Table of contents

A model is introduced to describe guided propagation of a linear or nonlinear pulse which encounters a localized nonlinear defect, that may be either static or breather-like. The model with the static defect directly applies to an optical pulse in a long fiber link with an inserted additional section of a nonlinear fiber. A local breather which gives rise to the nonlinear defect affecting the propagation of a narrow optical pulse is possible in a molecular chain. In the case when the host waveguide is linear, the pulse has a Gaussian shape. In that case, an immediate result of its interaction with the nonlinear defect can be found in an exact analytical form, amounting to a transformation of the incoming Gaussian into an infinite array of overlapping Gaussian pulses. Further evolution of the array in the linear host medium is found numerically by means of the Fourier transform. An important ingredient of the linear medium is the third-order dispersion, that eventually splits the array into individual pulses. If the host medium is nonlinear, the input pulse is naturally taken as a fundamental soliton. The soliton is found to be much more resistan t to the action of the nonlinear defect than the Gaussian pulse in the linear host medium, for either relative sign of the bulk and local nonlineari ties. In this case, the third-order-dispersion splits the soliton and wavepackets generated by the action of the defect.

The masses of the three silicon isotopes are important parameters for a re-definition of the kilogram based on atomic properties. Using the Penning trap mass spectrometer SMILETRAP at the Manne Siegbahn Laboratory the mass of ²⁸Si was determined from the cyclotron frequencies of ²⁸S¹⁴⁺, ²⁸S¹³⁺ and ²⁸S¹²⁺ using ¹²C⁶⁺, ¹²C⁵⁺ and ¹²C⁴⁺ as well as H₂⁺ as mass references. Since H₂⁺ ions were used as intermediate mass reference the mass of the proton could be determined using in addition ²⁰Ne^10,9+ and ⁴⁰Ar^16+,14+ ions as mass references. By comparing the value of the proton mass determined this way with the accurate accepted value we could set an experimental limit of 0.35 ppb for the total uncertainties in our mass determinations. A value of 27.976 926 533.9 (80) u was obtained for the mass of ²⁸Si confirming the more accurate value obtained by the MIT-group using an entirely different method. Thus the mass of ²⁸Si has been determined by using two very different methods agreeing within an uncertainty <0.35 ppb.

In the framework of first Born approximation, elastic scattering of electron by hydrogen atom has been studied in the presence of two homogeneous, single mode and linearly polarized laser fields. One of the two fields has been chosen to be weak with respect to the other field. The radiation fields have been treated classically in the dipole approximation. The dressed wavefunctions of the bound states of the target have been constructed using first order time-dependent perturbation theory while the laser modified incident and scattered electron wave functions are given by Volkov solutions. Differential scattering cross-sections corresponding to one weak field photon emission have been calculated for different geometrical configurations of the applied laser fields with respect to incident electron momentum as well as the momentum transfer. The dependence of the cross-section results on the different geometrical situations and also on the laser field parameters has been explored. The influence of the introduction of the second laser field has also been investigated.

Spectra of mercury, thallium, lead, and bismuth were photographed from 70 Å to 250 Å on two grazing-inciden ce spectrographs with low-inductance vacuum sparks. About fifty-five 5p⁶5d-(5p⁶5f+5p⁶6p+5p⁵5d²+5p⁵5d6s) transitions were identified in each of the spectra of Tl XIII, Pb XIV, and Bi XV. The 5d²D_3/2,5/2 fine-structure interval was determined as 29267 cm^-1 in Tl XIII, 33195 cm^-1 in Pb XIV, and 37370 cm^-1 in Bi XV. Hartree-Fock and parametric least-squares-fitting calculations were carried out to interpret the 5p⁶5f+5p⁶6p+5p⁵+5d²+5p⁵5d6s configurations in these three ions. Earlier identifications of the 5p⁶¹S₀-5p⁵5d(3/2, 5/2)₁ transitions in Hg XIII, Tl XIV, Pb XV, and Bi XVI were revised.

The single electron emission from helium and lithium target atoms have been extensively studied by Sahoo et al. [Phys. Rev. A62, 022716 (2000)]. In the present work, we calculate the single ionization of Ne in encounter with protons, anti-protons, and alpha particles using the method same as Sahoo et al. We find out the total and differenti al ionization cross sections covering wide range of impact energy. The dependence of the cross sectional values on the projectile charges (-1, +1, +2) is analyzed. The present results are found to be encouraging when compared with existing experimental as well as theoretical findings.

Electron impact double ionization cross sections of C⁺ N⁺ O⁺ and Ne⁺ have been calculated in the modified double binary encounter model using accurate expression for σ_ΔE (cross section for energy transfer ΔE) given by Vriens and Hartree-Fock velocity distributions for the target electrons. The focussing action of the target ion on the incident electron has been incorporated along the line suggested by Thomas and Garcia. Contributions of ionization- autoionization have been included in the calculations. The present results show satisfactory agreement with experimental data except at low incident energies.

Compton profiles have been computed for variously ionized carbon atoms with configurations 1s^m2sⁿ2p^q, m = 1-2, n = 0-2, q = 0-2. The values of the Compton profiles from the present calculation can be used to interpret experimental cross sections of variously ionized carbon atoms colliding with other atoms. The calculation s have been performed in impulse approximation using numerical Hartree-Fock wave functions. Compton profiles of neutral carbon atoms, available in the literature, are in excellent agreement with the present calculation.

The Ru II spectrum emitted from a hollow cathode discharge has been recorded in the region 12 500–55 500 cm^-1 (8000-1800 Å) using a Fourier transform spectrometer. 538 Ru II lines have been measured with high accuracy (± 0.003–0.020 cm^-1). Improved energy level values have been derived from the lines and 17 new even levels have been found. The level structure has been interpreted by means of parametric calculations.

We describe undisputable experiments that categorically disprove absolutistic Kennard-Bartlett-type interpretations of unipolar induction.

Starting from a two line soliton solution of an integrable (2+1)-dimensional system in bilinear form, one can find a dromion solution that is localized in all directions for the physical field and/or the suitable potential (the physical field's derivatives). The interaction between two dromions is studied both analytical and numerical for the (2+1)-dimensional Nizhnik-Novikov-Veselev equation and the modified Korteweg-de Vries (mKdV) equation. The interaction may be elastic (without shape and velocity deformation) or inelastic depending on the form of multisoliton solution.

Transient self focusing of an intense short pulse laser in a plasma is strongly modified by a transverse magnetic field. The laser with Gaussian radial distribution of intensity exerts a ponderomotive force on electrons and sets in ambipolar diffusion of the plasma. The ambient magnetic field, however, strongly inhibits the process, when the electron Larmor radius is comparable to or shorter than the laser spot size r₀. As the plasma density is depleted, the laser beam becomes more and more self-focused

Plasma and quantum screening effects on the occurrence time for electron-ion scattering in dense high-temperature plasmas are investigated using the eikonal method. An effective pseudopotential model taking into account both the quantum-mechanical effects and the plasma screening effects is applied to describe the electron-ion interactions in dense high-temperature plasmas. The quantum and plasma screening effects on the elastic electron-ion scattering significantly reduce the time advance for small scattering angles, i.e. the scattering occurs later. However, the time advance is increased with increasing scattering angle due to the quantum and plasma screening effects.

The equilibrium properties of gravitating dusty plasmas are analyzed. The present analysis indicates that a proper equilibrium of a gravitating system requires the presence of a large scale electric field. It is found that such an electric field, arising from the charge separation plays a decisive role in maintaining the equilibrium. Explicit expressions for plasma particle number densities are presented. The results could resolve the problem of Jeans's swindle in a nonuniform plasma with massive dust grains.