• Volume 18, Issue 5

      May 1982,   pages  385-460

    • Black hole physics in globally hyperbolic space-times

      P S Joshi J V Narlikar

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      The usual definition of a black hole is modified to make it applicable in a globally hyperbolic space-time. It is shown that in a closed globally hyperbolic universe the surface area of a black hole must eventually decrease. The implications of this breakdown of the black hole area theorem are discussed in the context of thermodynamics and cosmology. A modified definition of surface gravity is also given for non-stationary universes. The limitations of these concepts are illustrated by the explicit example of the Kerr-Vaidya metric.

    • 2S-excitation of atomic hydrogen by electrons at intermediate energies

      J N Das N Saha

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      The method of Das developed recently to analyse elastic scattering of electrons by atoms has been extended in the present paper to inelastic scatterings. The method has been applied for the computation of 2S-excitation, cross-sections at two typical intermediate energiesviz. 54.4 eV and 100 eV energies. Some of the results are compared with available experimental results and are found to be in satisfactory agreement with these.

    • A green function approach to shear viscosity coefficient

      A K Heblekar A S Wagh I M Boswarva

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      Modified transport equations are derived from Kadanoff and Baym kinetic equations, suitable for the study of thermal transport coefficients. These equations include the Hartree average energy term which has been ignored in the previous studies of thermal transport coefficients. They are linearised and the successive perturbation method is employed to solve them. The solutions are applied to shear viscosity coefficient of gases and the results are compared with the recent experimental measurements for several complex and simple gases. The potential assumed is a hard core one with a perturbation tail. The agreements are particularly good for gases with low molecular weight and in the high temperature range. For complex molecules even in the low temperature range, the agreement is better than the previous calculations. The formula derived yields the explicit temperature dependence of the viscosity coefficient.

    • The infrared and laser Raman spectra of K2Zn(SO4)2 · 6H2O

      B Singh Shashi Prabha Gupta B N Khanna

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      The Raman spectra of the single crystal of K2Zn(SO4)2·6H2O belonging toC2h5 space group in the 40–1200 cm−1 region in different scattering geometries and their spectra ofthe microcrystalline salt in the 1500-50 cm−1 region have been reported. The dynamics of the crystal has been described in terms of 186 phonon modes under the unit cell approximation. The weak bands in the region 400–900 cm−1 have been assigned to the libratory modes of H2O molecules in contradiction to the assignments reported by Ananthanarayanan. The ambiguities existing in the literature about the assignments ofν2c andν5c modes of [Zn(H2O)6]2+ have also been removed. The translatory and libratory modes of different units of the crystal have been identified and assignments are made using farir and Raman data on various isomorphous tutton salts.

      It has been inferred that both SO42− tetrahedron and [Zn(H2O)6]2+ octahedron undergo linear as well as angular distortions from their free state symmetries in the crystal.

    • On the mass spectroscopy of charmed multiquark hadrons

      G Bhamathi K Prema A Ramachandran

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      The possible existence of charmed multiquark hadrons are investigated using phenomenologicalmit bag model and the SU(4) flavour symmetry. The masses of 6q, 9q and 15q systems having the same quantum numbers as the physically interesting ordinary nuclei, hypernuclei and supernuclei are estimated. We find that several new states with distinct signatures are predicted.

    • Higgs boson production in pp and$$p\bar p$$ collisionscollisions

      Mohammad Sami

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      The associated production of Higgs particles andZ (W) bosons inpp and$$p\bar p$$ collisions is studied. The total cross-section of the processpp$$\left( {p\bar p} \right)$$ →HXl+l is estimated.

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