• Volume 14, Issue 1

      January 1980,   pages  1-102

    • Helicon-phonon interaction for oblique propagation in potassium

      Roschen Idiculla K S Viswanathan

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      The dispersion equation for oblique propagation of the wave in thexy plane for helicon-phonon interaction has been derived and numerical studies have been carried out on the nature of variation of the four different modes with the magnetic field and the inclination of the magnetic field with the direction of propagation.

    • A mean-field, effective medium theory of random magnetic alloys. II. The random heisenberg model

      Abhijit Mookerjee

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      A classical Heisen berg model is analysed. The interaction is of the RKKY type and only between sites randomly occupied by magnetic atoms. The possible phases are described at various temperatures and concentration of magnetic atoms. The procedure is realistic and not the ‘exactly’ solvable kind studied by earlier workers.

    • Sound velocity change in doped displacive ferroelectrics

      U C Naithani B S Semwal

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      An expression is obtained for the sound velocity change in doped displacive ferroelectrics, in the presence of an electric field by considering higher order anharmonic terms in the modified Silverman-Joseph Hamiltonian. The mass and force constant changes due to impurity may give cancellation effects. The presence of higher order anharmonicity decreases the sound velocity which in turn varies with the applied electric field. The sound velocity decreases anomalously near the Curie temperature.

    • Effect of transverse static magnetic field on stimulated brillouin scattering of electromagnetic wave

      S Guha N Apte

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      Stimulated Brillouin scattering of a plane polarised electromagnetic wave propagating perpendicular to a static magnetic field has been investigated analytically in ann-type piezoelectric semiconductor-plasma. Using coupled mode theory the dispersion relation is obtained and the threshold value of the amplitude of electromagnetic wave for the onset of instability is studied for both the forward and back-scattered modes. The role of the magnetostatic field on the threshold conditions for the unstable mode has been discussed.

    • Coefficients of viscosity of a gaseous plasma

      D Adhikari S K Majumdar

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      We present here an order of magnitude calculation for the coefficients of viscosity with the assumption that the drift velocity introduces asymmetry both in the single-particle distribution functionf1 and the correlation functionP(1, 2). These asymmetric parts have been estimated considering the self-relaxation of the system when the cause of drift velocity is suddenly removed. Using these, the kinetic part of the coefficient of electron viscosity has been calculated and the result fairly agrees with similar studies by others. The potential part of shear viscosity coefficient is found to be zero while both parts of the coefficient of bulk viscosity are non-zero.

    • Effect of dielectronic recombination excitation in the solar x-ray lines of calcium-ions

      Suresh Chandra

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      The effect of dielectronic recombination as an excitation process in the intensity of solar x-ray lines of calcium ions is investigated. It is found that x-ray line intensities are enhanced by 15% to 88% with the inclusion of dielectronic recombination as an excitation mechanism.

    • A decomposition theorem for SU(n) and its application to CP-violation through quark mass diagonalisation

      P P Divakaran R Ramachandran

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      It is proved that the groupG=SU(n) has a decompositionG=FCF whereF is a maximal abelian subgroup andC is an (n − 1)2 parameter subset of matrices. The result is applied to the problem of absorbing the maximum possible number of phases in the mass-diagonalising matrix of the charged weak current into the quark fields; i.e., of determining the exact number of CP-violating phases for arbitrary number of generations. The inadequacies of the usual way of solving this problem are discussed. Then=3 case is worked out in detail as an example of the constructive procedure furnished by the proof of the decomposition theorem.

    • $${}_{\Lambda \Lambda }^{10} Be$$ in Faddeev-Yakubovsky formalismin Faddeev-Yakubovsky formalism

      H Roy-Choudhury V P Gautam D P Sural

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      The four-body dynamical equations for two distinct pairs of identical particles derived earlier are applied to investigate the system$${}_{\Lambda \Lambda }^{10} Be$$. The two-body potentials have been taken to be of the Yamaguchi form, and the Bateman approximation has been used for the other amplitudes. From the set of coupled integral equations, the separation energy, BΛΛ, for the two Λ particles in$${}_{\Lambda \Lambda }^{10} Be$$ is obtained as 43·97 MeV.

    • Prediction for Z-mass is a crucial test of the standard model

      S K Soni

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      In schemes with oneW boson and twoZ-bosons (mediating the charged and neutral current interactions involving ordinary fermions) based on the direct product and simple groups, SU(2) × U(1) ×u′(1) andG × U(1) (G is a simple group of rank two), the following two questions are discussed. (1) What are the necessary and sufficient conditions for minimal reducibility of the effective four-fermion neutral current interaction (involving νμ-hadron, electron-hadron and νμ-electron sectors) to the corresponding prediction of the standard model? (2) In what way are the masses of the twoZ-bosons constrained relative to the mass of the neutral boson of standard model? The answers to these questions are given first by keeping the underlying Higgs structure, responsible for gauge-boson (and fermion) mass generation, completely arbitrary (called Higgs-independent case) and then by making a specific choice for the Higgs structure resulting in a natural mass relation for theW andZ-bosons that is an exact counterpart toMW(S)/2=MZ(S)/2 sec2ϑW for the standard model (called Higgs-dependent case). The distinction between these two cases is brought out clearly as also that between the direct product and simple groups. Whether or not any assumption is made about the Higgs structure, with either the direct product or the simple group, it is concluded that in general there is aZ-boson lighter than the neutral boson of the standard model.

    • Coulomb effect in rotating nuclei in the Thomas-Fermi approach

      K Andhradev R G Kulkarni

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      The effect of nuclear Coulomb potential in rotating nuclei has been studied in the Thomas-Fermi approach. The numerical calculations of typical rotating nuclei show that Coulomb potential plays an important role in the rotational mass regions 150–190 and >224.

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