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In the present study, rheocasting process was adopted to synthesise AZ91D composites reinforced with silicon carbide (SiC) particulates. Particle-matrix interfacial reaction, distribution of particles, hardness and mechanical properties of as cast and T4 heat-treated alloy-composites were reported. The rheocast composite materials reveal uniform distribution of SiC particulates. The composite materials show an increase in hardness and elastic modulus compared to unreinforced rheocast alloy. She ultimate tensile strength and ductility of composite materials were lower than those of the unreinforced alloy. 15 lm particles-composite shows significantly higher elastic modulus than the 150 lm SiC particles-composite.

Atomic coherence resonances such as electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) signals are observed in a Doppler broadened multi-level system for the D 2 line of 85 Rb atoms in a vapour cell considering different types of atom-laser coupling schemes. Besides the coherence resonances, the nonlinear resonances like velocity selective optical pumping (VSOP) dips and velocity selective resonances (VSR)are also observed for the non-zero velocity selective groups of atoms. In the presence of pump, control and probe laser fields, we observe two EIT signals in a double -type system and two EIA signals in a double V-type system. We are able to see the EIA signal for the non-zero velocity group of atoms when the pump laser is locked with an open transition by a small red detuning. We also report the experimental observation of simultaneous EIT and EIA signals in a ( +V)-type system. The effect of frequency tuning of the control laser is also studied in the presence of the frequency locked pump laser. A simple theoretical analysis explains the experimental results.