• Volume 29, Issue 4

      October 1987,   pages  1-422

    • Low temperature heat capacity of YBa2Cu3O7

      N Nambudripad S K Dhar

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      We have measured the heat capacity of superconducting, single phase YBa2Cu3O7 in the temperature range 2 to 18 K. An extrapolation of the data between 4 and 9 K gives aC/T (T → 0) of ∼ 25 mJ/mole K2. The Debye temperature obtained from the high temperature linear portion ofC/T vsT2 plot is 325 K.

    • A note on traversal time for tunneling

      A M Jayannavar

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      A simple approach to study the traversal time for tunneling is given. By using the WKB wave function to evaluate the velocity field of particles in the barrier region, an expression for the traversal time τ=εdx[m/2(V(x)-E)]1/2 is obtained in conformity with the recent results.

    • An analysis of a quantum chromodynamic structure function

      D K Choudhury A Saikia

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      We obtain an approximate solution of Altarelli-Parisi equations yielding a sample of quantum chromodynamic structure function. The SLAC-MIT data are analysed with it. Possible effects of intrinsic charm and higher twist are also included. Agreement is found to be good forx⩾0.25.

    • On the solutions of the Wick-Cutkosky model in the instantaneous approximation

      G P Malik L K Pande

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      By reexamining the analysis of Basu and Biswas, based on the stereographic projection method of Fock and Levy, it is shown that the general solution of the Wick-Cutkosky model in the instantaneous approximation, hitherto unreported, involves only one quantum number; this is contrasted with the well-known solution which involves two quantum numbers, but for which the spectrum is degenerate with respect to one of them. The latter situation is shown to hold under a rather special circumstance.

    • Poincaré gauge theory from self-coupling

      Eric A Lord

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      Poincaré gauge theory is derived from a linear theory by the method suggested by Gupta for deriving Einstein’s general relativity from the linear theory of a spin-2 field. Non-linearity is introduced by requiring that a set of tensor fields be coupled to the Noether currents of the Poincaré group (energy-momentum and spin).

    • An experimental limit on the coupling of a light neutral pseudoscalar particle to hadrons

      D Indumathi C V K Baba A Roy S C Vaidya

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      Detailed results of an experiment, looking for a short-lived neutral particle decaying by ane+e pair in the decay of the 3.68 MeV (3/2) state in13C, whose decay is predominantly M1, are presented. An upper limit of 7 × 10−5 has been placed on the branching ratio for decay through such a particle with a mass in the range 1.7 to 1.9 MeV/c2. This leads to an upper limit of 10−6 for the coupling of such a particle to nucleons. Such a limit rules out the explanation of thee+ ande peaks recently observed in heavy ion collisions, as due to the decay of a neutral particle.

    • Semi-classical smoothing in a non-monotonic field

      A K Dutta J M Pearson

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      It is pointed out that the semi-classical method of Jennings, Bhaduri and Brack for smoothing the total energy of a system of non-interacting fermions in a potential wellV(r) breaks down in the fourth-order term if this potential is non-monotonic. This means that the method as it stands can only be used by neglecting the Coulomb force on protons. We propose a modified treatment for the fourth-order term which appears to be entirely satisfactory.

    • Evaluation of one-centre electron interaction integrals over slater type atomic orbitals

      Anil Kumar P C Mishra

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      Simplified expressions for one-centre electron interaction integrals in general and Slater-Condon parameters as well as repulsion integrals of the type (aa|aa) in particular have been obtained over Slater-type atomic orbitals. Results calculated using these expressions are in agreement with those due to other authors.

    • Elastic nonlinearity parameters of tetragonal crystals

      Jacob Philip

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      The equations of motion for the propagation of finite amplitude elastic waves in crystals of tetragonal symmetry have been derived starting from the expression for the elastic strain energy. The equations have been solved for a finite amplitude sinusoidal wave propagating along the pure mode directions which are [100], [110] and [001] for the tetragonal group TI. The solutions corresponding to longitudinal wave propagation yield expressions for the amplitudes of the fundamental and generated second harmonic for these directions in terms of certain combinations of second and third order elastic constants of the medium. The results will aid the experimenter to determine these constants using ultrasonic harmonic generation technique.

    • Tetrahedral manganese (II) complexes—intense and unique type of mechanoluminophores

      B P Chandra M S K Khokhar R S Gupta B Majumdar

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      Intense and unique type of mechanoluminescence (ML) is found in tetrahedral manganese (II) complexes. During the excitation of ML by the impact of a piston onto the crystal, the ML intensity initially increases with time, attains a maximum value and then decreases. After retardation of the piston, the decay rate of ML is faster during crystal deformation; however, its value decreases after cessation of the deformation and becomes equal to the decay rate of phosphorescence. The ML disappears below the melting point. Since the crystals of tetrahedral manganese (II) complexes are centrosymmetric, the local non-centrosymmetric sites near the defects are attributed to be responsible for the mechanoluminescence excitation.

    • Optical birefringence and order parameter of three nematogens

      M Mitra S Paul R Paul

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      Results of the measurement of refractive indices and densities of three nematic liquid crystals at different temperatures are reported. The molecular polarizabilities have been calculated from refractive indices using both the Vuks’ and the Neugebauer’s relations. The orientational order parameters are determined from the polarizability values. The variation of order parameter with temperature for these compounds shows a reasonably good agreement with Maier and Saupe theory except near the clearing points where the experimental values are less than those obtained from the theory. The possible reasons for this have been discussed.

    • X-ray and dielectric studies of Sm2(MoO4)3

      M Roy R N P Choudhary H N Acharya

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      The polycrystalline samples of Sm2(MoO4)3 have been prepared by heating appropriate quantities of oxides. The X-ray powder diffraction technique has been used to provide information about lattice parameter, space group and basic structure. The dielectric constant has been measured as a function of frequency (560 Hz-13 MHz) and temperature (30–220°C) to know the ferroelectric transition temperature.

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