Some operator convex functions of several variables
  We obtain operator concavity (convexity) of some functions of two or three variables by using perspectives of regular operator mappings of one or several variables. As an application, we obtain, for $ 0<p < 1,$ concavity, respectively convexity, of the Frech\'{e}t differential mapping associated with the functions $t \to t^{1+p} $ and $t \to t^{1-p}.$ 
Zhihua Zhang
math.FA