Boston-based DataXu , provider of a real-time online ad bidding and optimization system, has secured $11 million in Series B funding to add to the $7.8 million in financing it raised in an earlier round (April 2009). The company, which was a finalist at last year's edition of the TechCrunch50 conference and startup launchpad, raised the additional capital from Menlo Ventures and prior investors Atlas Venture and Flybridge Capital Partners.