The stock market finished strong the three-week period ended Jan. 8. The Dow Jones ended with a 1.8 percent increase while the Valley 50 had a gain of 0.7 percent. Big gainers include Vitesse Semiconductor Corp. in Camarillo with a 29 percent gain after company executives scooped up shares. Qualstar Corp., the Simi Valley computer tape maker, benefitted from its interim Chief Executive Steve Bronson buying additional shares, rising 23 percent. The biggest loser was Tix Corp., the Studio City discount ticket seller, with a drop of 15 percent. Tix bought back 5.4 million shares in late December from Baker Street Capital LP, a Los Angeles investment firm.