arXiv subjects

Abhijit Sen

Publications and source records attributed to Abhijit Sen.

97 records · Page 6Linked to original sources

arXiv2004

Nonlinear saturation of magnetic curvature driven Rayleigh Taylor instability in three dimensions

We present three dimensional fluid simulation results on the temporal evolution and nonlinear saturation of the magnetic curvature driven Rayleigh-Taylor (RT) instability. The model set of coupled nonlinear equations evolve the scalar electric field potential $ϕ$, plasma density $n$ and the parallel component of the magnetic vector potential $ψ$. The simulations have been carried out in two limits, (i) a low resistivity case in which RT is the only linearly growing mode, and (ii) a high resistivity case where the drift wave is unstable and for which the magnetic curvature parameter is set to zero to ensure the absence of the RT growth. Our simulations show nonlinear stabilization in both these limits. The stabilization mechanism is similar to that observed in earlier two dimensional simulations, namely the generation of zonal shear flows which decorrelate the radially extended unstable modes. However the nature of the saturated nonlinear state in the 3d case differs from that of 2d in some important ways such as by having significant levels of power in short scales and by the presence of electromagnetic fluctuations. Though, in the linear regime the electromagnetic effects reduce the growth rates, in the nonlinear regime their presence hinders the process of stabilization by inhibiting the process of zonal flow formation. Thus the parameter regime for which nonlinear stabilization takes place is considerably reduced in three dimensions.

physics.plasm-ph↗

arXiv2004

Phaselocked patterns and amplitude death in a ring of delay coupled limit cycle oscillators

We study the existence and stability of phaselocked patterns and amplitude death states in a closed chain of delay coupled identical limit cycle oscillators that are near a supercritical Hopf bifurcation. The coupling is limited to nearest neighbors and is linear. We analyze a model set of discrete dynamical equations using the method of plane waves. The resultant dispersion relation, which is valid for any arbitrary number of oscillators, displays important differences from similar relations obtained from continuum models. We discuss the general characteristics of the equilibrium states including their dependencies on various system parameters. We next carry out a detailed linear stability investigation of these states in order to delineate their actual existence regions and to determine their parametric dependence on time delay. Time delay is found to expand the range of possible phaselocked patterns and to contribute favorably toward their stability. The amplitude death state is studied in the parameter space of time delay and coupling strength. It is shown that death island regions can exist for any number of oscillators N in the presence of finite time delay. A particularly interesting result is that the size of an island is independent of N when N is even but is a decreasing function of N when N is odd.

nlin.CD↗

arXiv2002

A Computational Algorithm for /pi(N)

An algorithm for computing /pi(N) is presented.It is shown that using a symmetry of natural numbers we can easily compute /pi(N).This method relies on the fact that counting the number of odd composites not exceeding N suffices to calculate /pi(N).

math.GM↗

arXiv2002

An Extension to Fermat's Factorisation and a simple primality test

An extension to the factorisation principle as suggested by Fermat is presented.We start from a symmetry of natural numbers and obtain the factorisation principle therefrom.Later it is extended further to test the primality of any natural number and finally used to factorise any given number.

math.GM↗

arXiv2002

The extent of strangeness in equilibration in quark-gluon plasma

The evolution and production of strangeness from chemically equilibrating and transversely expanding quark gluon plasma which may be formed in the wake of relativistic heavy ion collisions is studied with initial conditions obtained from the Self Screened Parton Cascade (SSPC) model. The extent of partonic equilibration increases almost linearly with the square of the initial energy density, which can then be scaled with number of participants.

nucl-th↗

arXiv2001

Evolution of strangeness in equilibrating and expanding quark-gluon plasma

We evaluate the strangeness production from equilibrating and transversely expanding quark gluon plasma which may be created in the wake of relativistic heavy ion collisions. We consider boost invariant longitudinal and cylindrically symmetric transverse expansion of a gluon dominated partonic plasma, which is in local thermal equilibrium. Initial conditions obtained from the self screened parton cascade model are used. We empirically find that the final extent of the partonic equilibration rises almost linearly with the square of the initial energy density. This along with the corresponding variation with the number of participants may help us distinguish between various models of parton production.

nucl-th↗

arXiv1999

Hadronic modes in the quark plasma with an internal symmetry

We show that requiring the quark partition function to be color singlet of SU(3) color gauge group leads to reordering the thermodynamic potential in terms of the colorless multi-quark modes ($q{\bar q}, qqq, {\bar q}{\bar q}{\bar q}, ...$) at any given temperature. In accord with the "preconfinement" property of QCD, under a suitable confining mechanism, these could evolve into color singlet hadrons/baryons at low temperatures. At fairly high temperatures these multi-quark color singlet structures propagate in the plasma like hadronic modes, just as in the more familiar low temperature phase. This suggests that there exists a strong correlation in the plasma at all temperatures which is in conformity with lattice results.

nucl-th↗