• Volume 45, Issue 5

      November 1995,   pages  1-462

    • Estimation of parameters of gravitational waves from coalescing binaries

      R Balasubramanian B S Sathyaprakash S V Dhurandhar

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      In this paper we deal with the measurement of parameters of the gravitational wave signal emitted by a coalescing binary system of compact stars. We present the results of Monte Carlo simulations carried out for initial LIGO, incorporating the first post-Newtonian corrections to the waveform. Using the parameters so determined, we estimate the direction to the source. We stress the use of the time-of-coalescence rather than the time-of-arrival of the signal to determine the direction of the source. We show that this can considerably reduce the errors in the determination of the direction of the source.

    • Nonlinear dynamics of a two-dimensional lattice

      Nabonita D Chowdhury Sankar P Sanyal

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      The dynamics of the nonlinear excitations in a two-dimensional (2D) φ4-diatomic lattice, with nonlinear on-site electron-phonon coupling at the polarizable ion site has been presented, without considering the self consistent phonon approximation. One of the major results obtained from our calculations is in the understanding of continuous structural phase transition, where we have obtained the minimum in soft mode frequency at a soft mode temperatureTs (>Tc), not at critical temperatureTc. This occurs due to the anisotropy of such 2D systems.

    • Microscopic theory of single particle and pair condensation of an attracting bose gas as the basis for superfluidity and superconductivity

      S Dzhumanov P K Khabibullaev

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      A consistent and unified microscopic theory of superfluidity and superconductivity is developed on the basis of two-stage Fermi-Bose-liquid (FBL) (in particular case, one-stage Bose-liquid) scenarios. It is shown that these phase transition scenarios is accompanied, as a rule, by the formation of composite bosons (Cooper pair and bipolarons) with their subsequent single particle (SPC) and pair condensation (PC). A brief outline of the modified and generalized BCS-like pairing theory of fermions is presented. In an analogy to that, a detailed boson pairing theory is developed. The SPC and PC features of an attracting 3d- and 2d-BG as a function of the interboson coupling constant in the complete range 0≤TTB is studied in detail. It is argued that the coexistence of the order parameters of attracting fermions ΔF and bosons ΔB leads to the superfluidity (in3He) and superconductivity (in superconductors) by two FBL scenarios. One of these scenarios is realized in the so-called fermion superconductors (FSC) and the other in the boson superconductors (BSC) in which the gapless superconductivity is caused by the absence of the gap ΔSF in the excitation spectrum of bosons and not by the presence of point or line nodes of the BCS-like gap ΔF. The new adequate definitions for basic superconducting parameters of FSC and BSC are given. The theory proposed is consistent with the experimental data available.

    • Temperature dependence electron spin resonance spectra of a magnetic fluid

      R V Upadhyay D Srinivas R V Mehta P M Trivedi

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      ESR spectra of a laboratory synthesized kerosene base magnetic fluid containing ultrafine magnetic particles (average diameter of 100A) of Zn0.1 Fe0.9Fe2O4 are recorded at different temperatures. A narrow signal was observed above the melting point of the carrier liquid (200 K) which can be attributed to a very small volume fraction of superparamagnetic particles in the system. The peak-to-peak line width for both low and high field cooled configurations show an increase with decreasing temperature. This observed behaviour has been explained by considering various energy terms which contribute to the line width.

    • Dielectric properties of nano-particles of zinc sulphide

      Binny Thomas M Abdulkhadar

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      The dielectric properties of nano-particles of ZnS have been studied over a temperature range from 300 to 525 K. The dielectric constant, dielectric loss and ac conductivity of the samples are larger than those of bulk ZnS crystals. Dielectric properties of composites consisting of nano-particles of Ag of different concentrations dispersed in nano-particles of ZnS have also been studied.

    • Generation of picosecond optical pulses from single heterostructure GaAs diode laser and their emission characteristics

      V N Rai M Shukla H C Pant

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      Emission characteristics of a single heterostructure GaAs diode laser are reported using a simple driver circuit. It provides a single picosecond time duration optical pulse, a pulse train or a broad optical pulse depending on the amplitude and time duration of the electrical pump pulse. Results show that relaxation oscillation frequency depends on the amplitude of pumping current pulse as well as on some inherent property of diode laser, which seems to be the level of impurity in lasing medium. Variation of relaxation oscillation frequency with amplitude of current pulse shows only the qualitative agreement with the reported theoretical predictions.

    • Ion cyclotron instabilities in a mildly relativistic hydrogen-deuterium fusion plasma

      Chandu Venugopal P J Kurian G Renuka

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      A dispersion relation for the perpendicular propagation of the electromagnetic ion cyclotron wave around the second harmonic of the deuterium ion gyrofrequency in a mildly relativistic, anisotropic Maxwellian plasma with hydrogen as the majority species and deuterium as the minority component has been derived. The work has been carried out in the frame of reference of the majority hydrogen ions; to these ions the waves at 2ΘD would be at its own gyrofrequency.

      Using a small quantityɛ to order all relevant parameters of the plasma, it was possible to derive the dispersion relations in a simple form. To the lowest order the relativistic factors do not enter the dispersion relation. The plasma can now support two modes—one above and the other below the hydrogen gyrofrequency in agreement with the assumptions. This was also verified numerically using a standard root solver thereby justifying the correctness of the ordering scheme.

      In the next higher order, the dispersion relation is a quartic equation and is sensitively dependent on the relativistic factors. The plasma can now support four modes, both above and below the hydrogen gyrofrequency and consistent with the ordering scheme used. However the modes can now coalesce resulting in complex conjugate roots to the dispersion relation thereby indicating an instability.

      The advantage of such a scheme is that two dispersion relations — one of which is independent of the relativistic factors and the other which is sensitively dependent on them can be separated out.

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