• Volume 19, Issue 5

      November 1982,   pages  421-524

    • Some theoretical studies on concurrent events in photoelectron spectroscopy

      M S Gopinathan B J Cherayil

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      Concurrent events in photoelecron spectroscopy such as photoionisation, shake-up and shake-off transitions are studied using atomic wavefunctions recently developed by one of the authors and the concept of the Slater transition state. Various transition energies and intensities are calculated to test the efficiency of the wave-functions and the applicability of the transition state method to these processes. It is concluded that the method is reliable enough to be useful in the assignment of these transitions in the experimental spectrum.

    • Atomic diamagnetic susceptibilities from the statistical Thomas-Fermi-Amaldi theory

      Maria C Donnamaria Eduardo A Castro Francisco M Fernández

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      We report the calculation of atomic diamagnetic susceptibilities from the statistical Thomas-Fermi-Amaldi theory. The importance of the Fermi-Amaldi correction for the Thomas-Fermi theory is examined. The calculated values are compared with those obtained from self-consistent-field wave functions as well as with respect to available experimental data. Several general trends are pointed out and the advantages of the statistical procedure are stressed.

    • Lattice dynamical study of body-centred tetragonal indium

      V Ramamurthy S B Rajendraprasad

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      The phonon dispersion curves, phonon frequency distribution function as well as the lattice specific heat of body-centred tetragonal indium have been deduced using a lattice dynamical model which includes central, angular and volume forces. Six elastic constants, four zone boundary frequencies and an equilibrium condition were used in the evaluation of the force constants. It is shown that this model is elastically consistent and satisfies the symmetry requirements of the lattice, the phonon frequencies of indium deduced from it are in very good agreement with the experimental values of Reichardt and Smith and the theoretical values of Garrett and Swihart, and theθD values compare well with the experimental values over a wide temperature range. The apparent discrepancies in the phonon dispersion curves and theθD-T curves obtained from deficient models, importance of umklapp processes and the significance of angular forces in the lattice dynamical models are discussed.

    • Optical absorption spectrum of Cr3+ in natural ruby

      B J Reddy L Rama Moorthy

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      Two sharp line-like bands calledN andR lines on the red side, a close doublet (B lines) on the violet side and two broad bands are observed for natural ruby. At liquid air temperature the splitting ofR line was found and also three sharp-bands calledR, R′ andB lines are identified with spin-forbidden transitions of2E,2T1 and2T2. The two broad bands calledU band andY band are assigned accordingly to the spin-allowed transitions4T2 and4T1 respectively. The observed bands of natural ruby have been attributed to Cr3+ ion in an octahedral environment with trigonal distortion. The crystal field parameters which gave a good fit to the observed band positions areB=732 cm−1,C=4.25B,Dq=1830 cm−1,V=−1996 cm−1 andλ=34 cm−1.

    • Mechanoluminescence and high pressure photoluminescence of (Zn, Cd) S phosphors

      B P Chandra

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      The mechanoluminescence spectra of (Zn, Cd)S phosphors shift towards shorter wavelength side as compared to the photoluminescence spectra, however, the photoluminescence spectra shift towards shorter wavelength side with increasing pressure with less pressure coefficient. This finding eliminates the thermal population mechanism and suggests the electrical excitation mechanism for the mechanoluminescence excitation. The decay of mechanoluminescence after the deformation (Zn, Cd)S phosphors may be controlled by the recombination rate of holes and electrons, i.e. by the finite times required for the liberation of the electrons from the traps and for the electron transport, and consequently the decay of mechanoluminescence may be similar to the decay of photoluminescence.

    • Coherent potential approximation for a disordered diatomic linear chain having diagonal and off-diagonal randomness

      P Nayak S N Behera

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      A coherent potential approximation (cpa) for a mixed diatomic linear chain including both mass and force constant changes has been developed. In this case an impurity atom substituted at a particular site in one of the sublattices couples with two nearest neighbour atoms in the other sublattices. The diatomic linear chain is therefore considered as a tetratomic linear chain, the size of the unit cell being twice the original. Thecpa density of states and the dielectric susceptibility have been calculated. The numerical values of the later have been calculated in theata (averaget-matrix approximation) limit. Comparison of these results with the experimental and other computer calculations show a qualitative agreement.

    • Effect of electromagnetic perturbation on charge imbalance in a superconductor: A two-fluid description

      B A Mattoo Y Singh

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      Using a generalized two-fluid pictures for the charge of superconductor and ordinary Boltzmann equation for quasiparticle excitations, the effect of frequency and wave-vector dependent electromagnetic perturbation on charge imbalance near transition temperatureTC is studied. In a situatiod where both the effective charge and distribution function of quasiparticles deviate from their equilibrium values, the charge imbalance is shown to possess a propagating solution at frequencies greater than inelastic scattering rate. In situations where charge imbalance is created by injection of quasiparticles, the charge imbalance relaxation rate is shown to decrease. We also study the effect of applied perturbation on quasiparticle diffusion length and hence on superconductor—normal interface boundary resistance.

    • Intensity distribution in theA2Π –X2Σ+ system of Yttrium monoxide

      S P Bagare N Sreedhara Murthy

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      The integrated intensities of a few bands in the vibrational structure of the astrophysically significant ‘orange’ system of the molecule yttrium monoxide, have been measured experimentally by the technique of photographic photometry. The effective vibrational temperatures of the source are found to be 2402±180 K and 2901±230 K for the subsystemsA2Π3/2X2Σ+ andA2Π1/2X2Σ+ respectively.

    • Weinberg-Salam model and chiral symmetry of mesons

      M S Sri Ram

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      Weinberg-Salam model is considered in the light of SU(4) × SU(4) chiral symmetry for mesons. The Higgs doublet and the pseudoscalar mesons mix in this framework. Consequences of this mixing for the Higgs decays and the nonleptonic decays of the mesons are explored.

    • Strong coupling expansion in the massive Thirring model

      R Banerjee

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      A strong coupling expansion of the Green functions in the massive Thirring model is formulated. Expressions obtained for the fundamental fermion mass and theβ function agree with the known qualitative features of these physical quantities.

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