• Volume 7, Issue 1

      July 1976,   pages  1-61

    • On the widths ofK levels of heavy elements

      T V Krishnan N A Narasimham

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      The ratios of the widths ofK levels of heavy elements with atomic number 70 to 92 have been calculated with relativistic wave functions, retardation, screening and field theoretical corrections to relativistic energy. The calculated values have been compared with the available observed data and good agreement has been obtained.

    • Thermonuclear reaction rates from (p, n) reactions

      S Kailas M K Mehta

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      Thermonuclear reaction rates for the temperature range 1≤T9≤5 have been extracted from experimentally measured (p, n) cross sections for45Sc50Ti,51V,54Cr,55Mn and59Co nuclides below 5 MeV bombarding energy. These reaction rates are important in the build-up of medium and heavy nuclides in the stellar evolution process and nucleosynthesis. To enhance the usefulness of these reaction rates in astrophysical calculations, they have been fitted to an analytic function of temperature, valid throughout the temperature range considered here.

    • Gas-liquid phase transition

      A C Biswas

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      A theorem has been proved giving a sufficient condition for a first order phase transition in a gas. The corresponding fugacity expansions for the isotherms in the different phases have been derived.

    • Two site spin correlation function in Bethe-Peierls approximation for Ising model

      Deepak Kumar

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      Two site spin correlation function for an Ising model above Curie temperature has been calculated by generalising Bethe-Peierls approximation. The results derived by a graphical method due to Englert are essentially the same as those obtained earlier by Elliott and Marshall, and Oguchi and Ono. The earlier results were obtained by a direct generalisation of the cluster method of Bethe, while our results are derived by retaining that class of diagrams, which is exact on Bethe lattice.

    • Colour centres in powdered KI

      S V Moharil B T Deshmukh

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      Fine powder of KI was coloured in an electrodeless discharge. Due to quick bleaching of the F centres produced in this method, it was possible to prepare the samples that were almost free from the F centres. High concentration of the electron deficient centres could be produced, which were studied by measuring the diffused reflectance. A band at 354 nm is shown to be composed of two overlapping bands. Further, growth of a band appearing at 265 nm is studied. Bleaching characteristics of the samples are studied and it is shown that, similar to F centre bleaching, bleaching of these samples also proceeds in at least two steps. The difference between two components of the bleaching curves is quite marked. Further it is showed that the components are related to the presence of different absorption bands and appear at different stages of colouration.

    • Normal modes of oscillations of lattices

      R N Chaudhuri

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      Polynomial equations are obtained for the solutions of the vibrational frequencies of a simple cubic, primitive orthorhombic and tetragonal Bravais lattices of finite size with particles connected to their nearest neighbours through both central and non-centrarl forces, but with arbitrary forces connecting the surface atoms to the rigid walls. The exact expressions of the different normal modes of oscillations and the amplitudes of vibration of different particles in various modes are obtained by solving three decoupled partial difference equations.

    • Infrared spectra of BeSO4.4H2O and its deuterated analogue in 4000–1200 cm−1 region

      Bipin K Srivastava D P Khandelwal H D Bist

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      IR spectra of BeSO4.4H2O and its deuterated analogue at ∼300 K and ∼110 K are reported in the region 4000–1200 cm−1 using thin film and nujol mull techniques. The observed bands have been assigned as the internal modes of the water and the overtones and combinations of various modes using the recently revised assignments of SO42− and Be(aq)4 fundamentals in the region 1200–250 cm−1 (Srivastavaet al 1976). The splitting of the internal modes of water has been discussed in the light of the effects of deuteration and cooling and it is shown that all the water molecules in a unit cell are asymmetric but crystallographically equivalent.

    • Raman processes in free-free transitions in the presence of intense laser beam

      Man Mohan Puran Chand R K Thareja

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      The differential cross section for the electron scattering accompanied by simultaneous absorption or emisson of one Raman photon and the inverse bremsstrahlung process in an intense laser beam is calculated.

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