• Volume 40, Issue 2

      February 1993,   pages  1-136

    • Effect of dissolved air content on single bubble sonoluminescence

      Vijay H Arakeri

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      It has been recently demonstrated that a single gas bubble in a liquid medium can be driven hard enough by an acoustic pressure field to make it emit light which is visible to the naked eye in a dark room. This phenomenon termed as single bubble sonoluminescence has shown some extraordinary physical properties. In the present investigation we have shown that dissolved air content has a significant influence on this phenomenon.

    • Internal pressure, ultrasonic velocity and viscosity of multi-component liquid systems

      J D Pandey A K Shukla Neelima Tripathi G P Dubey

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      Ultrasonic velocity, density and viscosity were measured in two ternary liquid systems namely,n-pentane +n-hexane + benzene(I) andn-hexane + cyclohexane + benzene(II) and one quaternary liquid system,n-pentane +n-hexane + benzene + toluene (III). The experimental as well as literature values of thermal expansion coefficient and iso-thermal compressibility of pure liquid components were utilized to deduce the ideal value of internal pressure and excess internal pressure for the above liquid systems at 298·15K using two different approaches. In the conventional approach one needs the experimental values ofα andβT of mixtures for computing internal pressure, which was not possible. The second method which is proposed here utilizes only the density, ultrasonic velocity and viscosity data of the mixture. This method is used in computing internal pressure and its excess value for multicomponent liquid systems. A satisfactory agreement has been observed.

    • Dielectric properties of Pb(Mg1/4Zn1/4Nb1/2)O11/4

      S Sharma R N P Choudhary R Sati

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      Polycrystalline samples of Pb(Mg1/4Zn1/4Nb1/2)O11/4 have been synthesized by high temperature columbite precursor solid state reaction technique. Using X-ray diffraction (XRD) technique, compound formation in single phase cubic structure was observed and XRD analysis provided preliminary structural data. Detailed studies of dielectric properties of the compound reveal that this compound has high dielectric constant and diffuse phase transition in a wide range of temperatures around the Curie temperature. The charge deficiency of the compound presumably gets compensated in the high temperature columbite precursor process of sample preparation which is supported by single phasic form of the material.

    • Electrical and photo-electrical properties of a chalcopyrite semiconductor AgInSe2

      Navdeep Goyal

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      In this paper we report the electrical and photoelectrical properties of AgInSe2. Nyquist plots for AgInSe2, obtained at different temperatures, are perfect arcs of a semicircle with their centres lying below the abscissa at an angleα. Finite values ofα (the distribution parameter) clearly indicate a multirelaxation behaviour. Transient and steady state photoconductivity of AgInSe2 has been studied at different temperatures and illumination levels. The lnIph vs lnF curves at different temperatures follow the empirical relation:IphFγ. Values of γ are close to 0.5 at all the temperatures, suggesting a bimolecular recombination. Decay of the photocurrent, when the illumination is switched off, shows that during decay, photocurrent has two components, i.e. a fast decay in the beginning and a slow decay thereafter. Decay time constant for slow decay process decreases with increasing temperature, suggesting that recombination is a thermally activated process in the temperature range studied.

    • Optical mode-coupling in a ring due to a back-scatterer

      A Venugopalan Deepak Kumar R Ghosh

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      The coupling of light waves travelling clockwise and counterclockwise along an optical ring due to a back-scattering element is studied. An asymmetric mode splitting occurs as a consequence of the discontinuity suffered by the waves at the scattering point. The mode splitting shows up in an interference pattern and lends itself to an experimental verification.

    • High resolution optogalvanic study in nitrogen discharge

      P R Sasi Kumar B Ambadi V P N Nampoori C P G Vallabhan

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      Doppler limited high resolution spectrum in the wavelength region 17224 to 17236 cm−1 of the first positive system (B3ΠgA3Σu+) of the N2 molecule is recorded by optogalvanic spectroscopic technique using a single mode ring dye laser. It is observed that the intensity and line width of the rotational line increase with the discharge current. Dependence of the collision broadening coefficient on the current was also evaluated.

    • Critical current densities of high pressure oxygen sputtered thin films of YBa2Cu3O7−x by non-resonant rf absorption method

      V V Srinivasu S V Bhat G K Muralidhar G Mohan Rao S Mohan

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      The critical current densities (Jc) have been measured at 77K in high pressure oxygen sputtered thin films of YBa2Cu3O7−x superconductor using the non-resonant rf absorption technique. High values ofJc (∼ 105 A/cm2) are observed in these relatively large area (∼ 1·2 cm2) films.

    • Simple and inexpensive3He insert for an ac susceptometer

      S Ramakrishnan K Ghosh Girish Chandra

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      The design of a simple and inexpensive3He insert for the existing ac susceptometer is described. The system uses a home built mutual inductance bridge for the ac susceptibility measurements from 0·4 K to 300 K. Simple and inexpensive design with the top loading facility are the main features of this set up. The insert can also be used as a continuously3He operating refrigerator down to 0·5 K.

    • Establishment of the mercury fixed point around 0°C using volumetric method

      J K N Sharma A K Bandyopadhyay

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      The paper describes the determination of melting pressure of mercury around 0°C using the volume method at the National Physical Laboratory. Also described are the details of the experimental set-up and the estimation of the uncertainty in the measurement of pressure. The equilibrium pressure in the flat region of the melting curve over which bulk transformation occurs, is established by increasing/decreasing the pressure. The scatter in the obtained data for equilibrium pressures is within the limit of experimental uncertainty of the measurement of pressure. The average observed value for the melting pressure of mercury at 0·002°C is 756·93±0·25 MPa agreeing well with the reported value of Dadsonet al [1] and Molinaret al [2a, b].

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