• Volume 28, Issue 4

      April 1987,   pages  1-424

    • A lagrangian basis for ashtekar’s reformulation of canonical gravity

      Joseph Samuel

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      A manifestly covariant Lagrangian is presented which leads to the reformulation of canonical general relativity using new variables recently discovered by Ashtekar.

    • Equivalent potentials for a nonsymmetric non-local interaction

      G C Sett U Laha B Talukdar

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      Scattering formalisms which incorporate antisymmetrization of the projectile with respect to identical particles in the target result in a nonsymmetric non-local interaction. Such an interaction constraints the relative wavefunctions to be orthogonal to redundant states forbidden by the Pauli principle. Concentrating on the nonsymmetric non-local kernel of Saito we try to visualize the mechanisms by which a potential can ensure the required orthogonality. We achieve this by replacing the Saito kernel by an effective symmetric non-local potential. The constructed symmetric potential is found to be phase-equivalent only but not off-shell equivalent to the original kernel. This difference in the off-shell behaviour is attributed to the dynamical origin simulating the redundant states. In close analogy with one of our recent works we also derive an energy-momentum dependent equivalent to the local potential. Our solution of the pseudo inverse problem is exact and provides a basis for writing the phase—and quasiphase—equations. We present numerical results in support of this.

    • On the short-time behaviour of quantum unstable systems

      V J Menon

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      We consider the survival amplitudeA(t) for a normalized decaying state whose energy spectral density vanishes asymptotically as an inverse power. By using simple calculus a Taylor expansion ofA(t) is derived aroundt=0, the form of the remainder term identified, and a physical significance given to the other coefficients. It is shown that the Taylor remainder may contain logarithms oft besides powers.

    • Thermodynamic properties of molecular fluid mixtures of hard ellipsoids

      A K Singh U N Singh S K Sinha

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      Thermodynamic properties of molecular fluid mixtures of hard ellipsoids are calculated. Numerical results are given for equation of state and excess-free energy of the binary mixture of both additive and non-additive hard ellipsoids. It is found that the equation of state and free energy of mixtures increase with increase of anisotropy parameterx0.

    • Local quantum statistics in arbitrary curved space-time

      P Pronin I Kulikov

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      A local quantum statistics based on a finite temperature field theory in an arbitrary Riemann space-time is considered. The expressions have been derived for the partition functions, the grand thermodynamic potential and the particle distributions 〈nk〉 of massive scalar gas and fermion gas in arbitrary space-time. It is shown that the chemical potential depends on the geometry of manifold.

    • Microscopic theory of soliton propagation in a mixture of two boson fluid films

      A C Biswas

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      A microscopic theory of soliton propagation in a mixture of two boson fluids atT=0°K has been provided.

    • Interpolation model for molecular reorientation in gases and liquids

      S K Deb A K Sood

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      The interpolation model for molecular reorientation in gases and liquids has been extended to the case for symmetric top molecules. It has been compared with experimental correlation functions for linear as well as prolate and oblate symmetric top molecules. The agreement is excellent for systems where the intermolecular torque is small. With increasing torque, there is discrepancy at short times whereas at intermediate and long times the decay is described quite well. However for liquids at low temperatures, the description of molecular reorientation within the framework of this model is unsatisfactory.

    • Production of tachyons and antiparticles in extended manifolds of general relativity

      A P Trofimenko V S Gurin

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      The extended space-time manifold in a uniformly accelerating reference frame is considered both for positive and negative accelerations. An analogy between the light barrier and a black hole event horizon in the theory of relativity is drawn. It is shown that bradyon-tachyon-antibradyon transformations are possible in the proper reference frame by a constant acceleration, i.e. for the light barrier penetration.

    • Modifications in high energy higher order Born approximation

      K Suja H S Desai

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      A systematic study is made to find out the differential scattering cross-section in the case of electron-atom collisions. The first and the second Born terms ofO(1/ki) are calculated in the framework of Yates high energy higher order Born approximation. The second Born term ofO(1/ki2) is calculated using the second order Wallace term, the third term is calculated using the Glauber-eikonal series of Yates. The method is applied to the elastic scattering of electrons by atomic hydrogen in the energy range 100–400 eV and by helium for energies 200 eV and 400 eV. Comparison is made with other theoretical results and the experimental data.

    • Weak electron acoustic double layers in a multicomponent plasma

      K S Goswami S Bujarbarua

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      Formation of electron acoustic double layers in a magneto-plasma with two ion species is investigated. The existence of double layers propagating almost perpendicular to the magnetic field in a plasma with two distinct ion species and cold electron is discussed.

    • Refinement of twinned crystal data

      Sandhya Bhakay-Tamhane A Sequeira

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      The refinement of structure from diffraction intensities measured from a twinned crystal involves the evaluation of intensity contributions from the various twin domains in the crystal and the corresponding structure factor derivatives. The modifications in the standard least-squares refinement program required for analysis of data from a twinned crystal sample are discussed. The procedure can be extended to cases involving more than two types of twin domains or to samples having mixed phases. The results and limitations of structure refinement using data obtained from a twinned LiKSO4 crystal in various low-temperature phases are illustrated.

    • Precession photography of fibres: Prediction of patterns

      M Sundaramoorthy

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      The Buerger precession method of recording x-ray diffraction patterns can also be used for fibres. This method has some advantages over the conventional flat plate method. Since the fibre has inherent cylindrical symmetry, the precession photograph of the fibre is equivalent to the ‘rotation-precession’ photograph of a single crystal. An analytical prediction of diffraction patterns of the rotation-precession photography is discussed. Also, experimental data are provided to confirm the validity of the equations derived.

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