Tokyo stocks were mixed Friday morning, as modest bargain-hunting offset earlier losses that tracked overnight falls on Wall Street. The 225-issue Nikkei Stock Average fell 138.18 points, or 0.36 percent, from Thursday to 38,782.08. The broader Topix index was up 5.12 points, or 0.19 percent, at 2,742.66. The U.S. dollar rose to the upper 155 yen range in Tokyo on prospects of a wider interest rate differential between Japan and the United States after long-term U.S. Treasury yields rose overnight. The yen was additionally sold after the Bank of Japan said it would keep its regular operation p…