• Volume 25, Issue 5

      November 1985,   pages  513-633

    • deSitter space-time and rotation

      P C Vaidya

      More Details Abstract Fulltext PDF

      A metric containing a parameterb is presented. It represents two distinct families of space-times, the Taub-nut family and the deSitter family, according asb=1 andb=4 respectively.

      The metric of the deSitter family of space-times contains a further parameterm. Whenm=0, the space-time is the usual homogeneous and isotropic deSitter space-time. But ifm≠0, the metric represents a space-time which is homogeneous but not isotropic satisfyingRikgik. In this space-time, the 4-velocity of an observer at rest will have non-zero twist. The metric withb=4,m≠0 is interpreted as a metric representing a “rotating deSitter space-time”.

    • Conformally invariant field theories in two dimensions and corresponding statistical mechanical models

      Virendra Singh B Sriram Shastry

      More Details Abstract Fulltext PDF

      Belavin, Zamlodochikov and Polyakov have recently proposed a class of conformally invariant field theories in two dimension with exactly determined rational critical indices. We establish a tentative identification of a subset of these theories in terms of the O(n) model and theq-state Potts model in 2-dimensions for appropriaten andq.

    • Pionic corrections to the masses of heavier hadrons in the bag model

      K P Tewari C P Singh

      More Details Abstract Fulltext PDF

      The influence of pionic corrections to the masses of heavier hadrons is investigated in the cloudy bag model. After determining the bag parameters from ordinary baryons and mesons the heavier hadron mass spectrum is calculated. A sizable amount of pionic correction is observed which has improved the masses favourably.

    • Neutron-proton elastic scattering at high energies and small momentum transfers

      Fazal-E-Aleem Mohammad Saleem

      More Details Abstract Fulltext PDF

      It is shown that the most recent measurements of differential cross-section at small momentum transfers, integrated and total cross-sections, and the slope of np elastic scattering from 100 to 400 GeV/c are successfully fitted by using the simple Regge pole model proposed by the authors several years ago.

    • Computer calculation of positron diffusion and annihilation in atomic hydrogen

      K V Sinha P S Grover

      More Details Abstract Fulltext PDF

      We have performed a computer-aided analysis of position behaviour in atomic hydrogen. Effect of electric, magnetic and temperature fields on the diffusion and annihilation of positrons has been studied. Electric field is varied over a wide range of 0–200 V cm−1 amagat−1, magnetic field over 0–30 kG while the temperature range considered is 300–10,000°K. The position decay rate decreases with electric and temperature fields but increases with magnetic fields. However, the effect of these fields is reversed on the diffusion coefficient.

    • Semiempirical molecular orbital calculations for ketene dimers

      C P D Dwivedi

      More Details Abstract Fulltext PDF

      The semiempirical molecular orbital method known as symmetrically orthogonalised intermediate neglect of differential overlap (sindo) has been employed to determine the geometry, bonding, binding energy, ionisation potential, dipole moment and net charges of diketene and cyclobutane-1,3-dione molecules. Results obtained have been compared with available experimental data.

    • Einstein A-coefficients for pure rotational transitions in D2O

      Suresh Chandra D A Varshalovich W H Kegel

      More Details Abstract Fulltext PDF

      Einstein A-coefficients for the electric-dipole transitions between the rotational levels up to 785 cm−1 in the ground vibrational state of D2O are calculated. The A-values are used to compute the mean-radiative life-times of the levels.

    • Efficiency calibration of Si(Li) and HpGe detectors in the energy range of 5–60 keV

      H R Verma

      More Details Abstract Fulltext PDF

      A method is described for the efficiency calibration of Si(Li) and HpGe detectors in the 5–60 keV energy region. The method utilizes theK x-ray lines from54Mn,65Zn,75Se,85Sr,88Y,109Cd,137Cs,141Ce and159Dy in addition to57Co and241Am radioactive sources to have sufficient number of data points. Since the emission intensities are required at variousK x-ray energies from the decay of these sources, this paper reports theK x-ray emission intensities per 100 disintegrations for these nuclei using the latest adopted data for gamma ray intensities, electron capture and internal conversion coefficients, fluorescence yield values and the relative intensities of the fourK x-ray lines.

    • Emission spectrum of MgCl molecule in 5030-4380Å

      A B Darji N R Shah P M Shah M B Sureshkumar G S Desai

      More Details Abstract Fulltext PDF

      The emission spectrum of diatomic magnesium chloride molecule has been reinvestigated in the region 5030-4380 Å (B2Σ+A2Π transition) at a higher dispersion. The vibrational assignments of the bands are confirmed by observing the vibrational isotope shifts due to isotopes of magnesium and chlorine. Precise values of the vibrational constants are determined for theB2Σ+ state.

    • Ion-sound turbulence due to shock gradients in collisionless plasmas

      N Gopalswamy G Thejappa

      More Details Abstract Fulltext PDF

      The dispersion relation for ion sound waves generated in a perpendicular shock is derived and the energy density of ion-sound turbulence is obtained using quasilinear theory. The result is compared with the lower hybrid turbulence generated under similar conditions. It is shown that ion-sound turbulence is a better candidate for the generation of type-I radio bursts in the solar corona.

    • Theoretical optimization of metalp–n silicon Schottky barrier solar cell

      C Francis Xavier G A Sevariraj Vikram Kumar

      More Details Abstract Fulltext PDF

      The theoretical optimization of the design parametersNA,ND andWP has been done for efficient operation of Au-p-n Si solar cell including thermionic field emission, dependence of lifetime and mobility on impurity concentrations, dependence of absorption coefficient on wavelength, variation of barrier height and hence the optimum thickness ofp region with illumination. The optimized design parametersND=5×1020 m−3,NA=3×1024 m−3 andWP=11.8 nm yield efficiencyη=17.1% (AM0) andη=19.6% (AM1). These are reduced to 14.9% and 17.1% respectively if the metal layer series resistance and transmittance with ZnS antireflection coating are included. A practical value ofWP=97.0 nm gives an efficiency of 12.2% (AM1).

    • A simple approach to evaluation of lattice sums

      Subinay Dasgupta D Sen S Sengupta

      More Details Abstract Fulltext PDF

      It is shown that starting from a Fourier transform relation one can derive, in a surprisingly simple manner, all the well-known results of lattice summation, that have been obtained so far by a complicated use of the Ewald theta transformation. We show that the Ewald transformation follows directly from the Fourier transform relation.

    • Three-body interactions, rotational invariance and the elastic consistency of lattice dynamical models for face-centred tetragonal indium

      V Ramamurthy S B Rajendraprasad

      More Details Abstract Fulltext PDF

      The origin of the elastic inconsistency ofdaf, mas andgtf models for non-cubic solids and the failure of their force constants to comply with all the rotational invariance conditions are analysed by resolving the atomic displacements of face-centred tetragonal indium along three mutually perpendicular directions. It is shown that a lattice dynamical model suffers from these deficiencies as a consequence of its neglect of three-body interactions as well as the mixed neighbour interactions associated with the angular forces, while thecgw model which incorporates both these interactions is elastically consistent and its potential energy rotationally invariant. The degree of equivalence that exists among the force constants ofdaf, mas, gtf andcgw models, the distortions introduced by the elastic inconsistency into the phonon dispersion curves of fct indium as well as the consequences of imposing the rotational invariance conditions on the force constants of a lattice dynamical model are discussed.

    • On the critical temperature of a superconducting system

      C M Srivastava

      More Details Abstract Fulltext PDF

      Based on the assumption that in the groundbcs state the net gain in energy is equivalent to the repulsive electron-ion and electron-electron Darwin interactions, an expression forTc has been obtained which depends on only a few atomic parameters. The theory provides a criterion for the occurrence of superconductivity and yields satisfactory values ofTc for metals and alloys, and ternary chalcogenides and borides. It explains the difference inTc in the crystalline and amorphous states as well as the pressure dependence ofTc. The possibility of occurrence of high temperature superconductivity has been explored.

  • Pramana – Journal of Physics | News

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.