• Volume 28, Issue 2

      February 1987,   pages  1-228

    • High-temperature superconductivity in the 100 K region in perovskite-related oxides of the Ln-Ba-Cu-O (Ln=Y or La) system

      P Ganguly A K Raychaudhuri K Sreedhar C N R Rao

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      Oxides of the Y-Ba-Cu-O system are found to show onset of superconductivity in the 100–120 K region.

    • Implementation and comparative study of random sequences for nonlinear least square data fitting

      Tapas Bandyopadhyay P K Sarkar

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      A numerical study of nonlinear least square data fitting using random numbers from the congruential generator and several quasi-random generators is presented. The results indicate that at least up to five dimensions some of the quasi-random sequences yield better accuracy than the congruential pseudo-random sequence. Some recommendations for selecting the generators of quasi-random sequences are also given.

    • Kerr-Newman metric in deSitter background

      L K Patel Sharda S Koppar P V Bhatt

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      In addition to the Kerr-Newman metric with cosmological constant several other metrics are presented giving Kerr-Newman type solutions of Einstein-Maxwell field equations in the background of deSitter universe. The electromagnetic field in all the solutions is assumed to be source-free. A new metric of what may be termed as an electrovac rotating de-Sitter space-time—a space-time devoid of matter but containing source-free electromagnetic field and a null fluid with twisting rays—has been presented. In the absence of the electromagnetic field, our solutions reduce to those discussed by Vaidya.

    • Analytic representation for3He form factors

      K N Agrawalla M K Parida

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      A modifiedN/D method is applied for the cases of3He charge and magnetic form factors. Anomalous cut positions are computed using possible exchanges at the photon-3He electromagnetic vertex. and one of them is found atta=0.0618 GeV2. TheD-function is used to parametrize the two-pion cut while theN-function is taken to represent the effect of an anomalous or the three-pion cut. Excellent fits to the available experimental data on charge and magnetic form factors are obtained and several useful information on the form factors computed.

    • Relativistic effects on meson spectra

      S P Misra S Naik A R Panda

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      The meson masses are considered to retain total relativistic effects for spinors instead of Fermi-Breit approximation. This necessitates a diagonalization approach instead of solutions of differential equations. Correction over Fermi-Breit form appears to be significant. For heavy quark systems agreement with experiment is found. The method will be quite useful if the quark-antiquark dynamics becomes sufficiently known.

    • Isotope shift studies in the spectrum of boron monosulphide

      Sheila Gopal G Lakshminarayana

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      The spectrum of boron monosulphide has been excited in microwave discharge and photographed at moderate dispersion. TheC2ΠrX2Σ+,B2Σ+A2Πi andA2ΠiX2Σ+ band systems extending from 2100–9000 Å have been obtained for B32S and B34S species. Isotope shifts for all these band systems have been measured. Comparison of the observed isotope shifts with the theoretically calculated isotope shifts confirms the emitter as well as the vibrational assignments of all these band systems.

    • Electron impact excitation of hydrogen and helium in Coulomb-projected Born methods

      C S Singh D K Rai

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      Coulomb-projected Born methods for the theoretical study of electron impact excitation of hydrogen and helium are reviewed. The results obtained by using different forms of Coulomb-projected Born methods are compared with other theoretical and experimental results and analyzed. The inadequacy of the variable charge Coulomb-projected Born approximation (VCCPB)—the most recent form of the Coulomb-projected Born methods—in giving good results in processes where exchange is dominant is discussed in detail. The ‘modified’ VCCPB approximation obtained by modifying the VCCPB method to remove its shortcomings is also discussed and its application to electron impact excitation of 23s state of helium is studied.

    • Near perpendicular propagation of ion cyclotron modes in a deuterium-hydrogen-oxygen fusion plasma

      Chandu Venugopal

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      A dispersion relation for the near perpendicular propagation of the electromagnetic ion cyclotron wave has been derived in a fusion plasma that has deuterium as a majority species, hydrogen as a minority species and fully ionized oxygen as an impurity constituent; all being modelled by loss cone distribution functions. The wave has a frequencyω around the deuterium ion gyrofrequency-ΩD and a wavelength much longer than its Larmor radiusγLD(kγLD<1); the plasma itself being characterized by large ion plasma frequencies (ωPD2>ΩD2). Two modes, a low frequency (LF) and a high frequency (HF) mode of opposite electrical energy can propagate in the plasma; the instabilities that arise are thus due to an interaction of modes of opposite energies. We find that while hydrogen tends to destabilize the plasma, the impurity oxygen ions have the reverse effect. Also the plasma is most stable when the ratios of the perpendicular components of oxygen-to-deuterium and hydrogen-to-deuterium temperatures are kept low. Detailed studies of the wave propagation characteristics and energy reveal the close resemblance of a loss cone plasma containing oxygen to a stable Maxwellian plasma in regard to wave stability, propagation and energy.

    • Temperature invariance ofS0-parameter of polymers

      B K Sharma R R Reddy

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      The parameterS0 which is characteristic of molten alkali halides and liquids has also been shown to be characteristic of a wide variety of polymers. Calculated data using the volume expansivity of the polymer establish the temperature invariance and constancy of theS0-parameter which retains, on an average, a constant value of 1.11 for polymers. Further understanding of the significance of fractional free volume andS0-parameter in describing various thermoacoustic properties and the anharmonic behaviour in polymers, has been developed.

    • Collective excitation modes in the intermediate and superconducting states of doped and undoped indium and lead

      V V Joshi K D Chaudhuri

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      Ultrasonic attenuation was studied in pure In, In + 0.003 at.% Pb, pure Pb and Pb + 0.003 at.% In in the intermediate states (for the magnetic fields 0.7Hc and 0.9Hc) and superconducting states, for frequencies varying from 9.9 to 29.7 MHz, in the temperature range 4.2 to 1.4K. Collective excitation modes were observed in both the states for all the samples. There exist two distinct phases in the intermediate state but only one phase in the superconducting state in all the samples. The first phase was dependent on the magnetic field and independent of the concentration and nature of the dopant. The second phase was independent of the magnetic field and dependent essentially on the concentration of vacancies and marginally on the concentration of the dopant. The origin of the two phases has been discussed.

    • A three-body force shell model calculation of Schottky defect formation energies of ionic crystals with CsCl structure

      V Mishra S P Sanyal R K Singh

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      A three-body force shell model (TSM) for the calculation of Schottky defect formation energies in solids with cesium chloride structure has been developed by incorporating the effects of long-range three-body interactions (TBI) in the shell model. These TBI in the defect lattice arise from the deformation of electron shells when the nearest neighbour ions get relaxed from their equilibrium position. This model has been used to calculate the cation and anion extraction and Schottky defect formation energies of CsCl, CsBr, CsI, TlCl, TlBr and NH4Cl crystals. The calculated values of these defect properties agree reasonably well with their measured values.

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