The Nikkei stock index rose Tuesday for the fourth straight trading day and briefly climbed above the 40,000 mark for the first time in three months on optimism about the U.S. economic outlook. The 225-issue Nikkei Stock Average ended up 304.75 points, or 0.77 percent, from Friday at 39,910.55. The broader Topix index finished 17.37 points, or 0.64 percent, higher at 2,723.57. Japanese financial markets were closed Monday for a national holiday. On the top-tier Prime Market, gainers were led by insurance, bank and electric appliance issues. The U.S. dollar mostly remained firm in the upper 149…