Table of contents

A systematic explicit derivation is given for variational derivatives of transformation functions in field theory with respect to parameters variations, also known as the quantum dynamical principle (QDP), by introducing, in the process, two unitary time-dependent operators which in turn allow an otherwise non-trivial interchange of the orders of the parameters variations of transformation functions with specific time-dependent ones. Special emphasis is put on dependent fields, as appearing, particularly, in gauge theories, and on the Lagrangian formalism. The importance of the QDP and its practicality as a powerful tool in field theory are spelled out, which cannot be overemphasized, and a complete derivation of it is certainly lacking in the literature. The derivation applies to gauge theories as well.

The dust acoustic solitary waves (DASWs) in the presence of hot adiabatic dust in cylindrical and spherical geometries are investigated in an unmagnetized dusty plasma. The modified Korteweg–de Vries (mKdV) has been derived by using the reductive perturbation technique. The numerical solutions of the mKdV equation have been presented in both the geometries for hot dust plasmas. It is found that the amplitude of the dust acoustic wave (DAW) increases with the increase of dust temperature in both the geometries. However, the hot dust has more effect on DASW in spherical geometry as compared to the cylindrical case. These results might be very useful to explain the salient features of multidimensional DAWs for space and laboratory plasmas.

We have studied the problem of particle–antiparticle pair creation from vacuum in external fields considering Schwinger's method. The effective action is calculated respectively for scalar and spinor quantum electrodynamics (QED) in the presence of a constant electromagnetic field plus a Volkov plane wave. It is shown that the plane wave has no influence on the process of pair creation.

In this paper, results of theoretical calculation of energy levels for the [Kr] 4d_3/2nd_3/2 (J= 1), [Kr] 4d_3/2ng_7/2 (J= 2), [Kr] 4d_5/2ng_9/2 (J=2), [Kr] 4d_5/2ng_7/2 (J=2), [Kr] 4d_5/2ns_1/2 (J=2) and [Kr] 4d_5/2nd_5/2 (J=1) series of doubly excited atom Sr are presented using the weakest bound electron potential model (WBEPM) theory. The comparison of the results with the perturbations and those without the perturbations shows that the effect of proper foreign levels is important in the calculation of energy levels, so we think perturbations of foreign levels should be taken into account in the calculation of doubly excited states of Sr I. The accuracy of most of our results is better than 1 cm⁻¹ with few of them being more than 1 cm⁻¹. Therefore, we can say that the WBEPM theory is an efficient one for calculating energy levels of doubly excited Sr I.

Measurements of sample activation by nuclear reaction from MeV particles in the JET tokamak are reported. The samples are used as flux monitors for fusion plasma particles in the MeV energy range. Activation products generated by MeV neutrons, protons and deuterons were found and two nuclear reactions possibly due to α particles were registered, though at a level close to the detection limit.

Adopting a new method of quantum radiation as tunnelling, and taking energy conservation into account, the tunnelling radiation characteristics of the stationary axial symmetric NUT-Taub black hole are studied. The result shows that the tunnelling rate of particles at the event horizon of the black hole is relevant to Bekenstein–Hawking entropy and the real spectrum is not precisely thermal at all.

In this work, the solution of an inverse problem concerning a diffusion equation with source control parameters is presented. The homotopy perturbation method is employed to solve this equation. This method changes a difficult problem into a simple problem which can be easily solved. In this procedure, according to the homotopy technique, a homotopy with an embedding parameter p∊[0,1] is constructed, and this parameter is considered a 'small parameter', so the method is called the homotopy perturbation method, which can take full advantage of the traditional perturbation method and homotopy technique. The approximations obtained by the proposed method are uniformly valid not only for small parameters, but also for very large parameters. The fact that this technique, in contrast to the traditional perturbation methods, does not require a small parameter in the system, leads to wide applications in nonlinear equations.

Understanding of processes such as carrier mobility, electron transfer reactions, chemical reactions in fluids, electron solvation in fluids and electron attachment and localization in clusters relies crucially on the understanding of electron dynamics in fluids at the molecular level. Because of its very small mass, an electron is a quantum object and some of its properties such as diffusion coefficient of a solvated electron in water can be explained only by resorting to quantum mechanical formulation. In this study, we have solved the Bloch NMR flow equations to describe the evolution of the wavelike properties and find the wave functions which can be useful to solve a particular fluid flow problem quantum mechanically. Based on the uncertainty principle, a wave packet is assumed to initially describe the fluid particle (electron) under study. Then, when the particle encounters a force (so its potential energy is no longer zero), the force modifies the wave packet. Finding such propagation techniques, and applying them appropriately can provide useful techniques to find solutions to biological, medical and physical problems which otherwise could not be easily solved.

The Hamiltonian, path integral and BRST formulations of the Chern–Simons–Higgs theory in two-space one-time dimensions are investigated under appropriate gauge-fixing conditions, in the broken (or frozen) symmetry phase, where the phase φ (x^μ) of the complex matter field Φ(x^μ) carries the charge degree of freedom of the complex matter field and is, in fact, akin to the Goldstone boson.

The nonlinear properties of small amplitude electron-acoustic solitary waves (EASWs) have been investigated in an unmagnetized collisionless four-component plasma system consisting of a cold relativistic electron fluid, non-thermal hot electrons obeying a non-thermal distribution, a relativistic electron beam and stationary ions. It is found that the basic set of fluid equations is reduced to a Korteweg–de Vries (KdV) equation, which governs the nonlinear characteristics of EASWs. The effects of relativistic electrons and energetic population parameter δ on the nature of EASWs are discussed.

Stark broadening parameters (width and shift) of six Ar I spectral lines: 522.1, 549.6, 518.6, 560.7, 603.2 and 696.5 nm, corresponding to the transitions 3p⁵nd →3p⁵ 4p for n=7–5 and 4p'→4s have been calculated on the basis of the impact theory within the semi-classical perturbation approach. The case of the quasistatic ions has also been examined. The conditions of use of the presented results have been discussed. The considered lines are in the optical part of the spectrum and are of interest for laboratory research, particularly surface wave sustained discharges, and astrophysical purposes. The obtained results are compared with published experimental results and values calculated by other authors. The influence of the used coupling (j{\text-}L or LS) and oscillator strengths (The Opacity Project (TOP) database or Coulomb approximation) has also been considered.

We present a simple theoretical analysis of the effective electron mass (EEM) at the Fermi level for III–V, ternary and quaternary materials, on the basis of a newly formulated electron energy spectra in the presence of light waves whose unperturbed energy band structures are defined by the three-band model of Kane. The solution of the Boltzmann transport equation on the basis of this newly formulated electron dispersion law will introduce new physical ideas and experimental findings under different external conditions. It has been observed that the unperturbed isotropic energy spectrum in the presence of light changes into an anisotropic dispersion relation with the energy-dependent mass anisotropy. In the presence of light, the conduction band moves vertically upward and the band gap increases with the intensity and colours of light. It has been found, taking n-InAs, n-InSb, n-Hg_1−xCd_xTe and n-In_1−xGa_xAs_yP_1−y lattice matched to InP as examples, that the EEM increases with increasing electron concentration, intensity and wavelength in various manners. The strong dependence of the effective momentum mass (EMM) at the Fermi level on both the light intensity and wavelength reflects the direct signature of the light waves which is in contrast with the corresponding bulk specimens of the said materials in the absence of photo-excitation. The rate of change is totally band-structure-dependent and is influenced by the presence of the different energy band constants. The well known result for the EEM at the Fermi level for degenerate wide gap materials in the absence of light waves has been obtained as a special case of the present analysis under certain limiting conditions, and this compatibility is the indirect test of our generalized formalism.

L-shell x-ray yields of molybdenum bombarded by highly charged Ar^q+ ions (q=11–16) are measured. The x-ray production cross-sections are extracted from the yields data. The energy of the incident Ar ions ranges from 200 to 350 keV. After the binding energy correction, experimental data are explained in the framework of binary-encounter-approximation (BEA). The direct ionization is treated in the united atom (UA) limit (Lapicki and Lichten 1985 Phys. Rev. A 31 1354), not in the separate atom (SA) limit. The calculation results of BEA (Gacia and Fortner 1973 Rev. Mod. Phys. 45 111) are much lower than the experimental results, while the results of binding energy modified BEA are basically in agreement with the experimental results.

Much progress has been made in the measurement of oscillator strengths in neutral and singly-ionized atoms, providing a database for use in important applications. However, for multiply-charged ions, measured data for oscillator strengths are almost exclusively limited to low-lying unbranched transitions. Although extensive measurements of ionic lifetimes exist, the lack of branching fraction measurements in multiply-charged ions prevents these data from being converted to oscillator strengths. A significant factor leading to this deficiency involves the lack of adequate line intensity calibration standards in the vacuum ultraviolet spectral region 2000–400 Å. Here we review the interrelationships connecting these rate parameters, indicate some of the important applications for which they are needed, describe the experimental limitations that currently exist, and suggest possible methods for extending these measurements below 1000 Å.