US stocks Friday closed out a holiday-shortened week mostly lower as outgoing Federal Reserve Chairman Ben Bernanke called for continued efforts to cement the economic recovery. The Dow Jones Industrial Average rose 28.64 (0.17 percent) to 16,469.99. The broad-based S&P 500 slipped 0.61 (0.03 percent) to 1,831.37, while the tech-rich Nasdaq Composite Index declined 11.16 (0.27 percent) to 4,131.91. Trading volume was low with many people still on holiday for the New Year and a major snowstorm buffeting the Northeast. Stocks rose shortly after Bernanke said in a speech at a conference of economists that policy makers should aim to boost hiring and spur the economy. But markets quickly gave up those gains, with little other news to stimulate trade. Chipmaker Micron Technology dipped 3.2 percent after RBC Capital Markets downgraded the stock, arguing it is overvalued in light of sectoral and company-specific challenges. General Motors fell 3.4 percent after reporting a 6 percent drop in auto sales in December. Ford Motor rose 0.5 percent after notching a 2 percent December sales gain. Drugstore chain Rite Aid shot up 8.5 percent after reporting that same-store sales for December rose 2.9 percent over the prior-year period. Delta Air Lines added 5.5 percent after reporting that a key revenue-per-passenger benchmark increased 10 percent in December over a year ago. Delta said it benefited from "continuing strong demand." FireEye, which provides security to information technology systems, surged 38.6 percent after announcing it was acquiring another security company, Mandiant, for about $1 billion. FireEye said the deal would improve its capacity to detect and respond to incidents. Food company General Mills dipped 0.3 percent afer announcing that it would produce Cheerios cereal without genetically modified ingredients in the US. 3D Systems, which makes 3D printers, rose 2.4 percent after announcing the purchase of Gentle Giant Studios, which provides 3D modelling for the entertainment and toy industry, for an undisclosed sum. Bond prices fell. The yield on the 10-year bond rose to 3.00 percent from 2.99 percent Thursday, while the 30-year increased to 3.93 percent from 3.92 percent. Bond prices and yields move inversely.