A time-dependent model for pair creation in a pulsar magnetosphere is developed in which the parallel electric field oscillates with large amplitude. Electrons and positrons are accelerated periodically, and the amplitude of the oscillations is assumed to be large enough to cause creation of upgoing and downgoing pairs at different phases of the oscillation. With a charge-starved initial condition, we find that the oscillations result in bursts of pair creation in which the pair density rises exponentially with time. The pair density saturates at N AE ' E 2 0 /(8 m e c 2 À thr ), where E 0 is the parallel electric field in the charge-starved initial state and À thr is the Lorentz factor for effective pair creation. The frequency of oscillations following the pair creation burst is given roughly by ! osc ¼ eE 0 /(8m e cÀ thr ). A positive feedback keeps the system stable, such that the average pair creation rate balances the loss rate due to pairs escaping the magnetosphere.

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This work investigates the effects of carbon/glass/basalt hybridization and fabric structure on the low velocity impact resistance of fibre reinforced plastic composites. Interply hybrid specimens used in the study were fabricated in a sandwich-like stacking sequence using a vacuum assisted resin infusion molding technique. Low velocity impact tests were carried out to study effects of hybridization and fabric structure on the impact resistance of composite laminates. A continuum damage mechanical model was developed and validated for nonhybrid woven fabric laminates at different impact energy levels. Residual damage characteristics in the crosssectional view were identified using a 3D surface scanning system and an X-ray computed tomography (CT) method. On the basis of experimental results, numerical simulation was conducted to analyse the damage mechanisms of the hybrid laminates. Experimental results showed that: (a) hybrid laminates with carbon fibre as the core exhibited superior impact resistance for sandwich-like stacking sequence; (b) similar impact behaviors appeared for carbon laminates hybrid with either basalt or glass fibre; (c) for basalt fibre, weave fabric composite laminates exhibited better energy absorption capability and deformation resistance than cross-ply laminates reinforced by unidirectional fabrics.

It is proposed that radiation belts similar to the ones in the planetary magnetosphere can exist for a pulsar with a relatively long period and a strong magnetic field. In the belts located in the closed field line region near the light cylinder relativistic pairs are trapped and maintained at a density substantially higher than the local Goldreich-Julian corotation density. The trapped plasma can be supplied and replenished by either direct injection of relativistic pairs from acceleration of externally-supplied particles in a dormant outer gap or in situ ionization of the accreted neutral material in the trapping region. The radiation belts can be disrupted by waves that are excited in the region as the result of plasma instabilities or emitted from the surface due to starquakes or stellar oscillations. The disruption can cause an intermittent particle precipitation toward the star producing radio bursts. It is suggested that such bursts may be seen as rotating radio transients (RRATs).Comment: 11 pages, 3 figures, accepted for publication in MNRA

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