• Volume 16, Issue 1

      January 1981,   pages  1-107

    • Raman study of temperature dependence of lattice modes in calcite

      A K Sood A K Arora V Umadevi G Venkataraman

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      The temperature dependence of the line width and the peak position of theEg librational mode (of nominal frequency 285 cm−1) and theEg translational mode (of nominal frequency 155 cm−1) in calcite (CaCO3) have been studied by laser-Raman spectrometry. The role of orientational relaxation as a possible process contributing to the line width has been evaluated. It is concluded that reorientations do not play a major part in relation to the present observations. It is further shown that the latter can be understood on the basis of cubic and quartic anharmonic processes. The data also suggest that certain phonon interactions earlier considered insignificant for peak shift in calcite, do contribute significantly.

    • The localised modes due to P defects in cadmium telluride

      K Ramachandran T M Haridasan

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      Dutt and Spitzer experimentally observed the localised vibrational modes related to the phosphorus defects in CdTe andr eported that P would go either to substitutional or interstitial site. In this paper we have theoretically investigated the P defect behaviour in CdTe for those two possible sites by Green’s function technique and we believe from our calculations that P goes interstitially rather than substitutionally.

    • Lattice sum calculations and a Mössbauer study on electric field gradient in phlogopite

      Anjali Krishnamurthy Bipin K Srivastava S Lokanathan

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      Lattice sum contributions have been calculated at the two octahedral sites in a phlogopite mica assuming a systematic distribution of octahedral cationic charges. This, unlike the case of a random distribution of charges, is able to reproduce broad features of quadrupole doublet spectra in Mössbauer experiments suggesting that the doublet assignments in terms of the two structural sites,M1 (trans) andM2(cis), are quite valid. Angle dependence of Mössbauer spectra has also been studied for a ferric-rich phlogopite mica sheet to determine the orientation of the EFG principal axis component and the sign of the quadrupole coupling constant. Quadrupole splitting values and the positive sign of coupling constants match the theoretical predictions quite well but the model fails to predict the observed EFG orientation.

    • A phenomenological bag model with variable bag pressure

      K Babu Joseph M N Sreedharan Nair

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      We examine the consequences of a variable (density-dependent) bag pressure term and a fixed hadronic size in the phenomenological MIT bag model for hadron spectroscopy. Mass spectrum of the low-lying baryons and mesons, baryon magnetic moments and the hadron mass splittings are estimated. These are found to be in closer agreement with experiment than the MIT results.

    • High momentum nucleons in the nucleus

      S Saini B K Jain

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      Using Jastrow form for the nuclear wave function, single-particle distributions in the momentum space are extracted for the correlation functions corresponding to the Reid soft core, Hamada-Johnston and Ohmura-Morita-Yamada (OMY) hard core potentials. The correlations functions used for this purpose are the numerical solutions of the Schrödinger type equation for the realistic potentials and analytical form for the OMY potential. It is found that the calculated momentum distributions, with Woods-Saxon basis functions, differ significantly beyond 400 MeV/c. Comparison with the experimental proton momentum distribution from (γ, p) reaction suggests that while the OMY potential results are nearer to the experimental values, the realistic potentials do not introduce the high momentum components to the required extent.

    • Baryon magnetic moments in a quark model

      Avinash Sharma Satish Kanwar

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      The magnetic moments of uncharmed and charmed baryons are considered to arise through single-quark and two-quark transitions in a quark model. The magnetic moment operator is taken to transform as:Tβα ˜aT11, +bT22 +cT33 +dT44, whereTβα are members of SU(4)20′-plet. The assumption, that the magnetic moment operator obtains contribution from the single and two-quark transitions, yields good results for the magnetic moment values of uncharmed baryons. Magnetic moments of charmed baryons can be expressed in terms of one parameter.

    • Lippmann-Schwinger equation

      Suprokash Mukherjee

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      It is established that the solution of the Lippmann-Schwinger equation for scattering is unique, despensing an earlier proof of non-uniqueness.

    • Two-potential formula continued off-the-energy-shell

      B Talukdar M Chatterji M Kundu

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      We derive an off-energy-shell generalization of the two-potential formula by using a coordinate-space approach and apply the formalism to construct algorithms for studying spatial behaviour of the fully off-shellT matrix. We also suggest some future applications of the proposed theory.

    • Stimulated raman scattering from plasma modes in magnetoactive semiconductors

      S Guha N Apte

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      Stimulated scattering off electron plasma mode is investigated analytically for the case when the pump wave is an intense circularly polarised electromagnetic wave propagating parallel to a homogeneous dc magnetic field in an isotropic semiconductor-plasma. The threshold electric field of the pump necessary for the stimulated Raman scattering and the growth rate of the parametrically unstable mode have been obtained for two cases (i)B0=0 and (ii) B0 ≠ 0. It is seen that the magnetic field does not significantly affect the threshold electric field as well as the growth rate provided the cyclotron frequency is small compared to the frequency of the pump wave. The threshold conditions are also found to be insensitive to the electron thermal velocity.

    • Quantum chromodynamics corrections to polarised deep-inelastic electron-nucleon scattering

      V Gupta S M Paranjape H S Mani

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