• Volume 16, Issue 2

      February 1981,   pages  109-171

    • Two-state random walk model of lattice diffusion. 1. Self-correlation function

      V Balakrishnan G Venkataraman

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      Diffusion with interruptions (arising from localized oscillations, or traps, or mixing between jump diffusion and fluid-like diffusion, etc.) is a very general phenomenon. Its manifestations range from superionic conductance to the behaviour of hydrogen in metals. Based on a continuous-time random walk approach, we present a comprehensive two-state random walk model for the diffusion of a particle on a lattice, incorporating arbitrary holding-time distributions for both localized residence at the sites and inter-site flights, and also the correct first-waiting-time distributions. A synthesis is thus achieved of the two extremes of jump diffusion (zero flight time) and fluid-like diffusion (zero residence time). Various earlier models emerge as special cases of our theory. Among the noteworthy results obtained are: closed-form solutions (ind dimensions, and with arbitrary directional bias) for temporally uncorrelated jump diffusion and for the ‘fluid diffusion’ counterpart; a compact, general formula for the mean square displacement; the effects of a continuous spectrum of time scales in the holding-time distributions, etc. The dynamic mobility and the structure factor for ‘oscillatory diffusion’ are taken up in part 2.

    • Feedback stabilization of drift cyclotron loss cone instability by modulated electron sources

      Avinash R K Varma

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      It is shown that the drift cyclotron loss cone instability can be suppressed by modulating electron density within the plasma. With the feedback in +90° phase the critical density gradient needed for the onset of the drift cyclotron loss cone instability increases approximately linearly with the gain. Typically with the gain of −50Ωi the critical density gradient can be pushed up by as much as two orders of magnitude and minimum mirror plasma radius can be brought down in the same proportion.

    • Continuous quantization procedure in quasiclassical scattering: Application to atom-Morse oscillator collisions

      Ramakrishna Ramaswamy

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      The recently developed method of continuous quantization is applied to the atom-Morse oscillator collinear collision problem. This geometrical formulation of the classical scattering process allows for the extraction of transition probabilities for classically forbidden processes with reasonable accuracy. The accuracy of this method over the simple (histogram) quasi-classical procedure is demonstrated for two-model systems.

    • On the C-X system of diatomic mercury chloride

      A K Rai S B Rai D K Rai

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      The C-X system of diatomic mercury chloride has been re-investigated in emission. The previous vibrational assignments of this system by Horne and others have been confirmed by measurement of the chlorine isotopic shift and improved vibrational constants for the ‘C’ state determined.

    • Electrical resistivity studies of benzidine-TCNQ and its inclusion compound under high pressure

      A K Bandyopadhyay S V Subramanyam

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      Electrical resistivity studies of the charge transfer complex benzidine—TCNQ and its inclusion compound, have been carried out up to pressures 8 GPa. Two types of behaviour were observed in these complexes under high pressure and this difference is interpreted and discussed.

    • Photo and electroluminescence properties in Zns: (Cu, La) and Zns: (Ag, La) phosphors

      L N Tripathi B R Chaubey C P Mishra

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      A method for preparation of ZnS: (Cu, La) and ZnS: (Ag, La) phosphors is described. Photo and electroluminescence of these phosphors have been studied. The voltage and frequency variation of EL brightness have also been reported. The results agree with the collision-excitation mechanism in the Schottky barrier. The emission of blue, green and yellow bands has been interpreted in terms of different electronic transitions. Simultaneous action of both the field and the 3650 Å radiation has been studied. An attempt has also been made to explain the quenching and enhancement.

    • Electroluminescence of CaSO4: Sm phosphors

      S G Sabnis S H Pawar

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      CaSO4 phosphors activated with Sm3+ impurity in varying concentrations have been prepared and their electroluminescence systematically studied. The voltage and frequency dependence of brightness is discussed and conclusions are drawn regarding the possible mechanism involved in the process.

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