• Volume 41, Issue 5

      November 1993,   pages  1-477

    • Geometric phase as a simple closed-form integral

      Apoorva G Wagh Veer Chand Rakhecha

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      For a general evolution of a quantal system, the geometric phase measured with reference to a given initial state is derived as an integral of a function of the pure state density operator by invoking the Pancharatnam connection continuously.

    • A model for the analysis of the heat release from a supercooled liquid at the glass transition

      M Rajeswari A K Raychaudhuri

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      In this paper we present a phenomenological model to analyze the heat release at the glass transition as observed in the continuous cooling calorimetry when a supercooled liquid freezes into the glassy state. We developed this model for the quantitative analysis of the experimental data to obtain the specific heat and the parameters which govern the structural relaxation. A description of the model and the detailed analysis are presented and the relaxation parameters are compared with the corresponding values obtained from the specific heat spectroscopy. Our analysis reveals several interesting aspects which include the effects of delayed enthalpy relaxation and the nonequilibrium structural relaxation time on the observed specific heat, the temperature dependence of the equilibrium configurational specific heat and the validity of the Vogel-Fulcher equation for the relaxation time.

    • Thermal expansion of orthorhombic and tetragonal phases of the highTc superconductors RE1Ba2Cu3Oy (RE=Y, Gd, Dy)

      O M Prakash Ashok Rao O Prakash P N Dheer

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      Measurements of the coefficient of linear thermal expansion α have been carried out for the orthorhombic and tetragonal phases of RE1Ba2Cu3Oy(RE=Y, Gd, Dy) compounds using a high resolution capacitance dilatometer in the temperature range 77–300 K. All the superconducting samples exhibit a jump Δα at their respective transition temperatures,Tc. Evidences of, sample-to-sample variation in α values and dependence of Δα on the sample preparation conditions, have been obtained. The non-superconducting samples, in general, exhibit lower values of α possibly because of lowering of oxygen content.

    • Magnetic properties of ultra-fine particles of Mn0.5Fe0.5Fe2O4 spinel system

      R V Upadhyay R V Mehta

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      A systematic study of the magnetic properties of ultra-fine particles of Mn0.5Fe0.5Fe2O4 spinel system has been undertaken. The effect of temperature on the magnetic properties of particles and the ferrofluid has been studied. Analysis of the data yields information on the anisotropy constant, particle size distribution and superparamagnetic behaviour. The results are explained on the basis of existing theories.

    • Electric field gradient in transition metal — scandium

      B B Panigrahi N C Mohapatra

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      Electric field gradient inhcp transition metal scandium has been calculated as the sum of contributions from lattice ions and conduction electrons. For the lattice contributionqlatt, a point-charge model has been assumed. The contribution from conduction electronsqel, on the other hand, has been evaluated by carrying out an energy-band calculation using non-local transition-metal model potential. The results obtained are:qel=−106.11×1013 esu/cm3 andqlatt=122.17×1013 esu/cm3. The net field gradient (qel+qlatt) of 16.06×1013 esu/cm3 agrees quite well with the experimental result, |qexpt|=13×1013 esu/cm3. Directions of further improvement in the theory are discussed.

    • Heating mechanism in relation to the laser machining process

      Bekir S Yilbas Ahmet Z Sahin

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      Laser workpiece interaction mechanism is an important phenomenon which will assist in the development of laser machining systems. The interaction mechanism is generally complicated and depends on the laser and workpiece properties. In the present study a mathematical analysis for the laser material removal by evaporation and radial ejection of liquid is carried out. In the analysis the time unsteady problem is solved and nucleation explosions are predicted.

    • SERS studies on 1–4 dihydroxyanthraquinone at Ag electrode

      V G Srikanth S Edwin Jayaraj V Ramakrishnan

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      Raman scattering studies on 1–4 dihydroxyanthraquinone (DHAQ) at Ag electrode have been carried out to investigate the enhancement in the spectral line intensity after adsorption. Charge transfer between the adsorbate and the substrate is more pronounced for certain normal modes of vibration. It is found that the DHAQ molecules are lying with their molecular plane on the top of the metal surface. Laser induced fluorescence spectra of DHAQ have also been analysed with a view to assign the relative orientation of absorption and emission dipoles.

    • A design of an inexpensive demountableX-ray tube

      V S Pai N V Moghe V B Sapre

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      An inexpensive and simple demountable X-ray source, having facilities to excite X-rays either by bombardment of a target by electrons or by fluorescence, has been developed using a stainless steel chamber having six ports. A cathode assembly from a burnt out sealed off Machlett X-ray tube was carefully removed and reused in the present set-up after replacing the filament. A conventional vacuum system consisting of a rotary and diffusion pumps has been utilized for evacuating the chamber. The set-up can be conveniently utilized to carry out X-ray emission spectroscopic work.

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