• Volume 29, Issue 3

      September 1987,   pages  1-320

    • Relation between highTc superconductivity and structure: A study of Ba3+xCu6O14+δ and YBa2Cu3O7−δ systems

      A K Ganguli L Ganapathi K Sreedhar R A Mohanram P Ganguly C N R Rao

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      Superconductivity is found in tetragonal La3−xBa3+xCu6O14+δ and La, Ba)6−xSrxCu6O14+δ even though they do not possess Cu-O chains or the K2NiF4 structure. Resistivity measurements confirm the occurrence of a transformation from chain-superconductivity to sheet-superconductivity in YBa2Cu3O7−δ as δ is varied in the range 0.0–0.5.

    • Synergism in electron gas in crossed fields

      R Pratap

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      An electron gas in crossed electric and magnetic fields of arbitrary strength is considered in the framework of nonequilibrium statistical mechanics. It is known that more than one independent frequency existing in a system, which are of comparable magnitude, can generate coherent synergic radiation. In the present system three independent frequencies exist: viz the synchrotron frequency due to the magnetic field, the hopping frequency due to the electric field, and the plasma frequency. It is shown that all these can combine to generate a new synergic coherent radiation. The results also show the possibility of interpreting the quantum nature of Hall conductance as due to density function alone. Besides these, the solution admits the Schubnikov-de Haas oscillation of the electrical conductivity due to change in the fields.

    • Economic models for Dirac neutrinos in grand unified theories

      Anjan S Joshipura Utpal Sarkar

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      It is shown that dimension five non-renormalizable interactions can produce light Dirac neutrinos in an extension of the minimal SU(5) GUT containing additional SU(5) singlets and global U(1) symmetries.

    • Bohr-Coster diagrams for multiply ionized states of light elements in the rangeZ = 10 to 20

      Lakshmi Natarajan A V Tankhiwale Chintamani Mande

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      Calculations in the L-S coupling approximation of the average total energies of various defect electron configurations with single or doubleK shell and varying number ofL shell vacancies for some light elements in the rangeZ = 10 to 20 are reported. The calculations show that the linear trend observed for normal Bohr-Coster diagrams (√E vsZ curves for the usual X-ray energy states) persists in the case of multiply ionized atomic states as well.

    • Laser photoacoustic spectroscopy of iodine molecule: Single and two-photon absorption

      Putcha Venkateswarlu G Chakrapani M C George Y V Rao C Okafor

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      Photoacoustic spectroscopy of iodine molecule has been studied in gas phase using nitrogen laser-pumped tunable dye laser. The experiment yielded the vibrational spectrum corresponding toX1Σ+(0g+)→B3Π(0g+) transition up to the convergence limit. The photo-acoustic spectrum in the region 17580–18850 cm−1 is presented along with the vibrational analysis. Five of the vibrational bands reported earlier by Venkateswarlu, Kumar and McGlynn have been partially resolved and the structure of one of them has been analyzed and shown to be due to an overlap of (14, 2) and (12, 1) bands. The analysis was based on a comparison with the highly resolved spectrum of Gerstenkorn and Luc. The structure observed in the region 20200–20750 cm−1 which is beyond the convergence limit of the transitionX1Σ+(0g+)→B3Π(0u+) has been analyzed as due to two-photon absorption. Most of the bands could be assigned to two transitions both originating in the ground state and terminating in two different electronic states 1g andE(0g+), atTe=40821 cm−1 (orT0=41355 cm−1) andTe=41411 cm−1 (orT0=41355 cm−1) respectively.

    • Rotational analysis of 4730 Å band of MgCl

      A B Darji M B Sureshkumar P M Shah N R Shah

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      Magnesium chloride was excited in a high frequency discharge source and the 4730 Å band was photographed at an inverse dispersion of 0.48 Å mm−1 in a two meter plane grating spectrograph. The rotational analysis of the band has been carried out and the molecular constants of the upperB2Σ+ state are reported for the first time. Observation of rotational isotopic shifts due to Cl37 supports the rotational analysis. The electronic transition involved is identified to beB2Σ+A2Π1/2(a) (inverted).

    • New studies of X-ray diffraction line profiles from aggregates of distorted crystallites I

      G B Mitra T B Ghosh

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      The fourth central moment of an X-ray diffraction profile from an aggregate of distorted crystallites has been expressed by Mitra (1964a) as a function of the crystallite size, strain and strain gradients in the specimen. While the usual methods of line profile analysis yield information regarding either the apparent strain or the rms strain, the present study provides additional information regarding strain distribution in the form of strain derivatives and rms displacements of atoms over a given distancet in the direction of study. The strain parameters like 〈ee′〉, 〈ee″〉 have been obtained from fourth moment of the strain profile against range plots. The strain parameters thus obtained have subsequently been used to determine the rms displacements of the atoms. Alloys of copper and zinc at different stages of cold working and annealing have been studied by this method. The results have been discussed in the light of dislocation distribution, polygonisation and grain growth as well as distortion waves in the distorted crystals.

    • Dielectric properties of RbCl-RbBr mixed crystals

      G Sathaiah Lalitha Sirdeshmukh

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      A systematic measurement of dielectric constant and loss on RbCl-RbBr mixed crystals in various compositions has been carried out in the frequency range 100 Hz to 100 kHz and in the temperature range from room temperature to 320°C. From these measurements the static dielectric constant, the Szigeti charge, the conductivity and the activation energy for conduction are evaluated. All these properties show a nonlinear composition dependence. Semiempirical equations proposed earlier are employed to evaluate the dielectric constant as a function of composition. The validity of these relations is also discussed.

    • Renormalized-free-atom model and Compton profile of hcp cobalt

      B L Ahuja B K Sharma O Aikala

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      Compton profile of cobalt has been calculated employing the renormalized-free-atom model for fcc as well as hcp phases choosing several 3d-4s configurations. The results have been compared with recent gamma-ray measurements on polycrystalline Co. Best agreement between theory and experiment is found for 3d74s2 configuration. Comparison with free electron model has also been made for this case.

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