“…Particularly, as the fractional order semilinear evolution equations are abstract formulations for many problems arising in engineering, physics, chemistry and economy, the theory of fractional evolution equations has attracted increasing attention in recent years and it has developed into an important branch of fractional calculus and fractional differential equations. For more details about fractional calculus and fractional evolution equations, we refer to [1], [3], [5], [6], [9], [10], [12], [13], [18], [19], [22], [26], [31], [32], [33], [34], [35], [36], [37], [38] and the references therein.…”