Table of contents

Peristaltic pumping by a sinusoidal travelling wave in the wall of a two-dimensional channel filled with a viscous incompressible couple-stress of a magneto-fluid is investigated theoretically and graphically. A perturbation solution is obtained which satisfies the momentum equation for the case in which the amplitude ratio is small. The results show that the mean axial velocity decreases with increasing couple-stress parameter η and magnetic parameter M. The phenomenon of reflux is discussed. Numerical results are reported for various values of the physical parameters.

Physical systems concerned here are those in which the one dimensional Modified Complex Ginzburg–Landau equation or one of its derivative forms holds. By using this propagation equation, it is shown that the Lange and Newell's criterion for modulational instability of stokes waves can be recovered by performing the Stuart and Di Prima's method.

The standard relativistic de-Broglie–Bohm theory has the problems of tacyonic solutions and the incorrect non-relativistic limit. In this paper we obtain a relativistic theory, not decomposing the relativistic wave equations but looking for a generalization of non-relativistic Bohmian theory in such a way that the correct non-relativistic limit emerges. In this way we are able to construct a relativistic de-Broglie–Bohm theory both for a single particle and for a many-particle system. At the end, the theory is extended to the curved space-time and the connection with quantum gravity is discussed.

A more rigorous treatment of the Schwarzschild metric by making use of the energy-momentum tensor of a single point particle as source term shows that

g₀₀ = -{1 - 2GM/c²r - (8G²M²/c⁴r²) (θ(r) - 1)} exp[2(θ(r) - 1)]

g_rr = {1 - 2GM/c²r - (8G²M²/c⁴r²) (θ(r) - 1)}^-1.

The existence of a discontinuity at r = 0 leads to an infinite repulsive force that will change the ultimate fate of a free fall test particle to a bouncing state.

Semi-analytical investigations using the orientation-free discrete gas-kinetic theory are performed in order to link the non-equilibrium but stationary solitons found in the randomly and approximately boundary treatment for the interactions between gases and solid-surfaces with vorticity at the pseudo-flat walls. The stationary solitons thus obtained from the integrable system of partial differential equations are subjected to different but limited dissipations depending on the intrinsic parameter of rarefaction. We also address the linear stability of our results in brief.

Data on the total cross sections for the pp → ppη, pn → pnη, and pn → dη reactions and the pp → ppη differential cross section near threshold are analysed in a one-meson-exchange model. After including initial and final-state nucleon–nucleon distortion, the magnitude and most of the energy dependence are well reproduced. It is found that the contribution of ρ-exchange is larger than that of π-exchange. With destructive ρ/π interference in the pp case, the model explains quantitatively the pp → ppη/pn → pnη cross section ratio and the slope of the pp → ppη differential cross section. Such an agreement would be destroyed by any significant η-exchange term. The residual energy dependence may be associated with η-nucleon rescattering that has not been taken into account. The pn → pnη/pn → dη ratio depends weakly upon the nature of the particle exchanges, being determined primarily by the nucleon–nucleon final state interactions. The proton analysing power is predicted to remain small in the low energy region.

Effective collision strengths for transitions among the energetically lowest 46 fine-structure levels belonging to the (1s²) 2s²2p², 2s2p³, 2p⁴, 2s²2p3s, 2s²2p3p and 2s²2p3d configurations of Fe XXI are computed, over an electron temperature range of 5.6 ≤ log T_e ≤ 7.4K, using the recent Dirac Atomic R-matrix Code (DARC) of Norrington and Grant. Results are presented for transitions within the ground configuration only, and are compared with earlier R-matrix calculations. Large discrepancies are observed for many transitions, especially at lower temperatures.

The emission spectrum of CaS from a King-type furnace has been recorded in the region 13,150–16,150 cm^-1 by a Fourier Transform spectrophotometer (FTS). The CaS B¹Σ⁺–X¹Σ⁺ transition has been rotationally analysed. Molecular constants have been calculated for both states. The principal molecular constants for the B¹Σ⁺ state are T_e = 15,220.775(3), ω_e = 409.064(2), ω_ex_e = 0.8200(3) and Be = 0.1666769(7) cm^-1.

In order to test the prediction of the LS coupling approximation for several light elements (B, C, N, O, F and Ne), the line intensity ratios of the 3s–3p multiplets along the isoelectronic sequences of lithium and beryllium and line intensity ratios of 3s–3p and 3p–3d multiplets along isoelectronic sequences of boron, carbon, nitrogen, oxygen and fluorine have been investigated experimentally. The light sources were two low-pressure pulsed arcs. The plasma electron densities were determined from the width of the He II P_α line.

Energy levels, radiative decay rates and electron-impact collision strengths are presented for neon-like copper. Calculations are done for the 65 levels belonging to the eight configurations 1s²2s²2p⁶, 1s²2s²2p⁵3l (l = s, p, d), and 1s²2s²2p⁵4l (l = s, p, d, f). SUPERSTRUCTURE and DISWAV/JAJOM codes have respectively been used for the atomic structure and electron-ion collision calculations in fine-structure scheme. The collision strengths are calculated for three electron incident energies: 110, 330, and 550 Ry. These data are required for population kinetics modeling and spectral analysis of high temperature plasmas.

The spectra of singly and doubly ionized praseodymium have been observed by means of Fourier transform spectroscopy in the region 2800–8000 Å. In Pr II improved wavelengths are reported for 49 lines. For 31 lines gf-values have been determined by means of branching fractions combined with recently measured lifetimes. The hyperfine structure patterns have been analyzed for 44 lines, and magnetic hyperfine constants A have been derived for 8 odd and 18 even levels. Using the observed Pr II transitions improved energy levels are reported. Accurate wavelengths are given for 15 strong transitions in Pr III. The gf-values from this study have been applied to obtain and discuss the solar abundance of praseodymium.

Spectral lines emitted by laboratory plasmas or of astrophysical interest are studied through A(z₁, z₂) and B(z₁, z₂) broadening and shift functions. Discrepancies in the numerical values of the functions for various impact parameters between the results of different authors and ours are presented. They are up to 30% or 40% in some cases. They are good candidates for the contribution to the reduction of the theory-experiment discrepancies found in the hydrogenous lines profiles and in some isolated spectral lines. This is the case for the 4471 Å, 4921 Å and 5016 Å of HeI in the electron density range Ne(cm^-3) > 5.1015(cm^-3).

We present the results of an experiment in which electrons have been scattered on CN^- ions, over a collision energy range 0–60 eV. The experiment was performed at the heavy ion storage ring CRYRING. The CN^- ions were stored in the ring and merged with a monoenergetic electron beam that was guided in to and out of the ring using strong magnetic fields. Both neutral and positive fragments from the collision process were detected with surface barrier detectors. It was found that pure detachment completely dominates over those channels which involves breaking the molecular bond. The threshold energy for the detachment process was found to be 7 eV. The cross section rose from zero to a maximum of about 5 · 10^-16 cm² just below 30 eV, after which it remained essentially constant. The threshold region was carefully investigated in an attempt to find resonance structure arising from the possible existence of the doubly charged ion, CN^2-. The statistical uncertainty in the data was, however, too large to conclusively prove or disprove the existence of such a resonance.

The impact parameter method is applied to the proton and antiproton collision with hydrogen atom in the 2s-state in the incident energy range 1 ≤ E ≤ 10000 keV. Cross sections for the excitation of the 3l-state in both processes are presented and compared to each other to investigate the influence of the sign of the projectile charge on the excitation cross-sections.

Stable two-dimensional dust clusters are found by Molecular Dynamics simulation using two model interaction potentials. The clusters can be in either solid or liquid state. The results of the two models are discussed.

Using Vlasov-kinetic model, a dispersion relation of the low-frequency and electrostatic lower-hybrid wave is obtained accounting for the streaming of ions and dust charge fluctuations in a finite temperature and collisionless magnetized dusty plasma. It is found that the damping of this mode is the sum of the Landau damping and the charge fluctuation effect. This lower-hybrid mode can be excited when the ion streaming velocity in the direction of the magnetic field exceeds the parallel phase velocity of the mode and when the magnitude of the Landau damping exceeds the magnitude of the damping due to the dust charge fluctuation. Thus, the lower-hybrid-like mode in a dusty plasma will be damped rapidly by the unmagnetized ions compared to that due to the dust charge fluctuation process.

The topological map of the domain of the projectile velocity (ν) and impact parameter (b) for the Landau damping effect on the semiclassical electron-ion collisional ionization process is investigated in dense plasmas. The ionization probability is obtained by introduction of the longitudinal plasma dielectric function. The domains of the projectile velocity and impact parameter for the Landau damping effect are respectively found to be 0.5 < ν_T/ν < 1 where ν_T is the electron thermal velocity, and 1.5 < b/a_Z < 2 where a_Z, is the hydrogenic ion with nuclear charge Z. It is also found that the Landau damping effect on the electron ionization probability increases with increasing projectile energy.

Using the model proposed by Stenflo, we demonstrate that acoustic gravity waves found in one region of space can be synchronized with acoustic gravity waves found in another region of space using techniques from modern control theory.

We examine the underlying physics and mathematical details of the electron magnetohydrodynamic (EMHD) equations in plasmas.

Charge and mass fluctuations in dusty plasmas are revisited by invoking overall conservation of charge and mass in the combined dusty plasma, including external sources. If electrons and ions lost to the grains are not replenished, a stationary state cannot be achieved in the usual spherical probe model. For a true stationary state other charging mechanisms are needed besides primary electron and ions currents to the grains. A general multispecies model describes the physics transparantly, without getting lost in computational details or being tied to a particular charging model. The characteristic damping of the dust-acoustic mode is described. Even in an open dusty plasma, where electrons and ions are injected, the broad conclusions'remain the same, as far as the damping of the dust-acoustic waves is concerned.

The change of F-band absorption of x-ray irradiated NaCl single crystals, when they were subjected to strong electric fields after irradiation, was studied. Contrary to the report of D Enakshi and K V Rao (1985 Nucl. Tracks10 71; 1985 Physica Scripta31 219), it was observed that the application of electric fields, whether they are AC or DC, does not give any appreciable effect on the stability of F-centers.

We present a theoretical study of the simultaneous effects of magnetic and electric fields on the ground state energy of an exciton confined in CdS and CdSSe spherical quantum dots. The effect of the quantum confinement is described by an infinitely deep potential well in the framework of the effective mass approximation. The effects of the external perturbations are treated within the Hassé variational method. The variations of the diamagnetic coefficient D are determined as a function of the dot radius R. The influence of the quantum confinement and the magnetic field strength on the excitonic polarisability α is analysed.

By using a dynamical model giving both the IR reflectivity and transmittivity of a semiconductor after an intense photo-plasma production, it is possible to derive several electrical parameters, as Auger recombination, radiative recombination and impurity recombination. The model has been tested on previous experimental works and used to analyse the 10.6 µm dynamical transmission reflection induced by a 1.06 ns excitation in Ge optical windows.

The influence of a spatially dependent magnetic field on the orbital motion of an electron in a wide pill-box is evaluated. Expressions for the velocity components perpendicular to the magnetic flux lines are obtained. these form the basis for the derivations of the analytical expressions for the particle trajectories. The results for the special case when the initial radial velocity is zero are suggestive of potential applications, for example, current- amplification'or the generation of high magnetic fields in semiconductor nanostructures. A brief discussion of the overall results is also given in the context of the problem of the critical field of a current-carrying type II superconducting cylinder.

This paper presents a method for the determination of dose rate in thermoluminescence (TL) dating. The dose rate is determined from high resolution gamma spectrometry measurements. In particular, our analysis is focused on dose to quartz minerals. A Canberra spectrometer with a HPGe detector of moderate sensitivity and Marinelli geometry (0.5 l capacity) with a shield is applied. A method for spectral analysis of natural radioactivity is presented in detail. Spectral analysis is based on the Sampo90 computer program. A uranium pitchblende source used for system calibration in TL dating was investigated. The numerical deconvolution of multiplets with strongly overlapping peaks in the gamma spectrum is experimentally verified. Several multiplets are used in the calibration procedure. Problems of cascade transitions and matrix absorption are discussed.