Table of contents

By applying a factorization ansatz to the eigenfunction, an exact analytic solution to the stationary Schrödinger equation in two dimensions is obtained with the potential V(r) = Ar^-4 + Br^-3 + Cr^-2 + Dr^-1. The restrictions on the parameters of the studied potential and the angular momentum quantum number m are also presented.

The solution of the Dirac equation for a massive spin ½ particle in a Yukawa-type potential is investigated by transforming the radial form of the Dirac equation into the Whittaker equation from which we have obtained the desired solutions for the regions near the boundaries of the upper and lower energy continuum, E ≈ ∓ m. Comparison is made with earlier studies.

The Morse potential is used to obtain analytical solutions of the lowest stationary states of the H₂ and HCl molecules. We construct the Husimi distributions for several states and show that the phase space distribution of these states retain several features of its classical limit. Similar results have been reported for one dimensional systems. For the specific case of the central potentials, we show how to treat the angular variables in a consistent way.

The problem of a relativistic spinning particle in interaction with an electromagnetic plane wave field is treated via path integrals. The dynamics of the spin of the particle is described using the supersymmetric action proposed by Fradkin and Gitman. The problem has been solved by using two identities, one bosonic and the other fermionic, which are related directly to the classical equations of motion. The exact expression of the relative Green's function is given and the result agrees with those of the literature. Further, the suitably normalized wave functions are also extracted.

The K_β transitions of Ar ions, excited in an electron beam ion trap, were detected with the help of an x-ray crystal spectrometer. The spectrum was analyzed by using Hartree–Fock calculations with Cowan computer code. High-energy features above 3190 eV, belonging to the K_β transitions in trapped Ar III and Ar IV ions, were observed in the spectrum. An unfitted maximum at 3192 eV was interpreted as the result of 1s–3d excitation of inner shell electrons in Ar II ions.

The spectrum of five times ionized iridium, Ir VI, was investigated in the 420–1520 Å wavelength region. The analysis has led to the determination of the 5d⁴, 5d³6s and 5d³6p configurations. Thirty of thirty four theoretically possible 5d⁴ levels, 27 of 38 possible 5d³6s levels and 96 of 110 possible 5d³6p levels have been established. The levels are based on 711 classified spectral lines. The level structure of the configurations has been theoretically interpreted using the orthogonal operators technique. The energy parameters have been determined by a least squares fit to the observed levels. Calculated energy values and LS-compositions, obtained from the fitted parameter values are given.

With a high-current wall-stabilized arc, operated in helium with small admixtures of CO₂, relative line strengths for some prominent infrared multiplets of neutral carbon have been measured. The results are analyzed in conjunction with previously obtained experimental data in the visible and near infrared region of the spectrum. Our experimental results are compared with those resulting from the Russell-Saunders coupling scheme and with recent sophisticated intermediate coupling calculations. The results of this paper may be helpful for the improvement of atomic structure codes used for line strength calculations. The determined relative line strengths may also be useful in astrophysical applications.

We report results of a theoretical survey on the presence of intense long wavelength spectral lines in the near UV and visible spectral range arising from transitions within the 4p^k (k = 1–5) and 4p⁶4d^k (k = 1–9) ground configurations in heavy ions. Ten such transitions with λ > 1500 Å were found in uranium ions. The density dependence of the corresponding line intensities is calculated for selected ions in the range 10⁹–10¹⁸ cm^-3. Based on previous experimental measurements in the UV spectral range, performed for similar transitions within M-shell ground configurations, it is expected that most of these lines would be sufficiently bright to be observed in future EBIT experiments, and in emission produced by other low density laboratory facilities.

The spectrum of cerium was recorded in 100–1240 Å regions on a variety of normal and grazing incidence spectrographs using a conventional vacuum triggered spark and a laser produced plasma source. The tenth spectrum of cerium was investigated for the first time. Thirty-four lines were classified in Ce X in the 225–732 Å region. Eight levels belonging to the odd parity configurations and seventeen levels of the even parity configurations have been established. The least-squares-fitted parametric calculations and Hartree–Fock calculations were carried out and they interpret the spectrum satisfactorily.

The 2s²2p³3s, 3p and 3d configurations in O-like Cl X have been analyzed using 19 new 3s–3p and 3p–3d transitions. The spectra were obtained using the beam-foil method, and the new lines, which occur between 635 and 868 Å, have an estimated wavelength uncertainty of 0.03 Å. The analysis is supported by isoelectronic comparisons and theoretical calculations. This work is part of an isoelectronic study of the O- and N-sequences aimed at identifying n = 3, Δn = 0 transitions in abundant elements in the solar coronal spectrum recorded by the SUMER instrument onboard the SOHO satellite.

The general explicit expressions for the average energy distance between two configurations using the squares of interconfiguration matrix elements as weight coefficients are obtained. Two types of CI are investigated considering this quantity: configurations with all levels equally influencing the levels of the other configuration and the configurations with their upper levels mainly interacting with those of the other configuration. It is demonstrated that the obtained energy distance enables to estimate the averaged correlation correction and mixing weights rather accurately and thus can be useful for the selection of sets of admixed configurations and for other applications.

Analytical formulae for total cross sections for electron scattering by atoms which are close to the noble gases (Ne, Ar and Kr), for electron energies ranging from 0.5 to 10 keV, have been obtained in this study. We have shown, previously, that molecular total cross sections, at these energies, depend on target polarizability and the number of target electrons. A similar behaviour has been supposed for total cross sections of some atoms (N, O, F, P, S, Cl, As, Se and Br). The obtained expression depends on atomic parameters and it is based in some correlation derived from noble gases. The applicability of the formula has been checked by comparison with available data for atomic oxygen.

By employing a dielectric approach, the energy loss of a pair of test charged projectiles passing through a multicomponent dusty plasma, retaining two ion correlation effects is computed. The numerical results are presented when the two projectiles lie inside R < λ_D or outside the Debye sphere R > λ_D or their separation is of the order of Debye length R ≃ λ_D. For a given separation R, smaller energy loss per unit path length occurs for collinear projectiles than for parallel ones. The contribution to the energy loss due to interference term is also investigated for different test charge velocities and for different relative orientations of the two projectiles. Results of this analysis can be useful in the fields of ICF, Tokamak, Plasma Processing as well as in Space and Astrophysical plasmas.

It is shown that the nonlinear equation governing the dynamics of the magnetic field perturbation in a nonuniform dusty magnetoplasma admits a stationary solution in the form of a propagating shock. The relevance of our investigation to the nonlinear magnetic field propagation in cosmic plasmas is pointed out.

We consider the process of generation of electromagnetic waves as a consequence of the merging of two Langmuir plasmons. The case of a hot plasma in a magnetic field is investigated. It is shown that under such conditions the frequency of Langmuir plasmons can vary over the range from 0.8 to 1.1 of the Langmuir frequency of electrons. The spectrum and polarization of electromagnetic radiation are analyzed. It is shown that allowance for the thermal motion of plasma particles under the conditions involved permits electromagnetic waves in the range from 1.6 to 2.2 of the Langmuir frequency of electrons to be generated. The degree of circular polarization of the radiation can reach 50% even in the case of an isotropic spectrum of Langmuir turbulence.

Turning points for transitions between the electrostatic and electromagnetic discharge modes in low-frequency (≈ 500 kHz) inductively coupled plasmas have been identified and cross-referenced using time-resolved measurements of the plasma optical emission intensities, RF coil current, and ion saturation current collected by a single RF-compensated Langmuir probe. This enables one to monitor the variation of the plasma parameters, power transfer efficiency, which accompany the discharge hysteresis. The excitation conditions for the pure and hybrid modes in the plasma are considered, and the possibility of the TM_mnl → TE_m'n'l' transitions at higher frequencies are discussed.

The charging of a dust grain in an unmagnetized plasma is re-examined. A description of the far-field dipole-like potential is presented for the case when the dust grain absorbs electrons and ions from the background plasma. The dust particle dynamics in the effective potential is analyzed. Also examined are the electron and ion currents that reach the dust grain surface in a Maxwellian plasma. Finally, it is shown that the trapped ions produce only an insignificant current and therefore have little effect on the dust grain surface potential.

Inhomogeneous, collisionfree and bounded plasmas may support large potential drops even for steady electron motion. We present an experimental investigation of the exdended potential drops and transient current pulses, which form when a voltage drop U_a is suddenly applied to a magnetized, collisionfree plasma column with an axial ion density minimum. For well magnetized electrons the resistance at the current maximum agrees with the "intertial resistance" which is approximately proportional to U_a^1/2 for U_a much larger than the electron thermal temperature. The sharp drop following the current maximum is caused by the radial redistribution of the unmagnetized ions due to the transient radial electric field. For larger times (t > 10ω_pi^-1) the measured resistance becomes approximately proportional to U_a as in the strong double layer that finally forms.

An analytical solution has been proposed for the calculation of self-diffusion coefficients (SDC) of molecules in a medium with obstacles of spherical shape. SDC has been estimated using a classic equation for the probability of diffusion displacement of a molecule in a homogeneous medium and taking into account the fraction of possible trajectories in the presence of obstacles. The calculation has given a more exact result for stationary conditions in comparison with Wang's theory and Bell's cell model.

The photoreflectance (PR) spectra of MOCVD grown Zn:Al_xGa_1-xAs with 0 < x < 0.55 and carrier concentration, N, of ∼ 5 × 10¹⁷ to ∼ 1 × 10¹⁹ cm^-3 was studied at the E₁ transition energy. Of particular interest was the effect of varying N and x on E₁, the broadening of the Γ₁ structure. Within the experimental error, Γ₁ was found to increase as x increases. The slope of Γ₁ with log(N) initially decreases as x is increased to 0.29, which is possibly due to a decrease in the translational periodicity of the sample. For 0.30 < x < 0.39, the slope increases sharply which may be due to an increase in the near-surface field with increasing N and decrease in the static dielectric constant, ε_s. The drop of the slope in the region 0.40 < x < 0.49 is probably due to the "crossover region" behavior of Al_xGa_1-xAs from direct to indirect band. After the transition is crossed over, the slope again shows an upward trend in the range 0.50 < x < 0.55, as expected.

To get some insight into the mechanisms of cryopreservation that characterize disaccharides, and to clarify the reasons that make trehalose the most effective bio-protector, we report measurements on trehalose, maltose, and sucrose aqueous solutions. To analyse the interaction mechanisms of the three homologous disaccharides with water, we have investigated the volumetric properties of the three disaccharide solutions, by performing density and ultrasonic velocity measurements at different concentration and temperature values. In addition, we analyse the thermal properties of trehalose, maltose and sucrose aqueous solutions by using Differential Scanning Calorimetry (DSC) and Thermogravimetry (TGA). What emerges from these studies is that trehalose shows, in comparison with maltose and sucrose, the smallest values of the partial molar volume in all the investigated temperature range, this circumstance being indicative of a more packed conformational arrangement especially at the lowest temperatures. Furthermore, trehalose reveals, in respect to the other disaccharides, the greatest structural sensitivity to temperature changes. Finally, calorimetric measurements indicate a greater effectiveness of trehalose in destroying the tetrahedral network of water compatible with the formation of ice, supporting the hypothesis of a higher "fragile" thermodynamic character of the trehalose-water system at high dilution. Preliminary TGA and DTG findings reveal a noticeable stronger trehalose-water interaction mechanism and a significant higher thermal stability of the trehalose system.

The linear theory of the ion-acoustic instability in the E-region ionospheric plasma has been studied. The instability can generate ion-acoustic waves with dispersion equation ω = c_sk and with wavelengths of order of a metre in the region of small aspect angles θ < 1°. This instability can be used for interpretation of coherent backscatter type I events. Considering the ion-acoustic instability it is also possible to explain rocket measurements during the ROSE project of waves with phase velocities smaller than the ion-acoustic velocity and dependent on frequency.