Stocks pushed ahead Tuesday afternoon, extending rebound efforts from Monday's big losses. The Nasdaq jumped 1.1% and the S&P 500 rose 1%. The Dow Jones industrial average climbed 0.8%. All three have nearly recouped all of Monday's heavy losses. Volume was tracking higher across the board. Nasdaq trade was particularly heavy, possibly due to Dell's (DELL) buyout by an investor group. 3D Systems (DDD) extended its recent bounce, gaining 5% in