Existence of a unique positive solution for a singular fractional   boundary value problem
  In the present work, we discuss the existence of a unique positive solution of a boundary value problem for nonlinear fractional order equation with singularity. Precisely, order of equation $D_{0+}^\alpha u(t)=f(t,u(t))$ belongs to $(3,4]$ and $f$ has a singularity at $t=0$ and as a boundary conditions we use $u(0)=u(1)=u'(0)=u'(1)=0$. Using fixed point theorem, we prove the existence of unique positive solution of the considered problem. 
E.T.Karimov and K.Sadarangani
math.CA