A function Class of strictly positive definite and logarithmically   completely monotonic functions related to the modified Bessel functions
  In this paper we give some conditions for a class of functions related to Bessel functions to be positive definite or strictly positive definite . We present some properties and relationships involving logarithmically completely monotonic functions and strictly positive definite functions. In particular, we are interested with the modified Bessel functions. 
Jamel El Kamel and Khaled Mehrez
math.CA