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Papers by punyam satya-narayana

Research paper thumbnail of Current collection and current closure in the Tethered Satellite System

22nd Fluid Dynamics, Plasma Dynamics and Lasers Conference, 1991

ABSTRACT Current collection and closure-path modeling are examined analytically with respect to t... more ABSTRACT Current collection and closure-path modeling are examined analytically with respect to the Tethered Satellite System (TSS). A particle-in cell code is compared with a one-dimensional unmagnetized fluid code to model the behavior of a positively charged satellite in the ionosphere. The morphology of the sheath and the sheath-region processes are thus examined, and the influence of ions leaving the sheath region is found to cause the attraction of an electron current that is 40 times greater than the steady state value. The enhancement is transient and enhances the acceleration of the electrons in the sheath. A set of modified MHD equations, including those for ion inertia, quasineutrality, and electron drift, is employed to model TSS current closure. Whistler modes are found to exist and can be excited as the TSS passes through the ionosphere. Important conclusions include a significant fluctuation level in the steady state sheath, an ion void which affects the electron population, and some long-lived electrons trapped in the settled sheath with respect to two directions.

Research paper thumbnail of Hybrid simulations of whistler waves generation and current closure by a pulsed tether in the ionosphere

Geophysical Research Letters, 1994

The dynamic response of a magnetized collisionless plasma to an externally driven, finite size, s... more The dynamic response of a magnetized collisionless plasma to an externally driven, finite size, sudden switch-on current source across the magnetic field has been studied using a two dimensional hybrid code. It was found that the predominant plasma response was the excitation of whistler waves and the formation of current closure by induced currents in the plasma. The results show that the current closure path consists of: a) two antiparallel field-aligned current channels at the end of the imposed current sheet; and b) a cross-field current region connecting these channels. The formation of the current closure path occured in the whistler timescale much shorter than that of MHD and the closure region expanded continuously in time. The current closure process was accompanied by significant energy loss due to whisfier radiation. 1320, 1990. Stenzel, R.L., and J.M. Urmtia, Currents between tethered electrodes in a magnetized laboratory plasma, J. Geophys. Res., 95, 6209-6226, 1990. Urmtia, J.M., and R.L. Stenzel, Modeling of induced curents from electrodynamic tethers in a laboratory plasma, Geophys. Res. Lett., 17, 1589-1592, 1990.

Research paper thumbnail of Hybrid simulations of whistler waves generation and current closure by a pulsed tether in the ionosphere

Geophysical Research Letters, 1994

The dynamic response of a magnetized collisionless plasma to an externally driven, finite size, s... more The dynamic response of a magnetized collisionless plasma to an externally driven, finite size, sudden switch-on current source across the magnetic field has been studied using a two dimensional hybrid code. It was found that the predominant plasma response was the excitation of whistler waves and the formation of current closure by induced currents in the plasma. The results show that the current closure path consists of: a) two antiparallel field-aligned current channels at the end of the imposed current sheet; and b) a cross-field current region connecting these channels. The formation of the current closure path occured in the whistler timescale much shorter than that of MHD and the closure region expanded continuously in time. The current closure process was accompanied by significant energy loss due to whisfier radiation. 1320, 1990. Stenzel, R.L., and J.M. Urmtia, Currents between tethered electrodes in a magnetized laboratory plasma, J. Geophys. Res., 95, 6209-6226, 1990. Urmtia, J.M., and R.L. Stenzel, Modeling of induced curents from electrodynamic tethers in a laboratory plasma, Geophys. Res. Lett., 17, 1589-1592, 1990.

Research paper thumbnail of Parallelization and Optimization of a Large Eddy Simulation Code using OpenMP for SGI Origin2000 Performance

Parallel Computational Fluid Dynamics 1999, 2000

Research paper thumbnail of Evaluating Performance of OpenMP and MPI on the SGI Origin 2000 with Benchmarks of Realistic Problem Sizes

Distributed and Parallel Systems, 2000

EVALUATING PERFORMANCE OF OPENMP AND MPI ON THE SGI ORIGIN 2000 WITH BENCHMARKS OF REALISTIC PROB... more EVALUATING PERFORMANCE OF OPENMP AND MPI ON THE SGI ORIGIN 2000 WITH BENCHMARKS OF REALISTIC PROBLEM SIZES Csaba K. Zoltani, Punyam Satya-narayana, Dixie Hisley Computational and Information Sciences Directorate High Performance Computing Division US Army ...

Research paper thumbnail of Porting and Performance Evaluation of Irregular Codes using OpenMP

In the last two years, OpenMP has been gaining popularity as a standard for developing portable s... more In the last two years, OpenMP has been gaining popularity as a standard for developing portable shared memory parallel programs. With the improvements in centralized shared memory technologies and the emergence of distributed shared memory DSM architectures, several medium-to-large physical and logical shared memory con gurations are now available. Thus, OpenMP stands to be a p r omising medium for developing scalable and portable parallel programs.

Research paper thumbnail of APG, MD 21005 hisley, psatya@ arl. mil voice:(410) 278-9156† CIS Department University of Delaware

Research paper thumbnail of Porting and performance evaluation of irregular codes using OpenMP

Concurrency - Practice and Experience, Oct 1, 2000

In the last two years, OpenMP has been gaining popularity as a standard for developing portable s... more In the last two years, OpenMP has been gaining popularity as a standard for developing portable shared memory parallel programs. With the improvements in centralized shared memory technologies and the emergence of distributed shared memory DSM architectures, several medium-to-large physical and logical shared memory con gurations are now available. Thus, OpenMP stands to be a p r omising medium for developing scalable and portable parallel programs.

Research paper thumbnail of Current collection and current closure in the Tethered Satellite System

22nd Fluid Dynamics, Plasma Dynamics and Lasers Conference, 1991

ABSTRACT Current collection and closure-path modeling are examined analytically with respect to t... more ABSTRACT Current collection and closure-path modeling are examined analytically with respect to the Tethered Satellite System (TSS). A particle-in cell code is compared with a one-dimensional unmagnetized fluid code to model the behavior of a positively charged satellite in the ionosphere. The morphology of the sheath and the sheath-region processes are thus examined, and the influence of ions leaving the sheath region is found to cause the attraction of an electron current that is 40 times greater than the steady state value. The enhancement is transient and enhances the acceleration of the electrons in the sheath. A set of modified MHD equations, including those for ion inertia, quasineutrality, and electron drift, is employed to model TSS current closure. Whistler modes are found to exist and can be excited as the TSS passes through the ionosphere. Important conclusions include a significant fluctuation level in the steady state sheath, an ion void which affects the electron population, and some long-lived electrons trapped in the settled sheath with respect to two directions.

Research paper thumbnail of Hybrid simulations of whistler waves generation and current closure by a pulsed tether in the ionosphere

Geophysical Research Letters, 1994

The dynamic response of a magnetized collisionless plasma to an externally driven, finite size, s... more The dynamic response of a magnetized collisionless plasma to an externally driven, finite size, sudden switch-on current source across the magnetic field has been studied using a two dimensional hybrid code. It was found that the predominant plasma response was the excitation of whistler waves and the formation of current closure by induced currents in the plasma. The results show that the current closure path consists of: a) two antiparallel field-aligned current channels at the end of the imposed current sheet; and b) a cross-field current region connecting these channels. The formation of the current closure path occured in the whistler timescale much shorter than that of MHD and the closure region expanded continuously in time. The current closure process was accompanied by significant energy loss due to whisfier radiation. 1320, 1990. Stenzel, R.L., and J.M. Urmtia, Currents between tethered electrodes in a magnetized laboratory plasma, J. Geophys. Res., 95, 6209-6226, 1990. Urmtia, J.M., and R.L. Stenzel, Modeling of induced curents from electrodynamic tethers in a laboratory plasma, Geophys. Res. Lett., 17, 1589-1592, 1990.

Research paper thumbnail of Hybrid simulations of whistler waves generation and current closure by a pulsed tether in the ionosphere

Geophysical Research Letters, 1994

The dynamic response of a magnetized collisionless plasma to an externally driven, finite size, s... more The dynamic response of a magnetized collisionless plasma to an externally driven, finite size, sudden switch-on current source across the magnetic field has been studied using a two dimensional hybrid code. It was found that the predominant plasma response was the excitation of whistler waves and the formation of current closure by induced currents in the plasma. The results show that the current closure path consists of: a) two antiparallel field-aligned current channels at the end of the imposed current sheet; and b) a cross-field current region connecting these channels. The formation of the current closure path occured in the whistler timescale much shorter than that of MHD and the closure region expanded continuously in time. The current closure process was accompanied by significant energy loss due to whisfier radiation. 1320, 1990. Stenzel, R.L., and J.M. Urmtia, Currents between tethered electrodes in a magnetized laboratory plasma, J. Geophys. Res., 95, 6209-6226, 1990. Urmtia, J.M., and R.L. Stenzel, Modeling of induced curents from electrodynamic tethers in a laboratory plasma, Geophys. Res. Lett., 17, 1589-1592, 1990.

Research paper thumbnail of Parallelization and Optimization of a Large Eddy Simulation Code using OpenMP for SGI Origin2000 Performance

Parallel Computational Fluid Dynamics 1999, 2000

Research paper thumbnail of Evaluating Performance of OpenMP and MPI on the SGI Origin 2000 with Benchmarks of Realistic Problem Sizes

Distributed and Parallel Systems, 2000

EVALUATING PERFORMANCE OF OPENMP AND MPI ON THE SGI ORIGIN 2000 WITH BENCHMARKS OF REALISTIC PROB... more EVALUATING PERFORMANCE OF OPENMP AND MPI ON THE SGI ORIGIN 2000 WITH BENCHMARKS OF REALISTIC PROBLEM SIZES Csaba K. Zoltani, Punyam Satya-narayana, Dixie Hisley Computational and Information Sciences Directorate High Performance Computing Division US Army ...

Research paper thumbnail of Porting and Performance Evaluation of Irregular Codes using OpenMP

In the last two years, OpenMP has been gaining popularity as a standard for developing portable s... more In the last two years, OpenMP has been gaining popularity as a standard for developing portable shared memory parallel programs. With the improvements in centralized shared memory technologies and the emergence of distributed shared memory DSM architectures, several medium-to-large physical and logical shared memory con gurations are now available. Thus, OpenMP stands to be a p r omising medium for developing scalable and portable parallel programs.

Research paper thumbnail of APG, MD 21005 hisley, psatya@ arl. mil voice:(410) 278-9156† CIS Department University of Delaware

Research paper thumbnail of Porting and performance evaluation of irregular codes using OpenMP

Concurrency - Practice and Experience, Oct 1, 2000

In the last two years, OpenMP has been gaining popularity as a standard for developing portable s... more In the last two years, OpenMP has been gaining popularity as a standard for developing portable shared memory parallel programs. With the improvements in centralized shared memory technologies and the emergence of distributed shared memory DSM architectures, several medium-to-large physical and logical shared memory con gurations are now available. Thus, OpenMP stands to be a p r omising medium for developing scalable and portable parallel programs.