Stocks were narrowly mixed in early-afternoon action Wednesday, after giving up some morning gains. The Dow Jones industrial average fell 0.3%, but the Nasdaq and S&P 500 added 0.2% and 0.1%, respectively. Volume in the stock market today was tracking up slightly from Tuesday's levels. On the earnings front, Proto Labs (PRLB) soared 24% in giant turnover after its fourth-quarter profit and revenue beat forecasts. The stock executed a breakout in