Volume 52, Issue 3
March 1999, pages 237-350
pp 237-244 March 1999
An exact solution of Einstein’s field equations for anisotropic fluid distribution on the background of a pseudo-spheroidal spacetime has been reported. The models based on this solution are found to accommodate density variation of high degree from the centre to the boundary of the distribution and admit a subclass for which both the radial and tangential pressures vanish at the boundary of the configuration.
pp 245-256 March 1999
The field equations for the chiral invariant model of pion dynamics developed by Charap have been revisited. Two new types of solutions of these equations have been obtained. Each type allows infinite number of solutions. It has also been shown that the chiral invariant field equations admit invariance for a transformation of the dependent variables.
pp 257-267 March 1999
We present a brief analysis on the approximate methods for the determination of gluon distribution from the scaling violation of proton structureF2p in the low-x limit. In the leading order, a general low-x approximated relation is presented having more accuracy than the previous methods. Next-to-leading order correction is presented incorporating double-log-approximation. The proposed method is found to give good agreement with data. It may also be used to discriminate between the sets of gluon distributions in the low-x.
pp 269-273 March 1999
Here, we make an indirect phenomenological study of the possible presence of a CSB component in the λN interaction in medium and heavy hypernuclei using a semi-empirical formula for the difference in the ground stateBλ of hypernuclear isobars. We find that light hypernuclei are better suited than heavier hypernuclei for such information.
pp 275-279 March 1999
We examine the excitation dynamics of a model atom excited by a two commensurate (the fundamental and second harmonic) intense laser fields. We investigate that one can easily stabilize the quantum wave packet through suppression of photodetachment by changing the laser intensity and the relative phase between the two colors.
pp 281-291 March 1999
We have described here the physical basis for lasing without population inversion (LWOPI). This type of amplification is obtained basically by two mechanisms: (i) one is based on atomic interference and (ii) the other is based on Fano-type interference. We have shown here, in H2 molecules, amplification without population inversion is feasible by considering both the mechanisms.
pp 293-302 March 1999
The present contribution tries to find a scientific answer to the question of stability of an equilibrium plasma sheath in a colloidal plasma system under external gravity effect. A model equilibrium of hydrodynamical character has been discussed on the basis of quasi-hydrostatic approximation of levitational condition. It is found that such an equilibrium is highly unstable to a modified-ion acoustic wave with a conditional likelihood of linear driving of the so-called acoustic mode too. Thus, it is reported (within fluid treatment) that a plasma-sheath edge in a colloidal plasma under external gravity effect could be highly sensitive to the acoustic turbulence. Its consequential role on possible physical mechanism of Coulomb phase transition has been conjectured. However, more rigorous calculations as future course of work are required to corroborate our phenomenological suggestions.
pp 303-319 March 1999
We report here high-pressure x-ray diffraction (XRD) studies on tellurium (Te) at room temperature up to 40 GPa in the diamond anvil cell (DAC). The XRD measurements clearly indicate a sequence of pressure-induced phase transitions with increasing pressure. The data obtained in the pressure range 1 bar to 40 GPa fit five different crystalline phases out of Te: hexagonal Te (I) → monoclinic Te(II) → orthorhombic Te (III) → Β-Po-type Te(IV) → body-centered-cubic Te(V) at 4, 6.2, 11 and 27 GPa, respectively. The volume changes across these transitions are 10%, 1.5%, 0.3% and 0.5%, respectively.
Self consistent electronic band structure calculations both for ambient and high pressure phases have been carried out using the tight binding linear muffin tin orbital (TB-LMTO) method within the atomic-sphere approximation (ASA). Reported here apart from the energy band calculations are the density of states (DOS), Fermi energy (Ef) at various high-pressure phases. Our calculations show that the ambient pressure hexagonal phase has a band gap of 0.42 eV whereas high-pressure phases are found to be metallic. We also found that the pressure induced semiconducting to metallic transition occurs at about 4 GPa which corresponds to the hexagonal phase to monoclinic phase transition. Equation of state and bulk modulus of different high-pressure phases have also been discussed.
pp 321-332 March 1999
In the present paper, an equation of state has been obtained in case of liquid alkali metals like Na, K, Rb and Cs from sound velocity measurements. The theory developed gives very good agreement for both the sound velocity and the volume as a function of pressure at different temperatures in these liquid alkali metals. Further, the variation of non-linear parameter,B / A, as a function of pressure and temperature is also studied.
pp 333-340 March 1999
Electronic structure of hydrogen in NEG alloy [Zr0.70V0.246Fe0.054] is calculated by using nonlinear response theory [Kohn and Sham,Phys. Rev.A140,1133 (1965)]. The configurational energy is calculated by assuming the ideal hcp structure for NEG alloy. The calculated configurational energy predicts that hydrogen prefers octahedral (0)-site in NEG alloy.s-Type shallow bound state of energy -1.580 x 10-5 Ryd. suggests that hydrogen does not form NEG hydride and it stays as a free ion in NEG alloy. This conclusion confirms the prediction of Tripathiet al.
pp 341-350 March 1999
We present a detailed study of harmonic generation in Bi(Pb)SrCaCuO superconducting thick film prepared by screen printing technique. A comparative study of amplitude of harmonics of two films of different Jc have been carried out. The variation of amplitudes of the harmonics are studied as a function of magnitude of ac and dc field. The temperature dependence of amplitude of third harmonic (V3) is studied with increasing amplitude as well as frequency of ac field. These results are analyzed in the frame work of critical state model. V3-T curve also indicates the presence of two phases in Bi(Pb)SrCaCuO film.
Volume 93 | Issue 6
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