

Generation of surface waves by a drag current generated by a focused femtosecond pulse

A new nonlinear optical phenomenon—generation of surface waves by a drag current appearing at an inclined incidence of a focused femtosecond laser pulse—has been theoretically described. The generated waves have terahertz frequencies and their total energy increases with an increase in the effective frequency of electron–electron collisions and with a decrease in their density.     

Scattering of a plane wave by a nonlinear load array on a perfectly conducting shield covered by a dielectric layer

The problem of plane wave scattering by a nonlinear load array on a perfectly conducting shield covered by a homogeneous dielectric layer is solved by the integral equation method. The influence of the coating parameters on the array reflection coefficients at the fundamental and third harmonics of the incident wave are studied numerically. Taganrog Radiotechnical University, Taganrog, Russia Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 6, pp. 545–551, June, 2000.     

Production of a large-volume plasma by a hot-cathode arc

Probe measurements reveal that the plasma produced by a hot-cathode arc contains two groups of electrons, with temperatures 4 and 10 eV, with a density of 10¹⁰–10¹¹ cm^–3. These electrons are distributed uniformly over a volume of 0.2 m³. The discharge voltage is found as a function of the gas pressure and the heater current. Low-temperature regimes of the deposition of TiN coatings on metals and insulators after a plasma processing of the articles are described. The design of the discharge system is discussed.Institute of High-Current Electronics, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 115–120, March, 1994.     

Scattering of a sound wave by a vibrating surface

We report an experimental study of the scattering of a sound wave of frequency f by a surface vibrating at frequency F. Both the Doppler shift at the vibrating surface and acoustic nonlinearities in the bulk of the fluid, generate the frequencies f±nF (n integer) in the spectrum of the scattered wave. We show that these two contributions can be separated because they scale differently with respect to the vibration frequency and to the distance between the vibrating scatterer and the detector. We determine the parameter ranges in which one or the other mechanism dominates and present quantitative studies of these two regimes. Received 2 December 2002 / Received in final form 27 March 2003 Published online 4 June 2003 RID="a" ID="a"e-mail: fauve@physique.ens.fr RID="b" ID="b"UMR 8550     

Untwisting of a cholesteric elastomer by a mechanical field

A mechanical strain field applied to a monodomain cholesteric elastomer will unwind the helical director distribution. There are similarities with the classical problem of an electric field applied to a cholesteric liquid crystal but also differences. Frank elasticity is of minor importance unless the gel is very weak. The interplay is between the director being helically anchored to the rubber elastic matrix and the external mechanical field. Stretching perpendicular to the helix axis induces the uniform unwound state via the elimination of sharp, pinned twist walls above a critical strain. Unwinding through conical director states occurs when the elastomer is stretched along the helical axis.     

Elastic scattering of a photon by a neon-like ion

The differential cross sections of anomalous elastic scattering of a linearly polarized x-ray photon by a neon-like Si ion in the energy range near the K-and KL ₂₃-ionization thresholds are calculated. The calculation results are predictive.     

Vibrational excitation of a molecule by a resonance current

Correct expressions are obtained for calculating a tunnel-resonance current through molecules. The participation of molecular vibrations in the resonance charge transfer through a molecule and vibrational excitation of the molecule are determined by the reorganization energy E _r of the vibrational system depending on the displacement of the equilibrium position of vibrational modes in passing from the neutral molecule to the resonance state of a molecular ion. The mean excitation energy of the molecule during the propagation of an elementary charge changes from E _r at the voltage across electrodes close to the threshold up to 2E _r at voltages considerably exceeding the threshold voltage. An expression is obtained for the stationary vibrational temperature of the molecule, which is proportional to the resonance current.     

Capacitance of a coaxial line terminated by a gap

Capacitance of a coaxial line terminated by a gap is investigated. An electrostatic boundary-value problem of the coaxial line terminated by a gap is rigorously solved based on the Fourier sine transform, mode matching technique, and superposition. The capacitance of the coaxial line is represented in a fast-convergent series and computed in terms of the gap geometry and the gap permittivity.     

Scattering of a Klein-Gordon particle by a black hole

By using the curved space-time Klein-Gordon equation, the form of the wave function of a scalar particle near a nonrotating black hole is obtained. It is shown that although the radial wave function oscillates infinitely rapidly near the black hole, the probability density remains finite even on the event horizon. This is consistent with the fact that the Schwarzschild surface is nonsingular. An expression is given for the large angular momentum scattering differential cross section by comparing the asymptotic form of the radial wave equation with the corresponding Coulomb radial wave equation in ordinary quantum mechanics.