The Sensex at the Bombay Stock Exchange opened a modest 33 points higher, at 18,427, on Thursday morning, on selective buying by investors. Later, the Sensex slipped into negative territory, in volatile trade, before again rebounding, to stand 30 points, or 0.2 percent in the positive zone, at 18,425 in afternoon deals, a short while ago. Other Asian markets in Japan, China, Hong Kong, Singapore, South Korea and Taiwan were trading mixed, today, on worries about US economic growth. The US Dow Jones Industrial Average had lost 0.2 per cent, overnight.