Uptake of radioactive tryptophan by Mycobacterium tuberculosis H 37 Rv grown in vitro and in vivo was investigated. K m values indicated low affinity, and sodium azide inhibited uptake. Rifampin at the minimal inhibitory concentration had no effect, whereas ethambutol inhibited uptake only in the bacilli grown under in vitro conditions. The significance of these results is discussed.

Aluminium alloys due to their high strength combined with low density, durability, machinability and availability play a significant role in the development of metal matrix composites. The superior specific strength, stiffness, wear resistance and improved high temperature properties of aluminium matrix composites (AMC) make it a potential material for automotive, aerospace and defence applications [1-3]. AMCs are widely used in a variety of automotive applications, namely connecting rod, drive shaft, cylinder liner, cylinder blocks and brake rotor [4-6] , aircraft components, namely rotor vanes, fan exit guide vanes, etc. [7] and defence components, such as light weight body armour, track pad, etc. There are many methods available for the fabrication of particulate reinforced aluminium matrix composites such as diffusion bonding [8] , powder metallurgy [9] , infiltration techniques, spray deposition, stir casting, squeeze casting, etc. Among these methods, the conventional foundry based processes are quite promising. Further, the stir casting process is found to be more economical and suitable for mass production. The cost of preparing composite materials using casting route is about one-third to half that of the competitive methods and for high volume production, the cost will fall into one tenth [10]. Thermomechanical processes such as extrusion, rolling, forging etc. have been carried out on the cast composite billets in order to improve the strength and ductility by eliminating the cast defects. Among the above methods, hot extrusion is widely used for wrought aluminium alloys and their composites [11]. Hot extrusion has resulted in increased strength and tribological properties of the cast components [12,13]. Limited studies have been carried out on the evaluation of elevated temperature properties of composites, which are essential for components of engine, brake disc/drum, etc. This paper deals with the fabrication of Al 2014-SiC particulate composite, hot extrusion of the cast composites and the investigation of its microstructure and high temperature strength. The 2014 aluminium alloy is a high strength, heat treatable alloy widely used for aircraft components. Silicon carbide (SiC) is selected as a reinforcement owing to its high hardness and low coefficient of thermal expansion. SiC possesses high wear resistance and good mechanical properties, including high temperature strength and thermal shock resistance.