The $4 billion Atlantic Yards mixed-use development--the centerpiece of which will be the Barclays Center sports and entertainment arena, future home base of the NBA's Nets team--has new financial backing. Developer Forest City Ratner Cos. Inc. and Nets Sports and Entertainment have just signed a letter of intent to form a strategic partnership with an affiliate of Moscow-based international private investment fund Onexim Group for the development of the 22-acre project. The multi-faceted deal calls for Onexim to invest $200 million.