• M Mohan

      Articles written in Pramana – Journal of Physics

    • Effect of random density irregularities on nonlinear evolution of Langmuir waves in interplanetary medium

      B Buti M Mohan S K Alurkar

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      The evolution of nonlinear Langmuir waves in the interplanetary medium is investigated by appropriately accounting for the random density irregularities of the medium. A pair of modified Zakharov equations, which describe these waves, is solved numerically as an initial value problem for large scale (≫ 102 km) initial pertubations. For an ion acoustic-Langmuir solitary wave, the random irregularities damp the Langmuir wave by way of scattering and let the ion density perturbation radiate away in a few days. However an initial solitary or shock-like Langmuir wave excites the ion density perturbations within a fraction of a second, and then itself gets damped. These effects will strongly decelerate the collapse of large scale Langmuir waves. The possibility of detecting these processes, by means of interplanetary scintillation, is discussed.

    • Photoionization of the ground1Se and twenty lowest excited states of the Ne-like Fe16+

      M Mohan M Le Dourneuf Vinod Prasad A Kumar

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      TheR-matrix method is used to calculate cross-sections for the photoionization of Ne-like Fe16+ from ground 2s22p61Se and excited states belonging to 2s2p6 3l and 2s22p5 3l configurations. Configuration interaction wavefunctions are used to represent two target states of Fe17+ ion retained in theR-matrix expansion. The cross-sections are obtained as a function of kinetic energy (εk) of the ejected electron from 10 to 24 Ry. For low kinetic energy the cross-sections show series of Rydberg states which converge onto2Se threshold Fe17+. The calculations are carried out in the LS coupling.

    • Collisional excitation among the seven lowest states of TiXII

      M Mohan A Hibbert

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      Collision strengths have been calculated for electron impact excitation of sodium-like TiXII for all 21 transitions amongst its lowest seven states. Configuration interaction wave functions have been used to represent the target states. The standard and no-exchangeR-matrix codes have been used to calculate the contribution of partial waves withL⩽8 andL>8 respectively. Collision strengths are tabulated at selected energies in the range 26 to 50 Ryd. Effective collision strengths are tabulated for electron temperatures in the range logTe=4.0 to logTe=6.0, withTe in K. This is the first detailed calculation on this ion in which the effects of exchange, channel couplings and short-range correlation are taken into account.

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