V S Varma
Articles written in Pramana – Journal of Physics
Volume 12 Issue 5 May 1979 pp 427-437 Nuclear And Particle Physics
We study elastic α-particle scattering off
Volume 32 Issue 1 January 1989 pp 89-94 Rapid Communications
The finite-temperature Schrödinger equation, derived recently from the Bethe-Salpeter equation for the bound states of an electron and a proton interacting via the instantaneous Coulomb interaction, is studied in the coordinate space. An expression for the temperature-modified Coulomb potential is obtained and briefly discussed.
Volume 32 Issue 2 February 1989 pp 117-129 Quantum Mechanics
The Hartree-Fock procedure is used to study the behaviour of the ground state of a system of
Volume 35 Issue 1 July 1990 pp 1-9
The occurrence of discontinuities in the energy spectrum of the
Volume 36 Issue 5 May 1991 pp 489-496 Research Articles
The existence of finite discontinuities in the energy eigenvalue spectra of certain multiterm potentials when their coupling parameters attain suitably chosen limiting values has been reported in the literature. We show that such discontinuities are also characteristic of such well-known systems as generalized anharmonic oscillators and the doubly anharmonic oscillator in one dimension. The present study strengthens the general conjecture that eigenvalue spectra are likely to display discontinuities in situations where a potential undergoes an abrupt change in shape with smooth variation of its coupling parameters.
Volume 37 Issue 1 July 1991 pp 83-91
We study discrete nonlinear maps in which the control parameter is itself “modulated” by another discrete nonlinear map. We show that for a certain class of such maps, which includes for example the logistic map, the periodicity of the modulated signal is either one, independent of the periodicity of the modulating signal, or its periodicity is an integral multiple of the periodicity of the modulating signal or it is chaotic.
Volume 43 Issue 6 December 1994 pp 431-442
In this paper we have tried to stabilize the unstable fixed points for a class of 1-D maps by using a multiplicative nonlinear feedback control mechanism. We have also used such control to create new attractors (which did not exist in the original system), to suit our requirement. The control is also found to work in the presence of noise.
Volume 45 Issue 4 October 1995 pp 355-368
We demonstrate that chaos can be controlled using multiplicative exponential feedback control. Unstable fixed points, unstable limit cycles and unstable chaotic trajectories can all be stabilized using such control which is effective both for maps and flows. The control is of particular significance for systems with several degrees of freedom, as knowledge of only one variable on the desired unstable orbit is sufficient to settle the system onto that orbit. We find in all cases that the transient time is a decreasing function of the stiffness of control. But increasing the stiffness beyond an optimum value can increase the transient time. We have also used such a mechanism to control spatiotemporal chaos is a well-known coupled map lattice model.
Volume 48 Issue 1 January 1997 pp 259-270 Spatio-Temporal Chaos, Synchronization And Control
We review the subject of control of chaotic systems paying special attention to exponential control. We also discuss the application of synchronization of chaotic systems to security in communications.
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