Asymmetric Orientifolds, Brane Supersymmetry Breaking and Non-BPS Branes
  A new class of six-dimensional asymmetric orientifolds is considered where the orientifold operation is combined with T-duality. The models are supersymmetric in the bulk, but the cancellation of the tadpoles requires the introduction of brane configurations that break supersymmetry. These can be described by D7-brane anti-brane pairs, non-BPS D8-branes or D9-brane anti-brane pairs. The transition between these different configurations and their stability is analysed in detail. 
Carlo Angelantonj, Ralph Blumenhagen, Matthias R. Gaberdiel