Y. P. Varshni

Laser action in stellar envelopes

Model calculations for laser action in Hei are carried out, when helium plasma is rapidly cooled by expansion. Results are presented for four transitions, two of which, 31S→21P0 (λ7281) and 31D→21P0 (λ6678), show strong population inversion. Available observational evidence for possible laser action in these two lines in Wolf-Rayet and emission-line stars is summarized and discussed.

Endohedral vibrations of Na+ and K+ in C60

Abstract In certain endohedral systems a metallic ion is trapped inside C 60 such that the energy minimum corresponds to an off-centre position of the ion. A simple analytical function is proposed to represent the potential–energy curve for such systems. The applicability of this function to potential energy curves of endohedral Na + and Li + ions in C 60 is demonstrated and it is then used to calculate the structure of spectra for the two systems.

X‐ray Debye temperature for hexagonal crystals

With the Debye continuum model an analytical expression is derived for the X-ray Debye temperature (θM) of a hexagonal crystal in terms of the elastic constants and this expression is used to calculate θM for hexagonal crystals of 41 elements and compounds. Calculated results by numerical integration are also presented for the X-ray Debye temperature perpendicular to the hexad axis, θ⊥, and that parallel to it, θ||. The calculated results are compared with experimental values, wherever data are available. A correction factor for the effect of dispersion is determined from the experimental data.

An analytic approximation for the energy levels of neutral atoms

Using a screened coulomb potential, a simple formula is obtained for the shell binding energyEns of a neutral atom which gives accurate results over the entire range of the atomic number upto 84.

Wentzel–Kramers–Brillouin quantization rules for two-dimensional quantum dots

In this paper, we apply the semiclassical Wentzel–Kramers–Brillouin (WKB) approximation to an electron in a central force potential, confined in a two-dimensional disc, and we obtain the quantization rules for such a system. As explicit examples, we consider the two most widely studied potentials, viz., the parabolic potential (the harmonic oscillator) and the Hydrogenic impurity state (Coulomb potential) in two dimensions. Both the systems are confined within an impenetrable circular wall of radius r0: In particular, we determine the energies as well as eigenfunctions by this approach. On comparing these energies with those from exact numerical values, the agreement is found to be quite good. Moreover, the WKB approach is found to give a good estimate of the wave functions as well. These results suggest that the WKB approximation works well even for such rigid wall spatial confinement and the present approach can be applied to other confined systems such as those which are encountered in mesoscopic physics. r 2002 Elsevier Science B.V. All rights reserved.

Ovi and Heii emission lines in the spectra of quasars

The plasma-laser star model for quasars, which is based on the hypotheses that there is no red shift in the spectra of quasars and that the strength of the emission lines is due to laser action, is further developed. Continuity is shown to exist between the spectra of Ovi sequence planetary nuclei, Sanduleak stars, and 10 quasars. The Ovi λλ3811, 3834 and Heii λ4686 emission lines in the spectra of these 10 quasars are identified. Candidate identifications for other quasar lines are also suggested. Making use of the similarity between the spectra of Ovi sequence planetary nuclei and those of the 10 quasars, absolute magnitudes, temperatures, and masses of these quasars are estimated. The distribution of quasars in galactic coordinates is also discussed. Three predictions are made.

Extension of Fuda’s off‐shell analysis to screened Coulomb potentials for arbitrary l and limiting relations

The Ecker–Weizel approximation technique is applied to the Schrodinger equation for a class of screened Coulomb potentials (Yukawa, Exponential cosine screened Coulomb and Hulthen) for any arbitrary angular momentum l. We find that the centrifugal term can be combined with the central screening potential to generate an effective Eckart potential with energy dependent strength parameters for which the s‐wave Schrodinger equation is exactly solvable. Using this effective s‐wave potential in the formalism of Fuda and Whiting for off‐shell analysis, we obtain a closed expression for the off‐shell Jost solution fS,l (k,q,r) in which k is the on‐shell momentum, q is the off‐shell momentum and the subscript S means screening. It turns out that for nonzero angular momentum, usual Jost function  fS,l (k,q) can not be defined for finite screening parameter λ. However, we find that the Jost solution, as well as the Jost function defined in the limit λ → 0, show discontinuities at the on‐shell point q=k, similar to t...

The red-shift hypothesis for quasars: Is the earth the center of the Universe?

It is shown that the cosmological interpretation of the red shift in the spectra of quasars leads to yet another paradoxical result: namely, that the Earth is the center of the Universe. Consequences of this result are examined.

Alternative explanation for the spectral lines observed in quasars

It is shown that the emission lines observed in quasars can be satisfactorily explained as being due to laser action in certain atomic species in the expanding envelope of a star. There is no need to assume a redshift.

Valence charge density in indium arsenide

Abstract Valence charge densities of zinc-blende structure InAs calculated using an ab initio pseudopotential method are reported. It is found that as zinc-blende structure InAs is compressed, the changes in the charge density are gradual even as the volume at which it is unstable in favour of a rock salt structure is passed, and that under pressure the bond charges tend to move away from the anion sites towards the bond center sites.