• Volume 21, Issue 2

      August 1983,   pages  89-158

    • A new approach to charged-particle scattering in the presence of laser plus Coulomb-field

      Man Mohan

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      A new approach to charge-particle scattering in the presence of laser plus coulomb-field by using Fourier analysis technique is described. Explicit expressions for positive energy states and their asymptotic limits for the zero, one and two photon processes are evaluated exactly.

    • Core electron binding energies in heavy atoms

      M P Das

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      Inner shell binding of electrons in heavy atoms is studied through the relativistic density functional theory in which many electron interactions are treated in a local density approximation. By using this theory and the Δscf procedure binding energies of several core electrons of mercury atom are calculated in the frozen and relaxed configurations. The results are compared with those carried out by the non-local Dirac-Fock Scheme.K-shell binding energies of several closed shell atoms are calculated by using the Kohn-Sham and the relativistic exchange potentials. The results are discussed and the discrepancies in our local density results, when compared with experimental values, may be attributed to the non-locality and to the many-body effects.

    • First passage time distributions for finite one-dimensional random walks

      M Khantha V Balakrishnan

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      We present closed expressions for the characteristic function of the first passage time distribution for biased and unbiased random walks on finite chains and continuous segments with reflecting boundary conditions. Earlier results on mean first passage times for one-dimensional random walks emerge as special cases. The divergences that result as the boundary is moved out to infinity are exhibited explicitly. For a symmetric random walk on a line, the distribution is an elliptic theta function that goes over into the known Lévy distribution with exponent 1/2 as the boundary tends to ∞.

    • Significance of Hall measurements in Ga1−xAlxAs alloys at 300 K

      Ashok K Saxena B B Singh

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      The Hall mobility, electron concentration and resistivity have been measured as a function of alloy composition for Ga1−xAlxAs alloys at 300 K. The data have been explained on the multiconduction band structure of the alloys. The alloy composition for the direct-indirect conduction band minima cross-over, the electron mobility in theX minima and the activation energy of the deep level below these minima have been determined.

    • Analytical studies of gain optimization in CO2-N2 gasdynamic lasers employing two-dimensional wedge nozzles

      V Shanmugasundaram N M Reddy

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      An analytical method has been proposed to optimise the small-signaloptical gain of CO2-N2 gasdynamic lasers (gdl) employing two-dimensional (2D) wedge nozzles. Following our earlier work the equations governing the steady, inviscid, quasi-one-dimensional flow in the wedge nozzle of thegdl are reduced to a universal form so that their solutions depend on a single unifying parameter. These equations are solved numerically to obtain similar solutions for the various flow quantities, which variables are subsequently used to optimize the small-signal-gain. The corresponding optimum values like reservoir pressure and temperature and 2D nozzle area ratio also have been predicted and graphed for a wide range of laser gas compositions, with either H2O or He as the catalyst. A large number of graphs are presented which may be used to obtain the optimum values of small signal gain for a wide range of laser compositions without further computations.

    • Attenuation of shock parameters in air and water

      J Harvey J Nandakumar L V Krishnan

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      This paper describes the results of shock pressure measurements in the range of 1–25 MPa in water and in the range of 60–500 kPa in air. Pressure pulses were generated by exploding wire technique and measured with a quartz piezo-electric transducer. The attenuation with distance of shock overpressure, impulse and energy in shock front has been studied. Experimental data on shock attenuation in air is scarce and the results presented here confirm the attenuation behaviour derived from theoretical considerations.

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