Positive solutions of a system of non-autonomous fractional differential equations

Existence of positive solutions for the following system of fractional differential equations: D(alphai)u(i) =f(i)(t,u(1),u(2), ...u(2), ...u(n)), ui(0) =0, 0 < alpha(i) < 1, 1 less than or equal to i less than or equal to n, where D-alphai denotes Riemann-Liouville derivative of order alpha(i) has been studied. (C) 2004 Elsevier Inc. All rights reserved.