Table of contents

Radiative lifetimes of 11 odd-parity levels of neutral rhenium (Re I) were measured using time-resolved laser-induced fluorescence techniques. For ten levels, there were no previous results available. The new results have been used to assess the accuracy of calculations with a Hartree–Fock-plus-relativistic-corrections model that takes configuration interaction and core-polarization effects into account and they have allowed the deduction of reliable semi-empirical transition probabilities for 81 Re I lines.

A long wavelength plasma wave is driven by two copropagating lasers with frequencies ω_L1 and ω_L2 such that ω_L1 − ω_L2 ≈ ω_p. The plasma beat wave (ω₀, k₀) grows in amplitude and becomes susceptible to oscillating two stream instability, producing a low frequency electrostatic mode (ω,k) and two shorter wavelength Langmuir wave sidebands (ω_s,f, k_s,f ) with ω_s,f = ω ∓ ω₀ and k_s,f = k ∓ k₀ in a plasma having positive ions, negative ions and electrons. It is shown that the growth rate, and the amplitudes and phases of the sidebands are influenced by the density n_0n and temperature T_n of the negative ions. The effect of density on the instability is found to be more significant in a plasma that has positive and negative ions of higher temperatures.

This paper applies the variational iteration method to an initial value problem of parabolic type. This method is based on the use of Lagrange multipliers for identification of optimal values of parameters in a functional. This method is a powerful tool for solving various kinds of problems. Employing this technique, it is possible to find the exact solution or an approximate solution of the problem. Using the variational iteration method of He, a rapid convergent sequence is produced which tends to the exact solution of the problem. The results of this method are the same as with the results obtained by the Adomian decomposition method. The fact that this technique solves nonlinear equations without using Adomian polynomials can be considered as an advantage of this method over the Adomian decomposition procedure. The linear and nonlinear cases of the Fokker–Planck equation are considered and solved using the variational iteration method. To show the efficiency of the variational iteration method, several examples are presented.

Diverse phenomena exist in the ionosphere caused by the presence of dusty plasma objects. These have a bearing on problems of space communication and possibly on the Earth's weather, among others. Therefore, it is very important to study them so that many questions on the subject can be answered. In this paper, the interaction of plasma waves with these objects is studied and some instrumentation to measure such interactions is proposed. In particular, the interaction of ion-sound waves (ISW) by non-soliton and soliton pulses propagating in dusty plasma is investigated. It is shown that inclusions of dusty components of the ionosphere plasma behave as resonators for non-soliton pulses, so that ISW are excited. Korteveg–de Vries (KdV) solitons practically do not resonate with the inclusions of dusty plasma. Instead, the presence of dusty plasma inclusions can lead to the presence of transverse instabilities and the eventual destruction of the KdV solitons.

The characteristics of the emission spectra of Kr/Br₂ and Kr/I₂ mixtures driven by dielectric barrier discharge as a function of gas pressure were respectively investigated. It was found that the KrBr* excimer lamp provided an intense narrow band ultraviolet (UV) radiation at λ=207 nm, whose intensity was strongly influenced by gas pressure and buffer gas. The excimer radiation at λ=191 nm generated by the KrI* excimer lamp was very weak and less dependent on gas pressure due to predissociation which was confirmed by the strong emission of the atomic iodine line at λ=183 nm.

The effective operator A_Γ for the Auger l₁^N₁ l₂^N₂→ l₁^N₁+1 l₂^{N₂- 2}εl₃ transitions was determined in the nonrelativistic approximation in the second quantization representation in the case of normal ordering of electron creation and annihilation operators. The matrix element of A_Γ yields a partial Auger width of a level. The specific transitions when  l₂=1, 2 and l₁> 0 were considered in detail. The general formula for a matrix element of A_Γ was derived when a wavefunction with open-shells was presented in normal coupling. Compact expressions for the matrix elements of A_Γ in the case l₁^N₁ l₂² when N₁=1, 2, 4l₁+1 and 4l₁ were obtained. The selection rules for matrix elements of A_Γ are discussed by using the quasispin technique.

The delayed-choice experiments of the type introduced by Wheeler and extended by Englert, Scully, Süssmann and Walther (ESSW) (1992 Z. Naturf. a 47 1175–86), and others, have formed a rich area for investigating the puzzling behaviour of particles undergoing quantum interference. The surprise provided by the original delayed-choice experiment led Wheeler to the conclusion that 'no phenomenon is a phenomenon until it is an observed phenomenon', a radical explanation which implied that 'the past has no existence except as it is recorded in the present'. However Bohm et al (1985 Nature315 294–97) have shown that the Bohm interpretation (BI) gives a straightforward account of the behaviour of the particle without resorting to such a radical explanation. The subsequent modifications of this experiment led both Aharonov and Vaidman (1996 Bohmian Mechanics and Quantum Theory: An Appraisal ed J T Cushing, A Fine and S Goldstein (Dordrecht: Kluwer) pp 141–54) and ESSW to conclude that the resulting Bohm-type trajectories in these new situations produce unacceptable properties. For example, if a cavity is placed in one arm of the interferometer, it will be excited by a particle travelling down the other arm. In other words, it is the particle that does not go through the cavity that gives up its energy! If this analysis is correct, this behaviour would be truly bizarre and could only be explained by an extreme non-local transfer of energy that is even stronger than that required in an Einstein, Podolsky and Rosen (EPR)-type process. In this paper, we show that this conclusion is not correct and that if the BI is used correctly, it gives a local explanation, which actually corresponds exactly to the standard quantum mechanics explanation offered by ESSW.

There are several phenomena which require the application of a force in the axial direction of a magnetic flux tube, for example: solar plasma loops, where support of the plasma mass against gravity is required within those sections of the flux tube that have vertical components, the observed upward acceleration of the plasma in flux tubes forming the legs of quiescent prominences, and the acceleration of the fast solar wind. In this paper, we show that the origin of such axial forces is the magnetic pressure of an azimuthal magnetic field B_θ generated by currents flowing in circuits passing inside and outside the flux tube, and that the source of the EMF driving this circulating current is the difference between the temperature gradients inside and outside the flux tube, which generates a thermoelectric potential.

In this study, the chaotic behaviour of Pd₁₃ clusters is investigated in a wide total energy range. To identify interactions between atoms, the embedded atom potential is used in the computer simulation. Various analyses including power spectra, maximal Lyapunov exponents (λ) and rms bond-length fluctuations (δ) are carried out to identify the characteristics of the system. As a result of these analyses, it is observed that Lyapunov spectra can clearly indicate the co-existence region for Pd₁₃ clusters and exponents have fixed values above a certain total energy value of the system. In addition, while the fast Fourier transforms give the existence of diffusive motion above the transitional region, the correlation dimension values exhibit a smooth character relevant to the total energies of the system.

This paper presents a numerical method for solving the controlled Duffing oscillator. The method can be extended to nonlinear calculus of variations and optimal control problems. The method is based upon compactly supported linear semi-orthogonal B-spline wavelets. The differential and integral expressions which arise in the system dynamics, the performance index and the boundary conditions are converted into some algebraic equations which can be solved for the unknown coefficients. Illustrative examples are included to demonstrate the validity and applicability of the technique.

When the scalar potential is larger than the vector potential there are very few exactly solvable Klein–Gordon equations. Based on a general transformation between the unequal scalar and vector potential, in this paper, we employ two semiclassical methods to determine the bound state energy spectrum of the Klein–Gordon equation. To illustrate this procedure, the scalar potentials are chosen as the linear, exponential and linear plus Coulomb potentials and the corresponding energy spectra are analytically obtained. It is shown that the energy spectrum can be obtained by a simple algebraic method and our proposal methods can be extended to discuss the quasi-exactly solvable cases.

We determine the (bound) ground state of a neutron with anomalous magnetic moment in a given Aharonov–Casher configuration. We recast the description of the system in a supersymmetric form. Then the basic physical requirements for unbroken supersymmetry are established. We comment on the possibility of neutron confinement in this system.

The effects of partial coherence on the propagation of dispersive Alfvén waves in a magnetoplasma are investigated. In particular, nonlinear interactions between dispersive Alfvén waves and ion-acoustic perturbations are considered by means of a Wigner formalism. A set of governing equations consisting of a kinetic equation for dispersive Alfvén waves coupled nonlinearly to a ponderomotive force driven ion-acoustic wave equation is obtained. The governing nonlinear equations are used to derive a nonlinear dispersion relation that is appropriate for investigating the modulational instability of broadband Alfvén wavepackets. The spectral broadening of the Alfvén waves gives rise to new regimes for the growth rate of the modulational instability.

The modified BELL (MBELL) formula (Haque et al 2006 Phys. Rev. A 73 012708) has been applied to the M-shell ionization of neutral and ionic atoms to deduce the `generalized' parameters of the 3s, 3p and 3d orbits. A single set of parameters for each of these orbits and that previously determined for each of 1s, 2s and 2p orbits can reproduce satisfactorily the features of the total electron impact ionization cross-sections (EIICS) of 21 M-shell targets in the Na, Mg, Al, Si, P, S, Cl, Ar and Ca isoelectronic sequences. The generalized parameters are also found to provide an excellent account of the M-shell EIICS data of Pb, Bi and U atoms at relativistic energies in the range from 20 to 250 MeV.

The two-dimensional Ginzburg–Landau equation (GLE) is obtained from basic equations by a linear stability analysis. This equation governs the evolution of slowly varying envelopes of periodic spatio-temporal patterns related to Rayleigh–Bénard convective instabilities. In addition, the phase instabilities of the complex GLE (CGLE) with quintic and space-dependent cubic terms modelling the Eckhaus and zigzag convective instabilities are reported. We find soliton solution classes to the elliptic and hyperbolic CGLE, by applying the function transformation method. The two-dimensional CGLE is transformed to a sine-Gordon equation, a sinh-Gordon equation and other equations, which depend only on one function χ. The general solution of the equation in χ leads to a general soliton solution of the two-dimensional CGLE. The obtained solutions contain some interesting specific solutions such as plane solitons, N multiple solitons and propagating breathers. We also discuss the soliton stability of the CGLE.

The well-known (and easily observable) effect of the 'flow of heat from a hot to a cold body,' when the bodies are in contact and at relative rest, is explained in a simple and comprehensive way. Moreover, an account is given as regards the production of heat between sliding bodies with rough contacting surfaces. The procedure, grounded upon the laws of classical mechanics, is an extension of a new theory concerning the nature of heat, which was developed in a previous paper (Kapoulitsas G 2003 Phys. Scr. 6 99).

Experiments were conducted in a Mach 2.5 wind tunnel to explore the modification effect on the shock wave structure by a plasma spike generated by an on-board 60 Hz electric discharge in front of a 60° cone-shaped model, which was used as a shock wave generator. Modification of the shock by the plasma spike from an attached conic shock into a highly curved shock structure, which has increased shock angle and also appears in diffused form, is demonstrated. Due to the cyclic nature of the generated plasma an unsteady shock motion during one discharge period was observed. As shown in a sequence with increasing discharge intensity, the shock in front of the model moves upstream to become detached with increasing standoff distance from the model and with increasing dispersion in the spatial distribution of the shock front. Experimental results exclude the heating effect as a possible cause of the observed shock wave modification. A theory also using a cone model as the shock wave generator is presented to explain the observed plasma effect on the shock wave. Analysis shows that the plasma spike can effectively deflect the incoming flow before the flow reaches the cone model; such a flow deflection modifies the structure of the shock wave generated by the cone model from conic shape to a curved one. The shock front moves upstream with a larger shock angle, consistent with the experimental results.

A comment is presented on the XIIIth International Workshop on Low-Energy Positron and Positronium Physics (held at UNICAMP, Campinas, Brazil, 27– 30 July 2005). Exciting progress was reported on a range of antimatter research areas. The focus of the conference is on understanding fundamental positron and positronium scattering and annihilation from gas-phase atoms and molecules. Other hot topics included antihydrogen production and antimatter- and matter-bound states. We discuss some of the achievements and outstanding questions that have arisen during the past two years and discuss some directions for the future.

The decays of the 2p J=1/2 and J=3/2 levels of Li-like ions and of the 2s2p ^1,3P^o₁ levels of Be-like ions can be used as simple-atom test beds for lifetime measurements and for the development of accurate calculations of the transition rates. We have summarized and filtered the experimental data in order to obtain consistent data sets and isoelectronic trends that can be compared to theoretical predictions. The graphical presentation of line strength data enables direct comparison and evaluation of the merit of data along extended isoelectronic sequences. From this, the precision that is necessary in future meaningful experiments can be deduced.