Table of contents

In the present paper, comparison of characteristic shielding distance is determined by using a non-Maxwellian plasma. A modified version of the generalized Lorentzian distribution function, which is referred to as the (r, q) distribution, has been employed to derive the shielding distance with a modified power-law. The most surprising feature of a plasma containing superthermals is the strong dependence of plasma Debye length λ_D on spectral indices κ, r and q. It is observed that these spectral indices frustrate the Debye shielding distance. In the case of kappa, it is much smaller than that found for a Maxwellian plasma. We adopt the (r, q) distribution because it gives better data fit results, especially when there are shoulders in the profile of the distribution function along with a high-energy tail.

The nonlinear theory of symmetric surface wave excitation by a low-density electron tubular beam in a cylindrical plasma–vacuum–metal waveguide is presented. A set of nonlinear equations is derived that describes the time evolution of the plasma–beam interaction. The influence of the beam and waveguide structure parameters on the saturation amplitude and excitation efficiency of the surface wave is investigated both numerically and analytically. Thermalization of the electron beam in the wave-fields is studied as well.

Spectra of Ne emitted by a Penning discharge were recorded in the extreme ultraviolet (EUV) on a 10.7 m grazing-incidence spectrograph with phosphor image plates. The spectra provided 75 new lines of Ne II between 286 and 325 Å, from which 35 new energy levels of Ne II could be established. With these new levels, 86 unidentified lines from the NIST Pt–Ne atlas (Sansonetti J E et al 1992 J. Res. Natl. Inst. Stand. Technol. 97 1) could be classified. The identifications of two existing levels of Ne II were revised.

The well-known Poisson Summation Formula is analysed from the perspective of the coherent state systems associated with the Heisenberg–Weyl group. In particular, it is shown that the Poisson Summation Formula may be viewed abstractly as a relation between two sets of bases (Zak bases) arising as simultaneous eigenvectors of two commuting unitary operators in which geometric phase plays a key role. The Zak bases are shown to be interpretable as generalized coherent state systems of the Heisenberg–Weyl group and this, in turn, prompts analysis of the sampling theorem (an important and useful consequence of the Poisson Summation Formula) and its extension from a coherent state point of view leading to interesting results on the properties of von Neumann and finer lattices based on standard and generalized coherent state systems.

Combining perturbation theory with the Ritz variation method, an analytical approach to the ground-state energy, the first ionization energy J(1S₀) and the radial correlation expectation value ⟨r₁₂⁻¹ ⟩  (1S₀) for He-like atoms is given in this paper. The possibility to extend our present analytical model to the doubly excited states (nl)² is illustrated in this work by the calculation of the total energies and the radial correlation expectation value for the 2p^2 1D, 3p²¹D, 4p²¹D and 5p²¹D singlet doubly excites states of He-like atoms with Z⩽12. The results presented in this paper indicate that the present analytical approach can usefully be performed to show quantitatively the importance of electron correlations in the ground-state and in the doubly excited states mainly for high-Z helium isoelectronic series.

It is shown that the Lorentz condition can be discarded on potentials by introduction of an electric scalar field into the Maxwell's equations. This results in the appearance of space-charge and current fluctuations in the vacuum. These extra charges, unlike the usual charges, are time-dependent in nature. The non-conserved part of the charge density then causes production of the electric scalar field which further contributes to the electric and magnetic vector fields. This contribution then makes it possible to create an ideal square wave electric vector field from an exponentially rising and decaying charge.

The possibility of teleportation is certainly the most interesting consequence of quantum non-separability. In the present paper, the feasibility of teleportation is examined on the basis of the rigorous ensemble interpretation of quantum mechanics if non-ideal constraints are imposed on the teleportation scheme. Importance is attached both to the case of noisy Einstein–Podolsky–Rosen (EPR) ensembles and to the conditions under which automatic teleportation is still possible. The success of teleportation is discussed using a new fidelity measure which avoids the weaknesses of previous proposals.

In this paper, by introducing a transformation and utilizing the trial function method, it is quite interesting that three nonlinear partial differential equations called the KdV equation, Boussinesq equation and CDGSK equation have exactly the same trial function form and that their explicit and exact solutions which include solitary wave solutions, singular travelling wave solutions, and triangle function-type periodic wave solutions can be easily derived in a unified and concise way. Among them, some are new travelling wave solutions of physical interest.

The principal obstacle to long-time operation of silicon detectors at the highest energies in the next generation of experiments arises from bulk displacement damage which causes significant degradation of their macroscopic properties. The analysis of the behaviour of silicon detectors after irradiation conduces to a good or reasonable agreement between theoretical calculations and experimental data for the time evolution of the leakage current and effective carrier concentration after lepton and gamma irradiation and large discrepancies after hadron irradiation and this in conditions where a reasonable agreement is obtained between experimental and calculated concentrations of complex defects. In this paper, we argue that the main discrepancies could be solved naturally considering as primary defects the self-interstitials, classical vacancies and the new predicted fourfold coordinated silicon pseudo-vacancy defects. This new defect is supposed to be introduced uniformly in the bulk during irradiation, has deep energy level(s) in the gap and it is stable in time. Considering the mechanisms of production of defects and their kinetics, it was possible to determine indirectly the characteristics of the Si_FFCD defect: energy level in the band gap and cross-section for minority carrier capture. In the frame of the model, the effects of primary defects on the degradation of silicon detectors are important in conditions of continuous long-time irradiation and/or high fluences.

Stark widths of the singly ionized gallium lines for several triplets and singlets in the visible spectral region are calculated using a modified semi-empirical method (MSEM). Results are given at electron density N_e=10¹⁷ cm⁻³ and at electron temperature ranging from 5000 to 40 000 K. The comparison of our MSEM calculated data with both experimental and semi-classical method (SCM) calculated data, available in the literature, shows good agreement for the triplet lines. But, for the singlet lines, there are no data for comparison.

We report the discovery of 23 new energy levels of even parity and 21 new energy levels of odd parity of the tantalum atom. The results given here are based on investigations of the hyperfine structure of 221 new spectral lines of the tantalum atom (Ta I) by means of laser spectroscopic methods, detecting laser-induced fluorescence. The excitation wavelengths were extracted from high-resolution Fourier transform spectra.

Exact solutions to the Dirac equations with a time-dependent mass and a static magnetic field or a time-dependent linear potential are given. Matrix elements of the coordinate, momentum and velocity operator are calculated. In the large quantum number limit, these matrix elements give the classical solution.

Starting from the bilinear form of the (2+1)-dimensional Sawada–Kotera (SK) equation, the y-periodic soliton, the algebraic soliton and the solution to describe the interaction between the y-periodic soliton and the algebraic soliton are obtained. The behaviours of interaction between the y-periodic soliton and the algebraic soliton are analysed in detail. Some representational graphs are also given to make the problem much clearer.

Charged particle dynamics in a superimposed axially symmetric electrostatic potential well and a uniform magnetic field is studied within the framework of adiabatic theory. An approximate expression for the adiabatic invariant of the motion is derived. The condition for particle trapping in the potential well is established by taking into account finite gyroradius effects.

The paper considers the free convection heat transfer due to the combined action of radiation and a transverse magnetic field with variable suction. We adopt the differential approximation to describe the radiative flux in the energy equation. The governing coupled partial differential equations are linearized on the assumption that the flow variables are linear functions of the Eckert number E_c and analytical closed form solutions are sought approximately for the velocity, temperature, surface skin friction and the rate of heat transfer assuming an optically thin medium. Results obtained indicate that increasing the plate velocity increases the flow velocity with this increase being more dramatic for higher values of the free convection. These results are in good agreement with earlier results reported in the literature and correct an omission in some previously reported works.

We study the second-order Coleman–de Luccia instanton which appears as the curvature of the effective potential reaches a sufficiently large value. We show how one can find the approximative formula for this instanton by perturbative expansion in the case when the second derivative of the effective potential divided by the Hubble parameter squared is close to −10, and we perform a numerical study of this instanton in the case of quasi-exponential potential.

We have studied the effect of impurity scattering on the quantum transport through double AB rings in the presence of spin-flipper in the middle lead in terms of one-dimensional quantum waveguide theory. The electron interacts with the impurity through the exchange interaction leading to spin-flip scattering. Transmissions in the spin-flipped and non-spin-flipped channels are calculated explicitly. It is found that the overall transmission and the conductance are distorted due to the impurity scattering. The extent of distortion not only depends on the strength of the impurity potential but also on the impurity position. Moreover, the transmission probability and the conductance are modulated by the magnetic flux, the size of the ring and the impurity potential strength as well.

Time differential perturbed angular correlation measurements in La_0.7Ca_0.3Mn_0.995Hf_0.005O₃ (LCMO) and La_0.7Sr_0.3Mn_0.995Hf_0.005O₃ (LSMO) using ¹⁸¹Hf/Ta probe nuclei reveal the presence of two distinct hyperfine components, identified with Mn⁴⁺ rich and deficient sites. The occurrence of hole rich and deficient sites in the paramagnetic (PM) state of the samples is mainly attributed to cationic inhomogenity. Effect of phase separation is seen across PM to ferromagnetic transition in LCMO, while it is absent in LSMO at the bulk Curie temperature. Signature for lattice distortion in Mn³⁺ rich zones is seen in the case of Ca-doped manganite, while such an effect is much smaller in the case of the Sr-doped system. The present atomic scale study thus reveals that the phase separation effects and Jahn–Teller distortions might be essential for doped manganites to exhibit Colossal magneto resistance effects.

The influence of both the quantum degeneracy and the finite-rate heat transfer between the working substance and the heat reservoirs on the optimal performance of an irreversible Stirling cryogenic refrigeration cycle using an ideal Fermi or Bose gas as the working substance is investigated, based on the theory of statistical mechanics and thermodynamic properties of ideal quantum gases. The inherent regeneration losses of the cycle are analysed. Expressions for several important performance parameters such as the coefficient of performance, cooling rate and power input are derived. By using numerical solutions, the cooling rate of the cycle is optimized for a given power input. The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal regions of the coefficient of performance and power input are determined. In particular, the optimal performance of the cycle in the strong and weak gas degeneracy cases and the high temperature limit are discussed in detail. The analytic expressions of some optimized parameters are derived. Some optimum criteria are given. The distinctions and connections between the Stirling refrigeration cycles working with the ideal quantum and classical gases are revealed.

We present an analogy of Fano resonances in quantum interference to classical resonances in the harmonic oscillator system. It has a manifestation as a coupled behaviour of two effective oscillators associated with propagating and evanescent waves. We illustrate this point by considering a classical system of two coupled oscillators and interfering electron waves in a quasi-one-dimensional narrow constriction with a quantum dot. Our approach provides a novel insight into Fano resonance physics and provides a helpful view in teaching Fano resonances.

The energy spectrum of electrons in narrow band gap semiconductor nanocrystals which have position dependent band gap in an external non-uniform electric field which compensate the position dependence of the band edge of the valence band potential is studied theoretically taking into account the non-parabolicity of electrons in dispersion laws. The exact solutions of the Kane equations with strong spin–orbital interaction are determined via the band-gap changes as a function of position. The band edge gap potential is taken as the ring-shaped non-spherical oscillator potential

A three-level Lambda-configuration atomic vapour may exhibit simultaneously negative permittivity and permeability in the optical frequency band, and an isotropic left-handed vapour medium could therefore be realized within the framework of quantum optics. One of the most remarkable features of the present scheme is that both the refractive index and the photon helicity reversal inside the vapour can be controllably manipulated by an external coupling light field. The phenomenological Hamiltonian that describes the process of helicity reversal is constructed and the time-dependent Schrödinger equation governing the time evolution of the polarization states of the lightwave is solved by means of the Lewis–Riesenfeld invariant theory. The transition between the polarization states (and hence the accompanied photon helicity reversal), which is exactly analogous to the transition operation between bits in digital circuit, may be valuable for the development of new techniques in quantum optics and would have potential applications in information technology.

The propagation of a spatiotemporal solitary pulse through a nonlinear semiconductor doped inhomogeneous medium has been analysed employing a variational technique. We have identified a new class of soliton which can possess the same energy but different width. Stability analysis is employed to check the robustness of the soliton, which shows that the identified soliton is stable.

We present the exact solutions of the Klein–Gordon equation with equal scalar and vector ring-shaped potentials.

The charge reduction effect, produced by the nonlinear Debye screening of high-Z charges occurring in strongly coupled plasmas, is investigated. An analytic asymptotic expression is obtained for the charge reduction factor (f_c) which determines the Debye–Hückel potential generated by a charged test particle. Its relevant parametric dependencies are analysed and shown to predict a strong charge reduction effect in strongly coupled plasmas.

The area under the glow curve (no thermal quenching and same dose) is conserved only in thermoluminescence (TL)–time plots and should not be conserved in TL–temperature plots. Further for the same heating rate, the glow peak height has to be the same in time as well as in temperature plots for a given dose and the glow peak height will increase with the increase of the heating rate. However, to conserve area in TL–temperature plots, the TL intensity should be divided by the respective heating rate and this will lead to the decrease of glow peak height in TL/β–temperature plots, which is the artifact of the normalization process.

In the paper by Kumar et al, some criticism is advanced to the analysis of the glow curves measured under different heating rates in the laboratory, which appeared in our recent paper [M.S. Rasheedy and E.M. Zahran, 2006 Phys. Scr., 73 98–102]. According to this analysis the area under the glow curve is conserved in both TL–time plots and TL–temperature plots. On the contrary, Kumar et al supposed increase of the area under the glow curve with increasing the heating rate in the case of TL–temperature plots. Since this criticism discredits a physical reason for conservation of the area under the glow curves due to conservation of the imparted dose at different heating rates, a reply appears to be timely.

In this paper, we present a brief overview of atom interferometry. This field of research has developed very rapidly since 1991. Atom and light wave interferometers present some similarities but there are very important differences in the tools used to manipulate these two types of waves. Moreover, the sensitivity of atomic waves and light waves to their environment is very different. Atom interferometry has already been used for a large variety of studies: measurements of atomic properties and of inertial effects (accelerations and rotations), new access to some fundamental constants, observation of quantum decoherence, etc. We review the techniques used for coherent manipulation of atomic waves and the main applications of atom interferometers.

The XXIV International Conference on Photonic, Electronic, and Atomic Collisions (XXIV ICPEAC) was held in Rosario, Argentina, on 20–26 July 2005, following ICPEAC in Santa Fe, USA, in 2001 and in Stockholm, Sweden, in 2003. This was the first ICPEAC in Latin America and the second one in the Southern Hemisphere, after ICPEAC in Brisbane, Australia, in 1991. The next ICPEAC (25th) will be held in Freiburg (Germany) in 2007.

Effective Hamiltonians are often used in quantum physics, both in time-dependent and time-independent contexts. Analogies are drawn between the two usages, the discussion framed particularly for the geometric phase of a time-dependent Hamiltonian and for resonances as stationary states of a time-independent Hamiltonian.