US graphics card maker Nvidia Corporation (NASDAQ:NVDA) publishes second-quarter earnings after Wednesday's closing bell, though again it has already flagged that quarterly revenue will fall US$1.4bn short of the US$8.1bn guided, as sales of gaming chips weakened. Profit margins are expected to be softer too, hit by a running down of excess inventory, while cost control will also be one of the key issues Wall Street will be watching.