The Sensex at the Bombay Stock Exchange gained 41 points, or 0.2 per cent, to 20,145 in opening trade, this morning, on sustained buying by funds, on hopes of a rate cut by the Reserve Bank, and some better-than-expected corporate earnings. Later, the Sensex turned volatile, and after moving in and out of the positive zone, stood 12 points, or 0.1 per cent in negative territory, at 20,092 in afternoon trade, a short while ago.Stock markets in Japan, China, Hong Kong, Taiwan, Indonesia and South Korea were trading mixed, today.