No abstract

In sensor networks, the adversaries can inject false data reports from compromising nodes. Previous approaches for filtering false reports, notably statistical en-route filtering, adopt a simple strategy for grouping sensor nodes that requires redundant groups and thus decrease the filtering effectiveness. Worse still, they either suffer a threshold problem, which may lead to complete breakdown of the security protection when the threshold is exceeded, or are dependent on sink stationarity and specific routing protocols, which cannot work with mobile sinks and various routing protocols. In response to these, this paper proposes a scheme, referred to as Grouping-based Resilient Statistical En-route Filtering (GRSEF), in which nodes are grouped once deployed without requiring redundant groups and a location-aware approach based on terrain division along multiple axes is proposed for key derivation. The design of GRSEF, which is independent of sink stationarity and routing protocols, provides a well suitable en-routing filtering solution for sensor networks with mobile sinks. Analytical and simulation results verify that the scheme significantly improves the filtering effectiveness and efficiently achieves the resiliency against node compromise.

No abstract

The relation between magnetic field topography and operating voltage is investigated in a 1kW Hall thruster discharge channel in order to focus the ion beam effectively and optimize the performance. The curvature of magnetic field line (α) is introduced to characterize the differences of topologies. The optimized magnetic field distribution under each operating voltage is obtained by experiment. Through the curvature transformation, we find that the area of (α > 1) in the channel gradually decreases with the increase of the operating voltage. In response to the results above, two dimensional plasma flows are simulated employing Particle-in-Cell method. The distributions of the electric potential, ion density and ion radial velocity are calculated to understand the important influence of the relation above on ion beam focusing. The numerical results indicate that magnetic field curvature and thermal electric field control the ion beam in the ionization and acceleration zone, respectively. The magnetic field topography and discharge voltage interact with each other and together form the focusing electric field. The ion radial mobility is suppressed effectively and the ion beam is focused to the channel centerline. In addition, for a given voltages, when the area of (α > 1) is larger than the optimal scope, the electric potential lines excessively bend to the anode causing ion over focus; contrarily, the electric potential lines will bend to the exit and defocus ions. All these results suggest the relation between magnetic field topography and discharge voltage is important to the ion radial flow control and performance optimization of the Hall thruster.