• Volume 19, Issue 4

      October 1982,   pages  303-420

    • SU2 ⊗ U1 gauge model of electroweak interaction with (V + A) strangeness-changing charged current

      L K Pandit

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      We construct a model of renormalizable electroweak interaction with (V+A) strangeness-changing charged current in the framework of the minimal spontaneously broken SU2 ⊗ U1 gauge theory, taking our motivation from the recently reported measurement of the electron asymmetry in polarizedΣ-hyperonβ-decay by Keller and co-workers. The model avoids strangeness-changing but admits charm-changing pieces in the neutral current. Several phenomenological consequences of the model are discussed together with a comparison with the standard model of electroweak interaction.

    • Non-renormalization of the weak vertex in gauge theories with integrally charged quarks

      G Rajasekaran M S Sri Ram

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      We give current algebra arguments to show that toO(α) the colour octet vertices do not renormalize the effective weak vertex between colour singlet hadrons in models with broken colour symmetry. The result does not depend on the details of the mixing between colour gluons and electro-weak bosons.

    • Two million volt terminal tandem accelerator

      M G Betigeri T P David S C Hiremath P K Iyengar M K Mehta V S Raju P Singh J N Soni

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      Design and construction details of a horizontal 2 MV Tandem Van de Graaff accelerator built at Bhabha Atomic Research Centre are given. A terminal voltage of 2.15 MV has been achieved. Energy analysed Corona stabilized beams of protons and oxygen ions have been obtained. Experiments have been carried out to test the performance of the accelerator.

    • Design of an accelerating tube for electrostatic accelerators

      P Singh T P David M G Betigeri

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      An accelerating tube has been designed and fabricated. Ion optical properties with different input beam geometries for 25 keV protons have been studied. An optimum voltage gradient in the first few sections required to obtain a focussed beam is determined. The tube has been installed in the 2 MV tandem accelerator built at Trombay and the performance of the tube is discussed.

    • Orientational order parameters of nematogenic trans-4-propyl cyclohexyl-4 (trans-4-alkyl cyclohexyl) benzoates

      Srinivasa M M M Abdoh N C Shivaprakash J Shashi-Dhara Prasad

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      The refractive indices and densities of three members of trans-4-propyl cyclohexyl-4 (trans-4-alkyl cyclohexyl) benzoates are reported as functions of temperature in the nematic and isotropic phases. The principal molecular polarizabilities and order parameters (S) have been evaluated using the anisotropic internal field model (Neugebauer’s approach). Also order parameters have been estimated by studying the dipole-dipole splittings in the wide line proton magnetic resonance (PMR) spectra. The results obtained are in close agreement with those obtained from refractive index measurements.

    • Violation of the second law of black hole physics by tachyons

      K C Das

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      It is shown that the interaction of a class of positive energy tachyons decreases the area of the horizon of theT-S, ∂=3 metric even in the case of a reversible transformation (Mir=constant). This is a violation of the second law of black hole physics.

    • Simple variational approach to the thermal properties of ionic crystals

      Rajaram Nityananda Ramesh Narayan

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      The thermal properties of ionic crystals are analysed using the variational principle of classical statistical mechanics. The Einstein and Debye pictures of the lattice vibrations are adopted as trial Hamiltonians. No explicit calculation of the lattice spectrum is needed. The variational result for the thermal expansion in the Einstein picture is identical to that recently derived by Narayan and Ramaseshan by a physically motivated thermal force picture. The agreement with experimental values in the alkali halide family of crystals is surprisingly good, the root mean square error being about 14%. The parameters in the interionic potential used are obtained from the lattice spacings and compressibilities of the crystals and not from anharmonic properties. The Debye picture gives about equally good results for the thermal expansion, but better results for the thermal vibration amplitudes of the ions. It differs from the Einstein picture in incorporating correlated vibrations of atoms and in having an explicit Coulomb contribution to the thermal properties. It is suggested that the theory given in this paper has a useful role to play in studies of thermal expansion and phase stability for large families of ionic crystals when combined with semi-empirical theories.

    • Lattice thermal expansion of silver indium disulphide

      P Kistaiah K Satyanarayana Murthy K V Krishna Rao

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      Lattice parameters of chalcopyrite type compound silver indium disulphide (AgInS2) were determined as a function of temperature by the x-ray method in the temperature range 28 to 685°C. Using these data, the coefficients of thermal expansion,a anda, were evaluated by a graphical method. The temperature dependence ofa anda is represented by a suitable equation. The anisotropic thermal expansion of AgInS2 is explained in terms of the thermal expansion of the Ag-S and In-S bonds of the AgInS2 lattice.

    • Luminescence in ZnS: La and ZnS: (Mn, La) phosphors

      L N Tripathi C P Mishra B R Chaubey

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      The photo (PL) and electro (EL) luminescence in ZnS: MnLa and ZnS: La have been studied. The enhancement and quenching of emission bands have been observed on the simultaneous application of sinusoidal field and photons. The wave shape, voltage, frequency and temperature dependence of EL brightness have been reported. A study of the phosphorescence and thermoluminescence of these phosphors is also carried out and it is observed that the trap-depth changes slowly with temperature and activator concentration. An attempt has been made to calculate the trap depth by studying temperature dependence of EL brightness. The results are reported and discussed.

    • K-shell ionisation cross-sections of Cu, Ge, Mo, Ag and Sn by protons of energy 0.3 to 1.8 MeV

      D Bhattacharya S K Mitra

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      K-shell ionisation cross secions of Cu, Ge, Mo, Ag and Sn in proton impact have been measured systematically in the energy range 0.3 to 1.8 MeV. Thin targets have been used in transmission geometry. Data are compared with the predictions of the PWBA and the PWBA modified to include corrections due to Coulomb retardation of the projectile, increased binding of the target electron during collision and the relativistic nature of theK-shell electrons. The intensity ratiosKα/Kβ have also been obtained as a function of proton energy for all the five elements.

    • Force field calculation for inplane vibrations of ethylene usingcndo/Force method

      A Jothi G Shanmugam A Annamalai Surjit Singh

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      cndo/Force method is used to evaluate redundancy-free internal valence force field (rfivff) for inplane vibrations of ethylene. The bending force constants, the stretch-band and bend-bend interaction force constants are predicted reasonably well in magnitude and sign by this method; whereas stretching force constants and stretch-stretch interactions are overestimated. Initial force field is set up by transferring stretching force constants from structurally-related molecules and including the rest of the force constants fromcndo force field. The field so constructed is subjected to refinement by the least square method. A total of 64 vibrational frequencies of C2H4, C2D4, C2H2D2 and their13C isotopic modifications are used to determine force field containing 15 parameters. The final force field is found to be reasonable on the basis of frequency fits, potential energy distribution and band assignments.

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