• Volume 32, Issue 6

      June 1989,   pages  721-845

    • Colour symmetry double point groups

      K Rama Mohana Rao N Nirmala

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      Thirty four distinct composition series arising out of the 32 crystallographic double point groups are employed to re-derive in a simple and elegant fashion all the 169 distinct colour symmetry groups generated by the 32 double point groups, exploiting the idea of colour generators. The advantage of the method employed and some possible applications of these colour groups are discussed. The resulting colour groups are tabulated.

    • Radiating Kerr particle in Einstein universe

      P C Vaidya L K Patel

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      A generalized Kerr-NUT type metric is considered in connection with Einstein field equations corresponding to perfect fluid plus a pure radiation field. A general scheme for obtaining the exact solutions of these field equations is developed. Two physically meaningful particular cases are investigated in detail. One gives the field of a radiating Kerr particle embedded in the Einstein universe. The other solution may probably represent a deSitter-like universe pervaded by a pure radiation field.

    • Spherically symmetric charged perfect fluid distributions executing shear-free motion

      D C Srivastava

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      A method to obtain exact solutions characterizing spherically symmetric charged perfect fluid distributions undergoing shear-free motion has been discussed. This method makes use of the criterion that the solution be free from movable critical points as has been employed earlier by Shah and Vaidya. Two solutions have been obtained, one of which is new and the other is the recent solution due to Sussman.

    • The Vaidya solution in higher dimensions

      B R Iyer C V Vishveshwara

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      The Vaidya metric representing the gravitational field of a radiating star is generalized to spacetimes of dimensions greater than four.

    • A quark model study of semileptonic baryon decays in the electronic decay modes

      D P Rath S N Jena

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      A relativistic quark model based on Dirac equation with the independent-quark confining potential of the form (1 +γ0)[a ln(r/b)] is used to compute the weak electric and magnetic form factors for semileptonic baryonic decays in the electronic decay modes. The values obtained for (g2/g1) agree with the non relativistic results and those for (f2/f1) agree with the MIT bag model values of Donoghue and Holstein. The SU(3) symmetry breaking does not generate appreciable departures in (f2/f1) values from corresponding Cabibbo values.

    • Criterion for a unique non-relativistic quark model

      R Nag S N Mukherjee S Sanyal

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      We have calculated the mean square charge radii of the neutron and proton, and compared them with the experimental values, to construct a unique non-relativistic quark potential model. It is shown for the first time that, contrary to general belief, it is possible to reproduce simultaneously the baryon mass spectrum and the electromagnetic sizes of neutron and proton using a single potential model. It was found necessary to add admixtures of excited states of the nucleon in the unperturbed ground state wavefunctions.

    • Hamilton’s theory of turns and a new geometrical representation for polarization optics

      R Simon N Mukunda ECG Sudarshan

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      Hamilton’s theory of turns for the group SU(2) is exploited to develop a new geometrical representation for polarization optics. While pure polarization states are represented by points on the Poincaré sphere, linear intensity preserving optical systems are represented by great circle arcs on another sphere. Composition of systems, and their action on polarization states, are both reduced to geometrical operations. Several synthesis problems, especially in relation to the Pancharatnam-Berry-Aharonov-Anandan geometrical phase, are clarified with the new representation. The general relation between the geometrical phase, and the solid angle on the Poincaré sphere, is established.

    • A neutron diffractometer with a linear position sensitive detector

      S K Paranjpe Y D Dande

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      A powder diffractometer with a linear position sensitive detector (PSD) has been designed and fabricated at BARC. The system is in operation at Dhruva reactor. The PSD has been tested for the position linearity and the uniformity of efficiency. The resolution Δd/d of the diffractometer has been found to be 1·3%. The data can be analyzed using profile refinement technique.

    • Consolidation of YBaCuO powders by shock loading

      N C Soni Ram Prasad Ashok Mohan M D Vora S Banerjee C V Tomy S K Malik H S Yadav K R K Rao

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      Superconducting oxide-copper monoliths have been fabricated by shock-wave loading using cylindrical and plane geometries. Bulk densities up to 96% T.D. have been obtained by varying detonation parameters. The superconducting properties, interface bonding and microstructure of the compacts have been evaluated.

    • High resolution magic angle spinning NMR studies of31P and11B in fast ion conducting AgI-Ag2O-P2O5 and AgI-Ag2O-B2O3 glasses

      M C R Shastry K J Rao

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      Silver iodide-based fast ion conducting glasses containing silver phosphate and silver borate have been studied. An attempt is made to identify the interaction between anions by studying the chemical shifts of31P and11B atoms in high resolution (HR) magic angle spinning (MAS) NMR spectra. Variation in the chemical shifts of31P or11B has been observed which is attributed to the change in the partial charge on the31P or11B. This is indicative of the change in the electronegativity of the anion matrix as a whole. This in turn is interpreted as due to significant interaction among anions. The significance of such interaction to the concept of structural unpinning of silver ions in fast ion conducting glasses is discussed.

    • Thermal diffusion near glass transition in Ge-Se glasses measured by photoacoustics

      K N Madhusoodanan Jacob Philip

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      The glass transition in GexSe1−x) (0·1 ⩽x ⩽ 0·25) glasses has been investigated using the photoacoustic (PA) technique. It is found that the PA amplitude and phase undergo anomalous changes at the glass transition temperatureTg. The amplitude has critical minimum and phase has maximum values atTg. The variation of the thermal diffusivity, determined by measuring the frequency dependence of the PA amplitude and phase, with temperature shows sharp decrease near the glass transition temperature. The temperature dependence of the optical energy gap also has been measured and it shows a decrease with temperature for all compositions, the rate of decrease being higher for temperatures greater thanTg.

    • Fermi surface of the noble metals

      Rajeev Ahuja A K Solanki T Nautiyal S Auluck

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      We report calculations of extremal areas of four Fermi surface (FS) orbits of the noble metals using the linear muffin tin orbital method in the atomic sphere approximation. Our calculations indicate that thel = 3 potential parameters and increase in the number of k-points in the Brillouin zone (BZ) summation from 240 to 916 have no significant effect on the FS. All calculations were performed self-consistently including up tol = 2 potential parameters and with 240 k points in the BZ summation. Calculations were performed with the exchange, correlation potentials (XCP) of Barth-Hedin, Barth-Hedin modified by Janak, SlaterXα, and the Vosko-Wilk-Nussair. Results compared with other theoretical calculations indicate that none of the above XC potentials give an accurate representation of the FS for all the noble metals. We feel that the inclusion of the non-locality of XCP may give a better account of the FS geometry.

    • A possible mechanism of cold fusion

      J K Bhattacharjee L Satpathy Y R Waghmare

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      A possible mechanism for the occurrence of nuclear fusion at room temperature is presented. Neutralization of the positive charge of the deuteron nucleus by its orbiting electron due to large enhancement of effective mass results in the vanishing of the Coulomb barrier which facilitates fusion at room temperature.

    • Anharmonic oscillators in higher dimension: Accurate energy eigenvalues and matrix elements

      V T A Bhargava P M Mathews M Seetharaman

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