Collisional properties of ultracold K-Rb mixtures
  We determine the inter-species s-wave triplet scattering length a3 for all K-Rb isotopic mixtures by measuring the cross-section for collisions between 41K and 87Rb in different temperature regimes. The positive value a3=+163(+57,-12)a0 ensures the stability of binary 41K-87Rb Bose-Einstein condensates. For the fermion-boson mixture 40K-87Rb we obtain a large and negative scattering length which implies an efficient sympathetic cooling of the fermionic species down to the degenerate regime. 
G. Ferrari, M. Inguscio, W. Jastrzebski, G. Modugno, G. Roati, A.   Simoni