Electron-drift driven ion-acoustic mode in a dusty plasma with collisional effects

Instabilities of ion-acoustic waves in a dusty plasma with electron-drift, collisional, and dust charge fluctuations effects, have been investigated. The regimes are clearly marked out where the theory is applicable. The critical electron-drift velocity required to drive the instability is predicted. It is also shown that electron thermal conductivity and charged grains concentration enhance the growth of the ion-acoustic mode whereas ion-viscosity, ion-thermal conductivity, and dust charge fluctuations have a stabilizing effect.Comment: 7 pages, 3 PS-LaTeX figures (to be published in Physics of Plasmas

Ion-acoustic solitons in warm magnetoplasmas with super-thermal electrons

In this work, the phenomenon of formation of localised electrostatic waves (ESW) or soliton is considered in a warm magnetoplasma with the possibility of non-thermal electron distribution. The parameter regime considered here is relevant in case of magnetospheric plasmas. We show that deviation from a usual relaxed Maxwellian distribution of the electron population has a significant bearing in the allowed parameter regime, where these ESWs can be found. We further consider the presence of more than one electron temperature, which is inspired by recent space-based observations[key-2].Comment: 10 pages, 5 figure

Effect of sheared flows on classical and neoclassical tearing modes

The influence of toroidal sheared equilibrium flows on the nonlinear evolution of classical and neoclassical tearing modes is studied through numerical solutions of a set of reduced generalized MHD equations that include viscous force effects based on neoclassical closures. In general, differential flow is found to have a strong stabilizing influence leading to lower saturated island widths for the classical tearing mode and reduced growth rates for the neoclassical mode. Velocity shear, on the other hand, is seen to make a destabilizing contribution

From Cluster to Grid: A Case Study in Scaling-Up a Molecular Electronics Simulation Code

This paper describes an ongoing project whose goal is to significantly improve the performance and applicability of a molecular electronics simulation code. The specific goals are to (1) increase computational performance on the simulation problems currently being solved by our physics collaborators; (2) allow much larger problems to be solved in reasonable time; and (3) expand the set of resources available to the code, from a single homogeneous cluster to a campus-wide computational grid, while maintaining acceptable performance across this larger set of resources. We describe the sequential performance of the code, the performance of two parallel versions, and the benefits of problem-specific load balancing strategies. The grid context motivates the need for runtime algorithm selection; we present a component-based software framework that makes this possible

Thermal instability of an expanding dusty plasma with equilibrium cooling

We present an analysis of radiation induced instabilities in an expanding plasma with considerable presence of dust particles and equilibrium cooling. We have shown that the equilibrium expansion and cooling destabilize the radiation condensation modes and the presence of dust particles enhances this effect. We have examined our results in the context of ionized, dusty-plasma environments such as those found in planetary nebulae (PNe). We show that due to the non-static equilibrium and finite equilibrium cooling, small-scale localized structures formed out of thermal instability, become transient, which agrees with the observational results. The dust-charge fluctuation is found to heavily suppress these instabilities, though in view of non-availability of convincing experimental data, a definitive conclusion could not be made.Comment: 23 pages, 14 figure

Temperature dependence of the resistance of metallic nanowires (diameter ≥\geq 15 nm): Applicability of Bloch-Gr\"{u}neisen theorem

We have measured the resistances (and resistivities) of Ag and Cu nanowires of diameters ranging from 15nm to 200nm in the temperature range 4.2K-300K with the specific aim to assess the applicability of the Bloch-Gr\"{u}neisen formula for electron phonon resistivity in these nanowires. The wires were grown within polymeric templates by electrodeposition. We find that in all the samples the resistance reaches a residual value at T=4.2K and the temperature dependence of resistance can be fitted to the Bloch-Gr\"{u}neisen formula in the entire temperature range with a well defined transport Debye temperature ($\Theta_{R}$). The value of Debye temperature obtained from the fits lie within 8% of the bulk value for Ag wires of diameter 15nm while for Cu nanowires of the same diameter the Debye temperature is significantly lesser than the bulk value. The electron-phonon coupling constants (measured by $\alpha_{el-ph}$ or $\alpha_{R}$) in the nanowires were found to have the same value as that of the bulk. The resistivities of the wires were seen to increase as the wire diameter was decreased. This increase in the resistivity of the wires may be attributed to surface scattering of conduction electrons. The specularity p was estimated to be about 0.5. The observed results allow us to obtain the resistivities exactly from the resistance and gives us a method of obtaining the exact numbers of wires within the measured array (grown within the template).Comment: 9 pages, 10 figure